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Switch question without voltage drop

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superflux

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I have attached an image.

I have 2 voltage sources coming in the circuit (X and Y). If voltage is present on X, then Y is not needed. X takes priority in this circuit, so Y is only used if no voltage is present at X.

Currently, I am using a mechanical switch as in the top diagram. I want to get away from this; however, I need 5v at Z whether using X or Y.

If I use a transistor, such as a PNP, in the lower diagram, which would tell me if X is off, then I would have to use a Diode on X to prevent the voltage from Y altering the state of the transistor. When I add the diode, I will get a minimum of a .6 voltage drop which I cannot have. I must have 5 volts at Z.

I'm looking for solutions.


Thanks!


 
Last edited:

superflux

New Member
Hopefully this will help a bit:

I'm using a PIC 16F88 to read voltages from an automotive sensor. The "Load" would be the ADC input (PORTA,4). I have a 1k resistor before the ADC port to reduce the current.

I haven't calculated the "base" resistor for the PNP transistor, but it shouldn't take much current to saturate the transistor.
 
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