Regulating a 12V power supply ??

[jtice]

I have a 12V 10 amp power supply.
I am wanting to know if there is a devise I can hookup to it, and regulate the voltage, and amperage comming from it.

The purpuse will be to test different led and resistor configurations.
Basically, I need to be able to dail in the exact valtage and amps I want.
I know there are actual power supplies that do this, I have seen them for around $80, but, this power supply I have is very nice, so I didnt want to completely replace it.

I would prefer something with a digital readout if not too pricey.

Thanks alot for your help.

 

[EvilLithiumMan]

I suspect that even if you recieve 100 replies, there won't be any two of them that match.

Yes - there are many approaches to modding your supply. It all depends on time, money and level of expertise. Do a search in Google for things like "12v regulated supply" "adjustable DC power suppy schematic" "current regulated power supply". You will find dozens of schematics and approaches and probably a few good electronics forums.

You will need some knowledge of basic DC theory; a Community College course may be in order. Never-the-less, it sounds as though you already have the most important element - a willingness to learn and a 'do it yourself' attitude.

(I apologize if you were hoping for a 'Just go to Radio Shack and buy a Whack-A-Doo 5000 Dual Metered Adjustable Volatge/Current module' response. If time is of the essence, then you probably should buy something off the shelf. But knowing how things work can save you lots of dollars in the long run. When Nimh cells came to market, I didn't have to trash my Nicad chargers, I modded them. And then I modded those to handle the Li-Ion I currently use).

 

[jtice]

Evil,
I dont nessesarily want to modify my power supply, but rother, add something to it.

Plug the power supply (unmodded) into a variable regulator.

I have seen plenty of variable power supplies, but sence I have a nice one now, I wanted to just add something to it, and use it. Instead of buying an entirely new system.

 

[Doug Owen]

A useful idea, and fairly easy to implement if you don't need full 12 Volt range.

I suggest looking into the LM723 ($.29 at Jameco, currently, pun intended). It's a standard 'open frame' linear regulator which will do 150 mA 'barefoot' and over 10 amps with the proper external transistor. Good voltage control, excellent current regulation, option for constant current or current foldback, minimum parts count, what more did you want?

Doug Owen

 

[jtice]

OK, a couple questions...

Whats the difference between foldback current, and constant current?

What you mentioned, is it able to be easily adjusted?
I need simple fast adjustment, for current and voltage.

 

[Doug Owen]

[ QUOTE ]
jtice said:
OK, a couple questions...

Whats the difference between foldback current, and constant current?

What you mentioned, is it able to be easily adjusted?
I need simple fast adjustment, for current and voltage.

[/ QUOTE ]

Constant current I think you understand, you hit that current and the supply then controls output voltage to maintain that current. In foldback systems, once current hits the setpoint, limiting pulls it back to a safe value (say a quarter of that value) until you either remove the load, get the current under the new 'safety' value, or reset the system. Kind of like a smart circuit breaker.

Yes, it's adjustable from 2 to 37 Volts (assuming the raw supply is up to it). Getting under 2 Volts can be done, but it takes more parts.

Current as well.

Check the spec sheet.

Doug Owen

 

[jtice]

I am not sure how to go about using that chip.
I want something with digital readout.
Basically, I am wanting to make some thing like this, out of my power supply.
http://www.circuitspecialists.com/prod.itml/icOid/18
Or, should I just sell mine, and buy one like this?

 

[Doug Owen]

[ QUOTE ]
jtice said:
I am not sure how to go about using that chip.
I want something with digital readout.
Basically, I am wanting to make some thing like this, out of my power supply.
http://www.circuitspecialists.com/prod.itml/icOid/18
Or, should I just sell mine, and buy one like this?

[/ QUOTE ]

I guess I don't know what you should do. Given certain skills, the LM723 is a very simple part. It needs a small capacitor, a transistor (to boost output current) and 3 resistors in the Figure 4 circuit from the spec sheet. Two of those resistors set the voltage (formula there), the third the current limit. For meters you might buy two of Rob's $10 DMMs.

Or buy the one on the web....

Doug Owen

 

[Floating Spots]

I've had good luck getting Sorensen or Xantrex supplies on Ebay.
I got one that lists for $765 for $110 delivered.
This was for a 300 watt quarter rack supply.
Some of the 60 watt linear quarter racks may be had cheaper.
The prices fluctuate wildly on these on Ebay.
Some are steals while others I wouldn't touch.
You just have to watch for a while....

 

[star882]

Have you tried the MAX797?
http://www.maxim-ic.com/quick_view2.cfm?qv_pk=1190&ln=
It says that the max output is 6v, but if you read the datasheet, you will find out how to raise the Vout above 6v.

You can also try the MXL1074 if you want a simpler circuit (but less current).
http://www.maxim-ic.com/quick_view2.cfm?qv_pk=1276&ln=