JP2004304883A - Motor driving circuit and motor driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To offer a motor driving circuit and a motor driving method which can prevent the breakage of a transistor without enlarging the chip size, concerning a motor driving circuit, which has at least a pair of transistors for supplying motor coils with currents and for drawing in currents from the motor coils, and to provide a motor driving method. <P>SOLUTION: This motor drive circuit, which has at least a pair of transistors (QA1 and QA2) for supplying the motor coils (Lu, Lv, and Lw) with currents and for drawing in the currents from the motor coils (Lu, Lv, and Lw), has a matrix circuit (134) which turns on one transistor (QA2) and turns off the other transistor (QA1) out of the pair of transistors (QA1, and QA2) at short brake, and a protective circuit (141) which clamps the base potential of the transistor (QA1) on the side of being turned off at the time of short brake to off potential out of the pair of transistors. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a motor drive circuit and a motor drive method, and more particularly, to a motor drive circuit and a motor drive method having at least a pair of transistors for supplying current to a motor coil and drawing current from the motor coil.
[0002]
[Prior art]
FIG. 12 shows a block diagram of a conventional motor drive circuit.
[0003]
The motor drive circuit 1 is a circuit for driving the three-phase brushless motor M, and mainly includes a U-phase drive circuit 10a, a V-phase drive circuit 10b, a W-phase drive circuit 10c, amplifiers 11a, 11b, 11c, and a matrix circuit. 12 are included. Note that the motor drive circuit 1 is usually formed as an IC chip.
[0004]
The motor M is provided with detection elements 13a, 13b, and 13c for detecting rotation of the rotor of the motor M. The detection elements 13a, 13b, and 13c are arranged at intervals of about 120 degrees about the rotation center of the motor M, and output detection signals according to the magnetic field generated by the rotor magnet 111 of the motor M. The output detection signals of the detection elements 13a, 13b, 13c are supplied to the motor drive circuit 1.
[0005]
The detection signal from the detection element 13a is supplied to the matrix circuit 12 through the amplifier 11a in the motor drive circuit 1, and the detection signal from the detection element 13b is supplied to the matrix circuit 12 through the amplifier 11b in the motor drive circuit 1. The detection signal from the element 13c is supplied to the matrix circuit 12 through the amplifier 11c in the motor drive circuit 1. The matrix circuit 12 generates U-phase, V-phase, and W-phase three-phase control signals based on the detection signals from the detection elements 13a, 13b, and 13c.
[0006]
Among the control signals generated by the matrix circuit 12, the U-phase control signal is supplied to the U-phase drive circuit 10a, the V-phase control signal is supplied to the V-phase drive circuit 10b, and the W-phase control signal is supplied to the W-phase drive circuit 10c. Supplied.
[0007]
The U-phase drive circuit 10a generates a U-phase drive signal from the U-phase control signal from the matrix circuit 12, and supplies the U-phase drive signal to the U-phase coil Lu constituting the motor M. The V-phase drive circuit 10b generates a V-phase drive signal from the V-phase control signal from the matrix circuit 12, and supplies the V-phase drive signal to the V-phase coil Lv constituting the motor M. The W-phase drive circuit 10c generates a W-phase drive signal from the W-phase control signal from the matrix circuit 12, and supplies the generated W-phase drive signal to the W-phase coil Lw constituting the motor M.
[0008]
FIG. 13 is a circuit configuration diagram of the U-phase drive circuit 10a, and FIG. 14 is a cross-sectional view on the IC chip.
[0009]
The U-phase drive circuit 10a is configured to include transistors QA1 to QA4, a parasitic diode DA1, parasitic transistors QAS11, QAS12, QAS13, QAS2, QAS3, and a resistor RA2.
[0010]
Note that the V-phase drive circuit 10b and the W-phase drive circuit 10c have the same configuration as the U-phase drive circuit 10a, and a description thereof will be omitted.
[0011]
The transistor QA3 of the U-phase drive circuit 10a is configured by a PNP transistor. The transistor QA3 is formed on a P-type semiconductor substrate 21 as shown in FIG. 14, and includes an N-type buried layer 22, an N-type epitaxial layer 23, P-type diffusion layers 24 and 25, and an N + type diffusion layer 26. The epitaxial layer 23 is used as a base, the P-type diffusion layer 24 is used as an emitter, and the P-type diffusion layer 25 is used as a collector.
[0012]
The power supply voltage Vcc is applied to the emitter of the transistor QA3, the collector is connected to the base of the transistor QA1, and a first switching signal is supplied from the matrix circuit 12 to the base. The transistor QA3 turns off when the first switching signal forming the U-phase control signal is at a high level, and turns on when the first switching signal is at a low level.
[0013]
The transistor QA1 is configured by an NPN transistor. The transistor QA1 is formed on a P-type semiconductor substrate 21 as shown in FIG. 14, and includes a buried layer 27, an N-type epitaxial layer 28, a P-type diffusion layer 29, an N-type diffusion layer 30, and N-type diffusion layers 31, 32. , N-type diffusion layer 33. The N-type epitaxial layer 28, the N-type diffusion layers 31, 32, and the N-type diffusion layer 33 form a collector, the P-type diffusion layer 29 forms a base, and the N-type diffusion layer 30 forms an emitter. ing.
[0014]
The power supply voltage Vcc is applied to the collector of the transistor QA1 through the current detection resistor R, the emitter is connected to the output terminal Tout, and the base is connected to the collector of the transistor QA3. Further, a bias resistor RA2 is connected between the base and the emitter of the transistor QA1.
[0015]
Transistor QA2 is formed of an NPN transistor. The transistor QA2 includes a buried layer 34, an N-type epitaxial layer 35, a P-type diffusion layer 36, an N-type diffusion layer 37, N-type diffusion layers 38 and 39, and a contact N-type diffusion layer 40 formed on the semiconductor substrate 21. It is configured. The N-type epitaxial layer 35, the N-type diffusion layers 38 and 39, and the N-type diffusion layer 40 are used as a collector, the P-type diffusion layer 36 is used as a base, and the N-type diffusion layer 37 is used as an emitter.
[0016]
The collector of the transistor QA2 is connected to the output terminal Tout, the emitter is grounded, and the base is supplied with the second switching signal constituting the U-phase control signal from the matrix circuit 12. The transistor QA2 turns on when the second switching signal is at a high level, and turns off when the second switching signal is at a low level.
[0017]
Further, the transistor QA4 includes an NPN transistor, and includes an N-type buried layer 41, an N-type epitaxial layer 42, a P-type diffusion layer 43, and N-type diffusion layers 44 and 45 formed on the semiconductor substrate 21. Have been. The buried layer 41, the epitaxial layer 42, and the diffusion layer 45 serve as a collector of the transistor QA4, the diffusion layer 43 serves as a base of the transistor QA4, and the diffusion layer 44 serves as an emitter of the transistor QA4. The transistor QA4 has a base and a collector connected to a connection point between the emitter of the transistor QA1 and the output terminal Tout, and an emitter connected to the collector of the transistor QA3, and functions as a protection element.
[0018]
A parasitic transistor QAS2 having the buried layer 22, the epitaxial layer 23, and the diffusion layer 26 as a base, the diffusion layer 24 as an emitter, and the semiconductor substrate 21 as a collector is formed by the structure as shown in FIG. At the same time, the buried layer 27, the diffusion layers 31, 32, and the diffusion layer 33 are used as collectors, the buried layer 32, the diffusion layers 36, 37, and the diffusion layer 38 are used as emitters. A parasitic transistor QAS12 is formed as a base. Further, the N-type buried layer 51, the N-type epitaxial layer 52, and the N-type diffusion layer 53 are used as collectors, the buried layer 32, the diffusion layers 36, 37, and the diffusion layer 38 are used as emitters, and the semiconductor substrate 21 is used as a base. A parasitic transistor QAS13 is formed.
[0019]
Next, the operation of the U-phase drive circuit 10a will be described.
[0020]
In the motor drive circuit 1, when the first switching signal and the second switching signal are both set to low level, the transistor QA1 turns on and the transistor QA2 turns off. As a result, a current is output from the output terminal Tout to the coil Lu, and the current can be supplied to the coil Lu. When both the first switching signal and the second switching signal are set to a high level, the transistor QA1 is turned off and the transistor QA2 is turned on. Thus, current can be drawn from the coil Lu to the output terminal Tout side. Further, by setting the first switching signal to a high level and the second switching signal to a low level, both the transistors QA1 and QA2 are turned off, and the current supply to the coil Lu can be stopped.
[0021]
FIG. 15 shows an operation waveform diagram of the drive current during normal operation.
[0022]
As shown in FIG. 15, the U-phase drive circuit 10a, the V-phase drive circuit 10b, and the W-phase drive circuit 10c change the first and second switching signals at timings at which the U-phase, V-phase, and W-phase move 120 ° different from each other. By controlling the drive current to flow through the coils Lu, Lv, Lw, the rotor can be rotated.
[0023]
In such a motor M, a short brake operation is performed in which the coils Lu, Lv, Lw are short-circuited to ground to stop the rotation of the rotor. During the short brake operation, the U-phase drive circuit 10a turns off the transistor QA1 and turns on the transistor QA2, and switches the corresponding transistors of the V-phase drive circuit 10b and the W-phase drive circuit 10c in the same manner as the U-phase drive circuit 10a. . As a result, the coils Lu, Lv, Lw are simultaneously short-circuited to the ground, and a short brake state is set.
[0024]
FIG. 16 is an operation explanatory diagram of a main part of the U-phase drive circuit 10a.
[0025]
In the normal operation, the transistor QA1 is turned on and the transistor QA2 is turned off, so that the current I1 as shown in FIG. 16A is supplied to the U-phase coil Lu. By turning off the transistor QA1 and turning on the transistor QA2, a current I2 as shown in FIG. 16A is drawn from the U-phase coil Lu.
[0026]
When the motor M is stopped from a rotated state, all the coils Lu, Lv, Lw are short-circuited to the ground to obtain a braking force, that is, a so-called short brake is applied.
[0027]
At this time, in order to short-circuit the coils Lu, Lv, and Lw to the ground, the transistor QA1 is turned off, the transistor QA2 is turned on, and the coils Lu, Lv, and Lw are short-circuited as shown in FIG.
[0028]
It should be noted that a prior art document corresponding to the motor drive circuit could not be found.
[0029]
[Problems to be solved by the invention]
However, in the motor drive circuit, the potential of the output terminal Tout decreases in the U-phase drive circuit 10a, the V-phase drive circuit 10b, and the W-phase drive circuit 10c due to the back electromotive force generated in the coils Lu, Lv, Lw during the short brake operation. . For example, when the potential of the output terminal Tout decreases in the U-phase drive circuit 10a, the emitter potential of the parasitic transistor QAS11 decreases, and the transistor QAS11 turns on. When the transistor QAS11 turns on, the parasitic transistor QAS2 turns on.
[0030]
When the parasitic transistor QAS2 turns on, the collector current of the parasitic transistor QAS11 further increases. That is, the parasitic current increases. When the collector current of the parasitic transistor QAS11 increases, the collector current of the transistor QA3, that is, the base current of the transistor QA1 increases.
[0031]
Assuming that the current amplification factor of the transistor QA1 is β and the base current of the transistor QA1 is Ib, the collector current Ic of the transistor QA1 is
Ic = β × Ib
Is represented by
[0032]
Therefore, when the parasitic current increases and the base current Ib of the transistor QA1 increases, the collector current of the transistor QA1 is output by multiplying the base current Ib by β. As a result, a through current flows from the power supply through the transistors QA1 and QA2. When the through current flows, the temperature of the junction rises in the transistors QA1 and QA2, and there is a possibility that the element is destroyed.
[0033]
At this time, in order to prevent the destruction of the transistors QA1 and QA2, it is necessary to increase the element size of the transistors QA1 and QA2. However, when the element size of the transistors QA1 and QA2 is increased, there is a problem that the chip size of the motor driving IC increases.
[0034]
The present invention has been made in view of the above points, and an object of the present invention is to provide a motor driving circuit and a motor driving method capable of preventing a transistor from being destroyed without increasing a chip size.
[0035]
[Means for Solving the Problems]
The present invention provides a motor drive circuit having at least a pair of transistors (QA1, QA2) that supplies current to a motor coil (Lu, Lv, Lw) and draws current from the motor coil (Lu, Lv, Lw). A short brake control circuit (34) for turning on one transistor (QA2) of the pair of transistors (QA1 and QA2) and turning off the other transistor (QA1) during short brake; A protection circuit (141) for turning off the base potential of the transistor (QA1) which is sometimes turned off.
[0036]
According to the present invention, the transistor (QA1) can be reliably turned off by clamping the base potential of the transistor (QA1) to the off-potential during short-circuit braking by the protection circuit (141). (QA1, QA2) are both turned on, and the flow of through current can be prevented. Therefore, it is possible to cope with a decrease in the output terminal voltage such as during a short brake without increasing the element size of the output transistors (QA1, QA2).
[0037]
It should be noted that reference numerals are for reference only, and do not limit the scope of the claims.
[0038]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a block diagram showing an embodiment of a motor drive system according to the present invention.
[0039]
The motor drive system 100 of the present embodiment includes a three-phase brushless motor M, hall elements 101-1 to 101-3, and a motor drive circuit 102.
[0040]
FIG. 2 shows a configuration diagram of the three-phase brushless motor M.
[0041]
The three-phase brushless motor M shown in FIG. 2 is an outer rotor type motor, and includes a rotor magnet 111 magnetized to have multiple polarities, a U-phase coil Lu wound around a stator yoke 112, a V-phase coil Lv, and a W-phase coil. Includes coil Lw. The rotor magnet 111 is rotatably disposed around the stator yoke 112.
[0042]
A control current is supplied to the Hall elements 101-1 to 101-3 via a resistor R1, and an output voltage corresponding to an applied magnetic field is generated at the output terminal. The Hall elements 101-1 to 101-3 are arranged, for example, at approximately 120 ° intervals around the rotation center of the motor M, and output a voltage corresponding to the magnetic field generated by the rotor magnet 111. The output voltages of the Hall elements 101-1 to 101-3 are supplied to the motor drive circuit 102.
[0043]
The motor drive circuit 102 includes a motor drive IC (integrated circuit) 103, voltage sources 104 and 105, a resistor R2, and a capacitor C1.
[0044]
The output terminal of the Hall element 101-1 is connected to the terminals T1 and T2 of the motor driving IC 103. The output terminal of the Hall element 101-2 is connected to the terminals T3 and T4 of the motor drive IC 103. Further, the output terminal of the Hall element 101-3 is connected to the terminals T5 and T6 of the motor driving IC 103.
[0045]
A power supply voltage Vcc is applied from a voltage source 104 to a terminal T7 of the motor driving IC 103. To the terminal T8 of the motor driving IC 103, a voltage obtained by lowering the driving voltage Vcc from the voltage source 104 by the resistor R2 is applied. One end of the U-phase coil Lu is connected to the terminal T9 of the motor driving IC 103. One end of the V-phase coil Lv is connected to the terminal T10 of the motor driving IC 103. One end of the W-phase coil Lw is connected to the terminal T11 of the motor driving IC 103. The other ends of the coils Lu, Lv, Lw are connected to each other. The coils Lu, Lv, Lw have a so-called star-connected configuration.
[0046]
Further, a rotation control signal is supplied from an external circuit to the terminals T12 and T13 of the motor driving IC 103. Further, the terminal T16 of the motor driving IC 103 is grounded.
[0047]
The motor driving IC 103 supplies a driving current such that a rotating magnetic field is generated in the coils Lu, Lv, Lw based on the output voltages of the Hall elements 101-1 to 101-3. At this time, the drive current is controlled based on the rotation control signal supplied to the terminals T12 and T13.
[0048]
Next, the motor driving IC 103 will be described in detail.
[0049]
FIG. 3 is a block diagram of the motor driving IC 103.
[0050]
The motor driving IC 103 is configured to include hall amplifiers 131 to 133, a matrix circuit 134, an output unit 135, and a rotation control circuit 136.
[0051]
The Hall amplifier 131 has a non-inverting input terminal connected to the terminal T1 and an inverting input terminal connected to the terminal T2. The Hall amplifier 131 shapes the output voltage of the Hall element 101-1 into a rectangular wave, and supplies the output voltage to the matrix circuit 134. The Hall amplifier 132 has a non-inverting input terminal connected to the terminal T3, and an inverting input terminal connected to the terminal T4. The Hall amplifier 132 shapes the output voltage of the Hall element 101-2 into a rectangular wave and supplies it to the matrix circuit 134. The hall amplifier 133 has a non-inverting input terminal connected to the terminal T5 and an inverting input terminal connected to the terminal T6. The Hall amplifier 133 shapes the output voltage of the Hall element 101-3 into a rectangular waveform and supplies the output voltage to the matrix circuit 134.
[0052]
The matrix circuit 134 generates U-phase, V-phase, and W-phase three-phase control signals based on rectangular waves from the hall amplifiers 131 to 133. The three-phase control signal generated by the matrix circuit 134 is supplied to the output unit 135. The matrix circuit 134 includes a short brake control circuit described in the claims. During the short brake operation, one of the pair of transistors QA1 and QA2 is turned on, and the other transistor QA1 is turned on. Control is performed to turn off.
[0053]
The output unit 135 is configured to include a U-phase drive circuit 135a, a V-phase drive circuit 135b, and a W-phase drive circuit 135c. The U-phase drive circuit 135a controls the U-phase drive current supplied to the output terminal T9 based on the U-phase control signal from the matrix circuit 134. V-phase drive circuit 135b controls the V-phase drive current supplied to output terminal T10 based on the V-phase control signal from matrix circuit 134. The W-phase drive circuit 135c controls the W-phase drive current supplied to the output terminal T11 based on the W-phase control signal from the matrix circuit 134.
[0054]
The rotation control circuit 136 is supplied with a rotation control signal from terminals T12 and T13. The rotation control circuit 136 controls the matrix circuit 134 based on the rotation control signals from the terminals T12 and T13. The signal supplied from the matrix circuit 134 to the output unit 135 is controlled.
[0055]
Next, the U-phase drive circuit 135a, the V-phase drive circuit 135b, and the W-phase drive circuit 135c that constitute the output unit 135 will be described. Since the U-phase drive circuit 135a, the V-phase drive circuit 135b, and the W-phase drive circuit 135c have the same configuration, the configuration of the drive circuit will be described in detail using the U-phase drive circuit 135a as an example.
[0056]
FIG. 4 is a circuit configuration diagram of the U-phase drive circuit 135a. 9, the same components as those in FIG. 9 are denoted by the same reference numerals, and the description thereof will be omitted.
[0057]
The U-phase drive circuit 135a includes a protection circuit 141 that turns off the base potential of the transistor Q1A during a short brake.
[0058]
FIG. 5 is a circuit diagram of the protection circuit 141.
[0059]
The protection circuit 141 of the U-phase drive circuit 135a includes a current source 201, transistors Q11, Q21 to Q23, Q31 to Q33, Q41 to Q43, and resistors R11 to R13.
[0060]
The transistor Q11 is formed of an NPN transistor, and has a base supplied with a short brake control signal. The transistor Q11 turns on when the short brake control signal is at a high level and turns off when the short brake control signal is at a low level. When the transistor Q11 is on, the current from the current source 201 connected to the collector is output from the emitter, and when off, the current output from the emitter is stopped.
[0061]
The emitter current I11e of the transistor Q11 is supplied to a current mirror circuit including NPN transistors Q21 to Q23 and a resistor R11. The current mirror circuit including the transistors Q21 to Q23 and the resistor R11 draws a current I23c corresponding to the emitter current I11e of the transistor Q11 from the collector of the transistor Q23.
[0062]
The transistor Q23 draws the collector current I23c from a current mirror circuit including the PNP transistors Q31 to Q33 and the resistor R12. The current mirror circuit including the transistors Q31 to Q33 and the resistor R12 outputs a current I33c corresponding to the collector current I23c of the transistor Q23 from the collector of the transistor Q33.
[0063]
The collector current I33c of the transistor Q33 is supplied to a current mirror circuit including NPN transistors Q41 to Q43 and a resistor R13. The current mirror circuit including the transistors Q41 to Q43 and the resistor R13 draws a current I43c corresponding to the collector current I33c of the transistor Q33 from the collector of the transistor Q43.
[0064]
The collector current I43c of the transistor Q43 is connected to the base of the transistor QA1, and draws current from the base of the transistor QA1 during a short brake.
[0065]
Next, the operation of the U-phase drive circuit 135a during a short brake will be described.
[0066]
FIG. 6 shows an operation waveform diagram of the U-phase drive circuit 135a. 6A shows a short brake control signal, FIG. 6B shows a voltage waveform at the output terminal T9, and FIG. 6C shows a power supply current waveform. In FIG. 6, a solid line indicates a waveform when the protection circuit 141 is provided, and a dashed line indicates a waveform when the protection circuit 141 is not provided.
[0067]
At time t0, a short brake operation is instructed, the transistor QA1 is turned off and the transistor QA2 is turned on by the first and second switching signals, and the short brake control signal goes high as shown in FIG. Then, the voltage at the output terminal T9 drops below the GND potential due to the back electromotive force generated in the motor coil Lu as shown by the solid line in FIG. 6B. At this time, the voltage of the output terminal T9 gradually increases to the GND potential until the rotation of the motor rotor stops at time t2.
[0068]
At this time, in this embodiment, the protection circuit 141 is driven by the short brake control signal indicated by the solid line in FIG. 6A, and the base potential of the transistor QA1 is clamped to the off potential, so that the transistor QA1 is reliably turned off. Therefore, the transistors QA1 and QA2 are both turned on and no through current flows through the transistors QA1 and QA2, so that the power supply current sharply decreases as shown by the solid line in FIG. In this case, the current consumption is about the current of the motor driving IC 103.
[0069]
On the other hand, when the protection circuit 141 is not provided, the transistor QA3 is turned on by the back electromotive force of the motor coil Lu, whereby the transistor QA1 is turned on, and a through current flows through the transistors QA1 and QA2. , QA2 is destroyed. As a result, the voltage of the output terminal T9 rises to approximately the power supply voltage as shown by the dashed line in FIG. 6B, and the power supply current becomes maximum as shown by the dashed line in FIG. 6C. .
[0070]
FIG. 7 shows a characteristic diagram of the power supply current with respect to the motor rotation speed of the U-phase drive circuit 135a.
[0071]
According to the present embodiment, the base potential of the transistor QA3 is clamped to the off-potential by the protection circuit 141 during short-circuit braking, so that the output transistor QA1 can be reliably turned off during short-circuit braking. For this reason, even if the back electromotive force of the motor coil increases due to the increase in the rotation speed of the motor rotor as shown by the one-dot chain line in FIG. 7, the output transistor QA1 is turned on by the effect of the back electromotive force of the motor coil, and FIG. As shown by the solid line, the power supply current does not increase. Therefore, it is possible to prevent a breakthrough of the output transistors QA1 and QA2 due to a through current flowing through the output transistors QA1 and QA2.
[0072]
For this reason, the withstand voltage of the output transistors QA1 and QA2 can be set small. Therefore, it is possible to increase the element size of the transistors QA1 and QA2, and it is possible to prevent the transistors QA1 and QA2 from being destroyed due to a decrease in the output terminal voltage during a short brake without increasing the chip size of the motor driving IC.
[0073]
In this embodiment, the base potential of the transistor QA1 is forcibly reduced by the current mirror circuit including the transistors Q31 to Q33 and the resistor R12 and the current mirror circuit including the transistors Q41 to Q43 and the resistor R13. Although the off-potential is used, the circuit configuration can be simplified.
[0074]
FIG. 8 is a circuit configuration diagram of a modification of the protection circuit 141. 5, the same components as those of FIG. 5 are denoted by the same reference numerals, and the description thereof will be omitted.
[0075]
The protection circuit 141 of the present modification is configured such that the base potential of the transistor QA1 is directly turned off by the collector current I23c drawn from the transistor Q23. According to this modification, the transistors Q31 to Q33, Q41 to Q43, and the resistors R12 and R13 can be omitted. However, when it is necessary to increase the current amplification factor, for example, it is necessary to set the emitter areas of the transistors Q21 to Q23 to be large.
[0076]
FIG. 9 is a block diagram showing a modification of the U-phase drive circuit 135a. 4, the same components as those of FIG. 4 are denoted by the same reference numerals, and the description thereof will be omitted.
[0077]
The U-phase drive circuit 135a of the present modified example is configured to include, in addition to the protection circuit 141, a second protection circuit 151 that clamps the base potential of the transistor QA3 to the off potential at the time of short braking.
[0078]
FIG. 10 is a circuit configuration diagram of the second protection circuit 151. 5, the same components as those of FIG. 5 are denoted by the same reference numerals, and the description thereof will be omitted.
[0079]
The second protection circuit 151 has a clamp circuit 152. The clamp circuit 152 includes an NPN transistor Q51 and a resistor R14, and forms a constant voltage circuit that generates a constant voltage by the collector current I43c of the transistor Q43. The clamp circuit 152 is driven by the collector current I43c of the transistor Q43, and clamps the base potential of the transistor QA3 to the off potential at the time of short brake.
[0080]
According to the present embodiment, the base potential of the transistor QA1 can be set to the off-potential by the protection circuit 141 and the transistor QA3 can be set to the off-potential by the second protection circuit 151 at the time of short braking, so that double protection can be performed. Transistor QA1 can be reliably turned off.
[0081]
FIG. 11 is a circuit configuration diagram of a modified example of the second protection circuit 151. 8, the same components as those of FIG. 8 are denoted by the same reference numerals, and the description thereof will be omitted.
[0082]
In this modification, the clamp circuit 152 is directly driven by the collector current I23c of the transistor Q23.
[0083]
According to this modification, the transistors Q31 to Q33, Q41 to Q43, and the resistors R12 and R13 can be omitted, so that the circuit configuration can be simplified.
[0084]
Further, in the above-described embodiment, the description has been given by taking the drive circuit of the three-phase brushless motor as an example. However, it is needless to say that the present invention is not limited to this and can be applied as a drive circuit of a DC motor or the like.
[0085]
Further, in this embodiment, the base potential of the output transistor QA1 is set to the off potential during the short brake operation, but the base potential of the transistor QA3 may be simultaneously clamped to the off potential.
[0086]
【The invention's effect】
As described above, according to the present invention, the transistor can be reliably turned off by clamping the base potential of the transistor to the off potential at the time of short braking by the protection circuit, so that both the output transistors are turned on by the parasitic current, It is possible to prevent a through current from flowing, and thus to cope with a decrease in output terminal voltage such as during a short brake without increasing the element size of the output transistor.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a motor drive system according to the present invention.
FIG. 2 is a configuration diagram of a motor M.
FIG. 3 is a block diagram of a motor driving IC 103;
FIG. 4 is a block diagram of a U-phase drive circuit 135a.
FIG. 5 is a circuit configuration diagram of a protection circuit 141.
FIG. 6 is an operation waveform diagram of a U-phase drive circuit 135a.
FIG. 7 is a characteristic diagram of a through current with respect to a motor rotation speed of a U-phase drive circuit 135a.
FIG. 8 is a circuit configuration diagram of a modification of the protection circuit 141.
FIG. 9 is a block diagram of a modification of the U-phase drive circuit 135a.
FIG. 10 shows a circuit configuration diagram of a second protection circuit 151.
FIG. 11 is a circuit configuration diagram of a modified example of the second protection circuit 151.
FIG. 12 is a block diagram of a conventional motor drive circuit.
FIG. 13 is a circuit configuration diagram of a U-phase drive circuit 10a.
FIG. 14 is a cross-sectional configuration diagram on the IC chip of the U-phase drive circuit 10a.
FIG. 15 is an operation waveform diagram of a drive current in a normal operation.
FIG. 16 is an operation explanatory diagram of a main part of the U-phase drive circuit 10a.
[Explanation of symbols]
Reference Signs List 100 motor drive system M motor, 101-1 to 101-3 Hall element, 102 motor drive circuit 103 motor drive IC, 104, 105 voltage source Lu U-phase coil, Lv V-phase coil, Lw W-phase coil 134 Matrix circuit 141 Protection circuit, 151 Second protection circuit, 152 Clamp circuit

Claims (8)

A motor drive circuit having at least a pair of transistors for supplying current to the motor coil and drawing current from the motor coil,
A short brake control circuit that turns on one transistor and turns off the other transistor among the pair of transistors during short brake,
A protection circuit for setting a base potential of a transistor that is turned off at the time of short brake among the pair of transistors to an off potential. The protection circuit includes a current source that outputs a current,
A switching element that is turned on during the short brake and outputs a current from the current source;
When the switching element is turned on, a drive current generation circuit that generates a drive current according to the current from the current source,
An off-potential setting circuit that is driven by the driving current generated by the driving current generation circuit and sets an off-potential to a base potential of a transistor that is turned off during short-circuit braking of the pair of transistors. The motor drive circuit according to claim 1. The off-potential setting circuit controls a current supplied to a base of a transistor that is turned off at the time of short brake among the pair of transistors based on the driving current generated by the driving current generation circuit, thereby turning off the transistor. 3. The motor driving circuit according to claim 2, wherein the motor driving circuit has a potential. A current supply transistor that switches a transistor that is turned off during short braking among the pair of transistors,
5. The motor drive circuit according to claim 1, further comprising another protection circuit that clamps a base potential of the current supply transistor to an off potential during a short brake. The other protection circuit includes a current source that outputs a current,
A switching element that is turned on during the short brake and outputs a current from the current source;
When the switching element is turned on, a drive current generation circuit that generates a drive current according to the current from the current source,
5. The motor drive circuit according to claim 4, further comprising: a clamp circuit driven by the drive current generated by the drive current generation circuit to clamp a base potential of the current supply transistor. 6. The motor drive circuit according to claim 5, wherein the clamp circuit includes a constant voltage circuit that generates a constant voltage based on the drive current generated by the drive current generation circuit. A motor driving method for a motor driving circuit having at least a pair of transistors that supplies current to a motor coil and draws current from the motor coil,
During short braking, one of the pair of transistors is turned on and the other transistor is turned off,
A motor driving method, characterized in that a base potential of a transistor that is turned off at the time of short braking among the pair of transistors is set to an off potential. 8. The motor driving method according to claim 7, further comprising clamping a base potential of a current supply transistor that switches a transistor that is turned off during the short brake to an off potential during the short brake. .

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