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110VAC Inverter for Automobile

This circuit will allow you to operate small devices like laptop computers inside your automobile without an expensive automobile power supply. The circuit takes advantage of the fact that power transformers are linear devices and can be used to step up as well as step down. This is evident by the fact that the supply drives the secondary and the output is on the primary.

Warning: this supply produces dangerous and lethal voltages. Use extreme caution when testing this circuit. In addition, make sure the assembly is enclosed in a plastic case. Do not package this circuit in a metal or aluminum case!

The design depends on the windings ratio and the value of the car battery to produce an AC waveform of approximately 95 volts RMS. No filtering is performed on the secondary since the transformer blocks most of the sharp edges from the input waveform.

All of the devices (14013, 555, 14020, and 4049) should have their supply pins connected to the +12 supply. The nice thing about CMOS logic is that it will operate over a wide range of voltages. Before connecting the center tap of the transformer, adjust R3 until the signal on U5 pin 13 is 120Hz.

The 14013's are used to produce a 60Hz square wave with an accurate 50% duty cycle and to force the FET switches operate in a break-before-mate manner. The 4049's have enough drive capability to snap the FET's off and on very quickly.

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