# Switchover between two power supplies using FETs

Trying to create a switch-over with two p-channel MOSFETS using arduino. I need to switch between 2 sources with a GPIO pin from my arduino. I've looked into ideal diodes such as the LTC4414 and the LTC4415 but its hard to get them with my local supplier and I want to see if this is possible using FETs. I've seen some solutions using just diodes but I am not really interested in the inefficency they introduce.

The purpose is to do a power switchover e.g. source 1 dies, source 2 switches on.

Source 1: 11.4v, 1300mah nimh

Source 2: 12 DC wall adapter

The circuit it powers will sometimes require somwhere between 2-4 amps peak.

Would the following circuit work?? I don't have any p-channel mosfets to test it out (side note: recommendations welcome). I'm trying to keep everything through-hole (yes I know ... relic of the past) but I don't have the necessary gear to solder small stuff.

• – Ignacio Vazquez-Abrams Nov 27 '16 at 21:35
• i'm looking at your design, but I fail to understand it fully. all it does is switch from wall to batt when wall isnt present. but more components would have to be introduced to make this happen only when given the high/low signal from the MCU? – Jeffrey Dang Nov 27 '16 at 21:58
• Your current circuit has some problems. Let me ask some questions. Do you need IO control of the switchover, or would it be OK to make it so Source 2 is the priority source? In other words, so whenever Source 2 is present, Source 1 will be disconnected? Also, I assume you do not want current to flow into Source 1, right? And you also do not want current to be supplied by Source 1 when Source 2 is present? Because you may need two back-to-back FET's in series with Source 1. Also, maybe you only need a diode on Source 2. Not a FET. Please answer all questions. – mkeith Nov 27 '16 at 23:45
• How much voltage drop is acceptable? – ThreePhaseEel Nov 28 '16 at 1:21
• Note that you're feeding 12V from SOURCE2 into your Arduino via R4, so your circuit will blow up instantly. – Dmitry Grigoryev Dec 7 '16 at 15:35