Primary-side control of resonant converters

Patent metadata

Field	Value
Publication number	US-9935556-B1
Application number	US-201715418340-A
Country	US
Kind code	B1
Filing date	Jan 27, 2017
Priority date	Jan 27, 2017
Publication date	Apr 3, 2018
Grant date	Apr 3, 2018

Abstract

A method for controlling a resonant converter includes maintaining an output current equal to an output power of the converter divided by an output voltage of the converter in response to a secondary current of a transformer being greater than or equal to a maximum output current. The output power is maintained at a constant output power in response to the output power being greater than or equal to a maximum output power, and the secondary current being less than the maximum output current. Maintaining the output current ratio and the constant output power each comprises changing the duty cycle of a primary-side switch configured to gate a primary current of the transformer. The output voltage is limited to a maximum output voltage in response to the secondary current being less than the maximum output current, and the output power being less than the maximum output power.

First claim

What is claimed is:

1. A resonant converter comprising:
an active clamp flyback (ACF) controller configured to control a primary-side switch configured to be coupled to a primary winding of a transformer having the primary winding magnetically coupled with reverse polarity to a secondary winding, the primary winding having a first terminal and a second terminal wherein the primary-side switch is configured to be connected in series with the second terminal and a current sense module, the primary winding configured to have an input voltage connected between the first terminal and a ground reference, and conducting a primary current from the first terminal to the ground reference in response to the primary-side switch being activated, and the secondary winding conducting a secondary current in response to the primary-side switch being deactivated; and
the active clamp flyback (ACF) controller comprising:
a current control circuit configured to maintain an output current equal to an output power divided by an output voltage in response to the secondary current being greater than or equal to a maximum output current, the output power determined from the primary current sensed by the current sense module, and the output voltage equal to a voltage across the secondary winding,
a power control circuit configured to maintain a substantially constant output power in response to the output power being greater than or equal to a maximum output power, and the secondary current being less than the maximum output current, the substantially constant output power determined by a sample of the output voltage, and
a voltage control circuit configured to limit the output voltage to a maximum output voltage in response to the secondary current being less than the maximum output current, and the output power being less than the maximum output power.

2. The resonant converter of claim 1 wherein the output current is maintained by changing a duty cycle of the primary-side switch, and wherein the active clamp flyback (ACF) controller is configured to determine the duty cycle by dividing an activation duration of the primary-side switch by an activation period.

3. The resonant converter of claim 1 wherein the substantially constant output power is maintained by changing a duty cycle of the primary-side switch, and wherein the active clamp flyback (ACF) controller is configured to determine the duty cycle by dividing an activation duration of the primary-side switch by an activation period.

4. The resonant converter of claim 1 wherein the determination of the output power comprises:
an integrator configured to integrate the primary current sensed by the current sense module, during an activation duration of the primary-side switch, to determine an integrated primary current,
a peak detector configured to detect a peak of the integrated primary current,
a multiplier circuit configured to multiply the input voltage with the peak of the integrated primary current to form a numerator, wherein the input voltage is determined by a scaled voltage across an auxiliary winding magnetically coupled with the primary winding, and
a divider circuit configured to divide the numerator by the activation duration to determine the output power.

5. The resonant converter of claim 4 further comprising a low pass filter to dampen a high frequency oscillation of the primary current from the activation of the primary-side switch.

6. The resonant converter of claim 1 wherein the output voltage is determined by a scaled voltage across an auxiliary winding magnetically coupled with the primary winding.

7. The resonant converter of claim 1 wherein the secondary current is determined from the primary current sensed by the current sense module, and divided by a turns ratio, wherein the turns ratio equals a first number of windings of the primary winding divided by a second number of windings of the secondary winding, wherein the first number of windings is less than the second number of windings.

8. The resonant converter of claim 1 wherein the maximum output power is a predetermined value of the output power, the maximum output current is a predetermined value of the output current, and the maximum output voltage is a predetermined value of the output voltage.

9. A controller for a converter comprising:
a current control circuit configured to maintain an output current equal to an output power of the converter divided by an output voltage of the converter in response to a secondary current of a transformer of the converter being greater than or equal to a maximum output current, wherein the output current ratio is maintained by changing a duty cycle of a primary-side switch of the converter configured to gate a primary current of the transformer;
a power control circuit configured to maintain a substantially constant output power in response to the output power being greater than or equal to a maximum output power, and the secondary current being less than the maximum output current, the substantially constant output power determined by a sample of the output voltage, wherein the substantially constant output power is maintained by changing the duty cycle of the primary-side switch; and
a voltage control circuit configured to limit the output voltage to a maximum output voltage in response to the secondary current being less than the maximum output current, and the output power being less than the maximum output power.

10. The controller of claim 9 wherein the maximum output power is a predetermined value of the output power, the maximum output current is a predetermined value of the output current, and the maximum output voltage is a predetermined value of the output voltage.

11. The controller of claim 9 wherein the determination of the output power comprises:
an integrator configured to integrate the primary current, during an activation duration of the primary-side switch, to determine an integrated primary current,
a peak detector configured to detect a peak of the integrated primary current,
a multiplier circuit configured to multiplying an input voltage of the converter with the peak of the integrated primary current to form a numerator, and
a divider circuit configured to divide the numerator by the activation duration to determine the output power.

12. The controller of claim 11 further comprising a low pass filter (LPF) configured to dampen a high frequency oscillation of the primary current from the activation of the primary-side switch.

13. The controller of claim 9 wherein the controller is configured to determine the duty cycle by dividing an activation duration of the primary-side switch by an activation period equal to a period of an oscillator.

14. A method for forming a controller for controlling a resonant converter comprising:
configuring the controller to maintain an output current equal to an output power of the resonant converter divided by an output voltage of the resonant converter in response to a secondary current of a transformer of the resonant converter being greater than or equal to a maximum output current, wherein maintaining the output current ratio comprises changing a duty cycle of a primary-side switch of the resonant converter configured to gate a primary current of the transformer;
configuring the controller to maintain a substantially constant output power in response to the output power being greater than or equal to a maximum output power, and the secondary current being less than the maximum output current, wherein the substantially constant output power is determined by sampling the output voltage and maintaining the substantially

Assignees

• Semiconductor Components Ind Llc

Inventors

• RANA Dibyendu
• Wang Zhao-Jun

Classifications

• H02M3/33523 Primary

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

• H02M3/33507 Primary

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

• H02M1/08

  Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters · CPC title

• H02M1/32

  Means for protecting converters other than automatic disconnection · CPC title

• H02M2001/0009

  Electricity · mapped topic