Methods and circuits for sensing isolated power converter output voltage across the isolation barrier

Patent metadata

Field	Value
Publication number	US-11711023-B2
Application number	US-202217742846-A
Country	US
Kind code	B2
Filing date	May 12, 2022
Priority date	May 14, 2021
Publication date	Jul 25, 2023
Grant date	Jul 25, 2023

Abstract

A control circuit for an isolated power converter includes a first sensing circuit that senses a secondary side output voltage and produces a pulse wave modulation (PWM) signal having a duty cycle that is proportional to a value of the secondary side output voltage. The PWM is transferred across the converter isolation barrier to the primary side, and a primary side circuit receives the PWM signal and outputs a control signal. A controller determines the value of the secondary side output voltage from the control signal and uses the value to control primary side power switching devices of the isolated power converter to regulate the secondary side output voltage at a selected value.

First claim

The invention claimed is:

1. A control circuit for an isolated power converter, comprising:
a first circuit that senses a secondary side output voltage of the isolated power converter and produces a pulse wave modulation (PWM) signal having a duty cycle that is proportional to a value of the secondary side output voltage;
a first isolator that transfers the PWM signal across an isolation barrier to a primary side of the isolated power converter;
a first primary side circuit that receives the PWM signal from the first isolator and outputs a control signal;
a first microcontroller; and
a feedback circuit comprising:
a second circuit that senses the secondary side output voltage of the isolated power converter and uses the sensed secondary side output voltage and a reference voltage to produce an error voltage; and
a second isolator that transfers the error voltage across the isolation barrier to the primary side of the isolated power converter;
wherein a steady state output voltage is determined using the error voltage;
wherein the first microcontroller calculates a steady state gain using the steady state output voltage and a steady state value of the control signal, and uses the steady state gain to calibrate an actual gain of the first circuit that senses the secondary side output voltage to determine an actual secondary side output voltage; and
wherein the first microcontroller controls primary side power switching devices of the isolated power converter to regulate the secondary side output voltage at a selected value.

2. The control circuit of claim 1 , wherein the first primary side circuit comprises a filter that filters the PWM signal from the first isolator;
wherein the control signal comprises a filtered PWM signal having a voltage value proportional to the value of the secondary side output voltage.

3. The control circuit of claim 2 , wherein the first primary side circuit comprises a switch that shapes the PWM signal received from the first isolator by reducing a falling time and rising time of the PWM signal.

4. The control circuit of claim 1 , wherein the first circuit that senses the secondary side output voltage comprises a comparator that produces the PWM signal.

5. The control circuit of claim 1 , wherein the first circuit that senses the secondary side output voltage comprises a second microcontroller that produces the PWM signal.

6. The control circuit of claim 5 , wherein the first isolator outputs the PWM signal to the first microcontroller;
wherein the first microcontroller measures a logic high time interval (T_high) of the PWM signal and uses the T_high interval to control the primary side power switching devices of the isolated power converter to regulate the secondary side output voltage at the selected value.

7. The control circuit of claim 1 , wherein the second circuit that senses the secondary side output voltage comprises an error amplifier that produces the error voltage.

8. The control circuit of claim 1 , wherein the first primary side circuit comprises a sampling circuit including a capacitor that is charged and discharged according to a duty cycle of the PWM signal received from the first isolator;
wherein the first microcontroller samples a voltage across the capacitor at a sampling time set by a period of the PWM signal received from the first isolator;
wherein the control signal comprises the sampled voltage across the capacitor.

9. The control circuit of claim 1 , wherein the first and second circuits that sense the secondary side output voltage comprise a second microcontroller that produces the PWM signal and a PWM error signal from the secondary side output voltage;
wherein the first isolator transfers the PWM signal across the isolation barrier;
wherein the second isolator transfers the PWM error signal across the isolation barrier;
wherein the first primary side circuit filters the PWM signal and outputs a first control signal;
wherein a second primary side circuit comprises a filter that filters the PWM error signal and outputs a second control signal;
wherein the first microcontroller uses the first control signal and the second control signal to control the primary side power switching devices of the isolated power converter to regulate the secondary side output voltage at the selected value.

10. A method for controlling an isolated power converter, comprising:
using a first circuit that senses a secondary side output voltage of the isolated power converter and produces a pulse wave modulation (PWM) signal having a duty cycle that is proportional to a value of the secondary side output voltage;
using a first isolator to transfer the PWM signal across an isolation barrier to a primary side of the isolated power converter;
using the PWM signal received from the first isolator at the primary side to produce a control signal;
using a first microcontroller to determine the value of the secondary side output voltage from the control signal;
using a second circuit that senses the secondary side output voltage of the isolated power converter and uses the sensed secondary side output voltage and a reference voltage to produce an error voltage; and
using a second isolator to transfer the error voltage across the isolation barrier to the primary side of the isolated power converter;
wherein a steady state output voltage is determined using the error voltage;
wherein the first microcontroller calculates a steady state gain using the steady state output voltage and a steady state value of the control signal, and uses the steady state gain to calibrate an actual gain of the first circuit that senses the secondary side output voltage to determine an actual secondary side output voltage; and
wherein the first microcontroller controls primary side power switching devices of the isolated power converter to regulate the secondary side output voltage at a selected value.

11. The method of claim 10 , wherein the control signal is produced using a first primary side circuit comprising a filter that filters the PWM signal from the first isolator;
wherein the control signal comprises a filtered PWM signal having a voltage value proportional to the value of the secondary side output voltage.

12. The method of claim 11 , comprising shaping the PWM signal received from the first isolator at the primary side by reducing a falling time and rising time of the PWM signal.

13. The method of claim 10 , wherein the first circuit that senses the secondary side output voltage comprises a comparator that produces the PWM signal.

14. The method of claim 10 , wherein the first circuit that senses the secondary side output voltage comprises a second microcontroller that produces the PWM signal.

15. The method of claim 14 , wherein the first isolator outputs the PWM signal to the first microcontroller;
wherein the first microcontroller measures a logic high time interval (T_high) of the PWM signal and uses the T_high interval to control the primary side power switching devices of the isolated power converter to regulate the secondary side output voltage at the selected value.

16. The method of claim 10 , wherein the second circuit that senses the secondary side output voltage comprises an error amplifier that produces the error voltage.

17. The method of claim 10 , wherein the first primary side circuit comprises a sampling circuit including a capacitor that is charged and discharged according to a duty cycle of the PWM signal received from the first isolator;
wherein the first microcontroller samples a voltage across the capacitor

Assignees

• Univ Kingston

Inventors

• Liu Yan-Fei
• Chen Yang
• He Binghui
• Liu Wenbo
• Sheng Bo

Classifications

• H02M3/33576 Primary

  having at least one active switching element at the secondary side of an isolation transformer · CPC title

• H02M1/0003

  Details of control, feedback or regulation circuits · CPC title

• H02M3/01 Primary

  Resonant DC/DC converters · CPC title

• H02M3/3353 Primary

  having at least two simultaneously operating switches on the input side, e.g. "double forward" or "double (switched) flyback" converter · CPC title

• H02M3/33515

  with digital control · CPC title