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Electronics => Electronics => Topic started by: parthik on March 17, 2008, 08:36:20 AM

Title: ULN 2803-
Post by: parthik on March 17, 2008, 08:36:20 AM
I am driving a unipolar stepper motor with a ULN 2803 and a avr ATMEGa32

the problem is that i have to increase the current input to the stepper motor to 1.7A(each motor) to make it run .
But the rating of ULN is 500mA which made me burn many ULN's...

My friend runs steppermotor using 1A(for both motors).

also can u show me a ULN circuit diagram? cause I have got it from a book so not sure if it would work. ....
I am using a 9v stepper motor and .8A current but when i fit the wheels , the stepper doesnt move until i increase the current upto 1.7A.
PLz help
Title: Re: ULN 2803-
Post by: Rebelgium on March 17, 2008, 09:13:26 AM
If the ULN can only let 500mA pass, another circuit won't increase that...
Title: Re: ULN 2803-
Post by: parthik on March 17, 2008, 11:28:10 AM
but how cme my motor consumes so much current?...

its a minebea unipolar stepper motor .
Title: Re: ULN 2803-
Post by: izua on March 17, 2008, 03:22:40 PM
make a power stage with 4 transistors, or if you wish to do bipolar stepping, with two h-bridges.
Title: Re: ULN 2803-
Post by: Rebelgium on March 18, 2008, 04:15:04 AM
but how cme my motor consumes so much current?...

its a minebea unipolar stepper motor .

-because that's just a characteristic of that type of motor.
-because the motor shaft is jammed and the motor stalls.
-because you connected the the motor wires wrong.

choose one  ;)
I suspect the last choice most.
Title: Re: ULN 2803-
Post by: paulstreats on March 18, 2008, 07:47:31 AM
here is a circuit showing a uln2003 driving a motor, it connects the same as the uln2803.

(http://www.cs.uiowa.edu/~jones/step/examplef/3.gif)

Ignore everything in the diagram but the uln2003, and just connect your microcontroller outputs to the left side of it where the 4 wires are now.

The 500ma rated current for the darlington array is for a single darlington set(pin), so if you had a couple of darlingtons you can probably connect them in such a way as to share the load between more than 1 pin. Before you do this, definately make sure that your stepper is connected properly otherwise it will just increase current draw
Title: Re: ULN 2803-
Post by: ed1380 on March 18, 2008, 07:57:31 AM
check the datasheet to see if stacking is allowed.
you could put them on top of each other and double the ouput
Title: Re: ULN 2803-
Post by: karmax on March 27, 2008, 02:09:37 PM
pls use driver with 4 transistor or attach 4 ic in parllel