1W LED For Automotive Applications
This simple circuit lets you run a 1W LED from the battery of your car. IC MC34063 is used here as a buck converter. It is a monolithic switching regulator sub-system intended for use as a DC-DC converter. The device consists of an internal temperature-compensated reference, a comparator, a controlled duty-cycle oscillator with an active current-limit circuit, a driver and a high-current output switch. These functions are contained in an 8-pin dual in-line package. Another major advantage of the switching regulator is that it allows increased application flexibility of the output voltage.
Fig. 1 shows the circuit of 1W LED for automotive applications. Fig. 2 shows the internal diagram of IC MC34063, while Fig. 3 shows a 1W LED. The non-linear voltage-to-current relationship and variation in forward voltage with temperature necessitate the use of a 320mA constant-current power source as provided by this supply. The current through LED1 is sensed by a 15-ohm resistor (R4) and the sensed voltage is fed to the controller to maintain a constant current. Resistor R1 limits the peak current given to IC1. With capacitor C2 (470pF), the oscillator runs at about 100 kHz.
Once the circuit is ready, do not connect the LED directly: First, use a 10-ohm, 5W resistor as the dummy load and verify the current and voltage across the dummy. Run the dummy for a few minutes. If the result is satisfactory, replace the dummy with the actual LED1. Inductor L1 used here is a salvaged drum core of size 8×10mm2 with 70 turns of 33SWG enameled copper wire, giving an inductance of about 220 µH.
Assemble the circuit on a general-purpose PCB and enclose in a suitably small cabinet. Solder the IC base for easy troubleshooting. Fix the inductor and the LED1 (using a suitable heat-sink) in the PCB. Like all light bulbs, LED lighting is not water-proof. If used outdoors, it must be mounted in a sealed enclosure. Thermal management is very important for the power LED. Otherwise, a high temperature will shorten its life.
EFY note. During testing at EFY Lab, we used an LED from Kwality Photonics whose part number is KLHP3433.
 Fig. 1: 1W white LED for automotive |
 Fig. 2: Internal diagram of MC34063 |
Once the circuit is ready, do not connect the LED directly: First, use a 10-ohm, 5W resistor as the dummy load and verify the current and voltage across the dummy. Run the dummy for a few minutes. If the result is satisfactory, replace the dummy with the actual LED1. Inductor L1 used here is a salvaged drum core of size 8×10mm2 with 70 turns of 33SWG enameled copper wire, giving an inductance of about 220 µH.
 Fig. 1: 1W LED |
EFY note. During testing at EFY Lab, we used an LED from Kwality Photonics whose part number is KLHP3433.
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