JP2508757B2 - Motor drive circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a motor drive circuit, and is particularly suitable for use in a motor drive circuit that interrupts a drive current supplied to a motor coil of a brushless motor or the like.

[Outline of Invention]

The voltage level of the coil drive voltage is discriminated, and when the rise or fall of the drive voltage changes in the vicinity of the threshold voltage of the switching element, it is changed with a large time constant. By changing the time constant with a small time constant in the part, even if the time constant is set to a long time constant in order to suppress the generation of spike voltage, a motor drive circuit that does not increase the deviation of the operation time at the start and end of energization of the drive current Is.

[Conventional technology]

When the drive current supplied to the motor coil is interrupted by a switching element such as a transistor, a spike voltage is generated due to the inductance of the motor coil. This spike voltage adversely affects the equipment in which the motor is arranged and the equipment arranged in the vicinity thereof, such as radiation noise.
The magnitude of the spike voltage increases as the magnitude of the current flowing through the motor coil changes rapidly. Therefore, conventionally, the drive voltage of the switching element is gently changed by a time constant circuit so that the drive current does not change abruptly.

FIG. 7 shows a conventional motor drive circuit, and FIG. 8 shows a waveform diagram of the drive voltage applied to the switching transistor Q of FIG.

When the movable contact c of the switch SW1 is switched to the switching contact a side at time t ₀ in FIG. 8, the motor control voltage Vs supplied to the terminal 30 is applied to the time constant circuit 32. Time constant circuit 32
Is composed of a resistor R and a capacitor C. When the motor control voltage Vs is applied, the terminal voltage Vc of the capacitor C rises as shown by the solid line in FIG. The switch SW1 represents a switching signal source that performs phase switching in a brushless motor.

The terminal voltage Vc of the capacitor C is given to its base as a drive voltage of the switching transistor Q. Therefore, when the terminal voltage Vc of the capacitor C becomes higher than the threshold voltage V _f of the transistor Q at time t ₁ ,
The transistor Q is turned on and the drive voltage Vcc is applied to the motor coil L. As a result, as shown in FIG.
A drive current i ₁ flows through the motor coil L of a certain phase I, and the magnetic field generated thereby causes a rotor (not shown) to rotate.

When the movable contact c is switched to the switching contact b side at time t ₂ , the motor control voltage Vs is not applied to the time constant circuit 32. Therefore, the charge stored in the capacitor C is changed to the resistance R
, The terminal voltage Vc of the capacitor C drops and becomes lower than the threshold voltage _Vf at time t ₃ as shown in FIG. For this reason, the transistor Q is turned off at the time point t ₃ , and the drive current i ₁ stops flowing in the motor coil L of the phase I (see FIG. 9).

On the other hand, at time t ₂ , the changeover switch of the next phase II motor coil drive circuit (same configuration as in FIG. 7) is changed over to apply the motor control voltage to the time constant circuit. Therefore, when the terminal voltage Vc 'of the capacitor of this circuit rises as shown by the alternate long and short dash line in FIG. 8 and becomes higher than the threshold voltage V _f at time t _4, it becomes phase II as shown in FIG. The drive current i ₂ flows.

As described above, when the drive current to be supplied to the motor coil L is interrupted, the rising and falling waveforms are smoothed by the RC time constant circuit so that the spike voltage is not generated.

[Problems to be solved by the invention]

However, when the RC time constant circuit is used, there is a time difference t _r from when the motor control voltage Vs is applied at the time point t ₀ to the time point t ₁ at which the energization is actually started.

Also, the threshold voltage V of the transistor Q
_{If f} is not set to 1/2 of the motor control voltage Vs, the change gradient of the base voltage Vc near the threshold voltage _Vf will be different between the rising and falling.

That is, for example, as shown in FIG. 8, when the threshold voltage V _f is in the vicinity of the motor control voltage V _s , the change gradient at the fall becomes steep. Therefore, an RC time constant is required so that spike voltage does not occur even on the steep slope of change. However, the larger the RC time constant, the larger the operating time delays t _r and t _f .

Also, the time difference t _f at the end of energization and the time difference t _r at the start of energization
If and do not match, the current is cut off or the currents overlap and the torque ripple increases.

That is, when t _r > t _f , as shown in FIG. 9, a current cutoff occurs in which no drive current flows in any phase between time points t ₃ and t ₄ . Therefore, at the phase switching point, a torqueless portion is generated between the torques T ₁ and T ₂ due to the magnetic fluxes I and II of each phase and the currents i ₁ and i ₂ .

On the contrary, when the time difference t _r > t _f , as shown in FIG. 10, when the motor coil to which the motor control voltage Vs is applied is switched from the phase I to the phase II side at the time point t ₂ , the driving current flows to the phase II. At time t ₃ when i ₂ starts to flow, the drive current i ₁ is still flowing in the phase I. That is, the driving currents i ₁ and i ₂ flow in an overlapping manner between the times t ₃ and t ₄ . Therefore, the torques T ₁ and T ₂ overlap each other.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to suppress the generation of spike voltage and reduce the deviation of the operating time at the start and end of energization of drive current.

[Means for solving problems]

The motor drive circuit of the present invention includes a switching element (transistor Q ₄ or T _r ) for connecting and disconnecting the drive current supplied to the motor coil L, and a large or small time constant τ ₂ , τ ₃ or τ ₄ ,
A time constant circuit 7 or 10 having τ ₅ for controlling the switching element Q ₄ (T _r ) to have a time constant at the rise / fall of the drive voltage, and a change in the rise or fall of the drive voltage. And the time constant circuit 7 before and after the discrimination point.
The level detection circuit 4 (comparator 11) for switching the time constant of (10) is provided, and the above-mentioned when the drive voltage passes the input threshold voltage V _T (V _f ) of the switching element Q ₄ (T _r ). This is a configuration that increases the time constant.

[Action]

When the time constant circuit 7 (10) gives a time constant to the voltage change of the drive voltage Vc (Vc ₁ ) of the switching element Q ₄ (T _r ), the spike voltage is generated when the drive current supplied to the motor coil L is interrupted. Try not to occur. The time constant circuit 7 (1
0) has large and small time constants τ ₂ and τ ₃ (τ ₄ , τ ₅ ), and the level detection circuit 4 (10) discriminates the voltage change of the drive voltage Vc (Vc ₁ ) that controls the switching element. Then, a large time constant is selected when the voltage value passes through the threshold voltage of the switching element Q ₄ (T _r ) to make the voltage change gradient gentle.

〔Example〕

FIG. 1 is a circuit diagram of a motor drive circuit showing an embodiment of the present invention.

Positive polarity motor control command voltage applied to control terminal 1
The polarity of Vs is inverted to a negative voltage by the inverter 2, and this negative voltage is applied to the gate electrodes of the MOS type transistors Q ₁ and Q ₂ connected in parallel.

The transistor Q ₁ is a P-channel enhancement type and the transistor Q ₂ is an N-channel depletion type. Therefore, while the positive polarity motor control command voltage Vs is applied to the control terminal 1, the drain and the source of the transistor Q ₁ are conductive and the drain and the source of the transistor Q ₂ are non-conductive.

The line connecting the source of the transistor Q ₁ and the drain of the transistor Q ₂ is grounded via the capacitor C, and the non-grounded side of the capacitor C and the gate electrode of the switching transistor Q ₄ are connected. Further, the drain of the transistor Q ₁ is connected to the terminal 3 via the resistor R ₁ , and the terminal 3 is supplied with the enhancement voltage V _E.

Therefore, when the motor control command voltage Vs is applied to the control terminal 1 at time t ₀ in FIG. 2, the time constants τ ₁ , (τ ₁ = C ×) of the time constant circuit 7 including the resistor R ₁ and the capacitor C.
R) with a change gradient corresponding to the terminal voltage Vc of the capacitor C
Rises to the enhancement voltage V _E value. At the time t ₁ of this rising process, the terminal voltage Vc of the capacitor C
Becomes higher than the threshold voltage V _T of the switching transistor Q ₄ . Therefore, at the time point t ₁ , the drain and source of the transistor Q ₄ become conductive, and the drive voltage Vcc applied to the drain terminal side is applied to the motor coil L connected to the source side. Therefore, the drive current i ₁ (see FIG. 3) flows through the motor coil L (phase I), and the rotor (not shown) is rotated by the magnetic field generated thereby.

Motor control command voltage Vs given to control terminal 1
However, when it is no longer applied at time t ₂ , the transistor Q ₁ becomes non-conductive and the transistor Q ₂ becomes conductive. Therefore, the electric charge stored in the capacitor C is discharged through the discharge circuit 8, and the terminal voltage Vc of the capacitor C that has risen to the enhancement voltage V _E drops.

The discharge circuit 8 includes a detection circuit 4 that detects the terminal voltage Vc of the capacitor C in order to switch the time constant between τ ₂ and τ ₃ . Then, the above-mentioned terminal voltage Vc is the preset reference voltage V
When it is higher than _A, it is discharged by the discharge circuit 8 having a small time constant, and when the terminal voltage Vc is lower than the reference voltage V _A, it is discharged with a large time constant.

That is, the source of the transistor Q ₂ is connected to the series circuit of the resistors R ₂ and R _3, and the series circuit of the resistor R ₄ and the N-channel enhancement type transistor Q ₃ is connected in parallel with the series circuit to obtain the resistance. One end of R ₃ and the source of the transistor Q ₃ are connected and grounded. Also, the resistance R ₂
And a connection point 5 between R ₃ and R ₃ and the gate electrode of the transistor Q ₃ are connected.

The reference voltage V _A is set at the connection point 6 between the resistors R ₂ and R ₄ . The threshold voltage of the transistor Q ₃ is set to V _T ′
Then, the reference voltage V _A is Becomes Therefore, when the terminal voltage Vc of the capacitor C applied to the connection point 6 is higher than the reference voltage V _A , the transistor Q ₃ becomes conductive, and when it is low, it becomes non-conductive. The value of the reference voltage V _A can be freely set by changing the voltage division ratio of the resistors R ₂ and R ₃ .

When the transistor Q ₃ is conducting, the electric charge of the capacitor C is discharged through the series circuit of the resistors R ₂ and R ₃ and the resistor R ₄ connected in parallel with the series circuit. Therefore, the time constant τ ₂ of the discharge at this time is Becomes

When the terminal voltage Vc of the capacitor C becomes lower than the reference voltage V _A , the transistor Q ₃ becomes non-conductive, so that the electric charge of the capacitor C is discharged only by the series circuit of the resistors R ₂ and R ₃ . Therefore, the time constant τ ₃ of the discharge at this time is τ ₃ = C × (R ₂ + R ₃ ).

Since τ ₂ > τ ₃ , the capacitor C discharges rapidly when the terminal voltage Vc is higher than the reference voltage _VA , and conversely, when the terminal voltage Vc becomes lower than the reference voltage _VA , discharges with a gentle voltage change gradient. To do.

Therefore, the threshold voltage V _T of the transistor Q ₄
In the vicinity, the change gradient of the discharge voltage can be made gentle to suppress the generation of spike voltage. Further, since the period for discharging rapidly is provided, the time difference t _f from the start of discharging at the time point t ₂ to the interruption of the drive current i ₁ supplied to the motor coil L at the time point t ₃ can be shortened. It is also possible to adjust the time constants τ ₁ and τ ₂ so that t _f and the time difference t _r at the start of energization are substantially matched.

In order to reduce the channel resistance of the transistor Q ₄ , the value of the enhancement voltage V _E is set to be significantly higher than the threshold voltage V _T. Therefore, when discharging with the same time constant as the charging time constant τ ₁ , the time difference t _f until the terminal voltage Vc of the capacitor C becomes lower than the threshold voltage V _T becomes long.

When t _r = t _f , the control command voltage Vs is changed to the next motor coil phase I at the time point t ₂ of phase switching, as shown in FIG.
When applied to I, the terminal voltage Vc 'of the capacitor of the drive circuit rises substantially to the threshold voltage V _T of the transistor Q ₄ at time t ₃ . Therefore, as shown in FIG. ₃ , at the time t ₃ , the drive current i ₂ is supplied to the next phase II motor coil at substantially the same timing as the drive current i ₁ which was being supplied to the previous phase I motor coil stops flowing. It begins to flow. For this reason, there is no current cutoff or current overlap, and the torques T ₁ and T _{2 in} which the phases are accurately switched for the magnetic fluxes I and II of the respective phases can be obtained, and the torque ripple can be reduced.

The capacitor C may be an independent capacitance element, or the gate capacitance of the transistor Q ₄ may be used.

A circuit for switching the time constant may be provided on the side that charges the capacitor C.

 FIG. 4 shows a modification of the embodiment shown in FIG.

In the motor drive circuit of this embodiment, a bipolar transistor _Tr is used as a switching element, a drive voltage Vcc is applied to the collector, and a motor coil L is connected to the emitter.

When the movable contact c of the switch SW1 is switched to the switching contact a side, the motor control command voltage Vs applied to the control terminal 1
Is smoothed by the time constant circuit 10 and applied to the base of the transistor T _r . The time constant circuit 10 comprises a capacitor C ₁ and a resistance circuit 12. The resistor circuit 12 is formed by connecting a resistor R ₁₁ in parallel to a series circuit of a resistor R ₁₀ and a switch SW2, and a comparator 11 controls opening / closing of the switch SW2.

The terminal voltage Vc ₁ of the capacitor C ₁ is input to the inverting input terminal of the comparator 11, and the reference voltage _VA is input to the non-inverting input terminal. Comparator 11 as well as to turn on the switch SW2 when the terminal voltage Vc ₁ is lower than the reference voltage V _A, is turned off when high.

Therefore, the time constant τ ₄ when the terminal voltage Vc ₁ is lower than the reference voltage V _A is In addition, the time constant τ ₅ when the terminal voltage Vc ₁ is higher than the reference voltage _VA is τ ₅ = C ₁ × R ₁₁ .

tau _4> tau ₅ So, by setting lower than the threshold voltage V _f of the transistor T _r the reference voltage V _A as shown in FIG. 5, the terminal voltage Vc at the time of start of energization
₁ (base voltage of the transistor T _r ) can be rapidly raised to the reference voltage V _A to reduce the time difference T _r, and the voltage change in the vicinity of the threshold voltage V _f can be moderated.

Further, at the end of energization, the discharge is performed with a large time constant τ ₅ until the reference voltage V _A value is reached, so that the voltage change in the vicinity of the threshold voltage V _f can be moderated. Furthermore, the terminal voltage Vc ₁
Discharges with a small time constant τ ₄ after the voltage drops below the reference voltage, the time difference t _f can be reduced. Therefore, the same effect as the embodiment of FIG. 1 can be obtained.

Note the terminal voltage Vc ₁ opens the switch SW2 when lower than the reference voltage, may be closed when high. In this case, as shown in FIG. 6, the reference voltage V _A is set higher than the threshold voltage V _f of the transistor T _r .

〔The invention's effect〕

As described above, the present invention discriminates the voltage level of the coil drive voltage, and when the rise or fall of the drive voltage changes in the vicinity of the threshold voltage of the switching element, it is changed with a large time constant, and the change gradient is gentle. Therefore, the generation of spike voltage can be suppressed. Moreover, since the above-mentioned change gradient is made steep at the portion exceeding the threshold voltage or the portion before exceeding the threshold voltage, even if a large time constant is given as described above, the driving voltage at the rising or falling and the operation of the switching element are It is possible to reduce the deviation without increasing the deviation. Therefore, it is possible to reduce the torque ripple by reducing the discontinuity and the overlap of the drive current that are likely to occur at the phase switching point.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a motor drive circuit showing an embodiment of the present invention, FIG. 2 is a waveform diagram of a drive voltage applied to the gate electrode of the switching transistor of FIG. 1, and FIG. 3 is a drive for energizing a motor coil. FIG. 4 is a time chart showing the switch timing of the electric current, FIG. 4 is a circuit diagram of a motor drive circuit showing a modification of the embodiment shown in FIG. 1, and FIGS. 5 and 6 are the driving applied to the base of the switching transistor shown in FIG. FIG. 7 is a waveform diagram of the voltage, FIG. 7 is a circuit diagram of a conventional motor drive circuit, FIG. 8 is a waveform diagram of the drive voltage applied to the base of the switching transistor of FIG. 7, and FIG. A time chart, FIG. 10 is a time chart showing switch timing at which currents overlap. In still code used in the drawings, 4 ...... potential level detection circuit 7, 10 ...... time constant circuit 8 ...... discharge circuit 11 ...... comparator Q _4, T _r ...... transistor V _r, V _f ...... threshold voltage τ _{1 to} τ ₅ ... Time constants.

Claims (1)

(57) [Claims] 1. A switching element for connecting and disconnecting a drive current to be supplied to a motor coil, and a time constant circuit having large and small time constants and having a time constant for rising / falling of a drive voltage for controlling the switching element. A level detection circuit that discriminates a voltage change at the rise or fall of the drive voltage and switches the time constant of the time constant circuit before and after the discrimination point, wherein the drive voltage is the input threshold voltage of the switching element. A motor drive circuit having a large time constant when passing through.