adjustable output for ac-dc rectifier

[jn1009]

how to make 12v ac dc rectifier

I have a really simple question. I am trying to create an ac-dc rectifier with adjustable dc output. I figured I would be able to buy one online, but have been unable to find it yet. So, I just figured I would make one. My basic theory is to connect a 120v ac voltage converter (small transformer) to a rectifier which should be able to give me an adjustable dc ouput. However, after searching radio-shacks and the internet I have been unable to find a schematic for such a device. The closest thing I found was "VM 1868 - Switching AC to DC Power Supply" but that only goes up to 12v DC. here is the link for the device above: https://www.voltage-converter-transformers.com/switching-ac-dc-supply.html
I want to use the device to replace batteries in battery hungry electronics. I have one that uses 6 D-cell batteries and eats a set of new batteries every week.

ANy advice on how to make one or where to buy one would be great.

 

[banjo]

ac dc rectifier

What you are looking for is a battery eliminator. Do a web search and you will get lots of hits. Typically the AC is first reduced in voltage by a transformer. Next the AC is rectified to DC. Then this DC supply is regulated down to the voltage you need. By using an adjustable DC regulator, you can get any voltage you want. Take a look at the LM317. This is a very popular regulator IC. If you device draws lots of current, be sure to use a heatsink.

 

[nxtech]

You can also try straight recitification. That is just elminate the transformer and replace it with a high current resistor, an X2 rated cap, a zener of your voltage choice, then a recfiting diode. See Microchip app note AN954 or On Semi app note AN8146/D.

**broken link removed**

https://www.onsemi.com/pub/Collateral/AND8146-D.PDF

In either circuit there is (or should be) a series fuse, parallel MOV, series resistor, series X2 cap, parallel zener, series diode, and a parallel capacitor (filtering) before the LM317.

Hope this helps.

Eric

 

[nonot]

Could you implement some type of switching power supply? You could use a uproc for the feedback to control the switching.

Alternatively, once you've converted AC to DC you could use a resistor network with a pot to feed an op-amp, with a current amplifier to follow the circuit.

 

[sahn001]

As nonot said, switching method is easy and simplest way..
Check this out,