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TIP142 Stepper motor driver

crazybuoy

Sep 19, 2010
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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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davenn

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have a look at where the "stepper motor common wire" is going to
the motor wont run with it in that location

also look how the +24V is wired..... when any one of the transistors is switched on
the 24Volts will be grounded At the moment the 24V is going to all coils of the
stepper motor contineously... that is... it isnt being switched therefore the motor
wont work even if the "stepper motor common wire" was in the correct place

go have another try and come back with a new drawing and see how you do :)
its all in the learning

D
 
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crazybuoy

Sep 19, 2010
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Yes, I understand that I should only provide +24 to motor's common wire. I also recognize the common wire. How about the value of resistor?
 

davenn

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Yes, I understand that I should only provide +24 to motor's common wire. I also recognize the common wire. How about the value of resistor?

no the common wire should go to GND and the switched 24V to each of the coils of the motor
dont worry about the resistor at the moment, you have much bigger problems to deal with

read my second paragraph above and see if you can figure out where you went wrong
with the outputs of the transistors

I'm trying to guide you to fault find for yourself rather than give you the answers outright
you wont learn anything if I do that :)

another hint..... ignore the O1 label for a moment.... just take 1 transistor, the top one, Q1, you have 24V going to the collector of the darlington transistor. The emitter is going to ground (GND) .... what do you think is going to happen if you turn the transistor on by applying base volts ?

Dave
 
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crazybuoy

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Thanks much, now I understand that I should only provide +24 to motor's common wire. And what if I increase the value of resistor for more security of COM port?
 

davenn

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Thanks much, now I understand that I should only provide +24 to motor's common wire. And what if I increase the value of resistor for more security of COM port?

again I say... forget about the resistor you still have much bigger problems.....
you didnt answer the questions I asked or read where I said the common wire should go.

to quote my last Question to you....
another hint..... ignore the O1 label for a moment.... just take 1 transistor, the top one, Q1, you have 24V going to the collector of the darlington transistor. The emitter is going to ground (GND) .... what do you think is going to happen if you turn the transistor on by applying base volts ?

can you see what is going to happen ? you are going to short cct the +24V to ground
via the collector/emitter jnct of the transistor. This, putting it very mildly, is gonna be VERY BAD for the transistor

So.... if you have the +24V going to the collectors of each transistor, where do you think the emitters of each transistor should be connected to ?

Dave
 

crazybuoy

Sep 19, 2010
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Thank very much, now I have understand that the transistor will be shorted and the motor will also not turn with same polarity input from coil & common wire.
 

davenn

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Thank very much, now I have understand that the transistor will be shorted and the motor will also not turn with same polarity input from coil & common wire.

where do you think the emitters of each transistor should be connected to ?

Dave
 

crazybuoy

Sep 19, 2010
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Actually, I find this citcuit using Tip120 and I only replace it with Tip142 as it can handle more amp & volt.

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?
 

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crazybuoy

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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?
 

(*steve*)

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What is driving the bases of those transistors?

And it's a 48V motor right?

Is it a 6 wire stepper motor? And the other wires are connected to -24V?

I'm no real expert in this sort of stuff, but you're not providing enough information.
 

crazybuoy

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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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(*steve*)

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No.

But it may have something to do with the power dissipated in the transistors.

What current do the motor windings draw at 48 volts (it seems you're using 48 volts for the motor)?
 

(*steve*)

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It is mentioned thus, but you show the rails as being +24V and -24V. That is 48V, not 24V.

Do I assume you are correct, or your schematic is?

Have you measured the voltage across the transistors when they're turned on? Do you know the current that they're passing? Are they saturated (is it near Vce(sat) for the device?)

What is the power dissipation?

Do they have a heatsink?

How many degC/W is the device case to air (with a heatsink if you have one)?
 

aharrison

Nov 14, 2010
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In your diagram, you have notated the transistor emitters as "-24V." This is not correct; you should show this point as ground. This same ground point should be connected to your driving logic's ground.

You should have +24V connected to the motor common wire, as you show it.

The transistor base resistors (R1, 2, 3 and 4) should be selected according to the transistor hFE and the collector current drawn by each motor winding. The general equation is Rb = (Vlogic-Vbe)(hFE) / Ic, where Rb is the base resistor, Vlogic is the voltage provided for a logic "1" state by your driving circuit, Vbe is the transistor base-to-emitter "on" voltage, hFE is the transistor's gain, and Ic is the motor coil current. So, as an example, given a motor coil current of 1A, a Vlogic of +5V, and an hFE of 1000 for the TIP142 transistor, Rb = (5V-3V) (1000) / 1A = 2000 Ohms. In these assumptions, I am ignoring the TIP142's internal resistors, which would use about 370uA of the base current, and I am using the Vbe(on) value of 3V from the Fairchild TP142 data sheet.

You may want to add back-EMF protection diodes across each motor winding, Type 1N4004 will work for a small motor using 1A per coil. These diodes will protect the transistors from the voltage induced in the motor windings when they turn off, and also possibly prevent inadvertent upsets in your driving logic. However, doing so may also affect the torque characteristics of the motor by maintaining winding circulating current. Also, add a decoupling capacitor from your motor's common wire to ground, such as a low-impedance 100uF, 35-50V electrolytic type.

If the motor still doesn't run, examine the logic sequence driving the bases. A four-channel oscilloscope would be ideal for this purpose. I hope this helps.
 
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