I need build or find an off the shelf item that will allow me to switch between two step down supply voltages, i.e., 1.5 volts and 12v via a logic signal. Supply would be 3A max.
For example a high signal would have the device supply 1.5 volts and low signal would have the device supply 12v. Any ideas?
Simple Change over relay.?
I thought of a relay but would rather not use a mechanical device.
Use 2 logically controlled elelectronic swiches. I have one to swich mains, 230 bolt AC on, or off, by an UNO.
Same project? PWM would be the easy, cheap and flexible solution but it seems you're still trying to do it the hard way.
@wvmarle
Up to 3 Amps to handle…..
Connect the low voltage permanently via diode, switch the high voltage on demand.
That will reduce the 1.5 volts because of the voltage drop across the diode. Min the demand of as much as 3 Amps.
Increase the supply voltage by the diode drop.
Could work as long as the current is not varying too much. Anything using 1.5 volt very likely calls for some precision. Let Op tell about that.
Perhaps it turns out that a 4-20mA current loop output shall be implemented.
@DrDiettrich
Current loop? Supplying as much as 3 Amps?
I'm looking at using the NDP6020P p-channel mosfet.
The specs state the the maximun gate to source voltage is +-8v.
Does this mean that the gate voltage can be greater than the source voltage by as much as 8v?
Are You sure You must use P-channel MOSFETs? Logical N-channel MOSFETs interfaces much more easily to stuff like Arduinos.
Of course a current loop can be operated using a wallwart with 3A printed on it.
duinoMike:
Does this mean that the gate voltage can be greater than the source voltage by as much as 8v?
A source/gate voltage of more than 8volt (positive or negative) will damage the fet.
This is a low voltage fet, with a very low threshold voltage (~0.7volt).
Probably very fragile (ESD), so take care.
Leo..
Hi,
Is this the what you want to use it for?
https://forum.arduino.cc/index.php?topic=634982.0
Tom... 
Yes, I need high side switching to choose between the two supply voltages. The two options I have come up with are:
Two high side p-channel mosfets one with a "supply voltage" of 1.5 volts but would be triggered by a "LOW" or ground at the the gate. Otherwise it would be 5v at the gate. The other mosfet would have a supply voltage of 12v and high/low or 5v or ground. If this does not work out, option 2.
The 12v p-channel on one side, on the the other a DC-DC step down converter supplying 1.5v with an N-channel mosfet turning the converter off and on.
I prefer option #1 above, simpler. Getting back to my original question, can I have a 1.5v supply voltage on the p-channel mosfet with 5v from Arduino turning it off?
1.5volt on the source and 5volt on the gate (mosfet off) is 3.5volt difference.
1.5volt on the source and 0volt on the gate (mosfet on) is 1.5volt difference.
Both are within the 8volt limit.
Not sure if the mosfet can provide enough current with only 1.5volt gate drive.
Don't know if you already have cross-posted this elsewhere,
but is that 12volt coming from mains power and the 1.5volt from a battery?
Can't you use a 12volt relay with NC contacts for the 1.5volt source.
Leo..
@duinoMike, do not cross-post. Threads merged.