Fault-latch circuit protects switchers


Posted on Mar 3, 2013

Many power-supply designers like to have a regulator latch off in the event of an overcurrent situation or other fault condition. Yet, many PWM controllers do not internally support this latch-off function. Most do, however, have a power-good output and an enable function. The circuit in Figure 1 adds that latch-off capability at low cost in little additional space. The design is based on the LMS33460, which is a power-supply monitor in a tiny, five-lead SC-70 package.



You just need to combine it with a few small passive parts, and the circuit is complete. When the Enable Input signal goes high, the voltage at the top of C1 rises quickly to 5V. Because the output voltage is not yet alive, PGOOD stays low, charging C1




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