Redirected sequential flyback regulator

• US 6,172,883 B1
• Filed: 01/22/1999
• Issued: 01/09/2001
• Est. Priority Date: 01/22/1999
• Status: Expired due to Term

• Current Assignee: Dell USA LP (Dell Technologies Inc.)
• Original Assignee: Dell USA LP (Dell Technologies Inc.)
• Inventors: Cummings, John, Kates, Barry K.
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): Patel, Rajnikant B.
• Application Number:
  US09/236,132
• Time in Patent Office: 718 Days
• Field of Search: 363/21, 363/97, 363/98, 363/95, 364/708, 364/707, 361/686
• US Class Current: 363/21.18
• CPC Class Codes: H02M 3/33561 having more than one ouput with independent control
• CPC Class Codes: H02M 3/33576 having at least one active switching element at the secondary side of an isolation transformer

Abstract

A switching flyback regulator circuit for providing a plurality of regulated DC voltage power supplies. The flyback regulator circuit includes a primary inductive element coupled in series with a first switch to turn charging current flow through the primary inductive element ON and OFF. A first secondary inductive element having a first end coupled to supply a first power source. A second secondary inductive element has a first end coupled to produce the second power source, and a second end coupled to a second switch to turn current flow through the second secondary inductive element ON and OFF. The first secondary inductive element and the second secondary inductive element are magnetically coupled to the primary inductive element. A control circuit generates a ramped voltage signal having a negative slope to control the ON and OFF duty cycle of the second switch such that when the first switch is operated to allow the primary inductive element to discharge, current flows through the first secondary inductive element before current flows in the other secondary inductive element. The current through the second switch is zero when the second switch is turned OFF and ON, thereby eliminating switching losses and improving efficiency of the flyback regulator circuit.

Claims

1. A computer system comprising:

a memory having a set of program instructions stored therein;

a plurality of electrically-operated components including a first component coupled to receive power from a first power source and a second component coupled to receive power from a second power source;

a regulator circuit operable to provide the first power source and the second

power source, the regulator circuit including;

a first inductive element coupled in series with a first switch to turn current flow through the first inductive element ON and OFF;

a second inductive element having a first end coupled to produce the first power source, and magnetically coupled with the first inductive element;

a third inductive element magnetically coupled with the first inductive element, the third inductive element having greater inductive capacity than the second inductive element, a first end coupled to produce the second power source, and a second switch to turn current flow through the third inductive element ON and OFF; and

a control circuit coupled to control the ON and OFF duty cycle, of the second switch such that when the current is allowed to discharge through the first inductive element, current flows through the third inductive element subsequent to current flow in the second inductive element.

2. The computer system, as set forth in claim 1, further comprising a ramped voltage generator circuit that outputs a ramp voltage signal, the control circuit being coupled to receive the ramp voltage signal.

3. The computer system, as set forth in claim 2, wherein the magnitude of the ramp voltage signal decreases during each duty cycle of the first switch.

4. The computer system, as set forth in claim 3, wherein the control circuit includes:

an error amplifier for generating an error signal indicative of the voltage output by the second power source;

a pulse width modulator coupled to receive the feedback signal and the ramp voltage signal, the pulse width modulator generating a driver signal; and

a latch circuit coupled to receive the driver signal and to output the driver signal to the second switch.

5. The computer system, as set forth in claim 1, wherein the first, second, and third inductive elements comprise a flyback regulator, the flyback regulator further comprising a feedback circuit coupled between the first inductive element and the second inductive element.

6. The computer system, as set forth in claim 2, wherein the ramped voltage generator circuit includes a third switch coupled in parallel to the third inductive element, a capacitor coupled in parallel to the third switch, and a current sink coupled in parallel to the capacitor.

7. A regulator circuit for providing a plurality of regulated DC voltage power supplies, the regulator circuit comprising:

a first inductive element coupled in series with a first switch to turn charging current flow through the first inductive element ON and OFF;

a second inductive element having a first end coupled to produce the first power source, and magnetically coupled with the first inductive element;

a third inductive element magnetically coupled with the first inductive element, the third inductive element having greater inductive capacity than the second inductive element, a first end coupled to produce the second power source, and a second switch to turn current flow through the third inductive element ON and OFF;

a control circuit coupled to control the ON and OFF duty cycle of the second switch such that when the first switch is operated to allow the first inductive element to discharge, current flows through the second inductive element before current flows in the second inductive element.

8. The regulator circuit, as set forth in claim 7, further comprising a ramped voltage generator circuit that outputs a ramp voltage signal, the control circuit being coupled to receive the ramp voltage signal.

9. The regulator circuit, as set forth in claim 8, wherein the magnitude of the ramp voltage signal decreases during each duty cycle of the first switch.

10. The regulator circuit, as set forth in claim 9, wherein the control circuit includes:

an error amplifier for generating an error signal indicative of the voltage output by the second power source;

a pulse width modulator coupled to receive the feedback signal and the ramp voltage signal, the pulse width modulator generating a driver signal; and

a latch circuit coupled to receive the driver signal and to output the driver signal to the second switch.

11. The regulator circuit, as set forth in claim 7, wherein the first, second, and third inductive elements comprise a flyback regulator, the flyback regulator further comprising a feedback circuit coupled between the first inductive element and the second inductive element.

12. The regulator circuit, as set forth in claim 8, wherein the ramped voltage generator circuit includes a third switch coupled in parallel to the third inductive element, a capacitor coupled in parallel to the third switch, and a current sink coupled in parallel to the capacitor.

13. A method for generating a plurality of regulated DC voltage supplies utilizing a flyback regulator, the flyback regulator including a primary inductive element magnetically coupled to a plurality of secondary inductive elements wherein one of the secondary inductive elements is coupled to a first switch, the one secondary inductive element having a greater inductive capacity than the other secondary inductive elements, the method comprising:

opening the first switch coupled with the one secondary inductive element;

charging the primary inductive element with a charge current over a controlled time period;

opening a second switch coupled to the primary inductive element, thereby reversing polarity of the inductive elements and causing magnetizing current to flow through another one of the secondary inductive elements; and

determining when to close the first switch subsequent to opening the second switch to allow current to flow through the one secondary inductive element.

14. The method, as set forth in claim 13, further comprising generating a ramped voltage signal having a negative slope, and closing the first switch based on the ramped voltage signal and an error signal.

15. The method, as set forth in claim 14, wherein determining when to close the first switch comprises:

generating an error signal indicative of the voltage output by the second power source; and

generating a driver signal based on the feedback signal and the ramped voltage signal, the driver signal being set to close the first switch when the ramped voltage is less than or equal to the feedback signal and to open the first switch when the primary inductor begins charging.

16. The method, as set forth in claim 13, further comprising determining when to open the second switch coupled to the primary inductive element based on a signal from a control circuit between the primary inductive element and one of the secondary inductive elements.

17. The method, as set forth in claim 14, wherein generating the ramped voltage signal includes coupling a third switch in parallel to the one secondary inductive element, coupling a capacitor in parallel to the third switch, and coupling a current sink in parallel to the capacitor.

18. A method for changing the output sequence of a regulator circuit utilizing a flyback regulator to generate a plurality of DC voltage supplies, the flyback regulator including a primary inductive element magnetically coupled to at least two secondary inductive elements, the method comprising:

opening a first switch coupled in series with one secondary inductive element;

charging the primary inductive element with a charge current over a controlled time period;

discharging the current stored in the primary inductive element by opening a second switch coupled to the primary inductive element;

generating a ramped voltage signal having a negative slope;

generating an error signal indicative of the voltage output by a DC voltage supply circuit coupled to the one secondary inductive element; and

generating a driver signal based on the error signal and the ramped voltage signal, the driver signal being set to close the first switch when the ramped voltage is less than or equal to the error signal and to open the first switch when the primary inductor begins charging.

19. The method, as set forth in claim 18, wherein the current stored in the primary inductive element is discharged based on a signal from a control circuit coupled between the primary inductive element and one of the secondary inductive elements.

20. The method, as set forth in claim 18, wherein generating the ramped voltage signal includes coupling a third switch in parallel to the one secondary inductive element, coupling a capacitor in parallel to the third switch, and coupling a current sink in parallel to the capacitor.