Transformer-coupled switching power converter having primary feedback control

• US 6,385,059 B1
• Filed: 11/14/2000
• Issued: 05/07/2002
• Est. Priority Date: 11/14/2000
• Status: Expired due to Term

• Current Assignee: Dialog Semiconductor Incorporated (Renesas Electronics Corporation)
• Original Assignee: iWatt, Inc. (Renesas Electronics Corporation)
• Inventors: Muegge, Mark R., Telefus, Mark D.
• Primary Examiner(s): Vu, Bao Q.
• Application Number:
  US09/713,132
• Time in Patent Office: 539 Days
• Field of Search: 363/21.12, 363/21.15, 363/21.18, 363/21.1, 363/21.04, 363/21.07, 363/41, 363/97, 363/131
• US Class Current: 363/21.15
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence

Abstract

Control circuitry for controlling the delivery of power from a source voltage to a load in a transformer coupled power converter. The control circuitry includes a power switch having an input coupled to the source, an output, and an activation gate, the power switch, when cycled ON and OFF, defining a pulses of power at the load. A pulse generator is coupled to the power switch, the pulse generator producing a train of constant frequency, constant ON time switching pulses for driving the power switch activation gate. A pulse rate controller responsive to an error signal is coupled between the pulse generator and the power switch, the pulse rate controller regulating an output voltage at the load by controlling the rate of switching pulses delivered to the power switch activation gate over time. The error signal is derived by estimating the output voltage at each switching cycle from the primary side current, while compensating for the expected loss between the source and the load for each power switch cycle.

Claims

1. Control circuitry for controlling the delivery of power from a source voltage to a load in a transformer coupled power converter, the control circuitry comprising:

a power switch having an input, an output, and an activation gate, the power switch, when cycled ON and OFF, defining a pulse of power at the load;

a pulse generator coupled to the power switch, the pulse generator producing switching pulses for cycling the power switch;

a pulse rate controller responsive to an error signal and coupled between the pulse generator and the power switch, wherein the pulse rate controller regulates an output voltage at the load by controlling the rate of switching pulses that cycle the power switch over time; and

error signal generation circuitry coupled to the power switch output for generating the error signal based at least in part on a compensation signal corresponding to an expected loss between the source and the load for each power switch cycle.

2. The control circuitry of claim 1, further comprising current sensing circuitry for sensing a current flow through the power switch output.

3. The control circuitry of claim 2, wherein a peak current through the power switch output for each power switch cycle is sensed and compared with the compensation signal to derive an estimate of the source voltage.

4. The control circuitry of claim 3, the power converter transformer having a flyback-biased secondary winding, the control circuitry further comprising a voltage sensing circuit for sensing a flyback voltage at the power switch input following each power switch cycle, wherein the sensed flyback voltage is compared to the estimated source voltage derived in the same or a neighboring power switch cycle in order to derive an estimate of the output voltage.

5. The control circuitry of claim 4, further comprising a reference voltage set to a scaled desired output voltage, wherein the estimated output voltage is scaled and the error signal is derived by comparing a scaled estimated output voltage to the reference voltage.

6. The control circuitry of claim 4, the power converter transformer further comprising a forward-biased secondary winding.

7. A switching power supply for controlling the delivery of power from a source to a load in a transformer coupled power converter, comprising:

a power switch that cycles ON and OFF and couples the source to the load; and

control circuitry responsive to an error signal for regulating the output voltage without varying the duty cycle of the power switch.

8. The power supply of claim 7, wherein the control circuitry comprises

a pulse generator coupled to the power switch, the pulse generator producing switching pulses for cycling the power switch;

a pulse rate controller responsive to an error signal and coupled between the pulse generator and the power switch, wherein the pulse rate controller regulates an output voltage at the load by controlling the rate of switching pulses delivered to the power switch over time; and

error signal generation circuitry coupled to an output of the power switch for generating the error signal based at least in part on a compensation signal corresponding to an expected loss between the source and the load for each power switch cycle.

9. The power supply of claim 8, further comprising current sensing circuitry for sensing a current flow through the power switch.

10. The power supply of claim 9, wherein a peak current through the power switch for each power switch ON cycle is sensed and compared with the compensation signal to derive an estimate of the source voltage.

11. A transformer-coupled power converter employing the switching power supply of claim 10, the transformer having a flyback-biased secondary winding, the control circuitry further comprising a voltage sensing circuit for sensing a flyback voltage at a drain terminal of the power switch following each power switch ON cycle, wherein the sensed flyback voltage is compared to the estimated source voltage derived in the same or a neighboring power switch ON cycle in order to derive an estimate of the output voltage.

12. The power converter of claim 11, the control circuitry further comprising a reference voltage set to a scaled desired output voltage, wherein the estimated output voltage is scaled and the error signal is derived by comparing the scaled estimated output voltage to the reference voltage.

13. The power converter of claim 11, further comprising a forward-biased secondary winding.