JP3545214B2 - Motor drive circuit - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a motor drive circuit suitable for reducing fan noise.
[0002]
[Prior art]
FIG. 8 is a circuit block diagram showing a conventional motor drive circuit.
[0003]
In FIG. 8, the drive coils (1) and (2) are structurally fixed to the stator constituting the motor, one end of the wiring is grounded via a power supply VCC, and the drive current IL1, IL2 flows complementarily. The Hall element (3) is structurally fixed at a predetermined position on the side of the stator constituting the motor, and is connected between the power supply VCC and ground and supplied with power on the wiring, and the relative positional relationship between the stator and the rotor. Output the sine wave signals H + and H− of opposite phases in response to The amplifier (4) compares the sine wave signal H + with the sine wave signal H− having the opposite phase, and outputs a rectangular wave signal F. The control circuit (5) generates a control pulse C every time the rectangular wave signal F rises and falls. The resistor (102) and the capacitor (103) are connected in series between the power supply VCC and the ground, and the capacitor (103) charges according to a time constant determined by the resistance value of the resistor (102) and the capacitance of the capacitor (103). The charge / discharge control circuit (104) discharges the charge stored in the capacitor (103) every time the control pulse C is supplied. Therefore, a sawtooth signal D is generated on the non-ground side of the capacitor (103). The resistor (105) and the thermistor (106) are connected in series between the power supply VCC and the ground, and a non-ground side of the thermistor (106) generates a reference voltage Vref that changes in response to a change in ambient temperature. The comparator (107) compares the sawtooth signal D with the reference voltage Vref, and outputs a comparison signal E which goes high when the sawtooth signal D is lower than the reference voltage Vref. The control circuit (5) current-amplifies and outputs the drive signals A and B based on the comparison signal E. The NPN transistors (6) and (7) are connected between the other end of the drive coil (1) and the ground in Darlington connection, and the high level of the drive signal A is supplied to the base of the NPN transistor (6). Then, the NPN transistors (6) and (7) are turned on, and the drive current IL1 flows through the drive coil (1). Similarly, the NPN transistors (8) and (9) are connected between the other end of the drive coil (2) and the ground in a state of Darlington connection, and the high level of the drive signal B is applied to the base of the NPN transistor (8). When the level is supplied, the NPN transistors (8) and (9) are turned on and the drive current IL2 flows through the drive coil (2). The capacitor (100) is connected between the base and the collector of the NPN transistor (6), and has a slope at the fall of the drive current IL1. The capacitor (101) is connected between the base and the collector of the NPN transistor (8), and has a slope at the fall of the drive current IL2. The capacitors (100) and (101) are provided to minimize the torque fluctuation of the motor. Then, the drive currents IL1 and IL2 alternately flow through the drive coils (1) and (2) to rotate the motor.
[0004]
[Problems to be solved by the invention]
FIG. 9 is a waveform diagram showing the drive currents IL1 and IL2. The drive currents IL1 and IL2 (= IL) are represented by the following equations.
[0005]
IL = (VCC−Vsat−Ec) / RL
However, VCC: power supply voltage Vsat: saturation voltage Ec of drive transistors (7), (9) ... counter electromotive voltage RL: resistance component of drive coils (1), (2) By the way, during rotation of the motor, In the vicinity T near the phase switching point at which the drive currents IL1 and IL2 are switched, the back electromotive voltage Ec decreases, and the drive current IL increases. However, with the drive current IL in the vicinity T of the phase switching point, the efficiency of the rotation torque generation of the motor is originally poor, and the magnitude of the drive current IL is disturbed, and the rotation torque of the motor is reduced due to a sudden change in the drive current IL. There is a problem that it fluctuates and induces vibration noise of the motor.
[0006]
Further, the resistance value of the thermistor (106) decreases as the ambient temperature increases. That is, the reference voltage Vref decreases, and the falling edge of the rectangular wave signal E moves to the left. Therefore, when the ambient temperature rises beyond the specific temperature, the falling of the driving currents IL1 and IL2 exceeds the phase switching point due to the capacitance of the capacitors (100) and (101). And the starting end overlap, the motor is braked, the driving efficiency of the motor is greatly reduced, and the motor cannot be rotated at high speed.
[0007]
On the other hand, the resistance value of the thermistor (106) increases as the ambient temperature decreases. That is, the reference voltage Vref rises, and the falling of the rectangular wave signal E moves to the right. Therefore, when the ambient temperature falls below the specific temperature, the low-level periods of the drive signals A and B both become longer, and the motor cannot obtain a sufficient air volume and static pressure for forcibly cooling the housing. The conventional circuit shown in FIG. 8 is not suitable for a device such as a housing that requires a sufficient forced air cooling capability for a fan.
[0008]
Therefore, an object of the present invention is to provide a motor drive circuit that realizes noise reduction of a motor and improvement in drive efficiency.
[0009]
[Means for Solving the Problems]
The present invention has been made in order to solve the above problems, and based on a sine wave signal generated by a Hall element according to a relative positional relationship between a stator and a rotor constituting a motor, a first coil and a first coil are provided. In a motor drive circuit having a first drive transistor and a second drive transistor for driving a second coil in a complementary manner, the motor drive circuit changes in one direction when the first and second coils are driven and the phase of the first and second coils is changed. Means for comparing a sawtooth wave signal that changes in the other direction at the time of switching with a reference voltage that changes in response to a temperature change, and outputs a first rectangular wave signal; The first full-wave signal is compared with a sample-and-hold signal obtained by amplifying or attenuating the first full-wave signal and sampling and holding a second full-wave signal having a different amplitude at the timing of the first rectangular wave signal. Means for outputting a second rectangular wave signal for simultaneously turning off the first and second drive transistors in the vicinity of the phase switching point of the second coil and the upper and lower limits of the reference voltage that changes in response to a temperature change. Limiting means for setting a minimum rotation speed and a maximum rotation speed of the motor with respect to a temperature change.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
The details of the present invention will be specifically described with reference to the drawings.
[0011]
FIG. 1 is a circuit block diagram showing a motor drive circuit according to the present invention. In FIG. 1, the same elements as those in FIG. 8 are denoted by the same reference numerals, and description thereof will be omitted. FIG. 2 is a waveform diagram showing the overall operation of FIG. 1, and FIG. 3 is a waveform diagram showing the relationship between the sawtooth signal and the reference voltage.
[0012]
In FIG. 1, a control circuit (10) converts a sine wave signal output from an amplifier (4) into a rectangular wave signal A. The control pulse generating circuit (11) is supplied with the rectangular wave signal A, and generates a control pulse B at the rising and falling points of the rectangular wave signal A. The resistor (12) and the capacitor (13) form a time constant circuit, and charge according to the resistance value of the resistor (12) and the capacity of the capacitor (13). The charge / discharge control circuit (14) is connected to the control pulse generation circuit (11), and discharges the charge stored in the capacitor (13) when the control pulse B is supplied. At the time of discharging, the minimum value of the charge stored in the capacitor (13) is limited to the voltage V1, and does not become lower than the voltage V1. Therefore, a sawtooth signal C for discharging to the minimum voltage V1 is generated from the connection point of the resistor (12) and the capacitor (13) every time the phase is switched. The resistor (15) and the thermistor (16) are connected in series between the power supply VCC and the ground, and generate a voltage V2 (> V1) that changes in response to an ambient temperature change from a connection midpoint. The selection circuit (42) selects and outputs one of the voltages V2 and V4 higher than the voltage V1. The thermistor (16) has a characteristic that the resistance value decreases as the ambient temperature increases. The selection circuit (42) selectively outputs the voltage V4 when the voltage V2 becomes lower than the voltage V4 due to a change in the ambient temperature. The first comparator (17) compares the sawtooth signal C with the voltages V2, V4, V5 (V4 <V2 <V5). That is, the first comparator (17) compares the saw-tooth wave signal C with the voltage V2 when the voltage V2 is between the voltages V4 and V5, and when the voltage V2 falls below the voltage V4, the first comparator (17). Is compared with the voltage V4, and when the voltage V2 rises above the voltage V5, the sawtooth signal C is compared with the voltage V5. Then, the first comparator (17) sets the high level when the voltages V2, V4, V5 are higher than the sawtooth signal C, and sets the low level when the voltages V2, V4, V5 are lower than the sawtooth signal C. A first comparison signal D (first drive-off signal) is output. The high-level period of the first comparison signal D is shorter as the ambient temperature of the thermistor (16) is higher and longer as the ambient temperature is lower.
[0013]
The absolute value circuit (18) outputs an absolute value signal E obtained by taking the absolute value of the sine wave signals H + and H- output from the Hall element (3) at the midpoint of the amplitude. The amplifier (19) outputs an attenuation signal F obtained by attenuating the absolute value signal E at an attenuation rate determined by the resistance values of the resistors (20) and (21). The absolute value signal E and the attenuation signal F are given a common DC bias by the reference voltage (32). Note that the attenuation signal F is a waveform when the control pulse B and the comparison signal D do not act on a sample and hold circuit described later. A sample-and-hold circuit (22) samples and holds the attenuated signal F at the falling edge of the comparison signal D, and then holds the attenuated signal F down to the minimum voltage of the absolute value signal E at the rising edge of the comparison signal D. It outputs a wave signal G. The second comparator (23) compares the absolute value signal E with the trapezoidal wave signal G. When the trapezoidal wave signal G is higher than the absolute value signal E, the second comparator (23) is at a high level, and the trapezoidal wave signal G is lower than the absolute value signal E. During the period, a second comparison signal H (second drive-off signal) that is at a low level is output. The second comparison signal H is generated by a predetermined width before the phase switching of the drive coils (1) and (2). The OR circuit (41) adds the first comparison signal D and the second comparison signal H, and the first and second driving transistors (7) (7) near the first and second half of the phase switching point of the driving coils (1) and (2). 9) is to output an addition signal K for turning off simultaneously. When the first and second comparison signals D and H are added, the rising of the first comparison signal D and the falling of the second comparison signal H are based on the control pulse B. Chattering does not occur at the junction of the rising edge and the falling edge of the second comparison signal H. The control circuit (10) is supplied with the addition signal K, and based on the addition signal K, a first drive signal I for turning on the first drive transistor (7) and a second drive transistor (9) for turning on the second drive transistor (9). The second drive signal J is output. Thus, the drive currents IL1 and IL2 flow through the drive coils (1) and (2), and the motor rotates.
[0014]
From the above,
(A) In the vicinity of the first half of the phase switching point, the drive currents IL1 and IL2 can be set to zero before being affected by the decrease in the back electromotive voltage Ec, so that the drive currents IL1 and IL2 suddenly fall from a high level. Can be prevented and the motor can be made quieter.
[0015]
(B) When the amplitudes of the sine wave signals H + and H− fluctuate due to variations in the characteristics of the Hall element (3), or when the period of the sine wave signals H + and H− fluctuate due to a change in the rotation speed of the motor. However, since the simultaneous OFF period of the first and second drive transistors (7) and (9) in the vicinity of the first half of the phase switching point can be made constant and the drive current IL can be prevented from rising sharply, the variable speed motor Suitable for reducing noise.
[0016]
(C) Under the condition of constant ambient temperature, in the vicinity of the second half of the phase switching point, the drive currents IL1 and IL2 can be made zero continuously from the vicinity of the first half, so that the reactive current can be ignored and the reduction in the drive efficiency of the motor can be prevented.
[0017]
(D) Since the trapezoidal wave signal G is created from the attenuation signal F, even if the width of the first comparison signal D is affected by a change in the resistance value of the thermistor (16) due to a change in the ambient temperature, the second comparison signal H is not changed. It is inevitable that fluctuation of the rotation torque of the motor and the accompanying noise can be prevented.
[0018]
The following effects are obtained.
[0019]
However, the ends of the driving currents IL1 and IL2 exceed the phase switching point due to the capacitance of the capacitors (100) and (101), and the starting ends of the driving currents IL1 and IL2 approach the phase switching point as the ambient temperature increases. And the end and start ends of the drive currents IL1 and IL2 overlap, and the effect (c) cannot be expected. Thus, the present invention can prevent the drive efficiency of the motor from lowering even when the ambient temperature rises, and can reliably obtain the effect (c).
[0020]
FIG. 7 is a waveform diagram showing changes in drive currents IL1 and IL2 with respect to the ambient temperature.
[0021]
In FIG. 7, a period T0 is, for example, a simultaneous OFF time of the first and second driving transistors (7) and (9) at room temperature (25 ° C.), and a driving current IL is caused by the capacitance of the capacitors (100) and (101) during the period T1. It is a time required for the drive current IL to fall to zero, and for the sake of convenience of description, it is assumed that the fall of the drive current IL exceeds the phase switching point of the first and second coils (1) and (2). The period T2 is a time width during which the start end of the drive current IL tends to fluctuate as the ambient temperature increases, and the period T3 is a time width during which the start end of the drive current IL obtained according to the present invention can fluctuate. According to the present invention, the end and the start of the drive currents IL1 and IL2 can be prevented from overlapping.
[0022]
Now, the signal output operation of the sawtooth signal C, the first comparison signal D, and the trapezoidal signal G in FIG. 1 will be described using one embodiment circuit.
[0023]
FIG. 4 is a circuit diagram showing one embodiment of the charge / discharge control circuit (14). FIG. 4 shows that the base voltage of the transistor (25) and the emitter voltage of the transistor (26) having the same potential are varied according to the on / off state of the transistor (24).
[0024]
In FIG. 4, when the control pulse B is not generated, the transistor (24) is turned off, and the base voltage of the transistor (25) and the emitter voltage of the transistor (26) are obtained by subtracting the voltage across the resistor (28) from the power supply VCC. It becomes the voltage Vmax. Therefore, the capacitor (13) charges with a time constant determined by the resistance value of the resistor (12) and the capacitance of the capacitor (13), and the terminal voltage of the capacitor (13) rises. Although the generation cycle of the control pulse B changes in accordance with the number of rotations of the motor, the time constant is set to a value such that the charging voltage of the capacitor (13) does not reach the voltage Vmax during the generation cycle of the control pulse B. Is set to On the other hand, when the control pulse B is generated, the transistor (24) is turned on, and the base voltage of the transistor (25) and the emitter voltage of the transistor (26) are the divided voltage V1 (<Vmax) of the resistors (28) and (29). It becomes. At this time, since the non-ground side voltage of the capacitor (13) is higher than the voltage V1, the accumulated charge of the capacitor (13) is discharged to the voltage V1 via the transistor (27). This operation is repeated, and a sawtooth signal C is generated.
FIG. 6 is a circuit diagram showing one embodiment of the comparator (17) and the selection circuit (42). At normal temperature, the voltage V2 is a value between the voltages V4 and V5 due to the resistance of the thermistor (16).
[0025]
In FIG. 6, the NPN transistors (43) and (44) are differentially connected, a voltage V2 is applied to the base of the NPN transistor (43), and the resistor (45) ( 46) The voltage V4 divided in (47) is applied. The combined value of the resistances (45) and (46) is equal to the resistance value of the resistance (28), and the resistance values of the resistances (29) and (47) are equal, that is, the voltage V4 is higher than the voltage V1. Therefore, when the voltage V2 is higher than the voltage V4, the NPN transistor (43) is turned on, so that the reference voltage V2 is applied to one input of the comparator (17), and the comparator (17) has a sawtooth waveform. The signal C is compared with the reference voltage V2. When the ambient temperature rises and the voltage V2 becomes lower than the voltage V4, the NPN transistor (44) is turned on. Therefore, the reference voltage V4 is applied to one input of the comparator (17). The detector (17) compares the sawtooth signal C with a reference voltage V4. The reference voltage V4 is a value that can shorten the first comparison signal D only in the period T3. As a result, it is possible to prevent the drive currents IL1 and IL2 from overlapping, and to prevent generation of a reactive current. When the ambient temperature decreases and the voltage V2 becomes higher than the voltage V5 divided by the series resistors (48) and (49), the PNP transistor (50) turns off and the PNP transistor (51) turns off. Turning on, the comparator (17) compares the sawtooth signal C with the reference voltage V5. As described above, the reference voltage V2 is limited between the minimum voltage V4 and the maximum voltage V5, and is suitable for a device that constantly rotates the fan according to the ambient temperature. Then, the function of limiting the upper and lower limits of the reference voltage in FIG. 5 can be integrated on one chip.
[0026]
FIG. 5 is a circuit diagram showing an embodiment of the amplifier (19), the sample hold circuit (22), and the comparator (23).
[0027]
In FIG. 5, an amplifier (19) is provided with a series body composed of a resistor (31) and a reference voltage (32) at the input of an absolute value signal E. Therefore, the absolute value signal E represented by the current is converted by the resistor (31) with reference to the minimum voltage V3. The voltage-converted absolute value signal E is attenuated via an internal differential amplifier circuit and a current mirror circuit at an attenuation rate Rb / (Ra + Rb) determined by the resistance values Ra and Rb of the resistors (20) and (21). It becomes the attenuation signal F. Here, a sample and hold circuit (22) is interposed between the output of the amplifier (19) and the input of the comparator (23). In the sample and hold circuit (22), when the control pulse B is generated, the NPN transistor (33) is turned on, and the electric charge stored in the capacitor (34) is discharged. At this time, since the first comparison signal D is at a high level until the sawtooth signal C exceeds the voltage V2 after the generation of the control pulse B, the transistor (35) is turned on, the transistor (36) is turned off, and the capacitor is turned on. (34) performs charging through the diode (37). Thereafter, when the first comparison signal D changes to low level, the transistor (35) is turned off and the transistor (36) is turned on, so that all the current of the current source (38) flows through the collector-emitter path of the transistor (36), The capacitor (34) stops charging, and the terminal voltage of the capacitor (34) is maintained. The Darlington-connected transistors (39) and (40) are for minimizing the amount of discharge of accumulated charges when the capacitor (34) is in the voltage holding state. Thus, a trapezoidal wave signal G is generated.
[0028]
【The invention's effect】
According to the present invention, in the vicinity of the first half of the phase switching point of the first and second coils, the coil current can be made zero before being affected by the decrease in the back electromotive voltage, so that the coil current rapidly rises from a high level. The inconvenience of falling can be prevented, and the noise of the motor can be reduced. Further, even when the amplitude of the sine wave signal fluctuates due to the variation in the characteristics of the Hall element, or when the period of the sine wave signal fluctuates due to a change in the rotation speed of the motor, the vicinity of the first and second half of the phase switching point may be reduced. Therefore, the simultaneous OFF period of the first and second drive transistors can be made constant, and a steep rise of the coil current can be prevented, which is suitable for reducing the noise of the variable speed motor. In addition, even if the ambient temperature increases, it is possible to prevent the ends of the respective coil currents flowing through the first and second coils from overlapping with each other, thereby preventing a reduction in the driving efficiency of the motor. Further, a one-chip integrated circuit can provide a motor drive circuit that limits the upper and lower limits of the reference voltage that changes in response to a change in the ambient temperature, and that can always rotate the fan at a speed corresponding to the ambient temperature.
[Brief description of the drawings]
FIG. 1 is a circuit block diagram illustrating a motor drive circuit according to the present invention.
FIG. 2 is a waveform diagram showing an entire waveform of FIG.
FIG. 3 is a waveform diagram showing a relationship between the sawtooth signal of FIG. 1 and a reference voltage.
FIG. 4 is a circuit diagram showing a specific example of a sawtooth signal generation circuit of FIG. 1;
FIG. 5 is a circuit diagram showing a specific example of a trapezoidal wave signal generation circuit of FIG. 1;
FIG. 6 is a circuit diagram showing a specific example of the selection circuit of FIG. 1;
FIG. 7 is a waveform diagram showing a drive current waveform according to a change in ambient temperature.
FIG. 8 is a circuit block diagram showing a conventional motor drive circuit.
FIG. 9 is a waveform diagram showing a coil current waveform of FIG.
[Explanation of symbols]
(1) (2) Drive coil (3) Hall element (7) (9) Drive transistor (10) Control circuit (11) Control pulse generation circuit (14) Charge / discharge control circuit (17) First comparator (19) Amplifier (22) Sample hold circuit (23) Second comparator (41) OR circuit (42) Selection circuit

Claims (1)

A first drive transistor that complementarily drives the first coil and the second coil based on a sine wave signal generated by a Hall element according to a relative positional relationship between a stator and a rotor that constitute a motor for rotating the fan; And a motor drive circuit having a second drive transistor,
A comparison is made between a sawtooth signal that changes in one direction when the first and second coils are driven and changes in the other direction when the first and second coils are switched, and a reference voltage that changes in response to a temperature change. Means for outputting a first rectangular wave signal;
A sample-and-hold in which a first full-wave signal obtained by full-wave conversion of the sine wave signal and a second full-wave signal obtained by amplifying or attenuating the first full-wave signal and having different amplitudes are sampled and held at the timing of the first rectangular wave signal. Means for comparing the signal with a signal and outputting a second rectangular wave signal for simultaneously turning off the first and second drive transistors near the phase switching point of the first and second coils;
Means for limiting an upper limit and a lower limit of the reference voltage that changes in response to a temperature change, so as to constantly rotate the fan at a speed according to an ambient temperature ;
A motor drive circuit comprising the.

Images