Flyback converter and method of operating the same
AssigneeInnoscience (Suzhou) Technology Co., Ltd.
InventorsTao Zhang, Jihua Li, Yulin Chen
Life of this patent
Estimating the term…
Abstract
The subject application provides a zero-voltage switching flyback converter comprising: a transformer having a primary winding and a secondary winding; a primary switch and a secondary switch for conducting the currents flowing in the primary winding and secondary winding respectively. A timing control method for operating the flyback converter are provided to accomplish zero-voltage switch by turning on the secondary switch twice within one switching power cycle.
Claims16
A flyback converter comprising:
- a transformer having a primary winding receiving an input voltage and a secondary winding providing an output voltage;
- a primary switch coupled to the primary winding, having a source terminal, a drain terminal and a gate terminal;
- a secondary switch coupled to the secondary winding, having a source terminal, a drain terminal and a gate terminal;
- a zero-crossing detection (ZCD) circuit having a first input connected to a first end of the secondary winding for detecting a drain-to-source voltage of the secondary switch, a second input connected to a second end of the secondary winding for detecting the output voltage, the ZCD circuit is configured to generate a ZCD signal based on the drain-to-source voltage of the secondary switch and the output voltage;
- a controller configured to obtain the ZCD signal from the ZCD circuit via a ZCD node and generate control signals to turn the primary switch and the secondary switch on and off alternately such that:
- the primary switch is turned on to conduct a primary current in the primary winding to start a power cycle when a voltage across the drain terminal and the source terminal of the primary switch reaches a value less than a reference voltage value;
- the primary switch is turned off when the primary current reaches a value greater than a reference current value;
- the secondary switch is turned on, for a first time within the power cycle, to conduct a secondary current in the secondary winding after the primary switch being turned off for a non-overlapping delay;
- the secondary switch is turned off, for the first time within the power cycle, when the secondary current reaches a zero-value;
- the secondary switch is turned on, for a second time within the power cycle, in response to a falling edge of the ZCD signal occurring immediately after an event count reaches a corresponding count threshold;
- the secondary switch is turned off, for the second time within the power cycle, following the secondary switch being turned on for a second-on time interval;
- and
- the primary switch is turned on to initiate a next power cycle following the secondary switch being turned off for the second time within the power cycle for a second-off time interval.
A method of operating a flyback converter having a transformer comprising a primary winding receiving an input voltage and a secondary winding providing an output voltage, a primary switch being coupled to the primary winding and having a source terminal, a drain terminal and a gate terminal, and a secondary switch being coupled to the secondary winding and having a source terminal, a drain terminal and a gate terminal, the method comprising:
- turning on the primary switch by a controller to start a power cycle and conduct a primary current in the primary winding when a switching voltage reaches a value less than a reference voltage value, wherein the switching voltage is indicative of a drain-to-source voltage of the primary switch;
- turning off the primary switch by the controller when the primary current reaches a value greater than a reference current value;
- turning on, for a first time within the power cycle, the secondary switch by the controller to conduct a secondary current in the secondary winding after the primary switch being turned off for a non-overlapping delay;
- turning off, for the first time within the power cycle, the secondary switch by the controller when the secondary current reaches a zero-value;
- receiving a zero-current detection (ZCD) signal from a ZCD circuit via a ZCD node, wherein the ZCD signal is generated by the ZCD circuit based on a drain-to-source voltage of the secondary switch and the output voltage;
- turning on, for a second time within the power cycle, the secondary switch by the controller in response to a falling edge of the ZCD signal occurring immediately after an event count reaches a corresponding count threshold;
- turning off, for the second time within the power cycle, the secondary switch by the controller after the secondary switch being turned on for a second-on time interval;
- and
- turning on the primary switch by the controller to initiate a next power cycle following the secondary switch being turned off for the second time within the power cycle for a second-off time interval.
Dependencies are inferred from the claim text.