UNL2004a Darlington Array overheating and melting breadboard.

Other Hardware Motors, Mechanics, Power and CNC
1

hi

2

so I have a UNL2004a darlington array that I´m using to drive a unipolar stepper motor.

I followed the motor knob tutorial on arduino.cc

I have a bench lab power supply that is providing the motor with 2.5v, the current draw is 800ma.

I´m having issues with overheating of the darlington array.
so my question is, is this the current draw too great for the array and if so should I add resistors to prevent it or change to a ready made unipolar motor driver ?

thanks

r.

3

btw, the motor needs 2.5v and 800ma to run. thats what is specified on it anyway and there are no heating issues with the motor itself.

4

so my question is, is this the current draw too great for the array

Each darlington can only drive 500mA, and about 650mA for the package.
See:-
http://www.thebox.myzen.co.uk/Tutorial/Power_Examples.html

the motor needs 2.5v and 800ma to run

You normally run a motor like this with a current regulating chopper driver not a darlington.
You use higher voltage, normally 12 or 24 V.
Like these:-

5

If you want to drive a low voltage unipolar stepper motor in unipolar mode you
would use MOSFETs, not darlingtons, darlingtons waste 1 to 2V, you only have
2.5V to start with.

Choose logic level MOSFETs with Rds(on) < 0.2 ohms or so and they'll handle it OK.
Choose ones with Rds(on) < 0.04 ohms and they won't even get warm.

You haven't said how many wires the motor is - if its 6 or 8 wires it can be
configured as bipolar and driven via chopper-drive IC. If its 5 wires it cannot and
you are stuck with unipolar drive.

If you have 4-wire motor you are confused!

6

Don't lots of stepper motors have four wires ?

Like this diagram Pololu - Bipolar stepper motor wiring diagram.

7

michinyon:
Don't lots of stepper motors have four wires ?

Like this diagram Pololu - Bipolar stepper motor wiring diagram.

They do but you can't drive them with simple darlingtons, you need a H-bridge.