DC-DC step up?

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I'm currently working on a project that has 1 component (a dc water pump) that requires +12V. I'd like to use the current +5V supply the rest of the project uses however I'm not exactly sure how to get up to 12V. This is all a bit new to me so I checked out the DC-DC wikipedia entry where I read up on step-up converters which seems to be what I'm looking for. If so, can anyone point me in the right direction as to what exactly I need in order to build one? Or is there a better option available such as a simple/cheap IC?

Thanks!

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It is certainly possilbe to build one, but...

If you are only building one device, and your goal is to focus on the remainder of the project, a small voltage converter module is the fastest / easiest approach.

How much current does the 12 V motor require? Be aware that the start up current will be higher than the steady state current.

Are you drawing power from a 5 V regulator? Can you tap into the 5 V supply input? It is very inefficient power and heat wise to go from X volts, down to 5 Volts, then back up to 12 volts.

Digikey Part number: 179-1003-ND as an example, is a 5 V input, 12 V, 500 mA output, 6 W, power supply module.

Digikey has 100's to select from.

JC

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It would help to know how much current the pump takes, and how much is available from your 5V supply.

Four legs good, two legs bad, three legs stable.

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Thanks guys,

I'm at work right now so I can't be sure but I think the pump requires 1A. I am coming off of a voltage regulator (7805 I think), I see what you mean about the inefficiencies from going down then back up. I think my supply is around +9V.

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If your supply is around 9V it's probably possible to run the motor directly from it if it can source the current you need. You can usually run motors with less voltage than they are rated for - they just run slower.

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I had the same plan, no luck =[. I don't think it's pushing enough current.

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Not because of inefficiency, just simple arithmetic. Vanilla 7805 = 5V @ 1A, to boost that to 12V @ 1A just aint possible.

Four legs good, two legs bad, three legs stable.

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Well thats why I'm askin' = ], after looking the prices on these things ~$30+ - would it just be a better option to use a separate supply in conjunction with a relay to trigger the pump?

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If you are looking for efficiency you need a switcher. Otherwise, you just need a 12V transformer and a bridge rectifier and a BFC and you have a nifty unregulated supply to run the pump. The V will be a little hot when the pump isnt running... around 16V, but it will pull down to 12V under load. Pump shouldnt care.

Imagecraft compiler user

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Starting with a power supply that is appropriate for the pump, rather than going through the 5 V stage is a much better plan.

At that point, however, you probably do not need TWO power supplies. Think of replacing the present power supply with the new one, not adding to the current one.

I.E., Use your 10-12 V transformer or 12 V wall wart, etc., to power both the motor, AND to be the primary source feeding your +5 V regulated supply. This eliminates another 120 vac plug, cord, additional transformer, additional bridge rectifier, etc.

JC

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sfriederichs wrote:
If your supply is around 9V it's probably possible to run the motor directly from it if it can source the current you need.

Or run the 12V booster from the 9V input. How much current can that supply give?

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DocJC wrote:
Use your 10-12 V transformer or 12 V wall wart, etc., to power both the motor, AND to be the primary source feeding your +5 V regulated supply. This eliminates another 120 vac plug, cord, additional transformer, additional bridge rectifier, etc.

JC

Thanks guys!

I think I'll try to take this route.

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You surely have an old computer lying around, out of which you can take the power supply, haven't you?
Zoltan

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Ohh, now thats not a bad option - I guess it'll come down to a trade off on visual style - the big clunky power supply isn't exactly appealing to the eye with my little project.

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There are various 12V switchers that can supply a couple of amps that come with various electronic gizmos. I have a couple from external DVD drives that can have both 12V and 5V lines, with an amp or two each. You might want to watch around for such units.