Simple Circuit Provides Latching Fault Protection

摘要

The latch transistors Q1 and Q2 feed base current to each other and discharge the VDD bias through R13. The line input voltage keeps a small amount of current flowing into the latch through the pull-up resistor R2 to keep the transistors active. The latch can thus only be reset by removing the input voltage and waiting for the clamp capacitors to completely discharge.