According to the positive recovery effect of the diode, at the moment when the diode is turned on, the potential of the anode of the diode will be much higher than that of the cathode and last for hundreds of nanoseconds, so a large current can be generated.

During the operation of the diode circuit, the current will charge C1, so the potential of VE will be raised, which means that the voltage between ve and VISO is reduced, that is, the stabilized + 15V voltage between VISO and VE is discharged. In practical application, this process occurs periodically and is synchronized with the switching frequency. Therefore, from a macro point of view, the + 15V at the secondary side of the driver will fall. When it falls to 12V, the driver will touch the undervoltage protection.

Solution: place a bidirectional TVs transient suppression diode, which can block the above current path. This problem is solved.

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