Patent ID: 8405422

Claim:
A level shift circuit configured to transmit an input signal from a primary side voltage system to a system that is operated by a secondary side voltage system and that is different from the primary side voltage system, the circuit comprising: a first series circuit including a first resistor and a first switching device, the first series circuit being connected between a high voltage side power supply voltage in the secondary side voltage system and a low voltage side power supply voltage in the primary side voltage system; a second series circuit including a second resistor and a second switching device, the second series circuit being connected between the high voltage side power supply voltage in the secondary side voltage system and the low voltage side power supply voltage in the primary side voltage system; a latch malfunction protecting circuit configured to operate in the secondary side voltage system, and being configured to have a voltage inputted at a first connection point, the first connection point being configured to connect the first resistor and the first switching device; the latch malfunction protecting circuit being configured to have a voltage inputted at a second connection point, the second connection point being configured to connect the second resistor and the second switching device; a latch circuit configured to operate in the secondary side voltage system and configured to receive an output of the latch malfunction protecting circuit as input; a third switching device connected in parallel to the first resistor; a fourth switching device connected in parallel to the second resistor; and a logic gate circuit configured to operate in the secondary side voltage system and configured to have the voltage at the first connection point inputted and to have the voltage at the second connection point inputted, the first switching device having a signal inputted in the primary side voltage system that is configured to selectively turn-on and turn-off the first switching device; the second switching device having a signal inputted in the primary side voltage system that is configured to selectively turn-on and turn-off the second switching device, the latch malfunction protecting circuit being configured to transmit a signal based on the voltages at the first and second connection points when any one of the first and second switching devices is turned-on, the latch malfunction protecting circuit being configured to selectively stop transmission of the signal based on the voltages at the first and second connection points when the first and second switching devices are simultaneously turned-on; and the logic gate circuit being configured to turn-on the third and fourth switching devices when both of the voltages at the first and second connection points are lower than a threshold voltage of the logic gate circuit.