The invention discloses an over-current protection circuit of a direct-current electronic 
contactor, which is characterized in that a drain 
electrode of an NMOS switching 
transistor is connected witha positive 
electrode of a direct-current power supply, and a source 
electrode is connected with a negative electrode of the direct-current power supply through a load; and a 
control signal of a single-
chip microcomputer is input into a grid electrode of the NMOS switching 
transistor through a 
driving circuit. Multiple paths of the NMOS switching 
transistor are connected in parallel. The drain electrode of the NMOS switching transistor is connected with a non-inverting input end of a 
differential amplifier through a 
relay protection circuit and a differential 
resistor, the source electrode ofthe NMOS switching transistor is further connected with an inverting input end of the 
differential amplifier through a 
relay coil equivalent 
resistor and a differential 
resistor, and the output end ofthe 
differential amplifier is connected with an AD conversion module of the single-
chip microcomputer. The driving 
signal controls the NMOS switching transistor to be switched on. The over-current protection circuit samples 
voltage at the drain electrode end and the source electrode end of the NMOS switching transistor, and when the 
voltage exceeds a set threshold value, over-current shutdown protection is performed. The over-current protection circuit is simple in design, the use cost of the circuit can be reduced, and the reliability and the stability of the circuit during working can be improved.