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Low-pass Filter?

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You could use a low voltage, high current Class-D amplifier to drive an ordinary power transformer in reverse to stepup the voltage.
You could use a high frequency oscillator to drive a small stepup transformer, rectify its high voltage then use the DC for a high voltage Class-D amplifier.

Either way is complicated. The highest power from an IC that I have seen is only 240W.

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1. I don't understent how many LM358 should I use in this circuitry? (about 100W inverter?)
2. May i test this scheme without transformer or with small trasformer without load just for test?
3. Some one have compete PCB for 100W inverter?

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Hi...I 've just built the 500W inverter circuit as part of my final year project...

Without connecting the circuit to a transformer (floating the circuit output), am I supposed to get 24VAC measuring between the collectors and the 12VDC? 'cause I couldn't get anything from that...

TNX

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oh...Thank you very much...

Now I know why I can't get anything from the circuit...hehe~~~

One more thing? Just wondering how does the opamp work? Is it functioning as a voltage follower? I thought the input to the opamp is 12V square wave and then the opamp should not be operating at its linear region...right? or is it like a schmitt trigger but instead of positive feedback, it is functioning in negative feedback?

Thank you...really appreciate for your help...

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Now I know why I can't get anything from the circuit...hehe~~~

Transistors work better when they have a power supply, don't they?

Just wondering how does the opamp work? Is it functioning as a voltage follower? I thought the input to the opamp is 12V square wave and then the opamp should not be operating at its linear region...right?

Yes, the opamp is a voltage follower. With a square-wave input it has a square-wave output. A square-wave is not linear and the level is so high that the output of the opamp saturates with it.

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OK.  This is the one I build my circuit. Do I common ground the two 0V terminals of the transformer and connect it to 12VDC? The collectors are connected to the 12V terminals of the transformer, am I right?

Thank you....

post-22854-14279143063385_thumb.gif

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Hi Hericlj,
Good, you built the fixed circuit.
The transformer doesn't have 0V terminals. Its primary winding has a center-tap that is connected to the fused and switched positive 12V, and it has two terminals for the collectors of each side's output transistors.
The emitter resistors of the transistors are connected to 0V and everything with the ground triangle is connected to 0V. The negative terminal of the 12V car battery is also connected to 0V in the circuit.

The circuit doesn't need to be earthed. We say its negative wire is its "ground".

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Hi Audioguru:

Thank you for your help...Sorry, I am a begginer in power electronics, so actually i don't know what a center-tap step up transformer looks like. I bought one with 240VAC primary  and two 12V, two 9V, two 0V output terminals at secondary, and thought I could use it to step up the voltage....

I actually connect the collectors to the 12V terminals on the seconday, and 12V DC to the 0V terminals (I tied the two 0V terminals togeter), and the primary side of the transformer is conncted to the load....

So when I switch the power on, the whole thing is current shorted.....

Am I seriously wrong?  Great Thanks....

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I actually connect the collectors to the 12V terminals on the seconday, and 12V DC to the 0V terminals (I tied the two 0V terminals together), and the primary side of the transformer is conncted to the load....

You wired the transformer so that the 12V windings cancel, instead of adding.
Connect one 12V wire to the other winding's 0V wire. Then you will have a 24V center-tapped transformer. Look at my sketch.

So when I switch the power on, the whole thing is current shorted.....

It won't be shorted the way you wired it. It just won't work.
What does it do that makes you think it is shorted? With a 500W load, the current from the battery will be 50A which is nearly a short.

post-1706-14279143078209_thumb.png

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Thank you so much....:)

Actually when I did that experiment last week, I didn't connect any load to the transformer, and I was using those 3A(max) DC Power Source to power this circuit....So when I switched it on, the power source reaches its limited output current and wouln't give 12V out....I thought that was current-shorted....

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Hi Farhad,
A square-wave or modified sine-wave inverter should power an AC electric motor fine at its full speed. I have read on the web that an electronic motor speed control won't work properly unless the waveform is a true sine-wave.

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Hi...sorry I still have problem in the inverter circuit...

This time i put a rectifier circuit and used the main supply to power the inverter so that current limit won't be a problem. But still, when I switched it on, nothing comes out. The transformer is shorted between one wire's 12V and the other wire's 0V terminals. Even without powering the circuit, the transformer is still shorted so the collectors of the transistors are shorted...When I removed the transformer, the collectors are isolated again!.....

Just to make sure I did it in the right way:  one wire's 12V is connected to the other's 0V, and this is also connected to 12VDC...The remaining 12V and 0V is connecting to the collectors of the transistors respectively....

Or do I have to buy a centre-tapped transformer instead?

Cheers...

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