This document presents the results of a 3-Phase auxiliary power supply designed with the UC3845 PWM driver and an ESBT, the new STC03DE170, as main switch. This work is supplemented by the release of a 45W dual output SMPS demo board, widely used as auxiliary power supply in 3-phase motor drive applications. Moreover, the ESBT base driving circuit and some guidelines for the optimization of the power dissipation are given. The influence of parasitic capacitance on ESBTs is also described in detail. Furthermore, the slope compensation has been added in order to remove the oscillation during max input voltage and min load. Accordingly, the discussion in theory is presented. Finally, the realization methods of the output short circuit's protection function are provided.
This document presents the design results of a 3-phase auxiliary power supply based on the UC3845 PWM driver and the STCO3DE170 Emitter Switched Bipolar Transistor (ESBT). A 45W dual output SMPS demo board is used as a reference implementation for 3-phase motor drive applications. The note covers the base driving circuit design, optimization of power dissipation, and protection methods.
The document details the design of a proportional base driving circuit using a current transformer to optimize performance across variable loads. It also analyzes the influence of parasitic capacitance between the ESBT collector and ground on turn-on power dissipation and ringing, providing a small signal equivalent circuit model.
| Output Voltage 1 | 15V/2A |
|---|---|
| Output Voltage 2 | 15V/1A |
| Maximum Output Power | 45W |
| Converter Efficiency | >75% |
| Switching frequency | 100 kHz |
| Reflected fly back voltage | 400 V |
The design uses the UC3845 PWM driver.
The main switch is the STCO3DE170 Emitter Switched Bipolar Transistor (ESBT).
Slope compensation is added to remove oscillation during high input voltage and minimum load conditions.