Tracing a Boost Converter Output Short Circuit Path

A boost converter can stop switching while input current continues flowing into an output short. The reason may be a direct path through the inductor and rectifying element. Review that path before relying on an enable pin or switch current limit as complete output fault protection.

Draw the disabled circuit

Start with the actual power stage, including MOSFET body diodes, external rectifiers, input protection, and any disconnect switch. Draw a second schematic with controlled switches in their disabled states. Trace every possible input to output current path, rather than treating an integrated regulator as an ideal block.

The TI discussion of boost converter load disconnect describes why a separate disconnect arrangement may be necessary and examines an input switch implementation. A stated shutdown function and a stated load disconnect function should therefore be checked separately in the selected device documentation.

Identify which current is limited

Find the current sense location and the element controlled by each protection function. A limit that turns off the boost switching transistor may not interrupt a path that bypasses that transistor. Likewise, input protection may respond too slowly to protect another component from the initial discharge of stored energy.

List the fault current paths during the first instant, during sustained fault operation, and during recovery. Include the output capacitor discharge separately from energy supplied by the input. Those mechanisms can stress different copper paths and components.

Review a disconnect as a power component

If a disconnect is required, check its blocking direction, body diode arrangement, operating voltage, current rating, and fault response. Evaluate startup charging as well as the output short. A switch that interrupts a sustained fault must also survive the transition into its blocking state.

Define whether the intended response is a latched shutdown, periodic retry, or controlled current limit. Consider what repeatedly charging the output capacitor does to the switch and input source. The protection policy should be consistent with the load’s recovery behavior.

Verify with a controlled fault test

Use a current limited source and a test arrangement appropriate to the expected stored energy. Observe input current, output voltage, enable state, and the relevant switch voltage. Start with bounded fault duration and confirm the instrumentation can capture the initial event.

Record the actual source impedance and fault connection resistance. A long test lead can substantially alter the result. Acceptance evidence should show that the defined protection response occurs and that the identified current paths remain within their reviewed limits. A low output voltage by itself proves neither disconnection nor safe fault current.