Quasi-resonant switching power supply

Patent metadata

Field	Value
Publication number	US-9627977-B2
Application number	US-201314103262-A
Country	US
Kind code	B2
Filing date	Dec 11, 2013
Priority date	Dec 20, 2012
Publication date	Apr 18, 2017
Grant date	Apr 18, 2017

Abstract

A quasi-resonance switching power supply quickly determines the number of bottom skips corresponding to the load condition even in abrupt load change. The quasi-resonance switching power supply is provided with a bottom skipping control function and a capacitor to hold a voltage corresponding to the load condition of the switching element over one switching period of the switching element. The quasi-resonance switching power supply comprises a bottom skipping number determining circuit that compares the voltage held on the capacitor with comparison reference voltages selected from a plurality of reference voltages for determining the number of bottom skips, and revises the comparison reference voltage according to the comparison result. The processing of comparison and revision is executed multiple times in one switching period of the switching element. Thus, the bottom skipping number determining circuit determines the number of bottom skips corresponding to the voltage held on the capacitor.

First claim

What is claimed is:

1. A quasi-resonance switching power supply that utilizes resonance phenomenon in a resonance circuit including an inductance and a resonance capacitor connected to an ON-OFF driven switching element of the quasi-resonance switching power supply, and that turns ON the switching element at a timing of a bottom of a resonant voltage, the quasi-resonance switching power supply comprising:
a bottom detecting circuit that detects a bottom of the resonant voltage developed upon turning OFF of the switching element;
a bottom skipping number determining circuit that determines a number of bottom skips corresponding to a load of the switching element; and
a turn ON control circuit that turns ON the switching element when a number of bottoms detected by the bottom detecting circuit reaches the number of bottom skips determined by the bottom skipping number determining circuit; wherein
the bottom skipping number determining circuit comprises a capacitor that holds a voltage corresponding to the load of the switching element over one switching period of the switching element, and sequentially compares the voltage held on the capacitor with a plurality of reference voltages for determining the number of bottom skips in one switching period of the switching element to determine the number of bottom skips corresponding to the voltage held on the capacitor.

2. The quasi-resonance switching power supply according to claim 1 ,
wherein
the plurality of reference voltages for determining the number of bottom skips correspond to delay times after a timing of turning OFF of the switching element; and
the bottom skipping number determining circuit comprises:
an up-down counter that increases or decreases the number of bottom skips according to a comparison result between the voltage held on the capacitor with an upper limit voltage and a lower limit voltage set by selecting from the plurality of reference voltages;
a reference voltage selecting circuit that changes reference voltages set as the upper limit voltage and the lower limit voltage corresponding to the number of bottom skips set in the up-down counter; and
a selection operation control circuit that instructs the reference voltage selecting circuit to execute changing processing for the reference voltages at multiple times in one switching period of the switching element to settle the number of bottom skips set in the up-down counter.

3. The quasi-resonance switching power supply according to claim 2 wherein
the plurality of reference voltages for determining the number of bottom skips are (N+1) different voltages that divide a range of the voltages held on the capacitors into N steps corresponding to a magnitude of the load of the switching element, N being an integer of two or larger; and
the reference voltage selecting circuit selects, from the plurality of reference voltages, the upper limit voltage and the lower limit voltage to specify a variation-permitting range of the voltage held on the capacitor according to a value of the up-down counter indicating the number of bottom skips.

4. The quasi-resonance switching power supply according to claim 2 , wherein the up-down counter performs processing of decrementing of the number of bottom skips and processing of incrementing of the number of bottom skips triggered by the selection operation control circuit repeatedly at multiple times in one switching period, the processing of decrementing being executed when the voltage held on the capacitor is higher than the upper limit voltage and the processing of incrementing being executed when the voltage held on the capacitor is lower than the lower limit voltage.

5. The quasi-resonance switching power supply according to claim 1 , wherein
the voltage corresponding to the load of the switching element is a voltage corresponding to a period of time from a timing of turning ON of the switching element to a timing of detecting a first bottom of the resonant oscillation voltage after turning OFF of the switching element.

6. The quasi-resonance switching power supply according to claim 5 , wherein
the capacitor is composed of first and second capacitors provided in parallel; and
the voltage corresponding to the period of time from a timing of turning ON of the switching element to a timing of detecting a first bottom of the resonant oscillation voltage after turning OFF of the switching element is accumulated on the first and second capacitors alternately in every switching period of the switching element and held over the next one switching period of the switching element to deliver for determining the number of bottom skips in the bottom skipping number determining circuit.

7. The quasi-resonance switching power supply according to claim 1 , wherein the voltage corresponding to the load of the switching element is a voltage corresponding to an ON period of time of the switching element.

8. The quasi-resonance switching power supply according to claim 1 , wherein the voltage corresponding to the load of the switching element is a voltage corresponding to a current running through the switching element at a time of turning OFF of the switching element.

9. An apparatus, comprising:
a minimum value detecting circuit configured to detect occurrences of a minimum value of a resonant oscillation voltage in a switching power supply including an inductance, a resonance capacitor and a switching element having a switching period;
a number determining circuit configured to determine a number M, M being a natural number including zero, of bottom skips corresponding to a load condition for the switching period; and
a control circuit configured to switch the switching element based on the minimum value detecting circuit detecting a number of occurrences of a minimum value of the resonant oscillation voltage corresponding to the number M;
wherein
the number determining circuit includes a voltage holding element configured to hold, over the switching period of the switching element, a voltage corresponding to the load condition; and
the number determining circuit is configured to
perform a comparison of the held voltage with at least one reference voltage, the at least one reference voltage including a plurality of reference voltages respectively corresponding to delay times, to determine the number M,
select an upper limit voltage and a lower limit voltage from among the plurality of reference voltages, and
increment or decrement the number M based on a comparison of the held voltage with the upper limit voltage and the lower limit voltage.

10. The apparatus of claim 9 , wherein the number determining circuit is further configured to change a selection of the upper limit voltage and the lower limit voltage based on a value of the held voltage.

11. The apparatus of claim 10 , wherein the number determining circuit is further configured to change the selection of the upper limit voltage and the lower limit voltage multiple times during the switching period.

12. The apparatus of claim 9 , wherein the voltage holding element includes at least one capacitor.

Assignees

• Fuji Electric Co Ltd

Inventors

• Sonobe Koji

Classifications

• H02M2001/0058

  Electricity · mapped topic

• Y02B70/1433

  Cross-Sectional Technologies · mapped topic

• H02M3/33507 Primary

  with automatic control of the output voltage or current, e.g. flyback converters (H02M3/33561, H02M3/33569 take precedence) · CPC title

• H02M2001/0032

  Electricity · mapped topic

• Y02B70/1491

  Cross-Sectional Technologies · mapped topic