Low Torque N-channel Mosfet H-bridge

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Omar El Kelany

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hi,
i made this h bridge as shown in the schematic...it works fine but gives very low torque....when i connect the motor to a power supply it draws about 4 amp but when i connect to the h bridge it draws 0.25 amp ....also i tried a bigger motor it didnt work at first(at low pwm) and it made a humming sound then at increasing the pwm it rotated about complete revolution then it started making small steps( about quarter revolution) making humming sound at stopping...help as soon as possible
thanks in advance



 
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Hi
1-How much is frequency of your PWM ?
2- why you didn't use eliminator filter in your out put terminals ?
3- why you've connected D1 and D2 across the mosfets ? your mosfets have internally diodes hence those diodes are not required .
4- see the voltage across the GS of each mosfet . and show me the results .
5- see the voltage across the motor and show me it .
6- see the voltage across the DS of each mosfet and show them .
By the way decrease the series resistor with gates from 330 ohms till 10 or 4.7 ohms .
7- Be sure that you don't have over lapp problem .
Best Wishes
Goldsmith
 

Thanks so much for ur concern
i tried varying pwm from 500hz up to 10k hz....but nothing happened..it affected slightly the step time and the reduce of humming sound but didnt solve the problem.....i will calculate the voltage acroos GS & DS and reply as soon as possible, also for point 7 (the overlap) you mean the dead time,right?? doesnt ir2110 makeup for it??
& thanks :-D
 

i tried varying pwm from 500hz up to 10k hz
Click to expand...
Hi again
I hope you know in PWM you must not change the frequency ! in PWM frequency is constant ! just pulse width has variations !
(the overlap) you mean the dead time,right??
Click to expand...
Why you think my mean was dead time ? dead time is a method to remove overlap problem . do you really know what is the meaning of the word overlap ?
I'm still looking to see your waveforms !
Good Luck
Goldsmith
 

thank u...ur advice about changing the resistance was useful...the torque is better now...but still not as running from supply :???:
sorry...but i didnt calculate the volt.....another thing, i didnt vary pwm frequency in the same trial...i just wanted testing the effect of varying the frequency on the humming sound
May u explain other methods of avoiding overlaping......thank u again
 

May u explain other methods of avoiding overlaping.
Click to expand...
Hi again
of course ! creating enough value of dead time in your PWM signals .

Recall : i've asked you to show me the waveforms but i don't know why you don't want show them to me ! how you expect that i find your problem without showing the wave ?

Best Luck
Goldsmith
 

sorry for late reply....but i dont have an oscilliscope...so i cant get the waveforms...i was trying to use theon in the college but it seems pretty difficult to convince them:-?
 

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