The point about that last circuit is that Q2 can't be turned off unless the PWM signal is a 15V signal. You need another transistor like Q1 to boost the PWM signal to 15V before Q2 can be turned on and off by the PWM signal.
The point about that last circuit is that Q2 can't be turned off unless the PWM signal is a 15V signal. You need another transistor like Q1 to boost the PWM signal to 15V before Q2 can be turned on and off by the PWM signal.