PURE SINE WAVE INVERTER using ir2110

I have the following waveform at the output of my Full-Bridge

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Despite of the PWM modulation, you would need a 50 Hz transformer to step up this waveform (in terms of windings per volt respectively core size for a particular output power). You can e.g. filter the PWM and have a 50 Hz voltage, so you won't need to enable the transformer to transmit the PWM modulation. In other words, there's no mid frequency involved.

I read somewhere that these transformers operate best at their resonant frequency.

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Resonant converters are an option, but not the only reasonable way to operate a high frequency transformer. The option is frequently used for high power converters beyond 5 or 10 kW.

So they cannot be used to step up a high-frequency PWM having a 50Hz sine-wave embedded into its varying duty cycle.

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You can transform a voltage of varying return-to-zero duty cycle, but not an asymmetric duty cycle without considerably increasing the turns per volt. So you effectively lose the advantages of a high frequency transformer.

Stepping up the input voltage to a constant DC bus voltage and chopping it to 50 Hz, with or without PWM, as mentioned by Audioguru is the most effective way to utilize a high frequency transformer.

What you need to understand is ferite core is only used for the dc-dc converter,meaning you have to step up 12v DC to 340vAC then you rectified it to back to DC again,now you can used you pwm signal to drive your H-BRIDGE with 340v DC then you will also have your 230vAC,output as sinewave when filtered.

Thanks a lot for your answers.

Actually we are making the inverter for 500W, 220Vac at the output. That means we cannot do filtering before the transformer because the current would be too much.

Secondly, if we use DC-DC conversion prior to the inverter H-bridge, what kind of converter would be the most suitable for this kind of application? (We would prefer a transformer-less design because here in Pakistan, availability of high frequency transformers and high-current inductors is an issue, though we can try and make inductors ourselves).

Another silly idea: With the waveform I posted in my previous post, it has high-frequency PWM and 50Hz sine-wave embedded into it. If I use a simple low-frequency transformer, wouldnt its windings act as a filter for the high-frequency components and I would effectively get the stepped-up 50Hz sine?

Yes, you can also used low frequency transformer,the secondary winding coil act as as an inductor then you calculate the value of your capacitor since your carrier frequency is known,you are to use low pass filter.

I agree, that you can use the leak inductance of a 50 Hz transformer as output filter. You would get a few additional core losses from the PWm, most likely neglectible.

We would prefer a transformer-less design. It's possible, but not reasonable for a step-up ratio of 25-30, I fear. The switched power of a boost converter is about Iprim*Vsec, resulting in considerably higher switching losses. Also the primary switching transistors must be rated for 400V and the rectifier diodes selected for a higher peak current. The core size of the boost inductor will be most likely larger than of the push-pull step-up transformer.

@ FvM: Thank you very much for the guidance so far. But a simple 50/60Hz Transformer gave nothing but noise and distortion when I applied my accelerating-decelerating PWM waveform to it. And since then, my H-bridge isnt working fine. So are you SURE a simple 50/60Hz transformer can be used to step up such a PWM waveform which is of a high frequency like 4KHz and contains 50Hz Sine as its Envelope?

Secondly, the High Frequency Transformer that I extracted from a Chinese Inverter is Center-tapped Primary and operates best at around 250KHz. But if given signals of low frequencies, it does not step them up.. instead it just gives ringing and distortion. Do you have any idea that if I apply my sinusoidal PWM signal (at 250KHz) with its envelope as the same 50Hz Sine, would it step up my Sine or not?

(Actually, I suspect it acts like a bandpass filter around 250KHz.. correct me if I am wrong here.)


I havent checked it yet because I had been using AVR ATMEGA16 for generating sinusoidal PWM and it cant generate 250KHz PWM... so IF the transformer can work this way, then I'll try and generate the sinusoidal PWM from some other source (like any PIC uC).

Thank you!

But a simple 50/60Hz Transformer gave nothing but noise and distortion when I applied my accelerating-decelerating PWM waveform to it.

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You should describe your measurement setup more detailed. I guess, it's mainly a case of inappropriate probing.

Secondly, the High Frequency Transformer that I extracted from a Chinese Inverter is Center-tapped Primary and operates best at around 250KHz. But if given signals of low frequencies, it does not step them up.

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Yes, this has been explained before.

Actually, I suspect it acts like a bandpass filter around 250KHz.. correct me if I am wrong here.

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Not exactly a bandpass, but the effect is similar. The most interesting point in this regard is, that it can't carry full voltage at considerable lower frequencies than the designed switching frequency without saturating the core. Insufficient primary inductance would be another problem. Basically a transformer core has a maximum flux measured in volt*secs per winding. If you halve the frequency, half the voltage will generate the same flux.

Re: pure sine wave inverter circuit

Audioguru said:

Your circuit does not show any supply voltages.
On the other website you said the Mosfets have a +170VDC supply. 170V is the peak of 120VAC.

So if you want 240VAC output then feed the mosfets from +340VDC.
I don't know if your Mosfets will work from 340VDC.

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if i use dc-dc converter for generating 340v dc fro 12v then how much current in it will flow and how much of current i have to make converter?? plz reply

Re: pure sine wave inverter circuit

rushipatel007@ymail.com said:

if i use dc-dc converter for generating 340v dc fro 12v then how much current in it will flow and how much of current i have to make converter?? plz reply

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The 340VDC must produce the same amount of power (plus a little more making heat) (P) as the load uses.
Use simple arithmatic (P/12V) to calculate the 12V current.

Re: pure sine wave inverter circuit

hi i m also doing this project so plz tell me that why in this ckt we need to feed mosfets from +340v dc. if we feed it from 220v dc then will it work???

---------- Post added at 19:31 ---------- Previous post was at 19:29 ----------

Audioguru said:

Your circuit does not show any supply voltages.
On the other website you said the Mosfets have a +170VDC supply. 170V is the peak of 120VAC.

So if you want 240VAC output then feed the mosfets from +340VDC.
I don't know if your Mosfets will work from 340VDC.

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hi i m also doing this project so plz tell me that why in this ckt we need to feed mosfets from +340v dc. if we feed it from 220v dc then will it work???

Please i need to build a 12VDC to +/-150VDC Converter. Any Ideas...It would be better transformerless......Thanks

TDS2285 IC can be used to become the host controller IC.

kabiru said:

What you need to understand is ferite core is only used for the dc-dc converter,meaning you have to step up 12v DC to 340vAC then you rectified it to back to DC again,now you can used you pwm signal to drive your H-BRIDGE with 340v DC then you will also have your 230vAC,output as sinewave when filtered.

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You can't step up DC with any transformer, it is impossible you need to convert the DC to AC or PWM first.

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A small PIC 10F series MCU can be used to generate your PWM signal.

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rashid0214 said:

TDS2285 IC can be used to become the host controller IC.

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A small PIC 10F series MCU can be used to generate your PWM signal.

@t chrismicro, when someone says 12v dc to 340v ac you should know that dc is been converted to ac, dc can't be step up it can only be step up from the source, one more thing is, i have been building power inverters over ten years now therefore i know what dc and ac mean