Active power supply ripple filter

Claim 1

A low noise electronic power supply filter circuit capable of high output currents for eliminating alternating current components from a direct current power supply and for tracking the direct current voltage of said power supply, comprising: (a) control means having a control terminal, an input terminal and an output terminal, said input terminal coupled to the power supply and said output terminals adapted to be coupled to a load, said control means controlling current from the input terminal to the output terminal; (b) reference means, coupled to the control means input terminal for generating a reference voltage which tracks approximately three diode drops below the power supply voltage; (c) amplifier means having an output coupled to the control terminal and having first and second input terminals, for amplifying a signal applied across the input terminals comprising an input transistor coupled to a darlington pair; (d) filter means, having an input coupled to the reference means for low pass filtering the reference voltage, and having an output coupled to the first input of the amplifier means thereby coupling the filtered reference voltage to said amplifier means; and (e) feedback means, coupled from the control means output terminal to the second input of the amplifier means, comprising three diodes in series such that approximately one diode drop is maintained across the control means.