Switching VCC With Transistor - Page 1
Forum section: electronics / beginners

author: halkabar
author_rank: Contributor
timestamp: March 01, 2016, 12:47:19 pm
content: My microcontroller is powered from the USB port and I want to switch power on and off for other 5V devices powered from an external DC plug kindof like I would with a relay. The GND is common through the whole system. I tried to Google it but I'm not sure what type of transistor to useThe devices are all 5V and the max current is about 1.5A.I'm looking for a preferably cheap single SMD chip/package solution if possibleThanks for helping!

author: Rager
author_rank: Contributor
timestamp: March 01, 2016, 01:04:34 pm
content: Hi,just use a N-Channel MOSFET with a low gate voltage between the device and GND. Somthing like that:That should be the simplest way :-)

author: Gyro
author_rank: Super Contributor
timestamp: March 01, 2016, 01:09:33 pm
content: Surely you need a P-Channel MOSFET so that the gate can be pulled to 0V to turn it on. If you use an N-Channel then you will need a more positive supply to turn it on.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 01, 2016, 01:10:59 pm
content: Quote from: Rager on March 01, 2016, 01:04:34 pmNot for common ground, it must be high side.While you could use a transistor (perhaps a PNP or P-channel), you'll probably have a better time with an integrated load driver like one of these:http://www.digikey.com/short/33fhq8You only need to provide a logic supply, logic input, and usually get a status signal back (indicating a fault, such as a shorted load).Tim

author: Rager
author_rank: Contributor
timestamp: March 01, 2016, 01:15:04 pm
content: I might be good I we know what kind of load you want to switch and if there are other signals going to the switched load.

author: kunzem
author_rank: Contributor
timestamp: March 01, 2016, 02:25:42 pm
content: i tend to use a p-channel mosfet with an bp-transistor on the gate that pulls to gnd, the gate is pulled up with 10k to vcc. this enables you to switch any voltage with low logic voltage.

author: Kilrah
author_rank: Unknown
timestamp: March 01, 2016, 03:58:30 pm
content: Quote from: T3sl4co1l on March 01, 2016, 01:10:59 pmHe said it currently has common ground, not that it necessarily has to be.More details needed to know whether low side switching is an option or not.

author: halkabar
author_rank: Contributor
timestamp: March 03, 2016, 10:30:01 am
content: I put together a little diagram to show my circuit. The big red box is the extra circuitry I'm trying to power!

author: Rager
author_rank: Contributor
timestamp: March 03, 2016, 10:35:40 am
content: Is there a specific reason why you want to switch the high side? Otherwise just use a N-Channel MOSFET on the low side and you are done. They are cheap and simple to use. You are switching with 5v and most mosfets do switch good at >4.5V

author: halkabar
author_rank: Contributor
timestamp: March 03, 2016, 11:07:49 am
content: http://hu.mouser.com/ProductDetail/Diodes-Incorporated/AP2511AMP-13/?qs=sGAEpiMZZMuCmTIBzycWfOPiiwtMaP0FBqtwgBaMU9XYd4x0FVpESQ%3d%3dSomething like this could do the trick right? It's fairly cheap and easy to use...

author: danadak
author_rank: Super Contributor
timestamp: March 03, 2016, 02:55:52 pm
content: Low side switching leaves the unconnected supply componentspotentially floating at the high side potential in the system. Thereare a few tradeoffs between low and high side switching, you cangoogle this to read various ap notes on the subject.Regards, Dana.