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Introduction Radio Frequency Identification (RFID) is a type of automatic identification technology that uses radio frequency to carry out wireless non-contact two-way data communication, with recording media (electronic tags or radio frequency cards) to read and write. The purpose is identifying the target and making data exchange. This is an extremely complex system, so it involves many parameters. Next, we will introduce several important parameters in detail. What is RFID? How RFID works? Catalog Introduction Ⅰ RFID Parameters Explained 1.1 Rx Sensitivity 1.2 SNR (Signal-to-Noise Ratio) 1.3 Tx Power 1.4 ACLR/ACPR 1.5 Modulation Spectrum/Switching Spectrum 1.6 SEM (Spectrum Emission Mask) 1.7 EVM (Error Vector Magnitude) 1.8 Interference Indicators 1.9 Dynamic Range, Temperature Compensation and Power Control Ⅱ FAQ Ⅰ RFID Parameters Explained Radio frequency identification involves many settings, that is, parameter selections. What are they? Here gives you the detailed descriptions as following mentioned. 1.1 Rx Sensitivity Receiving sensitivity is one of the most basic concepts, characterizes the lowest signal strength that the receiver can recognize without exceeding a certain bit error rate (BER), which is a general term that follows the definition of the circuit switched (CS) era. In most cases, BER or  Packet Error Rate (PER) will be used to examine the sensitivity. In the Long Term Evolution (LTE) era,  use throughput to define simply. LTE does not have a circuit-switched voice channel, but this is also a real evolution. Because for the first time we no longer use "standardization" such as 12.2kbps RMC (voice coding at 12.2kbps) to measure sensitivity, but the throughput that users can really feel.   1.2 SNR (Signal-to-Noise Ratio) When talking about sensitivity, we often refer to SNR (signal-to-noise ratio), we generally talk about the demodulation SNR of the receiver. We define it as the ability of the demodulator to not exceed a certain bit error rate, that is, SNR threshold for demodulation.So where do S and N come from? S means Signal, or useful signal; N means Noise. The useful signal is generally emitted by the communication system transmitter, and the source of noise is very wide. The most typical one is the famous -174dBm/Hz (natural noise). It is a quantity that has nothing to do with the type of communication system. In a sense, it is actually a noise power density related to temperature. In addition, how much bandwidth do we receive determine the noise, that is, the final noise power is integrated on the bandwidth by the noise power density. 1.3 Tx Power The importance of the transmission power is that the signal from the transmitter needs to pass through the fading of space to reach the receiver. So the higher the transmission power means the longer the communication distance.So should we consider SNR for our transmitted signal? For example, if the SNR of our transmitted signal is very poor, do we receive the same bad?This involves the concept just mentioned, the natural noise we assume that spatial fading has the same effect on both signal and noise (in fact, it is not, the signal can resist fading through coding but noise not) and it acts like an attenuator. For example, we assume spatial fading is -200dB, the transmitted signal bandwidth is 1Hz, the power is 50dBm, and the SNR is 50dB, then what is the SNR received by the receiver?The power of the signal received by the receiver is 50-200=-150Bm (bandwidth 1Hz), and the noise of the transmitter 50-50=0dBm through spatial fading, and the power reaching the receiver is 0-200=-200dBm (bandwidth 1Hz)? At this time, this part of the noise has already been "submerged" under the natural noise -174dBm/Hz. At this time, we only need to consider the "basic component" of -174dBm/Hz to calculate the noise to the receiver. Actually, this is applicable in most cases of communication systems.   1.4 ACLR/ACPR These parameters are explained together because they actually represent part of the "transmitter noise", but these noises are not in the transmitting channel, but the part that the transmitter leaks into the adjacent channels, which can be collectively referred to as "Leakage in the adjacent channel".ACLR and ACPR (actually one thing, but one is called in the terminal test, the other is called in the base station test), both are named after "Adjacent Channel". They both describe the machine pair interference from other equipment. And their power calculation of the interference signal is also based on a channel bandwidth. This measurement method considers the signal leaked by the transmitter and the interference to the equipment receiver of the same or similar standard-the interference signal falls into the receiver band with the same frequency and the same bandwidth. That is, form the same frequency interference to the signal received by the receiver.In LTE, the ACLR test has two settings: EUTRA and UTRA. The former describes the interference among the LTE systems, and the latter considers the interference of the LTE system to the UMTS system. So we can see that the measurement bandwidth of EUTRAACLR is the occupied bandwidth of LTE RB, and the measurement bandwidth of UTRA ACLR is the occupied bandwidth of UMTS signals (FDD system 3.84MHz, TDD system 1.28MHz). In other words, ACLR/ACPR describes a kind of "peer-to-peer" interference: the leakage of the transmitted signal interferes with the same or similar communication system.This definition is significant. For example, in the actual network, there are often signal leakage from neighboring cells from other or in the same region. In other words, the adjacent channel leakage of the system itself is typical for neighboring cells. Therefore, the process of network planning and optimization is actually the process of capacity maximization and interference minimization. In addition, from the other side of the system, the mobile phones of users in crowded people may also become a source of mutual interference.Similarly, in the evolution of communication systems, the goal has always been to "smooth transition", that is, to upgrade and transform existing networks into next-generation networks. Therefore, the coexistence of two or even three generations of systems should consider the interference between different systems. So the introduction of UTRA in LTE is to consider the radio frequency interference to the previous generation system UMTS.   1.5 Modulation Spectrum/Switching Spectrum In the GSM system, Modulation Spectrum and Switching Spectrum also play a similar role to adjacent channel leakage. The difference is that their measurement bandwidth is not the occupied bandwidth of the GSM signal. From a definition point of view, it can be considered that the modulation spectrum is a measure of the interference between synchronous systems, and the switching spectrum is a measure of the interference between asynchronous systems. In fact, if the signal is not gating, the switching spectrum will definitely cover the modulation spectrum.This involves another concept: in the GSM system, the cells are not synchronized, although it uses TDMA. In contrast, TD-SCDMA and later TD-LTE, the cells are synchronized.Because the cells are not synchronized, the power leakage of the rising edge/falling edge of the A cell may fall to the payload part of the B cell, so we use the handover spectrum to measure the interference of the transmitter to the adjacent channel in this state. And in the entire 577us GSM timeslot, the proportion of rising edge/falling edge is very small after all. What’s more, most of the time, the payload of two adjacent cells will overlap in time. In this case, the interference of the transmitter to the adjacent channel can be evaluated by referring to the modulation spectrum. Figure 1. RFID Chip 1.6 SEM (Spectrum Emission Mask) SEM is an in-band indicator, which is distinguished from spurious emission. The latter includes SEM, but the focus is on the spectrum leakage outside the working frequency band of the transmitter. In addition, its introduction is more based on the perspective of EMC (Electromagnetic Compatibility).SEM provides a spectrum template. When measuring the spectrum leakage in the transmitter band, see if there are any points that exceed the template limit. It can be said that it is related to ACLR, but it is not the same. ACLR considers the average power leaked into the adjacent channel, so it uses the channel bandwidth as the measurement bandwidth, and it reflects the "critical noise point" of the transmitter in the adjacent channel. Where SEM reflects the capture of over-standard points in adjacent frequency bands with a smaller measurement bandwidth (usually 100kHz to 1MHz), which reflects the noise-based spurious emission.If you scan the SEM with a spectrum analyzer, you can see that the spurious points on the adjacent channel will generally be larger than the ACLR average. Therefore, if the ACLR indicator itself has no margin, the SEM will easily exceed it. On the other hand, if the SEM exceeds the ACLR, it does not necessarily mean bad. For example, a common phenomenon is that there is LO spurious or a certain clock and LO modulation component (often very narrow bandwidth, similar to dot frequency) in the transmitter link, although ACLR is good, the SEM may exceed the standard.   1.7 EVM (Error Vector Magnitude) EVM is a vector, which means it has amplitude and angle. It measures the error between the actual signal and the ideal signal. This measurement can effectively express the "quality" of the transmitted signal. That is, the farther the point distance of the actual signal to the ideal signal, the greater the error and the greater the modulus of the EVM.Why is the SNR of the transmitted signal not so important? There are two reasons: the first is that it is often much higher than the SNR required for demodulation of the receiver. The second is the condition, that is, the worst case. The transmitter noise has already been submerged under the natural noise after a large spatial fading, and the useful signal is also attenuated to near the demodulation threshold of the receiver.But the "intrinsic SNR" of the transmitter needs to be considered in some cases, such as short-range wireless communication. Even without considering the spatial fading, demodulation of such high-order quadrature modulated signals alone already requires a high SNR. The worse the EVM, the worse the SNR and the higher the difficulty of demodulation. Engineers working on 802.11 systems often use EVM to measure Tx linearity. While engineers working on 3GPP systems, they like to use ACLR/ACPR/Spectrum to measure it.From the origin, 3GPP is the evolutionary path of cellular communication, and from the very beginning it has to pay attention to adjacent channel and alternative channel interference. In other words, interference is the number one obstacle that affects cellular communication rates. Therefore, 3GPP always aims at "minimizing interference" during its evolution, such as frequency hopping in the GSM era, spread spectrum in the UMTS era, and the RB concept in LTE era.The 802.11 system is an evolution of fixed wireless access. It follows the spirit of the TCP/IP protocol and aims at "service first". In 802.11, there use often time division or frequency hopping methods to achieve multi-user coexistence. The network layout is more flexible, and the channel width is also flexible and variable. In general, it is not sensitive to interference (or rather high tolerance).In layman's terms, the origin of cellular communication is to make phone calls, and users who cannot get through the phone will go to the telecommunications; while the origin of 802.11 is the local area network, you just wait at first when the network is not good.So this determines that the 3GPP series must take ACLR/ACPR and other "spectrum regeneration" performance as indicators, while the 802.11 series can adapt to the network environment at the expense of speed.Specifically, "Adapt to the network environment at the expense of speed" means that in the 802.11 series, different modulation orders are used to cope with the propagation conditions. When the receiver finds a signal difference, it immediately informs the opposite transmitter to reduce the modulation order. As mentioned earlier, SNR and EVM in an 802.11 system are highly correlated. To a large extent, a reduction in EVM can improve SNR. In this way, we have two ways to improve the receiving performance: one is to reduce the modulation order, thereby reducing the demodulation threshold; the other is to reduce the transmitter EVM, so that the signal SNR is improved.Because EVM is closely related to the demodulation effect of the receiver, EVM is used to measure the performance of the transmitter in the 802.11 system (similarly, in 3GPP, ACPR/ACLR is the index that mainly affects the network performance). In addition, the deterioration of EVM is mainly caused by non-linearity (for example, AM-AM distortion of PA), so EVM is usually used as a sign to measure the linear performance of the transmitter. Figure 2. RFID 1.7.1 Relations of EVM to ACPR / ACLR It is difficult to define the quantitative relationship between EVM and ACPR/ACLR. From the non-linearity of the amplifier, EVM and ACPR/ACLR should be positively correlated. That is, the AM-AM and AM-PM distortion of the amplifier will amplify the EVM, and also the ACPR/ACLR.However, EVM and ACPR/ACLR are not always positively correlated. For example, Clipping is commonly used in digital IF. It is to reduce the peak-to-average ratio (PAR) of the transmitted signal. The reduction of peak power can help reduce the ACPR/ACLR after passing through the PA. However, clipping will also damage the EVM. Because whether it is clipping (windowing) or using a filter, they all cause damage to the signal waveform, affecting the EVM. 1.7.2 Source Flow of PAR PAR (Peak-to-Average Ratio) is usually represented by a statistical function such as CCDF, and its curve represents the power (amplitude) value of the signal and its corresponding probability of occurrence. For example, if the average power of a certain signal is 10dBm, the statistical probability that it has a power exceeding 15dBm is 0.01%, and we can consider its PAR is 5dB.PAR is an important factor affecting transmitter spectrum regeneration (such as ACLP/ACPR/Modulation Spectrum) in modern communication systems. The peak power will push the amplifier into the nonlinear region and produce distortion. And the higher the peak power, the stronger the nonlinearity.In the GSM era, because of the constant envelope characteristic of GMSK modulation, PAR is 0. When designing GSM power amplifiers, we often push it to P1dB to get the maximum efficiency. After the introduction of EDGE, 8PSK modulation is no longer a constant envelope, so we tend to push the average output power of the amplifier to about 3dB below P1dB, because the PAR of the 8PSK signal is 3.21dB.In the UMTS era, whether WCDMA or CDMA, the PAR is much larger than that of EDGE. The reason is the correlation of the signals in the code division multiple access system. In other words,  when the signals of multiple code channels are superimposed in the time domain, the same phase may occur, and the power will show a peak at this time.The PNR of LTE is derived from the burstiness of the RB. OFDM modulation is based on the principle of dividing multi-user/multi-service data into blocks in both the time domain and the frequency domain, so that high power may appear in a certain "time block". LTE uplink transmission uses SC-FDMA. First, DFT extends the time domain signal to the frequency domain, which is equivalent to "smoothing" the burstiness in the time domain, thereby reducing PAR. Figure 3. RFID Applications 1.8 Interference Indicators The "interference index" here refers to the sensitivity test under various applied interferences in addition to the static sensitivity of the receiver. In fact, it is very interesting to study the origin of these test items.Our common interference indicators include Blocking, Desense, Channel Selectivity, etc. 1.8.1 Blocking Blocking is actually a very old RF indicator, as early as the invention of radar. The principle is to pour a large signal into the receiver (usually the first LNA that suffers the most), making the amplifier enter the nonlinear region or even saturate. At this time, on the one hand, the amplifier gain suddenly becomes smaller, and on the other hand, extremely strong nonlinearity occurs, so the function of amplifying useful signals cannot work normally.Another possible Blocking is actually done through the receiver's AGC. Large signals enter the receiver link, and the receiver AGC will reduce the gain to ensure dynamic range, but the useful signal level entering the receiver is very low. At this time, the gain is insufficient, and the amplitude of the useful signal entering the demodulator is insufficient.Blocking indicators are divided into in-band and out-of-band, mainly because the RF front-end generally has a band filter, which has an inhibitory effect on out-of-band blocking. However, the blocking signal is generally point frequency without modulation. In fact, point-frequency signals without modulation at all are rare in practice. In engineering, it is approximately point-frequency to replace various narrow-band interference signals.For solving Blocking, the key is RF. In other words, it is to expand the dynamic range of receiver. For out-of-band blocking, the rejection of the filter is also very important. 1.8.2 AM Suppression AM Suppression is a unique indicator of the GSM system. From the description point of view, the interference signal is a TDMA signal similar to the GSM signal, synchronized with the useful signal and has delay.This scenario simulates the signal of the neighboring cell in the GSM system. From the point of view that the frequency offset of the interference signal is greater than 6MHz (GSM bandwidth is 200kHz), this is a very typical neighboring cell signal configuration. So we can think that AM suppression is a reflection of the receiver's interference tolerance to neighboring cells in the actual work of the GSM system.Adjacent (Alternative) Channel Suppression (Selectivity)Here we collectively refer to it as "adjacent channel suppression". In the cellular system, in addition to the same-frequency cells, we must also consider adjacent-frequency cells in our networking. The reason can be found in the transmitter index ACLR/ACPR/Modulation Spectrum that we discussed before. Because of the transmitter's spectrum regeneration, there will be strong signals falling into adjacent frequencies (generally, the farther the frequency offset, the lower the level, so the adjacent channel is generally the most affected), and this kind of spectrum regeneration is actually related to the transmitted signal. That is, receivers of the same standard are likely to mistake this part of the regenerated spectrum as a useful signal for demodulation.For example, if two neighboring cells A and B happen to be neighboring frequency cells (such networking methods are generally avoided, here is just a assumption), when a terminal registered in cell A swims to the campus junction of two, but the signal strength of the two cells has not reached the handover threshold, the terminal still maintains cell connection with A, and the ACPR of the B cell base station transmitter is higher. So the terminal’s receiving frequency band has a higher ACPR component of B cell, which overlaps with the useful signal of cell A in frequency. Because the terminal is far away from the base station of cell A at this time, the received signal is weak. At this time, when the ACPR component of cell B enters the terminal receiver, it causes co-channel interference to the original useful signal.If we pay attention to the definition of the frequency offset of the adjacent channel selectivity, we will find that there is a difference between Adjacent and Alternative, which corresponds to the first and second adjacent channels of ACLR/ACPR. It can be seen that the "transmitter spectrum leakage (regeneration)" in the communication protocol and the "receiver adjacent channel selectivity" are actually defined in pairs. 1.8.3 Co-Channel Suppression (Selectivity) Co-frequency interference generally refers to the interference pattern between two cells.According to the networking principles we described earlier, the distance between two cells with the same frequency should be as far as possible. In addition, even if they are farther away, there will be signals leaking to each other, but the difference is in intensity. For the terminal, the signals of the two campuses can be regarded as "correct and useful signals" (of course, there is a set of access specifications on the protocol layer to prevent such false access). Frequency strength of both depends on its co-frequency selectivity. 1.8.4 Summery Blocking is big signal interferes with small signal, but the AM Suppression is small signal interferes with large signal.Single-tone Desense is a unique indicator of the CDMA system. It has a feature: the single-tone is an in-band signal and is very close to the useful signal. In this way, it is possible to generate two kinds of signals falling into the receiving frequency domain: First is due to near-end phase noise of the LO, the baseband signal formed by the mixing of the LO and the useful signal, and the signal formed by the mixing of the LO phase noise and the interference signal. Both will fall within the range of the receiver baseband filter, the former is a useful signal and the latter is interference. Second is due to the nonlinearity in the receiver system. The useful signal (with a certain bandwidth, such as 1.2288MHz CDMA signal) may produce intermodulation with the interference signal on the nonlinear device, falling in the receiving frequency domain and becoming interference.The origin of single-tone desense is that the CDMA system uses the same frequency band as the original analog communication system AMPS, and the two networks coexisted for a long time. So the CDMA system must consider the AMPS system's interference to itself.The explanation of Blocking in theory: the large signal entering the receiver causes the amplifier to enter the nonlinear region, and the actual gain becomes smaller (for useful signals).But it is difficult to explain two scenarios:Scenario 1: The pre-stage LNA has a linear gain of 18dB. When a large signal is injected to make it reach P1dB, the gain is 17dB. If no other influence is introduced (the default LNA NF, etc. have not changed), then the noise figure of the entire system is actually very limited. It is nothing more than the fact that the denominator of the latter-stage NF becomes a little smaller when it is included in the total NF, which has little effect on the sensitivity of the entire system.Scenario 2: The IIP3 of the previous LNA is very high, so it is not affected. The second level gain block is affected (the interference signal makes it reach near P1dB). In this case, the impact of the entire system NF is even smaller.Here is a point of view: the influence of Blocking may be divided into two parts. One part is that the gain mentioned in the textbook is compressed, and the other part is actually that after the amplifier enters the nonlinear region, the useful signal is distorted in this region. This kind of distortion may include two parts, one part is the spectrum regeneration (harmonic component) of the useful signal caused by pure amplifier nonlinearity, and the other part is the Cross Modulation of the large signal modulating the small signal.From this we also put forward another idea: if we want to simplify the Blocking test (3GPP requires frequency sweeping, which is very time-consuming), we may be able to select certain frequency points, which have the greatest impact on useful signal distortion when the Blocking signal appears.From an intuitive point of view, these frequency points may have: f0/N and f0*N (f0 is the useful signal frequency, and N is a natural number). The former is because the N-th harmonic component generated by the large signal in the nonlinear region is just superimposed on the useful signal frequency f0 to form direct interference, and the latter is superimposed on the N-th harmonic of the useful signal f0 and affects the output signal f0.According to Pascal's law, the waveform of the time domain signal is actually the sum of the domain fundamental frequency signal and each harmonic. When the power of the Nth harmonic in the frequency domain changes, the corresponding in the domain is the envelope change of the time domain signal (have distortion). Figure 4. RFID Readers   1.9 Dynamic Range, Temperature Compensation and Power Control These three indicators will only be shown when certain extreme tests are performed, but they themselves represent the most significant part of RF design. 1.9.1 Dynamic Range of the Transmitter The dynamic range of the transmitter characterizes the maximum and minimum transmission power without damaging other transmission indicators. This concept is very broad. If you look at the main effects, you can understand that the linearity of the transmitter is not compromised at the maximum transmission power, and the SNR of output signal is maintained at the minimum transmission power.Under the maximum transmit power, the output is often close to the nonlinear region of active devices at all levels (especially the final amplifier), and the nonlinearity that often occurs is spectral leakage and regeneration (ACLR/ACPR/SEM), modulation error (PhaseError/EVM). The most susceptible at this time is basically the linearity of the transmitter.Under the minimum transmit power, the useful signal output by the transmitter is close to the natural noise of the transmitter, and may even be submerged in the transmitter noise. At this time, what needs to be guaranteed is the SNR of the output signal. In other words, the lower the transmitter noise at the minimum transmit power, the better. 1.9.2 Dynamic Range of the Receiver The dynamic range of the receiver is actually related to the two indicators we talked about before, the first is the reference sensitivity, and the second is the receiver IIP3 (interference indicator).The reference sensitivity actually characterizes the minimum signal strength that the receiver can recognize. We mainly talk about the maximum receiving level of the receiver.It refers to the maximum signal that the receiver can receive without distortion. This distortion may occur at any stage of the receiver, from the previous LNA to the receiver ADC. For the front-level LNA, the only thing we can do is to increase IIP3 as much as possible so that it can withstand higher input power. For the subsequent step-by-step devices, the receiver uses AGC (automatic gain control) to ensure that the useful signal falls on the device within the input dynamic range. Simply put, there is a negative feedback loop: detect the received signal strength (too low/too high)-adjust the amplifier gain (up/down)-the amplifier output signal to ensure that it falls within the input dynamic range of the next stage device.Here we talk about an exception: the front-end LNA of most mobile phone receivers has AGC function. If you study their datasheet carefully, you will find that the front-end LNA provides several variable gain sections, and each gain section has its corresponding noise factor. Generally speaking, the higher the gain, the lower the noise factor. This is a simplified design. The design goal of the receiver RF link is to keep the useful signal input to the receiver ADC within the dynamic range and keep the SNR higher than the demodulation threshold (the SNR is not critical,  but "just enough"). Therefore, when the input signal is large, the front-stage LNA reduces gain, loss NF, and increases IIP3 at the same time. When the input signal is small, the front-stage LNA increases gain, reduces NF, and meanwhile reduces IIP3. Figure 5. RFID Discover 1.9.3 Temperature Compensation Generally speaking, we only have temperature compensation in the transmitter. Of course, the receiver performance is also affected by temperature. On the one hand, the receiver link gain decreases at high temperatures, and NF increases. On the other hand, at low temperatures, receiver link gain increases, and NF decreases. However, due to the small signal characteristics of the receiver, both gain and NF are within the range of system redundancy.It can also be subdivided into two parts: one part is the compensation for the power accuracy of the transmitted signal, and the other part is the compensation for the change in the transmitter gain with temperature.Transmitters of modern communication systems generally perform closed-loop power control (except for the slightly "old" GSM system and Bluetooth system). Therefore, the power accuracy of transmitters calibrated through production procedures actually depends on the accuracy of the power control loop. Generally speaking, the power control loop is a small signal loop, and the temperature stability is very high, so the demand for temperature compensation is not high, unless there are temperature-sensitive devices (such as amplifiers) on the power control loop.Temperature compensation for transmitter gain is more common, which has two common purposes:One is "visible", usually for systems without closed-loop power control (such as the aforementioned GSM and Bluetooth), this type of system usually does not require high output power accuracy, so the system can apply a temperature compensation curve (function) to keep the RF link gain within an interval. So that when the baseband IQ power is fixed and the temperature changes, the RF power output by the system can also be kept within a certain range.The other is "invisible", usually in a system with closed-loop power control. Although the RF output power of the antenna port is precisely controlled by the closed-loop power control, we need to keep the DAC output signal within a certain range (A common example is the need for digital predistortion (DPD) of the base station transmission system), then we need to control the gain of the entire RF link more accurately around a certain value.In the early stage of low accuracy and low cost accuracy requirements, temperature compensation attenuators are more common. Require higher accuracy requirements, the solution generally: temperature sensor + digital attenuator/amplifier + production calibration. 1.9.4 Power Control of the Receiver After talking about dynamic range and temperature compensation, let's talk about a related and very important index: power control.Transmitter power control is a necessary function in most communication systems. Commonly used in 3GPP, such as ILPC, OLPC, and CLPC. In addition, it must be tested in RF design.All transmitter power control purposes include two points: power consumption control and interference suppression.Let’s first talk about power consumption control: In mobile communications, in view of the changes in the distance between the two ends and the different levels of interference, for the transmitter, it is only necessary to maintain the signal strength enough for the receiver of the other party to demodulate accurately. If it is low, the communication quality is impaired, and if it is too high, the empty power consumption is meaningless. This is especially true for battery-powered terminals like mobile phones.Interference suppression is a more advanced requirement. In CDMA-type systems, because different users share the same carrier frequency (differentiated by orthogonal user codes), in the signal arriving at the receiver, user's signal is covered by the same frequency for other users. If the signal power of each user is high or low, the high-power user will drown out the low-power user’s signal. Therefore, the CDMA system adopts a power control method to control the power of different users reaching the receiver, and sends a power control command to each terminal to make the air interface power of each user the same. This kind of power control has two characteristics: the first is that the power control accuracy is very high (the interference tolerance is very low), and the second is that the power control cycle is very short (the channel may change quickly).In the LTE system, uplink power control also has the effect of interference suppression. Because LTE uplink is SC-FDMA, and multiple users also share carrier frequencies, which also interfere with each other, so the same air interface power.The GSM system also has power control. In GSM, we use power level to characterize the power control step length, each level is 1dB. It can be seen that GSM power control is relatively rough.Interference Limited SystemHere is a related concept: interference limited system. The CDMA system is a typical interference limited system. In theory, if each user code is completely orthogonal and can be completely distinguished by interleaving and de-interleaving, then the capacity of the CDMA system can be infinite. Because it can be used on limited frequency resources. The user code extended layer by layer distinguishes an infinite number of users. But in fact, since the user codes cannot be completely orthogonal, noise is inevitably introduced during multi-user signal demodulation. The more users there are, the higher the noise will be, until the noise exceeds the demodulation threshold. In other words, the capacity of the CDMA system is limited by interference (noise).The GSM system is not an interference limited system, but a time-domain and frequency-domain limited system. Its capacity is limited by frequency (a carrier frequency of 200kHz) and time domain resources (8 TDMAs can be shared on each carrier frequency user). Therefore, the power control requirements of the GSM system are not strict. 1.9.5 Transmitter Power Control and Transmitter RF Indicators Next, let's discuss the factors that may affect the transmitter power control in the RF design.For RF, if the power detection (feedback) loop design is correct, then we can do not much for the transmitter closed-loop power control (most of the work is done by the physical layer protocol algorithm), and the most important thing is the flatness in the transmitter band.Because the transmitter calibration can only be carried out on a limited number of frequency points, especially in the production test, the less frequency points the better. However, it is entirely possible for the transmitter to work on any carrier in the frequency band in practice. In a typical production calibration, we will calibrate the transmitter's frequency points to keep accuracy. So the closed-loop power control is correct at the calibrated frequency points. However, if the transmit power is not flat in the entire frequency band, some frequency points deviates greatly from the calibration frequency point. Therefore, the closed-loop power control with the calibration frequency point as a reference will have errors and even mistakes.   Ⅱ FAQ 1. What is RFID and how it works?RFID tags transmit data about an item through radio waves to the antenna/reader combination. ... The energy activates the chip, which modulates the energy with the desired information, and then transmits a signal back toward the antenna/reader. 2. What is RFID used for?RFID tags are a type of tracking system that uses radio frequency to search, identify, track, and communicate with items and people. Essentially, RFID tags are smart labels that can store a range of information from serial numbers, to a short description, and even pages of data. 3. Is RFID harmful to human?Electromagnetic fields generated by RFID devices—touted as a patient-safety technique to keep track of supplies, medical tests and samples, and people—could cause medical equipment to malfunction, according to a recent study of medical devices in Amsterdam published in the June 25 Journal of the American Medical. 4. What is RFID example?For example, an RFID tag attached to an automobile during production can be used to track its progress through the assembly line, RFID-tagged pharmaceuticals can be tracked through warehouses, and implanting RFID microchips in livestock and pets enables positive identification of animals. 5. What are the components of RFID?Every RFID system consists of three components: a scanning antenna, a transceiver and a transponder. When the scanning antenna and transceiver are combined, they are referred to as an RFID reader or interrogator. 6. Who discovered RFID?Charles WaltonRFID was, however, officially invented in 1983 by Charles Walton when he filed the first patent with the word 'RFID'. NFC started making the headlines in 2002 and has since then continued to develop. 7. How is RFID made?The antenna can be made of etched copper, aluminum or conductive ink, while the chip and antenna are typically put on a substrate that is PET or paper. ... Usually, this inlay is inserted into a printable label to create an RFID transponder that can be affixed to a product. 8. Where did RFID come from?The First RFID PatentsMario W. Cardullo claims to have received the first U.S. patent for an active RFID tag with rewritable memory on January 23, 1973. That same year, Charles Walton, a California entrepreneur, received a patent for a passive transponder used to unlock a door without a key. 9. What is a RFID system?Radio Frequency Identification (RFID) refers to a wireless system comprised of two components: tags and readers. ... Passive RFID tags are powered by the reader and do not have a battery. Active RFID tags are powered by batteries. RFID tags can store a range of information from one serial number to several pages of data. 10. What are the three parameters that define an RFID system?Every RFID system consists of three components: a scanning antenna, a transceiver and a transponder. When the scanning antenna and transceiver are combined, they are referred to as an RFID reader or interrogator. 11. What are the basic criteria in RFID?Many large organizations and government agencies have mandated that their suppliers provide goods with RFID tags. These published mandates may specify tag type, frequency, amount of memory, read range, read rate and speed, and protocol. In addition, the mandates may specify how the goods should be tagged. 12. What is the maximum read range of RFID module?Maximum read distance of 1.5 meters (4 foot 11 inches) - usually under 1 meter (3 feet) and you can use a single or multi port reader plus custom antennas to extend the read range to longer tag read distances or a wider RFID read zone. 13. What is RFID in supply chain management?+RFID (Radio Frequency Identification) is a form of extremely low-power data communication between a RFID scanner and an RFID tag. ... The tags are placed on any number of items, ranging from individual parts to shipping labels. 14. How many bits does an RFID tag have?It depends on the vendor, the application and type of tag, but typically a tag carries no more than 2 kilobytes (KB) of data—enough to store some basic information about the item it is on. Simple “license plate” tags contain only a 96-bit or 128-bit serial number. 15. Does RFID reader store data?An RFID tag can store large amounts of data additionally to a unique identifier • Unique item identification is easier to implement with RFID than with barcodes. • Its ability to identify items individually rather than generically.

ⅠIntroduction A diode is a semiconductor device that functions as a one-way current switch. It allows current to flow freely in one direction while severely limiting current flow in the opposite direction. Because they convert alternating current (ac) to pulsating direct current (dc), diodes are also known as rectifiers (dc). Diodes are classified based on their type, voltage, and current capacity. Diodes have polarity, which is determined by an anode (positive lead) and a cathode (negative lead) (negative lead). Catalog ⅠIntroduction Ⅱ Diode Related Video: Ⅲ How to Tell Which Way Round a Diode Should Be? 3.1 Examining the Markings 3.2 USing a Multimeter Ⅳ How to Check the Direction of a Diode? Ⅴ How to Check if a Diode Is Bad? Ⅵ How to Test a Diode Rectifier? Ⅶ How to Test Diodes with a Digital Multimeter？ 7.1 Diode Test Analysis Ⅷ FAQ     Ⅱ Diode Related Video: Diodes Explained - The basics how diodes work working principle pn junction Diode Video Description: Diodes Explained, in this tutorial we look at how diodes work, where diodes are used, why diodes are used, the different types. We look at diodes in half and full bridge rectifiers to convert AC to DC.   Ⅲ How to Tell Which Way Round a Diode Should Be? A diode is a two-terminal electronic device that conducts current in one direction while blocking current in the other. A diode, also known as a rectifier, is a device that converts alternating current (AC) to direct current (DC). Because diodes are essentially "one-way," it's critical to understand how to tell which end is which. You can usually tell by looking at the markings on the diode, but if they've worn off or don't exist, you can test the diode with a multimeter. 3.1 Examining the Markings     Figure1: P-type   Understand how a diode works. An N-type semiconductor is joined to a P-type semiconductor to form a diode. The N-type semiconductor serves as the negative end of the diode and is referred to as the "cathode." The P-type semiconductor, also known as the "anode," is the diode's positive end. The diode will conduct current if the positive side of a voltage source is connected to the positive end of the diode (the anode) and the negative side is connected to the negative end of the diode (the cathode). The current is blocked if the diode is reversed (up to a limit).   Figure2: schematic symbol   Discover the meaning of the diode schematic symbol. On schematics, diodes are represented by a symbol that explains how to install the diode. An arrow points to a vertical bar with a line extending from it. The arrow represents the diode's positive side, while the vertical bar represents its negative side. Consider the positive side flowing into the negative side, with the arrow indicating the flow direction.   Figure3: large band   Seek out the large band. If the schematic symbol is not printed on it, look for other items such as a ring, band, or line. A bulk of colored bands will be printed near the diode's negative side (cathode) on the majority of diodes. The band will wrap completely around the diode.   Figure4: Recognize the positive end of an LED Recognize the positive end of an LED. An LED is a light-emitting diode, and the legs usually indicate which side is positive. The positive, anode pin is on the longer leg. Examine the LED's outer casing if the pins have been trimmed. The negative, cathode pin is the one closest to the flat edge.     3.2 USing a Multimeter Figure5: Recognize the positive end of an LED Recognize the positive end of an LED. An LED is a light-emitting diode, and the legs usually indicate which side is positive. The positive, anode pin is on the longer leg. Examine the LED's outer casing if the pins have been trimmed. The negative, cathode pin is the one closest to the flat edge.   Figure6: Connect the diode   Connect the diode to the multimeter. Connect the positive lead to the diode's positive end and the negative lead to the diode's negative end. The meter's display should show a reading. If your meter has a Diode mode, the voltage will be displayed on the meter if it is connected positively to positive and negatively to negative. Nothing will be displayed if it is entered incorrectly. If your meter does not have a Diode mode, connecting it positive-to-positive and negative-to-negative will result in very low resistance. If you go the wrong way, you'll encounter a lot of resistance, which is sometimes expressed as "OL."   Figure7: Examine an LED Examine an LED. A light-emitting diode (LED) is a semiconductor that emits light. Set the multimeter to the diode function. Place one of the positive leads on one of the pins and the other on the other. If the LED illuminates, the positive lead is in contact with the positive pin (the anode) and the negative lead is in contact with the negative pin (the cathode). If it doesn't light up, it's because the leads are touching opposite pins.   Ⅳ How to Check the Direction of a Diode? Electronic circuits are designed to collaborate with other circuits to form a unit that performs a specific task. Many circuits, such as power regulation circuits, have to be safeguarded against power "spikes" and accidental polarity reversal. A diode is an electronic component that allows electricity to flow in only one direction while preventing potentially harmful reversals from reaching the sensitive circuit. The current flows into the diode's "cathode" (negative side) and then out the "anode" (positive side) toward the protected circuit. When installing a diode, you must be familiar with electronics standards. Understand the circuit's schematic diagram. Trace the electrical polarity as it passes through the circuit until it reaches the point where the cathode (negative side) of the diode is to be soldered to the board. In a schematic, a diode glyph has a vertical line on one side and a solid black arrow pointing to that line. The diode's cathode is represented by the vertical line. That end of the diode must face the direction of the negative current flow. Examine your diode thoroughly, using a magnifying glass if necessary. On the cathode (negative) end of every diode, there is either a colored dot or a band printed. On the cathode end of a black plastic diode, a white band will be painted, whereas glass diodes will have either a white or a black band. In the absence of polarity markings, use a digital multimeter to test the polarity of a diode. To measure "Ohms," simply turn the meter unit on and turn the dial. Connect the black (negative) test probe to one of the diode's metal legs and the red (positive) test probe to the other. Reverse the probes if there is no reading or only a "1" displayed on the meter. When you get an actual ohm reading on the display, make a note of which side the negative (black) probe is on. That is the diode's cathode (negative) side.   Tips: The small white band on the cathode side of a glass diode may be difficult to see. To make the white band move visible, place the glass diode on a dark piece of paper or fabric if necessary.On some types of diodes, the band colors can vary, but never the positioning. A diode's band is always on the cathode side. The color of the band is unimportant.Additional bands on some specialty diodes, such as Zener diodes, represent tolerance and voltage values. Even so, the polarity band is the first band at the end.   Ⅴ How to Check if a Diode Is Bad? Tools Digital multimeterSoldering ironDesoldering braidPliers     Ⅵ How to Test a Diode Rectifier? Testing a Rectifier With the Diode Function If your multimeter has a diode function, one of the dial settings will have a symbol that looks like a diode. When this option is selected, a voltage exists between the meter leads, and when you touch them to the diode terminals, the meter records the voltage drop. The voltage drop in the forward direction is usually in the range of 0.5 to 0.8 volts. Because no current flows in the opposite direction, the meter either reads 0 or OL, which stands for open loop. To begin the test, ensure that the circuit is unplugged and that all capacitors in the circuit have been discharged. You do not need to remove the diode from the circuit if you do this. Begin by connecting the negative meter lead (usually black) to the cathode of the diode and the positive lead (red) to the anode. Keep a close eye on the meter reading, which should be between 0.5 and 0.8 volts. If it's close to zero, the diode is faulty. Reverse the leads now. If you get a reading of 0 or OL, the diode is fine. If you get nearly the same voltage reading, the diode has shorted and is no longer operational.   Conducting a Diode Test With an Ohmmeter When performing a resistance test, the diode must be removed from the circuit. Before you begin, turn off the power and discharge any capacitors in the circuit. This is especially important when testing a microwave diode because the microwave's high voltage capacitor can cause a severe shock. Set the multimeter to measure resistance () and connect the black (negative) and red (positive) leads to the cathode and anode, respectively. The diode is forward-biased in this configuration, and you should get a resistance reading between 1 K and 10 M. Change the leads to the opposite terminals. Now that the diode has been reverse-biased, the reading should be infinity or OL. If the readings in both directions are the same, the diode is faulty.   Ⅶ How to Test Diodes with a Digital Multimeter？ Figure8: Diode Test mode The Diode Test mode on a multimeter generates a low voltage between the test leads. When the test leads are connected across a forward-biased diode, the multimeter displays the voltage drop. The Diode Test is carried out as follows: Ascertain that a) all power to the circuit is turned off and b) there is no voltage at the diode. Voltage may exist in the circuit as a result of charged capacitors. If this is the case, the capacitors must be discharged. Set the multimeter to measure alternating current or direct current voltage as needed.Set the dial (rotary switch) to Diode Test. It may share a dial position with another function.Connect the diode's test leads. Take note of the displayed measurement.The test leads should be reversed. Take note of the displayed measurement.   7.1 Diode Test Analysis For the most commonly used silicon diodes, a good forward-based diode has a voltage drop of 0.5 to 0.8 volts. The voltage drop in some germanium diodes ranges from 0.2 to 0.3 V. When a good diode is reverse-biased, the multimeter displays OL. The OL value indicates that the diode is operating as an open switch. A faulty (opened) diode prevents current from flowing in either direction. When the diode is opened, a multimeter will show OL in both directions. In both directions, a shorted diode has the same voltage drop reading (approximately 0.4 V). Figure9: Diode test analysis When the positive (red) test lead is on the anode and the negative (black) test lead is on the cathode, the diode is forward biased. A good diode's forward-biased resistance should be between 1000 and 10 M. When the diode is forward-biased, the resistance measurement is high because the current from the multimeter flows through the diode, resulting in the high-resistance measurement required for testing. When the positive (red) test lead is on the cathode and the negative (black) test lead is on the anode, the diode is reverse-biased. On a multimeter, the reverse-biased resistance of a good diode displays OL. If the readings in both directions are the same, the diode is faulty. Figure10: resistance   The resistance mode procedure is conducted as follows: Ascertain that a) all power to the circuit is turned off and b) there is no voltage at the diode. Voltage may exist in the circuit as a result of charged capacitors. If this is the case, the capacitors must be discharged. Set the multimeter to measure alternating current or direct current voltage as needed.Set the dial to Resistance (). It may share a dial position with another function.After the diode has been removed from the circuit, connect the test leads to it. Take note of the displayed measurement.The test leads should be reversed. Take note of the displayed measurement.When testing diodes in the Resistance mode, compare the readings to a known good diode for the best results.   Ⅷ FAQ 1. What are the 3 main uses of diodes? Application of Diode Rectifying a voltage: turning AC into DC voltages.Drawing signals from a supply.Controlling the size of a signal.Mixing (multiplexing) signals.As freewheeling of the inductive energy. 2. Are diodes AC or DC? It allows current to flow easily in one direction, but severely restricts current from flowing in the opposite direction. Diodes are also known as rectifiers because they change alternating current (ac) into pulsating direct current (dc). 3. What is diode made of? Today, most diodes are made of silicon, but other semiconducting materials such as gallium arsenide and germanium are also used. 4. What is diode resistant? Hence, diode resistance can be defined as the effective opposition offered by the diode to the flow of current through it. ... Ideally speaking, a diode is expected to offer zero resistance when forward biased and infinite resistance when reverse biased. 5. How diodes are formed? A diode is formed by joining two equivalently doped P-Type and N-Type semiconductor. ... At the point of contact of the P-Type and N-Type regions, the holes in the P-Type attract electrons in the N-Type material. Hence the electron diffuses and occupies the holes in the P-Type material.

IntroductionIn the era of smart phones, there are two ways to extend battery life, one is to directly use a large-capacity battery, and another is to use quick charge technology. Using large-capacity batteries is a easy way but with bulky piece of phones. Here let’s talk about the quick charge. How can you make the phone charge faster?How Does Fast Charging Work?CatalogIntroductionⅠ Quick Charge FactorsⅡ Battery Charging Basics2.1 Charging Heat2.2 Charging PowerⅢ Quick Charge Development3.1 USB Battery Charge 1.23.2 Qualcomm Quick Charge3.3 OPPO VOOC Charge3.4 Pump Express (PE)3.5 OnePlus Dash Charge3.6 Huawei SuperCharge3.7 Low Voltage Solution3.8 Quick Charge AgreementⅣ FAQ Ⅰ Quick Charge FactorsTo realize the quick charging function on the mobile phone, three elements need to be met: Charger, Battery, Charge IC. Adding a point, the charger needs to meet sufficient output current and voltage, because the wiring of the charger has a large parasitic resistance. If requiring a larger charging current, the on-load output voltage of the charger needs to be higher.Quick charge tech of smartphones is mainly divided into three categories: VOOC flash charge, Qualcomm Quick Charge 2.0, and MediaTek Pump Express Plus.At present, the mainstream modes of quick charge on the market include three modes: High voltage and constant currentLow voltage and high currentHigh voltage and high currentFigure 1. Fast ChargingⅡ Battery Charging Basics2.1 Charging HeatHow does the battery charge and solve the heat?Figure 2. Heating Up While ChargingThe basic condition for battery charging is that the charger voltage must be higher than the battery voltage to generate a charging current and complete the charge transfer process. At present, most of the batteries of mobile phones are composed of single lithium or multiple lithium. Generally, the working voltage of mobile phone batteries is about 3.3V~4.2V. During discharge, the voltage will drop, so the average voltage is about 3.7V-3.8V.When charging, the electric energy enters the mobile phone and is processed by the step-down circuit in the mobile phone, and then outputs a voltage of about 3.3~4.5V to charge the battery. And this voltage drop process is responsible for the charge management IC module in the mobile phone. It is responsible for converting the current output by the power supply into a current through the battery. In this process, there will be a certain loss, which will be transferred out of heat.2.2 Charging PowerIn the case of a certain battery level, power indicates the charging speed, the higher the power, the faster the charging speed.Power (P) = voltage (V) x current (I)In theory, increasing the current and voltage can higher the charging power of the battery, but lithium batteries are prone to battery damage or deflagration due to undervoltage or overvoltage. Thus mobile phones must be equipped with a complete power circuit. Among them, the charging control IC and the power control IC are the most important. Ⅲ Quick Charge DevelopmentAccording to theory, quick charge adjust the input value of the voltage and current, thereby shorten the charging time of the mobile phone. Next, let us take a look at the development history of it.The charging standard of mobile phones can be traced back to the era of feature phones, which can be started from the charging standard USB BC 1.2 (BC is the abbreviation of Battery Charge).3.1 USB Battery Charge 1.2The USB specification was first introduced in 1995. It was developed by USB Implement Forum (USB IF), including Intel, NEC Corporation, Compaq, DEC (American Digital Equipment Corporation), IBM (International Business Machines Corporation), Microsoft, and Northern Telecom.The USB BC1.2 standard was published by the USB IF in 2010. It refers to the ability to directly charge the battery of a portable device, and has become a key standard for establishing the correct way to charge the battery through the USB port. So BC1.2 is a set of official standards that can use USB interface to charge portable devices like mobile phones (including power-off charging). Here you may ask, what is the relationship between the USB specification protocol and fast charging?The emergence of USB BC 1.2 makes simultaneous charging and data transmission a reality. Although the USB interface was originally used by manufacturers to transfer data and connect devices such as keyboard or mouse instead of charging. Just think, wouldn't it be much more convenient if you can use the USB interface to charge these devices? So USB BC 1.2 came into being. Although the maximum voltage of the USB interface was still 5V at that time, and the maximum current of USB charging is 1.5A. Although it did not increase the voltage (mainly to adapt to other portable devices), but the USB interface can reach 7.5W with 1.5A current. At that time, the USB BC 1.2 is enough to cope with the charging of mobile phones.The emergence of USB BC 1.2 not only ended the chaotic scenes of USB charging specifications at that time, but it also has good support for hubs/distributors/HUB. So the USB interface data line has become the hot product of various manufacturers for a while. But there is also a data cable with a MicroUSB 2.0 interface (also known as the Android cable). It has only four wires inside, and its current carrying capacity is very limited (2A is the max).Although the USB BC 1.2 standard was able to meet the charging needs of mobile phones at the time, the development of mobile phones has not stopped. With the time goes by, mobile phones have more and more functions. In order to cope with daily use, the battery capacity has also become larger and larger, and the battery capacity has also exceeded 2000mAh, but with the extension of the charging time. When the cell phone battery capacity reaches 3000mAh or even 4000mAh, does it have to be charged overnight? So the charging speed again meets forward higher requirements.3.2 Qualcomm Quick ChargeIn 2013, it was the chip supplier Qualcomm who discovered this problem. Qualcomm first put forward the concept of "Fast Charge", and Quick Charge 1.0 was born. Improve the charging efficiency by increasing the input current, support 5V/2A, that is, the maximum charging power of 10W, breaking through the 1.5A current upper limit of the USB Battery Charge 1.2. In the same year, Huawei also introduced the "fast charge" concept to the first generation of Mate phones, which also supports 5V/2A input, and can fully charge a 4050mAh battery within 3.5 hours.In 2014, the situation was a little different. Qualcomm overturned the QC1.0 strategy and adopted a high-voltage quick charging solution.As mentioned above, P (power) = V (voltage) * I (current), because the data line of MicroUSB 2.0 can only support up to 2A current. Since it couldn’t to increase the current at that time, only adjust the voltage. For example, a fast charge with 18W power, if you want to use a 5V voltage, the current has exceeded 3A. A normal MicroUSB can never withstand such a high current. Using a voltage of 12V, the current only needs 1.5A, so the problems had be solved.The big advantage of this high-voltage fast charging tech is that the cost is relatively low (no need to buy different data cables), and the disadvantages are also obvious. The voltage of the charger is suddenly increased to twice as much, and the step-down heat is also extremely large for the mobile phone. So a major shortcoming of high-voltage quick charge is that the mobile phone generates serious heat during charging.This fast charging solution is the high-voltage QC2.0. It is the most popular and influential standard in the history of QC. For example, Samsung’s 2018 flagship Galaxy S9 still uses the QC2.0.Figure 3. Qualcomm Quick ChargeQC2.0 has improved the charging voltage from the conventional 5V that has been maintained for many years to 9V/12V/20V. It achieves 18W high-power power transmission at the same 2A current as QC1.0, and does not require special wires.QC2.0 has far-reaching influence because of its powerful compatibility. At that time, Micro USB was the standard configuration of smart phones, but it was restricted by the physical interface. Once the current exceeds 2A, it is prone to damage. The smart part of QC2.0 bypasses the restrictions of the Micro USB interface and the data cable, and only increases the charging speed by directly adjusting the input voltage. What’s more, QC2.0 quick charge tech has given peers a idea for reference.3.3 OPPO VOOC ChargeFor example, OPPO introduced VOOC (Voltage Open Loop Multi-step Constant-Current Charging). What OPPO uses here is another solution. There is a fact that normal MicroUSB data cable can't carry such a large current. Because the usual MicroUSB data cable has only five measuring points and four wires, so just increase their number. Therefore, the original VOOC charging head is extremely big because of integrates IC circuit.In addition, because the circuit is rebuilt, you can only use the official special data cable, and the ordinary MicroUSB data cable cannot achieve the fast charging effect. The shortcoming is obvious that the cost is high. But the biggest problem is that high-current charging has more damages. For example, it has been shortening the battery service life of many mobile phones because of VOOC quick charge a year later.Following the principle of "equivalent exchange", since such a heavy price has been paid, there will certainly be generous returns. The advantage of the first-generation VOOC fast charge is that with the 5V/5A 25W ultra-high power, OPPO mobile phones equipped with VOOC fast charge are extremely fast in charging speed. And it puts the heat source into the charger externally, and the heat generated by the mobile phone during charging is significantly less than that of the high-voltage fast charging solution. As a result, the high-voltage fast charging solution led by Qualcomm QC and the low-voltage and high-current fast charging solution led by OPPO VOOC have parted ways.VersionLaunch TimeVoltage/CurrentDescriptionVOOC 2.020155V/4ASame as the first versionVOOC 3.020195V/5ACharge the phone up to 55% in 30 minutesVOOC 4.0202010V/5A(50W)Charge the phone up to 67% in 30 minutesSuperVOOC20185V/6A (30W)Charge a two-cell battery in seriesSuperVOOC 2.0202010V/6.5A (65W)Successor of Super VOOC with GaN technologyThe key to fast charging of mobile phones is the small micro USB interface. At this time, USB type-C appears. Simply list its advantages, such as: support positive and negative plug compatibility, compatible with USB 3.1 standards, support 10Gbit/s transmission in maximum, support the USB Power Delivery charging protocol, support 5A current, the maximum can provide 100W of power. Therefore, the Type-C interface is inherently friendly to large currents.Qualcomm is a giant in mobile phone chips and communications patents, and by virtue of its dominant position, it can quickly popularize its fast charging standards to gain the standard license fee. However, various manufacturers have also begun to develop their own fast charging standards to share this big cake.3.4 Pump Express (PE)Also in 2014, MediaTek launched its own Pump Express (PE) quick charge tech, and Meizu's mCharge fast charging is based on this, and the later Pump Express Plus (PEP) fast charging. Huawei launched the Fast Charge Protocol (FSP) in the early days. As for Xiaomi and Nubia, many manufacturers that still use Qualcomm QC for their flagship mobile phones. They belong to high-voltage fast charging scheme.3.5 OnePlus Dash ChargeNext, let’s talk about OnePlus. Although OnePlus uses Qualcomm’s SoC, but chose a low-voltage and high-current charging solution, that is, Dash charge. It first debuted with the launch of OnePlus 3, where OnePlus promised 60% of full charge in just 30 minutes of charging.Seeing this, do you think that Qualcomm's high-voltage fast charging solution has won the victory, while the low-voltage solution can survive hardly?Of course not, the turning point is that more and more mobile phones are equipped with USB Type-C interface. By 2016, it has become popular. For example, Android flagship phones basically use this interface.3.6 Huawei SuperChargeIn the same year, Huawei improved its FastCharge (FCP) to SuperCharge (SCP). SCP can be said to be one of the fastest/good compatible fast charging representatives in the world, and is compatible with PD and Qualcomm QC protocols.3.7 Low Voltage SolutionMediaTek has also switched to a low-voltage solution. Pump Express technology has developed to 3.0. Pump Express 3.0 is the world's first fast charging solution that uses Type-C interface for direct charging. This solution can effectively prevent the phone from getting hot during charging. In a word, it is very safe.In 2017, Meizu released Super mCharge quick charge tech. It has a charging power of up to 55W at 11V/5A. Unfortunately, due to the inability to get mass production, this 55w super fast charge is still not applied to mobile phones, and replaced by MCharge4.0 fast charging technology. The earlier mCharge3.0 is a high-voltage fast charging solution (24W), and its charger output voltage can reach up to 12V; while mCharge4.0 (25W) belongs to low-voltage and high-current solution, with 5V output voltage and 5A current.Qualcomm began to discover the advantages of the low-voltage solution, so it uses the low voltage and high current solution in the QC4.0 fast charging protocol. Of course, it also supports high voltage fast charging at the same time.Although low-voltage and high-current solutions have basically ruled fast charging, the fast charging protocols of various companies are not compatible with each other. That is to say, although they all use Type-C, they must use the fast charging function of mobile phones corresponding to their own agreement. In other words, although they are all Type-C interfaces, the fast charge protocol is different.3.8 Quick Charge StandardFortunately, the USB IF has unified the fast charging standard. Mobile phones should employ fast charge according to the USB PD protocol. Adjust voltage and current. This standard is also supported by Google. However, various manufacturers make their own mobile phones, and use their own fast charging protocols. So the USB PD protocol has been put aside.The main reasons why mobile phone manufacturers have become more obsessed with constant voltage and high current over the years are: greater power and less charging heat. The USB PD3.0 has successfully incorporated Qualcomm's QC4 protocol. So far, USB PD3.0 has been the regular rule. In short, manufacturers who want to continue to develop their own charging technology, they only need to be based on the USB PD protocol. Moreover, the latest 100W fast charge has been successfully tested. Although large-scale commercial use is unlikely right now, the technical bottleneck will always be overcome.Every Fast Charging Standard Explained Ⅳ FAQ1. What is considered quick charge?For fast charging, you're looking at something that bumps the voltage up 5V, 9V, 12V, and beyond, or increases amperage to 3A and above. Keep in mind, your device will only take in as much power as its charging circuit is designed for.2. Does Quick Charge work with any cable?Do I need any specific equipment for fast charge? Fast charge requires 3 components – a compatible phone/tablet/laptop or other device, a charger that supports USB Fast charge, and a compatible cable. The cable will have USB-C at least on the charger end, and either USB-C or Apple Lightning on the device end.3. Is fast charging bad?The bottom line is, fast charging won't impact your battery life substantially. But the physics behind the technology means you shouldn't expect the battery to last longer than using a conventional “slow” charging brick.4. What phones use quick charge?Apple, Samsung, Google, OnePlus, LG, Sony, Motorola, Huawei, Xiaomi, OPPO, ViVo and Realme.5. What is the meaning of VOOC?The OPPO VOOC (Voltage Open Loop Multi-step Constant-Current Charging) Flash Charging system is a proprietary rapid-charge technology created by OPPO Electronics, which, at present, is able to charge certain OPPO devices from 0 to 75% in just 30 minutes.6. Which phones support VOOC?Realme Narzo 20 Pro (65W Dart Charging)Realme 7 (30W Dart Charging)Realme 7i (18W)Realme 6 (30W VOOC fast charging)Realme X2 (30W VOOC fast charging)7. What is difference between Dash and Warp Charge?The key difference in the two standards is the increase in wattage on the Warp Charge standard. ... In comparison, Dash Charge uses a 5V / 4A (20W) configuration, and both require dedicated Warp Charge / Dash Charge compatible cables to carry the energy.8. Can you use Dash charge with other phones?Dash charge won't harm the phone.. Yes it can. I don't think OnePlus' type C cables or charger are up to USB Type C specifications. I would advise to not do it and get the proper cables and charger for your other device.9. How fast is Huawei SuperCharge?46 mAh per minuteAn infographic put together by Hometop shows that Huawei Super Charge is the fastest at over 46 mAh per minute.10. What is MediaTek Pump Express?Pump Express 4.0 is the latest advance in MediaTek's family of charging innovations. This next-generation charging technology will change your (battery) life, cutting smartphone battery recharge times by over half, compared to a standard USB charger.11. What is MediaTek Pump Express 2.0?They use the MediaTek Pump Express 2.0 fast charging technology and reach a 35% (1,785mAh) in just 30 minutes giving several hours use. It can fully charge the huge battery via its USB-C connector from 0-100% to give 2 full days use in just 2.5 hrs.12. What is super flash charge?The company introduced its 65W SuperVOOC charging that can charge 4000mAh battery on the Reno Ace / Ace2 fully in about 30 minutes. ... The company's 125W fast charging is rumoured to charge the phone's battery from 0 to 100% in about 10 minutes.13. What is DART charge Realme?The Realme 30W Dart Charge Power Bank is an easy recommendation from our side for anyone who owns a compatible device. It comes with two-way fast charging and support for multiple quick charge protocol support. The power bank is also compatible with multiple smartphones apart from Realme.

ⅠIntroduction Motor capacitors temporarily store an electrical charge to provide additional torque and improve the performance and efficiency of a motor. Start capacitors provide added torque during motor startup and then exit the circuit when the motor reaches operating speed. Run capacitors assist the motor in maintaining a consistent charge while it is running. By balancing working power and supplied power, power factor correction capacitors reduce motor power consumption caused by heavy inductive loads. Motor capacitors are most frequently used to power motors in HVAC applications such as fans, blowers, and compressors, but they are also found in pumps, conveyors, and machine tools. What does a run capacitor look like? Catalog ⅠIntroduction Ⅱ Two Types of Motor Capacitor 2.1 What is the run capacitor？ 2.2 What is the starter capacitor? Ⅲ Run Capacitor Related Video Ⅳ Specifications of Run Capacitor Ⅴ Faulty Run Capacitor 5.1 When Is It Time to Replace a Run Capacitor? 5.2 Causes of Failure Ⅵ How To Replace a Start Run Capacitor? Ⅶ How Do They Work In an HVAC System? Ⅷ Dual Capacitors vs. Run Capacitors vs. Run Capacitors   Ⅱ Two Types of Motor Capacitor Motor capacitor include two types: run capacitor and starter capacitor. Let us have a look at the two capacitors.   2.1 What is the run capacitor？ Run capacitors are rated in the 3–70 microfarad range (uF). Voltage classification is also applied to rate run capacitors. The voltage levels are 370V and 440V. Starting capacitors have ratings greater than 70 microfarads (uF). Run capacitors are designed for continuous duty and remain energized throughout the lasting of the motor's operation. A capacitor is required to power a second phase winding in a single-phase electric motor. This is why the sizing is so crucial. The motor will not have an even magnetic field if the incorrect run capacitor is installed.This case will lead to the rotor hesitating at uneven spots. This pause causes the motor to become noisy, increases energy consumption, reduces performance, and causes the motor to overheat.   2.2 What is the starter capacitor? In contrast to run capacitors, which have a specific uF rating, starting capacitors are housed in a black plastic case and have an uF range. Start capacitors (with ratings of 70 microfarads or higher) are classified into three voltage classes: 125V, 250V, and 330V. A 35 uF at 370V run capacitor and an 88–108 uF at 250V start capacitor are two examples. Start capacitors increase motor starting torque and allow a motor to be rapidly cycled on and off. Start capacitors are designed for one-time use only. Start capacitors are energized for a short time, allowing the motor to reach 3/4 of its full speed before being disconnected from the circuit.   Ⅲ Run Capacitor Related Video   Start Capacitors & Run Capacitors for Electric Motors - Differences Explained by TEMCo run capacitor video descriped:  What's the difference between a start capacitor and a run capacitor? Can you use them interchangeably? See why these two types of capacitors cannot always be substituted for one another.   Ⅳ Specifications of Run Capacitor Most run capacitor applications employ capacitance ratings of 2.5-100 uf (microfarads) and voltages of 370 or 440 VAC. They are also usually rated at 50 and 60 Hz. Cases are typically round or oval in shape, with a steel or aluminum shell and cap. Terminals are typically 14" push-on terminals with 2-4 terminals per connection post.   Specifications of Run Capacitor   Ⅴ Faulty Run Capacitor 5.1 When Is It Time to Replace a Run Capacitor? As a general rule, a run capacitor will greatly exceed the start capacitor of the same motor. A run motor capacitor will wear down at different levels, making it more complicated to determine if it needs to be replaced. When a run capacitor begins to perform outside of its allowable range, the rated capacitance value usually drops. A "tolerance" will be specified for most standard motor run capacitors, describing how close the actual value may be to the rated capacitance value. It is usually within +/- 5% to 10%. For most motors, as long as the actual value is within 10% of the rated value, you're good to go. A run capacitor will occasionally bulge from internal pressure due to a flaw in the capacitor's construction or a non-capacitor-related motor issue. Most modern run capacitor designs will open the circuit, disconnecting the internal spiral membrane as a precautionary measure to keep the capacitor from popping. The test is simple: it is time to replace in both cases that it is  bulging and there is  no continuity between the terminals, Run Capacitor   5.2 Causes of Failure Depending on how close the run capacitor is to its design life, there could be several reasons why it failed.   Diagnosing and Replacing a Run Capacitor   Ⅵ How To Replace a Start Run Capacitor? When a new motor is installed, a new fan capacitor should always be installed. It is always a good idea to photograph or write down the wire coloring and connections. Turn off the power to the HVAC unit and use a meter to ensure it is completely off.Locate and remove the side panel where the electricity is fed into the unit.Locate the Stat Run Capacitor;  there will only be one in a Dual Run capacitor. If there are two, only the fan motor capacitor has to be replaced.Check the MFD and voltages, then connect the new connections from the old capacitor to the new capacitor one leg at a time to ensure they are correct. (For example, if you have two capacitors, one is for the compressor and the other is for the fan motor.)   Ⅶ How Do They Work In an HVAC System? A Start or Run Capacitor can be combined into a single capacitor with three leads known as a Dual Capacitor, or it can be split between two separate capacitors. The Start Capacitor gives a fan motor the torque it needs to start spinning and then turns off, whereas the Run Capacitor stays on and provides extra torque to the motor when needed. The motor will most likely not start if the Start Capacitor fails. If a Run capacitor fails, the motor will start, but the running amperage will be higher than usual, causing the motor to run hot and have a short life expectancy. There are three connections on a Dual Capacitor: HERM, FAN, and COM. HERM is for the Hermetically Sealed Compressor, FAN is for the Condenser Fan Motor, and COM is for the Contactor, which powers the Capacitor. If the unit has two capacitors, the larger of the two is the Run Capacitor. Keep in mind that the compressor frequently necessitates the use of a HERM capacitor (compressor). Run Capacitor circuit   Ⅷ Dual Capacitors vs. Run Capacitors vs. Run Capacitors The only benefit we can get from the dual-run capacitor design is that it comes in a small package with only three connections. Aside from that, there is no distinction between run and dual run capacitors. If there is enough space for mounting, it is acceptable to replace your original dual-run capacitor with two separate run capacitors. They typically have "C" connections for "common," "H" or "Herm" connections for "Hermetic Compressor," and "F" connections for "Fan." They'll also have two different capacitor ratings for the two parts. Start capacitors provide a high capacitance value required for motor starting in a very short (seconds) time. They are only designed for intermittent duty and will fail catastrophically if left on for an extended time. Run capacitors are continuous duty because they provide continuous voltage and current control to a motor's windings. They typically have a much lower capacitance value.   Ⅸ FAQ 1. What happens when a run capacitor goes bad? A bad motor capacitor may cause starting problems or could shut off the motor while running. Same principle on the dirty coil. ... If a Run capacitor goes bad then a motor can turn on but the running amperage will be higher than normal causing the motor to run hot and have a short life expectancy. 2. What is the difference between a capacitor and a run capacitor? The start capacitor creates a current to voltage lag in the separate start windings of the motor. The current builds up slowly, and the armature has an opportunity to begin rotating with the field of current. A run capacitor uses the charge in the dielectric to boost the current which provides power to the motor. 3. Can I run my AC without a capacitor? Most of the motors in your air conditioner can't run without a good capacitor. Like I said, they support these motors. They help the motor start and run efficiently. Some people have gone out to their air conditioner and noticed the fan wasn't spinning on their AC as it should be. 4. Can I use a run capacitor in place of a start capacitor? The capacitance and voltage ratings would have to match the original start capacitor specification. A start capacitor can never be used as a run capacitor, because it cannot not handle current continuously. 5. Do I need a start or run capacitor? Run capacitors are designed for continuous duty, and are energized the entire time the motor is running. Single phase electric motors need a capacitor to energize a second phase winding. ... Start capacitors increase motor starting torque and allow a motor to be cycled on and off rapidly. 6. What size run capacitor do I need? The run capacitor should have the exact microfarad (uf) that the motor is rated for. Capacitors rated above 70uf are considered Start Capacitors and are generally removed from the circuit electrically during operation. This is where the rule of +/- 10% of the rating came from, for Start Capacitors ONLY!

IntroductionThe 1N4007 is a general-purpose silicon rectifier diode, typically found in a plastic DO-41 axial package. It is widely used in various AC-to-DC rectifier circuits, bridge rectifier circuits, and general-purpose power supply applications. The 1N4007 utilizes the unidirectional conductivity of the P-N junction to convert alternating current into pulsed direct current. Due to its high reverse voltage rating (1000V) and low cost, it is one of the most popular components in electronics.Ⅰ 1N4007 Diode Specifications1.1 Rectifier Diode OverviewThe 1N4007 is a standard recovery rectifier diode. In low-power/low-current scenarios, the forward voltage (Vf) is typically around 0.7V to 0.8V. However, under its full rated load (1A), the forward voltage drop can reach up to 1.1V.Note on Frequency: The reverse recovery time (Trr) of the 1N4007 is in the microsecond (μs) range (typically 2μs to 30μs depending on conditions). This classifies it as a "slow" diode, meaning it is suitable for 50Hz/60Hz mains rectification but not suitable for high-frequency switching circuits (like high-frequency DC-DC converters), where Fast Recovery (FR) or Ultra-Fast (UF) diodes are required.Rectifier diodes make full use of unidirectional conductivity. They block the negative half-cycle of an AC waveform to convert it into a pulsating DC signal. To smooth this output, they are usually used in combination with a capacitor. The diode is connected in series, and the capacitor is connected in parallel to the load.Figure 1. 1N4007 Bridge Rectifier Circuit Example1.2 Nomenclature: What does 1N4007 mean?"1": Represents the number of junctions. In JEDEC nomenclature, "1" stands for a component with one P-N junction (a diode)."N": Stands for semiconductor device, registered with the EIA (Electronic Industries Alliance) / JEDEC."4007": The specific registration number indicating the device's electrical characteristics within the 1N400x series.1.3 1N4007 Pins and SymbolPINDescription1 (Marked with Band)Cathode (-)2 (Unmarked)Anode (+)1.4 1N4007 Basic Parameters (at 25°C)Type: Standard Recovery Silicon RectifierMax Average Forward Rectified Current (Io): 1.0 APeak Forward Surge Current (Ifsm): 30 A (for 8.3ms single half-sine-wave)Max Repetitive Peak Reverse Voltage (Vrrm): 1000 VMax DC Blocking Voltage: 1000 VMax Forward Voltage Drop (Vf): 1.1 V (at 1.0A current)Max Reverse Leakage Current (Ir): 5 μA (at rated DC blocking voltage)Typical Junction Capacitance (Cj): 15 pF (measured at 4V, 1MHz)Typical Thermal Resistance: 65 °C/W (Junction to Ambient)Operating Temperature Range: -55°C to +150°CFigure 2. Forward Current Derating Curve1.5 1N4007 FeaturesLow reverse leakage currentHigh surge current capability (up to 30A non-repetitive)RoHS compliant and available in Pb-Free packagesHigh-temperature soldering guaranteed: 260°C/10 seconds.Mechanical Data:Case: DO-41 Molded PlasticTerminals: Plated axial leads, solderable per MIL-STD-202Polarity: Color band denotes cathode endⅡ 1N4001-1N4007 Series ComparisonThe 1N400x series contains diodes that are physically identical and rated for the same current (1A). The only difference is the Maximum Repetitive Reverse Voltage (Vrrm). Because the 1N4007 has the highest voltage rating (1000V), it can replace any other diode in the series (1N4001 through 1N4006).ModelCurrent (A)Max Peak Reverse Voltage (V)Max RMS Voltage (V)1N4001150351N40021100701N400312001401N400414002801N400516004201N400618005601N400711000700Ⅲ Alternative Models & EquivalentsThe 1N4007 can often be replaced by higher-spec diodes.Higher Current: 1N5399 (1.5A) and 1N5408 (3.0A). Note: The 1N5408 has thicker leads and a larger body (DO-201AD) and may not fit all PCB holes designed for the 1N4007.Fast Recovery: If high-frequency performance is required, FR107 (Fast Recovery) or UF4007 (Ultra Fast) are excellent replacements. They share the same voltage/current ratings but switch off much faster.Schottky Diodes (Caution): While Schottky diodes like 1N5819 or 1N5818 have a lower forward voltage drop (higher efficiency), they usually have much lower reverse voltage ratings (often 20V-40V). Do not replace a 1N4007 with a Schottky diode in high-voltage circuits (like 110V/220V mains) or the diode will fail instantly. However, for low voltage (e.g., 12V) DC inputs, a Schottky like the SB1100 (100V) can be a more efficient substitute.ModelMax Reverse Voltage (V)Avg Rectified Current (A)Max Surge Current (A)Max Reverse Leakage (μA)1N4007100013051N539910001.55051N5408100032005FR10710001305 (Fast Recovery)Ⅳ 1N4007 vs. M7 (SMD Versions)When moving from Through-Hole Technology (THT) to Surface Mount Technology (SMT), the electrical equivalents of the 1N4007 are identified by different package codes.1N4007: This specifically refers to the DO-41 axial lead package (through-hole).M7: This is the SMA (DO-214AC) surface mount version of the 1N4007. It is electrically identical (1A, 1000V).A7: This is the SOD-123 surface mount version. It is smaller than the SMA package but carries similar specs (usually slightly lower thermal dissipation).SM4007: This generally refers to the MELF (DO-213AB) cylindrical surface mount package, though "SM4007" is sometimes used generically for any SMD version.Figure 3. DO-41 Package (1N4007)Summary: If you see a diode marked "M7" on a circuit board, it is a surface-mount 1N4007.Ⅴ 1N4007 Application Examples5.1 Solving Auxiliary Winding OvervoltageThe slow recovery characteristics of the 1N4007 can sometimes be advantageous over faster diodes in specific power supply applications.In Flyback power supplies, multi-output transformers can suffer from poor cross-regulation. A common issue is the VCC auxiliary winding voltage rising too high, triggering the IC's Over-Voltage Protection (OVP). This often happens because a fast diode (like the HER107) rectifies the high-frequency leakage inductance spike (the "ringing") at the leading edge of the waveform, rather than just the plateau voltage.Figure 4. IC Control CircuitSolution: By replacing the fast HER107 with a standard speed 1N4007, the slower turn-on time ignores the initial high-frequency spike. This effectively filters the peak voltage, lowering the average VCC voltage seen by the IC and preventing false OVP triggering.5.2 RCD Snubber EMI SuppressionIn RCD (Resistor-Capacitor-Diode) snubber circuits used to protect MOSFETs in Flyback converters, using a slow diode like the 1N4007 can help improve Electro-Magnetic Interference (EMI).Figure 5. RCD Absorption CircuitHow it works: A "fast" diode snaps off very quickly, which can induce high-frequency ringing. The 1N4007 takes longer to recover (reverse recovery). During this brief recovery period, a small amount of reverse current flows back. This "soft recovery" acts as a dampener, absorbing some of the oscillation energy and reducing the voltage stress and EMI radiation on the MOSFET drain.Trade-off: The downside is that the 1N4007 will generate more heat due to reverse recovery losses. This technique is generally suitable for lower-power adapters (<20W) where EMI is a priority and thermal overhead is available.Ⅵ FAQ1. What is a 1N4007 diode used for?It is a general-purpose rectifier diode used to convert AC to DC, prevent reverse polarity, and protect circuits from voltage spikes (flyback protection).2. What is the difference between 1N4001 and 1N4007?The only difference is the Peak Repetitive Reverse Voltage. The 1N4001 is rated for 50V, while the 1N4007 is rated for 1000V. 1N4007 can replace a 1N4001, but a 1N4001 cannot replace a 1N4007 in high-voltage circuits.3. Can I replace 1N4148 with 1N4007?Generally, No. The 1N4148 is a high-speed signal diode (very fast switching, low current). The 1N4007 is a power rectifier (slow switching, high current). • If you put a 1N4007 in a high-speed data circuit, it will be too slow and fail to work.• If you put a 1N4148 in a power circuit, it will likely burn out due to its lower current limit (200mA vs 1A).4. How much current can a 1N4007 diode handle?It can handle 1 Ampere of continuous rectified current. It can handle a non-repetitive surge of 30 Amperes (for less than 8.3ms), which is useful for inrush current at startup.5. What is the voltage drop of 1N4007?While often cited as 0.6V or 0.7V, under a full 1A load, the voltage drop is typically 0.9V to 1.1V.6. What is M7 diode?M7 is the surface-mount (SMD) code for the 1N4007 diode in an SMA package. It has the same electrical specs: 1A, 1000V. body { font-family: Arial, sans-serif; line-height: 1.6; color: #333; } h2 { color: #2c3e50; border-bottom: 2px solid #3598db; padding-bottom: 10px; margin-top: 30px; } h3 { color: #34495e; margin-top: 20px; } table { width: 100%; border-collapse: collapse; margin: 20px 0; } table, th, td { border: 1px solid #ddd; } th, td { padding: 12px; text-align: left; } th { background-color: #f2f2f2; } img { max-width: 100%; height: auto; display: block; margin: 20px auto; } .note { background-color: #f9f9f9; border-left: 6px solid #2196F3; padding: 10px; font-style: italic; } .warning { background-color: #fff3cd; border-left: 6px solid #ffc107; padding: 10px; }

IntroductionRelays are fundamental components in modern electronics, serving as switches that open and close circuits both electronically and mechanically. They regulate the flow of electricity by controlling circuit contacts. Even in 2025, with the rise of solid-state technology, electromechanical relays remain vital for high-current applications.Understanding the state of a relay is crucial:Normally Open (NO): The circuit is disconnected when the relay is inactive (not energized).Normally Closed (NC): The circuit is connected when the relay is inactive.When energy (electricity or an electrical charge) is supplied to the coil, these states change, allowing for precise control over high-power systems using low-power signals.Ⅰ What is a Relay and How Does it Work?A relay is an electrically operated switch. Traditional relays employ an electromagnet (coil) to mechanically operate a switching mechanism (contacts). When the coil is activated, it generates a magnetic field that moves the armature, changing the state of the contacts from open to closed (or vice versa).The relay diagrams below demonstrate the operational logic of standard relays.1.1 Sample Wiring Diagrams for a Normally Open RelayExample 1: A four-pin (normally open) relay with the switch placed on the positive side of the control circuit.Figure 1: Positive side switching configuration.Example 2: A four-pin (normally open) relay with the switch placed on the negative side of the control circuit.Figure 2: Negative side switching configuration.Ⅱ Relay Related Video Introduction Topic: Relay Terminal Numbering System, IEC Schematic Symbols, and Coil Voltage Explained.Video Description: In this tutorial, we explore how the Terminal Numbering system works (identifying relay pins), the IEC schematic symbol for 8-pin Ice Cube relays and Mini contactor relays, and critical information regarding Coil voltage. Specifically, we address why you cannot use DC voltage on a coil designed strictly for AC voltage.Ⅲ Why use a Relay?Relays allow a low-current circuit (like a microcontroller or dashboard switch) to control a high-current circuit (like a motor or headlight array). As of 2025, this isolation is critical for protecting sensitive digital electronics. Key advantages include:Safety & Protection: High-amperage power is kept away from the operator interface and sensitive control units.Cost & Space Efficiency: Thinner gauge wires connect the control switch to the relay, saving weight, space, and copper costs.Voltage Drop Reduction: Relays allow power to be routed directly from the source to the device over the shortest distance, minimizing voltage loss.Heavy Duty Compatibility: Heavy gauge cable is only required for the short run from the power source to the device (via the relay).3.1 Why does a Car Need a Relay?Automotive applications rely heavily on relays. Using a relay eliminates the need for high-current rated switches on the dashboard, which are bulky and expensive. Secondly, relays allow for decentralized power distribution; they can be placed closer to the load (e.g., headlights, electric motors, cooling fans) to ensure maximum efficiency. In modern Electric Vehicles (EVs), high-voltage relays are essential for battery management and safety disconnects.3.2 Why are Protection Devices used in a Relay?When an electromagnetic relay turns off, the magnetic field in the coil collapses rapidly, generating a significant voltage spike (Back EMF). This spike can damage sensitive components in the control circuit (like the ECU or transistors). To prevent this, Flyback Diodes or resistors are often installed across the relay coil. While resistors are more durable, diodes are generally more effective at clamping the voltage spike. The choice depends on the sensitivity of the driving circuit.Ⅳ How to Understand the Electrical Specifications of a Relay?Reading a relay's datasheet is vital for system longevity. Specifications are generally divided into two parts:Coil Ratings: Specifies the voltage (e.g., 12VDC, 24VDC, 120VAC) required to energize the electromagnet.Contact Ratings: Specifies the maximum voltage and amperage the internal switch can handle. Never exceed this rating.For Double Throw relays, you may see specifications formatted as "2 x switch"—one rating for the Normally Open (N/O) terminal and another for the Normally Closed (N/C) terminal (e.g., N/O: 35A at 14VDC, N/C: 20A at 14VDC).Ⅴ What’s the difference between 4 or 5 Pin Relays?The primary difference lies in the switching capability. A 4-pin relay typically controls a single circuit (on/off), whereas a 5-pin relay can switch power between two different circuits.4 Pin Relay (SPST - Single Pole Single Throw)4-pin relays typically feature two control pins (85 and 86) for the coil, and two power pins (30 and 87). They act as a simple on/off switch. When the coil is energized, the internal switch connects pin 30 to pin 87, powering the device.Figure 3: 4-Pin Relay (Open State)Figure 4: 4-Pin Relay (Closed/Energized State)5 Pin Relay (SPDT - Single Pole Double Throw)5-pin relays include two control pins (85 and 86), a common power pin (30), a Normally Open pin (87), and a Normally Closed pin (87A). This allows the relay to toggle power between two circuits. When at rest, power flows to 87A; when energized, power switches to 87.Figure 5: 5-Pin Relay SchematicNote: These diagrams are simplified to demonstrate functionality. If the relay coil is protected by a diode (internal or external), the coil terminal wired to the diode's anode must be connected to the negative ground to ensure proper polarity and protection.Ⅵ All Types of Relay SymbolsRelays vary by function, construction, and terminal configuration. Below is a list of common relay types and their schematic symbols.Electromagnetic RelayThe standard relay using a coil and magnetic field to move contacts mechanically.Figure 6: Electromagnetic Relay SymbolThermal Overload RelayThis relay uses a bimetallic strip instead of a magnetic coil. The strip bends as it heats up from current flow, opening auxiliary contacts to protect motors from overheating.Figure 7: Thermal Overload Relay SymbolSPST RelaySingle Pole Single Throw: Has four terminals total. It connects one input to one output.Figure 8: SPST Relay SymbolSPDT RelaySingle Pole Double Throw: Has five terminals. It features one common terminal that switches between a Normally Open (NO) and a Normally Closed (NC) terminal.Figure 9: SPDT Relay SymbolDouble Coil Latching RelayLatching relays maintain their contact position after the power is removed. A double coil version uses one coil to set the position and another to reset it.Figure 10: Latching Relay SymbolOvercurrent RelayDesigned to operate only when the current exceeds a specific threshold, protecting circuits from faults.Figure 11: Overcurrent Relay SymbolDifferential RelayActivates when there is a difference between two identical electrical quantities (e.g., input current vs. output current), commonly used in transformer protection.Figure 12: Differential Relay SymbolPulse RelayOperates based on pulse signals, toggling the contact state with each input pulse. Essential for lighting control systems.Figure 13: Pulse Relay SymbolOn/Off Time Delay RelayContains a timing mechanism that delays the closing or opening of contacts after the coil is energized or de-energized.Figure 14: Time Delay Relay SymbolRemanence RelayA specific type of latching relay that uses the magnetic remanence (residual magnetism) of the core to hold the position without continuous power.Figure 15: Remanence Relay SymbolNo Volt RelayAlso known as an Under-voltage Relay. It trips the circuit breaker when the voltage drops below a safe operational level.Figure 16: No Volt Relay SymbolAC and DC RelayWhile they perform similar switching functions, AC and DC relay coils are constructed differently regarding internal resistance and impedance.Figure 17: AC and DC Relay SymbolsPolarized RelayContains a permanent magnet in addition to the coil. The state of the contacts depends on the polarity of the input signal.Figure 18: Polarized Relay SymbolDistance Relay (Impedance Relay)Used primarily in high-voltage transmission lines. It detects faults by measuring the impedance on the line, which corresponds to the physical distance to the fault location.Figure 19: Distance or Impedance Relay SymbolⅦ FAQ1. What is the main purpose of a relay in a circuit?A relay acts as an electrically operated switch. It allows a low-power signal (like from a microcontroller) to control a high-power circuit (like a heater or motor), while keeping the two circuits electrically isolated.2. What is the circuit symbol for an amplifier vs. an aerial?While not relays, these are common components in related schematics:Amplifier: Represented by a triangle on its side. It increases signal strength.Aerial (Antenna): Often abbreviated as 'AE', it is the device used to transmit or receive signals.3. How is a relay connected to a transistor circuit?In a standard driver circuit, the relay coil is often connected to the Collector of a transistor. However, in an Emitter Follower configuration, the coil can be connected to the Emitter, where the input signal drives the Base and the output is taken from the Emitter load.4. How does a 12V automotive relay work?The relay is installed between the battery (power source) and the accessory (load). When the dashboard switch is flipped, it sends a small current to the relay coil. The coil energizes, closing the internal high-current contacts, allowing power to flow directly from the battery to the accessory.5. Why are symbols used in circuit diagrams?Schematic symbols provide a standardized, universal language for engineers. They show how components are electrically connected (logic), rather than their physical layout. This allows for easier troubleshooting and design verification.