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Stepper motor circuit problem

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Member level 3
Sep 22, 2006
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stepper motor circuits

Hi all........
Here is a circuit below which i am using for controlling a stepper motor through PC's parallel port.
The unipolar stepper motor has a holding torque of of 21 kgcm with 2 Amps current per phase.
Problem is that i am getting only 1A current in the four wires of the motor from the driver. I tried changing the TIP 122 with TIP 142 but it did not help and the current remained the same.
Can somebody help me plzzzzz in increasing this current to 2 Amps so that i can get the rated torque which right now is not so.

stepper torque 5v 5 ohm

You have a very simple circuit, where the current is limted only by the resistance of the motor's windings. Therefore, the only way to increase the current is to increase the voltage. Since you are getting 1A at 5V, you will need to increase the voltage to 10V to get 2A.

stepper motor power supply circuit

The rating of the motor is 5V and it is a 2 phase motor, so i think i cannot give 10V as the supply.

Secondly, there is one more point. The current in the Vcc leg of the motor is coming out to be 2A and in the other 4 wires it is 1A.
Here i have a basic doubt. When we say 2A per phase what do we exactly mean? Which leg of the motor should this 2A current be available????????

Thirdly, can you tell me if i can use a readily available 500mA, 5V DC adapter to give supply to my motor???????

measure stepper motor phase current

Please give us the name and type of the motor.

lm2676 problem

It is Sanyo Denki 103H8221

Added after 1 minutes:

Other details I have already given above.
Anything specific u can ask me.

stepper motor circuit

Your motor is a 103H8221-0441 which has 2.5 Ω/phase so 5 V will give 2 A/phase.
Measure the resistances of the windings to figure out what they mean by "phase".

If you doubt your transistors you can always short them to ground and measure
the current.


    Points: 2
    Helpful Answer Positive Rating
stepper motor problems

If the motor is rated at 5V/2A, then it looks like your power supply is not able to deliver the current. Have you actually checked that the power supply still produces 5V when one phase of the motor is on?
You can actually just connect a phase across the power supply, eliminating the transistors, if you suspect they are causing the problem.

For a unipolar motor a phase is each winding, so between one of the commons and one of the other wires. Check with an ohmmeter: you should measure a certain resistance (2.5 ohm) between the common and the phase and twice that (5 ohm) between two phase outputs that share the same common.

unipolar stepper motor circuit

I am still not very clear where should i measure if the motor is getting 2A current or not ?
Secondly i am using a heavy transformer with a current rating of 7Amps producing the 5V Vcc for me through 7805 after full wave rectification.

Added after 1 minutes:

There is one problem i have noticed today. The 7805 is giving me 5V at the output with a 11V input once the motor is not connected to the circuit. Once the motor is connected the input reduces to 6.5V and output reduces to 4.2V.
Thus my motor is only getting 4.2V and that's why i think i am not getting the required torque.
But why is this so?
I even tried connecting a 7806 but the output still remained 4.2V.
What is this strange phenomenon????????
How can i give my motor its required 5V.

stepper motor circuit pdf

The 7805 has internal thermal protection that will decrease the output voltage if the power dissipation is to big.
You need a big heat sink for it - and usually a 7805 isn't specified to source more than 1 A continuously
anyway so I recommend that you get some other regulator that can handle the power.

Even better is getting a transformer with a lower secondary voltage and feed the motor voltage from it -
after rectification and smoothing, of course.

6 phase motor circuit

I already am running the 7805 with large sized heat sink but still this problem is there.
Which other regulator can i use by the way. Can u suggest plzzzzz..........
Thanks very much, u have been of tremendous help.......

current regulator circuit to step motor

In fact Voltage sould not fall. I think that the transformer that you use is not effecient powerfull.

simple stepper motor circuits

Try using a chopper driver

many of them available everywhere

the common one is l298


current boosting circuits to get 5amp from 7805

You can also build a 5V switching regulator and keep the rest of the circuit the same.
For example, you can use LM2676 from National. It will give you at least 3A.

big stepper motor voltage measurement

I havn't still got to know where should i measure the current.........
Tell me that also.......

4 phase 5v unipolar stepper motor

Here is a simple modification that will boost the supply current and bypass the 7805 problem:
**broken link removed**

stepper motor windings

If you power one phase at a time, then you can measure it either in the common or in the phase lead.

motor na 5v

Rambo i am already running with that circuit u suggested as i knew 7805 could take only 1A.

Added after 6 minutes:

VVV i havn't understood.
What do u mean " power up one phase at a time". How to do it?????????

l298 fourphase unipolar

You can manually short-circuit the collector to the emitter of one transistor with
your ampere meter and read the true current.

One needs to understand the difference between "phase" and "winding".
Here you will find a clear explanation:
**broken link removed**

And here is a quote:
Usually stepper motors have two
phases, but three- and five-phase
motors also exist.
A bipolar motor with two phases
has one winding/phase and a unipolar
motor has one winding, with a center
tap per phase. Sometimes the unipolar
stepper motor is referred to as a “fourphase
motor”, even though it only has
two phases.
Motors that have two separate
windings per phase also exist—these
can be driven in either bipolar or
unipolar mode.

tip122 tip142

Just take the two wires of one phase and connect them to the 5V supply, with an ammeter in series. Make sure the ammeter has a low enough resistance so as not to influence the measurement. Pay special attention to the ammeter leads, too. They can introduce a lot of resistance.


    Points: 2
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