September 2011

Doc ID 018890 Rev 1

1/28

AN3410

Application note

A 93% efficient LED driver solution for the US market

Introduction

This application note describes an LED driver that meets present requirements for the US

market. It utilizes ST’s L6564 power factor controller in an unconventional circuit to regulate

the input power to a step-down switching regulator. The circuit also compensates for

variations in LED voltage drop, to maintain the average output current in a tight band over a

wide range of line voltage and LED characteristics. While the input current waveform is not

perfectly sinusoidal, power factor and harmonic content are well within the requirements for

the US commercial market. The form factor was designed to fit into the PAR38 envelope -

the driver and LEDs can be used to replace 65 W incandescent floodlamps.

– Output current 350 mA +/-3% over 90 V-138 V line range

– Load: 18 series-connected 1 W LEDs

– Efficiency > 93%

– Power factor > 0.97

– Dimmer safe

– Non-isolated

– L6564 transition-mode PFC controller

–STD5NM50 FET

– STTH1R04A fast recovery diode

– TS321AILT low power op amp

Figure 1.

Physical envelope

Figure 2.

STEVAL-ILL041V1 demonstration board picture

www.st.com