pnp transistor..need help

Thread Starter

daredavel

Joined Feb 22, 2010
32
hello sir! i have problem testing the 2n3906 pnp transistor..i dont know what is the correct pin config of the 2n3906..(E-B-C) or (C-B-E)..i've tested both config..but nothing happened..the bad part, my pic16f77 was damage..i don't know why..if it has any connection to the transistor.. i also have tested it in my breadboard, without the pic to make sure first that i have correct pin assignments..still i dont know how it operates..i cant make the led lit..i can figure out the correct pin assignments.

here is my schem:



Here's the setup i've tested on my breadboard to test the transistor:
5v supply

 

Thread Starter

daredavel

Joined Feb 22, 2010
32
@Alberto: My friend told me to its better to use pnp in multiplexer sir..and the the circuit is already running in the simlation using proteus.

@MMcLaren: i think so sir..because the multiplexer part was done by my friend..and also the programming..i'm the one in charge with the pcb and to make it running in actual..
low volts are req to activate the pnp transistor.. i haven't studied the program yet, but how can pic16f877 produce a logic 0? to activate the pnp? thank you so much!
 

Thread Starter

daredavel

Joined Feb 22, 2010
32
by the way sir, how can you output a logic 0 in pic16f877? to control the transistor? and Why is pnp is commonly used in multiplexer instead of npn? thank you sir!
 

AlexR

Joined Jan 16, 2008
732
As others have said you are better off using a NPN transistor if you are doing low side switching (transistor between load and earth). PNP transistors are generally used for high side switching (with the transistor between the supply rail and the load).

Get rid of R28, R29 and R31. They serve no purpose other than increasing the current though the transistors.

Also add 1K or 470Ω resistors in series each of the transistor bases to limit the base current and protect the PIC ports.

Of course you will need to change the software so that a logic 1 turns on a LED or segment rather than logic 0 as it does now.
 
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Thread Starter

daredavel

Joined Feb 22, 2010
32
if i use a npn sir..without the pull-up resistors or putting a pull-down resistor, my simulation goes haywire..if i connect the pull-up resistors R28,R29,R31..the simulation is working fine.. i dont know whats the reason behind..??
 
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