Unipolar stepper motor with ULN2003?

[musicworld1]

hi

Last time I was designing like this . I attack this to computer before start computer. After start I write codes and run only 3 steps. I find that IC and motor are going very much hot, then I disconnect all connections to IC. It really was near to be burnt, if I do not disconnect. What was the problem in circuit? I think it may be in its ground or +12V wire. Is it?

[vger]

Sounds like too much current for both the IC and Motor. What are the specs on the motor? The ULN2003 will only handle 1/2 Amp per output. That is the absolute maximum with only 1 output on. If you have the ULN2003N package IC then it will only handle that much current on one output for about 85% on time. If 2 outputs are on, then only for about 45% on time. Assuming you are using 2 coils energized at the same time, then you must limit the current to about 0.3 Amps. Take the coil resistance (measured from red to one of the other wires) times 0.3 to find the safe voltage to run this at.

Steve

[musicworld1]

I have found the reason not the solution, it is that I am using the computer power supply. The +12V point has 6 Amp, as written on info sticker of computer power supply. But ULN2003 require only 0.5 Amp, that’s why my whole system was getting so much hot. But how to arrange the correct power supply (12V & 0.5 Amp). Which is cheep & easy source?

[vger]

I believe you do not under stand the basics of electricity. Current (amps) in a circuit is based on 2 things, the voltage applied and the resistance of the circuit. A car battery is capable of delivering several hundred amps, but does not burn out a small little light bulb that draws only 0.5 amps. You will need to limit the current some other way. Reducing the voltage will do it, increasing the load resistance will do it.

Do you have a multimeter?
Does the motor have any label on it that says it's voltage or resistance rating?

You might try reducing the voltage from 12 Volts to 5 Volts.

Steve

[musicworld1]

I find some thing written on my motor. That is:
60C 45
5 DEG 13 (ohm) MAS
You can also read more about this motor from http://www.compucanjes.com/products/view/14268.html. what is basic formula to set at any system.

[vger]

Ok, 13 ohm... at 12 V that will be 0.92 amps. 12/13=0.92
If you reduce the voltage to 5 volts... 5/13=0.38
It will be 0.38 amps per coil. This is still too much for the ULN2003. You must use a different IC with this motor. Or you could use this motor with 5 volts if you add a 5 ohm resistor to each of the yellow, brown, black, and orange leads. You must also put a heat sink on the ULN2003.

Steve

[RomanLini]

For that simple a driver you can just buy 4 FETs, and connect the 4 gates to the parallel port and the 4 source pins to ground. It will function basically the same but you can drive 1A or 2A stepper motor from 12v with no problem.

[musicworld1]

Using power transistors like TIP120 is also batter. But would you like to suggest me a good professional design of stepper deriver of medium level? You may suggest more than one.