High-power white-LED driver operates on 1-2 alkaline cells

A single-IC driver for white LEDs delivers up to 1A from one or two alkaline cells (Figure 1). The IC (a controller for inductive step-up converters) includes the necessary power switches. Starting with input voltages as low as 1V, it maintains good efficiency while regulating the LED current. While delivering 0.5A it can operate from 0.8V to 3V, and while delivering 1A it can operate from 1.5V to 3V. The circuit operates well with sources of considerable internal resistance, like batteries at their end of life.

Figure 1. This white-LED driver operates on one or two alkaline cells, with starting voltages as low as 0.8V.

The IC’s internal gain block lets you implement a current-regulation loop with few external components: just a current-sense resistor, and an extra resistor to load the internal transconductance amplifier. A 5.1V Zener diode protects the circuitry by setting a voltage-regulation loop and by limiting output voltage when the output circuit opens.

Figure 2 shows the output-current regulation over the operating-voltage range at 0.5A (lower trace) and 1A (upper trace), and Figure 3 shows the corresponding efficiencies. Adding the potentiometer circuit shown allows efficient dimming of the light output. Control inputs ONA and ONB can be set for turning the LED on and off with a toggle switch or a momentary-contact pushbutton switch.

Figure 2. Output-current regulation vs. operating voltage for the Figure 1 circuit: 1A (top), and 0.5A (bottom).

Figure 3. Operating efficiency at 1A (top) and 0.5A (bottom) for the Figure 1 circuit.

Figure 1 connects the IC permanently ON. For other ON/OFF configurations, please consult the MAX1763 datasheet available at maxim-ic.com.