The function of the undervoltage tripper is to detect the voltage of the inlet line of the circuit breaker, and when the working voltage in the protected circuit drops to 35%~70% of the power supply voltage, the circuit breaker will be automatically disconnected to cut off the load power supply, so that the load electrical equipment connected to the circuit breaker will be protected from the damage of low voltage. It is suitable for domestic circuit breaker manufacturers such as Changkai, Zhengtai, Liangxin, Delixi, Nuoyak and so on. At the same time, the undervoltage tripper can be derived from the delay type.