High voltage temperature compensated foldback circuit

• US 4,587,476 A
• Filed: 09/29/1983
• Issued: 05/06/1986
• Est. Priority Date: 09/29/1983
• Status: Expired due to Fees

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Cushman, Glen P.
• Primary Examiner(s): Salce, Patrick R.
• Assistant Examiner(s): REBSCH, DONALD
• Application Number:
  US06/537,729
• Time in Patent Office: 950 Days
• Field of Search: 323/275, 323/276, 323/280, 323/303, 323/908, 323/273, 323/907, 361/57, 361/58, 361/93
• US Class Current: 323/276
• CPC Class Codes: G05F 1/5735 with foldback current limiting
• CPC Class Codes: Y10S 323/907 Temperature compensation of semiconductor

Abstract

A resistor (R3) reduces voltage between an input voltage and the emitter terminal of a series pass transistor pair (Q1, Q2). An operational amplifier (U1) compares this reduced voltage with a reference voltage that is less than, but varies with, the input voltage. The emitter voltage decreases until the current reaches a design limit. Then, a resistor senses the output voltage and pulls the operational amplifier'"'"'s input voltage down. This action causes the base current of the transistor pair (Q1, Q2) to decrease and the output current to foldback.

Claims

1. A foldback circuit, comprising:

a first conductor path including in series, an input terminal connectable to a direct current power supply, shutoff circuitry including transistor means, and an output terminal connectable to a load; and

control circuitry for the shutoff circuitry including an operational amplifier connected to operate the shutoff circuitry in response to a load demand which exceeds a current pass limit, to decrease the base current of the transistor means and cause the output current to foldback, said operational amplifier including a +V terminal connected to input voltage, a -V terminal connected to ground, an output terminal connected to the base of the transistor means, a noninverting input terminal, means powered by the input voltage and connected to provide a reference voltage at the noninverting input terminal which is less than but varies directly with the input voltage, an inverting input terminal, a conductor extending from a point in the first conductor path ahead of the shutoff circuitry to the inverting input terminal, and a foldback conductor extending from a point in the first conductor path between the shutoff circuitry and the output terminal to the inverting input terminal.

2. A foldback circuit according to claim 1, comprising a current pass limit resistor in the first conductor path ahead of the point of connection of the conductor which extends from a point in the first conductor path ahead of the shutoff circuitry to the inverting input, and a foldback resistor in the foldback conductor, said resistors determining the current pass limit of the circuit, and said foldback resistor replacing the current pass limit resistor when a predetermined current limit has been reached and the output current is folding back.

3. A foldback circuit according to claim 1, wherein the operational amplifier is a LM144 amplifier.

12. A foldback circuit according to claim 2, wherein the operational amplifier is a LM144 amplifier.

4. A foldback circuit, comprising:

a first conductor path including in series, an input terminal connectable to a direct current power supply, shutoff circuitry including transistor means, and

an output terminal connectable to a load;

control circuitry for the shutoff circuitry including an operational amplifier connected to operate the shutoff circuitry in response to a load demand which exceeds a current pass limit, to decrease the base current of the transistor means and cause the output current to foldback, said operational amplifier including a +V terminal connected to input voltage, a -V terminal connected to ground, and an output terminal connected to the base of the transistor means, a first voltage divider powered by the input voltage and connected to provide a reference voltage at the noninverting input terminal of the operational amplifier which is less than but varies directly with the input voltage;

a current limit establishing third resistor in the first conductor path in series between the input terminal and the shutoff circuitry, to establish an input voltage to the shutoff circuitry and establish the current limit of the circuit, and a second voltage divider connected to apply a fraction of the input voltage to the shutoff circuitry to the inverting input terminal of the operational amplifier.

5. A foldback circuit according to claim 4, comprising a fourth conductor path extending between the output of the operational amplifier and the base of the transistor means, and a fourth resistor in said fourth conductor path.

6. A foldback circuit according to claim 4, wherein the second voltage divider comprises a fifth conductor path including in series a third junction in the first conductor path, located between the current limit establishing third resistor and the shutoff circuitry, a fifth resistor, a fourth junction, a sixth resistor, and a ground, and a sixth conductor path extending from said fourth junction to the inverting input terminal of the operational amplifier.

7. A foldback circuit according to claim 6, comprising a seventh conductor path extending between the fourth junction and the output of the circuit, said seventh conductor path including an output sensing seventh resistor which senses the output voltage when the load demand exceeds the current limit, said output sensing seventh resistor functioning to pull down the voltage to the inverting input of the operational amplifier.

8. A foldback circuit according to claim 5, wherein the transistor means comprises a Darlington pair of PNP transistors.

9. A foldback circuit according to claim 8, wherein said Darlington pair of transistors comprises a first transistor having an emitter terminal connected to receive the input voltage to the shutoff circuitry, a collector terminal connected to the output, and a base, wherein the second transistor includes an emitter connected to the base of the first transistor, a collector connected to the output, and a base, wherein said fourth conductor path extends between the output of the operational amplifier and the base of the second transistor, and a third voltage divider comprising an eighth conductor path extending between the first conductor path and the fourth conductor path, and including in series a fifth junction in said first conductor path, an eighth resistor, a sixth junction, a ninth resistor, and a seventh junction in the fourth conductor path, and a ninth conductor path extending between the base of the first transistor and the emitter of the second transistor, an eighth junction in said ninth conductor path, and a tenth conductor path extending between the sixth and seventh junctions.

10. A foldback circuit according to claim 9, comprising an eleventh conductor path innerconnected between an input voltage region of the first conductor path and the +V terminal of the operational amplifier, and a twelfth conductor path including in series, a seventh junction in the eleventh conductor path, a first capacitor, and a ground.

11. A foldback circuit according to claim 10, comprising a thirteenth conductor path connected between the balance terminal and the compensation terminal of the operational amplifier, and a second capacitor in said thirteenth conductor path.

13. A foldback circuit, comprising:

an input terminal connectable to a direct current power supply;

an output terminal connectable to a load;

shutoff circuitry between the input and output terminals, including transistor means;

a current limit establishing resistor between the input terminal and the shutoff circuitry, to establish an input voltage to the shutoff circuitry on a current pass limit;

control circuitry for the shutoff circuitry including an operational amplifier connected to operate the shutoff circuitry in response to a load demand which exceeds the current pass limit, to decrease the base current of the transistor means and cause the output current to fold back;

a first voltage divider powered by the input voltage and connected to provide a reference voltage at the noninverting input of the operational amplifier which is lower than but varies directly with the input voltage;

a second voltage divider powered by the emitter voltage and including an output junction connected to provide a voltage signal to the inverting input of the operational amplifier; and

conductor means connected between the output junction of the second voltage divider and an output region of the circuit, said conductive path including an output sensing seventh resistor which senses the output voltage and pulls down the voltage to the inverting input of the operational amplifier when the load demand exceeds the current pass limit.

14. A foldback circuit according to claim 13, wherein the operational amplifier is a LM144 amplifier.

15. A foldback circuit according to claim 13, wherein a capacitor is provided within a conductor path which extends between the balance terminal and the compensation terminal of the operational amplifier.

16. A foldback circuit according to claim 13, wherein the transistor means comprises a Darlington pair of PNP transistors.

17. A foldback circuit according to claim 16, wherein said transistor means comprises a 2N5745 transistor, connected to receive the emitter voltage, paired with a 2N3868 transistor.

18. A foldback circuit according to claim 17, wherein the operational amplifier is a LM144 amplifier.