Resonant converter and driving method thereof

Patent metadata

Field	Value
Publication number	US-2017310231-A1
Application number	US-201715645372-A
Country	US
Kind code	A1
Filing date	Jul 10, 2017
Priority date	Feb 11, 2014
Publication date	Oct 26, 2017
Grant date	—

Abstract

A resonant converter includes a first switch on a primary side and a second switch coupled to the first switch, a first synchronous rectification switch on a secondary side conducted according to a switching operation of the first switch, a second synchronous rectification switch on the secondary side conducted according to a switching operation of the second switch, and a switch control circuit configured to detect a waveform of one end voltage of at least one of the first synchronous rectification switch and the second synchronous rectification switch, determine one of a below region and an above region, and differently control conduction duration of the first and second synchronous rectification switches according to a determined result.

First claim

What is claimed is:

1 . A resonant converter, comprising:
a first switch on a primary side and a second switch coupled to the first switch; a first synchronous rectification switch on a secondary side configured to conduct according to a switching operation of the first switch; a second synchronous rectification switch on the secondary side configured to conduct according to a switching operation of the second switch; and a switch control circuit configured to detect a waveform of one end voltage of at least one of the first synchronous rectification switch and the second synchronous rectification switch, determine from the detected waveform of the one end voltage whether an operating frequency of the resonant converter is higher or lower than a resonant frequency, and differently control conduction duration of the first and second synchronous rectification switches when a result of the determination indicates that the operating frequency of the resonant converter is higher than the resonant frequency.

2 . The converter of claim 1 , wherein when the determination indicates that the operating frequency of the resonant converter is higher than the resonant frequency, the switch control circuit extends the conduction duration of the first and second synchronous rectification switches to a time later than an off time of the first and second switches, respectively.

3 . The converter of claim 2 , wherein when the determination indicates that the operating frequency of the resonant converter is lower than the resonant frequency, the switch control circuit does not extend the conduction duration of the first and second synchronous rectification switches.

4 . The converter of claim 1 , wherein the switch control circuit is configured to turn on the first synchronous rectification switch for a duration spanning from a conduction time of the first synchronous rectification switch to a time delayed from a turn-off time of the first switch by a first extended duration calculated in an immediately preceding switching cycle, and turn on the second synchronous rectification switch for a duration spanning from a conduction time of the second synchronous rectification switch to a time delayed from a turn-off time of the second switch by a second extended duration calculated in the immediately preceding switching cycle, when the determination indicates that the operating frequency of the resonant converter is higher than the resonant frequency.

5 . The converter of claim 4 , wherein the switch control circuit is configured to calculate the first extended duration by subtracting a first duration and a dead time between the first and second synchronous rectification switches from a duration spanning from a turn-on time of the first switch to a conduction end time of the first synchronous rectification switch, in which the first duration is calculated by subtracting a dead time of the first switch and a dead time of the second switch from a maximum on-time of the first switch.

6 . The converter of claim 5 , wherein the switch control circuit counts enabled duration of a clock signal to determine a switching frequency of the first and second switches, and the enabled duration of the clock signal corresponds to the maximum on-time of the first switch.

7 . The converter of claim 4 , wherein the switch control circuit is configured to calculate the second extended duration by subtracting a first duration and a dead time between the first and second synchronous rectification switches from a duration spanning from a turn-on time of the second switch to a conduction end time of the second synchronous rectification switch, in which the first duration is calculated by subtracting dead time of the first and second switches from maximum on-time of the second switch.

8 . The converter of claim 7 , wherein the switch control circuit counts enabled duration of a clock signal which determines a switching frequency of the first and second switches, and the enabled duration of the clock signal corresponds to the maximum on-time of the second switch.

9 . The converter of claim 1 , wherein the switch control circuit comprises:
an SR on-time determiner configured to detect an end voltage of the first synchronous rectification switch and an end voltage of the second synchronous rectification switch, detect a first conduction duration of the first synchronous rectification switch and a second conduction duration of the second synchronous rectification switch in an immediately preceding switching cycle, and set an on-time of each of the first and second synchronous rectification switches in a next switching cycle based on a duration obtained as a result of subtracting a second dead time between the first and second synchronous rectification switches from the detected first and second conduction durations; and an SR on-time compensator configured to calculate a first extended duration by subtracting a first duration of the first synchronous rectification switch and the second dead time from a duration spanning from a turn-on time of the first switch to a conduction end time of the first synchronous rectification switch, and calculate a second extended duration in the immediately preceding switching cycle by subtracting a first duration of the second synchronous rectification switch and the second dead time from a duration spanning from a turn-on time of the second switch to a conduction end time of the second synchronous rectification switch.

10 . The converter of claim 9 , wherein the SR on-time compensator is configured to calculate the first duration of the first synchronous rectification switch based on a duration obtained as a result of subtracting a first dead time of the first and second switches from a maximum on-time of the first switch in the immediately preceding switching cycle, and calculate the first duration of the second synchronous rectification switch based on a duration obtained as a result of subtracting the first dead time from a maximum on-time of the second switch in the immediately preceding switching cycle.

11 . The converter of claim 9 , wherein the switch control circuit further comprises an SR control signal generator configured so that when the operating frequency of the resonant converter is higher than the resonant frequency, the SR control signal generator turns on the first synchronous rectification switch for a duration spanning from the conduction time of the first synchronous rectification switch until a time that is delayed from the turn-off time of the first switch by the first extended duration, and turns on the second synchronous rectification switch for a duration spanning from the conduction time of the second synchronous rectification switch until a time delayed from the turn-off time of the second switch by the second extended duration.

12 . The converter of claim 11 , wherein when the operating frequency of the resonant converter is lower than the resonant frequency, the SR control signal generator is configured to turn on the first synchronous rectification switch for a duration spanning from the conduction time of the first synchronous rectification switch to a time when the on-time of the first synchronous rectification switch set by the SR on-time determiner elapses, and turns on the second synchronous rectification switch for a duration spanning from the conduction time of the second synchronous rectification switch to a time when the on-time of the second synchronous rectification switch set by the SR on-time determiner elapses.

13 . A method of driving a resonant converter which comprises a first switch and a second switch on a primary side, a

Assignees

• Fairchild Korea Semiconductor Ltd

Inventors

• Lee Won-Tae
• Baek Hyeong Seok
• Jang Ji-Hoon
• Choi Hang-Seok
• Choi Moon-Ho

Classifications

• H02M3/33592 Primary

  having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer · CPC title

• H02M1/14

  Arrangements for reducing ripples from DC input or output · CPC title

• H02M3/28 Primary

  using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate AC · CPC title

• Y02B70/1433

  Cross-Sectional Technologies · mapped topic

• H02M2001/0058

  Electricity · mapped topic