Autonomous active clamp circuit

• US 5,091,817 A
• Filed: 12/28/1987
• Issued: 02/25/1992
• Est. Priority Date: 12/03/1984
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Routh, Kevin C., Alley, Robert P.
• Primary Examiner(s): DEBOER, TODD
• Application Number:
  US07/136,501
• Time in Patent Office: 1,520 Days
• Field of Search: 361/54-60, 361/83, 361/86, 361/91, 361/111, 361/18, 361/6
• US Class Current: 361/56
• CPC Class Codes: H02H 9/047 Free-wheeling circuits

Abstract

An autonomous active clamp circuit clamps voltage across an inductive load. The clamp closes when the voltage across it exceeds some value substantially above peak line voltage, conducts with a low voltage drop, and opens when the current going through it reaches nearly zero.

Claims

1. An active clamp comprising:

a source of induced voltage of any polarity to be clamped;

controllable switch means connected to said source of induced voltage to be clamped and responsive to a control signal for clamping said induced voltage when said controllable switch means is conductive; and

circuit means coupled to said controllable switch means for generating said control signal, said circuit means rendering conductive said controllable switch means when the magnitude of said induced voltage exceeds a predetermined value, thereafter said circuit means rendering nonconductive said controllable switch means when current flowing in said controllable switch means returns to zero, said circuit means comprising;

DC supply means for providing regulated power for said circuit means;

first comparator means coupled to said DC supply means and to said source of induced voltage for providing an over-voltage signal when the magnitude of said induced voltage exceeds said predetermined value;

second comparator means coupled to said DC supply means and to said source of induced voltage for providing a zero current signal when the magnitude of said induced voltage is below a second predetermined value;

flip-flop means for generating said control signal coupled to the outputs of said first and second comparator means, said flip-flop means being set upon receiving said over-voltage signal and being reset upon receiving a zero current signal; and

zero current pulse stretching means including a monostable multivibrator having its trigger coupled to the output of said second comparator means and having its output coupled to said flip-flop means, said multivibrator generating a stretched pulse signal for keeping said flip-flop means reset during the duration of said stretched pulse.

2. An active clamp comprising:

rectifier means having inputs adapted to be connected to a source of induced voltage of any polarity to be clamped;

controllable switch means coupled to the outputs of said rectifier means and responsive to a control signal for clamping said induced voltage when said controllable switch means is conductive; and

circuit means coupled to said controllable switch means for generating said control signal, said circuit means rendering conductive said controllable switch means when the magnitude of said induced voltage exceeds a predetermined value, thereafter said circuit means rendering nonconductive said controllable switch means when current flowing in said controllable switch means returns to zero, said circuit means comprising;

DC supply means for providing regulated power for said circuit means;

first comparator means coupled to said DC supply means and to said source of induced voltage for providing an over-voltage signal when the magnitude of said induced voltage exceeds said predetermined value;

second comparator means coupled to said DC supply means and to said source of induced voltage for providing a zero current signal when the magnitude of said induced voltage is below a second predetermined value;

flip-flop means for generating said control signal coupled to the outputs of said first and second comparator means, said flip-flop means being set upon receiving said over-voltage signal and being reset upon receiving a zero current signal; and

zero current pulse stretching means including a monostable multivibrator having its trigger coupled to the output of said second comparator means and having its output coupled to said flip-flop means, said multivibrator generating a stretched pulse signal for keeping said flip-flop means reset during the duration of said stretched pulse.

3. An active clamp comprising:

a source of induced voltage of any polarity to be clamped;

controllable switch means connected to said source of induced voltage to be clamped and responsive to a control signal for clamping said induced voltage when said controllable switch means is conductive; and

circuit means coupled to said controllable switch means for generating said control signal, said circuit means rendering conductive said controllable switch means when the magnitude of said induced voltage exceeds a predetermined value, thereafter said circuit means rendering nonconductive said controllable switch means when current flowing in said controllable switch means returns to zero;

said circuit means comprising;

DC supply means for providing regulated power for said circuit means;

first comparator means coupled to said DC supply means and to said source of induced voltage for providing an overvoltage signal when the magnitude of said induced voltage exceeds said predetermined value;

second comparator means coupled to said DC supply means and to said source of induced voltage for providing a zero current signal when the magnitude of said induced voltage is below a second predetermined value; and

flip-flop means for generating said control signal coupled to the outputs of said first and second comparator means, said flip-flop means being set upon receiving said over-voltage signal and being reset upon receiving a zero current signal.

4. The active clamp recited in claim 3 wherein said circuit means further comprises:

power-up means coupled to said DC supply means and to said flip-flop means for keeping said flip-flop means reset whenever the DC voltage provided by said DC supply means is below a selected value.

5. An active clamp comprising:

a source of induced voltage of any polarity to be clamped;

controllable switch means connected to said source of induced voltage to be clamped and responsive to a control signal for clamping said induced voltage when said controllable switch means is conductive;

circuit means coupled to said controllable switch means for generating said control signal, said circuit means rendering conductive said controllable switch means when the magnitude of said induced voltage exceeds a predetermined value, thereafter said circuit means rendering nonconductive said controllable switch means when current flowing in said controllable switch means returns to zero; and

a diode bridge rectifier for coupling said source of induced voltage to said controllable switch means;

said controllable switch means comprising an IGT, the collector of said IGT being coupled to the positive output of said rectifier, the emitter of said IGT being coupled to the negative output of said rectifier, and the gate of said IGT receiving said control signal.

6. An active clamp comprising:

rectifier means having inputs adapted to be connected to a source of induced voltage of any polarity to be clamped;

controllable switch means coupled to the outputs of said rectifier means and responsive to a control signal for clamping said induced voltage when said controllable switch means is conductive; and

circuit means coupled to said controllable switch means for generating said control signal, said circuit means rendering conductive said controllable switch means when the magnitude of said induced voltage exceeds a predetermined value, thereafter said circuit means rendering nonconductive said controllable switch means when current flowing in said controllable switch means returns to zero;

said circuit means comprising;

DC supply means for providing regulated power for said circuit means;

first comparator means coupled to said DC supply means and to said source of induced voltage for providing an overvoltage signal when the magnitude of said induced voltage exceeds said predetermined value;

second comparator means coupled to said DC supply means and to said source of induced voltage for providing a zero current signal when the magnitude of said induced voltage is below a second predetermined value; and

flip-flop means for generating said control signal coupled to the outputs of said first and second comparator means, said flip-flop means being set upon receiving said over-voltage signal and being rest on receiving a zero current signal.

7. The active clamp recited in claim 6 wherein said circuit means further comprises:

power-up means coupled to said DC supply means and to said flip-flop means for keeping said flip-flop means reset whenever the DC voltage provided by said DC supply means is below a selected value.