Hi, experts!
What is, in your opinion, the best transistor switch for this app?

+12V
|
|
|
LOAD----<-<-<-- Transistor Base----<-<-<---PIC output (max 10-20mA)
(5-10A)
(3-4 A may also work)
|
|
|
GND

The load is a stepper motor winding so of course i need 4 switches.
I am looking at BD679 or BD649, but I'm, open for suggestions.
I want a clean, simple circuit so darlington transistors are preferred.

 

We ask that posters not hijack existing threads by placing their questions in the existing flow. Especially when the thread is 2 years old - http://forum.allaboutcircuits.com/showthread.php?t=6168. It can be confusing as to which question is being replied to.

Perhaps you might think of a current limiting resistor in the base circuit.

 

I am very sorry I did that. Can I move it to a new thread or post it again to a new thread?

Anyway, yes, a resistor limits base current to 10mA.
Transistor idea?

 

Which type of stepper?

Sometimes an IC like the SN754410 (quad half H-Bridge driver, upgraded L293D) is a simpler solution for small steppers, for the currents you need, an IC driving the transistors also frees up some pins on the PIC.

 

As has been pointed out already, you have failed to tell us which type of stepper motor you are using. This information goes to the heart of the solution you request.

Knowing whether it is a bipolar or a unipolar will help us help you.

hgmjr

 

Thanks !

 

bdx53 or tip122

 

I did my first tests using small steppers and the 2N2222 was enough.

With a Darlington transistor, your 10 mA base current could be much more than what you need. It all depends what stepper (thus what transistor) you use.

Restating the obvious.

Buena suerte.