Texas Instruments Incorporated
Startup/brownout active clamping for capacitor-drop power supply

Abstract:

A circuit includes a rectifier, a charge pump, and a clamp control circuit. The rectifier has an input configured to be coupled to an alternating current (AC) power source. The rectifier rectifies an AC signal from the AC power source to produce a rectified voltage on a first voltage node. The rectifier includes a first transistor coupled to a ground node and to the input. The first switch has a first control input. The charge pump is coupled to the first voltage node. The charge pump is configured to generate a second voltage on a second voltage node. The voltage regulator is coupled to the second voltage node. The clamp control circuit is coupled to the first and second voltage nodes and has an output node coupled to the first control input.