When B is pressed in the given circuit, the capacitor (C) is charged. When we pull the button, the current of the electrical charge accumulated on C triggers the transistor T1 and T2 through the R resistor. The transmitted T2 transistor activates the relay. After a while, the electrical load on the capacitor plates will end, the transistors go to the cut, the relay returns to its initial position and the lamp goes off.
Because the value of the resistance connected to the base of the T1 transistor is too large, the end of the line draws a very small current. This allows the capacitor to discharge for a very long time.
LONG-TIME DELAYED TURN-OFF TIME RELAY CIRCUIT DIAGRAM WITH DARLINGTON CONNECTION
Electronic circuit diagrams were extracted from various sources (pdf, doc, etc.) shared on the internet and transferred to the site. Thanks to the people who prepared the work.
The symbol of NPN and PNP is shown in the figure below. The arrow in the symbol indicates the direction of flow of conventional current in the emitter with forward biasing applied to the emitter-base junction. The only difference between the NPN and PNP transistors is in the direction of the current.