Power supply question

Kaos Kidd

I would like to know if AMPS double in connected regulators.

For example:
I have a very healthy 12v DC power supply that can deliver up to 20 amps.
My intention is to put a voltage divider to create two 6 volt rails.· Each 6 volt rail will power a 5 volt and 3 volt voltage regulator.· That's a total of 4 regulators in all.· Tie in the grounds into one common ground, some heat sync compound and a good heat sync tied across all four regulators.
If I'm that close to the max safe output of·one regulator, should I:

be content with four seperate power busses?

If I tie the 3 volt output from each 3 volt regulator into one 3 volt rail:
Will the·total available amps·on the 3 volt rail be the sum of the regulator's max output?
Will the amp draw be spread out across the regulators?





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Propeller + Hardware - extra bits for the bit bucket =· 1 Coffeeless KaosKidd

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Javalin

Ouch - the voltage divider is massivly in-effeciant. Look at switching voltage regulators - you can get them as a complete part (i.e. minimum external parts required). You'll typically get > 80% efficiancy too. As they are so efficant there is minimal heat loss - compared to a linear Low dropout reg - which looses the exces voltage as heat.

P = V x I

Power (watts) = Voltage by Current.

So if you halve the voltage you have to double the current = yes. Obviously if you loose loads on the conversion it doesn't quite work that simply.
>Will the amp draw be spread out across the regulators?
no - unless you spread the load yourself.· You generally shouldn't have two regulators feeding the same load - I forget exactly why - I think they
oscillate or something.· You can purchase 5amp, etc, regs.

J

Post Edited (Javalin) : 4/15/2008 9:43:48 AM GMT

Ale

Yes and No.

Yes if you trasform power (but the efficiency is never 100%, near 90% is more normal).

No if you do not transform power. i.e. Using a series regulator means that the difference voltage between input and output times the current is lost power in the regulator.

This is basic stuff, has nothing to do with the propeller. Please read the datasheets for a common series regulator like the 7805 and for a switching regulator like the TL494. Plus, at national semiconductor's site (www.national.com) for these and other regulators (like LM317) there are application notes that describe how regulators work, the different types and so on. Please download them and read them, and try the circuits so you can see and experiment with those circuits. The best way to learn.

Edit: Ops, javalin I did not see you post.. I was just writing!, is ok.

Post Edited (Ale) : 4/15/2008 9:51:44 AM GMT

stevenmess2004

I don't think that connecting regulators in parallel because each one of them puts out a slightly different voltage which can cause problems. It is fairly simple to just include a big transistor or mosfet driven by the regulator to give you more current. What you want is something like this www.elecfree.com/circuit/power-supply/7805-mj2955-power-supply-5v-5a-for-digital-circuit/

If you do this than you shouldn't need the voltage divider.

Edit: Thinking about this some more. You can connect regulators in parallel but you have to put a small resistor on the output of them so that you don't get into problems with the different voltages.

Post Edited (stevenmess2004) : 4/15/2008 11:58:13 AM GMT

Kaos Kidd

I was just wondering what my options were.
The issue is I'm drawing enough through one regulator that it's very warm (not hot)...
I heat synced it, but in thinking about it, and reading everyone's replies...
that a larger regulator or a new dedicated power supply will solve the issue..
Thanks every one.

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Propeller + Hardware - extra bits for the bit bucket =· 1 Coffeeless KaosKidd

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hippy

Kaos Kidd said...
The issue is I'm drawing enough through one regulator that it's very warm (not hot).

Warm not hot ( in fact not "ouch" hot ) is in my experience acceptable. I have a 12V-6V linear regulator for a very old digital camera ( ~1A draw ) with a largish heatsink which doubles as a hand warmer.

It's not so much how much current your source can deliver but how much is used and how much the regulator has to dissipate.

stevenmess2004

There is no problem if the regulator is only warm. In fact, most regulators have protection devices to turn them off if they get too hot. If you have the data sheet for the regulator it should have temperatures for the regulator to run at and some thermal conduction figures. These allow you to choose the right size heatsink for the voltage drop/current that you want to run at. If you get a switchmode regulator than it will be much more efficient but I think that they need a few more components than normal linear regulators (not sure as I have never used one).

If you have a data sheet I can show you the calcs you need to do to figure out the heatsink/voltage/current you can do with the regulator you've got.

Ken Peterson

switchers are more expensive than linears and they produce electrical noise which may or may not be a problem in your case. It's a trade-off. If you have a very high power app, or perhaps one supplied by batteries that needs more efficiency, then the added cost of a switcher is well spent.

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The more I know, the more I know I don't know.· Is this what they call Wisdom?