The PWM oscillation cycle alternates between the Threshold pin for the duration of the 1 ms to 2 ms ON halfcycle is adjusted by R1, and the Trigger pin for the 18 ms to 19 ms OFF halfcycle. C2 > C1 to compensate for D1 forward drop
Figure 2 . The PWM oscillation cycle alternates between the Threshold pin for the duration of the 1 ms to 2 ms ON halfcycle is adjusted by R1, and the Trigger pin for the 18 ms to 19 ms OFF halfcycle. C2 > C1 to compensate for D1 forward drop