Enable and disable of diode emulation in a DC/DC converter

• US 20050200342A1
• Filed: 05/26/2004
• Published: 09/15/2005
• Est. Priority Date: 03/12/2004
• Status: Active Grant

• Current Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Original Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Inventors: Rudiak, Jerry A.
• Granted Patent: US 7,205,751 B2
• Time in Patent Office: Days
• US Class Current: 323/282
• CPC Class Codes: H02M 3/1588 comprising at least one synchronous rectifier element H02M3/1582, H02M3/1584 take precedence
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A method of enabling and disabling diode emulation for a DC/DC converter which generates an output voltage including detecting a diode emulation request signal indicative of enabling or disabling diode emulation and delaying enabling or disabling diode emulation until after the output voltage begins changing. Diode emulation is enabled while the output voltage is decreasing or has reached a predetermined level and an optional delay may be included. Diode emulation is disabled while the voltage is increasing. A diode emulation control circuit includes a first circuit that determines when the output voltage is changing and a second circuit that selectively enables or disables diode emulation in response to a diode emulation enable/disable signal after the output voltage begins to change.

Claims

1. A method of enabling and disabling diode emulation in a DC/DC converter which generates an output voltage, comprising:

detecting a diode emulation request signal indicative of enabling or disabling diode emulation; and

delaying enabling or disabling diode emulation until after the output voltage begins changing.

2. The method of claim 1, further comprising:

said detecting a diode emulation request signal comprising detecting a request to enable diode emulation; and

enabling diode emulation after the output voltage begins decreasing.

3. The method of claim 2, wherein said enabling diode emulation comprises enabling diode emulation after the output voltage decreases by a predetermined amount.

4. The method of claim 2, wherein said enabling diode emulation comprises enabling diode emulation after the output voltage begins decreasing and after a predetermined delay.

5. The method of claim 2, wherein said enabling diode emulation comprises enabling diode emulation after the output voltage decreases by a predetermined amount and after a predetermined delay.

6. The method of claim 5, wherein the predetermined delay is determined by counting cycles of a pulse width modulation (PWM) signal provided from the DC/DC converter.

7. The method of claim 1, further comprising:

said detecting a diode emulation request signal comprising detecting a request to disable diode emulation; and

disabling diode emulation while the output voltage is increasing.

8. The method of claim 1, further comprising:

said detecting a diode emulation request signal comprising detecting a request to disable diode emulation; and

disabling diode emulation after a predetermined delay.

9. The method of claim 8, wherein the predetermined delay is determined by counting cycles of a pulse width modulation (PWM) signal provided from the DC/DC converter.

10. A diode emulation control circuit for a DC/DC converter which provides an output voltage, comprising:

a first circuit that determines when the output voltage is changing; and

a second circuit, coupled to said first circuit, that selectively enables or disables diode emulation in response to a diode emulation enable/disable signal after the output voltage begins to change.

11. The diode emulation control circuit of claim 10, wherein said first circuit comprises a comparator that determines when the output voltage has dropped by a predetermined amount.

12. The diode emulation control circuit of claim 11, wherein said second circuit comprises a logic gate that enables diode emulation after the output voltage has dropped by said predetermined amount.

13. The diode emulation control circuit of claim 11, wherein said first circuit further comprises:

a converter that converts a voltage identification signal to a voltage level signal indicative of a new voltage level;

a slew rate controller that inputs said voltage level signal and that outputs a soft voltage signal that ramps from a current voltage level to said new voltage level; and

an offset voltage device, coupled to said converter, that outputs a voltage level offset signal;

wherein said comparator compares said voltage level offset signal with said soft voltage signal.

14. The diode emulation control circuit of claim 13, wherein said first circuit further comprises a first delay circuit, coupled to an output of said comparator, that outputs a low voltage signal after the output voltage has dropped by said predetermined amount and after a predetermined delay.

15. The diode emulation control circuit of claim 14, wherein said first delay circuit delays a predetermined number of cycles of a pulse width modulation (PWM) signal generated by the DC/DC converter.

16. The diode emulation control circuit of claim 14, wherein said second circuit comprises:

a second delay circuit that receives said diode emulation enable/disable signal and that outputs a delayed diode emulation enable/disable signal; and

gate logic that enables diode emulation when said low voltage signal and said delayed diode emulation enable/disable signal are provided.

17. The diode emulation control circuit of claim 16, wherein said second delay circuit delays a predetermined number of cycles of a pulse width modulation (PWM) signal generated by the DC/DC converter.

18. The diode emulation control circuit of claim 10, wherein said second circuit comprises a delay circuit that disables diode emulation in response to said diode emulation enable/disable signal after a predetermined delay.

19. A DC/DC converter for a microprocessor, the microprocessor providing a voltage identification (VID) signal indicative of a desired supply voltage and providing a diode emulation request (SLP) signal coincident with said voltage identification signal, said DC/DC converter comprising:

a switching circuit that switches an input voltage through an output inductor to provide a supply voltage for the microprocessor in accordance with a pulse width modulation (PWM) signal, said switching circuit having a diode emulation mode of operation; and

control logic, coupled to said switching circuit, that receives the VID and SLP signals, that provides said PWM signal, and that includes a diode emulation control circuit for selectively enabling or disabling said diode emulation mode of operation of said switching circuit after said supply voltage begins changing.

20. The DC/DC converter of claim 19, wherein said diode emulation control circuit comprises:

a comparator circuit that determines when said supply voltage decreases by a predetermined amount; and

an enable/disable circuit, coupled to said comparator circuit and responsive to said SLP signal, that enables diode emulation after said supply voltage decreases by said predetermined amount and that disables diode emulation after a first predetermined delay after said supply voltage begins to increase.

22. The DC/DC converter of claim 20, further comprising a delay circuit coupled to said comparator circuit that adds a second predetermined delay after said supply voltage decreases by said predetermined amount before enable diode emulation.

23. The DC/DC converter of claim 20, wherein said enable/disable circuit comprises:

a delay circuit that delays said SLP signal by said first predetermined delay and that provides a delayed SLP signal; and

gate logic responsive to said comparator circuit and said delayed SLP signal.

21. The DC/DC converter of claim 209, wherein said comparator circuit comprises:

a digital to analog converter (DAC) that converts said VID signal to an analog voltage signal;

a slew rate controller that generates a soft control signal based on said analog voltage signal; and

a comparator that determines when said soft control signal decreases to within a predetermined voltage offset of said analog voltage signal.