This is a design of LED driver circuit. This circuit is work with based on 2two transistor. This is the figure of the design circuit.
The operation of the circuit is begin from the output current is almost constant over an input-voltage range of 1.2 to 1.5V and is insensitive to variations of transistor gain. Transistors Q1 and Q2 form an astable flip-flop.R1 and C define the on-time of Q2. During that time, Q1 is off, and the voltage at the base of Q1 and the current in inductor L ramp up. When the voltage at the base of Q1 reaches approximately 0.6V, Q1 turns on, and Q2 turns off. This switching causes “fly back” action in inductor L. The voltage across the inductor reverses, and the energy stored in the inductor transfers to the LED in the form of a down-ramping pulse of current. During fly back time, voltage across the LED is approximately constant. The voltage for yellow and white LEDs is approximately 1.9 and 3.5V, respectively. When the current through the LED falls to zero, the voltage at the collector of Q2 falls sharply, and this circuit condition triggers the next cycle
The operation of the circuit is begin from the output current is almost constant over an input-voltage range of 1.2 to 1.5V and is insensitive to variations of transistor gain. Transistors Q1 and Q2 form an astable flip-flop.R1 and C define the on-time of Q2. During that time, Q1 is off, and the voltage at the base of Q1 and the current in inductor L ramp up. When the voltage at the base of Q1 reaches approximately 0.6V, Q1 turns on, and Q2 turns off. This switching causes “fly back” action in inductor L. The voltage across the inductor reverses, and the energy stored in the inductor transfers to the LED in the form of a down-ramping pulse of current. During fly back time, voltage across the LED is approximately constant. The voltage for yellow and white LEDs is approximately 1.9 and 3.5V, respectively. When the current through the LED falls to zero, the voltage at the collector of Q2 falls sharply, and this circuit condition triggers the next cycle
