DZW75-48/50(50II) input circuit

(1) The 220V (50Hz) AC voltage is filtered by the Z1 line filter and sent to the contact of the AC overvoltage and undervoltage protection relay K2. During normal operation, the K2 contact should be closed upward, and the AC 220V voltage is connected to the AC current limiting resistor. R4 (R4 is short-circuited by the K1 contact after a period of delay after startup) is sent to the power frequency bridge rectifier for rectification. After smoothing and filtering by the parallel capacitor bank, a voltage output of approximately 300V DC is obtained to complete the power frequency AC/DC conversion. R2 is the bleeder resistor. (2) The Z1 line filter is used to suppress and absorb the interference of strong pulses on the power grid to the rectifier and improve the reliability of the rectifier. At the same time, the line filter's good common-mode and differential-mode insertion losses can effectively suppress the high-frequency interference signals generated by the reverse output of the high-frequency switching converter, isolate the rectifier from the power grid, and avoid mutual interference. (3) AC overvoltage and undervoltage protection circuit, the AC 220V voltage filtered by the line filter is sent to the step-down transformer. (4) AC current limiting delay circuit. The AC voltage can be connected to the machine within the normal working range. After the AC power is connected, the auxiliary power supply is established and a period of delay after the auxiliary power is established before the AC limit is reached. When the current resistor is short-circuited, this period of time is called the AC current-limiting delay, which is completed by the AC current-limiting delay circuit.