CONVERTER AND CONTROL METHOD THEREOF

• US 20190280604A1
• Filed: 01/13/2019
• Published: 09/12/2019
• Est. Priority Date: 03/09/2018
• Status: Active Grant

• Current Assignee: Delta Electronics Incorporated
• Original Assignee: Delta Electronics Incorporated
• Inventors: SONG, Hai-Bin, FU, Qi, ZHOU, Jian, XU, Dao-Fei, ZHANG, Jin-Fa
• Granted Patent: US 10,644,606 B2
• Time in Patent Office: Days
• CPC Class Codes: H02M 1/0032 Control circuits allowing low power mode operation, e.g. in standby mode
• CPC Class Codes: H02M 1/0054 Transistor switching losses periodically suspending operation of switching converter in low power mode H02M1/0035
• CPC Class Codes: H02M 1/088 for the simultaneous control of series or parallel connected semiconductor devices
• CPC Class Codes: H02M 1/348 Passive dissipative snubbers
• CPC Class Codes: H02M 3/33569 having several active switching elements H02M3/3353 takes precedence
• CPC Class Codes: H02M 3/33576 having at least one active switching element at the secondary side of an isolation transformer
• CPC Class Codes: H03K 5/24 the characteristic being amplitude
• CPC Class Codes: Y02B 70/10 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

Abstract

A converter includes a transformer, a primary side switch, a load detection circuit, a state detection circuit and a control circuit. The transformer is configured to output a voltage to a load. The primary side switch is coupled to a primary winding and a primary ground terminal. The load detection circuit is configured to detect a load state of the load and output a load state signal. The state detection circuit is configured to detect a reference time point. The control circuit is configured to output a control signal to turn on or off the primary side switch. The control circuit further sets a blanking time according to the load state signal, such that the primary side switch is turned on when a drain-source voltage of the primary side switch is at a valley of the resonance after the blanking time starting from the reference time point.

Claims

1. A converter, comprising:

a transformer comprising a primary winding and a secondary winding;

a primary side switch electrically coupled to the primary winding and a primary ground terminal;

a secondary side switch electrically coupled to the secondary winding and a load;

a load detection circuit configured to detect a load state and correspondingly output a load state signal;

a state detection circuit configured to detect a reference time point; and

a control circuit configured to output a control signal to turn on or turn off the primary side switch, wherein the control circuit is configured to set a blanking time according to the load state signal, such that the primary side switch is turned on when a drain-source voltage of the primary side switch is at a valley of a resonance after the blanking time starting from the reference time point.

2. The converter of claim 1, wherein a length of the blanking time is negative correlation with a magnitude of the load state signal.

3. The converter of claim 2, wherein when the converter is in very light load, the control circuit generates a turn on signal to turn on the primary side switch after the blanking time starting from the reference time point without considering the valley.

4. The converter of claim 1, wherein the state detection circuit is configured to detect the drain-source voltage of the primary side switch, and records a time point when the drain-source voltage of the primary side switch starts to oscillate as the reference time point.

5. The converter of claim 4, wherein the state detection circuit comprises a sensing capacitor and a comparator, a first terminal of the sensing capacitor is electrically coupled to the primary side switch and the primary winding, a second terminal of the sensing capacitor is electrically coupled to the comparator, when the drain-source voltage of the primary side switch starts to oscillate, the sensing capacitor generates corresponding voltage change and current change, so that the comparator correspondingly outputs a start signal to the control circuit to record the reference time point.

6. The converter of claim 4, wherein the transformer comprises a primary auxiliary winding, the state detection circuit comprises a comparator;

two terminals of the primary auxiliary winding are respectively connected to a first input terminal of the comparator and the primary ground terminal, when a cross voltage of the primary auxiliary winding starts to oscillate, the comparator correspondingly outputs a start signal to the control circuit to record the reference time point.

7. The converter of claim 6, wherein a second terminal of the comparator is connected to the primary ground terminal, so that the comparator outputs the start signal to the control circuit to record the reference time point when the cross voltage of the primary auxiliary winding starts to oscillate and cross zero voltage.

8. The converter of claim 6, wherein a second terminal of the comparator is connected to a reference voltage, so that the comparator outputs the start signal to the control circuit to record the reference time point when the cross voltage of the primary auxiliary winding starts to oscillate and cross the reference voltage.

9. The converter of claim 1, wherein the state detection circuit is configured to detect a drain-source voltage of the secondary side switch and records a time point when the drain-source voltage of the secondary side switch starts to oscillate as the reference time point.

10. The converter of claim 1, wherein the load detection circuit is configured to detect a negative peak value of a drain-source voltage of the secondary side switch, and outputs the load state signal according to the negative peak value of the drain-source voltage of the secondary side switch.

11. The converter of claim 1, wherein the control circuit detects whether a drain-source voltage of the secondary side switch is at a peak value of a resonance through a peak detection circuit, and the primary side switch is turned on when the drain-source voltage of the secondary side switch is at the peak value of the resonance after the blanking time starting from the reference time point.

12. The converter of claim 1, wherein the control circuit detects whether the drain-source voltage of the primary side switch is at the valley the resonance through a valley detection circuit, and the primary side switch is turned on when the drain-source voltage of the primary side switch is at the valley of the resonance after the blanking time starting from the reference time point.

13. The converter of claim 1, wherein the state detection circuit is configured to detect a time point when a secondary current in the secondary winding drops to zero, and records the time point as the reference time point.

14. A control method of a converter, comprising:

detecting a load state by a load detection circuit and correspondingly outputting a load state signal;

setting a blanking time by a control circuit according to the load state signal;

detecting a reference time point by a state detection circuit; and

outputting a control signal to a primary side switch of the converter by the control circuit so as to turn on the primary side switch when a drain-source voltage of the primary side switch is at a valley of a resonance after the blanking time starting from the reference time point.

15. The control method of claim 14, further comprising:

detecting the drain-source voltage of the primary side switch by the state detection circuit, and recording a time point when the drain-source voltage of the primary side switch starts to oscillate as the reference time point.

16. The control method of claim 15, further comprising:

detecting an oscillation of the drain-source voltage of the primary side switch by a sensing capacitor; and

outputting a start signal to the control circuit to record the reference time point by the comparator.

17. The control method of claim 14, further comprising:

detecting an oscillation of the drain-source voltage of the primary side switch by a primary auxiliary winding of the transformer.

outputting a start signal to the control circuit to record the reference time point by a comparator when detecting an oscillation of the cross voltage of a primary auxiliary winding of a transformer of the converter.

18. The control method of claim 17, wherein the comparator outputting the start signal to the control circuit when the cross voltage of the primary auxiliary winding starts to oscillate and cross zero.

19. The control method of claim 17, wherein the comparator outputting the start signal to the control circuit when the cross voltage of the primary auxiliary winding starts to oscillate and cross a reference voltage.

20. The control method of claim 14, wherein a length of the blanking time is negative correlation with a magnitude of the load state signal.

21. The control method of claim 14, further comprising:

detecting a drain-source voltage of a secondary side switch of a secondary side rectifier circuit of the converter by the state detection circuit; and

recording a time point when the drain-source voltage of the secondary side switch starts to oscillate as the reference time point.

22. The control method of claim 14, further comprising:

detecting a time point when a secondary current in a secondary winding becomes zero; and

recording the time point as the reference time point.