Control method and control apparatus for flyback circuit

Abstract

The present invention discloses a control method and a control apparatus for a Flyback circuit. The Flyback circuit includes a primary switch, a secondary rectifier unit, a transformer and an output capacitor. The secondary rectifier unit includes a first terminal and a second terminal, which are electrically connected to the transformer and the output capacitor, respectively. In the control method for a Flyback circuit, after the secondary rectifier unit is controlled to be turned on once or twice according to the input voltage and / or output power of the Flyback, the primary switch is turned on to achieve the zero-voltage-switching. According to the invention, the zero-voltage-switching (ZVS) of the primary switch can be achieved under the entire input voltage range and the entire load range without adding additional power devices.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 201611108738.5 filed in P.R. China on Dec. 6, 2016, the entire contents of which are hereby incorporated by reference.[0002]Some references, if any, which may include patents, patent applications and various publications, may be cited and discussed in the description of this invention. The citation and / or discussion of such references, if any, is provided merely to clarify the description of the present invention and is not an admission that any such reference is “prior art” to the invention described herein. All references listed, cited and / or discussed in this specification are incorporated herein by reference in their entireties and to the same extent as if each reference was individually incorporated by reference.TECHNICAL FIELD[0003]The present invention relates to a control method and a control apparatus for a Flyback circuit, and par...

AI Technical Summary

Benefits of technology

The present invention solves the problem of high switching losses in the Flyback circuit. It achieves ZVS (Zero Voltage Switching) of the primary switch for the entire input voltage and load range without adding any additional power devices. Additionally, it improves the efficiency of the light load and reduces the loss caused by the control strategy.

Problems solved by technology

It can achieve zero-voltage-switch (ZVS) of primary switch at low line input condition, but for high line input condition, the turning on loss of primary switch is still considerable despite its valley-switching operation.

As frequency rises, switching loss of the primary switch of the Flyback converter rise in direct proportion, which leads to serious efficiency drop, especially at high line input condition.

Although the active clamp Flyback can achieve ZVS of the primary switch, an additional switch is needed, thereby increase cost.

To apply the above method, there is a limiting condition: the circuit must operate in a BCM (boundary conduction mode) within the entire input voltage range and the entire load range; if it operates in a DCM (discontinuous conduction mode), that method cannot be adopted.

This has a serious impact on the light load efficiency at high line input condition.

Therefore, under the condition of high-voltage input and light load, the operating frequency will become very high, and the switching loss will seriously affect the efficiency.

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