ST AN2936 APPLICATION NOTE

AN2936

Application note

10 W SMPS with HV power MOSFET and the L6565

for three-phase industrial applications

Introduction

This document introduces a solution for industrial power supplies fed by a three-phase
mains. It uses a high voltage power MOSFET with 1500 V breakdown voltage to optimize
the operation of a quasi-resonant flyback converter based on the primary controller L6565.

The STEVAL-ISA034V1 demonstration board has been designed and developed for low
power applications. The board features two isolated outputs, 12 V and 5 V, and is capable of
delivering up to 10 W.

The board can be ordered through order code STEVAL-ISA034V1.

Figure 1. 10 W board prototype

AM01332v1

March 2009 Rev 1 1/10

www.st.com

Contents AN2936

Contents

1 Demonstration board description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.1 Bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2 Related documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

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AN2936 Demonstration board description

1 Demonstration board description

The STEVAL-ISA034V1 demonstration board is based on a quasi-resonant flyback
converter topology and uses the STP3N150 1500 V power MOSFET as the primary switch.
The STP3N150 employs STMicroelectronics’ proprietary high voltage Mesh Overlay
technology. Characteristic of this technology, the switch features very low R
low gate charge and high switching performance. The device is available in the TO-220, TO­247 and TO-220FH packages.

The demonstration board is designed in accordance with the specifications in Ta b l e 1 .

Table 1. Main specifications

Parameter Value

Input voltage range 185 to 460 Vac

Input frequency range 50/60 Hz

Output 1 12 V @ 0.6 A

Output 2 5 V @ 0.55 A

Output power 10 W

DS(on)

per area,

Safety EN60950

EMI EN55014

The input section is equipped with two connectors: CON1 for 400 Vac input voltage, and
CON2 for 230 Vac input voltage. The output voltages are available on CON3, with a shared
ground between the two outputs.

The converter is controlled by the L6565, a primary controller for quasi-resonant ZVS (zero­voltage switching) flyback converters. The device is capable of controlling power variations
in the mains voltage by means of line voltage feed-forward. In light load conditions the
device features a special function which automatically lowers the operating frequency while
maintaining operation as close to ZVS as possible. In addition to very low startup and
quiescent currents, this feature helps to maintain low consumption from the mains in light
load conditions.

The device also includes a disable function, an on-chip filter on current sense, an error
amplifier with a precise reference voltage for primary regulation and effective two-level
overcurrent protection. The transformer reflected voltage is set to 400 V, providing enough
margin for leakage inductance voltage spikes. A small RCD clamper circuit is used to limit
excess voltage on the drain of the power MOSFET. During normal operation, the L6565 is
powered by the auxiliary winding of the transformer, via diode D7. A spike killer circuit for the
auxiliary voltage fluctuations is present, but not connected (Q2, C12, R15). The primary
current is measured using an external sensing resistor (R21) for current mode operation.
Output voltage regulation is performed using secondary feedback on the 5 V output.

The feedback network consists of a programmable voltage reference, TL431, driving an
optocoupler which ensures the required insulation between the primary and secondary
sections. The optotransistor drives the feedback pin (COMP), which controls the operation
of the device. LC filters have been added on both of the outputs to reduce the high
frequency ripple, using moderate output capacitor values.

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