How can I reduce the voltage output from power supply?

[Mark42]

I have a 120 v AC to 20 v DC (1 amp) power supply that was used to power a PC printer. I now want to use this supply to power another device but I want to reduce the voltage to about 12v dc.

What do I need from Radioshack to cut back the voltage and still keep the 1 amp output?

 

[Windykid]

Re: How can I reduce the voltage output from power supply?

Possibly a large variable resistor.

 

[i386]

Re: How can I reduce the voltage output from power supply?

IMHO, a 12V 1A power supply would be easier to obtain and cheaper too than trying to hack something up. Not to mention safer.

Where I used to work, we had all sorts of power supplies that looked like the ac adaptors you see powering everything these days. Instead of having a cord with connector on the end, they had screw terminals so you can wire them to whatever you need. We used them to power security and alarm panels. I'm pretty sure they're available in just about any configuration needed. You're welcome to PM me if you want to go any further in this direction. I still have good contacts there.

 

[JB]

Re: How can I reduce the voltage output from power supply?

You would need a 12v regulator circuit with a 1A output capability, Mark.

A EE could design you one using easy to find, but not cheap parts, but it would be a lot simpler to just get a 12v, 1A power supply.

 

[Xcusme]

Re: How can I reduce the voltage output from power supply?

A LM7812 12 volt voltage regulator should work fine. I'd figure on a heat sink too.
example:
http://www.radioshack.com/product/i...&cp=2032058.2032230.2032279&parentPage=family

 

[gonefishie]

Re: How can I reduce the voltage output from power supply?

Save yourself the trouble and go buy another one. It's a lots more complicated to alter the voltage output of a power supply then just a voltage regulator. I know this for a fact. I used to build them all the time.

 

[bruceb58]

Re: How can I reduce the voltage output from power supply?

This is a no-brainer. Forget the regulator. Pay the $10 for a different power supply. The power dissipation(8W) alone would kill the part without a heatsink on a T0-220 package and would likely be damaged even with a heatsink.

What are you trying to power?

Look on Ebay...there are many on there.

By the way, I am an electrical engineer.

 

[bruceb58]

Re: How can I reduce the voltage output from power supply?

Here is one for you:

http://cgi.ebay.com/Power-Supply-12...ryZ79816QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

 

[JB]

Re: How can I reduce the voltage output from power supply?

It wouldn't have to dissipate 8W, Bruce. Pulse modulation and a filter with about a .5s rise time would dissipate much less, but cost a LOT more.

 

[bruceb58]

Re: How can I reduce the voltage output from power supply?

JB...you are correct...you could also build a DC-DC switching power supply for that matter.

 

[Mark42]

Re: How can I reduce the voltage output from power supply?

Thanks for all the input. I took the majority advice and found a power supply from an old laptop that is 1amp at 16vdc. That will work just fine.