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LAUNCHXL-F28069M: PWM Spikes (Noises)

Troodon
Intellectual 615 points

Part Number: LAUNCHXL-F28069M

Hello all,

I generate 1000Hz EPWM1A and EPWM1B pwm signals for my h-bridge inverter. I use igbt driver core modules so I convert these pwms to 15V. When igbt modules are not active, my pwm signals are suitable. 

But when igbt driver cores trigger their processes, with the transmission of igbt modules, there are spikes on the pwms.

Until the driver cores give error, these spikes remain, then pwm signals become normal again.

I tried some filtering methods but didn't work. I apply those pwms to igbt driver's pwm input with the circuit below.

Signal gnd and my launchpad's gnd are combined.

As this behavior's reason, I read several posts about: ecap, eqep behavior, length of cable, inductive resistance but these could not clarify the situation for me.

Any advice? Thank you.

  • 0
    TI__Mastermind 42195 points

    Troodon,

    the first thing we should confirm is that the spikes are real and not noise coupling through the oscilloscope. Can you confirm this to be the case?

    Secondly, are you using any sort of Isolation?

    This design shows one way to add isolation https://www.ti.com/tool/TIDA-01456 

    Regards,
    Cody 

  • 0 in reply to Cody Watkins
    Intellectual 615 points

    Hello Cody,

    Yes, the spikes are real because igbt driver core modules give error after 28% duty and below this value, the current values are higher than normal.

    There is isolation between 2 sides (primary/control, secondary/power) of the driver core but the point was insulating the launchpad and primary side of the driver core, too. I have used an optocoupler and transistor circuit to insulate 3.3V side and 15V sides and their grounds (their grounds were combined.

    Now there are quite less spikes on 15V side that do not effect my operation as shown below.

    Thank you.