harrychoo

Inverter Circuit 12V DC to 230VAC Sine Wave

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The project of the 500W square wave inverter is here: http://www.electronics-lab.com/projects/power/033/index.html and is updated with a circuit that works.

You could make a pure sine wave inverter with a high current linear amplifier driving a transformer and waste a lot of battery power as heat, or you could make a complicated pulse-width-modulation (class-D) circuit drive a transformer with variable width pulses and waste less power. I have never seen a circuit because a pure sine wave is rarely needed.

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Hi Harry,
The modified 500W inverter is simply a CD4047 Cmos oscillator/divider/opposing outputs IC driving LM358 dual opamp buffers to increase its output currents. Each buffer drives sets of transistors connected in a darlington arrangement and the output transistors are paralleled for very high current. The transistors apply their high current swings to a center-tapped transformer that steps-up the voltage.

I haven't seen the schematic for a modified sine wave inverter. I heard that their output is a square wave with a step in it. I don't know how they make the step without overheating.
Maybe the transformer has a tap on its low-voltage winding and a separate output transistor drives the tap on each side to make the step.
Actually, a separate transistor would drive the full winding to make the step, and another transistor would drive the tap for full output on each side. ;D

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I have tried this circuit before, although on a breadboard but I couldnt get the right output.

You can't feed 50A from the car battery through the resistance of the wiring and contacts of a breadboard. Look at the size of the wires on booster cables. They can carry 50A.

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You might be alright if you tested it off load.

Good point, Alun! ;D
But not if it had a transformer from a microwave oven that wastes a few hundred Watts because it doesn't have enough turns, therefore its inductance is too low.

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Hi Harry,

This is a “modified sinus” inverter, as you can see it is much more complex than the square wave inverter. This one is more powerful but even at the same power level it will still be more complex to construct and build.  ;)

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Hi Audioguru,

Yes, this is closer to the sine wave than the square wave but not perfect though. I am sure that some equipment will be more forgiving to this waveform than to square wave. But obviously the circuit becomes more complex which is hereby proven by the fact that you had to look twice to see how it works! ;D ;D

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Hi Ante,
Since it pauses for half the time, then its transistor current must be double the amount of current in a square wave inverter. :o

I wonder why it uses expensive P-channel Mosfets instead of better, cheaper N-channel. ???

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Hi Audioguru,

The 16 MOSFETS  should be well spread out over a BIG heatsink. I don’t know if there are any big differences in price between N and P channel Mosfets, or maybe this guy had them in his junkbox anyway. ;D

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Hi Audioguru,

Yes you are correct, there are twice the number or more of the N type around but the Rds and the price does not differ that much. However I agree, N-channel would be a better choice for this inverter. I bet they came from his junkbox !  ;)

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The project of the 500W square wave inverter is here: http://www.electronics-lab.com/projects/power/033/index.html and is updated with a circuit that works.

You could make a pure sine wave inverter with a high current linear amplifier driving a transformer and waste a lot of battery power as heat, or you could make a complicated pulse-width-modulation (class-D) circuit drive a transformer with variable width pulses and waste less power. I have never seen a circuit because a pure sine wave is rarely needed.


That thread is actually a re-make of the project and not a correction. There were not many problems in it. Some traces were connected where they should not be and the decimals were off in the clock components. Either way, you have a square wave. Using a linear amp for a sine wave will waste too much energy. If you live in the arctic, it could certainly be beneficial as a heater.

Here is a schematic from a link ante sent me some time ago. This might be what you are looking for.

MP

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Another form of sinewave conversion and a much more effective way to do this is to use a micro to generate varying levels of square waves which are very close together in timing and which, when smoothed with a capacitor, will become a sine wave. This will give you the efficiency of a square wave inverter, but a sinewave output. See the drawing below. It is not a very good one but gives you an idea. You would need many more waves than in this depiction to get a smooth sine wave.
Hope this helps.

MP

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actually class D is a far cry from being digital. It is PWM. Class D uses triangle wave controlled by input signal (sine) to produce a PWM type of controlling signal. I was referring to a constant clocked squarewave controlled by a sinewave to produce varying heights of squarewaves, which when smoothed, creates a representative sinewave. Class D produces all the same height PWM waves. This is less useable as an inverter type circuit.  ;D

MP

post-555-14279142427846_thumb.gif

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Actually, since the digital PWM waves of a class-D amplifier all have the same height, and are also constantly clocked, there is far less heating than in your proposed "vaying heights" plan. Most fairly high power class-D amplifiers are surface-mount, and don't even need a heatsink.
Class-D amps are perfect for a sine-wave inverter. ;D

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