DC/DC converter with improved stability

• US 7,719,247 B2
• Filed: 09/29/2008
• Issued: 05/18/2010
• Est. Priority Date: 08/19/2005
• Status: Active Grant

• Current Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Original Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Inventors: Lipcsei, Laszlo, Hornet, Sorin
• Primary Examiner(s): Laxton; Gary L
• Application Number:
  US12/240,629
• Publication Number:
  US 20090027015A1
• Time in Patent Office: 596 Days
• Field of Search: 323/224, 323/271, 323/282, 323/284, 323/285, 323/351
• US Class Current: 323/282
• CPC Class Codes: H02M 1/143 using compensating arrangements for reducing noise from the supply in transmission systems H04B15/005
• 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 DC/DC converter includes a switch, an inductor, a capacitor, a resistor, and a voltage divider. The switch is coupled to the input voltage. The inductor is used for coupling the first switch to an output node of the DC/DC converter so as to generate the output voltage at the output node. The capacitor is coupled to the output voltage. The resistor is coupled to the capacitor in series, and is coupled to ground. The voltage divider is coupled across the capacitor so as to reduce the zero frequency of the DC/DC converter.

Claims

1. A DC-DC converter for converting an input DC voltage to an output DC voltage, comprising:

a first switch coupled to said input voltage and operable for generating said output DC voltage at an output node;

a capacitor coupled to said output node and operable for determining a zero frequency of said DC-DC converter;

a first resistor for coupling said capacitor to ground; and

a voltage divider coupled to said capacitor in parallel and coupled to said first resistor in series and operable for determining said zero frequency.

2. The DC-DC converter as claimed in claim 1, wherein said voltage divider comprises:

a second resistor; and

a third resistor coupled to said second resistor in series for generating a feedback voltage between said second resistor and said third resistor.

3. The DC-DC converter as claimed in claim 1, further comprising a controller for receiving a feedback voltage from said voltage divider, and for controlling said first switch in response to said feedback voltage to control said output DC voltage at a predetermined voltage.

4. The DC-DC converter as claimed in claim 1, wherein said capacitor comprises a ceramic capacitor.

5. The DC-DC converter as claimed in claim 3, further comprising:

a second switch for coupling said first switch to ground.

6. The DC-DC converter as claimed in claim 5, wherein said controller coupled to said second switch for controlling said first switch and said second switch according to said feedback voltage.

7. The DC-DC converter as claimed in claim 6, wherein said controller generates a second PWM signal to control said second switch.

8. The DC-DC converter as claimed in claim 6, wherein said second switch comprises a diode.

9. The DC-DC converter as claimed in claim 3, wherein said feedback voltage has a voltage ripple and said first resistor is operable for reducing said voltage ripple.

10. The DC-DC converter as claimed in claim 1, wherein said first switch comprises a metal-oxide semiconductor (MOS) transistor.

11. A method for converting an input DC voltage to an output DC voltage, comprising:

receiving said input DC voltage;

controlling a first switch to discontinuously couple said input DC voltage to an inductor for generating said output DC voltage;

coupling an capacitor to said inductor;

coupling said capacitor to ground through a first resistor; and

generating a feedback voltage signal based on said output DC voltage at a voltage divider coupled in parallel to said capacitor.

12. The method as claimed in claim 11, further comprising:

controlling said first switch according to said feedback voltage signal.

13. The method as claimed in claim 11, wherein said controlling said first switch further comprises:

controlling said first switch with a PWM signal.

14. The method as claimed in claim 11, wherein said voltage divider comprises a second resistor and a third resistor coupled in series.

15. The method as claimed in claim 11, further comprising:

providing a discharging path by a second switch coupled to said first switch and ground.

16. The method as claimed in claim 15, further comprising:

controlling said second switch according to said feedback voltage signal.

17. The method as claimed in claim 15, further comprising:

controlling said second switch with a PWM signal.

18. The method as claimed in claim 15, wherein said second switch comprises a diode.

19. The method as claimed in claim 15, wherein said second switch comprises a metal-oxide semiconductor (MOS) transistor.

20. The method as claimed in claim 11, wherein said capacitor comprises a ceramic capacitor.

21. The method as claimed in claim 11, wherein said first switch comprises a metal-oxide semiconductor (MOS) transistor.