Transistor Switch or Relay?

Thread Starter

wordizlife

Joined Sep 29, 2011
6
Hey Guys,
I am designing a circuit that will require a PIC16F877A to comunicate with another pic and the pc through serial communication. I want to be able to control a certain portion of the circuit and be able to cut power to it. I am currently using a 2n3904 as a switch, the base is connected to my microcontroller pin through a 10k resistor and there is a pull down resistor of 100k also. All the negative connections of that portion of the circuit are connected to the collector of the 2N3904 and the emitter to the circuit ground.

For some reason the transistor is not working, it says it can handle up to 200 ma of current and my circuit is putting out less then 150 ma. Should I be using a relay for this and controlling this relay with the transistor switch?

I have attached an image of the schematic, the highlighted blue line are the negative connections of the circuit I want to control.

Thanks
 

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ErnieM

Joined Apr 24, 2011
8,377
I'm with chrisw: I can't make out a thing on your schematic.

A good schematic follows a general form to make it comprehensible in a purely visual manor.
 

Thread Starter

wordizlife

Joined Sep 29, 2011
6
You don't need to get all the details. All you have to understand is that I am trying to control the power to two microcontrollers, a PIC18F2480 and a MCP2551 chip with the use a transistor. I have a 10kohm resistor that goes from my PIC16F877A pin to the base of the transistor and a pull down resistor of 100kohm from the base of the transistor to ground. My emitter is directly to ground and my collector is connected to the load.

what reasons would cause this not to work? The voltage is successfully switching to 5V at the 877A output but the transistor is not giving sign of life.

( I will be cleaning up that schematic to make it clearer because I do agree that it is messy, but for now the image I posted and the explanation should be good enough)
 

chrisw1990

Joined Oct 22, 2011
551
sorry, and im not intentionally being a pain, but i cant picture the words, your saying you have this and that resistor, thats great, but i cant picture it, and i cant imagine jack so youll have to draw a little sketch? on paint or something, just draw the basics, then we can get somewhere:D
 

LucyJW

Joined Apr 20, 2012
1
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