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

A rectifier having an input and an output and a method of controlling the rectifier. The rectifier comprises: (1) switching circuitry coupled between the input and the output, the switching circuitry adapted to operate in selected one of (a) an active bidirectional mode of operation and (b) an inactive unidirectional mode of operation to rectify substantially alternating current at the input to produce substantially direct current at the output and (2) control circuitry coupled between the rectifier output and a control input of the switching circuitry, the control circuitry capable of sensing an output current level of the rectifier and transitioning the switching circuitry between the active bidirectional mode and the inactive unidirectional mode as a function of the output current level thereby to prevent substantial reverse power flow through the rectifier. The rectifier is particularly useful in power systems having a plurality of rectifiers operating in parallel to prevent one rectifier from driving the other.

Circuit and method for controlling a synchronous rectifier converter

A synchronous rectifier for use with a clamped-mode power converter uses in one embodiment a hybrid rectifier with a MOSFET rectifying device active in one first cyclic interval of the conduction/nonconduction sequence of the power switch and a second rectifying device embodied in one illustrative embodiment as a low voltage bipolar diode rectifying device active during an alternative interval to the first conduction/nonconduction interval. The gate drive to the MOSFET device is continuous at a constant level for substantially all of the second interval which enhances efficiency of the rectifier. The bipolar rectifier device may also be embodied as a MOSFET device. The subject rectifier may be used in both forward and flyback power converters.

Low loss synchronous rectifier for application to clamped-mode power converters

Design trade-offs for different implementations of the forward power converter with synchronous rectifiers are presented, and effects of the synchronous rectifier driving method on the conversion efficiency are evaluated. Specifically, the merits and limitations of the RCD-clamp and active-clamp reset approaches for a power converter with self-driven synchronous rectifiers are discussed. Estimates of the upper limits of the efficiency improvements of the discussed synchronous rectification approaches relative to the Schottky diode implementation are derived. Finally, experimental comparisons of efficiencies for an offline, 3.3 V/20 A forward power converter power stage are presented and compared with the theoretically estimated ones. >

Evaluation of synchronous-rectification efficiency improvement limits in forward converters

A power converter with a self synchronized synchronous rectifier includes one or two drive windings to provide positive drive to the control electrodes of the controlled switches (FETs) of a self synchronized synchronous rectifier. The polarities of these windings are selected so that the switched devices are driven appropriately to rectify the periodic signal output of the secondary winding of the power transformer of the converter. In some arrangements one or two drive windings are included as extra windings in the power transformer and connected to provide the proper polarity drive signals. The turn ratios of the drive windings to the other windings are selected to provide the proper gate drive signal levels. In an alternative arrangement a separate drive transformer may be provided to supply the gate drive signals.

Self-synchronized drive circuit for a synchronous rectifier in a clamped-mode power converter

A simple and efficient MOSFET synchronous rectification circuit suitable for forward DC-DC power converters is proposed. The main feature of this circuit is the addition of a capacitor in parallel with the drain source of the MOSFET used as a rectifying device. This capacitor extends the conduction period of the MOSFET used as a freewheeling device. As a result, a 92% efficiency at 5 V for 10 A output is achieved. >

A simple and efficient synchronous rectifier for forward DC-DC converters

A highly efficient, low-profile 300-W power pack is developed for telecommunications systems. To reduce power loss and component size, the power stage is divided into three 100-W on-board power supply modules, each with a simple and efficient MOSFET synchronous rectifier. Efficiency is 90% at 5 V for 60-A output, and power pack width is less than 10 mm. >

A highly efficient, low-profile 300-W power pack for telecommunications systems

A high-efficiency low-profile 30 W power supply module suitable for telecommunications systems, such as the integrated services digital network (ISDN), has been developed This module has an efficiency of 90% and is only 72 mm high A simple MOSFET synchronous rectifier and a low-profile transformer with a flat E core and planar windings were used Its volume is 37 cm/sup 3/ and its power density is 08 W/cm/sup 3/ (13 W/in/sup 3/) It is half the size of a conventional module under natural convection cooling conditions >

N. Murakami

Papers

A simple and efficient synchronous rectifier for forward DC-DC converters

A highly efficient, low-profile 300-W power pack for telecommunications systems

A high-efficiency 30 W board mounted power supply module