I'm currently stuck on a problem when trying to drive a 140V DC motor using an H-Bridge with 4 high-power mosfets and 4 IR2125 drivers.
I'm using as input to the drivers a signal generator of 5V in PWM with a duty cycle of 80% at 30kHz. The applying to the mosfets Q4 and Q5, nothing happens. What I could do is bypassing the high-mosfet on the left (by connecting one terminal of the motor to VDD - M1 to VDD), and then only switching the low-side mosfet (Q5).
But with this configuration obviously I get no direction control of the motor! I don't understand why I'm not being able to turn MOSFETs Q4 and Q5, or Q3 and Q6 as a normal bridge configuration would do. I'm not sure if this has something to do with the fact that this driver accepts only PWM as input.
PS: In my circuit I've shorted the input of the drivers that control mosfets Q4 and Q5. Same for inputs of drivers that control Q3 and Q6.
The extra-circuitry around the drivers was taken from the application note of the chip. In the circuit VCC is 12V, VDD is 166V, VSS is floating.
Attached is a picture of the bridge I've built. Thanks! schematic http://oi61.tinypic.com/1041b3o.jpg