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

2/10

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 RDS(on) per area, low gate charge and high switching performance. The device is available in the TO-220, TO-

247 and TO-220FH packages.

The demonstration board is designed in accordance with the specifications in Table 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
	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.

3/10