inverter transformer for sine wave generation

[GastonRafaelMelo]

Hi to all, I want to make a transformer for 12dc to 230vac inverter. The only doubt i have is the secondary feedback winding. I check the app note SLAA602A from texas instruments but there is not references to the transformer. What is the value I can use for the secondary winding in the transformer? 12Vac for feedback control?
Regards
Gastón

 

[BradtheRad]

A few basic parameters:

Size secondary wire gauge for your expected maximum current at 230V.

Number of turns should be upwards of 30x the number of primary turns. (230/12 plus 15 or 20 percent to make up for losses)

Size primary Henry value to admit expected current draw during each 1/2 cycle at 12V. Expect to add or remove turns to achieve desired performance.

Core should be sufficiently massive so it does not saturate at your expected peak current. (Peak =1.4x nominal)

 

[GastonRafaelMelo]

Hi BradtheRad, thanks for your reply. I found this old thread about the same Im asking auxiliary winding. If you could find the app note SLAA602A from texas instrument you will find that it uses a transformer with an auxiliary winding in the secundary for feedback control. How can this auxiliary reflect the change on loads? What is the voltage output? Or is just as easy as to take only from the secondary winding the feedback voltage to control the changes on loads?
Regards
Gaston

 

[BradtheRad]

When the load draws greater current, it reduces current available to the auxiliary winding... causing a drop in voltage from the auxiliary. At least that's one way to look at it.

Or does greater load watts cause higher flux levels in the transformer (and higher voltage in the auxiliary)? Another way to look at it.

Sorry I don't have more experience. One similar experiment I tried was to wrap a few turns of loose 14 gauge around a small transformer. The 14 gauge carried power to a refrigerator. I hooked up an led to a winding on the transformer. When the refrigerator motor turned on, the led lit dimly.

This suggests you can likewise experiment with a few loose turns of wire around a transformer. It should act in reverse fashion, that is to generate greater or lesser mV AC in response to power going through your transformer. Sufficient to use as a feedback signal.

 

[GastonRafaelMelo]

Thanks again. But i want to know about the voltage and current to get the feedback to microcontroller. 12Vac and about current how much mA? or is lower Vca and X mA?

 

[BradtheRad]

Usually 0 to +5V is permissible range to apply at the ADC of a micro-controller running at 5V.

As for current level, depending on internal input impedance, it needs less than 1 mA.

 

[kabeer02]

Usually is 12v - 15v Ac.. Thats auxiliary windings from a transformer a voltage divider is always used to vary the voltage from 0-5v dc...