The WMZ13A series composite PTC thermistor can be used to solve the protection problems of overvoltage, overheating and overcurrent encountered by low-power LED driving power supplies. It is the preferred overvoltage protection solution in the design of many LED drive power supply manufacturers. However, the fact that the varistor cannot pass a continuous large current and will gradually fail due to the reduction of the varistor voltage during the response process determines the reality that the failure rate of the varistor during use remains high. Designers have to gradually increase and increase the size and varistor voltage parameters of the varistor, but the high residual voltage drop after increasing the varistor voltage will have an adverse effect on the circuit. Secondly, the NTC thermistor, as a power surge suppressor, only protects the switching tube and electrolytic capacitor from impact when the switching power supply is powered on. Due to its low resistance during normal operation, it is powerless to affect line pulses and operating surges. In particular, switching operations with short intervals are fatal to switching power supplies that use NTC for surge suppression. In addition, the fuse used in the primary part of the switching power supply often melts due to the pressure-sensitive response during transient overvoltage, causing unnecessary maintenance. When using a PTC thermistor as a resettable fuse, since the rated operating current of the PTC thermistor is closely related to the ambient temperature, in order to take into account the operating current of the PTC thermistor at the lowest operating voltage and the highest ambient temperature, the PTC thermistor is The resistor is slow or does not protect against overvoltage in normal or low temperature environments. This increases the probability of failure of the LED drive power supply's downstream circuit. Due to the above reasons, we have developed an appropriate composite PTC thermistor, which does not need to consider the impact of lower ambient temperature on the response speed, and can appropriately reduce the impact of surge voltage and group pulse on the LED drive power supply. When an unexpected overvoltage occurs, the nS level responds immediately in a short time, clamping the power supply voltage within the residual voltage range of the varistor. The power supply operates normally and returns to the original working state after the overvoltage is reduced. Specifically, a PTC thermistor and a varistor are packaged together, and the current and temperature generated when the varistor is over-voltage are used to make the thermistor respond quickly, and the impact of the rise in the resistance of the thermistor on the voltage and current is reflected. Come to protect the varistor. Due to the comprehensive protection effect of current and voltage between the thermistor and varistor, without worrying about damage to the varistor, in the design of this composite PTC thermistor, we have The rated operating current of the varistor and thermistor is also boldly designed: the rated operating current of the product is designed to be as large as possible while ensuring the protection effect. In order to verify the long-term working reliability of the composite PTC thermistor. After a long period of time on the high-voltage aging life test bench, our company powered on the 450V high voltage for 1 minute and cut off the power for 5 minutes. Among the 200 samples, the thermistor and varistor were intact.

　　Use a high-voltage self-restoring fuse with over-current protection and a varistor. The varistor is a varistor with a varistor voltage of 390V. The varistor voltage can be clamped to 390V, which is better than the commonly used 471K clamp. Voltage is low. The self-restoring fuse can limit the current to protect the varistor and subsequent equipment. When the circuit is working normally, the lightning protection module flows normally. If the protected equipment fails, short-circuit, overcurrent, or overload, the composite self-restoring fuse will The thermistor will operate in a high-resistance state, cutting off the current to protect the equipment. If the fault is removed, the thermistor's self-recovery fuse will return to normal, and the circuit can work normally again. When an instantaneous spike pulse occurs in the power supply, the varistor will act and conduct, clamping the voltage at 390V to protect the equipment behind it. , when the power supply is overvoltage for a long time, the varistor conducts. At this time, the varistor clamps the voltage at 390V so that the equipment can operate normally. On the other hand, the conduction of the varistor causes the circuit to pass The current of the resettable fuse increases, causing the resettable fuse to operate. At this time, the resettable fuse limits the current on the one hand. Since the resistance of the resettable fuse increases, a part of the voltage is added to both ends of the fuse, plus the clamping of the varistor behind it. The operating voltage of the device can be stabilized at the required operating voltage of the device. During lightning protection, the self-restoring fuse has a certain resistance value, which can limit excessive lightning current from damaging the varistor. It can also isolate the lightning high voltage in the line outside the varistor, thereby effectively protecting the varistor and the varistor. Follow-up equipment