batteriespower supplyswitches
I want to make a device that allows the user to switch between two different power sources (a wall mount and batteries).
I could perform this circuit using two DPDT switches, but I would need to switch the two switches each time I want to change sources. Is there a simpler way to perform this function without using relays?
Here's a schematic of my device as a reference:
Well I finished it, basically I had to switch the source instead of the drain using comparators to prevent the transistors of acting like resistors and draining power. For those interested here falstad simulation the actual circuitry what we choose/created is placed.
It basically switches either one of them (by means of a comparator, op amp in circuit, - I simply forgot active items when placing this question). It switches based on some reference values. Experience in practical comparators dictated now that the source for the comparator always should have a higher voltage than both inputs - thus the inputs should simply be halved. Also from experience we had to add a "pull up" resistor. But other than that the circuit worked.
The digital schematics are there to provide hysteresis as the solar cell array can only provide power for half the time (values of current source & capacitor bank are adapted to be able to simulate without waiting hours).
Best Answer
The easiest solution (Initially suggested by @PeterJ) Would be to simply switch only the power connection:
simulate this circuit – Schematic created using CircuitLab
Alternatively, you can probably get away with just using some schottky diodes:
simulate this circuit
Wow, Circuitlab is a clumsy tool. It doesn't have entry/exit ports? Or Schottky Diodes? Really?
But if you're really loading your RPi or it's USB ports, the drop in the diodes could be large enough that you get brownouts, which would be a real pain in the ass to diagnose.
The best solution, I think, would be to put the diodes before the voltage regulator.
This would mean you would have to have a higher power supply voltage (>7V), but it would solve the problem with the diode Vf described above.