Zero-pressure-dropping device

The invention discloses a zero-pressure-dropping device which comprises an operational amplifier, a first relay, a second relay, a first diode and a second diode. An output end of the operational amplifier is connected with an inversed input end. An input end Ui is connected with a positive going input end of the operational amplifier through the first relay. An output end Uo is connected with the inversed input end of the operational amplifier through the second relay. The first diode and the second diode are connected in parallel in an inversed mode between the positive going input end and the inversed input end of the operational amplifier. The first diode D1 and the second diode D2 connected in parallel and in an inversed mode are arranged between the input end of the operational amplifier and the output end of the operational amplifier, so that damage, caused by an extremely large input interference signal, to the operational amplifier and influence on the normal operation of the circuit are effectively avoided.