Flyback derived power convertor topologies are attractive because of their relative simplicity when compared with other topologies used in low power applications. Incorporation of active-clamp circuitry into the flyback topology serves to recycle transformer leakage energy while minimizing switch voltage stress. The addition of the active-clamp circuit also provides a mechanism for achieving zero-voltage-switching (ZVS) of both the primary and auxiliary switches. ZVS also limits the turn-off di/dt of the output rectifier, reducing rectifier switching losses, and switching noise due to diode reverse recovery. This paper analyzes the behavior of the ZVS active-clamp flyback operating with unidirectional magnetizing current and presents design equations based on this analysis. Experimental results are then given for a 500 W prototype circuit illustrating the soft-switching characteristics and improved efficiency of the power converter. Results from the application of the active-clamp circuit as a low-loss turn-off snubber for IGBT switches is also presented.

Utilization of an active-clamp circuit to achieve soft switching in flyback converters

A power converter nearly losslessly delivers energy and recovers energy from capacitors associated with controlled rectifiers in a secondary winding circuit, each controlled rectifier having a parallel uncontrolled rectifier. First and second primary switches in series with first and second primary windings, respectively, are turned on for a fixed duty cycle, each for approximately one half of the switching cycle. Switched transition times are short relative to the on-state and off-state times of the controlled rectifiers. The control inputs to the controlled rectifiers are cross-coupled from opposite secondary transformer windings.

High efficiency power converter

Resonant DC to DC flyback converter topologies having one or more transformers and a primary side resonant subcircuit are optimally controlled by providing independently derived duty cycles for driving the main transformer and resonant semiconductor switches to prevent cross-conduction thereof and minimize reverse recovery losses.

Controller for high efficiency resonant switching converters

The evolution of the forward power converter is first reviewed, in a tutorial fashion, from the classic to the contemporary. Salient features are then discussed and results are compiled to form practical design guidelines. Performance parameters are discussed, including operating principle, voltage conversion ratio, efficiency, device stresses, small-signal dynamics, noise and EMI and parts count. The extension of each converter to a synchronous rectifier and/or to a current doubler is also discussed.

The forward converter: from the classic to the contemporary

An interleaved flyback electrical power converter system having a plurality of flyback power converters operated in continuous mode, each converter utilizing a power switch operated under zero voltage switching conditions. The interleaved flyback power converter system is highly efficient and compact, and is suitable for use in high power, high frequency applications.

Interleaved continuous flyback power converter system

A zero voltage switched flyback power converter which realizes soft switching for every semiconductor is proposed. The sinusoidal resonant current flows through the secondary side rectifier diode and zero current switching of the diode is realized. Diode recovery is not generated. The proposed converter can operate with constant frequency pulse width modulation. High frequency switching and low noise are achieved. >

N. Nagagata

Papers

Zero voltage switching approach for flyback converter