This design uses a boost topology. Specifically this circuit uses the LM2623 which is a high efficiency, general purpose, step-up DC-DC switching regulator for battery-powered and low input voltage systems. The LM2623 uses a PFM topology which provides switching until the output voltage is reached and then skips pulses to maintain the output voltage, thus inherently making the circuit very efficient.
The LM2623 provides a constant output with +/- 5% regulation. But in High brightness LEDs, it is important to regulate the load current. The load current in the LED is regulated by using an LM321. The load current is sensed across R8 (0.15 ohm resistor). R2/R3 sets the reference point for the output load current (set to 150mV). The output load can be changed by adjusting the voltage divider.
Notes: A1 in the schematic (the LM321) is represented as U2 in the PCB layout.
Schematic
Example Schematic Showing Connection for all Components.
Example Schematic Showing Connection for all Components.
