计算推挽式变压器实例.pdf

SWITCHING POWER SUPPLY DESIGN: LM5030 PUSH-PULL CONVERTER Written by Michele Sclocchi michele.sclocchi@ National Semiconductor Push-pull topology is a derivative of two forward converters operating 180 degrees out of phase. This configuration allows operation in the first and third quadrant of the hysteresis loop, with a better utilization of the magnetic core of the transformer. The maximum voltage stress of the switching MOSFETs is twice the input voltage which is the same as the the forward topology. A current mode PWM converter avoids run away of the flux core by monitoring the current of each of the push-pull transistors and forcing alternate current pulses to have equal amplitude. This document is an explanation of the equations used in an accompanying Mathcad file. The Mathcad file helps with the calculation of the external components of a typical Push-Pull topology. Notes for the Mathcad file: Write down the power supply requirements in the following boxes: X := xx Get the results from the following boxes: Rsultsxx := Listed below are the equations used to calculate the circuit: Input voltage: - Minimum input voltage: Vi min := 35⋅volt - Maximum input voltage: Vi max := 75⋅volt - Nominal input voltage: Vi nom := 48⋅volt Output: - Nominal output voltage, maximum output ripple, minimum output current, maximum output current Vo1 := 12⋅volt Vrp1 := 100⋅mV Io1min := 0.5⋅amp Io1max := 5⋅amp Vo2 := 3.7⋅volt Vrp2 := 120⋅mV Io2min := 0.1⋅amp Io2max := 0.500⋅amp Vdfw := 0.9⋅volt (diodes forward voltage drop) Pomin := (Vo1 + Vdfw) ⋅Io1min + (Vo2 + Vdfw) ⋅Io2min