bootstrap circuit problem ????????

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omid_juve

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i use this bootstrap circuit (for my knowledge) to drive a dc 12vfan for pc with
800 ohm resistance as a load and the pwm signal is coming from a micro to
the base of the npn transistor the vgate is becoming a pwm signal with a peak of 1v so the fan couldn't be turned on can you please help me how i can fix this problemn??
 

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Your pwm signal has maximum amplitude of 1v which it seem's to be low,your motor may not work the way you want but try to increase the pwm voltage if posible.
 

I posted that schematic (on another website?) as an explanation of how the bootstrapping works.
The gate voltage should be a high of about 23.3V, not 1V. It must be measured with an oscilloscope, not a voltmeter.
The input signal at PAD1 goes only to the 1k resistor and is a square-wave of about 10kHz with a duty-cycle around 50-50 and a switching voltage from near 0v to near +5V.

The load is 0.47 ohms to about 47 ohms.
 


my input signal to the 1k resistor is the same as what you said(+5v 1khz 50,50 i checked with oscope) but i don`t know why when it goes to the gate the peak voltage became +1v but i guess it`s due to the resistance (800 ohm) of my cpu fan . so please guide me if any change should i use for this circuit.
Thanks
 


nobody plz???
 

Can you upload the circute diagram so that we can analysed it and know the problem.
 

kabiru said:
Can you upload the circute diagram so that we can analysed it and know the problem.
Click to expand...
please check it for your reference
thanks
 

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