Converter and control method thereof

• US 10,644,606 B2
• Filed: 01/13/2019
• Issued: 05/05/2020
• 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
• Primary Examiner(s): Tran, Nguyen
• Application Number:
  US16/246,539
• Publication Number:
  US 20190280604A1
• Time in Patent Office: 478 Days
• Field of Search: 363 2112- 2118
• 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, wherein the state detection circuit is configured to detect a time point when a secondary current in the secondary winding drops to zero or when the drain-source voltage of the primary side switch starts to oscillate, and sets the reference time point based on the 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 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.

5. 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.

6. 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, wherein the control method further comprises;

detecting a time point when the drain-source voltage of the primary side switch starts to oscillate by the state detection circuit or when a secondary current in a secondary winding becomes zero; and

setting the reference time point based on the time point.

7. The control method of claim 6, 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.

8. The control method of claim 6, wherein a length of the blanking time is negative correlation with a magnitude of the load state signal.