problem in h-bridge hardware

Thread Starter

syed hassan

Joined Mar 11, 2015
13
hello everyone
i am facing a problem due to which my project has been stuck around. i need your urgent help
actually i am trying to implement the following circuit at bread board and testing it at low voltages
my problem is the V(gs) is zero due to which no current is passing through mosfet and mosfets are unable to turn on
what step do i need to take in order to make this circuit work efficiently
at inputs i am applying a pwm signal of 50Hz with dead time of 100 usec
can anyone plz help me out in troubleshoot my problem?
 

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crutschow

Joined Mar 14, 2008
29,799
To troubleshoot, you trace the signal, either from the source to the MOSFET, or from the MOSFET back to the source, to see where the signal is disappearing. It's sort of a detective "whodunit" game.
It requires understanding everything about how the circuit is supposed to operate and then determining what part is not operating as planned.
Troubleshooting is often the most difficult part of any electronic design.
 

Thread Starter

syed hassan

Joined Mar 11, 2015
13
To troubleshoot, you trace the signal, either from the source to the MOSFET, or from the MOSFET back to the source, to see where the signal is disappearing. It's sort of a detective "whodunit" game.
It requires understanding everything about how the circuit is supposed to operate and then determining what part is not operating as planned.
Troubleshooting is often the most difficult part of any electronic design.
i have done it many times but what i think is the function of bootstrap is not being performed as it should be.due to which gate voltage is exactly the same as that of source voltage.while it should be 10v more than the source voltage.
now i want you to help me out how i cater this issue?
 

MaxHeadRoom

Joined Jul 18, 2013
25,212
As Alec t says.

I still am wondering why you would chose a Pic with a PWM module and not take advantage of it?
This will turn on the relevant lower FET and PWM the top one, also with the hi-lo side switches the PWM signal can not be 100% pulse width.
Max.
 

Thread Starter

syed hassan

Joined Mar 11, 2015
13
As Alec t says.

I still am wondering why you would chose a Pic with a PWM module and not take advantage of it?
This will turn on the relevant lower FET and PWM the top one, also with the hi-lo side switches the PWM signal can not be 100% pulse width.
Max.
max i am unable to get what you are trying to say.can you please elaborate it ?
and one more thing that i want you to tell me that i am using 33uf electrolytic capacitor along 100nf ceramic capacitor for bootstrap purpose.will it work for my circuit and provide necessary voltage to gate to turn on the mosfet?
 

MaxHeadRoom

Joined Jul 18, 2013
25,212
If you study the 18F4431 manual it will explain using the CCP module in PWM mode.
This is the results obtainable for outputs.
The IR PWM high side switch requires the bottom FET on and the upper switching a PWM signal <100%, IOW both upper and lower cannot be full on.
Max.
 

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Thread Starter

syed hassan

Joined Mar 11, 2015
13
If you study the 18F4431 manual it will explain using the CCP module in PWM mode.
This is the results obtainable for outputs.
The IR PWM high side switch requires the bottom FET on and the upper switching a PWM signal <100%, IOW both upper and lower cannot be full on.
Max.
max i appreciate your kind replies
but my issue is not pwm but the gate to source voltage and bootstrapping mechanism
can you please guide me in this respect
i have already generated pwm signal using pic18f4431 and ccp module in pwm mode
 
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