# Effects of PWM waveform polarity on PWM-driven hardware

What difference does it make for a certain PWM-driven hardware (such as a DC motor) if the PWM signal starts high or low?

• Let's assume that t = 0 when you apply the PWM starting with low and drive the motor. The motor will start spinning. If you apply the PWM starting with high then the motor will start spinning "tON" seconds earlier than before. Commented Jan 31, 2019 at 9:42
• You should take a piece of graphic paper and start drawing some PWM signals, draw sets of two (same duty cycle) signals one starting low, the other starting high. Realize that the repetition period of a PWM signal will be much faster than the response time of a DC motor. Will it make any noticable difference to the motor? Commented Jan 31, 2019 at 9:44
• So it will hardly make a difference? Commented Jan 31, 2019 at 9:46
• Also DC motors rotation direction depends on the polarity of its power supply(ex. +/- forward , -/+ backward) in a H bridge configuration. Commented Jan 31, 2019 at 9:49
• Considering the fact that switching the power voltage supply on and off really fast, we get an average voltage supply to the DC. The greater the duty cycle, the higher the average value. Correct me if I'm wrong, but it shouldn't make a sensible difference for the motor's performance or characteristics if the PWM signal starts high or low. Commented Jan 31, 2019 at 9:55