Another factor which can heavily impact the amount of switching losses in the system is the frequency of the input PWM signals. The MOSFETs must enter the switching region at both the beginning and end of the respective input pulse (turn off and turn on). With a higher PWM frequency, these pulses happen more often, thus increasing the amount of time each MOSFET spends in the switching region. This means that there is a proportional relationship between the amount of switching losses and the frequency of the input PWM signals (see Figure 2-3). A common value for the PWM frequency in 48V systems is approximately 20kHz. The reason this value is targeted is because this frequency is high enough to be out of the audible range for humans but is kept low to mitigate switching loss and nosie.

Figure 2-3 Switching Losses (48V at 0.5V/ns)