Design Description

The LM3405A LED driver has been used for this design. It is a current mode control buck switching regulator designed to provide a simple, high efficiency solution for driving high power LEDs (Typical Vf = 3.8V) . With a 0.205V reference voltage feedback control to minimize power dissipation, an external resistor sets the current as needed for driving various types of LEDs. The LM3405A uses internal compensation offering ease of use and predictable, high performance regulation over a wide range of operating conditions. Additional features include user accessible EN/DIM pin for enabling and PWM dimming of LEDs, thermal shutdown, cycle-by-cycle current limit and over-current protection.
With the advancement of high brightness LED technology, LEDs are rapidly evolving to become a common light source for general illumination. LEDs are regarded as a longer life, lower energy consumption light source without the toxic material in CFLs. This design is an example of an MR16 form factor LED bulb to replace a halogen light bulb. It is capable of providing 600mA constant current to drive high brightness LEDs from a 12V AC source. Thanks to the wide operating voltage range of the LM3405A (from 3VDC to 20VDC), a very small input capacitor can maintain continuous operation. Switching frequency is internally set to 1.6MHz, allowing the use of extremely small surface mount inductors and chip capacitors. All these factors help to squeeze the overall dimensions of the PCB to fit the stringent space constraints of the MR16 form factor and this makes LM3405A the best LED driver for this application.

•	RD-148 Reference Design Document

Additional Resources

Board Photo

• VIN range: 12VAC ±10%
• 0.6A output current
• Small PCB size
• Can drive a 1W LED
• Single LED application
• Over-current protection
• Thermal shutdown
• Integrated 1.0A NFET