Motor driving device having MOSFET, MOSFET, and motor having MOSFET

#The present invention relates to a motor driving device composing an inverter circuit by MOSFET, a MOSFET, and a motor having MOSFET. In particular, the MOSFET has enough current tolerance not inducing avalanche breakdown, latch-up breakdown, or short-circuit breakdown.

#Recently, a MOSFET is used widely as a switching element for output in an inverter circuit in a motor driving device. Motor load includes a large inductance component, and noise may be caused by counterelectromotive force of motor when changing phases, or switching element for output may be broken down due to circulating currents of regenerative energy when decelerating or stopping the motor. In particular, when MOSFET is used, since switching speed is fast and parasitic transistor is present owing to its structural characteristics, avalanche tolerance breakdown or latch-up tolerance breakdown may occur. It is attempted to prevent lead-through current from flowing by preventing the MOSFET of upper arm and MOSFET of lower arm of inverter circuit from being turned on simultaneously due to malfunction by noise.

#Various measures are proposed for preventing breakdown of MOSFET used as switching element for output in inverter circuit. For example, Japanese Patent Application Laid-Open No. 2003-333883 discloses a method of inserting a pause period when changing phases of inverter circuit. In a certain time after turning off the switching element of the conductive phase, the next switching element is turned on, and the switching elements of both upper arm and lower arm are not turned on simultaneously, so that lead-through current will not flow.

#FIG. 1 is an overall circuit diagram of motor driving circuit in preferred embodiment 1 of the invention.

#FIG. 2 is an equivalent circuit diagram of MOSFET of the same.

#FIG. 3 is a current tolerance measuring circuit diagram of MOSFET of the same.

#Preferred embodiment 1 of motor driving device of the invention is described below while referring to the accompanying drawings. FIG. 1 is an overall circuit diagram of motor driving circuit in preferred embodiment 1 of the invention.

#In FIG. 1, a series circuit 15 of two MOSFETs Q1, Q2 is connected between positive and negative terminals of a direct-current power source 11. Similarly, a series circuit 16 of two MOSFETs Q3, Q4, and a series circuit 17 of two MOSFETs Q5, Q6 are connected between positive and negative terminals of the direct-current power source 11, respectively. Between source and drain of these six MOSFETs, flywheel diodes D1, D2, D3, D4, D5, D6 are connected individually. A three-phase inverter circuit is composed of these six MOSFETs and six flywheel diodes. As six flywheel diodes, parasitic elements of MOSFETs may be used.

#Connection point PU of MOSFETs Q1 and Q2 is connected to U phase driving coil LU of motor, connection point PV of MOSFETs Q3 and Q4 is connected to V phase driving coil LV of motor, and connection point PW of MOSFETs Q5 and Q6 is connected to W phase driving coil LW of motor.