Why is the H-Bridge driver coupling low input into the high side

driverh-bridge

I have struggling for about a week with this problem and I am not sure how to fix it , so stack exchange community please help :).

Ok so basically I am making a h-bridge using 4-N channel mosfets, and in order to drive the high side I am using IRS2001 High and Low side drivers.

Here is my schematic :
enter image description here

Larger pic : http://i.stack.imgur.com/ayE0L.png

Here is an updated schematic of how my signals are inputted :

enter image description here

Larger pic : http://i.stack.imgur.com/EkNCB.png

I am using a 5kHz PWM signal to switch on for about 0.5secs and then turn off the mosfets to drive the motor in one direction and vice versa for the other direction.

The motor seems fine but when I probe the input and out of the gate driver I see problems.

The low output seems to couple with the high side output even though the high input signal is clean as shown in the oscilloscope output below.

Another question i have is what are the best capacitors to be using for this mosfet driver, at the moment i am using an electrolytic type capacitor around 10uF, is this applicable?

enter image description here

  • The green signal is the HO ( high output signal)
  • The yellow signal is the HIN ( high input signal)

enter image description here

  • The blue signal is the LIN( low in signal)

Here is where I am probing

enter image description here

So my question really is , why is this happening and how can I solve this ? Thanks

Best Answer

I think you are measuring the correct. Because high side MOSFET is off and low side MOSFET is switching middle point(VX in your case) voltage will swing between battery voltage and ground.

If you see low pin voltage and vx pin voltage they should be complimentary to each other.

Please post the low side gate voltage and VX voltage (zoomed)

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