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Simple circuit for switching between 2 power supplies?

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OradFarez

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Can anyone recommend a little circuit I could use to switch the power input between a 5V DC jack and the 5V USB power pin input?

I'm trying to create a way to power a circuit from either but neither can dump back into the other and I don't want to use series diodes because of the voltage drop at high currents. Ideally, I would like power always in from the DC jack if available and only switch to USB if no DC adapter is available.


Thanks for any help someone may have.
 

You can try schottky diode.
Schottky diode has very low voltage drop.
The low voltage drop can be about 0.3A or lower
depending on the current drawn.
This shouldn't affect your circuit much,
because most IC have relatively wide voltage supply range.

You can givce it a try. 1N5817, 1N5818, 1N5819, 1N5820, 1N5821, 1N5822

You can find a series of schootky diode in the table at the bottom of the webpage.
**broken link removed**
 

Hello. The current would be 0.5A through the USB input (which is the limit for one port) and the current through the DC jack could be up to 1.5A.


I have thought about the schottky diode option but the higher current ones drop 0.4-0.5V and that is too much.

I was hoping there might be a MOSFET based solution or similar?


Thanks for your help!
 

You will need the diode because of the FET internal protection diode
The 3pins DC POWER JACK pin 1 connected to GND (pin3) when the DC plug pull out and connect to DC power when the DC plug inserted
 

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    OradFarez

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Thank you both for these circuit options. It gives me more to consider.
 

Thanks. I was looking up MAXIM parts today. That particular one cannot supply enough current. Its only purpose is to charge a battery.

I'm looking at the MAX891L as a decent solution. It is a high side MOSFET that blocks power from the USB input when the DC jack is plugged in. I don't really need the OR'ing feature as much as I want blocking of both power sources used simultaneously. I think this will do it.
 

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