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In this article today, we will introduce 9 simple audio amplifier circuit design schematic diagram with detailed explanation, complemented with some knowledge about amplifier.     Catalog   I. What is an Audio Amplifier? II. Nine Simple Audio Amplifier Circuit Design Schematic Diagrams III. Some Knowledge about Amplifier FAQ     I. What is an Audio Amplifier? Let's watch a video first. This video shows us how to make a great sounding LM386 audio amplifier with bass boost An audio amplifier is a device that reconstructs an input audio signal on an output element that produces sound. The reconstructed signal volume and power level are ideal. They are truthful, effective, and low distortion. The audio range is from 20Hz to 20 kHz, so the amplifier must have a good frequency response within this range. Depending on the application, the power varies greatly. From milliwatts of headphones to several watts of TV or PC audio, to dozens of watts of mini home stereo and car audio, to hundreds of watts or more of more powerful household and commercial audio systems, until the power is big enough to meet the sound requirements of an entire cinema or auditorium.   The development of audio amplifiers has gone through three times. They are electron tube (vacuum tube) time, bipolar transistor time, and field-effect transistor time. The electronic tube audio amplifier has a round and sweet timbre, but it has the disadvantages of large volume, high power consumption, unstable operation, and poor high-frequency response. For the bipolar transistor audio amplifier, it has the advantages of a wide frequency band, large dynamic range, high reliability, long life, and high-frequency response is good. However, its static power consumption and on-resistance are very large, and the efficiency is difficult to improve. The third one is the field-effect transistor audio amplifier. It has the same round and sweet timbre as the electron tube and its dynamic range is wide. More importantly, it has a small on-resistance and can achieve high efficiency. Figure 1 II. Nine Simple Audio Amplifier Circuit Design Schematic Diagrams Next, I would like to introduce nine simple audio amplifier circuit design schematic diagrams.   Circuit Diagram 1 This circuit makes full use of the conventional LM317 voltage adjustment chip,  so that it not only completes the voltage stabilization function of the unstabilized voltage after filtering but also realizes the function of amplifying the audio signal picked up by the electret capacitive microphone. The electret capacitive microphone contains an impedance converter based on JFET, which converts the speech signal into a current form and adds it to the RP resistor, causing the corresponding voltage change. 220V AC output 36V unstable DC through transformer and bridge rectifier, and after filtering by the capacitor, the low resistance audio amplification signal input by the LM317 on the DC is fed into the capacitor and output to the loudspeaker. The implementation circuit is shown in figure 2.   Figure 2 After the circuit is installed, the voltage difference between the two inputs of the electret capacitive microphone should be adjusted first. This voltage difference is required to be less than 1.25VDC. By connecting an adjustable resistor between the LM317 adjustment end and the ground, the required limit can be achieved by adjusting the resistance by Rp. Secondly, the audio signal picked up by the microphone is easy to be interfered with by external noise. The addition of C1 can filter out part of the interference signal, but the required signal is also attenuated. Because the internal gain of the LM317 can compensate for the attenuation part, the loss caused by the introduction of C1 is negligible.    In order to avoid excessive loss, the capacity of C1 should be as low as possible, this circuit takes 15F. Finally, it should be noted that the minimum operating current requirement of the LM317 chip is 4 mA when the circuit is working normally, and a load resistor is used to absorb the 4mA current. If a low impedance loudspeaker is used, this load resistance must also be introduced to compensate for the signal distortion. In a practical circuit, if an 8Q impedance loudspeaker is used, at least 420Q load resistance is used to compensate for the possible signal distortion.   Circuit Diagram 2 Figure 3     Circuit Diagram 3 Adjust R1 so that the signal is not distorted at the maximum output, and reduce R2 to output more power. If there is a multimeter, the collector voltage of the transistor can be adjusted to about half of the power supply voltage. Figure 4     Circuit Diagram 4 In this design, the gain control of the preamplifier adopts DC volume control mode is realized as shown in figure 5. The preamplifier is an inverse proportional amplifier composed of a fully differential operational amplifier and resistor. Its gain is determined by the ratio of feedback resistance to input resistance. The external input DC analog control signal Vc is converted into control data through the gain control module (GainCon-troD), which is used to control the ratio of the feedback resistance of the preamplifier to the input resistance, and then adjust the change of the gain. Figure 5   The operational amplifier adopts a two-cascade structure, as shown in figure 6. In the first stage, a folded common-source common-gate amplifier with PMOS input is used to provide a large gain. At the same time, the common-mode range of the input is increased and the flicker noise is reduced. The load of the folded input tube adopts a current source load with a source feedback structure to increase the output impedance and reduce noise. The second stage uses a common-source amplifier to provide a large swing.    In order to maintain the stability of the closed-loop, Miller compensation capacitance is added. At the same time, in order to counteract the influence of the zero points of the right half-plane, the zero adjusting resistance in series with the compensation capacitor is inserted into the feedforward path of the compensation capacitor. In the design of the common-mode feedback circuit, the common-mode feedback structure with resistance distributor and amplifier is adopted.     Figure 6   Circuit Diagram 5 The audio amplifier uses very few peripheral components and works well at 2v. （The circuit is shown in figure 7）   The TDA7052 is a mono amplifier designed for battery-powered portable tape recorders and radios with an internal gain set at 40dB. Now the recorder and radio tend to be miniaturized and the battery consumption is reduced, which means that the power supply voltage is reduced, and the output power is also reduced. In order to compensate for this loss, TDA7052 uses the bridge drive load (ETL) principle, which can make the output power of 8 EU load up to 1.2 w.   Figure 7 lists the working parameters of TDA7052. Except for special instructions, the power supply is 6 v, the load impedance is 80, the input signal frequency is 1 kHz and the ambient temperature is 25 degrees.   Figure 7   Circuit Diagram 6   TDA2822 Fabrication of microphone Power Amplifier Circuit The circuit has few peripheral components, simple fabrication, but surprisingly good sound quality. A dual audio amplifier integrated circuit is used and its main characteristics are high efficiency and low power consumption. The typical value of static working current is only about 6mA. The integrated circuit has strong voltage adaptability (from1.8V to 15V DC) and will still have a power output of about 100mW even if it is used at a low voltage of 1.8V. The specific circuit is shown in figure 8. Figure 8   The electret microphone MIC converts the picked sound signal into an electrical signal, which is introduced from the foot 2 of U1 by C2 and W, and amplified by U1 audio to promote the loudspeaker pronunciation. The machine is connected with a BTL output circuit, which is good for improving sound quality and reducing distortion. At the same time, the output power is increased fourfold. When a 3v voltage is used, the output power is 350mW.   The resistance R1 and R2 are 1/4W metal film resistance, W is a small carbon film potentiometer and C2 is preferably a monolithic capacitor. If there is no good quality ceramic capacitance, select high quality, voltage resistant, and low leakage current electrolytic capacitor for C1, C4, and C3. Choose high sensitivity electret microphone as MIC, choose small button switch or toggle switch for K and choose TDA2822M or TDA2822 or D2822 for U1. According to the numerical value in figure 7, it can work normally without debugging.     Electret microphone detection For example, the R*100 of MF 47 multimeter is used to measure the Great Wall CZ Ⅲ electret microphone. When the black watch pen is connected to the core line and shell of the electret microphone, the multimeter pointer refers to the value at 3k Ω. When blowing hard, the pointer refers to the value at 4k Ω (and the resistance value of some microphones becomes smaller). If you blowhard and the multimeter pointer wobbles very little, you can adjust the two watch pens and try again. If the multimeter needle is still wobbling very little, the electret microphone is damaged.   In application, the drain D of the electret microphone must be connected to the positive electrode of the power supply through a resistance of 4.7 to 10k Ω, and then connected to the amplifier circuit, as shown in figure 9. Figure 9   Circuit Diagram 7    Add an amplifying circuit to the microphone  The electronic components are as follows：                                                                    resistance R1：1k Ω resistance R2：1m Ω resistance R3：1k Ω transistor vT：9014 capacitance：4.7 UF capacitance C2 ：4.7 UF battery：AA size battery     Figure 10    Working principle of amplifier circuit  Fig. 10 is a circuit diagram of the entire microphone amplifier circuit. As you can see from fig. 10, there are only six or seven originals of the whole circuit. The following is a brief description of how it works, in which the resistor R1 is responsible for providing the operating voltage to the microphone, R2 and R3 are responsible for providing the bias voltage for the transistor, and the capacitor C1 is responsible for coupling the signal of the microphone to the transistor for amplification. Finally, the amplified signal is coupled through capacitance C2 and sent back to the positive pole of the microphone line, that is, the outermost shielding layer of the microphone line (that is, the outer layer of copper mesh). Figure 10 is the material or electronic component we use to make it.    Considerations in production  The specifications of the electronic components required for the whole amplifier circuit are as follows: resistance R1：1K Ω resistance R2 ：1m Ω resistance R3 ： 1K Ω transistor VT ：9014 capacitance C1：4.7 μ F capacitance C2 ：4.7 μ F battery： a general AA size battery. △ Generally speaking, it can be used for about half a year if it is used normally.    Pay attention to the following points in the production process： 1. The pin of the transistor must be connected correctly; otherwise, it will not play the role of amplification. The pin distinguishes the following transistors lead down and the flat side facing itself. The transistors are E (emitter), B (base), and C (collector);   2. The microphone head is also polar. (see figure 4 for a specific distinction);   3. The polarity of the coupling capacitance can be distinguished by marking, and the pin with an arrow and marked "-" is a negative electrode, and the positive electrode is generally not marked   Because the components are few or can be directly welded in the shed, the circuit board can be directly installed into the base of the microphone, and the power lead of the circuit board can be connected to the battery slot reserved by the microphone.     Effect Test After trial, the effective distance of the microphone can reach 5 to 6 meters, and the effect is also obvious with the voice input function of Office Word 2003, and the speech can also be accurately recognized about 1 meter away from the microphone.   Circuit Diagram 8 A transistor is required. First, output the MP3 signal and use a lower power tube to amplify it. Then push medium power tube. This can achieve small distortion and have the coupling undone. This transistor circuit is simple, practical, and also easy to make.     Figure 11 The circuit is powered by a 9V single power supply. The input signal is coupled to the base of 9014 through 47uF capacitance. 9014 is responsible for preamplifier, and works in Class A state. 5.6K and 1.5K resistors are bias resistors of 9014, and 5.6K resistors are negative feedback resistors at the same time. 22 Ω resistors is a current series negative feedback resistor, which is used to increase the input impedance and reduce the linear distortion by 9014. The 470 Ω resistor is a 9014 collector load resistor used to convert the 9014 amplified current into a voltage, and two 1N4148 diodes are used to set the post-stage complementary tube in the pre-conduction region. OTL complementary output circuit is composed of 8050 and 8550. 3.3 Ω resistors are negative feedback resistors in series with emitters, which act the same as 22 Ω resistors. The 1000uf capacitor is the output capacitor, which is used to separate the DC and allow the AC signal to pass through. 8050 and 8550 are used as power output tubes to form a complementary push-pull output circuit, and the amplified current of 9014 is further amplified to push the loudspeaker. The static bias current of the push-pull circuit is set by two 1N4148, and the two 1N4148 are temperature compensation elements of two power output transistors at the same time. The voltage at the positive contact of the 1000uF electrolytic capacitor shall be half of the supply voltage. Because the conduction voltage of the silicon transistor base is 0.7 V, the base voltage of 8050 can be obtained to be about 5.2 V. From this, the static bias current of 9014 is (9- 5.2) / 470 =8 [mA]. The emitter voltage of 9014 is 8*22=0.176 V, and the base voltage is 0.176+0.7≈0.87V. Circuit Diagram 9 As long as R3 is increased, the gain of the amplifier can be increased. The parallel capacitor C4 at both ends of R3 is used to provide low resistance path filtering to high frequency to prevent high frequency self-excitation. J1 is a jumper, when J1 is turned on, foot 1 is grounded and the full power amplifier works; when J1 is disconnected, foot 1 is VDD, micro-power off, and the amplifier does not work. Jumper J2 can also control the operation of the amplifier. When J2 is disconnected, the + IN end is unbiased and the amplifier does not work. But if it is connected,  the amplifier works. LM4819 high gain audio amplifier circuit is shown in figure 12. Figure 12   III. Some Knowledge about Amplifier      Distortion  Also referred to as THD+N, Total Harmonic Distortion + Noise is simply a measure of the effect that an amplifier will have on sound output. The lower the distortion is, the closer your amp’s output will be to the original recording’s sound. The more distortion that there is, the more coloration there will be to the sound. Just keep in mind that your speakers will also have an impact upon sound, so choose them wisely by matching them with the right amplifier for the clearest sound.    Left and Right Signals  Crosstalk is a term that refers to the measure of how much of the right signal is mixed with the left signal. Amps come as a single unit, but they need to send signals out separately to the speakers so that you can hear things like a piano on the right and a singer to the left. If there is a lot of crosstalk, though, it will be much more difficult to decipher where the different sounds are coming from.    Power  When you look at an amp’s specs, you will also notice that there is a number for the power output, which is basically how loud the music can go. For the average listener, a 10W amp would be sufficient, as it will let you play your music loudly without creating any distortion. If you are really looking for a super loud amp, though, you can go as high as 100W. It really depends upon what your preferences are, what you will be using your amp for, what speakers you have, and how much room you have.    Connections  Your amp should have plenty of inputs for anything and everything that you wish to plug into it. You could have a 3.5mm connection for your iPod, and you could have a USB connection for your laptop, as a couple of examples. Just don’t sacrifice sound quality for more inputs.    Signal vs. Noise  There will always be some background noise within your amplifier, just as there is always some background noise in your own environment. What you want is an amp that will ensure the background noise is not obvious or perceptible. This will ensure that you will hear all of the music but none of the noise. Checking the signal to noise ratio on an amp will give you clearer insight into how well the product will work in this area.   FAQ   1. What does an audio amplifier do? An audio power amplifier (or power amp) is an electronic amplifier that amplifies low-power electronic audio signals such as the signal from radio receiver or electric guitar pickup to a level that is high enough for driving loudspeakers or headphones.   2. What is the difference between a speaker and an amplifier? Speakers are those things that make sound. The amplifier is what delivers sound to the speakers. Amps are usually radios and speakers are what you plug into the amp/receiver to hear the sound. ... The speakers plug into the sound card which in this case would loosly be called the amplifier.   3. Does amplifier improve sound quality? An amplifier simply increases(magnifies)the components of sound quality. If the quality of the input sound is poor, it will be a louder poor sound ; meaning you will hear the poorness of the sound more. It amplifies everything, the good and the bad.   4. Why do you need an amplifier? An amplifier is the device that turns the low voltage signals from your source equipment into a signal with enough gain to be used to power a pair of speakers. ... The second does the 'heavy lifting' and adds the gain to the signals in order to be used to power a pair of speakers. This is the power amplifier.   5. Which is better amplifier or receiver? A receiver is definitely the more convenient choice of the two, but that doesn't mean that it comes without any downsides. Usually a Lower Quality Amplifier - Though the quality of receiver amps is definitely increasing, you still don't have a completely dedicated amp with a receiver.   6. Which is more important speaker or amplifier? A speakers performance is highly variable and its sound will depend on the amp driving it. But the greatest amp (whatever that is) will sound like crap if the speaker sounds like crap. The quality of the speaker is the ultimate limitation of your system (assuming proper set up and room integration)   7. Can I hook up 8 ohm speakers to a 4 ohm amplifier? Yes, you can use 8 ohm speakers with a 4 ohm amplifier. Just wire two 8 ohm speakers of the same wattage in parallel.   8. How much money should I spend on an amp? If it's just for practicing in your bedroom, you can get a perfectly adequate little practice amp for under $200. If you'll be playing in a band or gigging out, yeah, you probably should expect to spend in the $500-700 range at least.   9. Do you need an amp for a subwoofer? Subwoofers are designed to increase the bass frequencies, resulting in a deep, thumping sound. In most cases, they are paired with an amplifier to boost the sound. If you do not have the funds for both components, you can still hook up a subwoofer without an amplifier; it simply involves a little more know-how.   10. Which transistor is used in amplifier? In most of the electronic circuits, we use commonly NPN transistor configuration which is known as NPN transistor amplifier circuit. Let us consider a voltage divider biasing circuit which is commonly known as a single stage transistor amplifier circuit.     Reference Component LM3886TF LM4652TA LM4765T  

Warm hints: The word in this article is about 3000 words and  reading time is about 10 minutes.   The transformer is a static electrical device, mainly composed of an iron core (or magnetic core) and coil. The coils have two or more windings, of which the ones connected to the power are called primary coils, and the rest are called secondary coils. Transformers are widely used in electrical equipment such as household appliances, electronic equipment, switching power supply, and so on. Circuit symbols commonly used T as the beginning of the number, for example, T01, T201.    This article covers the construction, functions, classification, and design of transformers and materials used for building magnetic cores in transformers.     Catalogs   I. The Composition of Transformer II. The Construction and Functions of Transformer III. High-frequency Transformer Design Program 3.1 Program structure 3.2 Matters needing attention when doing the core material   selection 3.3 Ferrite magnetic material requirements IV. Power Transformer Classification V. Principle and method of Transformer Design FAQ   I. The Composition of Transformer 1）The primary side 2）The secondary side 3）Magnetizing inductance 4）Leakage inductance 5）Open-circuit or short-circuit measurement of the primary side leads to the  Magnetic inductance and the leakage inductance turns ratio respectively:  K=Np/Ns=V1/V2   II. The Construction and Functions of Transformer 1) Electrical isolation 2) Energy storage 3) Voltage change for same power input.   III. High-frequency Transformer Design Program   3.1 Program structure (1) Core material (2) Core structure (3) Core parameters (4) Transformer Winding Parameter (5) package assembly (6) Temperature rise check   (1) Core material Soft magnetic ferrite is widely used in switching power supply because of its own characteristics. It has the advantages of high resistivity, low AC eddy current losses, low price, and easy to be machined into magnetic cores of various shapes. The disadvantages are low working magnetic flux density, low permeability, large magnetostriction, and high sensitivity to temperature changes. Which kind of soft magnetic ferrite material can satisfy the design requirement of a high-frequency transformer more fully, only when it is carefully considered and the transformer design can reach the high-cost performance.   (2) Magnetic core structure The factors considered in the selection of magnetic core structure are as follows: reducing magnetic leakage and leakage inductance, increasing the area of coil heat dissipation, which is beneficial for shielding and makes it easier to wind coils, more convenient to wire for assembly and so on.   The magnetic leakage and leakage inductance are directly related to the magnetic core structure . If the magnetic core does not need air gap, then a enclosed ring-like or square type magnetic core may be used as far as possible.   (3) Magnetic core parameters In the design of core parameters, special attention should be paid to the operating flux density only limited by the magnetization curve, but also by the losses, and also related to the working mode of power transmission. When the flux changes in one direction, there is ΔB=Bs-Br, which is not only limited by the saturation flux density but also mainly by the losses (Losses cause temperature rise, which in turn affects magnetic flux density). The operating flux density Bm=0.6～0.7ΔB.   An air gap can decrease Br and therefore increase the flux density ΔB. The exciting current can be increased after using an air gap opening, but the core volume can be decreased either. For the two-way operation of magnetic flux, the flux density ΔB is twice the maximum operating flux density Bm, that is ΔB=2Bm. In bidirectional operating mode, we should pay attention to the problem of transformer DC magnetic bias due to the inequality of volt-second areas of positive and negative excitation variation, which is caused by different reasons. A small air gap will be needed in the core, or a DC capacitor can also be added to the circuit design.   Magnetic properties of ferromagnetic materials Magnetic hysteresis loops of the core   (4) Coil parameters Coil parameters include: turns, conductor section (diameter), wire form, winding arrangement and insulation. The conductor section (diameter) depends on the current density of winding, using taking 2.5～4A/mm2. When doing some choosing of section conductor diameter don’t forget to take the skin effect into consideration and do regulations necessary after some temperature rise tests of the transformer.   General winding arrangements: the primary winding is close to the core and the secondary windings & feedback windings are gradually arranged outward. The following two winding arrangements are recommended:   1) If the voltage of the original windings is high (for example, 220V) and meanwhile that of the secondary windings is low, a more appropriate arrangement is the secondary winding being close to the core, and then goes the feedback winding, the original winding is arranged on the outermost ends, which is advantageous to the insulation arrangement of the original winding to the core;   2) If we want to increase the coupling between the primary and secondary windings, we can make half of the original windings be close to the core, then goes the feedback winding and secondary winding, and the other half of the original winding being the outermost ends, which is an arrangement advantageous to reduce the leakage inductance.   (5) Assembly structure The assembly structure of high-frequency power transformers are divided into horizontal and vertical types. If you'd like to select the planar core, sheet magnetic core and thin-film magnetic core, then a horizontal-type assembly would do you good.   (6) Temperature rise tests The temperature rise tests can be carried out by calculation and sample test. The temperature rise is lower than the allowable temperature rise above 15 degrees, the current density and the cross-section of the wire are appropriately increased. Appropriately increase the current density and decrease the cross-section of the wire, and do the exact opposite if temperature rise exceeds the allowable value, such as increasing the diameter or enlarging the core if necessary, to increase the area of coil heat dissipation.       3.2 Matters needing attention when doing the core material selection (1) Soft ferrite, due to its low price, good adaptability, and high performance at high frequency, has been widely used in switching power supply.   (2) Soft ferrite is commonly divided into two series: Mn-Zn ferrite and Ni-Zn ferrite. The Mn-Zn ferrite is composed of Fe2O3，MnCO3，ZnO and so on, which is widely used in all kinds of filters, inductors, transformers, and so on below 1MHz. The Ni-Zn ferrite is composed of Fe2O3，NiO，ZnO and so on, which is widely used in all kinds of adjustable inductor windings, anti-jamming magnetic beads, antenna matching devices, and so on above 1MHz.    (3) Mn-Zn ferrite is the most widely used core in switching power supply, and the selection of its material depends on its use. The core for the input filter part of the power supply is mostly high-conductivity magnetic core, and its material number mostly is R4K～R10K, that is, the ferrite core of relative permeability is about 4000~10000, but the main transformer and output filter are magnetic materials with high saturation flux density, where Bs is about 0.5T (5000GS).     3.3 Ferrite magnetic material requirements   Ferrite magnetic materials for switching power supply shall meet the following requirements:   (1) High saturation flux density Bs and low residual flux density Br   The residual flux density Bs has a certain influence on the transformer and winding results. Theoretically speaking, the number of turns of transformer windings can be reduced and the copper loss can be reduced because of the high Bs. In practical applications, there are different types of circuits of high-frequency converters in switching power supply.    For transformers, their operations can be divided into two categories:   1) Bipolar: The circuit topologies include half-bridge, full-bridge, push-pull, etc. In the primary winding of the transformer, the excitation current is equal and opposite in direction during the positive and negative half-cycles. Therefore, the magnetic flux changes in the magnetic core of the transformer are symmetrically moved up and down. The maximum variation range of B is  ΔB=2Bm, and the DC component of the magnetic core is basically canceling out.   2) Unipolar: The circuit topologies include single-ended forward, single-ended flyback, etc. The transformer primary winding adds a unidirectional square wave pulse voltage in one cycle (this is the case for single-ended flyback). The magnetic flux density varies from the maximum Bm to the residual flux density Br in the unidirectional-excitation transformer core. If we decrease the Br and increase the saturation flux density Bs, then the △B will be increased, and the turns and copper loss will also be reduced.   (2) Transformers or inductors are divided into three categories according to their topology:   1) An DC-filter inductor's magnetic core only works in one quadrant, the topologies of this operating state including Boost, Buck, buck/boost inductors, single end flyback converter transformer, forward and all push-pull converters and output filter inductors.   2) The core of the transformer in the forward converter also works in one quadrant, but the transformer needs to magnetic reset.   3) The core of the transformer with push-pull topology is in bidirectional alternating magnetization. These kinds of converters include push-pull, half-bridge and full-bridge converters, AC filter inductors, and so on.   (3) Low power loss at high frequency   The power loss of ferrite not only affects the power output efficiency but also leads to the heating of the magnetic core and waveform distortion.   The heating problem of the transformer is very common in practical applications, which is mainly caused by copper loss and core loss of the transformer. If the selected Bm is too low and the turns of winding are too many, it will cause the winding to heat up and transfer the heat to the core at the same time, and vice versa.   When selecting the ferrite material, we must make the power loss change with temperature characterized by a negative temperature coefficient. This is because if the core loss is the main heating, making the transformer temperature rise up, which then will lead to a further increase of core losses, thus it will form a vicious circle and eventually make the power tube, transformer, and other components burn down. Therefore, in the researches of power ferrite at home and abroad, we must solve the problem of negative temperature coefficient of magnetic material power loss itself, which is also a remarkable feature of magnetic materials having met the requirements for power supply applications, such as PC40 from Japanese company TDK and R2KB from China manufacturers and so on.   (4) A relatively moderate permeability   (5) How we choose the appropriate relative permeability?    Well, this depends on the switching frequency of your actual circuit, mostly 2000, meanwhile its applicable frequency must be below 300kHz, and sometimes can be a little higher, but the maximum will not be higher than 500 kHz.   (6) A relatively high Curie temperature   Curie temperature is the temperature at which a magnetic material loses its magnetic properties, generally above 200 ℃. However, the actual operating temperature of the transformer should not be higher than 80℃, at which the saturation flux density Bs will drop to 70% of that at the normal temperature when the temperature is above 100℃. That is, the saturation flux density of the core will drop more seriously when the operating temperature is too high. Furthermore, when the temperature is higher than 100℃, the power loss has been experiencing a positive temperature coefficient, which will lead to a vicious circle. For R2KB2 materials, the temperature corresponding to the allowable power consumption has reached 110℃ and the Curie temperature is up to 240℃, which meets the requirements of high-temperature use.     IV. Power Transformer Classification Power transformers are divided into three categories according to their topology: (1) Flyback transformers; (2) Forward transformers; (3) Push-pull transformers (full-bridge/half-bridge converters)   The appropriate topologies for various core structures are shown in the following table:   Core structureTypes of converter circuitFlybackForwardPush-pullE cores++0Planar E Cores-+0EFD Cores-++ETD Cores0++ER Cores0++U Cores+00RM Cores0+0EP Cores-+0P Cores-+0Ring Cores-++    "+"=fit; "0"=normal; "-"=unfit Summary of High frequency transformer core.XLS V. Principle and Method of Transformer Design   (1) There are two main ways to design transformer: Area Product (AP) Method AP: The product of core effective cross section Ae and Area of window Aw PT-The calculation power of the transformer Ae-Core effective cross section Aw- Area of window Ko-Core window utilization coefficient, typically 0.4 Kf-Waveform coefficient, usually square wave being 4 and sine wave being 4.44 Bw-The operating magnetic intensity of core FS-Switching frequency Kj-Current density coefficient, usually 395A/cm2 X-Core structure coefficient     (2) According to the area product (AP) method, the general steps of designing transformer are as follows: 1. Select the core material to calculate the apparent power of the transformer; 2. Determine the core cross section AP and select the core size according to AP value; 3. Calculation of the primary side inductance and the number of turns; 4. Calculation of the length of air gap; 5. Calculating the line diameter according to the current density and the secondary side RMS current. 6. Determine whether the copper loss and iron loss meet the requirements (eg allowable loss and temperature rise)   Selecting the flyback topology, the basic parameters of the power supply are as follows: Input voltage: 175-264 VAC Output voltage: 21V Output current: 3A Output power P0=63W Frequency set at 60Khz Duty cycle set at 0.45 initially   1) Select the core material to determine the apparent power PT of the transformer   and select the PC40 material here considering the cost factor and check the PC40 data to get Bs=0.39T, Br=0.06T. In order to prevent the core from becoming saturated instantly, a certain margin is reserved. Let Bm= ΔBmax*0.6=0.198T, and pick up the 0.2T. For flyback topology, the transformer apparent power PT is:   2) Calculating AP values with Excel tables   Where, J is the current density, usually 395A/cm2, and Ku is the effective use coefficient of copper window, usually 0.2～0.4, now we set Ku as 0.4.    Based on the figure above, we select the core EE3528 due to its being greater than the calculated AP value, with the following parameters: Ae: 84.8mm2 AP：1.3398cm4 Wa：158mm2 AL：2600nH/H2 In order to adapt to the abrupt load current, the power supply is designed in critical mode and the critical current is: I0B=0.8×I0=2.4A     3) Calculation of the primary side inductance and the number of turns (A) Minimum input voltage Vimin=ViACmin*1.2=210V (B) Turns ratio n=[Vimin/(V0+Vf)]*[Dmax/(1-Dmax)] n=[210V/(21V+1V)*[0.45/(1-0.45)] n=7.8 (C) Peak secondary current ^IsB=2*IoB/(1-Dmax) ^IsB=2*2.4A/(1-0.45) ^IsB=8.72A (D) Secondary inductance Ls=(V0+Vf)*(1-Dmax)*[1/(Fs*1000)]/^IsB*1000000 Ls=(21V+1V)*(1-0.45)*[1/(60Khz*1000)]/8.72A*1000000 Ls=23.58Uh (E) Primary inductance Lp=n*n*Ls Lp=7.8*7.8*23.58uH Lp=1434uH   Primary and secondary peak currents (F) Calculation of peak secondary current in continuous mode ^Isp=Io/(1-Dmax)+(^IsB/2) ^Isp=3A/(1-0.45)+(8.72A/2) ^Isp=9.81A (G) Calculation of peak primary current in continuous mode ^Ipp=^Isp/n ^Ipp=9.8A/7.8 ^Ipp=1.257A (H) Calculating the turns of the primary and secondary auxiliary windings a) Number of turns in the primary side Np=Lp*^Ipp/(^B*Ae) Np=1434uH*1.257A/(0.2*84.8) Np=106.28T After rounding: Np=106T b) Number of turns in the secondary side Ns=Np/n Ns=106T/7.8 Ns=13.58T After rounding: Ns=14T c) Number of feedback turns Nv=(Vcc+Vf)/[(V0+Vf)/Ns] Nv=(14.5V+1V)/[(21V+1V)/14T] Nv=9.87T After rounding: Nv=10T   To avoid core saturation, an appropriate air gap is added to the magnetic loop, the calculation go as follows: The number of turns may need to be corrected by the air-gap flux edge effect.   4) There are two ways to calculate the wire diameters of the primary, secondary and auxiliary windings: Effective current of original side diameter: Iprms=Po/^n/Vimin Iprms=63W/0.8/210V Iprms=0.375A (A) Calculating the area of bare wire (B) Calculating the wire diameter (current density J to take 4A/mm2) Using two 0.18mm-diameter wires wound around or AWG #28 a single strand The secondary diameter: Use four wires with a diameter of 0.25mm (AWG #31) and wind around. Calculation of Skin Depth: The diameter of multi-strand parallel winding must be less than or equal to dwH, in single wire winding, however, if the diameter exceeds the dWH value,  the multi-strand wire winding should be taken into account.   5) Calculation of copper loss Pcu and iron loss Pfe (total transformer loss Ploss) (A) Calculating the loss of primary and secondary windings.  Where, MLT is the average turn length of magnetic core (B) Calculating the allowable total loss Ploss and allowable iron loss at efficiency η (C) According to the loss curve of iron core, the actual loss (iron loss per unit weight and actual iron loss) is obtained by: The Ploss is the loss of the whole circuit, including diode/MOSFET losses and other losses, the actual losses Pfe must be much smaller than the calculated one, so here is only for reference. (D) Calculating the loss per unit area by Φ=Ploss/As If the temperature rise caused by Φ is less than 25 degrees, then the design is wonderful.   6) Calculating the BW The working flux density BW should be below Bs-Br within the design specifications, that is Bw<Bs-Br, to avoid saturation of the core.   FAQ   1. What is the use of transformer? Transformers are employed for widely varying purposes; e.g., to reduce the voltage of conventional power circuits to operate low-voltage devices, such as doorbells and toy electric trains, and to raise the voltage from electric generators so that electric power can be transmitted over long distances.   2. What are the 3 types of transformers? There are three primary types of voltage transformers (VT): electromagnetic, capacitor, and optical.   3. What is the basic principle of transformer? A transformer consists of two electrically isolated coils and operates on Faraday's principal of “mutual induction”, in which an EMF is induced in the transformers secondary coil by the magnetic flux generated by the voltages and currents flowing in the primary coil winding.   4. Does a transformer convert AC to DC? A transformer is built to transfer the energy from one circuit into another circuit by way of magnetic coupling. ... An alternating current creates a magnetic flux in the core on its way through the first winding, inducing the voltage in the others. It can convert high and low voltages, it cannot convert AC to DC.   5. What are the main parts of transformer? There are three basic parts of a transformer: a. an iron core which serves as a magnetic conductor, b. a primary winding or coil of wire and. c. a secondary winding or coil of wire.   6. What are the classification of transformer? Depending upon the type of construction used, the transformers are classified into two categories viz.: (i) Core type, and (ii) Shell type. Depending upon the type of service, in the field of power system, they are classified as: (i) Power transformers, and (ii) Distribution transformers.   7. Can a transformer work on DC? As mentioned before, transformers do not allow DC input to flow through. This is known as DC isolation. This is because a change in current cannot be generated by DC; meaning that there is no changing magnetic field to induce a voltage across the secondary component.   8. How do you convert a transformer? This conversion is made by winding two separate conductors around a common iron core. Applying an alternating voltage to the primary conductor produces current which sets up a magnetic field around itself. This is known as mutual inductance.   9. What are two components of no load current in transformer? The no-load current of a transformer consists of two components: The Magnetization Current iM is the current required to produce the flux in the transformer core. The Core-loss Current ih+e is the current required to make up for hysteresis and eddy current losses.   10. Which type of transformer core is most efficient? SHELL CORE. The most popular and efficient transformer core is the SHELL CORE, as illustrated in figure (4). As shown, each layer of the core consists of E- and I-shaped sections of metal. These sections are butted together to form the laminations.   You May Also Like: Analysis of Calculation Theory for Transformer Temperature Rise Some suggestions about protecting transformers Learn Some Basic Knowledge about Capacitor Voltage Transformer      

CatalogⅠ IntroductionⅡ What are PNP and NPN transistors?NPN TransistorsPNP TransistorsⅢ What is the difference between PNP and NPN?NPN Transistors VS. PNP TransistorsNPN VS. PNP: Difference in SymbolNPN VS. PNP: Difference in ConstructionNPN VS. PNP: Difference in Connection for SensorsⅣ Applications of NPN and PNP TransistorsNPN Transistor ApplicationsPNP Transistor ApplicationsⅤ Benefits of PNP versus NPNⅥ How to choose a PNP or NPN sensor?Ⅶ ConclusionⅧ Frequently Asked Questions about NPN and PNP Ⅰ IntroductionPNP and NPN are two types of bipolar junction transistors (BJTs). BJTs are constructed of doped materials that can amplify current. It has PNP and NPN configuration options. PNP and NPN transistors can be used for amplification or switching. This article is going to explain the difference between NPN and PNP.  NPN/PNP Transistors Explained Ⅱ What are PNP and NPN transistors?Transistors are created by mixing two different types of semiconductors: n-type and p-type. Electron donor atoms are carried by n-type semiconductors.  while electron acceptor atoms are carried by p-type semiconductors (holes). NPN TransistorsThe NPN type transistor is made of a p-type semiconductor material with a low doping level. The emitter is doped with a donor impurity at a considerably greater doping level than the collector, while the collection is doped at a much lower level than the emitter. The NPN transistor's biasing arrangement is the inverse of the PNP transistor's. The voltages have been inverted. The electrons, which have a higher mobility than holes, are the primary charge carrier of the NPN type. As a result, the response time of an NPN type transistor is faster than that of a PNP type. As a result, NPN type transistors  are the most generally employed in high frequency related devices, and their simplicity of fabrication over PNP type transistors makes them the more commonly utilized of the two types.  PNP TransistorsA PNP transistor is made of an n-type semiconductor material with a low donor impurity doping concentration. The emitter is doped with a higher concentration of acceptor impurity than the collector, and the collection is doped with a lower concentration than the emitter. BE junctions are forward biased by applying a lower potential to the base, while BC junctions are reverse biased by applying a considerably lower voltage to the collector. The PNP transistor can function as a switch or an amplifier in this form. The holes which make up the majority of the charge carriers in a PNP transistor, have a poor mobility. As a result, the frequency response rate is reduced and current flow is restricted. When employed in a circuit, PNP and NPN transistors  behave similarly. However, the polarity of voltage source connections and current flow direction differ. In most cases, NPN transistors can be substituted with PNP transistors and vice versa, but the power supply polarity must be altered. Ⅲ What is the difference between PNP and NPN?NPN stands for Negative-Positive-Negative transistors, whereas PNP stands for Positive-Negative-Positive transistors. Let's take a deeper look at the operation of NPN and PNP transistors. When sufficient current is provided from the transistor base to the emitter, the NPN transistor is turned on. In order for current to flow into the base of an NPN transistor, the base must be linked to a positive voltage and the emitter must be connected to a negative voltage. When sufficient current flows from the base to the emitter, the transistor turns on, directing current flow from the collector to the emitter rather than from the transistor base to the emitter. The PNP transistor operates in the other direction. Current ordinarily flows from the transistor's emitter to the base, and when enough current flows from the emitter to the base, the transistor turns on, directing current from the emitter to the collector. In brief, the NPN transistor requires positive current from the base to the emitter, whereas the PNP transistor requires negative current to the base, but current must flow out of the base to ground. NPN Transistors VS. PNP Transistors NPNPNPTerminal PolarityEmitter – NegativeEmitter – PositiveBase – PositiveBase – NegativeCollector – PositiveCollector – NegativeLoad ConnectionLoad is connected between positive and the collector.Load is connected between emitter and ground.Direction of conventional currentThe direction of conventional current flow is from the collected to the emitter.The direction of conventional current flow is from the emitter to collector.Majority charge carriersElectrons are the majority carriers in NPN transistors.Holes are the majority carriers in NPN transistors. NPN VS. PNP: Difference in SymbolNPN-PNP-symbol NPN VS. PNP: Difference in ConstructionNPN-PNP-Construction NPN VS. PNP: Difference in Connection for SensorsThe main distinction between NPN and PNP is how they are used in a circuit. Sensors with NPN output configurations act as sinking output, whereas those with PNP output configurations act as sourcing output. NPN-PNP-sensor-connection Because so many common industrial automation sensors operate at 24 Vdc, it is critical to comprehend two major variations of these solid-state devices. Automation systems rely on discrete I/O signals, such as sensor inputs and field device outputs. These signals are used in various businesses and are powered by 120 volts. The usage of 24 Vdc is a safer and more common choice, and many end users prefer equipment with plug-and-cord connectors for ease of installation and repair. As it turns out, a little forethought is required to guarantee that 24 Vdc sensors and PLC discrete input (DI) modules are appropriately connected. PNP and NPN are the two types of 24 Vdc sensors. In order to function, these must be properly matched with sinking and sourcing DI modules. It isn't difficult, and there is, in fact, a somewhat conventional or at least typical way, as explained below. Transistor EffectsTransistors, which are semiconductor devices built to function as tiny relays, are used in solid-state electronics for discrete on/off sensor applications. They amplify a very small signal, such as the position sensing component of a proximity switch in order to turn on or off a bigger signal. This larger signal can be sent to a DI point, an indicator light, or any other device with a suitable current rating. Transistors are classified into two types: PNP (sourcing) and NPN (sinking). The letters "P" and "N" relate to the arrangement of semiconductor materials in PNP and  NPN transistors. The connections between transistors are known as the base, collector, and emitter. Fortunately, understanding semiconductor physics is not required for industrial automation. PNP versus NPN SwitchingBecause solid-state devices are active rather than passive, they often require a minimal amount of operating power. They are usually three-wire devices having leads or connections for: +24 Vdc0 VdcSwitched or sensor signal The device is powered by the +24 Vdc and 0 Vdc cables. The PNP or NPN style of the sensor determines how the switched lead is operated. When there is a "on" signal, there are two key things to remember about PNP versus NPN field sensor operation: PNP Sensor Wiring  NPN Sensor Wiring Ⅳ Applications of NPN and PNP TransistorsNPN Transistor ApplicationsWhile PNP and NPN sensors perform the same basic function, you may be wondering why one would be preferred over the other. There are certain distinctions, and NPN transistors are preferable in most circuit design applications. This is because "N" substrates can move electrons far faster than "P" substrates can transport positive electron holes. This provides a significant benefit in high-speed switching and amplifier circuit applications. In addition to this advantage, NPN transistors are easier and consequently less expensive to manufacture than PNP transistors. Certain circuits, however, benefit from PNP-type transistors and would be difficult, if not impossible, to implement without this second type of transistor. A class B amplifier is one such application, in which a matched pair of PNP and NPN transistors work in tandem to efficiently amplify oscillating signals. It's incredibly useful to have this second type of switching option accessible when creating a circuit. PNP Transistor ApplicationsIf you're just getting started with these components, industrial sensors can throw a wrench in your knowledge if you're not careful. PNP and NPN sensors, as they are commonly known, are both supplied with positive and negative power lines, and then output a signal to signify a "on" state. During a "on" state, PNP sensors produce a positive signal to your industrial controls input, whereas NPN sensors produce a negative signal. If you learnt to utilize sensors before learning about transistors, you can mistakenly believe that a PNP transistor is controlled by positive voltage. Of course, things don't work that way—quite the contrary, in fact—because the PNP and NPN sensor designations relate to the sort of transistor (or equivalent for more complicated devices—some can even be wired in either configuration) used within. The perceived stimulus serves as the base signal, and in the case of a PNP sensor, which is most commonly used in this application, the positive collector output is coupled to a PLC input signal. When turned on, NPN output sensors, often known as "sinking" output sensors, sink ground voltage to an input. The controls engineer never sees the base switching voltage (+ for NPN and – for PNP), making these words fundamentally ambiguous. Ⅴ Benefits of PNP versus NPNWhen true, PNP sensors connect +24 Vdc to the switched lead, while NPN sensors connect 0 Vdc to the switched lead. If a PNP cable is destroyed, the signal may short to ground and damage the sensor. If an NPN cable is damaged, the signal may short to ground, resulting in a false true signal, but there will be no damage to the circuit. The resulting logic is perhaps the most significant advantage of utilizing PNP instead of NPN since +24 Vdc=On=True is easier for programmers and technicians to use and troubleshoot than 0 Vdc=On=True. Ⅵ How to choose a PNP or NPN sensor?The type of circuit employed in the system determines whether PNP or NPN sensors are used. Most PLCs allow you to specify cards as PNP or NPN. Another point to keep in mind is that NPN and PNP sensors should never be used together on a PLC input card. Furthermore, if you have a specific type of PLC input card, such as NPN or PNP, it is critical that you select sensors that match. NPN sensors, for example, can be used with an NPN Input card or a "sourced type" Input card. However, PNP sensors cannot be used with an NPN input card. Ⅶ ConclusionWhile NPN transistors are more frequent as bare components for the reasons stated above, the PNP paradigm has found a home in the industrial control realm for at least two reasons. For starters, whereas NPN sensors may make the most sense to someone with an electrical engineering degree, PNP sensors—where a positive output implies a "on" state—may be more comprehensible to technicians and engineers from other disciplines who frequently have to interact with them. Another reason is that if an NPN sensor's output wire frayed and became grounded, it would be perceived by a controller as a "on" signal, which could be dangerous in particular conditions. NPN sensors are used in industry, and they are more prevalent in Asian production than in Europe and North America. As with circuit design, while one kind may be more suited most of the time, having both NPN and PNP alternatives provides some control flexibility. Ⅷ Frequently Asked Questions about NPN and PNP1. How do I know if my sensor is PNP or NPN?Turn on the device and take careful measurements of the voltage between 0V and the black wire. It is a PNP-type sensor if there is a voltage of +24V when the sensor is operating. When the sensor is operational, a 0V measurement on the multimeter indicates that it is most likely an NPN sensor. 2. What is sinking input?A sinking input or output circuit connects the electric load to ground. The voltage source for the electric load is provided via a sourcing input or output. 3. Is PNP digital or analog?Digital signals are often represented by NPN or PNP. Sensors are one type of gadget that might be NPN or PNP. To connect to a sensor, you must be able to match the type of signal used by the device. 4. How do PNP and NPN transistors work?A positive voltage is applied to the collector terminal of an NPN transistor to cause current to flow from the collector to the emitter. A positive voltage is applied to the emitter terminal of a PNP transistor to cause current to flow from the emitter to the collector. 5. Where are NPN and PNP transistors used?As a result, the most typical application for NPN devices is to switch the ground side of a circuit. To switch from the positive side, PNP devices are employed. Consider the straightforward scenario of a load and a voltage source. 

Introduction In general, the radio is constructed by mechanical devices, electronic devices, magnets, etc. It receives the audio signals emitted by broadcasting stations through converting electric wave signals. After the invention of the vacuum tube, the circuit and receiving performance of the radio had undergone revolutionary progress and improvement, that is valve radio. Later, with the development of technology, radios with transistors as the core gradually became popular. It's what we know as a transistor radio. Radios are still widely used for many functions. Here two main radios will be described in detail below. Catalog Introduction Ⅰ Valve Tube Radio 1.1 Vacuum Tube Radio Classifications 1.2 Advantages and Disadvantages of Valve Radio 1.3 German Vintage Valve Radio Models for Sale Ⅱ Transistor Radio 2.1 Transistor Radio Overview 2.2 Transistor Radio Selection Matters 2.3 Transistor Radio Brands for Sale Ⅲ Radio Further Development Ⅳ FAQ Ⅰ Valve Tube Radio The valve radio, also known as the vacuum tube radio, was a product of the early 20th century, and immediately became the new favorite of that era with the launch of the broadcasting station. By the late 1920s, vacuum tube radio equipment replaced the primitive spark-gap systems on most merchant ships. This new equipment could send and receive signals virtually worldwide, by using high frequency or "short-wave" bands. Tube technology allowed radio signals to be tuned with much greater precision than spark-gap. The basic design for tube radio was perfected by the 1930s and continued in use on merchant vessels into the 1980s. 1.1 Vacuum Tube Radio Classifications 🔺AM (Amplitude Modulation) RadioIn the era when tube radios were popular, AM radios were the mainstream products. Amplitude modulation wave modulates the high-frequency carrier with audio signal. Its waveform is symmetrical, the amplitude is the same as that of the modulated signal, and then obtain the audio signal after high-frequency component is filtered out. In addition, the frequency of the carrier signal (the frequency of the broadcasting station) is the carrier frequency.AM radios can receive medium-wave and short-wave broadcasts, and some can receive long-wave broadcasts. Since the mid-band frequency interval has been unified to 9KHz, its highest audio frequency is only 4KHz. So the sound quality is affected because of large electromagnetic interference.There are two main types of AM radios: direct-amplifier type and external (self) differential type1) Direct-amp radio, also called high-amp radio, its typical circuit structure is as follows:High Amplifier—Detection—Low Amplifier—Power AmplifierA circuit that uses a grid detector circuit and high-frequency positive feedback is called a regenerative radio, which can obtain higher sensitivity and amplitude selectivity. A regenerative radio with high amplifier and short wave can receive AM telegraph signals. Most of the old Japanese-made radios have such circuits. Direct-amp radios are prone to self-excitation of high-frequency signals, high-end and low-end gains are uneven, and regenerative radios without high-amplification have poor selectivity. In addition, the reed speakers with poor sound quality are generally used, so they are gradually replaced by superheterodyne radios.Simple regenerative radios mostly use reed speakers, which have high impedance (about 10K) and high sensitivity. It can be directly used as the load of the power amplifier tube, but the frequency range is only 350~3000Hz, so the sound quality is poor. Later regenerative radios applied moving coil speakers, and the sound quality was better. However, because of low impedance, an output transformer is required, and its primary impedance must match the load impedance of the power amplifier tube. Moving coil speakers are divided into permanent magnets, constant magnets and excitation. Among them, excitation horns are used in AC electronic tube radios, and their excitation coils can also be used as filter chokes. 2) Heterodyne RadioThe heterodyne radio adopts a frequency conversion circuit. The signal generated by its high-frequency oscillation circuit and the input signal have a certain frequency difference. After the two are mixed, a fixed intermediate frequency signal (455~465KHz) is generated. Some people call the oscillation frequency higher than the signal frequency a heterodyne type, and vice versa.Heterodyne plus intermediate frequency amplifier circuit is called superheterodyne. This type of circuit requires a single electron tube to oscillate, and later a multi-pole or composite tube dedicated to frequency conversion appears. The superheterodyne type is the most common circuit of commercial radios. It has an automatic volume control circuit and can add tuning instructions. The circuit principle will be described in detail later. The superheterodyne radio can obtain more stable and higher gain due to amplifying the fixed frequency. The disadvantage is that there is image frequency interference.The circuit structure of a typical superheterodyne radio is as follows:Frequency Conversion—Middle Amplification—Detection—Low Amplification—Power Amplification 3) Autodyne Frequency Conversion RadioUsing ordinary pentodes for frequency conversion is only suitable for the mid-band, and the middle frequency is 175KHz. Due to the popularization of special frequency conversion tubes, it is rarely used now. Figure 1. Vintage AM Radio 🔺FM (Frequency Modulation) RadioFM radio is a radio that transmits radio signals through the use of FM frequency modulation carrier. Due to the shorter wavelength, the signal transmitted is much better than that of the radio that uses the AM wavelength. However, due to the short wave, the transmission distance is relatively short.FM wave is to use audio signal to modulate the frequency of high frequency carrier. Its advantages include strong anti-interference ability, high signal-to-noise ratio, good frequency bandwidth and sound quality, in addition, the audio frequency can reach 20Hz~15000Hz. Because the FM wave works in the ultra-high frequency band, it can accommodate many radio stations. With its linear propagation characteristics, the same frequency can be reused at a distance of hundreds of kilometers, which can effectively solve the problem of congestion of medium and short wave radio stations.Modern FM broadcasting is compatible with stereo and mono channels(in the early days of stereo broadcasting, two frequencies were used and two radios for reception). Some hobbyists are likely to use a simple super-regenerative circuit to receive FM broadcasts. Because it works in a self-oscillation state, the work is unstable and has strong super-noise. 1.2 Advantages and Disadvantages of Valve Radio Advantages of Valve Radio 1) The valve tube circuit has a simple structure and good anti-overload performance.2) The characteristics of the power amplifier circuit of the tube radio are better than those of the transistor or integrated circuit power amplifier. The screen current of the Class A power amplifier circuit with an output transformer for output impedance matching has little change at zero signal and full signal. So the performance is stable, the distortion of the line work area is very small, and the harmonic content is very rich .3) The speakers used in valve radios are generally larger in diameter than those of transistor or integrated circuit radios.4) The IF circuit characteristics of tube radios are better than those of transistor or integrated circuit radios.5) Have collection value. Disadvantages of Valve Radio As for the shortcomings, valve tubes that are large in size and used as basic components, built-in accessories are also bulky, power consumption has also increased, the overall quality has become poor, inconvenient to carry, and poor seismic performance. In addition, it is very difficult to make FM stereo radio devices, because early tube radios can only receive shortwave and medium waves. These shortcomings eventually led to the replacement of tube radios by transistor radios. Vintage Valve Radios - Will they work? 1.3 German Vintage Valve Radio Models for Sale AEG RadioBlaupunktGerman EMUDGraetz Vintage RadioGrundig Vintage RadioHornyphon Vintage RadioVintage Koerting RadioGerman Metz Vintage RadioVintage Nordmende RadioPhilips Vintage RadioVintage Saba RadioVintage Siemens RadioTelefunken Radio Figure 2. Vintage Valve Radio Ⅱ Transistor Radio 2.1 Transistor Radio Overview The transistor radio is the second generation radio after the valve radio. Compared with vacuum tubes, transistors are small in size, light in weight, resistant to vibration, long in life, and low in power consumption. This kind of radios can be made compact and have relatively stable performance. Therefore, after the advent of transistor radios, a large number of portable radios and pocket radios have emerged. They are very convenient for daily use. The Regency TR-1 was the first commercially manufactured transistor radio by developed by Texas Instruments and IDEA Inc., introduced in 1954.Transistor radios use transistors to process and amplify signals. Simple to use, it is a small transistor-based radio receiver. 2.2 Transistor Radio Selection Matters To choose a good transistor radio, you must first understand four basic relationships:1) The larger the chassis volume, the better the sound quality.2) The larger the horn diameter, the better the sound quality.3) The larger the battery volume, the longer the relative service life of the battery.4) The longer the magnetic bar, the higher the sensitivity.Secondly, we should also pay attention to five points when selecting:1) The change after the power supply voltage is reduced should be small. When selecting, you can have listening trial, because the impact on a high-quality radio should not be significant.2) The distortion of the offset radio should be small. After finding a radio station, having the left and right adjustments, the distortion should be small. In addition, there should be no whistling sound, otherwise, the frequency characteristics of the intermediate frequency part are poor.3) The volume change should be small when turning the button.4) Human body induction has little influence. When a person's body is close to the radio, it will have a certain impact on the work of the radio. This situation is particularly obvious for shortwave.5) The noise should be small. Noise generally includes electrical noise and mechanical noise. Turn the radio to a place where there is no station, and turn on the volume to the maximum. At this time, the minimum sound is better. Listen to a program to check whether there are noises caused by resonance of certain components when the volume is loud. Finally, you should also pay attention to whether the tuning knobs and buttons are coordinated and effective, and whether the shell of the radio is damaged or not. Vintage Transistor Radios Show And Tell 2.3 Transistor Radio Brands for Sale EdifierGAORUI HOME TEXTILESONYRoltonHALFSUNPandaSoaiyNintaus Figure 3. Regency tr-1 Transistor Radio Ⅲ Radio Further Development With the advent and development of integrated circuits, transistors have been replaced by integrated circuits, that is the third-generation radios invention, sometimes also known as semiconductor radios.After the radio uses integrated circuits, not only the size can be made smaller, but also the reliability is high. As the number of integrated circuit components is getting larger and larger, radios made with it have better performance and more functions. The integration of radios has become an inevitable trend.   Ⅳ FAQ 1. What is a vacuum tube radio?A vacuum tube, also called a valve in British English, is an electronic device used in many older model radios, television sets, and amplifiers to control electric current flow. The cathode is heated, as in a light bulb, so it will emit electrons. ... The anode is the part that accepts the emitted electrons. 2. Do valve radios still work?A valve radio will never be as reliable as a transistor set, and short of ripping out the chassis and replacing it with a transistor circuit, we aren't going to make it that reliable. However, some designs of valve set are more unreliable than others, and the main factor seems to be heat. 3. What did valves do in radios?The valve was useful as an electronic switch and its first use was in radio circuits detecting signals. The valve has two elements - a wire and a metal plate surrounded by a vacuum. The electricity flows between them. 4. How does a tube radio work?The basic working principle of a vacuum tube is a phenomenon called thermionic emission. It works like this: you heat up a metal, and the thermal energy knocks some electrons loose. 5. When did radios stop using vacuum tubes?1950s-60s - Most vacuum tubes were replaced by transistors in the west. 1970s-80s Tubes are still used in many specialized applications like broadcast television and radio. 6. Why did we stop using vacuum tubes?Vacuum tubes suffered a slow death during the 1950s and '60s thanks to the invention of the transistor—specifically, the ability to mass-produce transistors by chemically engraving, or etching, pieces of silicon. Transistors were smaller, cheaper, and longer lasting.A transistor is a semiconductor device used in electronic circuits as to function as "on" and "off" switching and amplifying device in the electronic circuits. ... Radio is a device which transmit and amplifies signals. The modern radio uses transistor since it is smaller in size. 7. Are transistor radios still being made?Transistor radio is an obsolete term now, carried over from when having transistors rather than tubes made small radios possible. It has come to be analogous to a portable, battery-powered radio, so while I will be making some recommendations, they likely will have integrated circuits, rather than transistors.It is a radio receiver which uses transistors to amplify the sound. Transistor radios can be cheap and small and some use very little electric power. Some can amplify the weak radio waves that are usually not picked up by weaker vacuum tube radios. 8. What does a transistor radio do?The function of transistors in radios is straightforward. Sounds are recorded through a microphone and turned into electrical signals. Those signals travel through a circuit, and the transistor amplifies the signal, which is subsequently much louder when it reaches a speaker. 9. Why was the transistor radio invented?One goal was to find a replacement for fragile and energy-wasting vacuum tubes. Building on war-time research, John Bardeen and Walter Brattain, working with group leader William Shockley, developed a device they called a transistor. 10. Where was the transistor radio invented?There was a tremendous push during the war to reduce the size and power consumption of vacuum tubes, particularly because the receivers used in radio-controlled bombs depended on vacuum tube technology. “Not long after the war ended, the transistor was developed at Bell Labs, in 1947. 11. What is the name of first transistor radio?Regency TR-1In July 1954 the Texas Instruments and Industrial Development Engineering Associates (I.D.E.A.) companies embarked on a six month project to produce a pocket-sized radio for the Christmas market. The result was the Regency TR-1, the world's first pocket transistor radio.

Introduction In the FOC(Field Oriented Control) algorithm, the sampling current is the basis of the algorithm implementation and a very important part. So accurate current sampling can bring better result to the algorithm. In other words, if the current sampling is accurate, it will be very helpful for the subsequent coordinate transformation to obtain required results. From this we can see the role of current sampling in the entire FOC algorithm. Understanding Field-Oriented Control Catalog Introduction Ⅰ Current Sampling Method Ⅱ Three Sampling Methods and Precautions 2.1 Single-resistor Sampling 2.2 Dual-resistor Sampling 2.3 Triple-resistor Sampling Ⅲ The Key to Sampling Ⅳ Delay Source Ⅴ Delay Type and Typical Time Ⅵ Analysis in Details 6.1 PWM Dead Time Insertion 6.2 Optocoupler Delay and Pre-Driver Delay 6.3 Transistor Switching Delay 6.4 Other Delays Ⅶ FAQ Ⅰ Current Sampling Method In motor control, the current sampling method is generally to use PWM to trigger ADC to convert. Taking SoC(System-on-a-Chip) as an example, the ADC module will be configured to automatically sample and trigger conversion. When the trigger point set by the PWM module matches, the signal will be given to the ADC module. At this time, the sampling switch in circuit will be disconnected, and then the ADC module will start to convert, and the voltage of the corresponding sampling current can be obtained after the conversion is completed. The AD value of the signal, you can use this value in the program to write and verify the algorithm. Figure 1. Current Sampling Time Ⅱ Three Sampling Methods and Precautions Current sampling is the basis of FOC, including current sensor sampling and resistor sampling. Resistor sampling is widely used for its simple and low-cost characteristics. The method includes single-resistor sampling, dual-resistor sampling, and triple-resistor sampling. 2.1 Single-resistor Sampling The biggest difference between the single-resistor and the other two methods is that it cannot obtain two current signals at the same time. Even if two current signals are obtained, there is an error in estimating the third current signal. The formula Iu+Iv+Iw=0 is conditional, that is, the three currents must be recorded at the same time. When the inductance of the motor is larger, the two currents obtained are closer to the real situation. When the inductance is small, the deviation may be relatively large. So if the inductance of the current is large, single-resistor sampling can be selected.This method requires two samplings in one PWM cycle. In this case, it is necessary to analyze the switch state in the algorithm to clarify which phase current the reconstructed current corresponds to at the time of sampling. 2.2 Dual-resistor Sampling In the case of dual-resistor sampling, the sampled two-phase current must be used directly. Even if there is a deviation, it needs to be used. This method cannot be used to calculate the third-phase current based on the other two-phase sampling like the triple-resistor sampling. That is to say, this method needs to consider the problem of the sampling window. If the sampling current is to be guaranteed to be accurate, the sampling window must be large enough. To make the sampling window large enough, the PWM waveform needs to be deformed. But this will increase the execution time of the algorithm. The advantage of this approach is to reduce a current-sense resistor and an op amp.As shown in the figure below, the front of the red circle is the oscillating area. If the sampling window is small, only the oscillating area will not be able to obtain an accurate current. To process the sampling window, you can refer to the following figure, so that the obtained current will be more accurate. Figure 2. Current Sampling Zone 2.3 Triple-resistor Sampling This method is the simpler among the three methods. It directly uses three current-sensing resistors to sample the three-phase phase current of the motor, and the result obtained in this way is relatively straightforward. Using the formula Iu+Iv+Iw=0, recalculate the phase current of one phase with a small sampling window. So that the accuracy of the result obtained is the highest, and the implementation of the following related algorithms is easier. It is the advantage of this method. However, three current-sense resistors and three op amps are used, the hardware cost will be higher than the other two.   Ⅲ The Key to Sampling The current sampling includes peak current and average current sampling. Generally, the most common is the average current sampling and its control, so there are actually two ways to sample the average current. One is that the current-sense resistor is placed on the upper bridge of the inverter bridge. The other is that the current-sense resistor of the inverter bridge is connected to the lower end of the lower bridge.The general method is the latter. The current detection circuit corresponding to this method is relatively simple, and the corresponding power consumption will also be reduced. In this case, the freewheeling current is collected at the lower end, and then we can sample at the midpoint of the lower bridge opening. At this time, the corresponding current reflects the average current, so the corresponding current control is the average.Then, if we use the three-resistor sampling method, the selected ADC module must have at least the function of simultaneous sampling of three channels. So as to ensure that the three-phase currents obtained by sampling are the currents at the same time, and at this time, to meet the condition, Iu+ Iv+Iw=0.In the case of dual-resistor sampling, there are only two sampling resistors, and the obtained current cannot use the formula Iu+Iv+Iw=0. Therefore, even if the sampling window is small, if the algorithm is not processed, the double-resistor scheme has limitations. In order to get a better adaptation to the scene, algorithm compensation must be performed on the dual-resistor method, which is also the key point of it.Similarly, for the single-resistor sampling way, the corresponding current needs to be obtained according to different switch combinations, and it needs to be sampled twice in a PWM cycle. This method cannot satisfy Iu+Iv+Iw=0, and can only be determined by an algorithm. Compensation and correction are performed, so the single-resistor method is more difficult to take. However, if the difficulty can be solved, this method is the best and cheapest one.   Ⅳ Delay Source During the development of the motor-driven FOC control, have you encountered the situation that the motor is too noisy, inefficient or even unable to operate? All of this may be due to sampling anomalies of the phase currents, resulting in the inability to reconstruct the correct three-phase currents in the FOC algorithm. Here is an analysis of a factor that affects current sampling: the delay source.In the motor drive FOC control of double-resistor sampling, the sampling point is set as the middle moment when the lower tube of the drive bridge is turned on. Note that this is the middle moment when the lower tube of the drive bridge is turned on, not the middle moment of the PWM cycle output by the MCU. There are as many as seven delay sources in this typical drive topology because the PWM is calculated from the MCU to the ADC module where the current signal is sent to the MCU. Figure 3. MCU Output Ⅴ Delay Type and Typical Time The table below details the seven sources of delay that exist in motor drive system topologies and their typical timings. These delays will be superimposed together, and the effect is that the actual output PWM waveform lags behind the PWM waveform that the MCU calculates the expected output. According to this calculation, the phase current sampling point needs to lag the middle moment of the MCU calculating the expected output PWM waveform. Delay Type Typical Time PWM Dead Time Insertion 100ns-2μs Optocoupler Isolation to Pre-driver 40ns-300ns Pre-driver Switch Delay About 50ns MOSFET Switching Time 100ns-1μs Amplifier Delay <1μs Low-pass Filter Delay 1-2μs ADC Delay 50ns-200ns   Ⅵ Analysis in Details 6.1 PWM Dead Time Insertion In the three-phase brushless motor drive system, three bridge arms are required to control the current flow of the phase line, and there are two power devices on each bridge arm, such as MOSFET and IGBT. The pair of power devices cannot be turned on at the same time, otherwise a short circuit will occur. Here MOSFET is used as a power device to illustrate. In the control, dead time must be inserted to ensure that the upper and lower MOSFETs are not turned on at the same time. Typical values of dead time may be between 100ns and 2μs, depending on various factors in the system, such as MOSFET drive voltage and type.After the required PWM waveform is inserted into the dead time, what you get is that both the PWM midpoint and the rising edge are shifted to the right. When using the FOC control algorithm calculates the proper PWM, we start seeing the first delay, recording the dead time. Figure 4. Dead Time Insertion 6.2 Optocoupler Delay and Pre-Driver Delay The signal response of the various optocouplers and pre-drivers causes additional delays between the moment the MCU controls the FTM module to output the PWM waveform and the moment the MOSFET gate is controlled. The output of the pre-driver is delayed by a period of time (Delay1) compared to the waveform output from the MCU pins. Figure 5. Delay 1 6.3 Transistor Switching Delay Through the pre-driver, the PWM waveform reaches the MOSFET transistors, but due to their inherent characteristics, all transistors take a certain amount of time to turn on and off. This delay time varies depending on the transistor type and the voltage level required to switch between on/off. Delay 2 is the total delay between the theoretical switching point (CMP2) of the phase line voltage and the instant of the actual switching point. Figure 6. Delay 2 Finally, the gate voltage reaches the level that can make the transistor turn on, the current passes through the phase line and the sampling resistor, and a voltage difference is generated across the sampling resistor. The red waveform is the phase current waveform in an ideal state. At this time, there is a total delay time between the midpoint of the PWM cycle calculated and generated by the MCU, and the "phase current midpoint shift" is shown in the figure. Figure 7. Phase Current Midpoint Shift 6.4 Other Delays As shown in the figure below, the final delay chain that affects the current sampling is formed by the amplifier slew rate, the low-pass filter on the MCU pins, and the ADC slew rate. The time marked by the red circle in the figure is the correct current sampling time. It can be seen that the phase current sampling point is greatly delayed compared with the PWM midpoint output by the FTM. Figure 8. Other Delay In all and electrical and electronic circuits, there will be signal delay problems. And it is impossible to completely eliminate them, but the impact can be reduced by selecting low-delay devices. In the motor drive, in addition to selecting the appropriate device, it is also necessary to perform software compensation for the signal delay. The precise delay time of these delay sources mentioned in the article can be obtained by oscilloscope and calculation, and the correct current sampling time can be obtained by compensating for these delays in software. In this way, the data collected at the correct moment can be used as the data source for reconstructing the three-phase current of the motor in the FOC control.   Ⅶ FAQ 1. What is FOC algorithm?Field-oriented control (FOC), or vector control, is a technique for variable frequency control of the stator in a three phase AC induction motor. 2. What is FOC drive?Vector control, also called field-oriented control (FOC), is a variable-frequency drive (VFD) control method in which the stator currents of a three-phase AC or brushless DC electric motor are identified as two orthogonal components that can be visualized with a vector. 3. What is FOC brushless motor?FOC implementation allows the BLDC motor to run more efficiently (high power factor and better light load efficiency), more smoothly (lower torque ripples) with quick dynamic response (better dynamic performance to load and speed changes). 4. What is FOC in BLDC motor?Field oriented control (FOC) is an important control approach for Brushless DC motors. It resembles sinusoidal commutation but adds a major mathematical twist. Figure 3a shows control schemes for both sinusoidal commutation and field oriented control. 5. How is Bldc phase current measured?With a BLDC motor use an ac voltmeter to measure the voltage between any 2 wires of the 3 motor wires and then convert the line-to-line voltage to the phase voltage value by dividing the line-to-line voltage by 3 =1.73. 6. Do BLDC motors have inrush current?Handle Peak Inrush Current of a BLDC Motor to protect the Power Supply. Summary: BLDC motors have a Peak current on startup which is 3x or more the rated current. The motor has a rated current of 7.3A. 7. What causes motor inrush current?When an electrical device, such as an AC induction motor, is switched on, it experiences a very high, momentary surge of current, referred to as inrush current. ...The interaction of these two magnetic fields produces torque and causes the motor to turn.

IntroductionIn the lighting industry, people often have a misunderstanding about dimming LED lights. And the reality is that the application of LED light source dimming technology in engineering is often unsatisfactory. Why is this the case? Is the LED light source dimming technology immature, or the technology is difficult to master? So this article analyzes the LED dimmer to help readers to fully understand and master it.Dimming all kinds of LEDs?CatalogIntroductionⅠ Dimming LED Lights1.1 What is Dimming?1.2 LED Dimming Circuit Example1.3 LED Dimming Using SCRⅡ Dimming LED Using PWM2.1 LED Dimming Current2.2 LED PWM Dimmer2.3 LED PWM Dimming Advantages2.4 LED PWM Dimming Problems2.5 DALI PWM Dimmer IntroductionⅢ Main LED Dimmers ComparisonsⅠ Dimming LED Lights1.1 What is Dimming?LED dimmer switch is an electrical device that changes the luminous flux of the light source in the lighting device and adjusts the illuminance level. The purpose of the dimmer is to adjust the different brightness of the light. By reducing or increasing the rms voltage, the light output of different intensities produced by the average power lamp is promoted. Although variable voltage devices can be used for various purposes, this regulation is aimed at controlling lighting. Regarding the LED dimmer switch, we must first understand the volt-ampere characteristics of the LED. That is, the characteristics of the current flowing through the LED PN junction with voltage. Generally, the reverse characteristic curve changes steeply. When the voltage exceeds a certain threshold, the current will rise exponentially, thereby breaking down the LED PN junction. The forward voltage of the LED is also determined by its forward current. It can be seen from the figure that the change of the forward current will cause the corresponding change of the forward voltage, to be precise, the decrease of the forward current will also cause the decrease of the forward voltage. Therefore, when the current is lowered, the voltage of the LED will also decrease, which will change the relationship between the power supply voltage and the load voltage.Figure 1. Diode Volt-Ampere Characteristics CurveTherefore, from the volt-ampere characteristics of the LED, we can know that the dimming of the light source cannot be achieved simply by reducing the input voltage or input current of the LED. In addition, the waveform of the sine wave of the LED is different from the waveform of the incandescent lamp, so it cannot simply change its conduction angle to achieve the purpose of dimming.LED dimming methods can be divided into analog dimming and digital dimming. Analog dimming is to achieve dimming by changing the current in the LED loop. The power supply voltage remains unchanged, and the current in the loop is changed by changing the resistance value to achieve the effect of changing the brightness of the LED. Many analog dimming is an extension of this method. Its advantage is that the current can be continuous, but the range of adjustable current is often limited by hardware, and there are few adjustment gears. This method is not ideal for high-precision lighting equipment.Digital dimming, also known as PWM (Pulse Width Modulation) dimming, uses PWM waves to turn on and off the LED to change the on-time of the forward current to achieve the effect of brightness adjustment. This method is based on the fact that the human eye is not sensitive enough to the brightness flicker. If the frequency of brightness and darkness exceeds 100Hz, the average brightness is seen by the human eye, not the LED flickering. PWM adjusts the brightness by adjusting the ratio of light and dark time. In a PWM cycle, because the perceived brightness of human eyes to flicker is a cumulative process, that is, the brighter time accounts for the greater the proportion of the entire cycle. The longer the time, the brighter the human eye feels.1.2 LED Dimming Circuit ExampleFor example, in an LED lamp with an input of 24V, 8 1W high-power LEDs are connected in series. When the forward current is 350mA, the forward voltage of each LED is 3.3V, then 8 pieces in series is 26.4V, so a constant current source greater than 24V should be used. However, in order to dimming, the current is reduced to 100mA. At this time, the forward voltage is only 2.8V, and 8 pieces are connected in series to 22.4V. The load voltage becomes lower than the input voltage, so that a constant current source larger than 24V cannot work, and finally the LED will flicker.In this case, you may choose a step-down (wide voltage) constant current source, such as a 10V-30V constant current source for dimming. However, if this type is adjusted to a low forward voltage, the LED load current will also become very low. So the step-down ratio is very large, beyond the normal working range of constant current source, which will make LED unable to work and cause flicker. In addition, LED works at low brightness for a long time, which will reduce its efficiency and increase the temperature rise. Because the efficiency of the step-down constant current source is related to the voltage ratio, the larger the voltage drop ratio, the lower the efficiency. And greater power loss on the chip will damage the life of the constant current source and the LED light source.1.3 LED Dimming Using SCROrdinary incandescent lamps and halogen lamps usually use thyristors for dimming. Because they are pure resistance devices, and do not require the input voltage to be a sine wave. Their current waveform is always the same as the voltage waveform, no matter how the voltage waveform deviates from the sine wave, changing the effective value of the input voltage will dim the LED light .However, the adjustment of LED light source by thyristor dimming will cause unexpected problems, that is, the LC filter at the input will cause the thyristor to oscillate. This oscillation is indifferent to the incandescent lamp, human eyes can't see it at all because of thermal inertia. However, this dimming method will cause the driving power of LED produce audio noise and flicker. It will also destroy the waveform of the sine wave, thereby reducing its power factor value (usually lower than 0.5), which greatly reduces the system efficiency of the LED. Moreover, the thyristor dimming waveform increases the harmonic coefficient, and the non-sinusoidal waveform will cause serious electromagnetic interference on the line to pollute the power grid.Ⅱ Dimming LED Using PWM2.1 LED Dimming CurrentHere, you may ask: Lower voltage or current or thyristor dimming methods are not suitable for LED light source dimming, so what is the most suitable method?Is it an analog (0-10V) dimming method? May be not. Analog dimming faces a severe challenge, which is the output current accuracy. Almost every LED driver needs some kind of series resistance to distinguish the current, and the tolerance, offset and delay in the analog (0-10V) dimming drive cause a relatively fixed error, which will reduce the accuracy of the output current, and the final output current cannot be specified, controlled or guaranteed. Therefore, to ensure the dimming effect of the LED light source, one of the important rules is to reduce the output current error and improve the current accuracy in a closed loop system.2.2 LED PWM DimmerThe PWM dimming method can solve the above problems very well. Because diode characteristics, LED can realize fast switching, and its allowable switching speed can be as high as microseconds or more. Therefore, as long as the power supply is changed to a pulse constant current source, the brightness can be changed by PWM. This PWM dimming. This method is like a sluice that opens and closes in microseconds or more. The switching frequency of it is so fast that humans can’t recognize the state of its opening with the naked eye. As a result, people can only identify the speed of its switching frequency by the amount of water downstream. In addition, because the sluice changes the duty cycle of the output water flow (effective water flow), it does not change the instantaneous water pressure and flow rate, so the opening and closing action of the sluice gate will not affect the hydropower generation. The amount of water flowing down and power generation are just changed. Therefore, the PWM dimming method does not change the instantaneous voltage and current of the input LED PN junction, but changes the duty cycle of the output current to change LED brightness.2.3 LED PWM Dimming Advantages1) There will not be any LED chromatogram shift, because the LED always works between the full amplitude current and 0.2) It has a very high dimming accuracy, because the pulse waveform can be controlled to a high precision.3) Even if the light is dimmed in a wide range, there will be no flicker. Because it will not change the working conditions of the constant current source (boost ratio or step-down ratio), problems such as overheating are less to occur.4) It can be combined with digital (DALI/DSI/DMX 512) control technology for control, because the digital control signal can easily be transformed into a PWM signal.2.4 LED PWM Dimming Problems1) Because the LED is in a fast switching state, if the working frequency is very low, the human eye will feel flicker. In order to make full use of the residual visual phenomenon of the human eyes, its operating frequency should be higher than 100Hz, preferably 200Hz.2) Eliminate the howling caused by dimming. Although the human eye can't detect it above 200Hz, it is within the range of human hearing until 20kHz. At this time, it is possible to hear the slightest voice. There are two ways to solve this problem: One is to increase the switching frequency above 20kHz, out of the range of human hearing, another is to find out the sound-producing device and deal with it.At present, some manufacturers have solved the above problems well. A good LED light source dimming technology needs a good LED control signal technology to match and cooperate in order to become an effective, stable and reliable system. For example, the LED PWM dimming method has the advantage that the digital control signal can easily be converted into a PWM signal. At the same time, in the digital control signal of lighting, DALI (Digital Addressable Lighting Interface) has the unparalleled superiority of other lighting digital control methods, and it is also the mainstream of the current digital control application in the lighting industry. Therefore, the matching of PWM dimming mode and DALI takes into account their respective advantages, where PWM dimming technology solves the final dimming problem of LED light sources, and DALI solves the control, feedback and networking of each LED light.Figure 2. LED PWM Dimming Circuit2.5 DALI PWM Dimmer IntroductionThe biggest feature of DALI technology is that each lamp has an independent address. Through the DALI system software, a single lamp or any lamp set can be accurately dimmed and switched, regardless of whether the lamps are on strong current loop or not. That is to say, the lighting control has nothing to do with the strong current circuit. The DALI system software can independently address single or multiple lamps on the same strong current circuit or different circuits, to achieve individual control and arbitrary grouping set. This concept brings great flexibility to lighting control, which can meet different LED lighting requirements. Even after installation, they can still modify the control requirements at will, without having to do anything to the wiring.The following are the application advantages of PWM dimming method combined with DALI.1) The design is simple and easy to implement.In the design, as long as they are connected to each other through the digital signal interface, they are connected in parallel to the 2-core control line. All design process can be programmed by computer software during installation and debugging, which not only saves design costs, but also improve working efficiency.2) Simple and economical installationThe DALI control line has no special requirements for the wire and no polarity requirements during installation. It only requires the main power line to be separated from the control line. The control line does not need to be shielded. When the current on the control line is 250mA and the line is 300 meters long, the drop does not exceed 2V. The control line and the power line can be parallel, no need to bury the line separately. The compact design of the control components does not require a special control cabinet, so installation is simple and economical.3) Simple and convenient operationThe PWM LED driver with DALI control can automatically handle filament preheating, ignition, dimming, switching, fault detection and other functions. The user interface is very friendly. Users can operate and control without deep understanding, such as sending a change. According to the command of the scene, each relevant LED driver calculates the dimming rate according to the difference between the current brightness and the required installation brightness to achieve that all the LED light sources are synchronized to the required scene brightness.4) Accurate and reliable controlDALI is a digital signal, which is different from an analog signal. The signal of 1010 can realize disturbance-free control, and will not distort the control signal due to long-distance voltage drop. Therefore, even if the DALI digital signal control line and the strong wire are in the same line and tube, it will not be disturbed. The DALI signal is two-way transmission, which not only transmits control commands forward, but also feeds back the information of the LED driver's status, fault information, switch, and actual brightness value to the system.5) Wide range of applicationsNowadays, DALI interface is not only used for fluorescent lamp ballast dimming, various electronic transformers for halogen lamps, electronic ballasts for gas discharge lamps. DALI technology also employed in wide range of LED light control makes it more and more widely. Ⅲ Main LED Dimmers Comparisons1) SCR DimmingFigure 3. SCR Dimming Circuit Diagram✅Advantages: It has the advantages of high adjustment accuracy, small size, light weight, easy remote control, etc., which occupies a leading position in the market.❎Disadvantages: The front-cut LED dimmer is prone to generate noise, so it is not recommended for high-demand occasions. The minimum load will vary depending on the LED dimmer and light source. It is necessary to consider derating to adapt to the spike caused by the driver. The typical derating percentage should be 25%-30% of the maximum rated load of the dimmer circuit. 2) CMOS DimmingFigure 4. CMOS Dimming Circuit Diagram✅Advantages: There is no minimum load requirement, so that better performance can be achieved on a single LED lighting device or a very small load.❎Disadvantages: High cost, complicated dimming circuits, lack of high-power products, and poor stability. 3) 0-10V DimmingFigure 5. 0-10V Dimming Circuit Diagram✅Advantages: Simple application, good compatibility, high precision, better dimming effect than phase-cut dimming.❎Disadvantages: Need to add additional control lines and controllers. The dimming effect is related to the wire diameter, cable material, power current, and power supply quantity of 0-10V dimming. 4) DALI DimmingFigure 6. DALI Dimming Circuit Diagram✅Advantages: Accurate and smooth dimming, two-way communication, and strong anti-interference ability, mainly used in single lamp control.❎Disadvantages: Like 0-10V products, additional control circuits and controllers need to be added. 5) DMX512 DimmingFigure 7. DMX512 Dimming Circuit Diagram✅Advantages: Powerful control functions bring rich lighting effects to architectural lighting, night lighting, studios and variety shows.❎Disadvantages: Special wiring layout and types are required, and certain programming is required to set the basic colors and scenes, which is more costly for later maintenance. The ideal transmission distance of DMX signal is less than 200 meters. And meanwhile, in actual use, the signal is greatly interfered by the outside world. 6) SLC and Ready2mains DimmingFigure 8. LED Dimming via Ready2mains✅Advantages: The digital dimming signal is transmitted through the AC wire, without additional signal wires and wiring. Digital signal transmission has good anti-interference performance and excellent dimming effect.❎Disadvantages: At present, there are relatively few products using this type of digital dimming technology, so there are relatively few compatible products. Frequently Asked Questions about LED Dimmer1. What are LED dimmers?An LED dimmer is the term for a device that performs a dimming control operation within such an LED lighting device. LEDs react instantaneously to alterations in power input, making solid state lighting especially suitable for dimming scenarios. 2. Why do my LED dimmer lights flicker?LED bulb flickering can be traced in almost every instance to a non-compatible dimmer switch in the lighting circuit. ... LED bulbs don't have glowing filaments. When the dimmer switch goes off and on many times per second, the LED bulb becomes a flickering strobe light. 3. Do you need a special dimmer for LED lights?Use an LED Dimmer switchA standard dimmer switch cannot be used with an LED light as you will never be able to dim the LED light either completely or not very well. LED lights need their own special electronic dimmer switch to have a fully functioning and dimming light. 4. How do LED dimmer switches work?In the case of PWM, dimmable LEDs work by creating a dimming effect. Unlike traditional lighting such as incandescent, dimmable LED bulbs don't rely on voltage to dictate their level of brightness. Instead, they essentially rely on a cycle of being on and off. 5. What is the best dimmer switch for LED lights?Best Overall: Lutron Toggler Single-Pole/3-Way Light Dimmer.Best Budget: GE Slide Dimmer Rocker Wall Switch, Single Pole.Best Smart: Kasa Smart Dimmer Switch HS220.Best for Bedrooms: Lutron Maestro LED+ Dimmer Switch, Single-Pole or Multi-Location.Best for LED: Lutron Diva LED+ Dimmer Switch, Single-Pole or 3-Way.