Motor drive

Abstract

To provide a motor drive adapted to operate stably and suffer essentially no damage, even when a high voltage is applied between grounding terminals of upper and lower arms.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a motor drive according to a first embodiment;

FIG. 2 is a circuit diagram of a motor drive based on the above-described conventional technique;

FIG. 3 is a cross-sectional explanatory diagram of a horizontal MOSFET based on the conventional technique;

FIG. 4 is an explanatory diagram of the simulation waveforms obtained by simulating the turn-on of the lower-arm IGBT of the motor drive based on the conventional technique;

FIG. 5 is an explanatory diagram of electric current paths in a level-shifting circuit during the simulation in FIG. 3;

FIG. 6 is a circuit diagram of a motor drive according to a second embodiment;

FIG. 7 is a sectional view of a high-withstand-voltage IGBT for signal transmission in the second embodiment;

FIG. 8 is a perspective view of another high-withstand-voltage IGBT for signal transmission in the second embodiment;

FIG. 9 is an explanatory diagram of a relationship between gate width of the high-withstand-voltage IGBT for signal transmission in the second embodiment, and a voltage across a resistor 22;

FIG. 10 is a mounting diagram of an inverter-driving circuit including the IGBT of FIG. 8; and

FIG. 11 is a circuit diagram of a three-phase AC motor drive based on the second embodiment.

Claims

1. A motor drive comprising: an arm which includes a first electric power semiconductor-switching element and a second electric power semiconductor-switching element, both connected in series between major terminals; anda level-shifting circuit which transmits a control signal of the first semiconductor-switching element connected to a high-voltage side of the arm, from a low-voltage circuit to a high-voltage circuit;,wherein the signal-transmitting high-withstand-voltage element in the level-shifting circuit is an insulated-gate bipolar transistor.

2. The motor drive according to claim 1, further comprising in the level-shifting circuit: a logic filter which shuts off signals if the signals are both input at the same time to setting-signal and resetting-signal transmission circuit elements of the level-shifting circuit.

3. The motor drive according to claim 1, wherein: the insulated-gate bipolar transistor that is the signal-transmitting high-withstand-voltage element in the level-shifting circuit has both an emitter electrode and a gate electrode formed on a semiconductor substrate surface opposite to a semiconductor substrate surface which has a collector electrode.

4. The motor drive according to claim 3, wherein: the insulated-gate bipolar transistor ranges from 1 μm to 1,000 μm in gate width.

5. The motor drive according to claim 3, wherein the insulated-gate bipolar transistor includes: a first p-type semiconductor layer;an n− layer which is a second semiconductor layer formed on the first p-type semiconductor layer;a third p-type semiconductor layer formed in the n− layer which is the second semiconductor layer; and a fourth n-type semiconductor layer formed in the third semiconductor layer;and wherein:the gate electrode is disposed via an oxide film formed on an exposed section of the semiconductor substrate surface on which are formed the second semiconductor layer, the third semiconductor layer, and the third semiconductor layer;the collector electrode is disposed abutting on the first semiconductor layer;the source electrode is disposed abutting on both the third semiconductor layer and the fourth semiconductor layer; andthe n− layer which is the second semiconductor layer is thicker than a depletion layer which spreads when a rated voltage is applied.

6. The motor drive according to claim 5, wherein: when, with the insulated-gate bipolar transistor taken to have a rated voltage V, an impurity concentration in the n− layer which is the second semiconductor layer of the insulated-gate bipolar transistor is expressed as N (n−), a relative dielectric constant of silicon as εSi, a dielectric constant of vacuum as ε0, and an elementary charge as q, thickness “d (n−)” of the n− layer which is the second semiconductor layer of the insulated-gate bipolar transistor satisfies d(n−)>√[2×ε0×εSi×V/(q×N(n−))].

7. The motor drive according to claim 5, wherein: the insulated-gate bipolar transistor is equal to or less than 1×1018/cm3 in terms of peak concentration of a p+ layer which is the first semiconductor layer on which the collector abuts.

8. The motor drive according to claim 5, wherein: an upper-arm IC, a lower-arm IC, and the high-withstand-voltage IGBT for signal transmission are each formed in an independent semiconductor chip.

9. The motor drive according to claim 8, wherein: the upper-arm IC, the lower-arm IC, and the high-withstand-voltage IGBT for signal transmission are all molded in one package.

10. The motor drive according to claim 8, wherein: the semiconductor-switching element for motor control has a withstand voltage equal to or greater than 1,500 V.

11. A motor drive with three arms each including a first IGBT and a second IGBT, both connected in series between major terminals, the motor drive being adapted to drive a three-phase AC motor which is a load, the motor drive further comprising: three level-shifting circuits each for transmitting a gate signal of the first IGBT connected to a high-voltage side of any one of the arms, from a low-voltage circuit to a high-voltage circuit;wherein:a signal-transmitting high-withstand-voltage element of each of the three level-shifting circuits is an IGBT;and wherein:the signal-transmitting high-withstand-voltage IGBT includesa first p-type semiconductor layer;an n− layer which is a second semiconductor layer formed on the first p-type semiconductor layer;a third p-type semiconductor layer formed in the n− layer which is the second semiconductor layer; anda fourth n-type semiconductor layer formed in the third semiconductor layer;and further wherein:the gate electrode is disposed via an oxide film formed on an exposed section of the semiconductor substrate surface on which are formed the second semiconductor layer, the third semiconductor layer, and the third semiconductor layer;the collector electrode is disposed abutting on the first semiconductor layer;the source electrode is disposed abutting on both the third semiconductor layer and the fourth semiconductor layer; andthe n− layer which is the second semiconductor layer is thicker than a depletion layer which spreads when a rated voltage is applied.

12. A motor drive with three arms each including a first IGBT and a second IGBT, both connected in series between major terminals, the motor drive being adapted to drive a three-phase AC motor which is a load, the motor drive further comprising: three level-shifting circuits each for transmitting a gate signal of the first IGBT connected to a high-voltage side of any one of the arms, from a low-voltage circuit to a high-voltage circuit;wherein:a signal-transmitting high-withstand-voltage element of each of the three level-shifting circuits is an IGBT;and wherein:a semiconductor chip with the signal-transmitting high-withstand-voltage IGBT formed therein, and another semiconductor chip in which an arm-driving circuit and a logical circuit are formed constitute a semiconductor device mounted in a resin-molded condition in one package.