This voltage-booster circuit for driving one or more white LEDs uses a 555 timer as its main element (see the figure). The timer, IC1, functions as a resettable astable multivibrator where R1, R2, and ...

Click here to view a PDF of all the Design Ideas from this issue. Using a CMOS 555 timer and a single NPN transistor, you can drive as many as seven LEDs using a minimal amount of voltage and power ...