SELF-OSCILLATING CONVERTER

• US 20090058375A1
• Filed: 08/13/2008
• Published: 03/05/2009
• Est. Priority Date: 04/03/2006
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments Deutschland Gesellschaft Mit Beschrã¤Nkter Haftung (Texas Instruments, Inc.)
• Inventors: Scoones, Kevin, Gibson, Neil
• Granted Patent: US 8,148,963 B2
• Time in Patent Office: Days
• US Class Current: 323/225
• CPC Class Codes: H02M 3/1563 without using an external clock H02M3/158 takes precedence

Abstract

A converter has a main feedback path and two auxiliary feedback paths from an output node to an auxiliary differential input pair of a comparator. The auxiliary feedback paths have different RC time constants so that a differential ramp signal is effectively applied to the auxiliary differential inputs of the comparator. The circuit design compensates for a negligibly small equivalent series resistor of an output capacitor so that modern capacitors may be used without compromising the stable oscillation of the converter.

Claims

1. A self-oscillating converter including a load capacitor with a negligibly small equivalent series resistor and a feedback loop with a comparator to which a voltage difference between a reference voltage and an output voltage of the converter is applied, comprising:

a first auxiliary feedback path from an output node to a first differential input of the comparator, the first auxiliary feedback path having a first RC time constant;

a second auxiliary feedback path from the output node to a second differential input of the comparator, the second auxiliary feedback path having a second RC time constant different from the first time constant; and

circuitry for adding the differential voltage between the first and second differential inputs to the voltage difference applied to the comparator.

2. The converter of claim 1, wherein each of the first and second auxiliary feedback paths comprises a resistor and a capacitor connected in series to ground.

3. The converter of claim 2, further comprising a switching unit which, in response to a logic buck/boost control signal, inverts the first and second differential inputs relative to the applied differential voltage.

4. The converter of claim 2, wherein the comparator has two differential input pairs, a first pair being used with the feedback loop and a second pair being used with the first and second auxiliary feedback paths.

5. The converter of claim 4, further comprising a switching unit which, in response to a logic buck/boost control signal, inverts the first and second differential inputs relative to the applied differential voltage.

6. The converter of claim 5, wherein the load capacitor is a ceramic thin film capacitor.

7. The converter of claim 1, wherein the comparator has two differential input pairs, a first pair being used with the feedback loop and a second pair being used with the first and second auxiliary feedback paths.

8. The converter of claim 1, further comprising a switching unit which, in response to a logic buck/boost control signal, inverts the first and second differential inputs relative to the applied differential voltage.

9. The converter of claim 1, wherein the load capacitor is a ceramic thin film capacitor.