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Author Topic: L297 with external N CH Mosfet H Bridge Design  (Read 3151 times)
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usrrsr
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« on: May 22, 2012, 07:37:47 07:37 »

I have designing mosfet driver with L297 stepper motor driver IC. I have tested it in proteus & find works 100 % OK. But before going further to go for manufacturing of the PCB i want the experts opinion form Sonsivri members. I have attached Proteus file for both Unipolar and Bipolar motor.
Request to check wheather i am going wrong somewhere.
Note that i am assuming that L297 output pins will drive IRFZ44 MOSFET to give at least 7 Amp @ Vgs = 4.5V.
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zab
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« Reply #1 on: May 22, 2012, 08:26:37 08:26 »

Hi usrrsr,
I do'nt think that I will work. Basically  L297 stepper motor driver IC is used with  L298 IC.
Ic L297 does not have built in High side driver .Secondly high side transistor need 2 connections. one connected with gate second with source.

There is no difference between your bipolar and unipolar circuits.
bipolar transistor is current operated device while unipolar is voltage operated device. the way to bias these is quite different.
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usrrsr
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« Reply #2 on: May 22, 2012, 09:34:00 09:34 »

There is no difference between your bipolar and unipolar circuits.
bipolar transistor is current operated device while unipolar is voltage operated device. the way to bias these is quite different.
Thanks zab
I mean by "bipolar and unipolar circuits" means "bipolar stepper motor driver circuit  and unipolar stepper motor driver circuit "
I have used Mosfet which is Voltage activated device unlike transistor which is current driven as you said
The main idea behind making this project is to keep same bridge for Bipolar as well as Unipolar motor. I have studied the step sequence for both types of motor and bias these the way it will full feel the step sequence requirement of motors.

Incase of unipolar motor (5,6 wire) normally common pin is tied to Vcc then you need to pull rest of the pins to GND in proper step i have testing it in two coil activate mode ie in each step 2 coils are always activated to give more torque.

Incase of Bi-polar motor (4 wire) each pin is tied to Vcc / GND alternatively as per step sequence. I have full filled this basic requirment of both of this type of motor and hence i think protesu is in position to simulate it properly.

Also if you see block diagran of L293D,L298 and ignore safty circuit you will find my design much similar. Also L293d also used dual H bridge and some articles shows that it can drive both types of motor.

Awaiting for your comment on this

Posted on: May 22, 2012, 09:11:27 09:11 - Automerged

If you are constructing a new stepper driver, would not it be better to use a modern IC as the TB6560?
http://www.semicon.toshiba.co.jp/docs/application_note/en/TB6560AHQ-ANE_en_090324.pdf

I am alternatively evaluating the Allegro A4989 and LS8292 too and actually best for stepper driver with microstepping  
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gan_canny
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« Reply #3 on: May 22, 2012, 10:23:36 10:23 »

The point about the high side driver and separate gate connection is very important. In the H bridge the N FET's are stacked this effectively raises the ground potential of the high side FET . This means it effectively raises the gate voltage to fully turn on the high side FET relative to the low side FET. There are other issues to address like time to switch off and on the FET's ..You can't have the same side FETS on at the same time. It's a short circuit and FET's though they switch fast aren't instantaneous. An H bridge driver chip will manage all this and take care of the high side gate. The back EMF of the motors needs to be absorbed use a transorb or high amp protection diodes to protect the FET's.
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zab
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« Reply #4 on: May 22, 2012, 10:38:25 10:38 »

Incase of unipolar motor (5,6 wire) normally common pin is tied to Vcc then you need to pull rest of the pins to GND in proper step i have testing it in two coil activate mode ie in each step 2 coils are always activated to give more torque.
in this you need one transistor for each coil. You can use any transistor for this only thing to take care of biasing of transistors.

Incase of Bi-polar motor (4 wire) each pin is tied to Vcc / GND alternatively as per step sequence. I have full filled this basic requirment of both of this type of motor and hence i think protesu is in position to simulate it properly.

Here you need the H Bridge. You can use here any transistor but the biasing comes critical.
the high side transistors are used in common collector mode. means you on base B you require high voltage to shift Vcc voltage to emitter E of the transistors.this is for bipolar transistors. voltage on coil would be .5 lower than voltage provided on the base.
For lower side transistors operating in common emitter mode you only need .5 to .7 max. volt with respect to ground.


for unipolar high side transistor you need special circuitry.



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