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Author Topic: Best way to control (on/off) a 12v power supply?  (Read 571 times)
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Hi everyone,

I'm looking to turn a power supply on or off based on a logic signal from the Arduino. I've looked into some MOSFET's, but from what I've found I'd need 2 MOSFETS and an Op-Amp to be able to have it do what I need - albeit without being very elegant.

I've also looked into 12v switching regulators, but I'm having trouble understanding all the components I'd need to get this to work.

And finally, I've looked into 12v step-up regulators, but I doubt that I'd be able to draw 250mA out of that using just the Arduino output alone.

I'd really appreciate any advice in this area, as I'm a bit new to this.

Thanks!

Ameen
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Turning on/off the AC (to it)?
Or leaving that on and switching the PS's output on/off?
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Actually, there is no AC, just need a 12V DC input to a component and have to figure out a good way to switch that on and off
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You probably won't get a helpful answer unless you tell us what type of component (motor, lamp, sensor, etc.) is to be powered on and off, and how much current it requires.
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Also tell us:

- whether you need to switch the positive side of the 12V supply to the load, or the negative side, or it doesn't matter which side
- whether the negative side of the 12V supply is or can be connected to Arduino ground
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I need to switch positive supply, negative is grounded.
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You still haven't told us what sort of load you will be switching, although in the original post you imply that the current draw is 250mA. If it's a steady 250mA, then a PNP transistor configured as a high-side switch, driven by an NPN transistor, is the simplest solution. However, depending on the load, the surge current at switch-on could be many times greater, in which case it would be better to use a mosfet and perhaps a current-limiting circuit. So you need to tell us more about the load being switched.
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Sorry for not being specific enough, it is this component: http://www.ridetech.com/store/ridepro-2-way-airvalve-assembly.html

Each valve requires 12v at 0.5A to close, and I need to be able to control two gates.
« Last Edit: October 23, 2013, 08:52:05 pm by slahvalyn » Logged

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With such a small load, you'd get away with something like a Tip31 power transistor (and place a diode in for any inductive kickback ) and a 1k resistor to base.

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Although prices are coming down fast for fets check out this..

http://www.ebay.com.au/itm/10A-400V-N-Channel-Power-MOSFET-Fast-Switching-IRF740-/150975673259?pt=AU_B_I_Electrical_Test_Equipment&hash=item2326d9f3ab

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With such a small load, you'd get away with something like a Tip31 power transistor (and place a diode in for any inductive kickback ) and a 1k resistor to base.

He's already said that he wants to switch the positive supply to the load, not the negative supply, so this solution is not applicable.


Prices for mosfets in SMD packages are already low in many cases. However, assuming the OP wants to use breadboard, stripboard or perfboard to build this and doesn't want to solder to an SMD device, he'll need a P-channel mosfet in a TO220 or IPAK package. One of the cheapest is the old IRF9530. It can be driven from an NPN transistor and a couple of resistors. Or he could buy a ready assembled module here http://www.ebay.co.uk/itm/20V-High-Side-Switch-module-Arduino-chipKIT-Launchpad-/190900133017?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item2c7288dc99 and just add the flyback diode.

[EDIT: added schematic of the mosfet/transistor option]


* Scan 215.JPG (66.95 KB, 1653x1165 - viewed 21 times.)
« Last Edit: October 24, 2013, 04:13:59 am by dc42 » Logged

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On gadgets like that,   what is the significance of the square and round holes ?
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This is great! Thanks so much for your help, and for the diagram!

Btw, dc42, to me it looks as if the square and round holes are to differentiate between your signal and ground if you have it mounted MOS side up
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