Patent ID: 8253472

Claim:
A level shift circuit for transmitting an input signal from a primary electric potential system to a system operating in a secondary electric potential system at an electric potential different from that of the primary electric potential system, the level shift circuit comprising: a first series circuit comprising a first resistor and a first switching device connected in series between a high electric potential side of a power supply in the secondary electric potential system and a low electric potential side of a power supply in the primary electric potential system; a second series circuit comprising a second resistor and a second switching device connected in series between the high electric potential side of the power supply in the secondary electric potential system and the low electric potential side of the power supply in the primary electric potential system same as those of the first series circuit; a transmission circuit operated in the secondary electric potential system, and having input terminals to which a connection point of the first resistor and the first switching device in the first series circuit and a connection point of the second resistor and the second switching device in the second series circuit are respectively connected; and a storage device operated in the secondary electric potential system to which an output of the transmission circuit is inputted, wherein the first and second switching devices are inputted with input signals for the primary electric potential system to control turning-on and -off of the first and second switching devices, respectively, and an output impedance of the transmission circuit is made high when the electric potential at the connection point of the first resistor and the first switching device in the first series circuit and the electric potential at the connection point of the second resistor and the second switching device in the second series circuit are brought into a state equivalent to a state when the first and second switching devices are made simultaneously turned-on, wherein the storage device is a latch circuit comprising invertors and a resistor so that when the output impedance of the transmission circuit becomes high, a value immediate before said output impedance is outputted.