500w Modified Sine Wave Inverter Schematic

A simple but powerful, stable and efficient schematic diagram for a 500w modified sine wave inverter circuit. Originally I used a 555 timer and a CD4017 decade counter to produce the modified sine wave, but then I thought a simple PIC micro controller with its internal clock would produce a stable 50Hz frequency without the need for two IC

`s. As you can see its a very simple circuit. The CD4017 and 555 Timer circuit can be seen here should anyone want to try that. Some information on this circuit. The PIC16F628A is programmed to produce a logic 5v signal for 5ms at pin 17 then 15ms off. Then the same at pin 18, 5ms on then 15ms off (4. 17ms for 60Hz). That is one cycle which is then looped. This results in the signals below on the oscilloscope. (2 channel view) You can see the two 5v pulses from pins 17 & 18. These two pins are then sent to the gates of the STP55NF06L (or STP36NF06L) logic MOSFET`s. These are special power MOSFET`s that require just 5v to switch on fully. They also have a very low 0. 014 © Source to Drain resistance when on which means they can switch high currents without wasting power as heat. This keeps the whole system efficient. They do run cool although a heat sink is required. The main losses in power will be within the transformer itself. They are capable of switching loads up to 55A (or 30A for the STP36NF06L) which makes this a powerful inverter if used with a large (~800VA) transformer. Of course you could use a smaller transformer for small loads. The MOSFET`s could be in parallel pairs for even more power. Just give each its own 470 © gate resistor and a 22k © from each gate to source. I get around 240v AC from the 10-0-10 with a 12v battery but as this circuit is so efficient a 12-0-12 should give you no less than 220v AC at...

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