ULN2803 heats up

[sith108]

I connected my ATmega8 to a 12V Stepper Motor via ULN2803. The motor worked fine but the ULN2803 heats up so fast.
Why is this happening ?
Should i use some Zener diode or something ?

 

[ericgibbs]

I connected my ATmega8 to a 12V Stepper Motor via ULN2803. The motor worked fine but the ULN2803 heats up so fast.
Why is this happening ?
Should i use some Zener diode or something ?

Do you have any suppression diodes across the stepper windings.?

Whats the current requirement of the stepper.?

 

[sith108]

I'm using a Mitsumi M35SP-8 stepper motor.

Datasheet
https://www.electro-tech-online.com/custompdfs/2009/03/motor_m35sp_8_e-2.pdf

 

[sith108]

Do I need a zener diode?
What sort of zener diode do I need?
Why is the ULN IC getting heated up ?

 

[blueroomelectronics]

The ULN2803 can handle that stepper, it's not unusual that it gets hot. Don't add the zener though.

 

[sith108]

Thanks Sir

 

[blueroomelectronics]

PS you still need to connect clamp to +12

 

[sith108]

Yes. I got that.

 

[Willbe]

If the case boils water it is at 100C. Knowing θjc from the 2803 datasheet will let to calculate what junction temp it is running at.
If you can't touch the case it's at more than ~71C.

 

[mvs sarma]

Internal protection diodes are not enough
let there be additional protection diodes (like FR 306) close to the windings.. then it would behave better.

 

[Ubergeek63]

first of all, the clamp pin should be cennected directly to the rail.

second of all, you should, as has been mentioned, add external schottkys instead of relying on the internal clamps.

Third of all, if you want something done right, do it yourself. The ULN2003 is an antique darlington driver, using FETs would give you 20% more power.

Dan

 

[AlainB]

Hi,

The motor needs about the maximum of what the ULN2803 can give. Using a small computer fan will help to remove excessive heat. The schematic posted before show a ULN2003 witch is a 16 pins IC. The ULN2803 has 18 pins and it is possible to parallel inputs and outputs in order to use all the 8 inputs and outputs available for a single motor.

Alain

 

[mvs sarma]

Hi,

The motor needs about the maximum of what the ULN2803 can give. Using a small computer fan will help to remove excessive heat. The schematic posted before show a ULN2003 witch is a 16 pins IC. The ULN2803 has 18 pins and it is possible to parallel inputs and outputs in order to use all the 8 inputs and outputs available for a single motor.

Alain

By the way, providing a fan for a drive chip of a motor that takes less than 0.25A load, we travel nowhere, i fear.
the chip can be cooled by an heat sink pasted on it by some adhesive that would withstand heat of 70 deg Celsius.

 

[AlainB]

In order to obtain the maximum torque from the motor it should be run in full step mode, that is 2 phases (coils) energized at the same time. The current through the chip is then more near 0.5 A. I suppose that this is the way sith108 is driving is motor. Otherwise the chip would not heat so fast.

Anyways, I know a small fan will work. I experimented it. Heat sink would probably work too but I find it more complicated.

Alain

 

[Ubergeek63]

In order to obtain the maximum torque from the motor it should be run in full step mode, that is 2 phases (coils) energized at the same time. The current through the chip is then more near 0.5 A. I suppose that this is the way sith108 is driving is motor. Otherwise the chip would not heat so fast.

Anyways, I know a small fan will work. I experimented it. Heat sink would probably work too but I find it more complicated.

Alain

so switch to an Allegro FET based chip that will do all your stepper logic and current source it for you.

 

[AlainB]

Yes, of course, this will cure his ULN2803 problem. Once in the drawer, the chip will not heat a bit.

I am sure that we could add 100 more replies to this post stating how not to use the chip. But what is the point? This chip is a nice chip to learn about, not only for controlling a small stepper motor, and the question, witch is about overheating, worth an answer in my opinion.

Alain

 

[Ubergeek63]

Yes, of course, this will cure his ULN2803 problem. Once in the drawer, the chip will not heat a bit.

I am sure that we could add 100 more replies to this post stating how not to use the chip. But what is the point? This chip is a nice chip to learn about, not only for controlling a small stepper motor, and the question, witch is about overheating, worth an answer in my opinion.

Alain

of course it is. it is asked and answered between 2 and 4 times every month, and is always asked because there are so many hobbyist sites, new and old, praising the stupid thing as a godsend.

If someone is just playing to learn let them use what they want and not complain if it is not perfect. If, on the other hand, they have an actual thing they want to work reliably, let them be advised of the proper way to do it.

fact is, you can NOT be rid of overheating when you are trying to drive motors that want the full rated capacity of a chip, and if it is one meant to have heat sinking, you will be even worse off since there are not many hobbyists that will realize it never mind be able to do so.

Dan

 

[Roff]

Internal protection diodes are not enough

Do you have personal experience that confirms this?

let there be additional protection diodes (like FR 306) close to the windings.. then it would behave better.

The flyback diode is to protect the switch, not the motor. Therefore, the diode needs to be as close to the switch as possible. This way, it will also protect against stray wiring inductance.

 

[mvs sarma]

Do you have personal experience that confirms this?

The flyback diode is to protect the switch, not the motor. Therefore, the diode needs to be as close to the switch as possible. This way, it will also protect against stray wiring inductance.

Yes I have experiences
The reason for mounting it close to motor is, any back emf return path should generally be closer to the source of such back emf (obviously the inductive component)
. So I am sure, Ron, that the device be closer to the generator so that it needs to travel minimum to get a return path.

 

[Roff]

Yes I have experiences
The reason for mounting it close to motor is, any back emf return path should generally be closer to the source of such back emf (obviously the inductive component)
. So I am sure, Ron, that the device be closer to the generator so that it needs to travel minimum to get a return path.

I see your point. I hadn't thought about EMI problems that would be exacerbated by having the diode located far from the inductive load, so I now understand the need for mounting it close. In the case where there are long wires between the switch and the inductive load, a diode near the switch (built into the ULN series, but not into most other devices) is also desirable.