FPGA code for PWM with cRIO 9035

[FaresMZOUGHI]

Hello everyone,

I am trying to generate PWM signal for future control applications. For this, I am using the cRIO 9035 and the NI 9474 module and display the signal on a Tektronix TDS 2002C oscilloscope.

I want to generate high-frequency PWM, therefore, I use the LabVIEW FPGA interface. And I create a very simple and basic FPGA VI (PWM0) and call it in the host VI (PWM_FPGA) as shown in this Fig.1 and Fig.2.

Fig.1: Project Explorer and FPGA VI of the PWM.

Fig.2: Host VI.

I can generate the squared signal with both High and Low pulses. But when I increase the frequency I lose the low pulse as shown in the figures below:

F = 5Hz

F = 50Hz

F = 250Hz

F = 1kHz

F = 2kHz

F = 3kHz

F = 4kHz

F = 5kHz

Can anyone explain to me why do I have a problem with the Low pulse. Did I miss something? or do I have to add some sort of configuration?

Any help would be highly appreciated.

[nanocyte · Accepted solution]

Do you have a pull down resistor? If not, try one. Maybe ~10KOhm.

[FaresMZOUGHI]

It worked thank you very much. I connected the PWM signal to a power converter SEMIKRON which has an internal resistor 10kOhm.

Thank you for your quick response.