JP2838765B2 - Load drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for a load, and more particularly to a driving circuit for a step motor or the like.

[0002]

2. Description of the Related Art At present, an analog electronic timepiece uses a motor driven by a pulse as power for a timepiece movement for driving a hand. For example, a drive pulse whose polarity changes every second causes a rotor to rotate 180 degrees per second. Some are rotated by degrees. There are the following drive circuits for driving loads such as motors.

For example, as shown in FIG. 5, inverters i1 and i2 of a CMOS configuration are connected between power supply terminals VDD and VSS, and output terminals o of the inverters i1 and i2 are mutually connected.
1 and o2, the coil L of the motor m is connected, and the drive signal generation circuit g alternately applies drive signals having different potential levels to the input terminals in1 and in2 of the inverters i1 and i2, thereby connecting the motor m. It is driven.
For example, when "H" is applied to the input terminal of the inverter i1 and "L" is applied to the input terminal of the inverter i2, a drive current flows in a direction indicated by an arrow c in FIG. That is, the inverter i
The input terminals in1 and in2 of i and i2 are connected to i
When pulses are applied alternately as shown in n1 and in2,
Driving pulses having different polarities are applied between the terminals of the coil L of the motor m as shown by o1-o2 in the figure, and a driving current flows in both directions. Here, for convenience, the potential of the terminal o2 is shown with reference to the potential of the terminal o1 in FIG.

[0004]

SUMMARY OF THE INVENTION In such a case,
Since the drive voltage applied between the terminals of the coil L of the motor m is substantially equal to the power supply voltage, a change in the power supply voltage causes a change in the drive current. For example, in a device such as a timepiece using a battery as a power supply, the power supply voltage is generally about 1.6 V before use, but gradually decreases as time passes to about 1.2 V. Therefore, it is difficult to drive the motor stably.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a load driving circuit which can drive a load with a stable driving voltage irrespective of power supply voltage fluctuation.

[0006]

A first series circuit formed by connecting drains of first and second MOS transistors of different conductivity types is connected to a first power supply terminal and a potential different from the first power supply terminal. And the second power supply terminal. A second series circuit having a configuration similar to that of the first series circuit is connected between a first power supply terminal and a second power supply terminal, and a drain connection point of the first series circuit is connected to the second series circuit. A load is connected between the gate and the drain connection point. Further, a pair of series-connected impedance elements having the same impedance value are connected in parallel to the load, and a voltage at a connection point of each impedance element is compared with a reference voltage to generate an output according to the difference. A comparison circuit and a first series circuit;
First driving signal and the first drive signal generation circuit for generating a second drive signal alternately to turn off the MOS transistor, a first drive signal of the second series circuit for the MOS transistor off And a first switching circuit for supplying the output of the comparison circuit to the gate of the second MOS transistor of the first series circuit, and a second drive signal for turning on the output of the comparison circuit.
A second switching circuit for supplying to the gate of the second MOS transistor of the series circuit is provided for alternately the load
The above object is achieved by applying a driving voltage bidirectionally to the.

A third switching circuit for connecting the gate of the second MOS transistor of the first series circuit to a specific potential, a period during which the first drive signal is not generated, and a period during which the second drive signal is not generated. And a fourth switching circuit for connecting the gate of the second MOS transistor of the second series circuit to a specific potential.

[0008]

Next, a load driving circuit according to an embodiment of the present invention will be described. FIG. 1 is an electric circuit diagram showing a configuration of the present example.
In the figure, Tr1 is a P-channel type first MOS transistor, and Tr2 is an N-channel type second MOS transistor.
It is an S transistor.

Reference numerals 1 and 2 denote a first series circuit and a second series circuit, respectively.
Are connected together with the drains of a first MOS transistor Tr1 and a second MOS transistor Tr2, and are connected between a first power supply terminal VDD and a second power supply terminal VSS. ing. In the first series circuit 1 and the second series circuit 2, output terminals O1 and O2 are respectively connected to a connection point between the drains of the first MOS transistor Tr1 and the second MOS transistor Tr2. The first power supply terminal VDD is grounded, and the voltage of each terminal described below is used as a reference. For example, the second power supply terminal VSS is -1.5V.

Reference numeral 3 denotes a motor as a load, and its coil 3L is connected between the output terminal O1 of the first series circuit 1 and the output terminal O2 of the second series circuit 2.

Reference numerals 4 and 5 denote impedance elements. These impedance elements 4 and 5 are connected in series with each other, and are connected between an output terminal O1 of the first series circuit 1 and an output terminal O2 of the second series circuit 2. It is connected in parallel with the coil 3L. The resistance values of these impedance elements 4 and 5 are set equal, and the voltage at the connection point of these impedance elements 4 and 5 is an intermediate voltage between the output terminals O1 and O2.
As shown in FIG. 2A, the PN junction diodes 41 and 42 are arranged in opposite directions and in parallel with each other, and as shown in FIG. 2B, the PN junction diodes 41 and 42 in FIG. Instead, a device using diode-connected MOS transistors 43 and 44 can be used. In addition, a resistor may be used.
In the design of the IC, an optimum one may be used in consideration of the chip size and the current consumption.

Reference numeral 6 denotes a reference voltage source which always generates a constant reference voltage. Here, the details of the reference voltage source 6 are as shown in FIG. 3A. One MOS transistor TR1 forming the current mirror circuit CM1 and a diode-connected MOS transistor TR2 are connected in series, and a reference voltage is connected to this connection point. Is provided, and the other MOS transistor TR3 and the depletion type MOS transistor DT are connected in series. Here, the operation of the reference voltage source 6 will be described. The depletion type MOS transistor DT has a source and a gate connected, and a constant current flows regardless of the drain voltage. This MOS transistor D
The current value flowing through T is mirror-inverted by the current mirror circuit CM1, and a current having the same value flows through the diode-connected MOS transistor TR2, so that a constant reference voltage is output from the output terminal O6.

Reference numeral 7 denotes a comparison circuit. The positive input terminal 71 is connected to the connection point A of the impedance elements 4 and 5, and the negative input terminal 72 is connected to the output of the reference voltage source 6.
It compares the voltage at the connection point A of the impedance elements 4 and 5 with a reference voltage and generates an output according to the difference. Various types of comparison circuits can be used. Here, for example, a circuit as shown in FIG. 3B is used. Describing its configuration and operation, first, the gate of the P-channel MOS transistor TR4 is connected to the constant voltage source E, and the current between the drain and the source is kept constant. The drain of the MOS transistor TR4 has a P-channel type MOS transistor TR5.
And a N-channel MOS transistor TR6 in series, a P-channel MOS transistor TR7 and an N-channel MOS transistor T
A series circuit 74 formed by connecting R8 in series is connected. Here, the gate of the MOS transistor TR5 is used as the negative input terminal 72, a reference voltage is applied, and an output terminal O7 is provided at a connection point with the MOS transistor TR6. The MOS transistor TR6 forms a current mirror circuit CM2 together with the MOS transistor TR8. On the other hand, MOS transistor TR
The gate of 7 is used as a positive input terminal 71, a voltage at a connection point A of the impedance elements 4 and 5 is applied, and a current corresponding thereto flows. Also, the MOS transistor TR7
Of the current flowing through the MOS transistor T
R6, which causes the MOS transistor TR3
Is attracted to each other by the MOS transistor TR5 and the MOS transistor TR6, and the potential of the output terminal O7 rises and falls accordingly. That is,
When the voltage at the connection point A is lower than the reference voltage, the value of the current flowing through the MOS transistor TR6 also increases, and the output voltage of the output terminal O7 is lowered by the power supply terminal VSS. When the voltage of A is higher than the reference voltage, the value of the current flowing through the MOS transistor TR5 decreases, and the output voltage increases due to the drain of the MOS transistor TR5. In this manner, the comparison circuit 7 compares the voltage at the connection point A of the impedance elements 4 and 5 with the reference voltage and generates an output according to the difference.

Reference numeral 8 denotes a drive signal generating circuit which drives a first drive signal for driving the first MOS transistor Tr1 of the first series circuit 1 and a first MOS transistor Tr1 for the second series circuit 2. The second drive signal is alternately generated from output terminals p1 and p2.

Reference numerals 9 and 10 denote a first switching circuit and a second switching circuit, respectively, which are analog switches. These first switching circuit 9 and second switching circuit 9
The switching circuits 10 both receive the output of the comparison circuit 7, and their output terminals are connected to the gates of the second MOS transistors Tr2 of the first series circuit 1 and the second series circuit 2, respectively. The terminals 9c and 10c are connected to the terminals p1 and p2 of the drive signal generation circuit 8, respectively, and are turned on and off according to their outputs.

Tr3 and Tr4 are N-channel MOS transistors as third and fourth switching circuits, respectively. The MOS transistor Tr3 has a source connected to the power supply terminal VSS and a drain connected to the second MO of the first series circuit 1.
Connected to the gate of the S transistor Tr2, and
A first drive signal is applied to the gate via the inverter 11. The MOS transistor Tr4 has a source connected to the power supply terminal VSS, a drain connected to the gate of the second MOS transistor Tr2 of the second series circuit 2, and a gate connected to the second drive transistor via the inverter 12. A signal is applied. Next, the operation of this example will be described with reference to FIGS.
This will be described with reference to the waveform diagram of FIG.

First, when the motor 3 is not driven, the first,
The output terminals p1 and p2 of each of the second drive signals are both "L". Thereby, the first MOS transistor Tr1 of each of the first series circuit 1 and the second series circuit 2 is turned on, the both ends of the coil 3L of the motor 3 are at the same potential, and the motor 3 is not driven. In addition,
At this time, the first switching circuit 9 and the second switching circuit 10 are both turned off, and the third switching circuit Tr3 and the fourth switching circuit Tr4 are both turned on. The gate of each second MOS transistor Tr2 of the second series circuit 2 is connected to the potential of the power supply terminal VSS, and the second MOS transistor Tr2 is turned off.

Next, when driving the motor 3, see FIG.
As shown at 1 and p2, the first drive signal P1 and the second drive signal P2 are output alternately. Here, first, assuming that the first drive signal P1 is output and the output terminal p1 is set to "H", in the first series circuit 1, the first MOS transistor Tr1 is turned off, and the third switching circuit T1 is turned off.
When r3 is turned off, the gate of the second MOS transistor is cut off from the power supply terminal VSS, and when the first switching circuit 9 is turned on, the output voltage of the comparison circuit 7 is reduced to the second MOS transistor Tr2. Is applied to the gates.

Thus, the second MOS transistor T
r2 is turned on, and a drive current flows from the output terminal O2 of the second series circuit 2 to the output terminal O1 of the first series circuit 1.

Although not shown, it is assumed that a battery used as a power supply has just been used and the power supply voltage between the power supply terminals VDD and VSS has a certain value, for example, 1.5 V. At this time, a specific voltage is applied to both ends of the coil 3L, and the voltage at the connection point A of the impedance elements 4 and 5 takes a certain value, which is set by the comparison circuit 7. The comparison circuit 7 compares the voltage at the connection point A of the impedance elements 4 and 5, that is, 電 圧 of the voltage applied to the coil 3 L, with the reference voltage generated by the reference voltage source 6, and responds to the difference. Output voltage is being generated. Here, when the reference voltage generated by the reference voltage source 6 is V 1, which is the optimum voltage for driving the motor 3, the value of the power supply terminal V 1/2 is 1/2 of the value V 1/2.
The power supply terminal VDD is grounded, and the voltage at the connection point A is based on the power supply terminal VDD. At this time, the voltage output from the comparison circuit 7 has a certain value. With this voltage, the on-resistance of the second MOS transistor Tr2 of the first series circuit 1 is set to a certain value, so that the voltage at the connection point A is set to V1 / 2, and V1 is set across the coil 3L. Applied.

Here, the voltage of the battery drops, and the power supply terminal V
When the power supply voltage between DD and VSS decreases to, for example, 1.4 V, the voltage at the connection point A tends to increase. However, since the comparison circuit 7 operates to increase the output voltage as described above, M
The on-resistance of the OS transistor decreases, and the output terminal O1
Is pulled to the power supply terminal VSS side, and the voltage at the connection point A is V1 / 2.
Only the power supply terminal VDD is set to a lower value. As a result, the voltage applied to both ends of the coil 3L is maintained at V1.

Here, the on-resistance of the first MOS transistor Tr1 is set to a value that is negligibly lower than the resistance values of the impedance elements 4 and 5.

Also, when the second drive signal P2 is output and the output terminal p2 is set to "H", as in the case of the first series circuit 1, the second series circuit 2 Second
MOS transistor Tr2 is turned off, and the fourth switching circuit Tr4 is turned off.
The gate of the OS transistor is cut off from the power supply terminal VSS. At the same time, when the second switching circuit 10 is turned on, the output voltage of the comparison circuit 7 is applied to the gate of the second MOS transistor Tr2 of the second series circuit 2, and the second series circuit 2 2 MOS transistor Tr2 is turned on, and the output terminal O1 of the first series circuit 1 is turned on.
, A drive current flows to the output terminal O2 of the second series circuit 2. Also at this time, the drive voltage of the motor 3 is maintained at the desired value V1 by the operation of the comparison circuit 7.

That is, as shown in FIGS.
When the first drive signal P1 and the second drive signal P2 are alternately output, a drive voltage held at a desired value V1 is supplied to the motor 3 as shown in O1-O2 in FIG. In addition,
4O1-O2, the potential of the output terminal O1 of the first series circuit 1 is shown with reference to the potential of the output terminal O2 of the second series circuit 2 for convenience.

As described above, the comparison circuit 7 includes the motor 3
And the series connected impedance elements 4 and 5 are connected in parallel to the coil 3L, and the voltage at the connection point A is set to a voltage lower than the first power supply terminal VDD by half the drive voltage. For comparison with the reference voltage, the power supply voltage
Even if the voltage drops to about the optimum value V1 for the drive of the motor 3, the comparison circuit 7 always operates at the reference voltage without greatly affecting the reference voltage itself, and the drive voltage of the motor 3 becomes the desired value V1.
Can be held.

Further, since a constant driving voltage is always obtained, it is possible to suppress current consumption. Needless to say, since the impedance elements 4 and 5 connected in series are connected in parallel with the coil 3L of the motor 3, the current consumption by the impedance elements 4 and 5 is suppressed.

Further, since the midpoint voltage of the drive voltage of the motor 3 is compared with the reference voltage, only one comparison circuit 7 is required, and the increase in chip size and current consumption due to the provision of the comparison circuit can be minimized. It is possible.

[0028]

According to the present invention, a pair of identical units connected in series are provided.
Bidirectional alternating impedance elements with impedance value
Connected in parallel to the load to which the drive voltage is applied
The voltage at the connection point between the dance elements is compared with a reference voltage, and the drive voltage of the load is controlled accordingly. For this reason, the voltage at the connection point becomes the midpoint voltage of the drive voltage of the load.
Use a reference voltage that is not affected by power supply voltage fluctuations.
Therefore , a desired drive voltage can be always obtained irrespective of fluctuations in the power supply voltage, and the influence of a decrease in the power supply voltage, which is a problem when using a battery as a power supply, can be suppressed. Further, since the drive voltage is controlled, when the power supply voltage is high, unnecessary power consumption is suppressed, and the power consumption is reduced.

Moreover, the voltage at the connection point is equal to the drive voltage of the load.
Since the voltage becomes the midpoint voltage, one comparison circuit
Comparison operation is possible for drive voltage, and comparison by direction
There is no need to provide a circuit.
Minimizing increases in chip size and current consumption
Is also possible.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing a configuration of one embodiment of the present invention.

FIG. 2 is an electric circuit diagram showing a configuration of a main part of FIG.

FIG. 3 is an electric circuit diagram showing a configuration of a main part of FIG. 1;

FIG. 4 is a waveform chart for explaining the operation of FIG. 1;

FIG. 5 is an electric circuit diagram showing a conventional example.

FIG. 6 is a waveform chart for explaining the operation of FIG. 6;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st series circuit 2 2nd series circuit Tr1 1st MOS transistor Tr2 2nd MOS transistor 3 Motor (load) 4, 5 Impedance element 7 Comparison circuit 8 Drive signal generation circuit 9 1st switching circuit 10th Switching circuit 2 Tr3 Third switching circuit Tr4 Fourth switching circuit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁶ , DB name) H02P 8/00-8/38

Claims (2)

(57) [Claims] A first MOS transistor having a first conductivity type and a second conductivity type connected to each other;
Is connected between a first power supply terminal and a second power supply terminal having a different potential from the first power supply terminal, and a second series circuit having the same configuration as the first series circuit is connected to the first power supply terminal. Power terminal and second
And a load connected between the drain connection point of the first series circuit and the drain connection point of the second series circuit, and a pair of impedance connected in series and having the same impedance value. A first series circuit, wherein a comparison element is connected in parallel to the load, compares the voltage at the connection point of each impedance element with a reference voltage, and generates an output according to the difference. a first MOS transistor off and be <br/> Ru first drive signal and second drive signal and generating alternately a driving signal generation for the first MOS transistor off in the second series circuit A circuit, a first switching circuit that is turned on by a first driving signal, and supplies an output of the comparison circuit to a gate of a second MOS transistor of the first series circuit; and a second switching signal, which is turned on by a second driving signal. The above comparison circuit And a second switching circuit for supplying an output to the gate of the second MOS transistor of the second series circuit, the load
A drive circuit for a load , wherein a drive voltage is applied alternately and bidirectionally . 2. A period in which the first drive signal is not generated, a third switching circuit connecting the gate of the second MOS transistor of the first series circuit to a specific potential, and a period in which the second drive signal is not generated. , The second M of the second series circuit
2. The load driving circuit according to claim 1, further comprising: a fourth switching circuit that connects a gate of the OS transistor to a specific potential.