multiple powser supply switching.

Thread Starter

Kiyoshi7

Joined Mar 9, 2016
6
hey I'm making an analog PID board that is controlled by a pic24. but i'm having problems with the power supply. the parts that work are the PID +16v and -16v, my analog pwm 0v and 16v, but my mcu supply is the problem I can power it from the same source as the PID/PWM circuit (using a voltage regulator seeing that the pic uses up to 3.6v, 250mA). My problems are the following:
1. I don't know if I can use the same GND as the I power the pic from a usb or if I have to the usb's gnd.
2. the same as above but for the pickit3
I want to prioritize the pickit's supply (cause I don't want to interfere in the programming) over the usb and usb's supply over the PID/PWM's supply. Using the datasheet I know how to switch from a power supply to usb supply. I'm believe that when there is power on Vself, usb supply is turned off, so to do what I want i'd have to add another pnp (between Vself and the node at the transistor base), am I correct?
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Dodgydave

Joined Jun 22, 2012
8,601
Your regulator doesn't have a gnd supply, also what is the 100K resistor for on the output of the regulator? all gnds need to be connected together or your circuit wont work.
 

Thread Starter

Kiyoshi7

Joined Mar 9, 2016
6
thanks, that circuit is from the datasheet, I already altered it. ok so I don't have to isolate the pic from the rest of the circuit when it's connected to the usb or pickit and I won't destroy my usb port or pickit right?
 
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