hi need help in stepper driver

[ud23]

hi i am having problem in stepper driver crkt.my stepper motor is 1.8 step angle,2.8 A current per phase i design power mosfet H-Bridge. i do switching of mosfet when stepper not connected.but when i connect the motor the output of H bridge not switching i get continuous 24v dc from both polarity........ why this happens i hav no idea. can any one help its urgent ............

 

[alexan_e]

Post your schematic so we can see what is wrong.

Alex

 

[ud23]

here is schimatic

 

[alexan_e]

I don't see a problem in your bridge, I don't know if something goes wrong with the Dflip-flop and I don't know why you use it, you have an MCU that can generate the correct signals.
Another note is that you mention 24v , this is not shown in the schematic (you use Vcc for the mosfet) , in that case you need a level translator because the max Vgs of IRF9640 is 20v, you should drive it at about 12v, use two resistors at the collector as voltage divider and feed the gate from the voltage between them(for example 5K-5K).
If this is a real circuit you may have damaged the upper mosfets.
Also there is usually a deadtime between states and you can't do that using the flip-flop but this isn't the source of your output problem.

Alex

 

[ud23]

ht alexan u right no need of d filp-flop in ckt i tried with out d- filp flop but not get proper switching and damage my mosfet.. and as u said Vgs for IRF9640 is 20v but i give 24 v its working fine and i get my switching also good any other correction u see in schimatic......

dont use sms or short hand typing skills in this forum... type the complete words by spending few more seconds. this is the last warning and further posts and thread of yours will be deleted without informing you if continued

 

[alexan_e]

Vgs for IRF9640 is 20v but i give 24 v its working fine...

You are joking right, you are operating an electronic device above the max limit and you say it is OK?

Alex

 

[ud23]

so operating Vgs of IRF 9640 at 12v can slove problem??? i am not joking dear...

 

[alexan_e]

It depends, you may have already damaged your mosfet (I assume you talk of a real circuit), in this case it will not solve the problem.
Also if your driving signals are not correct it will not solve your problem.
Also make sure that you connect the correct part of the bridge to the end of each coil.

Alex

 

[ud23]

hi can IRFZ44 give high current at GATE voltage =3.3v? in its data sheet mention it can operate min 2v?????

 

[alexan_e]

The datasheet gives a gate threshold voltage of 2v min and 4v max , you should give at least 4v to be sure that it is turned fully on.
With 3.3v the Rds-on will be probably high and you will have heat problems because of the voltage drop on the mosfet

Alex

 

[ud23]

thnx alex but i have problem when i connect load at out put even only 1kohm resistor as load make stop switching of H bridge. only led can switch at load? why that happening can u pleas help me alex

 

[alexan_e]

What is the switching speed that you are using, do you use PWM or just the steps?
The flip--flop and the transistor can provide a very low current to the gate, this slows down the mosfet turn on/off.

Alex

 

[ud23]

hi i am using clk of 2kHz for D flip-flop and their input d1 and d2 very after 30ms steps?

 

[alexan_e]

try with a very low rate, for example 100hz or 10Hz instead of 2KHz to see if anything changes?
To have for high side mosfets of the bridge conducting (i get continuous 24v dc from both polarity as you said) can only mean thet you drive them the wrong way and they are turned on together.
Check all the connections.

Alex

 

[ud23]

hi alex i try with slow clk rate but still not working same problem occur as i mentioned b4 no polarity change at out put... what are other problems may have in hardware????

 

[ud23]

hi motor is running but it stops after 3 steps and it stops 24v smps also and IRFZ44 heat up so high why that happens???

 

[ud23]

hi here my prteuse ckt and hex file alex can u help me...

 

[alexan_e]

Your circuit schematic doesn't help, I don't have the time to design your circuit from scratch, Include your proteus project.

Alex

 

[ud23]

hi here protues project

 

[alexan_e]

The supply of the mosfets in the project is wrong, you have used VEE which is a -5v supply, if you replace it with Vcc or any other positive supply it works fine.

Alex