1w led driver


Posted on Feb 5, 2014

This circuit is designed to drive the 1W LEDs that are now commonly available. Their non-linear voltage to current relationship and variation in forward voltage with temperature necessitates the use of a 350mA, constant-current power source as provided by this supply. In many respects, the circuit operates like a conventional step-down (buck) swit


1w led driver
Click here to download the full size of the above Circuit.

ching regulator. Transistor Q1 is the switching element, while inductor L1, diode D1 and the 100mF capacitor at the output form the energy transfer and storage elements. The pass transistor (Q1) is switch-ed by Q2, which together with the components in its base circuit, forms a simple oscillator. A 1nF capacitor provides the positive feedback necessary for oscillation. The output current is sensed by transistor Q3 and the two paralleled resistors in its base-emitter circuit. When the current reaches about 350mA, the voltage drop across the resistors exceeds the base-emitter forward voltage of transistor Q3 (about 0. 6V), switching it on. Q3`s collector then pulls Q2`s base towards ground, switching it off, which in turn switches off the main pass transistor (Q1). The time constant of the 15kW resistor and 4. 7nF capacitor connected to Q2`s base adds hysteresis to the loop, thus ensuring regulation of the set output current. The inductor was made from a small toroid salvaged from an old computer power supply and rewound with 75 turns of 0. 25mm enamelled copper wire, giving an inductance of about 620mH. The output current level should be trimmed before connecting your 1W LED. To do this, wire a 10W 5W resistor across the output as a load and adjust the value of one or both of the resistors in the base-emitter circuit of Q3 to get 3. 5V (maximum) across the load resistor.




Leave Comment

characters left:

New Circuits

.

 


Popular Circuits

Auto 12V Fan Controller
Signal-combiner
Arduino project
The embedded microcontroller MC68HC912B32 background debugs the mode to design
LCD Display with Microcontroller
High voltage direct current
Two-Channel PC Based Oscilloscope USB
MFOS NOISE TOASTER Lo-Fi Noise Box
455 kHz IF WITH AF COMPRESSOR
Tesla coil circuit



Top