From the Q&A

With TJ Byers

Lightweight Power Inverter

Question:

I'm looking for a small 12-volt DC to 115-volt AC inverter that I can use to power an electric razor or clock radio from my car's cigar lighter. The commercial units start at about 150 watts and are overkill for what I want. Does your magic crystal ball have what I want?

T. Gifford
via Internet

Answer:

Let me have a look see. Yes, the image is starting to clear now. I see ... I see this.

This low-power inverter turns 10 to 16 volts into 60-Hz, 115-volts squarewave power-to-power razors and the like up to 25 watts. The 556 contains two 555 timers, one of which is wired as the master clock that oscillates at 60 Hz. The other is used as an inverter. The complimentary outputs (pins 5 and 9) are used to drive the TIP120 transistors in a push-pull mode. When pin 5 is high, pin 9 is low; when pin 5 is low, pin 9 is high. This causes the driver transistors to alternate conduction times, which forces the transformer to reverse magnetic polarity as they go back and forth. The output winding delivers an alternating squarewave of 115 VAC.