Low-power inverter using LM555 Timer IC

This document describes a basic circuit that can be used to power high impedance, high voltage, low current devices such as EL backlights and fluorescent tubes. This project got its genesis when I needed a simple, yet flexible inverter circuit for an EL backlight, using a 12 volt input. My specific need was to power the backlight for the wildly po
Low-power inverter using LM555 Timer IC - schematic

pular LCD-107 ( specs ) from All Electronics Corporation. However, this circuit is versatile enough that it should be able to power any EL strip or small (up to a few watts) fluorescent tube. Why build instead of buy an inverter Well, I actually bought one from one of the several surplus resale houses out there. It was apparently very poorly designed. I connected it to the backlight contacts, then to the +5V recommended, only to get a brief buzzing noise and some smoke for my trouble. I decided I could build a much more reliable, versatile inverter for just a few dollars (total cost is only about $6 for the semiconductors and transformer at your local Radio Shack), and set out to do it. It occurred to me that a simple 555 timer with a small step-up transformer should work well. The 555 timer is now ubiquitous, available on nearly any street corner via Radio Shack. For the transformer, many circuits use a filament transformer or other step-down transformer generally designed for use in a utility power supply. This wouldn`t do - it would be too large and cumbersome for my needs, and besides, I didn`t have a need for Big Power. I`d had good luck in the past using 8 ohm to 1k ohm audio output transformers in "tickle stick" inverter-type applications, so I thought this might work if driven with a good oscillator. I initially setup the circuit for 400Hz operation, with the timer driving the transformer directly through a 47uF...

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