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Inverters take dc from a battery (etc) and convert it electronically to ac power.

Inverters

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Block diagram of and inverter

Switches DC to AC

Transformer Rectifier FilterDC In

AC Out

DC Out

Output is sampled to adjust switching for voltage regulation

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Inverter OPERATION

• Inverters are classified by their ac output waveform.

– Square wave– Modified sine wave– True sine wave

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Inverter operationSine WaveSine Wave

Modified Square WaveModified Square Wave

Square WaveSquare Wave

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• Most smaller inverters are either square wave (cheap) or modified square wave.

Inverter operation

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Inverter operation

By closing and opening the switch rapidly, a square wave supply to the transformer is achieved. This used to be done mechanically with a “vibrator”. (Yeah! I know…)

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Inverter operation

The switches close in turn, producing a pseudo-AC in the primary.

Not that rectification is centre-tapped, full wave, with an L filter.

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Inverter operation

Here the rectifier is a full wave, bridge, with L filter.

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Inverter operation

A single winding is used here on the primary, with the switches closing is sequence to provide AC to the primary.

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VibratorVibratorHere is what one looks like. Inside are vibrating mechanical contact points that oscillate and generate a low voltage AC signal from the DC voltage applied to it from the battery. The AC signal then feeds a transformer where the voltage is increased.

AC OutAC Out

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Square waves • Cheap• Very poor regulation• Produce large amounts of RFI• Very rough AC• Large amounts of harmonics• Often used for small appliances eg; fluro lightsVery few but the very cheapest inverters any more are square

wave. A square wave inverter will run simple things like tools with universal motors with no problem - but not much else. These are seldom seen any more except in small, very cheap or very old inverters.