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12V / 230V 50Hz modified sine wave inverter

     Why modified sine wave? The disadvantage of rectangular inverters is (among other things) that the amplitude of the output voltage is only 230VDC, not 325VDC like in the 230VAC sine wave. Effective (RMS) value therefore corresponds to the network, but the amplitude differs considerably. The problem may occur especially in case of appliances with rectifier, where the rectified voltage will be about 30% smaller than when operating from the mains. Sine wave inverters are very complicated. Therefore a compromise between the rectangle and sinus is usually chosen, which is so called modified sine wave. It's a little misleading term because it differs from the sine wave a lot :). But the point is, that modified sine wave has the same effective (RMS) value and also the amplitude as a sine. Hence it is used by most factory manufactured inverters. The simplest way to generate the proper modified sine wave is using two halfbridges with a phase shift of 25%. The output voltage is therefore tri-state, switching in the order: +325V, 0V, -325V, 0V. The transformer is AC 230V / 9V and must be designed for the maximum required load. For higher power it is necessary to use adequate heat sinks (and MOSFETs that can be attached to them :)). If you use common heat sink for all MOSFETs it is necessary to use insulating pads. You can also connect multiple MOSFETs in parallel. The 12V supply must be sufficiently hard, the supply voltage should be in the range of 9 - 14V. If the supply voltage is lower than 9V, the control circuit IR2153 shuts down, preventing damage to the battery, inverter or powered appliance. At the input it is necessary to use a proper fuse.

When working with the power inverter be careful - the output voltage is lethal, although input is safe voltage. Output voltage is isolated from the ground, but if you touched both output terminal the voltage is similarly dangerous as the mains voltage. Everything you do at your own risk. Author does not take responsibility for any of your harm.

Schematic of the 12V / 230V 50Hz modified sine wave inverter.

MOSFET Gates and output waveforms

Inverter with SMD parts with L6571AD013TR and MOSFETs 06N03LA. This can be used for powers up to 50 - 100W.

Output waveforms at the scope

Note for lamas:
The power inverter is not a perpetual motion machine! Power input of the inverter is never lower than its output.

-The power transformer must match the power of the inverter, a miniature transformer does not allow you to build high power converter.

-The battery must match the required power and the required operating time. It is therefore necessary to choose a battery with a suitable capacity and discharge current. (For stupid: Inverter powering a kilowatt heater will not run on AA batteries and certainly not for weeks!)

-The drive is not designed to save electricity. You won't save electric bills by powering the appliances from this inverter while the inverter is being powered from a mains AC/DC power supply. I'd rather not even mention the operation from disposable batteries.