Flyback power converter with weighted frequency and quasi-resonance

Patent metadata

Field	Value
Publication number	US-9601983-B2
Application number	US-201514691446-A
Country	US
Kind code	B2
Filing date	Apr 20, 2015
Priority date	Apr 24, 2014
Publication date	Mar 21, 2017
Grant date	Mar 21, 2017

Abstract

The present invention provides a flyback power converter and a control circuit and a control method thereof. The flyback power converter includes: a power stage circuit, a voltage sense circuit, a current sense circuit, and a control circuit. When the flyback power converter operates in a quasi-resonant mode, the control circuit determines a time point of turning OFF a power switch in the power stage circuit according to a current sense signal, a pulse width modulation (PWM) frequency of a PWM signal, and a predetermined threshold, wherein the control circuit adaptively adjusts an ON period of the power switch, or adaptively adjusts an operation bandwidth or an amplifier gain of an error amplifier circuit in a feedback control loop according to the PWM frequency to mitigate an output voltage ripple.

First claim

What is claimed is:

1. A flyback power converter, comprising:
a power stage circuit, for operating a power switch therein to convert an input voltage to an output voltage according to a pulse width modulation (PWM) signal;
a voltage sense circuit, which is coupled to the power stage circuit, for generating a voltage sense signal according to the output voltage;
a current sense circuit, which is coupled to the power stage circuit, for generating a current sense signal according to a switch current flowing through the power switch; and
a control circuit, which is coupled to the power stage circuit, the voltage sense circuit, and the current sense circuit, for generating the PWM signal according to the voltage sense signal and the current sense signal;
wherein when the flyback power converter operates in a quasi-resonant (QR) mode, the control circuit determines a time point of turning ON the power switch according to a zero voltage crossing event (ZVC) of the output voltage which is indicated by the voltage sense signal that the output voltage changes from a non-zero voltage to zero voltage, and determines a time point of turning OFF the power switch according to the current sense signal, a PWM frequency of the PWM signal, and a predetermined threshold;
wherein the control circuit adaptively adjusts an ON period of the power switch according to the PWM frequency, to compensate an output voltage ripple;
wherein the control circuit adaptively adjusts the ON period of the power switch according to the PWM frequency by one or more of the methods listed below:
(1) adaptively adjusting the predetermined threshold to generate an adjusted threshold according to the PWM frequency, and when the current sense signal reaches the adjusted threshold, controlling the PWM signal to turn OFF the power switch; and
(2) adaptively processing the current sense signal to generate a current indication signal according to the PWM frequency, and when the current indication signal reaches the predetermined threshold, controlling the PWM signal to turn OFF the power switch;
wherein when the control circuit adaptively adjusts the predetermined threshold to generate the adjusted threshold, the control circuit includes:
a first QR control circuit, which is coupled to the voltage sense circuit, for generating a first set signal when a ZVC of the output voltage occurs, and generating a first QR mode indication signal when the flyback power converter operates in the QR mode;
a first frequency sense circuit, for generating a first period length signal according to the PWM frequency;
a first gain control circuit, which is coupled to the first QR control circuit and the first frequency sense circuit, for generating the adjusted threshold according to the first QR mode indication signal, the first period length signal, and the predetermined threshold;
a first comparison circuit, which is coupled to the first gain control circuit and the current sense circuit, for comparing the current sense signal with the adjusted threshold, to generate a first reset signal; and
a first PWM signal generation circuit, which is coupled to the first comparison circuit and the first QR control circuit, for generating the PWM signal according to the first set signal and the first reset signal;
wherein when the control circuit adaptively processes the current sense signal to generate the current indication signal according to the PWM frequency, the control circuit includes:
a second QR control circuit, which is coupled to the voltage sense circuit, for generating a second set signal when the ZVC of the output voltage occurs, and generating a second QR mode indication signal when the flyback power converter operates in the QR mode;
a second frequency sense circuit, for generating a second period length signal according to the PWM frequency;
a second gain control circuit, which is coupled to the second QR control circuit, the second frequency sense circuit, and the current sense circuit, for adaptively processing the current sense signal to generate a current indication signal according to the second QR mode indication signal and the second period length signal;
a second comparison circuit, which is coupled to the second gain control circuit, for comparing the current indication signal with the predetermined threshold, to generate a second reset signal; and
a second PWM signal generation circuit, which is coupled to the second comparison circuit and the second QR control circuit, for generating the PWM signal according to the second set signal and the second reset signal.

2. The flyback power converter of claim 1 , wherein when the control circuit adaptively adjusts the predetermined threshold to generate the adjusted threshold according to the PWM frequency, the gain control circuit includes:
a frequency weighting circuit, which is coupled to the QR control circuit and the frequency sense circuit, for generating a frequency weighting signal related to the PWM frequency according to the QR mode indication signal, the PWM signal, and the period length signal; and
a calculation circuit, which is coupled to the frequency weighting circuit, for generating the adjusted threshold according to the predetermined threshold and the frequency weighting signal.

3. The flyback power converter of claim 1 , wherein when the control circuit adaptively processes the current sense signal to generate the current indication signal according to the PWM frequency, the gain control circuit includes:
a frequency weighting circuit, which is coupled to the QR control circuit and the frequency sense circuit, for generating a frequency weighting signal related to the PWM frequency according to the QR mode indication signal, the PWM signal, and the period length signal; and
a calculation circuit, which is coupled to the frequency weighting circuit, for generating the current indication signal according to the current sense signal and the frequency weighting signal.

4. A flyback power converter, comprising:
a power stage circuit, for operating a power switch therein to convert an input voltage to an output voltage according to a pulse width modulation (PWM) signal;
a voltage sense circuit, which is coupled to the power stage circuit, for generating a voltage sense signal according to the output voltage;
a current sense circuit, which is coupled to the power stage circuit, for generating a current sense signal according to a switch current flowing through the power switch; and
a control circuit, which is coupled to the power stage circuit, the voltage sense circuit, and the current sense circuit, for generating the PWM signal according to the voltage sense signal and the current sense signal;
wherein when the flyback power converter operates in a quasi-resonant (QR) mode, the control circuit determines a time point of turning ON the power switch according to a zero voltage crossing event (ZVC) of the output voltage which is indicated by the voltage sense signal that the output voltage changes from a non-zero voltage to zero voltage, and determines a time point of turning OFF the power switch according to the current sense signal, a PWM frequency of the PWM signal, and a predetermined threshold;

wherein the control circuit adaptively adjusts an operation bandwidth of an error amplifier circuit according to the PWM frequency, and the control circuit includes:
a QR control circuit, which is coupled to the voltage sense circuit, for generating a QR mode indication signal when the flyback power converter operates in the QR mode;
a frequency sense circuit, for generating a period length signal according to the PWM frequency;
the error amplifier circuit, including:
a bandwidth control circuit, which is coupled to the QR control circuit and the frequency sense circuit, for generating an adjustmen

Assignees

• Chang Kuang-Fu
• Lin Tzu-Chen
• Luo Li-Di
• Richtek Technology Corp

Inventors

• Chang Kuang-Fu
• Lin Tzu-Chen
• Luo Li-Di

Classifications

• H02M2001/0058

  Electricity · mapped topic

• H02M3/33507

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

• Y02B70/1433

  Cross-Sectional Technologies · mapped topic

• H02M1/143 Primary

  using compensating arrangements (for reducing noise from the supply in transmission systems H04B15/005) · CPC title

• Y02B70/1491

  Cross-Sectional Technologies · mapped topic