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# TIP142 Stepper motor driver

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I am going to build following circuit to run stepper motor using TIP142. So is there any need to change any thing in this circuit? The schematic of circuit is attached with this post.

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When any of your darlington transistors turns on, it is a dead short from the +24V supply to ground. The coils in your motor are never powered because both of their wires are always at +24V.

All outputs of your darlington transistors are shorted together.

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The only thing which should be connected to +V is the stepper motor common wire.

You should consider using logic level MOSFETs rather than Darlington pairs because they turn off faster and have lower losses.

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Thanks, how about the value of resistor?

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That depends on the logic voltage and collector current.

With 2k2 and a logic voltage of 5V:
IB = (V-VBE)/RB = (5-1.4)/2200 = 1.6mA

So you'll be restricted to a couple of amps before the saturation voltage becomes unacceptable..

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Now, I have try this circuit with 24V DC, 1.7Amp power supply. But still the motor does take any step (forward or backward). I think the value of resister is very much big. What it should be? And I could not understand your formula. Now how can I use it with above power supply?

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IB = base current.
V = logic voltage, which you haven't given so I assumed 5V.
VBE = base emitter voltage which is on the datasheet and is typically 1.4V for a Darlington pair.

The TIP142's saturation voltage (VCEis specified with IB = IC/100.

With an IC of  1.7A and an IB of 17mA, VCE is typically 0.75V

If the base current is lower, then VCE will be higher, if IC is still 1.7A but IB is reduced to IC/4000 = 425

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• 2 weeks later...

Thanks guys, I have try to install 1K variable resistor and have adjust it to many values. But still the motor does not move any step. Is there any way to troubleshoot the circuit?

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There's no need for a variable resistor. You could have destroyed the controller output by setting it to too lower value. Use 220R, as I said in my previous post.

I would help you to troubleshoot the circuit if you post the whole circuit rather than just part of it.

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That's not the complete circuit, it doesn't show what's driving the transistors.

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• 3 weeks later...

Now following stepper driver is successful to run the steps of motor. But there is a problem that the transistors turn hot very quickly. What is problem here. I think the resistor is small. Is it?

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If you want help, post the complete circuit, including what is driving the transistors.

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