JPH07110150B2 - Motor drive circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a motor drive circuit having transistors arranged in a multi-phase bridge configuration in an output stage, and particularly to a counter electromotive force generated at the time of switching the conduction of each phase. The present invention relates to prevention of a malfunction of a parasitic transistor in an integrated circuit caused by that.

[Conventional technology]

FIG. 2 is a circuit diagram showing an output stage of a conventional three-phase brushless motor drive circuit. In the figure, Q1 to Q6 are NPN power transistors for motor drive.

The emitter of the transistor Q1 and the collector of the transistor Q2, the emitter of the transistor Q3 and the collector of the transistor Q4, the emitter of the transistor Q5 and the collector of the transistor Q6 are commonly connected to each other.
It is connected to the motor drive terminals U, V, and W of each phase of V-phase, V-phase, and W-phase. The motor coil 1 is connected to the motor drive terminals U, V, W. The collectors of transistors Q1, Q3, Q5 are the power supply V _CC , and the emitters of transistors Q2, Q4, Q6 are GND.
It is connected to the.

A more detailed circuit configuration will be described below by taking the W phase as an example. Transistors Q5 and Q6 A resistor R is placed between the emitter and base.
1 and R2 are connected respectively. Further, a Schottky barrier diode D1 for clamping the collector potential of the transistor Q6 at a constant value is provided between the collector of the transistor Q6 and GND.
Are connected.

Transistors Q7 and Q8 are current mirrors based on transistor Q7, and transistors Q9 and Q10 are transistors.
It constitutes a current mirror based on Q9. These current mirrors have a current I according to the speed signal for motor speed adjustment given from the terminal not shown.
_CTL is supplied to the bases of the transistors Q5 and Q6, respectively. Although the W phase has been described, the U and V phases have the same configuration.

FIG. 4 is a partial sectional view around the transistor Q6 when the circuit shown in FIG. 2 is formed on a semiconductor substrate. A buried N ⁺ collector layer 42 is formed in the upper layer portion of the P ⁻ type semiconductor substrate 41, and a P ⁺ type base region 44 and a P ⁺ type base region 44 are formed in the upper layer portion of the N ⁻ type collector region 43.
An N ⁺ type collector contactor region 45 is formed at a distance from each other, and an N ⁺ type emitter region 46 is further formed in the upper layer portion of the P ⁺ type base region 44 to form a transistor Q6. Then, this transistor is surrounded by a P ⁺ -type region 48 which is a separation layer, and is separated from the adjacent transistor. A GND potential is applied to the P ⁺ type isolation region 48 via the semiconductor substrate 41. Reference numerals 49, 50 and 51 are an N ⁺ type collector contact region, an N ⁻ type collector region and a buried N ⁺ collector region of the transistor adjacent to the transistor Q6. Then, the N ^- type collector regions 43 and 50 and the P ⁺ -type isolation region 48 cause lateral parasitic N
A PN transistor Q0 is formed.

Next, the operation will be described. In the three-phase brushless motor drive circuit, each phase is energized with a phase difference of 120 ° as shown in FIG. 3 based on a signal obtained from a position sensor (not shown) to drive the motor.

Considering now the timing on the outflow side, when switching from the U phase to the V phase, the transistor Q1 turns off and the transistor Q3 turns on. If there is a time difference between ON and OFF in this case, a counter electromotive voltage is generated because the output stage of the motor drive circuit is the L load of the motor coil 1. This occurs when switching from the V phase to the W phase or from the W phase to the U phase, and at the same time when switching the inflow side transistor.

As described above, for example, when a back electromotive voltage is generated at the motor drive terminal W (that is, the collector of the transistor Q6) and the back electromotive voltage is swung in the negative direction, the P ⁺ isolation region 48 is at the GND potential as described above. , Lateral parasitic transistor Q
When the base-emitter potential of 0 increases and exceeds the threshold value, the parasitic NPN transistor Q0 turns on.
As a result, a current is drawn from the adjacent N ⁻ type collector region 50, which causes a malfunction.

To prevent this, a Schottky barrier diode D1 is provided externally between the collector of transistor Q6 and GND as shown in Fig. 2, the collector potential of transistor Q6 is clamped to a negative constant potential, and parasitic by a back electromotive force. The transistor Q0 is not turned on.

[Problems to be Solved by the Invention]

The conventional motor drive circuit is configured as described above, and the Schottky barrier diode D1 is externally provided so that the parasitic transistor does not malfunction due to the back electromotive force. As described above, the power transistors (transistors Q1 to Q6) are included in the integrated circuit, and these transistors generate a relatively large amount of heat during operation of the motor drive circuit. Therefore, even if the ambient temperature decreases, the temperature in the integrated circuit does not change much, and as a result, the threshold voltage of the parasitic transistor in the integrated circuit does not change much. On the other hand, the threshold voltage of the external Schottky barrier diode D1 gradually increases as the temperature decreases. Therefore, the negative collector voltage of the transistor Q6 clamped by the Schottky barrier diode D1 decreases. If the temperature drops too much, the absolute value of the negative clamp potential becomes larger than the threshold voltage of the parasitic transistor Q0, and before the Schottky barrier diode D1 turns on and the clamp operation starts, the parasitic transistor Q0 turns on by the counter electromotive voltage. Resulting in. In this case, there is no point in providing the Schottky barrier diode D1 and the motor drive circuit malfunctions. There is also a problem that the cost increases if the external Schottky barrier diode D1 is externally attached as an individual element.

The present invention has been made to solve the above problems, and prevents a parasitic transistor from being turned on by a counter electromotive voltage without providing an external diode, thereby obtaining a low-cost motor drive circuit. With the goal.

[Means for Solving the Problems]

A motor drive circuit according to the present invention is a motor drive circuit having transistors arranged in a multi-phase bridge configuration at an output stage, which is provided for each phase and makes the transistors on the lower arm side of the corresponding phase conductive. When the potential at the common connection point between the conduction circuit and the transistor on the upper arm side and the transistor on the lower arm side of the corresponding phase, which is provided for each phase, becomes lower than a predetermined potential, the conduction circuit in that phase Activate
And a potential detection circuit for maintaining the potential of the common connection point in the phase at a constant potential.

[Action]

The potential detection circuit according to the present invention is provided for each phase, and when the potential at the common connection point between the transistor on the upper arm side and the transistor on the lower arm side of the corresponding phase becomes lower than the predetermined potential, the conduction in the phase is conducted. The circuit is activated and the transistor on the lower arm side is made conductive. As a result, the potential at the common connection point in the phase is maintained at a constant potential.

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment of the present invention. This figure shows only the W phase in the three-phase brushless motor drive circuit shown in FIG. In the figure, the difference from the conventional one is that when a negative back electromotive force is generated at the motor drive terminal W, a current is supplied to the base of the transistor Q6 to turn on the transistor Q6, so that the potential of the motor drive terminal W becomes almost equal. This is to force it to the GND potential.

The base of the transistor Q11 is resistors R3, R4 and diode D2.
The collector of transistor Q6 via the
In addition, the collectors are respectively connected to the power supply V _CC via the constant current source 11. The common connection point of the resistors R3 and R4 is connected to the power supply V _CC via the constant current source I2. And diode D2
Conducts when the potential of the motor drive terminal W becomes lower than the GND potential by the threshold potential of the diode D2 or less.

The transistors Q12 and Q13 form a current mirror based on the transistor Q12. The collector-base common connection point of the transistor Q12 is connected to the collector of the transistor Q11, and the emitter common connection point of the transistors Q12 and Q13 is connected to the base common connection point of the transistors Q9 and Q10. Then, when the transistor Q11 is turned on, the current mirror including the transistors Q12 and Q13 is disabled, and when it is turned off, the current mirror is activated. Other configurations are the same as the conventional one.

Next, the operation will be described. When the transistor Q5 is on and the current is normally supplied to the motor coil 1, the potential of the motor drive terminal W is higher than the GND potential. Therefore, the diode D2 does not turn on, and all the current from the constant current source I2 is supplied to the base of the transistor Q11. Therefore, the transistor Q11 turns on and the constant current source I1
Since the current from flows to GND through the transistor Q11,
The current mirror formed by the transistors Q12 and Q13 does not work. Therefore, no current is supplied to the base of the transistor Q6, and the transistor Q6 is in the off state.

On the other hand, when a negative counter electromotive voltage is generated at the motor drive terminal W and the potential of the motor drive terminal W becomes lower than the GND potential by the threshold voltage of the diode D2 or less, the diode D2 is turned on. Then, current is drawn from the base of the transistor Q11 and the transistor Q11 is turned off. Then, current is supplied from the constant current source I1 to the current mirror composed of the transistors Q12 and Q13, and this current mirror is activated. Then, a current is supplied to the base of the transistor Q6 via the current mirror composed of the transistors Q9 and Q10, and the transistor Q6 is turned on. Therefore, the electric potential of the motor drive terminal W is kept almost at the GND electric potential. Therefore, the parasitic transistor Q0 does not turn on unlike the conventional case. In this way, without providing the external Schottky barrier diode D1,
It is possible to prevent the parasitic transistor Q0 from turning on. When the electric potential of the motor drive terminal W is V1, IA: Current flowing through resistor R4 IB: Current flowing through resistor R3 IS: Saturation current k: Boltzmann constant T: Absolute temperature q: Charge amount. Make sure that IA + IB = I1.

In the above embodiment, the base current of the transistor Q6 is given through the transistors Q9 and Q10.
It may be given directly from the current mirror circuit composed of Q13.

〔The invention's effect〕

As described above, according to the present invention, the potential detecting circuit is provided for each phase, and the potential at the common connection point between the upper arm side transistor and the lower arm side transistor of the corresponding phase becomes lower than the predetermined potential. In this case, the potential detection circuit activates the conduction circuit in the relevant phase to render the transistor in the lower arm of the corresponding phase conductive and maintain the potential at the common connection point in the relevant phase at a constant potential. The potential at the common connection point between the high-side transistor on the side of the bipolar transistor and the high-polarity transistor on the side of the lower arm is maintained at a constant potential, and as a result, the parasitic transistor is prevented from turning on by the counter electromotive voltage without installing an external diode. And the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing an output stage of a conventional three-phase brushless motor drive circuit, and FIG. 3 is a circuit diagram showing the operation of the circuit shown in FIG. FIG. 4 is a partial cross-sectional view when the circuit shown in FIG. 2 is integrated into a circuit. In the figure, Q5 and Q6 are power transistors, and D2 is a diode. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A motor drive circuit having a transistor arranged in a multi-phase bridge configuration at an output stage, the conduction circuit being provided for each phase for conducting the transistor on the lower arm side of the corresponding phase, Provided for each phase, when the potential of the common connection point between the transistor on the upper arm side and the transistor on the lower arm side of the corresponding phase becomes lower than a predetermined potential, the conduction circuit in the phase is activated, A motor drive circuit comprising: a potential detection circuit that maintains a constant potential at the common connection point in the phase.