Resonant converter with capacitive mode control and associated control method

Patent metadata

Field	Value
Publication number	US-9812975-B2
Application number	US-201615272418-A
Country	US
Kind code	B2
Filing date	Sep 21, 2016
Priority date	Sep 24, 2015
Publication date	Nov 7, 2017
Grant date	Nov 7, 2017

Abstract

A control circuit used for controlling a resonant converter. The control circuit has a setting capacitor, N up thresholds and N low thresholds. If the resonant converter operates in the inductive mode, a setting voltage signal across the setting capacitor is respectively compared with the largest one of the N up thresholds and the smallest one of the N low thresholds in each operation cycle to generate a high-side control signal and a low-side control signal for controlling a high-side switch and a low-side switch of the resonant converter. If the resonant converter enters into the capacitive mode, the setting voltage signal is respectively compared with each of the N up thresholds and each of the N low thresholds operation cycle by operation cycle to generate the high-side control signal and the low-side control signal.

First claim

What we claim is:

1. A control method used for controlling a resonant converter, wherein the resonant converter comprises a setting capacitor used for regulating a switching frequency of the resonant converter, the control method comprising:
sensing a current flowing through a resonant inductor of the resonant converter to generate a current sense signal;
judging whether the resonant converter operates in an inductive mode or a capacitive mode based on the current sense signal;
providing N up thresholds and N low thresholds, wherein each of the N up thresholds is corresponding to each of the N low thresholds, and wherein each of the N up thresholds is higher than each of the N low thresholds correspondingly, and wherein N is a positive integer and is larger than or equal to 2;
when the resonant converter operates in the inductive mode, comparing a setting voltage signal across the setting capacitor with the largest one of the N up thresholds, and with the smallest one of the N low thresholds in each operation cycle to generate a high-side control signal and a low-side control signal respectively used for controlling a high-side switch and a low-side switch of the resonant converter, wherein the operation cycle comprises one or more switching cycles of the resonant converter;
when the resonant converter operates in the capacitive mode, comparing the setting voltage signal with each of the N up thresholds sequentially operation cycle by operation cycle, and with each of the N low thresholds sequentially operation cycle by operation cycle to generate the high-side control signal and the low-side control signal; and
changing the switching frequency of the resonant converter by varying the N up thresholds and the N low thresholds.

2. The control method of claim 1 , wherein the N up thresholds are identical, and wherein the N low thresholds are decreased operation cycle by operation cycle.

3. The control method of claim 1 , wherein the N low thresholds are identical, and wherein the N up thresholds are increased operation cycle by operation cycle.

4. The control method of claim 1 , wherein the N low thresholds are decreased operation cycle by operation cycle, and wherein the N up thresholds are increased operation cycle by operation cycle.

5. The control method of claim 1 , wherein both the high-side control signal and the low-side control signal have a first logic state and a second logic state, and wherein
when the setting voltage signal is higher than one of the N up thresholds, the high-side control signal changes from the second logic state to the first logic state, and the low-side control signal changes from the first logic state to the second logic state; and wherein
when the setting voltage signal is lower than one of the N low thresholds, the high-side control signal changes from the first logic state to the second logic state, and the second logic state of the low-side control signal changes from the second logic state to the first logic state.

6. The control method of claim 1 , wherein judging whether the resonant converter operates in the inductive mode or the capacitive mode comprises:
at the moment when the high-side switch is turned off, judging whether the current sense signal is higher than a zero-crossing threshold, wherein if the current sense signal is higher than the zero-crossing threshold, the resonant converter operates in the inductive mode, and wherein if the current signal is lower than the zero-crossing threshold, the resonant converter operates in the capacitive mode; and
at the moment when the low-side switch is turned off, judging whether the current sense signal is higher than a zero-crossing threshold, wherein if the current signal is higher than the zero-crossing threshold, the resonant converter operates in the capacitive mode, and wherein if the current signal is lower than the zero-crossing threshold, the resonant converter operates in the inductive mode.

7. The control method of claim 6 , wherein the zero-crossing threshold comprise a hysteresis signal having a first zero-crossing threshold and a second zero-crossing threshold, and wherein the first zero-crossing threshold is smaller than zero, and the second zero-crossing threshold is larger than zero, and wherein
at the moment when the high-side switch is turned off, if the current signal is higher than the first zero-crossing threshold, the resonant converter operates in the inductive mode, and if the current signal is lower than the second zero-crossing threshold, the resonant converter operates in the conductive mode; and wherein
at the moment when the low-side switch is turned off, if the current signal is higher than the first zero-crossing threshold, the resonant converter operates in the conductive mode, and if the current signal is lower than the second zero-crossing threshold, the resonant converter operates in the inductive mode.

8. A control circuit used for controlling a resonant converter, comprising:
a voltage sensing circuit, configured to sense an output voltage signal of the resonant converter to generate a feedback voltage signal;
a current sensing circuit, configured to sense a current flowing through a resonant inductor of the resonant converter to generate a current sense signal;
a mode judging circuit, configured to receive the current sense signal, and further configured to compare the current sense signal with a zero-crossing threshold to generate a mode signal, wherein the mode signal is configured to judge whether the resonant converter operates in an inductive mode or a capacitive mode; and
a frequency controller, configured to receive the mode signal and the feedback voltage signal, and further configured to generate a high-side control signal and a low-side control signal respectively used for controlling a high-side switch and a low-side switch of the resonant converter based on the feedback voltage signal and the mode signal, wherein the frequency controller comprises a setting capacitor, and wherein the frequency controller further comprises N up thresholds and N low thresholds, and wherein each of the N up thresholds is corresponding to each of the N low thresholds, and wherein each of the N up thresholds is higher than each of the N low thresholds correspondingly, and wherein N is a positive integer and is larger than or equal to 2, and wherein
when the resonant converter operates in the inductive mode, the frequency controller is configured to compare a setting voltage signal across the setting capacitor with the largest one of the N up thresholds, and with the smallest one of the N low thresholds in each operation cycle to generate the high-side control signal and the low-side control signal, wherein the operation cycle comprises one or more switching cycles of the resonant converter, and wherein
when the resonant converter enters into the capacitive mode, the frequency controller is configured to compare the setting voltage signal with each of the N up thresholds sequentially operation cycle by operation cycle, and with each of the N low thresholds sequentially operation cycle by operation cycle to generate the high-side control signal and the low-side control signal, and wherein
the frequency controller is further configured to change a switching frequency of the resonant converter by varying the N up thresholds and the N low thresholds.

9. The control circuit of claim 8 , wherein the N up thresholds are identical, and wherein the N low thresholds are decreased operation cycle by operation cycle.

10. The control circuit of claim 8 , wherein the N low thresholds are identical, and wherein the N up thresholds are increased operation cycle by operation cycle.

11. The co

Assignees

• Chengdu Monolithic Power Sys

Inventors

• Chen Yuedong

Classifications

• H02M2001/0009

  Electricity · mapped topic

• H02M1/088

  for the simultaneous control of series or parallel connected semiconductor devices · CPC title

• H02M3/33546 Primary

  with automatic control of the output voltage or current (H02M3/33561 takes precedence) · CPC title

• H02M3/3376 Primary

  with automatic control of output voltage or current · CPC title

• H02M1/0009

  Devices or circuits for detecting current in a converter · CPC title