transistor delay circuit circuit

The delay circuit introduced here has a delay time that is continuously adjustable from 0 to 120 minutes and can be used as a delay device for household appliances. This circuit has a simple structure and reliable operation, and can fully meet the needs of general household use. Working principle: The delay part is composed of BG1, BG2 and capacitor C to form a Miller integrating circuit. Before the power is turned on, the terminal voltage of C is zero. After the power is turned on, BG3 and BG4 are turned on, and the relay J is closed. At the same time, the capacitor C is charged. The charging current forms a loop through R2, C, and R. The potential of point a rises, causing b The potential at point A decreases, and the decrease in potential at point B limits the increase in potential at point A. As a result of the mutual compensation of the potentials of points a and b, the increase in the potential of point a is very small, and the charging current is nearly constant. When the potential at point b rises to about 10V, BG3 and BG4 are close to cutoff, relay J is released, and the delay process ends. Press the button AN, the capacitor C will quickly discharge through D1, the relay J will close, and the next delay process will begin.