Self-oscillating converter
View Patent ↗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.
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 switched node to a first input of 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 switched node to a second input of the first 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 a differential voltage between the first and second differential inputs to the voltage difference applied to the comparator for generating a voltage equivalent to a voltage that would have been generated across the equivalent series resistance of the load capacitor had the equivalent series resistance not been negligible.
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 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 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 applied differential voltage.
9. The converter of claim 1 , wherein the load capacitor is a ceramic thin film capacitor.