As you know, 2ProAC devices integrate PolySwitch polymer positive temperature coefficient (PPTC) overcurrent devices and metal oxide varistor (MOV) components in an innovative thermal protection device for overvoltage faults. Overcurrent protection and voltage clamping. This single device helps manufacturers meet industry test requirements, reduce component count and increase device reliability.
A common application of 2ProAC devices is LED lighting. The protection requirements for lightning strikes are less than 2kVsurge, and 2ProAC can protect against lightning strikes of 2kV. The picture below shows a customer LED circuit board debugged by a friend recently. The lightning strike requirement is 2kV. The 2ProAC is placed at the input of the LEDlighting circuit, plus the lightning strike waveform generator and AC coupling.
But strange things have happened! After the 2kVsurge is finished, the LED light does not light up. Since the circuit board is still connected to the 220V power supply, it is obvious that the 2ProAC does not protect the driver chip of the latter stage. After checking the driver chip, it is found to be damaged. Later, it was reduced to 1kVsurge, but it was still passed, and the driver chip was still broken. In this paper, the author analyzes the customer's circuit and finds that the topology of the customer circuit is a single-stage PFC structure. The advantage is that the circuit is relatively simple and can achieve a higher PFC value. However, the electrolytic capacitors commonly used in power switch circuits are not used in the circuit (generally about 47uF/400V), and replaced by high-capacitance capacitors with small capacitance values. It is because of this large electrolytic capacitor that the lightning protection capability of the single-stage PFC structure circuit is greatly reduced, and the driver chip is damaged when the lightning strike occurs. It can also be said that 2ProAC is coordinated with large electrolytic capacitors to pass the surge pulse, and also protects the electronic circuit of the latter stage. The lack of protection performance will be greatly reduced.
As can be seen from the above case analysis, the 2ProAC device's request through the customer's surge is closely related to the circuit topology of the client. The client PCB requires 2ProAC for lightning protection, while 2ProAC also requires client circuits (such as electrolytic capacitors) to work together to protect the vulnerable electronic circuits. Therefore, it is necessary to implement a reliable circuit lightning protection scheme according to the specific circuit and application of the customer.
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