BUCK CONVERTER for3watt LED
This circuit drives a 3watt LED.
You have to be careful not to damage the LED when setting up the circuit.
Add a 10R to the supply rail and hold it in your fingers.
Make sure it does not get too hot and monitor the voltage across the resistor. Each 1v represents 100mA.
The circuit will work and nothing will be damaged.
If the resistor "burns your fingers" you have a short circuit.
The BC557 multivibrator has a "mark-to-space ratio" determined by the 22n and 33k, compared to the 100n and 47k, producing about 3:1 The BD679 is turned ON for about 30% of the time.
This produces a very bright output, and takes about 170mA for 30% of the time.
You cannot measure this current with a meter as it reads the peak value and the reading will be totally false.
The only way to view the waveform is on a CRO, and calculate the current.
The 100-turn inductor allows the BD679 turn turn ON fully and "separates" the voltage on the emitter of the BC679 from the voltage on the top of the 3watt LED.
When the BD679 turns ON, the emitter rises to about 10v.
But the top of the LED NEVER rises above 3.6v.
The inductor "buffers" or "separates" these two voltages by producing a voltage across the winding equal to 6.4v and that's why the LED is not damaged.
When the transistor turns off (for 60% of the time), the magnetic flux produced by the current in the inductor collapses and produces a voltage in the opposite direction.
This means the inductor now becomes a miniature battery and for a very short period of time it produces energy to illuminate the LED.
The top of the inductor becomes negative and the bottom is positive.
The current flows through the LED and through the Ultra High-Speed 1N4004 diode to complete the circuit.
Thus the circuit takes advantage of the energy in the inductor.
A 500R pot is placed across the LED and a voltage is picked off the pot to turn on a BC547 transistor. This transistor "robs" some of the "turn-on" for the BD679 transistor to reduce the brightness of the LED.
Because the circuit is driving the LED with pulses, very high brightness is obtained with a low current. Our eyes detect peak brightness and you can compare the performance of this circuit with a DC driven LED.
কোন মন্তব্য নেই:
একটি মন্তব্য পোস্ট করুন