Maintenance of Repeated Breakdown of Rectification Diode in HY-U19 Electromagnetic Stove for Little Swan 3

2. Voltage regulation output is mainly achieved by ZD2 and ZD3, among which ZD2 and ZD3 play a role in voltage regulation control. When the switch power supply is working normally, ZD2 is in the off state, while ZD3 Jail is in the on state and outputs+18.0V and+5V normally. When+18.0V rises for some reason, ZD2 (16V voltage regulator diode) will reverse breakdown and conduct, Q1 (C3279) will conduct, U1 will turn off, and the+18.0V output will decrease, thus playing an automatic voltage regulation role. But when the output of+18.0V drops, ZD3 (5V voltage regulator diode) will be in a cut-off state, and there will be no output at+5V. At this time, the+18.0V load will not work. 3. The protection control circuit diode mainly has three protection control branches; (1) Overcurrent protection is mainly achieved by R7 (4.70) and Q1 (C3279), among which R7 is an overcurrent detection resistor. During normal operation, the sampling voltage at both ends of R7 is very small and does not affect Ql. However, when the conduction current of U1 (13005) increases for some reason, the current flowing through R7 increases, and the sampling voltage at both ends increases. When the voltage rises to the set value, R10 (51052) fP-Q1 saturates and conducts, and U1 is turned off, thus playing the role of overcurrent protection. (2) High voltage protection for the city grid: When the city grid voltage increases, the+300V voltage also increases. The voltage applied to the base of U1 (13005) through R4 and R5 starting circuits increases. When the voltage reaches the set value, ZD1 (9V voltage regulator diode) will reverse breakdown and conduct, and its conducting voltage will be applied to the base of Ql through R10 (51052), causing Ql to conduct and U1 to cut off, thus providing protection against high city grid voltage (or+300V voltage). From the above principle, it can be seen that the main reason for the breakdown of D4 (RF107) is the increase in+18V voltage, which is often caused by C3 failure or poor contact. In severe cases, U1, Q1, etc. can also be damaged by breakdown. diode,