I'm currently a uni student trying to control a 24V DC servomotor using an 80C517A micro. My code is able to accept an input and convert it into 13KHz PWM output. My problem begins when I try to use an TTL inverter to invert the PWM output so that I can have a linear relationship between the input voltage, and output voltage from the servomotor which represents its speed. My first problem was that it reached its maximum speed at around 90% duty cycle. The 2nd problem is that I damaged two of my PWM output port since using the TTL inverter. What might be the problem? Should I lower the frequency? I have read some of the pass messages, someone suggested 5Khz. But how do I work out what frequency to use for sure? And how should I protect the controller? Should I use a CMOS inverter instead?

Thank you for any help you may offer.

JZL