Active power supply ripple filter

• US 4,327,319 A
• Filed: 08/15/1980
• Issued: 04/27/1982
• Est. Priority Date: 08/15/1980
• Status: Expired due to Term

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Furman, Edward L., Swisher, Scott N.
• Primary Examiner(s): Shoop, William M.
• Assistant Examiner(s): Wong, Peter S.
• Application Number:
  US06/178,490
• Time in Patent Office: 620 Days
• Field of Search: 323/275, 323/281, 323/299, 323/303, 363/39, 363/47
• US Class Current: 323/303
• CPC Class Codes: G05F 1/468 characterised by reference voltage circuitry, e.g. soft start, remote shutdown

Abstract

An active power supply ripple filter with low noise and low power dissipation characteristics, which tracks the voltage of the power source with low voltage drop and high current capability. The circuit consists of a control transistor connected between one terminal of a power source and one terminal of a load, a reference circuit which tracks the supply voltage, a low pass filter which filters the reference voltage and an amplifier for driving the control transistor in response to the filtered reference voltage and a feedback voltage from the load. The circuit minimizes the voltage drop across the control transistor as well as minimizing the capacitance values required for the filter capacitors.

Claims

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.

2. The low noise electronic power supply filter circuit of claim 1, wherein the control means is a bipolar transistor.

3. The low noise electronic power supply filter circuit of claim 1 fabricated in integrated form wherein the filter means comprises a pinch resistor coupled from the reference means to the amplifier means.

4. The low noise electronic power supply filter circuit of claim 3 wherein the amplifier means comprises an npn input transistor coupled to a pnp darlington pair.