Flyback power converter, secondary side control circuit, and control method thereof

Patent metadata

Field	Value
Publication number	US-2016141966-A1
Application number	US-201514943662-A
Country	US
Kind code	A1
Filing date	Nov 17, 2015
Priority date	Nov 18, 2014
Publication date	May 19, 2016
Grant date	—

Abstract

The present invention provides a flyback power converter, a secondary side control circuit, and a control method thereof. The flyback power converter converts an input voltage to an output voltage, and provides a load current to a load circuit. The flyback power converter includes: a transformer circuit, a power switch circuit, a switch current sense circuit, a primary side control circuit, and a secondary side control circuit. The secondary side control circuit adaptively adjusts a frequency of a zero of a compensator gain function and/or a mid-frequency gain of the compensator gain function according to the load current, such that a number of poles of a system open loop gain function of the flyback power converter is at most more than a number of zeroes of the system open loop gain function by one under a crossover frequency.

First claim

What is claimed is:

1 . A flyback power converter, configured to operably convert an input voltage to an output voltage, and provide a load current to a load circuit, the flyback power converter comprising:
a transformer circuit, which includes:
a primary winding, configured to operably receive the input voltage;
a secondary winding, configured to operably generate the output voltage at an output node; and
a tertiary winding, configured to operably generate a voltage sense signal according to the output voltage;
a power switch circuit, which is coupled to the primary winding, and configured to operably operate a power switch therein according to an operation signal, so as to convert the input voltage to the output voltage; a switch current sense circuit, which is coupled to the power switch circuit, and configured to operably generate a switch current sense signal according to a switch current flowing through the power switch; a primary side control circuit, which is coupled to the tertiary winding, the switch current sense circuit, and the power switch circuit, and configured to operably generate the operation signal according to the voltage sense signal, the switch current sense signal, and a feedback signal; and a secondary side control circuit, which is coupled to the output node and the primary side circuit, and configured to operably generate the feedback signal according to the load current, and adaptively adjust a frequency of a zero of a compensator gain function and/or a mid-frequency gain of the compensator gain function according to a condition of the load current, such that a number of poles of a system open loop gain function of the flyback power converter is at most more than a number of zeroes of the system open loop gain function by one under a crossover frequency.

2 . The flyback power converter of claim 1 , further comprising an opto-coupler circuit, which is coupled between the primary side circuit and the secondary side circuit, and configured to operably generate an opto-coupler signal which is inputted to the primary side control circuit according to the feedback signal.

3 . The flyback power converter of claim 1 , wherein the secondary side control circuit includes:
a current regulator coupled to the load circuit, and configured to operably regulate the load current; a load current sense circuit, which is coupled to the current regulator, and configured to operably sense the load current and generate a load current sense signal according to the load current; a transconductance amplifier, which is coupled to the load current sense circuit, and configured to operably generate the feedback signal according to the load current sense signal, a current adjustment reference signal, and a compensation signal; and a compensator, which is coupled to the transconductance amplifier, and configured to operably generate the compensation signal according to the load current; wherein the compensator adaptively adjusts the frequency of the zero of the compensator gain function and/or the mid-frequency gain of the compensator gain function according to the condition of the load current, such that the number of poles of the system open loop gain function is at most more than the number of zeroes of the system open loop gain function by one under the crossover frequency.

4 . The flyback power converter of claim 2 , wherein the secondary side control circuit includes:
a current regulator coupled to the load circuit, configured to operably regulate the load current; a load current sense circuit, which is coupled to the current regulator, and configured to operably sense the load current and generate a load current sense signal according to the load current; a transconductance amplifier, which is coupled to the load current sense circuit, and configured to operably generate the feedback signal according to the load current sense signal, a current adjustment reference signal, and a compensation signal; and a compensator, which is coupled to the transconductance amplifier, and configured to operably generate the compensation signal according to the load current; wherein the compensator adaptively adjusts the frequency of the zero of the compensator gain function and/or the mid-frequency gain of the compensator gain function according to the condition of the load current, such that the number of poles of the system open loop gain function is at most more than the number of zeroes of the system open loop gain function by one under the crossover frequency.

5 . The flyback power converter of claim 3 , wherein the compensator includes:
a variable RC circuit, which is coupled to the transconductance amplifier, and configured to operably adjust an RC parameter of the variable RC circuit according to a load determination signal to compensate an output of the transconductance amplifier, so as to adjust the frequency of the zero of the compensator gain function and/or the mid-frequency gain of the compensator gain function; and a load determination circuit, configured to operably generate the load determination signal according to the load current and a load reference signal.

6 . The flyback power converter of claim 4 , wherein the compensator includes:
a variable RC circuit, which is coupled to the transconductance amplifier, and configured to operably adjust an RC parameter of the variable RC circuit according to a load determination signal to compensate an output of the transconductance amplifier, so as to adjust the frequency of the zero of the compensator gain function and/or the mid-frequency gain of the compensator gain function; and a load determination circuit, configured to operably generate the load determination signal according to the load current and a load reference signal.

7 . The flyback power converter of claim 5 , wherein the compensator further includes a hysteresis circuit, which is coupled between the variable RC circuit and the load determination circuit, and configured to operably adjust the load determination signal by a hysteresis effect.

8 . The flyback power converter of claim 6 , wherein the compensator further includes a hysteresis circuit, which is coupled between the variable RC circuit and the load determination circuit, and configured to operably adjust the load determination signal by a hysteresis effect.

9 . The flyback power converter of claim 5 , wherein the load determination circuit determines whether the load circuit is in a light load condition or a heavy load condition according to the load current, and when the load circuit is determined to be in the heavy load condition, the variable RC circuit adjusts the frequency of the zero of the compensator gain function to cancel the pole of an uncompensated system loop gain function corresponding to a target heavy load condition; when the load circuit is determined to be in the light load condition, the variable RC circuit adjusts the frequency of the zero of the compensator gain function and/or the mid-frequency gain of the compensator gain function, such that the number of poles of the system open loop gain function is at most more than the number of zeroes of the system open loop gain function by one under the crossover frequency.

10 . The flyback power converter of claim 6 , wherein the load determination circuit determines whether the load circuit is in a light load condition or a heavy load condition according to the load current, and when the load circuit is determined to be in the heavy load condition, the variable RC circuit adjusts the frequency of the zero of the compensator gain function to cancel the pole of an uncompensated system loop gain function corresponding to a target heavy load condit

Assignees

• Richtek Technology Corp

Inventors

• Huang Chun-Shih
• Wu Chang-Yu
• Chen Pei-Yuan

Classifications

• H02M3/33523 Primary

  with galvanic isolation between input and output of both the power stage and the feedback loop · CPC title

• H02M2001/0009

  Electricity · mapped topic

• H02M1/0032

  Control circuits allowing low power mode operation, e.g. in standby mode · CPC title

• H02M1/0025

  Arrangements for modifying reference values, feedback values or error values in the control loop of a converter · CPC title

• H02M1/0009

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