H bridge Problem

[ronsimpson]

Johansen, YOU GOT IT! Good job. I knew the top driver was unhappy. Its supply dies when the top MOSFET should be on. The cap to ground is why.

 

[ronv]

Logic

Then I think the logic needs to look like this so top and bottom FETs won't be on at the same time.

 

[ronsimpson]

RonV, I agree the logic was never understood. That is why I keep asking about the "PWM" signal from the micro. Your plan works.

Using the PCB he has;
Set one output to 0 and PWM the other output. The "0" will turn off a top on one side and a bottom on the other side. The other two MOSFET will drive the motor at some duty cycle. To reverse the motor PWM and 0 the outputs.

Do not ever have the two inputs high at the same time.

 

[keets]

Hi,
I am trying to drive 24v 120w dc motor using H-bridge of IRF840 driven by IR2110.at Appr.=11khz pwm frequency.I am using PIC184431 to control the motor.
I am using 22.1184 mhz crystal & PR2=124 with timer2 prescaler =4.
The circuit works fine.
But I encounter following problems.

At resistive loads it works fine i.e I can get linear dc o/p from 0 to 23 corresponding to 0% to 95% of duty cycle. But when motor is connected it doesn't start till duty cycle = appr.40%.then I get the linearity.
The circuit works fine at lighter loads.At higher load the mosfets get heated up and even at 95% of duty cycle unable to carry the load.

Please help.

 

[johansen]

do you need to allow the motor to free wheel?

try using a half bridge driver instead of driving the mosfets separately, ie, forced synchronous operation. then you won't have problems with the boot strap capactor not being charged because there is nothign to pull the middle node down to ground.

can you post a schematic?