Go Down

Topic: Best way to control (on/off) a 12v power supply? (Read 982 times) previous topic - next topic

slahvalyn

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

Runaway Pancake

Turning on/off the AC (to it)?
Or leaving that on and switching the PS's output on/off?
"Hello, I must be going..."
"You gotta fight -- for your right -- to party!"
Don't react - Read.
"Who is like unto the beast? who is able to make war with him?"

slahvalyn

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

jremington

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.
"It seems to run on some form of electricity"

dc42

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
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

slahvalyn

I need to switch positive supply, negative is grounded.

dc42

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.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

slahvalyn

#7
Oct 24, 2013, 03:50 am Last Edit: Oct 24, 2013, 03:52 am by slahvalyn Reason: 1
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.

cjdelphi

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.


cjdelphi

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


dc42

#10
Oct 24, 2013, 10:48 am Last Edit: Oct 24, 2013, 11:13 am by dc42 Reason: 1

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.


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


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]
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

michinyon

On gadgets like that,   what is the significance of the square and round holes ?

slahvalyn

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

Go Up