One of the single-junction transistor trigger circuits that is not affected by power grid fluctuations

The two circuits introduced below can convert the trapezoidal wave synchronization voltage into a rectangular pulse with a small intermittent period . Its working principle is
to chop the DC voltage by the periodic operation of a zero-volt switch synchronized to the grid frequency. Due to the use of a low-threshold voltage comparator
, fluctuations in the grid voltage have minimal impact on the intermittent width of the synchronization pulse. Therefore, the phase shift angle
is greatly reduced from the influence of grid voltage fluctuations, and the phase shift range is also expanded.
    The circuit is shown in Figure 16-10. It uses 555 time base integrated circuit Ai as a single-limit inverting voltage comparator; it uses 7812 three
-terminal fixed integrated voltage regulator A2 to provide stable operating power. Adjusting the potentiometer RP can change the phase shift angle of the output pulse ground e.