Issues with controlling bipolar stepper motor with H-Bridge

H-Bridge

Hi!
This is about stepper motors.......

I have a bipolar stepper motor (2 windings and 4 wires 2,6Amp, 24V) and are trying to controll it by using a H-bridge (Mos transistors) and a µ Processor.
I have 2 questions.
1:
Why using N-MOS and P-MOS transistors, why not only N or P?? (i have a schematic with N and P).
2:
My motor wants 2,6 Amps and i have to use current control, i know how to sense the volt over a resistor but if i nead 2,6A the resistor must be rated for i think 10W,is ther another way to regulate the current? switching?

Greatfull for some help.

Hi,
1.- N channel MOS are more common and less expensive, and not difficult to drive with 24V DC rail.
2.- You HAVE to regulate current by switching. Otherwise you end having some some sort of audio amplifier instead a motor control.
There are many ways to sense current. You could use SENSEFets, or try something like a IR2175
http://www.irf.com/product-info/datasheets/data/ir2175.pdf
Keep in mind that if you design your own current sense circuit using a resistor in series with the motor winding you'll have a huge common mode noise.
Best regards

jorgito said:

Hi,
1.- N channel MOS are more common and less expensive, and not difficult to drive with 24V DC rail.
2.- You HAVE to regulate current by switching. Otherwise you end having some some sort of audio amplifier instead a motor control.
There are many ways to sense current. You could use SENSEFets, or try something like a IR2175
http://www.irf.com/product-info/datasheets/data/ir2175.pdf
Keep in mind that if you design your own current sense circuit using a resistor in series with the motor winding you'll have a huge common mode noise.
Best regards

Click to expand...

I should design h-bridge drive for a dc servo motor.
How can i regulate current by switching? Could you please give some information?
Regards.

Hi ash,
There are many ways to switch transistors in a H-Bridge to control current. I think the 3 more common are Bipolar, Unipolar and Phase Modulation.
In the Bipolar you switch diagonals of the bridge alternatively, connecting forward or reverse voltage to the motor winding. This method causes more current ripple.
Unipolar switching uses a transistor ON and pulses the diagonal to modulate voltage to the motor winding. Usually you keep ON the lower TR in the bridge leg because is easier to keep switching the upper TR in a high voltage bridge.
Phase modulation keeps BOTH legs of the bridge switching at 50% duty cycle, but you change the phase between them to apply voltage to the winding.
If you switch both legs in phase, you are connecting the winding to 0 volts or rail voltage at the same time, effectively shorting the winding. But if you drive both legs 180 degrees apart, you are appling full voltage over the winding.
Try to search apps notes from Intenational Rectifier.
Hope this helps

Re: H-Bridge

Hi TrixMan

You can measure your current directly over the channel of your N-FET. In the 'on' state, the FET is nearly like a (very small) resistor. So you need no additional resistor (noise, oscillation, ...)

Bye

Re: H-Bridge

1:
Why using N-MOS and P-MOS transistors, why not only N or P?? (i have a schematic with N and P).

Click to expand...

It's basicaly the same...
many MOSFET process (called Tmos , dmos ...) features very low Rds-on (~10 mohms...)
that are ideal to reduce heat - dissipation by transistor and loss of power in h-bridge application

y motor wants 2,6 Amps and i have to use current control, i know how to sense the volt over a resistor but if i nead 2,6A the resistor must be rated for i think 10W,is ther another way to regulate the current? switching?

Click to expand...

... P=RI² .... if you want smaller resistor, use low ohmic value (and a good amp with it ...). seach for so-called "shunt-resistor"

As mr_ghz said, sense the Vds voltage is an easy way but don't expect accuracy !
moreover, current profile depends of the switching mode of the hbdrige.


To understand how to drive hbridge (switching) , can have a look to app notes/datasheet of hbridge manufacturers (st, national, ...)

Re: H-Bridge

"Why using N-MOS and P-MOS transistors, why not only N or P?? (i have a schematic with N and P)."

Because P-N (Cmos) configuration can be drive easyly. But If you use double N mos or double P mos, You need the extra voltage for driving the upper sides mos.

"My motor wants 2,6 Amps and i have to use current control, i know how to sense the volt over a resistor but if i nead 2,6A the resistor must be rated for i think 10W,is ther another way to regulate the current? switching?"

You can decrease the power lost of sense resistor, İf you use very small resistor for current sensing. If you need high signal voltage you can add a dc amplifier for current signals.

There are some methodes for current sensing but thats usualy expensive.
Forexample DC current transformers...

Re: H-Bridge

Have a look to www.allegromicro.com
there are many components to drive step motor.