Hello,

I´m building a small inverter (10W) with a CD4047 and 2 MOSFET´s (IRL3303), and I´m not getting 220Vac in the output of my transformer and I dont know why...Can sombody help me? I don´t know if it is the transformer (Already tried come different ones) or I am doing something wrong. I am just getting around 164Vac...

 

I will assume your supply voltage is 12 volts DC (You have not given this important piece of information.) Your output will be a square wave with a peak output value of about 220 volts. If it was a sine wave output that would corespond with an RMS value of about 156 volts.(220 divided by root 2) The reading you get will depend on the design of your meter. A true RMS meter would probably read close to 220 volts. Checking the output with an oscilloscope is the best way to see if it is working as designed.

Les.

 

Oh, I see! Thank you so much Les! Yes, my supply voltage is 12Volts DC. With my osclislloscope I am getting 165V (Cyc RMS)...
My meter is a Fluke 28II "True RMS meter", am I using this in wrong configuration for not getting the true RMS value?

Thank you again!

 

Are you doing this without a load on your 220VAC secondary?

It might be that the magnetizing current (that is the current that flows through the inductance of the primary) is loading down your 24V primary. Magnetizing current causes and IR drop in the primary winding that shows up as a distorted waveform that can have a much lower RMS value than you would otherwise have if the magnetizing current were lower,



In some cases the solution is a custom transformer, in others it is just getting a transformer with a higher turns ratio,

If you can post waveforms it might give some additional clues as to what is going on.

Edit: It might just be that your transformer does not have a good enough low frequency response to support 50 Hz or 60 Hz square waves and the resulting droop in the top and bottom of the square wave will cause the RMS voltage to be lower that it otherwise would be.

 

Thank you Sir!

I tried to put some load at the output of my transfomer, and it just dropes the voltage for about 140, i think it is ok, right?

Here is some waveforms:
- Drain MOSFET
- tranformer output

I think i understood you sir, about the magnetizing currente that is droping my primary voltage, right? But I´m not sure, where to measure that in my primary transformer...

Thank you for the help!

 

Your transformer's low frequency response does not seem to be the major problem.

Maybe we should have a look at what you want to power with the output of this circuit. It might be that you need a sine wave or something close to it.

You might need to find a transformer that can output 340 V Peak from a 12 volt input under your required load. This will not be easy because most transformers do not have enough information in their data sheets to be able to knwo how it will perform in the "reverse" mode.

When I did something like this I had to test several transformers before I found something that was acceptable.

 

Your transformer's low frequency response does not seem to be the major problem.

Maybe we should have a look at what you want to power with the output of this circuit. It might be that you need a sine wave or something close to it.

You might need to find a transformer that can output 340 V Peak from a 12 volt input under your required load. This will not be easy because most transformers do not have enough information in their data sheets to be able to knwo how it will perform in the "reverse" mode.

When I did something like this I had to test several transformers before I found something that was acceptable.

Thank you sir, for your help!

I will need a pure sine wave yes, because I will power some Zelio (PLC) and some detectors (sensors), It will be like less than 10W I suspect...

I´m building some sine wave circuits, with 3 555 and the circuit that i already have with the 4047...could you help me?

I think the problem is the transformer, but....

Thank you again!

 

After studying your waveforms a little more it is clear that the secondary to primary voltage ratio is not what one would expect with an ideal transformer. Most of the difference is probably ESR and magnetizing current.

Since you have a specific load to drive with it, and the voltage is on the low side rather than on the high side, it should be safe to try those loads and see whether they perform as they should. If you you're almost done. Otherwise, you need to either increase your drive voltage or go on a transformer hunt.

Make sure you evaluate performance with the transformer under a load that is the actual intended load or that simulates it -such as having a full wave bridge, a storage capacitor, and an appropriate resistive load in the case of simulating a switching type power supply.

Gets surprisingly complicated, doesn't it?

When you get the sine wave circuit together, post it in a new thread with a link back to this one if there are a lot of similarities in the circuits. Usually a fresh thread attracts more interest from those who can help than one with a lot of posts.

 

After studying your waveforms a little more it is clear that the secondary to primary voltage ratio is not what one would expect with an ideal transformer. Most of the difference is probably ESR and magnetizing current.

Since you have a specific load to drive with it, and the voltage is on the low side rather than on the high side, it should be safe to try those loads and see whether they perform as they should. If you you're almost done. Otherwise, you need to either increase your drive voltage or go on a transformer hunt.

Make sure you evaluate performance with the transformer under a load that is the actual intended load or that simulates it -such as having a full wave bridge, a storage capacitor, and an appropriate resistive load in the case of simulating a switching type power supply.


Gets surprisingly complicated, doesn't it?

When you get the sine wave circuit together, post it in a new thread with a link back to this one if there are a lot of similarities in the circuits. Usually a fresh thread attracts more interest from those who can help than one with a lot of posts.

Thank you Sir, for your prescious help and time!
I will do some experiences with the load and see it, when I I have my sine wave completed.

Yes, It does! But It is very funny once we make something work

I will create a new topic when I have my sine wave form completed and come tests!

Thank you again Sir!