a three - phase bridge inverter for controlling a motor with a variable speed includes a drive circuit therefor and an overcurrent protection circuit on one integrated chip . the inverter ic can be operated by directly inputting a direct current obtained by rectifying commercial 100 v . thus , the inverter chip reduces the size and the weight of a system , improves the usability , lowers the cost thereof and permits mass production fabrication . also , the life of the ic is increased by detecting current flowing through the inverter and the temperature of the chip and stopping the operation , when an abnormality is found .