Electronics > Beginners
How to change politary of a circuit
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1makermold:
How could I change the polarity of this circuit, to use PNP transistors
Pooldawg:

--- Quote from: 1makermold on May 29, 2019, 02:33:23 am ---How could I change the polarity of this circuit, to use PNP transistors

--- End quote ---

Without seeing what the two rail inputs are doing, it is a little tough.

You can simply swap in the transistor, however your "enable" for the transistor will also be swapped.  When it is a low, the transister will turn on, and when it is a high, it will turn off. Vs now it is off when low and on when hi. 

This simple video may help you:

MarkF:
Is this for Lionel Model Railroad?  Is it DCC?
This takes some thought.  I re-arranged the circuit to make it clearer to me.

   
mikerj:
What is the problem with using NPN transistors?
1makermold:
Yes this is a circuit for Lionel trains that run on 0-18 vac. It is not DCC
 What it does is when it gets a signal of positive dc voltage to the outside rail it turns on the optocoupler and it turns on the whistle, I would like to reverse the polarity so when I send a negative dc voltage to the outside rail it would activate a bell.
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