Work by the power supply controller IC2 and relay K1 composed it through the "Exhaust Fan" operating cycle counting, identifying and controlling the number of fan work. After reaching a predetermined number of operations, cutting through the relay K1 and fan control circuit includes the entire power supply. The circuit consists of ICZ, relay K1, SB2 and SBI composition. Component Analysis: T (total) = ln2 (R1 + 2 * R2) C, due to the displacement device, so there are a range of T 0.69 * 190 * 47/1000000 = 7 < T < 0.69 * 320 * 47/1000000 = 10. The circuit is calculated in order to achieve a period of 10, you need R1 = 30K, R2 = 60K, electrolytic capacitor 47uf, 555 pulse generated by the chip, the green LED lights to indicate the work, the yellow LED indicates stop. Relay K2 control capacitor charging and discharging.