July 2007

Rev 1

1/21

AN2528

Application note

Very wide input voltage range 6 W SMPS for metering

Introduction

This document presents the design of a universal input power supply for metering

applications. The design is mainly based on the following ST parts: an L6565 PWM driver

and STC04IE170HP as the main switch. It is linked with the release of the STEVAL-

IP001Vxx demo board (see Figure 1 below). The design is a complete solution for a 5 W

single output SMPS, which is widely used as a power supply in metering applications.

However the design method can be applied to an SMPS suitable for other applications

working on a three-phase mains and it can easily be upgraded for higher output power.

The ESBT base driving circuit as well as guidelines for the optimization of the power

dissipation are given.

The influence of parasitic capacitances of the transformer on the ESBT is also explained in

detail.

Finally, the most important waveforms and thermal results are given in Section 5 and

Section 6. They demonstrate the benefits of using a QR flyback with ESBT.

Refer to AN1889 and AN2254 for the overall design of an auxiliary power supply using

ESBT in flyback QR with L6565, while refer to AN2454 for the small signal power switch

model with all parasitic components.

Figure 1.

STEVAL-ISA030V1

www.st.com