CatalogⅠ What is Coolant Temperature SensorⅡ Function and Structure of Coolant Temperature SensorⅢ The Working Principle of Coolant Temperature SensorⅣ Application of Coolant Temperature Sensor in Vehicles  4.1 Location on Automobiles  4.2 Ways of Testing Coolant Temperature SensorⅤ How to Replace the Faulty Coolant Temperature  SensorⅥ Frequently Asked Questions about Coolant Temperature Sensor Analysis Ⅰ What is Coolant Temperature SensorEvery driver is aware that coolant/antifreeze is applied to keep an engine operating at peak efficiency. However, how do cooling systems recognize when the engine is at the proper operating temperature? We take a closer inspection at coolant temperature sensors in this guide, providing information on what they do and how they work, as well as step-by-step instructions for diagnosing and replacing a faulty sensor. A coolant temperature sensor (CTS) (also known as an ECT sensor or ECTS (engine coolant temperature sensor)) measures the temperature of the coolant/antifreeze mix in the cooling system, indicating how much heat the engine is producing. The sensor communicates with the vehicle's ECU and continuously monitors coolant temperature to ensure that the engine is operating at the proper temperature. Ⅱ Function and Structure of Coolant Temperature Sensor The coolant temperature sensor is installed on the water jacket of the engine block or cylinder head, contracting with the coolant directly. The CTS is applied to detect the temperature of the engine coolant. The internal part is equipped with a negative thermistor with negative temperature characteristics. The feature of a negative thermistor is that the higher the temperature, the smaller the resistance, the lower the temperature, the greater the resistance.Figure1: the circuit image of coolant temperature sensor The signal of the coolant temperature sensor is a correction signal, and its function is to inspect the temperature of the engine coolant. The temperature of the engine coolant transmit the signal to the ECU, and the ECU  measured temperature and correct the fuel injection volume according to the signal indication. When the cold car starts or the engine warms up, the ECU will correct the fuel injection.When the car is hot, the ECU will correct to inject the leaner mixture; the same way, when the engine coolant temperature signal is detected, the ECU controls the cooling and the fan is turned on and off. Ⅲ The Working Principle of Coolant Temperature Sensor Generally, the structure of the coolant temperature sensor seems to be a negative thermistor. Therefore, its temperature is inversely proportional to resistance, and its voltage is also inversely proportional to resistance. The range of temperature changes: -40 to 195°C. When the engine cools down from the start of the cold car to the hot car, the parameters of the fluid temperature sensor gradually increase, and the vehicle is idling when the engine is completely warmed up. The coolant temperature should be 85～105℃ when operating, if the parameter of CTS is  -40℃, it indicates that there is a short-circuit in CTS. If the parameter is higher than 185℃, it means that there was the same failure as-40℃. The voltage change range is 0 ~ 5V. When the temperature parameter is -40℃, the corresponding voltage is 4.98V，while the temperature parameter is 185℃, the corresponding voltage is 0.02V. The cooling system in a car with an internal combustion engine keeps the engine at the proper temperature and prevents it from overheating.  The temperature of the liquid coolant is measured by an engine coolant temperature sensor or ECT. A Negative Temperature Coefficient (NTC) thermistor is a type of engine cooling temperature sensor in which the electrical resistance decreases as the temperature rises. The ECT sensor's tip protrudes into a cooling system passage and is submerged in coolant.This vedio show that how coolant temperature sensor works Ⅳ Application of Coolant Temperature Sensor in Vehicles4.1 Location on Automobiles Many automobiles have multiple coolant temperature sensors. The primary ECT sensor (ECT sensor 1) is usually located near the thermostat in the cylinder head or block, or on the thermostat housing. Sensor for electrocardiography (ECT) the engine computer, or PCM, is connected to the ECT sensor. A second coolant temperature sensor could be installed in the radiator or in another part of the engine. Instead of or in addition to the ECT sensor, some cars use a cylinder head temperature or CHT sensor. The CHT sensor (shown in the photo) works in the same way, but it measures the temperature of the cylinder head metal rather than the coolant temperature. This enables the CHT sensor to accurately measure the temperature of the engine even when coolant is lost. This may help prevent overheating in some cases. The main computer is connected to an ECT sensor (powertrain control module or PCM). The PCM provides a constant reference voltage (typically 5 volts) and monitors the ECT sensor signal. When the temperature reaches a pre-determined level, the PCM adjusts the engine performance and operates the electric radiator fans based on this signal. If the sensor signal is missing or outside of the expected range, the PCM illuminates the Check Engine light and records the associated trouble code. 4.2 Ways of Testing Coolant Temperature SensorTesting the ECT/CHT Sensor Resistance: One method is to measure the sensor's resistance at various engine temperatures and compare the results to the service manual's specifications.We tested the resistance of the ECT sensor in this car, for example. Only when the sensor is disconnected from the circuit can the resistance be measured. The reason for this is that measuring the resistance of any electrical component that is still connected to the circuit will result in inaccurate results. When the engine was cold, the resistance was 2,953 Ohm. After the engine was fully warmed up, it dropped to 248.5 Ohm; see photo. This sensor complies with the manufacturer's specifications. Of course, the resistance specifications differ from car to car. Figure2:one way to test the resistance of senser  Checking the ECT/CHT Sensor Voltage:With the ignition on, another way to test the sensor is to measure the voltage across the sensor terminals. The voltage of the engine coolant temperature (ECT) sensor is measured. The voltage of the ECT sensor is being checked. The engine computer is linked to the sensor (PCM). The reference voltage (typically 5 volts) is supplied by the PCM, and the sensor ground is provided by another wire. The ground as well as the reference voltage must be checked first. The voltage drops as the sensor's resistance decreases as the engine warms up. We probed the ECT sensor inversely in this photo to keep it connected to the circuit. We measured 3.96 Volt when the car was cold. The voltage dropped to 0.988 Volt on a fully warmed-up engine. The multimeter will read 5 volts when the sensor is disconnected. If you don't see any voltage, the circuit is either open or shorted to the ground. One of the wires in the sensor harness, for example, could break or rub against a metal part, causing a short. Figure3: another way to test sensor Voltage  4.3  Symptoms of a bad or failing coolant temperature Poor fuel economy Poor fuel economy is one of the first signs of failure with the coolant temperature sensor. If the coolant temperature sensor fails, it can send a false signal to the computer, causing fuel and timing calculations to be thrown off. It's not uncommon for the coolant temperature sensor to fail and send a signal to the computer that's always cold. This will trick the computer into thinking the engine is cold when it isn't, causing it to consume more fuel than is necessary. The poor fuel economy will suffer as a result, and engine performance may suffer as a result. Black smoke from engine Black smoke from the vehicle's exhaust is another sign of a possible problem with the coolant temperature sensor. If the coolant temperature sensor fails and sends a cold signal to the computer, the computer may become confused and enrich the fuel mixture unnecessarily. If the fuel mixture becomes too rich, it will burn up in the exhaust pipes, resulting in black smoke. In severe cases, the black smoke may be so awful that the vehicle can not be started. Overheating engine An overheating engine is another sign of a problem with the coolant temperature sensor. The coolant temperature sensor can also fail in such a way that it sends an always-hot signal. This can cause the computer to compensate for a lean signal incorrectly, resulting in overheating, misfires, and even engine ping. Check Engine Light comes on Another sign of a problem with the coolant temperature sensor is an illuminated Check Engine Light. If the computer detects a problem with the sensor's signal or circuit in some vehicles, the Check Engine Light will illuminate. The Check Engine Light will stay illuminated until the trouble is resolved. Ⅴ How to Replace the Faulty Coolant Temperature SensorBegin with a cold engine. Drain the cooling system by jacking the car up and using jack stands. Wear safety glasses and glovesMterials:1. coolant collection pan2. flat head screwdriver3. new coolantTools:1. eyewear and golves 2. pliers3. funmel4. jack standsTip: Only do this job when the engine is completely cold and hasn't been running for at least an hour. Because you'll be underneath the car and the risk of coolant splashing in your face is high, it's a good idea to protect your face with a safety shield. If the engine is not cold, wear safety glasses and gloves to protect your hands from the hot coolant.  Step1: Locate the SensorThe CTS is usually found near the radiator or thermostat housing in the front of the engine. You may need to use a light or torch to locate it because it's a small component that's often found lower down inside the engine bay. If it's near the thermostat housing, removing the engine cover can also help you find it.Figure4: firstly, locate the coolant sensor   Step2: Remove the Connector Cable from the Terminal A connector connects the CTS to the ECU, which you must unfasten and remove. Do this with caution, as the plastic connector and wiring can be brittle and require replacement if they break. Remove the connector and place the cable somewhere out of the way.Figure5: release the connector   Step3: Loosen and Remove the Old Sensor Coolant sensors are installed similarly to spark plugs, so they must be unscrewed to be removed. Carefully loosen the sensor in an anticlockwise direction with a deep socket and ratchet, without applying too much pressure. A squirt of release spray can aid in the unsticking of stuck sensors. Remove the sensor from the socket by unscrewing it by hand once it is loose. Because coolant is likely to leak at this point, have a new one on hand or consider draining the coolant if necessary.Figure6: Remove the clip and old sensor   Step4: Install the New Sensor Clean the area with a rag or cloth to remove any dust or debris that could influence the new CTS' performance. Set the new sensor in the threads and hand-twist clockwise to ensure it is securely seated in the socket. Tighten the sensor with a torque wrench to the amount specified in the manufacturer's instructions.Figure6: install the new coolant sensor  Step5 : Reinstate the Connector Cable The only thing left to do now is reconnect the cable after the new sensor has been installed. Make sure the connector is clean and free of debris before carefully plugging it into the new sensor and tightening any clips to ensure a good connection. Start the engine to ensure the new sensor is working, and as it warms up, keep an eye on the temperature gauge on the dash to ensure the correct temperature is maintained.Figure7: reconnect the cableⅥ Frequently Asked Questions about Coolant Temperature Sensor Analysis1. Can you drive with a bad coolant sensor?It is possible to drive a vehicle with a faulty coolant temperature sensor as the management system defaults to a static reading. A vehicles coolant sensor is a critical component used by the engine management system. It directly effects, cooling and fueling of the engine and therefore effects how the engine performs. 2. What does the coolant temperature sensor do?A coolant temperature sensor (CTS) (also known as an ECT sensor or ECTS (engine coolant temperature sensor) is used to measure the temperature of the coolant/antifreeze mix in the cooling system, giving an indication of how much heat the engine is giving off. 3. What causes a coolant temperature sensor to fail?The engine may run in fail-safe mode:Many Check Engine light codes related to the (ECT) sensor; could also be caused by other reasons. Such as a bad thermostat or issues with the cooling system; including even a leaking head gasket. Therefore, The problem must be properly diagnosed. 4. How long do coolant temp sensors last?About 100,000 miles. Often, the engine coolant temperature sensor must be replaced at about 100,000 miles. If you don't properly maintain the engine cooling system, the sensor could fail much earlier. 5. Do you need to drain coolant to change coolant temperature sensor?Open the radiator valve and drain about two to three quarts of coolant. You only need to remove enough to drop the level below the sensor. Then close the drain valve. This will minimize coolant waste when you remove the sensor. 6. Can you run a car without a temperature sensor?Generally it should be ok to drive without the thermostat fitted, as it will only cause the engine to take longer to reach operating temperature. The thermostat is designed to allow the engine to reach ideal operating temperature as quickly as possible, so it would not be recommended to drive without it. 7. Can a bad coolant temp sensor cause rough idle?A faulty coolant sensor that always reads cold may cause the fuel control system to run rich, pollute and waste fuel. A coolant sensor that always reads hot may cause cold drive ability problems such as stalling, hesitation and rough idle. ... This also affects engine performance and fuel economy. 8. Does coolant temp sensor affect AC?In a properly operation system the engine coolant temperature should not affect the cooling of the air conditioner. The A/C condenser is located in front of the radiator and is first to receive the incoming airflow.    

IntroductionIn electronics, the diode has the unique characteristic of unidirectional conduction. The main functions are rectification, voltage stabilization, and detection. In addition, there are light-emitting diodes(LED) added with different materials for indication and illumination. In a diode circuit, current can only flow in from the anode and flow out of the cathode. According to different circuit requirements, there are many different types of diodes to choose from. Most of the early diodes were made of germanium single crystals. Later, with the solution of silicon materials and manufacturing processes, silicon tubes have been developed and popularized. Here's how to distinguish silicon(Si) diodes and germanium(Ge) diodes.CatalogIntroductionⅠ Circuit Properties: Si Tube vs Ge Tube1.1 Differences between Ge and Si Diode1.2 Differences between Ge and Si Transistor1.3 SummeryⅡ Common Diode Types UsesⅢ Common Transistor Models UsesⅣ New Development: SiC Schottky Diodes4.1 SiC Schottky Diode Basic4.2 SiC Tech Characteristics4.3 SiC Schottky Diode ApplicationsⅠ Circuit Properties: Si Tube vs Ge Tube1.1 Differences between Ge and Si DiodeThe circuit properties of Si diodes and Ge diodes are the same, and the manufacturing process is also the same. Due to the difference in materials, the thermal stability of Si diodes is good, and the thermal stability of Ge diodes is slightly poor.1) When the current is the same, the DC resistance of the Ge tube is smaller than that of the Si tube. However, as for AC resistance, the situation is opposite.2) According to experimental research, the Ge diode starts to have current at 0.2V in the forward direction, while the Si diode does not start to have current until 0.5V, that is to say, the initial voltages for the two to reach conduction are different.3) Under reverse voltage, the leakage current of silicon tube is much smaller than that of germanium tube. After the start of conduction, the Ge tube current increases slowly, and the Si tube current increases relatively quickly.4) The threshold voltage of silicon tube is higher than that of germanium tube, because the threshold current of silicon tube is much smaller than that of germanium tube. Generally, the threshold voltage of a silicon tube is about 0.5V~0.6V, and the threshold voltage of a germanium tube is about 0.1V~0.2V.5) Temperature changes have a greater impact on Ge diodes, but less on silicon diodes. Therefore, silicon tubes have better high temperature resistance than Ge tubes.6) Forward voltage required for diode conduction:Diode TypesForward Conduction VoltageSi0.7VGe0.15VIt can be seen from the above table that the forward voltage required for the silicon tube to be turned on is higher than that of the germanium tube, so the diode can be distinguished by knowing the forward voltage.In addition, there is a very direct method to measure your diode with the Ω barrier of a multimeter. As shown in the figure, the red pen (anode) of the multimeter is connected to the cathode of the diode, and the black pen (cathode) is connected to the anode of the diode. If the resistance of the tested diode is around 1kΩ, it is a germanium tube; if the resistance is 4~8kΩ, it is a silicon tube.Compared with germanium diodes, silicon diodes have higher voltage resistance, shorter response time, and stable performance. In most circuits, silicon tubes can replace germanium tubes, but its forward pressure drop is higher than that of germanium tubes. Therefore, in some specific environments, such as small signal detection circuits, germanium tubes are better.1.2 Differences between Ge and Si TransistorThe main difference is that the junction voltage drop is different, the forward voltage drop of the germanium tube is lower about 0.3V, and the silicon tube is higher about 0.7V. In addition, silicon materials are abundant and manufacturing processes are suitable for mass production, so they are widely used and become the protagonist of electronic devices.Germanium semiconductor materials have high electron mobility and are suitable for low-voltage and high-current devices, but the temperature characteristics of it is worse than that of silicon materials. The reverse leakage current of PN junctions is much larger than that of silicon materials. Therefore, silicon tubes have to be used in high-power devices and high back-pressure devices. The triode has two PN junctions. In terms of a PN junction, the forward voltage of the PN junction of the germanium tube is reduced to only 0.3V, while the silicon tube is 0.7V. The reverse withstand voltage germanium tube is very low, so it is easy to reverse breakdown. Therefore, the penetrating current of the Ge tube is relatively large, noise will be generated in the amplifying circuit, and it is easy to be damaged. 1.3 SummeryGermanium diodes was used a lot in early electronics, such as radios, but they have largely been replaced by silicon diodes. Because the structure of germanium crystals will be destroyed at higher temperature, while Silicon crystals are not easily damaged by excess heat. What's more, peak inverse voltage ratings of silicon diodes are greater than germanium diodes. As for price, Silicon material has low cost and its producibility of high quality silicon dioxide needed for impurity diffusion and surface passivation processes. Therefore, germanium tubes were only produced before the 1970s. Ⅱ Common Diode Types Uses① Zener DiodesThe Zener diode is also made of a PN structure. It is in the reverse breakdown state when working (the ordinary diode will be damaged in the reverse breakdown zone). When connected to the circuit, it should be reversed, that is, the anode of the Zener diode should be connected with the cathode of the voltage stabilizing circuit, so is the rest. The voltage stabilizing tube uses its reverse breakdown current to change in a wide range, the reverse breakdown voltage is basically unchanged, to achieve the purpose of voltage stabilization.② Light-emitting DiodesThe light-emitting diode emits light when it passes forward current, and has the performance of electro-optical conversion. The visible light includes red, yellow, green, blue, purple, etc. It is widely used in various electronic equipment as working status indicator.③ PhotodiodesThe reverse current of the photodiode increases with the increase of the light intensity. Its main feature is: the tube works in the reverse state, and the reverse current is proportional to the illuminance.④ Rectifier Diodes for AutomobilesThe working principle of the diode for automobile silicon rectifier generator is basically the same as that of other diodes, but the external structure is different from that of general diodes. It has one lead pole and the other pole is a shell. It is divided into two types: positive diode and negative diode. The terminal is the positive pole and the shell is the negative pole, while the leading end of the negative diode is the negative pole and the shell is the positive pole. In order to facilitate identification, the positive diode is usually coated with a red dot and the negative diode is coated with a black dot.⑤ Freewheeling DiodeFreewheeling diodes are common used in automobiles. In addition, fast recovery diode (a kind of semiconductor diode with good switching characteristics and short reverse recovery time) is mainly used for switching power devices (such as IGBT or MOSFET) of various power converters to play a freewheeling effect. Ⅲ Common Transistor Models UsesThe following table lists some commonly used transistor models and their main parameters, packages and alternative models.ModelBasic ParametersDescriptionPcVCBOVCEOVEBOhFEIC2SC2655(NPN, TO-92L)0.9W50V50V5V*2AHigh-speed switching tube, used for high-current PWM push-pull drive, complementary to the 2SA10202SC9013(NPN, TO-92)0.625W40V20V5V84-2020.5AComplementary to  the SS90122N5551(NPN, TO-92)0.63W180V160V6V30-2500.3AHigh voltage tube, complementary to the 2N5401KSP2222A(PN2222A)(NPN, TO-92)0.625W75V40V6V35-30006AUniversal switch type, complementary to the KSP2907AS8050(NPN, TO-92)0.625W40V25V5V50-3000.5AComplementary to the S8550BD681A(NPN, TO-12640W100V100V5V750-15004ACan drive large relays, Darlington tubeTIP41/A/B/C(NPN, TO-220)60W40~100V40~100V5V15-756AMiddle Power tubes, complementary to the TIP42, can be used for IGBT PWM driveMPSA44(NPN, TO-92)0.625W500V400V6V40-3000.3AHigh voltage tubeKSP2907A(PNP, TO-92)0.625W-60V-60V-5V50-3000.6ACommon-type, complementary to the KSP2222AS8550(PNP, TO-92)0.625W-40V-25V-5V50-3000.5AComplementary to the S80502SA1020(PNP, TO-92L)0.9W-50V-50V-5V40-2402AHigh-speed switch tube, complementary to the 2SC26552SA684(PNP, TO-92L)1W-60V-50V-5V50-3401ADarlington tubeTIP42/A/B/C(PNP, TO-220)65W-40~-100V-40~-100V-5V15-756AMiddle power tubes, complementary to the TIP41, can be used for IGBT PWM driveKSP94(PNP, TO-92)0.625W-400V-400V-6V40-3000.3AHigh voltage tubeⅣ New Development: SiC Schottky Diodes4.1 SiC Schottky Diode BasicSchottky diodes, also known as hot carrier diodes, form a Schottky barrier through metal and semiconductor contacts to achieve rectification. Compared with ordinary PN junction diodes, the reverse recovery inertia of it is very low. Therefore, Schottky diodes are suitable for high-frequency rectification or high-speed switching.Silicon carbide (SiC) is a high-performance semiconductor material, so SiC Schottky diode have advantages of higher energy efficiency, higher power density, smaller size and higher reliability. It can be used in power electronics to break the limit of silicon, and becomes the preferred device for new energy and power electronics.4.2 SiC Tech CharacteristicsSiC is a compound semiconductor composed of silicon and carbide. It provides a number of advantages over silicon. The band gap of SiC is 2.8 times that of silicon (wide band gap), reaching 3.09 eV. Its insulation breakdown field strength is 5.3 times that of silicon, up to 3.2MV/cm, and its thermal conductivity is 3.3 times that of silicon, about 49w/cm·k. Like silicon semiconductor materials, it can be made into junction devices, field-effect devices, and special Schottky diodes. Here is SiC characteristics:1) Silicon carbide single-carrier devices have a thin drift region and low on-state resistance, about 100-300 times smaller than silicon devices. Due to the small on-resistance, the forward loss of the silicon carbide power device is small.2) The silicon carbide power device has a high breakdown voltage due to its high breakdown electric field. For example, the voltage of commercial silicon Schottky diode is less than 300V, while the breakdown voltage of the first commercial SiC Schottky diode has reached 600V.3) SiC has higher thermal conductivity.4) SiC devices can work at higher temperatures, while the maximum operating temperature of Si devices is only at 150ºC.5) SiC has high resistance to radiation.6) The forward and reverse characteristics of SiC power devices vary little with temperature and time, and their reliability is good.7) SiC devices have good reverse recovery characteristics, with low reverse recovery current and switching loss.8) SiC devices can reduce the volume of power devices and circuit losses.4.3 SiC Schottky Diode ApplicationsSiC Schottky diodes can be widely used in medium and high power fields such as switching power supplies, power factor correction (PFC) circuits, uninterruptible power supplies (UPS), photovoltaic inverters, etc., which can significantly reduce circuit losses and improve circuit operating frequency.Substituting SiC SBD(Schottky barrier diodes) for the original silicon FRD(fast recovery diodes) in the PFC circuit can make the circuit work above 300kHz, and the efficiency remains basically unchanged, while the efficiency of the circuit using silicon FRD above 100kHz drops sharply. As the operating frequency increases, the volume of passive components such as inductors decreases correspondingly, and the volume of the entire circuit board decreases by more than 30%. Frequently Asked Questions about Silicon and Germanium Diodes1. Why silicon diode is better than germanium diode?The structure of Germanium crystals will be destroyed at higher temperature. However, Silicon crystals are not easily damaged by excess heat. Peak Inverse Voltage ratings of Silicon diodes are greater than Germanium diodes. Si is less expensive due to the greater abundance of element. 2. How can I tell if I have a Ge or Si diode?You can easily distinguish Silicon and Germanium Diodes. Silicon diodes should read approx 0.7V and Germanium diodes should read 0.3V. A little difficult to distinguish Schottky diodes though. They should show approx 0.2V which is close to 0.3V. 3. What are the differences between silicon and germanium semiconductor?The key difference between silicon and germanium is that the Germanium has d electrons, but Silicon does not have any d electrons. Silicon and germanium, are both in the same group (group 14) of the periodic table. Hence, they have four electrons in the outer energy level. 4. What is difference between silicon and germanium?Silicon and germanium have four valence electrons but at the given temperature germanium will have more free electrons and higher conductivity than silicon. Silicon is more widely used in the electronic device than germanium since it can be used at a higher temperature. 5. What is the difference between silicon and germanium transistors?To answer you actual question, there are two significant differences between silicon and germanium transistors: germanium has a low melting point and germanium transistors have much less tolerance for high temperatures. The forward voltage drop of a germanium junction is lower than for silicon.

IntroductionAs one type of relays, reed relays use an electromagnetic coil to control one or more flexible ferromagnetic metal reed switches directly. It is composed only by the contacts themselves that triggers the conduction in the secondary circuit. Reed relay switches can be used as magnetic proximity switches or relays, which are smaller in size, higher in speed and longer in working life than general mechanical switches. Here, let's explore this special relay.What is a Reed Relay? Characteristics IntroductionCatalogIntroductionⅠ A Special Relay: Reed RelayⅡ Structure Comparison: Relay vs Reed RelayⅢ Reed Relay CharacteristicsⅣ What is a Reed Relay Used For?Ⅰ A Special Relay: Reed RelayIn electronic circuits, relays are the switches which close and open the circuits contacts electronically as well as electromechanically. When the relay coil is energized or de-energized, it plays the role of automatic regulation, safety protection and circuit conversion. Relays are available with two main types. As everyone knows, relays are divided into mechanical relays and semiconductor relays.Figure 1. Mechanical Relay vs Semiconductor RelayOn the insulation detection circuit of BMS, we often use a device called PhotoMOS, which is used to switch the Wheatstone bridge. Actually, it is a semiconductor relay.Figure 2. PhotoMOS AQV258For example, AQV258 is a model we often choose.PhotoMOS is a semiconductor relay with LED as input and MOSFET as output, but we are not mainly discussing PhotoMOS today.In recent years, another device has appeared on the insulation detection circuit, which is called Reed Relay Switch, Reed Switch, Reed Relays, etc. It is also used for the switch of the Wheatstone bridge arm. Ⅱ Structure Comparison: Relay vs Reed RelayReed relay is a kind of mechanical relays, but its structure is different from the traditional electromagnetic relay. The traditional electromagnetic relay is an electrical relay that uses the suction force generated by the circuit in the input circuit between the electromagnet core and the armature to work. This kind of relay is large in size, slow in action, and limited in life, but it is reliable. With the development of electronic appliances in the direction of miniaturization, new requirements have been put forward for relays. In this case, reed relays can meet the needs of this development in many aspects.Figure 3. Electromagnetic Relay StructureThe reed relay is composed of two parts: a reed switch and a coil. Compared with other types of relays, it is more compact and has higher energy efficiency. The following describes its structure and principle in detail.As shown in the figure below, the magnetic reed switch consists of two magnetic reeds, which are sealed inside a glass tube. The two magnetic reeds have a contact overlap area at the middle end of the glass tube, and has a small gap. The inside of the glass tube is filled with inert gas, such as nitrogen, to prevent oxidation. In order to improve the strength of electrical breakdown, the inside of the glass tube can also be evacuated.Figure 4. Reed Relay StructureThe magnetic reed body is made of nickel-iron alloy, and the surface of the contact overlap area of the two magnetic reeds is plated with hard metals such as rhodium or ruthenium to play a role in wear resistance. Placing the magnetic reed switch in a magnetic field, when the two magnetic reeds are magnetized into opposite polarities, they generate attractive force, and the contact overcomes the elastic force to connect. Similarly, when the magnetic field disappears, the contact is pulled away without magnetic force.In order to allow the reed switch to be closed or opened by human control, the coil is wound on the surface of the glass tube, and the coil is energized, thus forming an electromagnet, which generates a magnetic field for the reed switch to act.Figure 5. Relay CoilTherefore, as a circuit switch device controlled by a magnetic field signal, the reed switch can be used as a sensor for counting and limiting (in the security system, it is mainly used for the production of door and window magnets). It is widely used in various communication devices. In practical applications, permanent magnets are usually used to control whether the two metal pieces are connected or not, so they are also called magnetic relay.What’s more, the more turns the coil has, the less current reed relay switch needs to work. The relationship between the number of turns and the working voltage is restricted by the following factors: the wire diameter of the coil, the number of turns, the resistivity of the conductor, and the size of the reed contact.In theory, the working principle of the reed relay is like a switch: when the permanent magnet is close to the reed switch or the magnetic field formed by the coil winding on the reed switch magnetizes the reed, the contact part of the reed will be attracted by the magnetic force. When the attractive force is greater than the elastic force of the reed, the normally open contact will attract and close; when the magnetic force is reduced to a certain extent, the contact is opened by the elastic force of the reed.Figure 6. Reed Relay Magnetic FieldThe lifespan of reed switches is shorter than that of semiconductor switches, but much longer than general electromagnetic relays. The following figure shows the operating parameters of a certain type of reed switch, which can be switched on and off millions of times.Figure 7. Life Test DataThe reason for using the reed relay in the bridge method is that it has higher insulation and withstand voltage regardless of the load end or input/output. Ⅲ Reed Relay Characteristics1) High reliabilityThe failure rate of general relays is set at 50ppm, so in order to meet this requirement, the quality level of reed switches is much higher than this standard. So far, there has not been any electromechanical device that can achieve this level of quality.2) High securityReed relay switch has excellent insulation properties. Its insulation resistance can reach up to 1015Ω, that is, its leakage current only has 10-15A. Such extremely low leakage levels are widely used in medical electronic equipment, such as probes inserted into the human body or cardiac pacemakers, because these equipment require no leakage current close to the heart, even if the current is microampere or submicroampere, which will change the electrical properties of key parts of the heart.3) High adaptabilityThe reed sensor is sealed. Because the switch components is airtightly sealed in an inert gas, it will not contact the external environment, so it can work in almost any environment without being sensitive to humidity and not affected by the outside world. At the same time, the reed switch has no special requirements for the ambient temperature and has a wide temperature adaptability. The typical working temperature range can be from -50℃ to +150℃, and no special additional conditions, restrictions or costs are required.4) Long lifespanBecause the reed switch is a wear-free component and does not use a sliding component, there will be no worn metals, ensuring practically unlimited mechanical service life. At the same time, because the contact made of inert precious metal rhodium has a high melting point, it can reduce the loss of arc power generation on the contact surface, so it is more resistant to wear and can maintain a longer working life. General reed switches can work up to a million times under low-level loads (less than 5V and lower at 10mA).5) Small sizeThe reed relay switch can be installed in a limited space and is very suitable for miniaturized equipment.6) Superior electrical performanceReed relay switches have a series of excellent electrical properties. For example, their contacts have extremely low on-resistance when they are turned on, typically as low as 50mΩ. In addition, their direct switching signals can range from a few nanovolts to thousands of volts, and the current ranges from micro An to An, etc.7) High speed operationSince each movable component has only a very small weight, the operating speed is very high, making the reed switch a part that can be used in transistor circuits or integrated circuits.Ⅳ What is a Reed Relay Used For?Reed relay switches have been widely used in many fields of automatic control systems, such as machinery, automobiles, electronics, electric power, petroleum, chemical industry, office automation, communications and other engineering. For example, in the military field, high-voltage reed relays are related to national defense components for modern weapons and equipment. Frequently Asked Questions about Reed Relay Basics and Uses1. What is a reed relay used for?Reed Relays are ideally used for switching applications requiring low and stable contact resistance, low capacitance, high insulation resistance, long life and small size. 2. What is the difference between relay and reed relay?A relay switch is composed of an electromagnet that actuates a high power switch made of two metallic contacts. ... A reed switch is composed only by the contacts themselves that triggers the conduction in the secondary circuit. 3. Why is reed relay used in a switching circuit?The reed relay consists of a switch with magnetic contacts that move under the influence of an external magnetic or the induced field from its solenoid. They have faster switching speed compared to the electromechanical ones but their switching current and voltage is lower mainly because of its contacts thickness. 4. What is required to operate a reed relay in a switching circuit?The coil surrounds the reed switch and generates the axial magnetic field needed to close the reed contacts. 5. Where is a reed switch used?Reed switches are used in fluid level sensors for brake fluid reservoirs and to monitor motor oil levels. They are also used in speed sensors for engine control and power steering. Automatic door locks, air bags, parking brakes, seat, door, and hood proximity sensors also utilize reed switches.

CatalogⅠ Definition of Fuel Pump RelayⅡ Function of Fuel Pump Relay Ⅲ Application of Fuel Pump Relay in Vehicles  3.1 The working principle of automobile relay  3.2 The function of automobile relayⅣ The Location of Fuel Pump RelayⅤ Symptoms of a bad Fuel Pump RelayⅥ How to Replace the Fuel Pump Relay   6.1  Part 1: Removing the fuel pump relay  Step 1:  Step 2:  Step 3:  Step 4:  Step 5:  Step 6:  Step 7:  Step 8:  Step 9:  6.2 Part 2:  Installing the new fuel pump relay  6.3 Part 3: Checking for fuel pump relay operation  6.4 Part 4: Test drive the vehicleⅦ  Frequently Asked Questions about Fuel Pump Relay Failure Analysis Ⅰ Definition of Fuel Pump Relay As most people are familiar with, the fuel pump is a component inside the fuel tank that enables the combustion engine to run by providing pressure in the fuel lines to push gasoline to the combustion engine.  The fuel pump can fail for a variety of causes, one of which is a less well-known problem with the fuel pump relay. A fuel pump relay is a compact unit with many sprockets on one side that are clipped onto the ignition system and is covered in a plastic container. A gasoline pump relay is, in some ways, similar to an automotive fuse in that it is an electrical component. It controls the flow of current to the electric fuel pump, ensuring that the component receives enough power to function properly but not so much that it is damaged. Fuel pumps consume a lot of power, which may cause the electrical system and the pump to overheat  if  it weren't for the relay.Ⅱ Function of Fuel Pump RelayIn general, the relay acts as a power monitor for the fuel pump, activating it when the ignition is turned on and turning it off when the vehicle is turned off. When the ignition switch is turned to the on position for the first time, the fuel pump can be heard humming. This provides fuel to start the vehicle, and once the vehicle is running, the vehicle's computer sends a signal, and the fuel pump relay turns off. The fuel pump in the vehicle will now be powered by another source, typically the oil pressure sending unit.The vedio shows that how a fuel pump relay worksⅢ Application of Fuel Pump Relay in VehiclesAutomobile relays are composed of a magnetic circuit system, contact system, and restoration mechanism, as indispensable circuit components, such as automobile lights, air conditioners, electric seats, electric doors and windows, ABS devices, etc. have control relays. 3.1 The working principle of automobile relayThe electromagnetic relay applies the principle of electromagnetic induction. When the coil goes through the DC, the coil generates a magnetic field, and the moving iron is attracted to drive the contact reed, which separates the static contacts and closes the moving contacts. The iron core loses its magnetism when the electromagnetic coil current is switched off, the moving iron core is reset by the spring force, the moving contract is unfolded, and the static one is closed.The contact in the off position is a typically open contact, and the contact in the on position is a normally closed contact when the relay coil is not activated.  Between a normally open contact and a normally closed contact, there is a moving contact called a changeover contact. There can exist one or more ordinarily open contacts, normally closed contacts, and conversion contacts in the same relay.  In most electromagnetic relays, there is only one coil. A text sign is commonly used to identify the relay coil and its contacts, and each group of contacts is identified with a subscript, to illustrate the relay plainly and simply on the circuit.3.2 The function of automobile relayBy controlling the current of the low-voltage line, the current of the high-voltage line is controlled, and it acts as a current switch. The main function of the car is to start the motor rotation by controlling the large current by small current, thereby driving the rotor of the magneto inside the generator to rotate, giving the ignition Input the ignition pulse signal to make the ignition  generate electric sparks, ignite the mixed gas in the cylinder and do work. Relays belong to the switch category. It takes advantage of electromagnetic and electrical  and mechanical principles to close or open contacts to drive or control related circuits. A relay is a control device that is consisted of two parts: a controlled system (input loop) and a control system (output loop) (output loop). The output quantity changes abruptly from zero to a given value (or from a certain value to zero) when the input quantity (electricity, magnetism, light, heat, and other physical qualities) reaches a certain value, allowing the circuit to be controlled, protected, regulated, and transmitted.Ⅳ The Location of Fuel Pump RelayThe majority of fuel-pump relay units are found beneath the dashboard, near the steering wheel. In certain circumstances, the unit is positioned near the engine's firewall or in the location where the steering column is attached. The fuel pump relay's end is usually at the center of the floorboard, under the carpet in the front area of the passenger or driver's side footwell. The fuel pump relays can be found in a variety of locations depending on the vehicle. If you have your owner's manual (and if you don't, you can get a new one from owner Manual), check it and look at the schematic to see where the location is. This is not an accurate list, it is only for a few models of vehicle. But it contains the most common locations where I've found this component.  If you need to find the exact placement of the fuel pump relay quickly, consult your service manual.Figure1: the general location of fuel pump replay• Driver’s Side Kicker PanelNissan prefers to hide the fuel pump relay beneath a plastic cover near the brake or gas pedal, which is held in place by a couple of bolts. To get to the part, simply remove the bolts and the cover! •  Near The Fuse BoxI've seen it in the fuse box or very close to the fuses in numerous Mazdas and Toyotas. • Passenger Side Firewall Near DipstickThe pump relay is located behind the oil dipstick near the strut/shock housing on older Mitsubishis, particularly the Evolutions.Ⅴ Symptoms of a bad Fuel Pump Relay• Engine stallsAn engine that suddenly stalls is one of the most obvious signs of a problem with the fuel pump relay. If the fuel pump relay fails while the vehicle is in operation, the fuel pump will lose power, causing the engine to stall. A malfunctioning relay may allow the engine to be restarted after a short period of time, but a relay that has fully failed will not.• Engine does not startA non-starting engine is another indicator of a malfunctioning fuel pump relay. The gasoline pump will be left without electricity if the fuel pump relay fails. When the key is turned, the engine may still crank, but it will not start owing to a lack of fuel. This symptom could be caused by a variety of different problems, so having the vehicle professionally assessed is essential.• Loss of PowerIf the automobile suddenly loses power while driving or slows down for no apparent reason, the gasoline relay could be to blame. This does not necessarily imply that the vehicle will stall. For a short period of time, the vehicle will continue to run normally. However, if you encounter a sudden lack of power while driving, you should get your automobile inspected and repaired immediately, as there is always the possibility that the car will come to a halt again, leaving you stranded in the middle of the road.• No noise from the fuel pumpWhen the key is turned on, there is no noise from the fuel pump, which could indicate a problem with the fuel pump relay. Most fuel pumps emit a low-volume hum or whine that can be heard from inside the vehicle, or from outside the vehicle, near the fuel tank, if you listen carefully. If the fuel pump relay fails, power to the fuel pump is cut off, rendering out operation and, as a result, silent when the ignition is turned on. The gasoline pump relay is a relatively simple component, yet it is important to the vehicle's proper operation. If you notice any of the above symptoms or suspect that your fuel pump relay is failing, have your vehicle inspected by a professional to determine whether the component needs to be replaced. Ⅵ How to Replace the Fuel Pump Relay6.1  Part 1: Removing the fuel pump relayMaterials Needed• Needle nose plyers• Ratchet with metric and standard sockets• Wheel chocksStep 1: Turning on the ignition key ，wait for the gasoline pump to operate.Also, listen for any buzzing or clicking noises coming from the fuel pump relay.Figure2: listen  noise from the relayStep 2: Start the engine. Check that there is oil pressure.An oil light may be the lone signal on some automobiles. When the indicator light turns off, there will be oil pressure.Figure3: check the oil light on dashboard Step 3: Park your vehicle on a flat, hard surface.Make sure the transmission is in a park (for automatic transmissions) or first gear (for manual transmissions) (for manuals).Figure4: Parking your vehicleStep 4: Place wheel chocks around the tires.Because the rear of the car will be raised, the wheel chocks will be around the front tires in this situation.Engage the parking brake to lock the rear tires from moving.Figure5: Place wheel chocks around the tiresStep 5: Install a nine-volt battery saver into your cigarette lighter.This will keep your computer activated and your vehicle's settings current. It's fine if you don't have a nine-volt battery saver.Figure5: Install a nine-volt batteryStep 6: Open the vehicle’s hood to disconnect your battery.Remove the ground line from the negative post of the battery to turn off the power to the fuel pump and sending unit.Figure6: open your engine and disconnect your batteryStep 7: Look in the engine area for the fuse box. The fuse box's lid must be removed.Figure7: Find the fuel boxNote: Some fuse boxes are secured with hex screws or bolts and must be removed using a ratchet. Clips hold the other fuse boxes in place. Step 8: Locate the fuel pump relay using the diagram on the fuse box cover.Using the schematic on the fuse box cover, look for the fuse for the fuel pump relay when you open the fuse box. Figure8: Locate the fuel pump Step 9: Remove the fuel pump relay from the fuse box. Pay attention to how the relay comes out as the new one needs to go in the same way.If your fuse box cover doesn't have any schematics on it, you can look up the engine compartment fuse box diagram in your owner's handbook. The number adjacent to the fuel pump relay is usually stated in the owner's manual so you can discover the number on the fuse box.Note: You may need to use a pair of needle nose players to pull out the fuel pump relay.Figure9: Remove the fuel pump relay6.2 Part 2:  Installing the new fuel pump relayMaterials NeededReplacement of fuel pump relayStep1 Install relay. Install the relay into the fuse box the same way  the old relay was removed.Step2 Put on the fuse box cover. Snap it into place.Note: If you had to remove screws or bolts from the cover, make sure you put them back correctly. They will strip out if you tighten them over.Step3 Remove the fuel cap from the fuel tank.  Replace the gasoline cap and double-check that it seals properly. 6.3 Part 3: Checking for fuel pump relay operation Step1 Reattach the ground line to the negative post of the battery. Remove the cigarette lighter's nine-volt battery saver.Wait for the gasoline pump to turn on. Step2 Tighten the battery tightly. Ensure that the connection is good.Step3 Turn the ignition key on. Listen for the fuel pump to activate.When the fuel pump stops generating noise, turn off the ignition. Restart the engine and listen for a buzz or click from the fuel pump relay. To experience the buzz or clicking action, you may need to have another person touch the fuel pump relay.Note: Before starting the engine, turn the ignition key on and off three or four times to ensure the fuel rail is full of fuel.Step4 Start the engine by turning the key to start. During the cranking time, keep an eye on how long the start will be engaged.Note: Most modern vehicles will not start up until the oil pressure has built up.Step5 Wheel chocks should be removed from the wheels. Place these in a safe place. 6.4 Part 4: Test drive the vehicleStep1 Drive the auto around the block. During the test, listen for any unusual noise from the fuel pump or fuel pump relay.Also, immediately accelerate the engine to ensure that the fuel pump is working properly. Step2  Monitor the dash for any engine lights.If your engine light turns on after replacing the fuel pump relay, you may need to have the fuel pump assembly diagnosed or there could be an electrical problem with the fuel system. If the problem persists, you should contact one of Your Mechanic's qualified technicians, who will test the fuel pump relay and diagnose the issue.  Ⅶ  Frequently Asked Questions about Fuel Pump Relay Failure Analysis1. What causes a faulty fuel pump relay?A gasoline pump relay might fail due to dust, electrical power surges, and other issues. Dust and rapid voltage surges can degrade the performance of a fuel pump relay, causing an engine to fail. Passenger Side Firewall Near Dipstick. 2.  Will a fuel pump work without a relay?What is a Fuel Pump Relay, and What Does it do? A fuel pump relay is a plastic covered part connected to the fuel pump. It is one of the most important parts of your vehicle. Without the fuel pump relay, you won't even be able to drive your vehicle. 3. Can AutoZone test a fuel pump relay?AutoZone makes checking fuel pressure easier than ever. ... While testing does entail some work, few things are more rewarding than successfully troubleshooting your fuel pump relay. And with a fuel pressure test gauge from AutoZone, it's easy. 4.  How does a car act when the fuel pump is going out?You'll notice a decrease in fuel efficiency, acceleration and power in your vehicle if your fuel pump is damaged. The low pressure caused by a faulty fuel pump means your engine isn't getting the fuel and air mixture it needs to give your car that regular power. Whining in the backseat. 5.  How long does a fuel pump relay last?Over time, the fuel pump relay can begin to show signs of wear and will have to be replaced. The fuel pump relay is designed to last the life of the car, but due to the grueling conditions it is exposed to, it will not usually last that long. 6. Where is the fuel pump reset button?Look for the fuel pump switch or inertia switch. This is a small box with a plastic button on top and an electrical connector at the bottom. On some vehicle models, this will be located in the luggage compartment. Look on a side panel for a small, round button which you can pry off with a small screwdriver. 7. Will a car start with a bad fuel pump?If your vehicle's fuel pump cannot get gas from the tank to the engine, you will have trouble starting your car. The car will struggle to start and run because the pump cannot push enough gas through. A worn pump loses its pressure and the engine is being starved of gasoline. 8. What would cause a fuel pump not to get power?If you there is no power to the fuel pump or the relay, then there may be a possible electrical issue with the vehicle. ... If there is an issue with the switch or the circuit, perhaps a wiring problem, then power to the fuel system may be cut off. 9. Will a bad fuel pump give a code?Bad Fuel Pump, Fuel Pressure Sensor Can Trigger 'Check Engine' Light, P0087 Code. ... The light is part of your vehicle's on-board diagnostics (OBD) system and can indicate anything from a loose gas cap to a major repair like a catalytic converter. 

IntroductionA clamper circuit is an electronic circuit that shifts the DC level of a signal to a desired level without changing the shape of the applied waveform. Unlike clipper circuits that cut or limit portions of a signal, clampers preserve the entire waveform while repositioning it vertically on the voltage axis. This is achieved by fixing a specific part of the pulse signal (such as the positive or negative peak) at a specified voltage value while maintaining the original waveform shape unchanged.What is a Clamper Circuit?Ⅰ Clamper Circuit ApplicationsClamper circuits are widely used in various electronic systems and display devices. Key applications include:Television Systems: Clamper circuits restore the DC component of video signals and maintain the synchronization pulse at a fixed voltage level, ensuring stable image positioning and proper sync signal separation.Oscilloscopes and Test Equipment: Used to stabilize waveform display by fixing reference levels, preventing image drift caused by varying scanning speeds or DC component loss.Radar and Sonar Systems: Employed to maintain consistent signal levels for accurate detection and ranging.Amplifier Protection: Protects sensitive amplifier input stages from excessive DC offset voltages.Power Supply Circuits: Helps in voltage regulation and transient suppression.Communication Systems: Restores DC levels in signal transmission and reception circuits.Digital Logic Circuits: Provides voltage level shifting between different logic families.A basic clamper circuit comprises a capacitor, a diode, and a resistor. More sophisticated designs may include additional components such as bias voltage sources. In the following sections, we will explore different types of diode clamper circuits and compare their characteristics and performance.Ⅱ Diode Clamper Circuit2.1 Why Use Diode Clamper Circuits?While diode clipper circuits limit or cut the amplitude of waveforms, many applications require preserving the complete waveform while shifting its DC level. Clamper circuits fulfill this requirement by shifting the signal vertically to position its peak value at a desired level without distorting the original waveform shape.A diode clamper circuit utilizes the relatively stable forward voltage drop of the diode (typically 0.6-0.7V for silicon diodes or 0.2-0.3V for Schottky diodes) and its low reverse leakage current characteristics. These properties enable the circuit to clamp the potential at specific points and maintain the peak or trough of periodically changing waveforms at predetermined DC levels.Dual-Diode Clamper Protection: In protection applications, two diodes connected in reverse parallel configuration provide bidirectional clamping. Only one diode conducts at any given time while the other remains in the off state. This arrangement limits both positive and negative voltage excursions to approximately ±0.6V (for silicon diodes), effectively protecting sensitive circuit components from overvoltage conditions and electrostatic discharge (ESD).2.2 Diode Clamper Circuit TypesDiode clamper circuits are classified into two main categories: positive clampers and negative clampers. Each category includes both simple (unbiased) and biased variants.✅ Diode Positive ClamperOperating Principle:Positive Half Cycle: The diode is reverse-biased (OFF), acting as an open circuit. The capacitor charges to the peak input voltage Vi through the load resistor.Negative Half Cycle: The diode becomes forward-biased (ON), acting as a short circuit. The capacitor maintains its charge, and the output voltage Vo ≈ 0V (or slightly positive due to diode forward voltage drop).According to Kirchhoff's voltage law, the output waveform can be calculated for both positive and negative cycle conditions.(1) Simple Positive Clamper (Unbiased)Figure 1. Simple Positive Clamper CircuitOperation:When Vi is in the negative half cycle: D → ON, capacitor C charges to voltage V (negative on left plate, positive on right plate), Vo ≈ 0V.When Vi is in the positive half cycle: D → OFF, Vo = VC + Vi = 2V (assuming input amplitude is V).(2) Biased Positive ClamperFigure 2. Biased Positive Clamper CircuitSimple Method to Determine Output Waveform:The reference point of the output waveform on the voltage axis is determined by the bias voltage V1.The diode orientation determines the direction of waveform shift. If the diode points upward , the waveform shifts upward; if it points downward , the waveform shifts downward.After determining the reference point and direction, sketch the original waveform on the output coordinate axis using the reference point as the baseline to obtain the clamped output waveform.↪️ Diode Positive Clamper Circuits Comparison:Figure 3. Positive Clamper Circuits Comparison✅ Negative Clamper Circuit(1) Simple Negative Clamper (Unbiased)Figure 4. Simple Negative Clamper CircuitOperation:When Vi is in the positive half cycle: D → ON, capacitor C charges to voltage V (positive on left plate, negative on right plate), Vo ≈ 0V.When Vi is in the negative half cycle: D → OFF, Vo = -(VC + |Vi|) = -2V (assuming input amplitude is V).(2) Biased Negative ClamperFigure 5. Biased Negative Clamper CircuitOperation:When Vi is in the positive half cycle: Diode D → ON, capacitor C charges to voltage V (positive on left plate, negative on right plate), Vo = +V1 or -V1 (depending on bias polarity).When Vi is in the negative half cycle: Diode D → OFF. With a sufficiently large RC time constant, Vo = VC + Vi (negative half cycle) ≈ -2V + bias voltage.↪️ Diode Negative Clamper Circuits Comparison:Figure 6. Negative Clamper Circuits Comparison✅ Key Design ConsiderationsDiode Orientation: The direction of the diode determines whether the waveform shifts upward (positive clamping) or downward (negative clamping).Bias Voltage: The bias voltage establishes the reference point (baseline) of the clamped waveform on the voltage axis.RC Time Constant: The product of capacitance (C) and load resistance (R) must be sufficiently large—typically RC ≥ 10T, where T is the period of the input waveform. This ensures the capacitor maintains its charge between cycles, preventing droop and maintaining clamping accuracy.Diode Selection: Choose diodes with low forward voltage drop (Schottky diodes for precision applications) and fast recovery time for high-frequency signals.Capacitor Selection: Use capacitors with low leakage current (film or ceramic types) to maintain charge stability.Ⅲ Practical Application: GPIO Protection Using Clamper CircuitsA practical application of clamping diodes is found in GPIO (General Purpose Input/Output) pin protection circuits. This example demonstrates the use of dual-diode clampers in the Qualcomm MSM8909 platform to prevent electrostatic discharge (ESD) damage and electrical overstress (EOS).Circuit AnalysisFigure 7. MSM8909 GPIO Internal Protection CircuitCircuit Configuration:Clamping diode D1: Cathode connected to VDD (positive supply rail), anode connected to GPIO pinClamping diode D2: Anode connected to GND (ground), cathode connected to GPIO pinProtection Mechanism:When input voltage > VDD: D1 conducts (forward-biased), D2 is off (reverse-biased). The GPIO pin voltage is clamped to approximately VDD + 0.6V, with excess current shunted to the VDD rail.When input voltage < GND: D1 is off (reverse-biased), D2 conducts (forward-biased). The GPIO pin voltage is clamped to approximately GND - 0.6V, with excess current shunted to ground.Normal operation (GND < Vin < VDD): Both diodes remain off, allowing normal signal operation without interference.This dual-diode configuration effectively limits the input voltage to the safe operating range of [GND - 0.6V, VDD + 0.6V], protecting the GPIO pin from ESD events and voltage transients.Diagnostic Procedure: Testing GPIO Protection DiodesTo determine whether a GPIO pin has been damaged by ESD or EOS, follow this multimeter-based diagnostic procedure:Equipment Required:Digital multimeter with diode test functionAnti-static wrist strap (recommended)Circuit schematic or pinout diagramTest Procedure:Power Down: Ensure the device is completely powered off and disconnected from all power sources.Test Diode D2 (Lower Clamp to GND):Set multimeter to diode test modeConnect RED probe to motherboard GNDConnect BLACK probe to the GPIO pin under testExpected Result: Forward voltage drop of 0.4-0.7V (typically 0.6V for silicon diodes)Failure Indication: Reading significantly outside this range indicates D2 damage:Very low reading (< 0.2V): Diode is shortedOpen circuit (OL or > 2V): Diode is openTest Diode D1 (Upper Clamp to VDD):Reverse probe connections:Connect RED probe to the GPIO pin under testConnect BLACK probe to VDD rail (or appropriate power pin)Expected Result: Forward voltage drop of 0.4-0.7VFailure Indication: Similar interpretation as D2 testReverse Bias Test (Optional):Reverse the probe connections for each testExpected Result: Open circuit (OL) or very high resistanceFailure Indication: Low resistance in reverse bias indicates diode breakdownImportant Notes:Always discharge any residual capacitance before testingSome modern ICs may have additional protection elements that affect readingsCompare readings with a known-good board when possibleDocument all measurements for troubleshooting recordsIf protection diodes are damaged, the internal GPIO circuitry may also be compromisedFrequently Asked Questions about Clamper Circuits1. What is a clamper circuit and what are its types?A clamper circuit is an electronic circuit that shifts the DC level of an AC signal to a desired voltage level without altering the shape of the waveform. Since the DC level is shifted, a clamper circuit is also called a level shifter. Clamper circuits utilize energy storage elements, primarily capacitors. A basic clamper circuit consists of a capacitor, a diode, a resistor, and optionally a DC bias voltage source. The main types are: positive clampers (shift waveform upward), negative clampers (shift waveform downward), and each can be either biased (with reference voltage) or unbiased (simple configuration).2. How do clamper circuits work?A clamper circuit operates by using a capacitor to store charge during one half-cycle of the input signal and a diode to control the charging and discharging process. During the half-cycle when the diode conducts, the capacitor charges to approximately the peak voltage of the input signal. During the opposite half-cycle, the diode blocks, and the capacitor voltage adds to (or subtracts from) the input voltage, effectively shifting the entire waveform up or down. The RC time constant must be large enough (typically RC ≥ 10T) to maintain the capacitor charge between cycles, ensuring consistent clamping action.3. What is a diode clamper circuit?A diode clamper circuit is a specific implementation of a clamper that uses a diode as the switching element to control the charging of the capacitor. The circuit consists of a capacitor, a diode, and a resistor arranged to shift the waveform to a desired DC level. The diode's unidirectional current flow property ensures that the capacitor charges during one half-cycle and maintains its charge during the other half-cycle, creating the clamping effect. The diode's orientation determines whether the circuit functions as a positive or negative clamper.4. How many diodes are used in a clamper circuit?A basic clamper circuit requires a minimum of one diode, along with a capacitor and a resistor. However, protection circuits and bidirectional clampers may use two diodes connected in reverse parallel (anti-parallel) configuration to provide clamping in both positive and negative directions. Some advanced designs may incorporate additional diodes for improved performance, temperature compensation, or multiple voltage level clamping. An independent DC voltage source may also be added to create biased clamper circuits with adjustable reference levels.5. What is a clamping diode used for?Clamping diodes serve multiple purposes in electronic circuits: (1) Level Shifting: They shift AC signals to desired DC levels in signal processing applications. (2) Voltage Protection: They protect sensitive components from overvoltage conditions by limiting voltage excursions to safe levels (typically within ±0.6V of supply rails). (3) ESD Protection: In integrated circuits, clamping diodes protect GPIO pins and other I/O interfaces from electrostatic discharge damage. (4) Transient Suppression: They absorb voltage spikes and transients in power supply and signal lines. (5) Signal Restoration: In video and communication systems, they restore DC components that may be lost during AC coupling or transmission.6. What is the difference between a clipper and a clamper circuit?Clipper circuits cut off or limit portions of the input waveform that exceed certain voltage levels, fundamentally changing the waveform shape. Clamper circuits preserve the entire waveform shape but shift its DC level (vertical position on the voltage axis). Clippers are used for waveform shaping and overvoltage protection, while clampers are used for DC restoration and level shifting. Clippers typically use diodes with resistors, while clampers require capacitors in addition to diodes and resistors.7. Why is the RC time constant important in clamper circuits?The RC time constant (τ = R × C) determines how quickly the capacitor charges and discharges. For proper clamping action, the RC time constant must be much larger than the period of the input signal (typically RC ≥ 10T). This ensures that: (1) The capacitor charges quickly during the conducting half-cycle of the diode, (2) The capacitor maintains its charge during the non-conducting half-cycle with minimal voltage droop, and (3) The clamping level remains stable across multiple cycles. If the RC time constant is too small, the capacitor will discharge significantly between cycles, resulting in poor clamping performance and waveform distortion.ConclusionClamper circuits are essential components in modern electronics, providing DC level shifting and voltage protection across a wide range of applications. Understanding the operating principles of positive and negative clampers, both biased and unbiased configurations, enables engineers to design effective signal conditioning and protection circuits. The practical application in GPIO protection demonstrates the critical role of clamping diodes in safeguarding sensitive integrated circuits from ESD and overvoltage damage. Proper component selection, particularly regarding the RC time constant and diode characteristics, is crucial for optimal clamper circuit performance.Note: This article was originally published in 2020 and has been updated in 2025 to reflect current technology standards, correct technical inaccuracies, and include additional practical information about clamper circuit applications and diagnostics.

IntroductionFLASH is a type of non-volatile memory that retains data even when power is disconnected. Unlike RAM, which can rewrite data at the byte level, flash memory operates differently. A flash memory chip consists of an array of data storage cells organized into blocks, with each block containing multiple pages (typically 64 to 256 pages in modern devices, though older devices used 32 pages). A page is usually 2KB, 4KB, 8KB, or 16KB in modern NAND flash, though the original specification was 512 bytes plus spare area, as flash was initially developed as a disk replacement technology.What Is Flash Memory?Ⅰ Types of Flash MemoryFlash memory is widely used as a storage medium in digital cameras, smartphones, tablets, USB drives, SSDs, and various consumer electronics. Flash memory cards come in various form factors depending on manufacturers and applications, including USB flash drives, CompactFlash (CF card), MultiMediaCard (MMC card), Secure Digital (SD card, microSD), Memory Stick, and XD-Picture Card (XD card). Note that SmartMedia (SM card) and Microdrive have been discontinued. While these flash cards have different physical formats and specifications, their underlying technical principles remain similar.Flash memory includes two main architectural types: NOR Flash and NAND Flash. NOR Flash is a random access device with dedicated address and data lines (similar to SRAM), allowing byte-level read and write operations and direct access to any memory location, making it an excellent ROM alternative, such as in computer BIOS chips. NAND Flash, however, lacks dedicated address lines and cannot be directly addressed. It is controlled by sending commands and addresses through an I/O interface, meaning NAND Flash can only be accessed in pages, making it more suitable for sequential data storage.Ⅱ NAND Flash MemoryNAND Flash is extensively used in high-capacity storage devices such as memory cards, USB drives, SSDs, eMMC, and UFS storage. NAND Flash cells are categorized by the number of bits stored per cell: SLC (Single-Level Cell), MLC (Multi-Level Cell), TLC (Triple-Level Cell), and QLC (Quad-Level Cell). SLC stores 1 bit per cell, MLC stores 2 bits, TLC stores 3 bits, and QLC stores 4 bits per cell.As more bits are stored in a single cell, the read/write performance decreases, endurance diminishes, but cost per gigabyte is reduced, making higher-density options more economical for consumer applications.ItemsSLCMLCTLCQLCBits Per Cell1234P/E Cycles50,000-100,0003,000-10,0001,000-3,000100-1,000Read Time (μs)255075100Program Time (μs)200-300600-900900-13501350-2000Erase Time (ms)1.5-234.56-8SLC is primarily used in enterprise, industrial, and military applications due to its high-speed writing, low error rate, and exceptional durability.MLC is targeted at consumer and prosumer applications, offering twice the capacity of SLC at lower cost. It's suitable for USB drives, smartphones, digital cameras, and consumer-grade SSDs.TLC has become the mainstream choice for consumer SSDs and SD cards due to its balance of cost, capacity, and acceptable performance for everyday use.QLC, introduced more recently, offers even higher density and lower cost per gigabyte, making it increasingly popular in budget SSDs and high-capacity storage solutions, though with reduced endurance.As a practical solid-state storage medium, NAND Flash has unique physical characteristics requiring specialized management. Designers face several key challenges:1) Erase-before-write requirement: Data cannot be overwritten directly; blocks must be erased before new data can be written2) Wear mechanism: Limited program/erase (P/E) cycles impose durability constraints3) Read/write interference: Operations can cause data errors in adjacent cells4) Data retention: Charge leakage over time can cause data loss5) Bad block management: Both factory defects and runtime failures must be managedKey technologies addressing these challenges include:1) Cell type selection: Choosing appropriate NAND type (SLC/MLC/TLC/QLC) based on application requirements2) Wear leveling algorithms: Distributing write operations evenly across all blocks to maximize lifespan3) Bad block management: Identifying and mapping out defective blocks to ensure data integrity4) Error Correction Code (ECC): Detecting and correcting bit errors using advanced algorithms like BCH or LDPC5) Write amplification mitigation: Minimizing unnecessary write operations to extend device life6) Garbage collection: Consolidating valid data and reclaiming space from partially used blocksData is stored as electrical charge in Flash memory cells. The amount of stored charge depends on the voltage applied to the Control Gate, which controls whether charge is injected or removed from the floating gate.1) For programming (writing) NAND Flash, voltage is applied to the Control Gate to inject electrons into the floating gate. When charge exceeds the threshold voltage (Vth), the cell represents a logical 0.2) For erasing NAND Flash, electrons are removed from the floating gate. When charge falls below the threshold voltage (Vth), the cell represents a logical 1. Ⅲ NOR Flash MemoryNOR Flash, similar to conventional memory, supports random access, enabling XIP (eXecute In Place) functionality. This allows code execution directly from the flash without copying to RAM, making it ideal for boot code, BIOS/UEFI firmware, and embedded system applications requiring immediate code execution.NOR Flash is categorized into two types based on host interface: Parallel NOR Flash and Serial NOR Flash.Parallel NOR Flash connects directly to the host controller with its contents mapped into the CPU address space, eliminating the need to copy to RAM. Early BIOS implementations used the FWH (Firmware Hub) interface, a parallel connection that has been largely obsoleted due to pin count and speed limitations.Serial NOR Flash is more cost-effective than Parallel NOR Flash and typically connects to the host processor or Platform Controller Hub (PCH) via SPI (Serial Peripheral Interface), Quad-SPI (QSPI), or Octal-SPI interfaces. Modern implementations support higher speeds through multi-lane configurations.Today, virtually all UEFI/BIOS firmware, embedded systems, IoT devices, and many consumer electronics use NOR Flash. Typical capacities range from 1MB to 256MB, with 16MB-128MB being common for modern UEFI implementations. While more expensive per gigabyte than NAND, NOR Flash offers superior reliability and random access performance.NOR Flash has slower erase speeds and lower erase cycle counts compared to NAND, but these limitations rarely impact BIOS/firmware performance or cause device failures due to the infrequent update nature of firmware. Ⅳ NAND Flash vs NOR FlashCompared with NOR flash memory, NAND flash memory requires fewer transistors per cell to store the same amount of data, resulting in smaller die size and higher storage density. This architectural difference makes NAND significantly more cost-effective for high-capacity storage applications.In terms of read speed, NOR flash memory offers faster random access than NAND flash memory, with typical access times of 50-100ns compared to NAND's page-based access. However, NAND flash memory significantly outperforms NOR in sequential write and erase operations. NAND's block-based erase operation is simpler and faster, erasing entire blocks (typically 128KB-4MB) at once.NOR flash memory requires all bits to be set to 1 during erase operations before programming. While NOR flash memory provides faster random access and simpler byte-level operations, its lower storage density and higher cost make it more suitable for code storage and execution. NAND flash memory provides extremely high cell density (modern single chips can exceed 1TB capacity), making it ideal for mass data storage with fast write and erase speeds. Additionally, NAND flash operates on page-based read/write units (typically 4KB-16KB) and block-based erase units, making it functionally similar to traditional disk drives.NAND Flash is more susceptible to bit errors than NOR Flash, necessitating robust Error Detection and Correction (EDC/ECC) algorithms. Modern NAND implementations use advanced ECC schemes like BCH (Bose-Chaudhuri-Hocquenghem) or LDPC (Low-Density Parity-Check) codes. Additionally, NAND Flash develops bad blocks over its lifetime. File systems like FAT on SD cards experience frequent rewrites of the file allocation table, and the P/E cycle count per block is critical to NAND Flash longevity. Balancing erase cycles across all blocks and managing bad blocks requires specialized firmware-level functionality including bad block management, wear leveling, ECC, and garbage collection. This management layer is called the FTL (Flash Translation Layer). Based on FTL implementation location, Flash Memory is categorized as Raw Flash or Managed Flash.Raw Flash requires the host system to implement FTL functionality, giving designers complete control but requiring significant software development. Managed Flash (such as eMMC, UFS, SD cards) includes an integrated controller that handles FTL operations transparently, simplifying host system design at the cost of reduced low-level control.Ⅴ Universal Flash Storage Versions ComparisonStorage performance significantly impacts device responsiveness and user experience. Universal Flash Storage (UFS) has become the dominant standard for high-performance mobile and embedded storage, replacing the older eMMC standard. UFS provides a standardized flash storage specification optimized for smartphones, tablets, automotive systems, and other performance-critical applications. Version numbers indicate generational improvements, with higher versions offering substantially better performance, features, and efficiency.✔️Version Comparison (Main Parameters)UFS Version1.01.12.02.13.03.14.0Introduced2011-02-242012-06-252013-09-182016-04-042018-01-302020-01-302023-09-14Bandwidth per lane300 MB/s600 MB/s1450 MB/s (HS-G3)2900 MB/s (HS-G4)5800 MB/s (HS-G5)Max. number of lanes12Max. total bandwidth300 MB/s1200 MB/s2900 MB/s (HS-G3)5800 MB/s (HS-G4)11600 MB/s (HS-G5)M-PHY version1.03.04.15.0UniPro version1.41.61.82.0✔️UFS 2.1 vs UFS 2.2The primary enhancement in UFS 2.2 over UFS 2.1 is the Write Booster feature, which significantly improves write performance. Write Booster uses SLC (Single-Level Cell) cache to accelerate write operations, providing faster application launches, improved browser cache loading, reduced video encoding times, and enhanced overall system responsiveness. This feature is particularly beneficial for burst write scenarios common in mobile devices.As eMMC has been phased out from mainstream consumer devices and NAND flash prices have decreased, UFS adoption has accelerated. UFS 2.2 briefly served as a transitional standard before UFS 3.x became mainstream in flagship devices.✔️UFS 3.0 vs UFS 3.1UFS 3.1 introduces three significant enhancements over UFS 3.0:1) Write Booster (Enhanced)Write Booster in UFS 3.1 is an enhanced version that increases device write speed substantially. This feature can boost write speeds up to 700 MB/s, compared to UFS 3.0's typical sequential write performance of around 500 MB/s. The mechanism works similarly to SLC caching in SSDs: a portion of TLC/QLC storage is dynamically configured to operate in SLC mode, providing faster write performance. Data is initially written to this high-performance buffer, then migrated to standard storage during idle periods, freeing the cache for subsequent operations.2) Deep Sleep ModeDeep Sleep enables the flash memory to enter an ultra-low-power state during extended idle periods, significantly reducing standby power consumption. This feature helps extend battery life during device standby and contributes to overall device thermal management. Deep Sleep can reduce idle power consumption by up to 40% compared to standard sleep modes.3) Host Performance Booster (HPB)HPB addresses long-term performance degradation by improving random read performance. As devices are used over time, file system fragmentation and the need to frequently reload the Logical-to-Physical (L2P) mapping table can cause performance degradation. HPB leverages the host device's RAM to cache portions of the L2P mapping table, reducing latency for random read operations. This is particularly effective at maintaining consistent performance after extended use, preventing the "slowdown over time" phenomenon common in storage devices. HPB can improve random read IOPS by up to 70% in fragmented scenarios.✔️UFS 4.0 - The Latest GenerationReleased in September 2023, UFS 4.0 represents the latest advancement in mobile storage technology. Key improvements include:• Doubled bandwidth: Up to 11.6 GB/s (5800 MB/s per lane with dual-lane configuration) using HS-G5 gear• Improved power efficiency: Lower power consumption per bit transferred compared to UFS 3.1• Enhanced thermal management: Better heat dissipation characteristics for sustained performance• Advanced features: Builds upon Write Booster, Deep Sleep, and HPB with further optimizationsUFS 4.0 is designed for next-generation flagship smartphones, tablets, and high-performance mobile devices requiring extreme storage bandwidth for 8K video recording, advanced computational photography, and AI workloads. Frequently Asked Questions about Flash Memory1. What are the different types of flash memory?Flash memory comes in two fundamental architectural types: NOR and NAND. NOR flash offers random access and execute-in-place capabilities, making it ideal for code storage. NAND flash provides higher density and faster write speeds, making it suitable for data storage. Within NAND flash, there are further subdivisions based on bits per cell: SLC (1 bit), MLC (2 bits), TLC (3 bits), and QLC (4 bits), each offering different trade-offs between performance, endurance, and cost. 2. What are the characteristics of flash memory?Flash memory has several distinctive characteristics: it is significantly less expensive than EEPROM and doesn't require batteries for data retention unlike SRAM. It is non-volatile, meaning data persists without power. Flash offers fast read access times (microseconds), high resistance to physical shock compared to hard disk drives, low power consumption, and silent operation. However, it has limitations including finite write/erase cycles, block-level erase requirements, and potential for bit errors requiring ECC. 3. What is the purpose of flash memory?Flash memory serves as a non-volatile storage solution widely used in embedded systems, consumer electronics, and enterprise storage. It retains data without power, can be electrically erased and reprogrammed, and offers advantages over traditional magnetic storage including faster access times, lower power consumption, better durability, and compact form factors. Flash memory evolved from EEPROM technology and has become the dominant storage technology for mobile devices, SSDs, USB drives, memory cards, and embedded systems. 4. What is the difference between NAND flash and NOR flash?NOR flash provides faster random read access and supports execute-in-place (XIP), allowing direct code execution without copying to RAM, making it ideal for firmware and boot code. However, it's more expensive and has slower erase/write operations. NAND flash offers higher storage density, lower cost per gigabyte, and much faster sequential write and erase speeds, making it ideal for mass storage applications. NAND is accessed serially through a shared I/O interface, while NOR has parallel address and data buses allowing random access. NAND requires more complex error correction due to higher bit error rates. 5. What is the difference between UFS and eMMC?UFS (Universal Flash Storage) is the successor to eMMC (embedded MultiMediaCard) and offers several significant advantages: UFS supports full-duplex operation allowing simultaneous read and write operations, while eMMC is half-duplex. UFS uses a faster serial interface with higher bandwidth (up to 11.6 GB/s in UFS 4.0 vs. 400 MB/s in eMMC 5.1). UFS also features command queuing for better multitasking performance, lower latency, and improved power efficiency. These advantages make UFS the preferred choice for modern flagship smartphones and high-performance mobile devices. 6. How does wear leveling work in flash memory?Wear leveling is a technique used to extend flash memory lifespan by distributing write and erase cycles evenly across all memory blocks. Since flash memory has a limited number of program/erase cycles per block, repeatedly writing to the same blocks would cause premature failure. Wear leveling algorithms track the erase count of each block and preferentially use blocks with lower erase counts for new writes. This ensures all blocks wear out at approximately the same rate, maximizing the overall device lifespan. Modern flash controllers implement sophisticated wear leveling algorithms as part of the Flash Translation Layer (FTL). 7. What is 3D NAND technology?3D NAND (also called V-NAND) is a flash memory architecture that stacks memory cells vertically in multiple layers, rather than arranging them in a single planar layer. This technology allows for higher storage densities without requiring smaller manufacturing process nodes. Modern 3D NAND implementations can have over 200 layers, significantly increasing capacity while improving performance and endurance compared to planar NAND. 3D NAND also offers better power efficiency and can achieve higher performance due to reduced cell-to-cell interference. This technology has become the standard for modern SSDs and high-capacity storage devices.