Regulated ac-dc converter

[cjl222]

I am looking for a circuit which will take an ac input from 5 V to 15V and will give an output of 12 VDC +/- 3% @ 3A throughout the input range. The frequency range is 90-1200 Hz and there needs to be aboy 200 vac isolation

 

[Heydave]

Begin on page 35 of this link:

http://www.linear-tech.com/pdf/an19fa.pdf

They have several regulators of this type that may have the switch current you need with isolation @ 3%. Note that with 5 volts input and 12 volts out @ 3 amps, the switch current will be quite high. You may want to have a load resistor to insure 3% regulation if the load is highly variable. You will probably need to design your own transformer to get the desired output voltage. The isolation mode for these regulators effectively uses the transformer turns ratio to determine the output voltage.
This 5 amp part may get close:

http://www.linear-tech.com/prod/datasheet.html?datasheet=210

If you can derate the output current for lower input voltage or parallel supplies, you might get there.

http://www.inventgineering.com/

 

[Skogsgurra]

You should be a little careful with the 10 V, though. Smoothing it after rectification will give you somewhere between 11.5 and 12 V when loaded and a little more than 12 V unloaded.

It is because of the peak rectification that takes place and since the peak voltage is sqrt(2) higher than the RMS value you will have a higher than expected voltage. So be prepared to adjust the turns ratio of the transformer.

Or use 12 V AC and put a linear regulator after the capacitors. Normal regulators need at least 3 V to "drop off" so you can not use 10 V AC. You need a high current regulator and a good heat sink if the load is 3 A.