Voltage-to-current converter drives white LEDs

Posted on Jan 13, 2013

You sometimes need to drive a white LED from one 1.5V battery. Unfortunately, the forward voltage of a white LED is 3 to 4V. So, you would need a dc/dc converter to drive the LED from one battery. Using the simple circuit in Figure 1, you can drive one white LED or two series-connected green LEDs, using only a few components. The circuit is a voltage-to-current converter, which converts the battery voltage to a current that passes through the LED. You can adjust this current and, thus, the brightness of the LED, by varying resistor R3.

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