Method of feedback regulating a flyback power converter

• US 4,996,638 A
• Filed: 02/15/1990
• Issued: 02/26/1991
• Est. Priority Date: 02/15/1990
• Status: Expired due to Fees

• Current Assignee: Astec International Limited (Emerson Electric Company)
• Original Assignee: Northern Telecom Limited (Nortel Networks Corporation)
• Inventors: Orr, Raymond K.
• Primary Examiner(s): Beha, Jr., William H.
• Application Number:
  US07/480,392
• Time in Patent Office: 376 Days
• Field of Search: 363/21, 363/97
• US Class Current: 363/21.15
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop

Abstract

A method of providing power regulation in power conversion equipment, where power regulation is implemented on the primary side of a transformer used to provide isolation of a power source from the load. The feedback mechanism utilizes current perturbations which are summed with the primary current in the power transformer. These perturbations are transformed with the load current to the primary side of the power transformer and extracted using signal processing means to regenerate a useful signal which is isolated from the load.

Claims

1. In a flyback power converter, having a primary and a secondary, a method of regulating voltage at an isolated output load, comprising the steps of:

(a) comparing the voltage across said load with a reference to obtain an error signal;

(b) comparing said error signal with a ramp signal to obtain a perturbation signal which varies in time according to the amplitude of said error signal;

(c) feeding said perturbation signal to said secondary so that it becomes induced at said primary, said perturbation signal being summed to the magnetizing current of said primary to provide a control signal when said primary is energized;

(d) detecting at the primary, the presence of said perturbation signal on said control signal; and

(e) regulating the voltage at said primary according to the presence in time of said perturbation signal on said control signal to thereby compensate for voltage variations at the output load.

2. A method as defined in claim 1, wherein said ramp signal is generated at said secondary when voltage is induced thereto from said primary.

3. A method as defined in claim 2, further comprising the steps of switching a current source on and off, in response to said perturbation signal to produce a current waveform with pulses that vary in time according to the amplitude of said error signal.

4. A method as defined in claim 3, wherein said control signal comprises a ramp waveform generated when said primary is energized, on which is superimposed an amplitude perturbation corresponding to said pulses of said current waveform.

5. A method as defined in claim 4, wherein said amplitude perturbations are detected by comparing said control signal with a ramp signal generated at said primary when said primary is energized.

6. A method as defined in claim 5, wherein power to said primary is removed when a perturbation is detected on said control signal.

7. In a flyback power converter, having a primary and a secondary, a method of regulating voltage at an isolated output load, comprising the steps of:

(a) measuring the voltage across said load;

(b) comparing said measured voltage with a reference to obtain an error signal;

(c) generating a first ramp signal on said secondary when voltage is induced thereto from said primary;

(d) comparing said first ramp signal with said error signal so as to obtain a perturbation signal which varies in time according to the amplitude of said error signal;

(e) switching a current source on and off, in response to said perturbation signal to produce a current waveform with pulses which vary in time according to the amplitude of said error signal;

(f) feeding said current waveform to said secondary so that it becomes induced at said primary, said current waveform being summed to the magnetizing current of said primary to provide a control signal when said primary is energized;

(g) generating a third ramp signal at said primary;

(h) comparing the voltage drop of said control signal across a sensing resistor with said third ramp signal, to recover said perturbation signal;

(i) opening a switch such that voltage across said primary is cut at each pulse of said perturbation signal; and

(j) closing said switch after a predetermined interval such that voltage is re-applied across said primary.