Reasons for ULN2003 to heat up

[Wond3rboy]

Hi, i wanted to know what could be the reasons for a ULN2003 driving a stepper motor would heat up, assuming all connections to be correct. One reason that i concluded was the current rating of the stepper motor( say a 1 Amp stepper motor being driven with the ULN2003 having an Ic of 500ma). Are there any other reasons?

 

[Nigel Goodwin]

It gets hot because it's dissipating power - it's a VERY inefficient chip, due to the way it's designed, with a fairly high voltage drop across each transistor.

Bear in mind, it's rated dissipation will be with the chip so hot you can't touch it.

 

[nsaspook]

Hi, i wanted to know what could be the reasons for a ULN2003 driving a stepper motor would heat up, assuming all connections to be correct. One reason that i concluded was the current rating of the stepper motor( say a 1 Amp stepper motor being driven with the ULN2003 having an Ic of 500ma). Are there any other reasons?

I usually epoxy a small heatsink on the chip when driving anything near the max power rating.

**broken link removed**

Even a small copper coin works. (cheaper)
US pennys before 1982 were almost pure copper.
**broken link removed**

 

[spicydeath82]

lol, i like the penny idea.

 

[kjennejohn]

Cool! (pun intended) Where can I get the finned heat sink?
kenjj

 

[nsaspook]

Cool! (pun intended) Where can I get the finned heat sink?
kenjj

Most online supply houses have them.

Heat Sinks | Newark.com

 

[kjennejohn]

Thanks for the tip. I'll have to put that under my "ElxSupplies" folder in Favorites.
It occured to me after posting that there is another possible QnD candidate for use as a heat sink: Binding clips.
These can be found at any stationary store or big box's stationary section. Naturally these only apply to devices with large sink tabs, installed upright, not against the board. The use of a paper clip in your photo made me think of these.
Later.
kenjj

 

[Blueteeth]

If it still gets super hot with a heatsink, thought about using MOSFET's ? Even the small SOIC ones can switch a few amps at a relatively low frequency without even getting warm. Although I guess that depends on what you're using to drive the ULN2003. Might be over kill, but they are so cheap these days.

 

[kjennejohn]

DigiKey carries the Vishay N-Channel IRF520 MOSFET for $1.70 each. This will handle 100V, 9.2 Amps! The data sheet is at:
https://www.electro-tech-online.com/custompdfs/2010/07/91017.pdf
This will handle up to 60W in free air, heatsinking will allow more dissipation and so more power. This part has its own internal reverse EMF protection diode. I have a motor controller board that has four of these. The gate lead is connected directly to a PIC processor pin, so this is easy to set up and use.
Later.
kenjj