Isolated power converter having primary feedback control

• US 6,370,039 B1
• Filed: 03/31/2000
• Issued: 04/09/2002
• Est. Priority Date: 11/19/1999
• Status: Expired due to Term

• Current Assignee: Dialog Semiconductor Incorporated (Renesas Electronics Corporation)
• Original Assignee: iWatt, Inc. (Renesas Electronics Corporation)
• Inventors: Telefus, Mark D.
• Primary Examiner(s): Vu, Bao Q.
• Application Number:
  US09/540,058
• Time in Patent Office: 739 Days
• Field of Search: 363/15, 363/16, 363/24, 363/25, 363/26, 363/40, 363/41, 363/131
• US Class Current: 363/15
• CPC Class Codes: H02M 1/007 Plural converter units in cascade push-pull DC/DC converters with pre-regulator H02M3/3374; DC-AC converters following a DC-DC stage including a high frequency transformer H02M7/4807; DC-AC converters following a DC-DC conversion stage generating periodically varying voltages H02M7/4826
• CPC Class Codes: H02M 1/008 Plural converter units for generating at two or more independent and non-parallel outputs, e.g. systems with plural point of load switching regulators
• CPC Class Codes: H02M 3/3376 with automatic control of output voltage or current

Abstract

The present invention comprises an isolated dual power supply having an internal feedback loop. The dual power supply comprises power converter responsive to an error signal for generating a DC internal regulated output voltage coupled to a DC/AC switching power converter having a transformer. The primary winding of the transformer is coupled to the DC internal output voltage and to one or more power switches. A control circuit drives the one or more power switches such that an alternating current having substantially a constant duty cycle flows through the primary winding. An error amplifier produces a control signal proportional to the difference of an output voltage at a load coupled to the secondary winding and a reference voltage equal to the maximum expected voltage losses at the load. The error signal is formed from a combination of the control signal and a signal proportional to the internal voltage output.

Claims

1. A power supply, comprising;

a voltage regulator responsive to an error signal for regulating a DC internal voltage output; and

a DC/AC switching power converter including a transformer having a primary winding coupled to the DC internal voltage output and one or more power switches;

a control circuit driving the one or more power switches at a constant duty cycle such that an alternating current having a constant duty cycle flows through the primary winding; and

an error amplifier having an input coupled to a current sensor, the current sensor sensing a voltage proportional to the current through the primary winding, the error amplifier having another input coupled to a reference voltage proportional to a maximum expected voltage loss on a load coupled to a secondary winding of the transformer, the error amplifier outputting a control signal proportional to the difference between the reference voltage and the voltage sensed by the current sensor;

wherein the error signal is based upon the control signal and a signal proportional to the internal voltage output.

2. The power supply of claim 1, wherein the voltage regulator is a pulse-width-modulated switching power converter, the pulse width modulation responsive to the error signal to thereby modulate the DC internal voltage output.

3. The power supply of claim 2, wherein the pulse-width-modulated switching power converter is a boost converter.

4. The power supply of claim 2, wherein the pulse-width-modulated switching power converter is a buck converter.

5. The power supply of claim 3, wherein the one or more power switches comprise a first power switch and a second power switch, the control circuit configured for alternately switching ON and OFF the first and second power switches, the first power switch being ON when the second power switch is OFF and the second power switch being ON when the first power switch is OFF, the control circuit alternately switching the first and second power switches such that the ON and OFF times of each power switch are substantially equal, wherein a first half cycle of the alternating current flows through the primary winding when the first power switch is ON, and a second half cycle of the alternating current flows through the primary winding when the second power switch is ON, whereby the constant duty cycle of the alternating current is substantially 50%.

6. The power supply of claim 5, wherein the primary winding is in series with a resonant capacitor, the resonant capacitor and a leakage inductance of the primary winding forming a series resonant tank having a resonant frequency less than or equal to a period of the control circuit, whereby each half cycle of the alternating current is a half-wave quasi-sinusoidal current and the DC/AC switching power converter is a resonant converter.

7. The power supply of claim 5, wherein the primary winding is in parallel with a resonant capacitor, the resonant capacitor and a leakage inductance of the primary winding forming a parallel resonant tank having a resonant frequency less than or equal to a period of the control circuit, whereby when the first power switch is ON, a first half-wave quasi-sinusoidal voltage is impressed across the primary winding, and when the second power switch is ON, a second half-wave quasi-sinusoidal voltage is impressed across the primary winding, the second half-wave quasi-sinusoidal voltage being antipodal to the first half-wave quasi-sinusoidal voltage.

8. The power supply of claim 5, wherein the pulse width modulation is further responsive to sensing the voltage across the secondary winding through an isolator.

9. The power supply of claim 8, wherein the isolator is an optoisolator.

10. The power supply of claim 1, wherein the voltage regulator is a linear regulator and the DC/AC switching power converter is a half-bridge power converter.

11. A power supply, comprising:

a voltage regulator responsive to an error signal for regulating a DC internal voltage output;

a plurality of DC/AC switching power converters, each DC/AC switching power converter including;

a transformer having a primary winding coupled to one or more power switches and the DC internal voltage output;

a control circuit to drive the one or more power switches at a constant duty cycle such that an alternating current having a constant duty cycle flows through the primary winding; and

an error amplifier having an input coupled to a current sensor, the current sensor sensing a voltage proportional to the current through the primary winding, the error amplifier having another input coupled to a reference voltage proportional to the maximum expected voltage loss on a load coupled to a secondary winding of the transformer, the error amplifier outputting a control signal proportional to the difference between the reference voltage and the voltage sensed by the current sensor, wherein the error signal is formed by combining each control signal with a signal proportional to the internal voltage output; and

a clock coupled to the plurality of DC/AC switching power converters, wherein the one or more power switches within a given DC/AC switching power converter from the plurality of DC/AC switching power converters arc switched synchronously with the one or more power switches in each of the DC/AC switching power converters remaining in the plurality of DC/AC switching power converters.

12. The power supply of claim 11, wherein the voltage regulator is a pulse-width-modulated switching power converter, the pulse width modulation being responsive to the error signal to modulate the DC internal voltage output, and wherein within each DC/AC switching power converter the one or more switches comprise a first and a second power switch, the control circuit alternately switching ON and OFF the first and second power switches, the first power switch being ON when the second power switch is OFF and the second power switch being ON when the first power switch is OFF, the control circuit alternately switching the first and second power switches such that the ON and OFF times of each power switch are substantially equal wherein a first half cycle of the alternating current flows through the primary winding when the first power switch is ON and a second half cycle of the alternating current flows through the primary winding when the second power switch is ON, whereby the constant duty cycle of the alternating current is substantially 50%.

13. The power supply of claim 11, wherein the pulse-width-modulated switching power converter is a boost power converter.

14. The power supply of claim 13, wherein, within each DC/AC switching power converter in the plurality of DC/AC switching power converters, the primary winding is in series with a resonant capacitor, the resonant capacitor and a leakage inductance of the primary winding forming a series resonant tank having a resonant frequency less than or equal to a period of the control circuit, whereby each half cycle of the alternating current is a half-wave quasi-sinusoidal current.

15. The power supply of claim 13, wherein, within each DC/AC switching power converter in the plurality of DC/AC switching power converters, the primary winding is in parallel with a resonant capacitor, the resonant capacitor and a leakage inductance of the primary winding forming a parallel resonant tank having a resonant frequency less than or equal to a period of the control circuit, whereby when the first power switch is ON, a first half-wave quasi-sinusoidal voltage is impressed across the primary winding, and when the second power switch is ON, a second half-wave quasi-sinusoidal voltage is impressed across the primary winding, the second half-wave quasi-sinusoidal voltage being antipodal to the first half-wave quasi-sinusoidal voltage.

16. A method of generating power, comprising:

generating an internal regulated voltage output using a voltage regulator wherein the regulation is responsive to an error signal;

coupling the internal regulated voltage output to a primary winding of a transformer by switching one or more power switches of a DC/AC switching power converter during a first period wherein a first half cycle of an alternating current flows through the primary winding;

uncoupling the primary winding from the internal voltage output by switching the one or more power switches during a second period wherein a second half of the alternating current flows through the primary winding, the duty cycle formed by the first and second period being kept constant;

forming the difference between a reference voltage proportional to the maximum expected voltage losses at a load coupled to a secondary winding of the transformer and a voltage proportional to the output voltage to form a control signal; and

combining the control signal with a signal proportional to the internal output voltage to form the error signal.

17. The method of claim 16, wherein the duty cycle is equal to 50%.