Discuss About Stepper Motors in the UK Electrical Forum area at ElectriciansForums.net

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Actually there is another forum discussion until reaching this cct here. It was an entire evolution of it.
This cct is working ok but in certain parameters. It is limited to power and heat over the Tr's.
Is working fine in the 5V range for 2 of my stepper motors that I tested with it. But if Im bringing up the voltage, to 10V, I get 140dgrC on one Tr and about 60dgrC on a few others. At 5V, everything stays at a constant 50dgrC which I call it normal and safe.
One of the test motor is a Nema17 17HS4401. The other one is a scrapped stepper. Both work fine at 5V and even at 10V, no one was heating. Over 5V, especially at 10V, only the driver's Tr's were cooked to (almost)death. I stopped the power after smelling hot metal in the air.
I am also receiving a couple of L298N IC's. They are coming in the mail, not arrived yet. But I dont expect much difference from them, compared to what I have here. It would be nice to be better ! I hope so.
- My question:
- How to make this cct more powerful? To drive more power through the coils of the stepper motor? (and not blow up it's Tr's!)
I already have 2 answers to this question in my mind, but I dont want to influence your answer. I expect to be pleasantly surprised. Haha.
4wire 2phase2coil Stepper Motor logic circuit v3.jpg
Thank you !
 
You have a fundamental problem with using BJTs like that, in that the switch off time is longer than the switch on time.

As the lower BJT only needs the voltage to go from 0 to 0.7v or so, whilst the upper one needs the voltage to swing down much further.

So when you drive one transistor on, the other which is on via the inverter will remain on for some time before switching off, resulting in both transistors on in series across the supply for a brief time.

I assume it is the lower one which gets too hot BTW.

You either need a delay between switching one off and the other on, or use FETs/MOSFETS which as long as you drive the gates correctly will avoid this.

EDIT:

You could of course just replace the whole driver circuit with a dual H bridge chip, which control this internally, something like the DRV8841, this is good for diving circ 2.5A in the coils up to 24V or so, which will allow a 5V circuit to drive a higher voltage on the motor, or the one you suggest.
 
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I have studied what you presented and here is a quick response.

1. The 2 phase bipolar stepper motor is being driven by the circuit in 'wave mode'. This means that only one of the two coils is energised at a time. The angular steps of rotation are 90 degrees.

2. The use of the CD4017 provides a state sequence 1000, 0100, 0010, 0001. This 4 bit code controls the two H bridges to energise the stepper motor as I have shown in the attached electrical art.

3. You could produce more torque by a factor of sqrt(2) ie 1.414 if you had a switching sequence which energised two coils at a time - see the link below and the section on 'Full Step two phase on' mode. Steps are still 90 degrees.

4. If you used the mode mentioned in (3) you could stick with the present coil currents and yet produce more torque. Would this be helpful? Of course the transistors need heat sinks etcetera.

5. I would use a H bridge ic designed for the purpose rather than make my own as you have done. If I had to make my own I would use paired npn and pnp power transistors but preferably complementary power mosfets - in both cases to avoid the inverters.

6. The use of a 4017 decade counter limits your ability to generate switching waveforms to control the H bridges. I would use binary counters with decoding to switch transistors by combinational logic or an eeprom.

Have a read through this:

Stepper Motor Basics - https://www.orientalmotor.com/stepper-motors/technology/stepper-motor-basics.html#:~:text=In%20the%20wave%20drive%20method,only%20one%20phase%20is%20energized.
 

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Here is the version that I tested already and is NOT working with the current logic cct and the IRFZ44N mosfets. I believe it should have worked with what I have here already. No?
1666548580049.png
 
There are two versions of this enhancement mode mosfet. The IRFZ44N which requires a gate to source voltage of at least 3V to start to turn on and 10V to be fully conducting. Your drive circuit does not achieve this for the upper two transistors.

There is also a version suited to being driven by 5V logic - the IRLZ44N - which turns on at about 3V and is fully conducting with 5V between gate and source.

But there is another problem with this circuit which is that the source of the upper transistors is not directly connected to 0V. So these source pins will be at a higher potential than 0V because there is the coil between their source pin and ground. And the coil is switched by the upper mosfet to a positive rail which can have a voltage higher than 5V. Your 4017 has a maximum output of about 4 to 5V and thus is unable to elevate the upper mosfet gate potential sufficiently high to turn the IRFZ44Ns on fully. The potential on these gates may not even exceed the minimum gate source voltage of 3V required to begin to turn them on.

I will say more tomorrow. A bit rushed but I hope you get the idea. Fortunately there are solutions.
 
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