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Need urgent help with uln2003!

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SOTX

New Member
hello there!

currently i am using the ULN2003 to drive a stepper motor exactly as indicated here

http://wiredworld.tripod.com/tronics/stepper_ckt.png

I've got it working and testing perfectly accordingly to my project needs a few months ago. Now that i test it back... the motor is turning oddly so i hooked up some LEDs to check and everything ELSE is ok accept for one major problem.

The ULN2003 is only outputting around 0.6V to the motor when it's suppose to be 12V

Does anyone have any ideas why???

THANK YOU!

ps: i am using a 8255 PPI chip to control it and the output voltage of the PPI is around 3.7V
 

MikeMl

Well-Known Member
Most Helpful Member
Do you still have 12V on the common terminal of the motor? Is your 12V supply current-limited? It looks to me that you should see near 12V on any motor phase that is Off, and VCEsat (~0.4V) on any phase that happens to be On.
 

SOTX

New Member
well my diode and my commons (from the motor) is connected to the 12V.

To test it, i am using a PC power supply therefore i doubt it's current limited (either way my whole project draws a max of 2A so it shouldnt be a problem).

The ULN2003 either gives out 0V or 0.6V (low/high)
 

Mikebits

Well-Known Member
How are you looking at the outputs of the ULN part? Scope? A DVM would not be able to measure the switching on the pins.

In other words, you would probably not measure the voltage you are expecting.
 
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Boncuk

New Member
The ULN2003 behaves just like any NPN-transistor. When it conducts the collector voltage is somewhere between 0.6 and 0.7. If does not conduct the stepper supply voltage should be at the collector since there is no current flow through the motor winding.

It does not have a HIGH or a Low output. It just conducts (switches ground to the motor).

Boncuk
 

SOTX

New Member
thx guys! it turned out that it was just my own stupidity like boncuk explained lol

in the mist of the stress i completely forgot that.

close thread
 
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