Your need to read my article on power inverter before you proceed on this page. Having done that, let's go.
figure 1, Inverter circuit. Click here to enlarge
Pulse generator circuit
The IC used in the pulse generator (oscillator) circuit is SG3524. This is what Texas Instruments says about the IC "The SG2524 and SG3524 incorporate all the functions required in the construction of a regulating power supply, inverter, or switching regulator on a single chip. They also can be used as the control element for high-power-output applications. The SG2524 and SG3524 were designed for switching regulators of either polarity, transformer-coupled dc-to-dc converters, transformerless voltage doublers, and polarity-converter applications employing fixed-frequency, pulse-width modulation (PWM) techniques. The complementary output allows either single-ended or push-pull application. Each device includes an on-chip regulator, error amplifier, programmable oscillator, pulse-steering flip-flop, two uncommitted pass transistors, a high-gain comparator, and current-limiting and shutdown circuitry".
|figure 2, SG352 pin configuration
'Pulse-width modulation (PWM)' and 'shutdown circuitry' are two of the features of this IC that make it my best choice of IC for pulse generator in inverter design. PWM makes the duty cycle achievable while shutdown circuitry makes it easy to shutdown the system in case any error/fault is detected or sensed from any of the protective circuitries like low battery shutdown, high temperature, short circuit, overload or as many as you have in your circuit.
The frequency is determined by the value of capacitor Rt and Ct connected to pin6 and pin7 respectively using the formula below.
||= R9 in my circuit and
The value of R9 and C1 in the circuit are the ideal values given by calculation, but in real life, you may not get exactly 50Hz. You are advised to replace R9 with 200k resistor and 100k variable resistor. Having done that, you will need an oscilloscope or multimeter with facility for measuring frequency to set your frequency. Connect the probe(s) to either pin11 or pin14 and ground, then increase the variable resistor from zero till your oscilloscope or meter reads 50Hz.
You also need oscilloscope to set your duty cycle. Connect the oscilloscope probe to either pin11 or pin14 andthe ground, vary VR1 and monitor wave-form on your oscilloscope. Alternatively, if you don't have an oscilloscope and you designed and constructed your transformer for modified sine-wave as discussed under transformer design in my article 'power inverter', setting of your duty cycle is easy and done when you have completed the construction. Connect AC voltmeter to the output of your inverter and vary VR1 till the voltage reads 220V.
Power is supplied to the oscillator circuit via IC2, LM7809 which produces 9V on closing on/off switch. The oscillator generates complementary pulses on pin11 and pin14 which drive power transistors MT1 and MT2. Each of the pins are connected to the ground via 10K resistor so that charges in the MosFet's gate can sink when the pulse is zero. This action causes current to flow through each half of the primary windings of the transformer at alternate halves and alternate current is produced at the secondary winding.
This inverter can deliver up to 1000 watt of power as drain-source current of the MosFets in this circuit is 110A while the effective current that flow in the primary windings of a 1000W transformer designed for modified sine-wave with 80% efficiency is 104A. However, I recommend it for just 500 watt despite the D-S current of the Mosfets. If you want to design it for higher capacity, increase the number of Mosfets and connect them in parallel.
A power inverter is not more than this. Click on inverter with low battery shutdown to see how a low battery shutdown circuitry is introduced to the same inverter. The inverter is the same except for the low battery shutdown; the six MosFets used is just to show you the arrangement when you increase the number of power transistors if the design requires more than two.
Battery level monitor
Lead acid battery charger
Power inverter circuit
Power inverter circuit with Low battery shutdown1
Power inverter circuit with low battery shutdown2