July 2011

Doc ID 018586 Rev 2

1/16

AN3360

Application note

3.2 W LED power supply based on HVLED805

Introduction

This application note describes the demonstration board of the all-primary sensing switching

regulator HVLED805 and presents the results of its bench evaluation. The board

implements a 3.2 W (16 V / 0.2 A) wide range mains LED power supply with constant

current.

HVLED805 combines a high-performance low-voltage PWM controller chip and an 800 V

avalanche rugged power MOSFET in the same package. The PWM chip is a quasi-resonant

(QR) current mode controller IC specifically designed for QR ZVS (zero voltage switching at

switch turn-on) flyback converters. The device provides constant output current (CC)

regulation using primary sensing feedback. This eliminates the need for the optocoupler, the

secondary voltage reference, and also the current sensor, while still maintaining quite

accurate regulation. The device can provide a constant output voltage regulation (CV). This

makes the application able to work safely when the LED string opens due to a failure.

However, an auxiliary winding is required in the transformer to correctly perform CV/CC

regulation, the chip is able to power itself directly from the rectified mains. This is useful

during CC regulation, where the flyback voltage generated by the winding drops.

Figure 1.

STEVAL-ILL037V1 demonstration board image

www.st.com