POWER SUPPLY WITH NONLINEAR FOLDBACK CURRENT LIMITER CIRCUIT

• US 3,801,894 A
• Filed: 09/15/1972
• Issued: 04/02/1974
• Est. Priority Date: 09/15/1972
• Status: Expired due to Term

• Current Assignee: Robert M. Spiegel
• Original Assignee: Robert M. Spiegel
• Inventors: Spiegel, Robert M.
• Primary Examiner(s): Goldberg, Gerald
• Application Number:
  US05/289,261
• Time in Patent Office: 564 Days
• Field of Search: 323/4,9,17,20,22T 317/31,33VR
• US Class Current: 323/276
• CPC Class Codes: G05F 1/5735 with foldback current limiting

Abstract

A power supply has transistors arranged to pass current from a power source to a load having a variable resistance so that current drawn by the load is variable. The circuit includes a comparator amplifier which compares a reference voltage with output voltage and actuates a bias control transistor for reducing conductance of the transistors when an overload occurs. A nonlinear current foldback means is connected in circuit with the bias control transistor to introduce a non-linear characteristic in the control of bias of the transistors.

Claims

1. A current limiter circuit comprising:

input terminals for receiving current from a power source;

output terminals for passing current to a load;

current transmissions components in circuit with said input and output terminals for passing said current to said load;

a current limiting means connected in circuit with said current transmission components for limiting current passing through said components to predetermined safe magnitudes; and

nonlinear current foldback means connected in circuit with said current transmission components, said nonlinear foldback means comprising a Zener diode whose resistance is low due to avalanching when the applied voltage is high and whose resistance is high due to cessation of avalanching when the applied voltage is low, so that said nonlinear current foldback means initially reduces the current through said current transmission components rapidly while reducing the voltage applied thereto slowly, and when current passing through said current transmission components has been reduced to a safe mangitude, the voltage applied thereto is reduced rapidly while the currenT passing thereto is reduced slowly.

2. A current limiter circuit as defined in claim 1, wherein said current transmission components are pass transistors, and said circuit further comprises a bias control means arranged in circuit with said transistors for varying the current conductance thereof, said bias control means being further connected in circuit with said current limiting means, so that the conductance of said transistors is controlled by said current limiting means when said load exceeds a preset value.

3. A current limiter circuit as defined in claim 2, wherein said bias control means comprises:

a comparator amplifier having two inputs and an output;

a first circuit means connecting one amplifier input to said output terminals;

a reference voltage source connected in circuit with the other input to said amplifier; and

circuit means connecting said output of said amplifier to said transistors and to said current limiting means, whereby said comparator amplifier produces a bias voltage to control the conductance of said transistors and said current limiting means denies the passage of said bias voltage to said transistors when said load exceeds a preset value.

4. A current limiter circuit as defined in claim 1, wherein said current limiting means comprises a normally non-conducting current limiting other transistor connected in circuit with said bias control means, whereby said current limiting transistor is rendered conductive when said load exceeds a preset value.