Led lighting application

High Power LED driver circuit

Led lighting application are requiring a constant current source. High power LEDs are usually operated at a 350mA current and higher, much as 1A. With the right heat sink and a constant current operation the service lifetime of the LEDs can be as long as 50000 hours - that means up to eleven years .

Integrated with a 2A power switch, the BD9001F flexible step-down switching regulator from Rohm offer a simple and efficient solution for the supply of high power LEDs.

Power LED driver circuit

Switching frequency is variable with the R3 resistor between 50 and 300 kHz. A higher frequency allows the use of small surface mount inductors and capacitors. For R3=270kOhm we have a switching frequency of about 140kHz. The supply current for LEDs is set by the R4 with this formula:

Id=(1+R2/(R2+R5))/R4

The values shown in schematic will give a current of about 0.64A for a input voltage of 9V. This circuit can be used to power multiple LEDs in series connection, 10pcs. or more but the L1 inductor must to be resized. The input voltage must be increased too. A software to selecting inductors it is available for free download at Würth electronik website.

Specifications:

Input voltage 7V up to 48V (min.7V for just one LED)
Soft start function with fixed time of 5ms
Built-in over current protection circuit
Built-in thermal shutdown protection circuit
Wide operating temperature range from -40°C to +95°C

BOM list:

U1 BD9001F
L1 33..100µH/min. 0.7A Isat inductor
D1 SS14 / SL22 / MBRS130LT3 SMD Schottky diode or 1N5822
D2,D3 Cree XLamp series min. 700mA rated
C1 220µF/16V low ESR electrolytic capacitor
C2 330µF/16V low ESR electrolytic capacitor
C5,C6,C7 1µF/25V ceramic capacitors
C3 4.7nF/50V ceramic capacitor
C4 100nF/50V ceramic capacitor
R1 150kΩ smd 1206 resistor
R2 1kΩ smd 1206 resistor
R3 270kΩ smd 1206 resistor
R4 6pcs. of 10Ω smd 1206 resistor in parallel
R5 47kΩ smd 1206 resistor
R6 100kΩ smd 1206 resistor

Component placement on Power LED driver board

C7 it is placed very close to the L1 inductor. The PCB can be make at low cost and quick using the toner transfer method. The results:

Led driver PCB

The heat sink from a CPU cooler is one the best alternative solution for dissipate the LEDs heat.

Led module with driver and heat sink

Orcad schematic and layout files are available for download.

Download circuit diagram in pdf format.

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