High Power LED driver circuit

[guclusat]

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

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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 atWürth 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