Analysis of the circuit principle of Jinkede TW435 timer

The rated voltage of the timer is AC220V/50Hz, the maximum output current is 10A, and the maximum load power is 2200W. The actual drawing of the timer circuit is shown in the figure below.

After the power is turned on, the AC220V voltage is first stepped down and limited by capacitor Cl (0.27μF) and resistor R1, then full-wave rectified by diodes D2~D5 and filtered by C2, and then limited by voltage regulator Z1 through the coil of relay J to obtain a DC voltage of about 16V. This voltage is stabilized by three-terminal voltage regulator U1 (78L05) to obtain a 5V voltage, which supplies power to pin ④ of microcontroller U2. At this time, pin ① of the microcontroller outputs a high level, transistors Q2 and Q1 are turned on successively, the relay coil is short-circuited by Q1, contact K is not attracted, and the output socket has no power; at the same time, the current that initially flows through the relay coil is changed to flow through the e and c poles of Q1, so that Z1 and U1 work normally, and the output voltage of 5V is used to power the microcontroller, which is in standby state at this time.

When the button S1 is pressed for the first time, the MCU pin ① changes from high level to low level, Q2 and Q1 are cut off due to loss of bias, the relay coil is energized, K is energized, and the output socket is energized. At the same time, the 8th pin of U2 outputs a low level, the 5V voltage is limited by the resistor R3, the indicator D1 lights up and flashes, and the flashing of D1 indicates that the timing time is 1h; when S1 is pressed for the second time, the 9th pin of U2 outputs a low level, and the indicator D2 flashes, indicating that the timing time is 2h; and so on, that is, the required timing time corresponds to the number of times S1 is pressed (the timing times are 1, 2, 4, 6, 8, and 10h respectively). When the indicator D6 flashes and then press AN, the MCU enters the standby state.

The vulnerable component of the timer is capacitor C1, and the capacity of the capacitor should not exceed 0.3μf when replacing it. Otherwise, Q1 is easily damaged.