AN1889 Datasheet, PDF (1/33 Pages) STMicroelectronics – The need to choose a high value of the fly-back voltage

AN1889
Application note
ESBT
STC03DE170HV in 3-phase auxiliary power supply
Introduction
The need to choose a high value of the fly-back voltage is well known to power supply
designers when efficiency and high duty cycle become important requirements. Three-
phase auxiliary power supplies, starting from a bulk voltage of 750 V, require theoretically
power transistors with a block voltage capability higher than 1200 V. Practical considerations
linked to better efficiency and safe margin may impose to choose devices with even higher
breakdown voltage (i.e. 1500 V, 1700 V). Looking at the power switches currently available,
while power bipolar transistors are strongly limited in switching frequency operation, Power
MOSFETs show a much lower current capability, which may limit their use to low power
applications. Recently available in the market, the ESBTs (Emitter Switched Bipolar
Transistors) represent a valuable and cost effective alternative for all those applications
where high voltage and high switching frequencies are a must.
This application note describes the realization of a 50 W 3-phase auxiliary power supply by
using the STC03DE170HV as main switch for the fly-back converter. Particular attention has
been given to the transformer design as well as to the ESBT driving circuit requirements.
August 2007
Rev 3
1/33
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