Patent ID: 7564294

Claim:
An inverter apparatus comprising: a plurality of half bridges in which a first voltage-drive type power semiconductor switching element located on the upper arm and a second voltage-drive type power semiconductor switching element located on the lower arm are connected in series, a drive circuit for sending a drive signal to the control electrode of said power semiconductor switching element by using the emitter potential or source potential of said power semiconductor switching element as a reference potential, and an isolated signal transmission means for converting an output signal of a control circuit which uses the signal ground potential as a reference potential into an input signal of said drive circuit which uses the emitter potential or source potential of the switching element as a reference potential; wherein an abnormal signal discriminating circuit is located between the input section of said drive circuit and said isolated signal transmission means; said abnormal signal discriminating circuit comprising an upper-arm side low pass filter for inputting an upper-arm side drive signal, a lower-arm side low pass filter for inputting a lower-arm side drive signal, a first common mode noise elimination circuit for inputting an output signal of the upper-arm side low pass filter and an output signal of the lower-arm side low pass filter, a first filter for inputting an output signal of the first common mode noise elimination circuit, eliminating a part of high frequency band in the frequency band which passed the upper-arm side low pass filter, and outputting the signal to an upper-arm side of said drive circuit, a second common mode noise elimination circuit for inputting an output signal of the lower-arm side low pass filter and an output signal of the upper-arm side low pass filter, a second filter for inputting an output signal of the second common mode noise elimination circuit, eliminating a part of high frequency band in the frequency band which passed the lower-arm side low pass filter, and outputting the signal to a lower-arm side of the drive circuit, and an abnormal signal output means for inputting an output signal of said first common mode noise elimination circuit, an output signal of said second common mode noise elimination circuit, an abnormal signal outputted by the upper-arm side drive circuit, and an abnormal signal outputted by the lower-arm side drive circuit, and then outputting an abnormal signal.