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26 Mar 2012

Power inverting system

The second stage of the circuit is the conversion of 12V DC voltage to 240V AC voltage using a power inverter. Power inverter is a very useful device which can convert Low voltage from a DC source to high voltage AC. This circuit converts the direct current from the battery, which is the source to the inverter, to 240V square wave alternative current so that we may empower those electric appliances which work on 240V AC instead of 12V DC. Short circuit/overload protection is also required for this system.

This circuit is designed using the CD 4047 IC which also acts as the oscillator providing 50 Hz square wave output to run the input drivers such as the TIP 122. The power transistors 2N3055 need to be mounted on proper heat sinks in order to achieve optimum thermal efficiency. The IC, CD4047, wired as an astable multivibrator produces two 180 degree out of phase 50 Hz pulse trains. These pulse trains are pre-amplified by the two TIP122 transistors which then are again amplified by four 2N3055 transistors (two transistors for each half cycle) to drive the inverter’s transformer. The 240V AC will be available at the secondary of the transformer from this process.
Bias resistors can be changed as per power output requirements and to maintain the quiescent current.
The power transformer must have a capacity of 10A in order to drive sufficient power without heating up at full load conditions. The maximum allowed output power of an inverter depends on two factors; the maximum current rating of the transformer primary and the current rating of the driving transistors.
Therefore this circuit makes use of a 10A fuse for short circuit/overload protection. Another optional fuse can be set at the source input to make the system better protected.
Further the regulated power from the voltage regulator, 7809, assisted with the zener diode (8.2V) produces a more stabilized output from CD4047, in the event of low battery conditions and full load conditions. To achieve better wave form from CD4047 the capacitor must be a non polarity type of 1µF.
The frequency for the output or the cycles per second can be adjusted using 200 kOhm variable resistor.

I am using a car battery of 32Ah as power source. The oscillation from the cd4047 is taking place at pin 10 and 11. However, the transistors are not operating. I am using a transformer which is 12 V, 10 A primary and 240V secondary in order to provide a maximum power of 100W.
The transformer is not operating as the current produced by the circuit is not sufficient enough.
You can find the circuit as attachment... help me out in this...

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