Converter and control method thereof

Patent metadata

Field	Value
Publication number	US-2018062529-A1
Application number	US-201715677007-A
Country	US
Kind code	A1
Filing date	Aug 14, 2017
Priority date	Aug 31, 2016
Publication date	Mar 1, 2018
Grant date	—

Abstract

A converter includes a transformer, a main switch, an active clamp circuit, and a control circuit. The transformer includes a primary winding and a secondary winding, and is configured to receive an input voltage and output an output voltage to a load. The main switch is coupled between the primary winding and a primary ground terminal. The active clamp circuit includes an auxiliary switch and a clamp capacitor. The auxiliary switch is coupled to the clamp capacitor in series, and the active clamp circuit is coupled in parallel to the two terminals of the primary winding or the main switch, and is configured to clamp the voltage across the main switch when it is OFF. The control circuit outputs an auxiliary switch control signal to turn on the auxiliary switch when the voltage across the main switch is at its first peak of the resonant voltage.

First claim

What is claimed is:

1 . A converter, comprising:
a transformer comprising a primary winding and a secondary winding, and configured to receive an input voltage and output an output voltage to a load; a main switch electrically coupled between the primary winding and a primary ground terminal; an active clamp circuit comprising an auxiliary switch and a clamp capacitor, wherein the auxiliary switch is coupled to the clamp capacitor in series, and the active clamp circuit is coupled in parallel to the two terminals of the primary winding or the two terminals of the main switch, and configured to clamp the voltage across the main switch when the main switch is off; and a control circuit configured to output an auxiliary switch control signal to control the auxiliary switch to be turned on when the voltage across the main switch is at one of the 1st to Nth peaks of the resonant voltage, wherein N is an integer.

2 . The converter of claim 1 , wherein the control circuit further configured to control the auxiliary switch to be off before a secondary current decreases to zero.

3 . The converter of claim 1 , wherein when the converter is at a heavy load condition, the control circuit is configured to control the auxiliary switch to be turned on when the voltage across the main switch is at the first peak of the resonant voltage.

4 . The converter of claim 3 , further comprising a secondary rectifier unit electrically connected to the secondary winding, wherein a secondary current flows through the secondary rectifier unit when the secondary rectifier unit is on, and the voltage across the main switch is at the first peak of the resonant voltage when the secondary current decreases to zero.

5 . The converter of claim 4 , wherein the control circuit is configured to control the auxiliary switch to be turned on at the moment of delaying for a period of time in which the secondary current drops from maximum to zero after the main switch being turned off.

6 . The converter of claim 1 , wherein when the converter is at a medium load condition, the control circuit is configured to control the auxiliary switch to be turned on when the voltage across the main switch is at one of the 2nd to Nth peaks of the resonant voltage, wherein N is an integer.

7 . The converter of claim 6 , wherein the converter further comprises an auxiliary winding, and the control circuit is configured to detect the zero-crossing points of the voltage across the auxiliary winding shifted from negative to positive, calculate a moment delaying for a phase angle of 90 degrees after the zero-crossing points and output the auxiliary switch control signal correspondingly, to control the auxiliary switch to be turned on when the voltage across the main switch is at one of the 2nd to Nth peaks of the resonant voltage.

8 . The converter of claim 1 , wherein when the converter is at a light load condition, the control circuit is configured to output the auxiliary switch control signal to control the converter to be operated in a fixed frequency mode or a voltage control oscillating mode or a burst mode.

9 . The converter of claim 1 , wherein the converter comprises a detecting unit, and the control circuit comprises a calculating unit, wherein the detecting unit is configured to detect at least one of a voltage signal and a current signal to obtain a detecting signal, and the calculating unit is configured to receive the detecting signal and calculate a period of time in which the secondary current drops from maximum to zero.

10 . The converter of claim 9 , wherein the detecting signal comprises the input voltage and an auxiliary winding voltage, and the calculating unit is configured to calculate the period of time in which the secondary current drops from maximum to zero according to a turn ratio between the primary winding and the secondary winding of the transformer, a turn ratio between the secondary winding and the auxiliary winding of the transformer, the input voltage, the voltage value of the auxiliary winding during the period of time in which the secondary current drops from maximum to zero, and a conducting time of the main switch, and configured to output the auxiliary switch control signal according to the period of time in which the secondary current drops from maximum to zero, to control the auxiliary switch to be turned on when the voltage across the main switch is at the first peak of the resonant voltage.

11 . The converter of claim 10 , wherein the calculating unit comprises a first pin, a second pin, a third pin, and a first current source, wherein the first pin is configured to receive an input voltage signal output by the detecting unit, and the second pin is configured to receive the voltage value of the auxiliary winding during the period of time in which the secondary current drops from maximum to zero output by the detecting unit, the third pin is connected to a first resistor and the first current source, the calculating unit calculates the period of time in which the secondary current drops from maximum to zero according to the value of the first pin, of the second pin, of the third pin, and the conducting time of the main switch.

12 . The converter of claim 9 , wherein the detecting signal comprises a primary current peak value and a voltage value of an auxiliary winding during the period of time in which the secondary current drops from maximum to zero, and the calculating unit is configured to calculate the period of time in which the secondary current drops from maximum to zero according to a turn ratio between the primary winding and the secondary winding of the transformer, a turn ratio between the secondary winding and the auxiliary winding of the transformer, the primary current peak value, the voltage value of the auxiliary winding during the period of time in which the secondary current drops from maximum to zero, and a magnetizing inductance, and configured to output the auxiliary switch control signal according to the period of time in which the secondary current drops from maximum to zero, to control the auxiliary switch to be turned on when the voltage across the main switch is at the first peak of the resonant voltage.

13 . The converter of claim 12 , wherein the calculating unit comprises a first pin, a second pin, a third pin, a fourth pin, a first current source and a second current source, wherein the first pin is configured to receive the primary current peak value output by the detecting unit, and the second pin is configured to receive the voltage value of the auxiliary winding during the period of time in which the secondary current drops from maximum to zero output by the detecting unit, the third pin is connected to a first resistor and the first current source, the fourth pin is connected to a second resistor and the second current source, the calculating unit calculates the period of time in which the secondary current drops from maximum to zero according to the value of the first pin, of the second pin, of the third pin, and of the fourth pin.

14 . A control method for a converter, comprising:
receiving, by a control circuit, a detecting signal; calculating, by the control circuit, a period of time in which a secondary current drops from maximum to zero according to the detecting signal, to determine the moment of the first peak of the resonant voltage of the voltage across a main switch; and outputting, by the control circuit, an auxiliary switch control signal to control an auxiliary switch to be turned on when the voltage across the main switch is at one of the 1st to Nth peaks of the resonant voltage, wherein N is an i

Assignees

• Delta Electronics Inc

Inventors

• Song hai bin
• Xu Dao Fei
• Zhou Jian
• Yang Le Yang
• Fu Qi
• Zhang Jin Fa

Classifications

• H02M3/33569 Primary

  having several active switching elements (H02M3/3353 takes precedence) · CPC title

• H02M3/01

  Resonant DC/DC converters · CPC title

• H02M1/342

  Active non-dissipative snubbers · CPC title

• H02M1/0009

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

• Y02B70/10

  Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes · CPC title