JP3198624B2 - Drive circuit for inductive load - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for an inductive load, and more particularly to a drive circuit suitable for driving a solenoid for driving a key of an automatic piano.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing a configuration of a conventional inductive load driving circuit. In FIG. 4, reference numeral 1 denotes a solenoid as an inductive load. One end of the solenoid 1 is connected to the collector of the NPN transistor 2, and the other end is supplied with the power supply voltage V. A diode 3 is connected to the solenoid 1 in parallel. This diode 3
Is provided to maintain the current flowing through the solenoid 2 up to that point as the kickback current when the NPN transistor 2 is switched from the ON state to the OFF state. The NPN transistor 2 has an emitter grounded, and has a base to which a drive pulse PWM is input via a resistor 4. The drive pulse PWM is pulse-width modulated by a pulse width modulation circuit (not shown) to a duty ratio corresponding to a target value of a current to flow through the solenoid 1.

According to such a configuration, an average current according to the duty ratio of the drive pulse PWM flows through the solenoid 1,
A driven body (not shown) is driven by a magnetic field generated by the solenoid 1 in association with this. FIG. 5 shows a relationship between a target current value (duty ratio) and an average current (relative current) actually flowing through the solenoid 1 in this drive circuit. This figure shows the relationship between the maximum value of the current target value and the maximum value of the current flowing through the solenoid 1 each of which is 100%. As shown in this figure, the current flowing through the solenoid 1 is directly proportional to the current target value.

[0004]

In the conventional driving circuit described above, even when the supply of the driving pulse PWM is stopped to cancel the driving of the driven portion, the kickback current still flows through the solenoid 1. . FIG. 6 shows a temporal change of the current i of the solenoid 1 when the NPN transistor 2 is cut off in the configuration shown in FIG. As shown in this figure, the current i is NPN
After the transistor 2 is turned off, it gradually decreases according to the exponential curve of the time constant τ. Here, the time constant τ is the solenoid 1
Is determined by the ratio of the inductance and the resistance of
As described above, in the conventional drive circuit, since the current continues to flow through the solenoid 1 even though the drive pulse is stopped, there is a problem that the operation of the driven portion to return to the state before the drive is slow. .

The present invention has been made in view of the above-mentioned circumstances, and provides a drive circuit for an inductive load capable of quickly releasing a kickback current of the inductive load when a drive pulse stops. With the goal.

[0006]

According to the present invention, there is provided first switch means interposed between one end of an inductive load to be driven and a ground line, and turned on by a pulse width modulated drive pulse; A first diode for passing a current from one end of the inductive load to a power supply, a second diode for passing a current from the ground line to the other end of the inductive load, and a driving pulse for a predetermined time. The state detecting means for detecting that the driving pulse is not supplied is interposed between the other end of the inductive load and the power supply, and the state detecting means detects that the driving pulse is not supplied for a predetermined time or more. and a second switching means which is turned OFF when the predetermined time, the drive pulse period
Longer .

[0007]

According to the above arrangement, a control pulse is generated during the period in which the drive pulse is being input, and the control pulse turns on the second switch means. Then, the first switch means is turned on by the drive pulse,
A current flows through a path of power supply → second switch means → inductive load → first switch means → ground. Also, during this time, when the first switch means is turned off by the drive pulse, the current flowing to the inductive load at that time is constituted by the first diode, the second switch means, and the inductive load. Decays slowly while circulating in a closed loop. When the supply of the drive pulse is stopped, the control pulse is not output, and both the first and second switch units are turned off. As a result, ground → second diode → inductive load → first diode →
Current flows through a path called a power supply. Since this current flows in the direction opposite to the direction from the power supply to the ground, it rapidly attenuates and the current value becomes zero.

[0008]

An embodiment of the present invention will be described below with reference to the drawings. <First Embodiment> FIG. 1 is a circuit diagram showing a configuration of a drive circuit for an inductive load according to a second embodiment of the present invention. In this drive circuit, one end of the solenoid 1 is connected to the collector of the NPN transistor 2, and the other end is connected to the collector of the PNP transistor 13. The power supply voltage V is applied to the emitter of the PNP transistor 13 and the collector is grounded via the diode 14 in the reverse direction.
Further, between the power supply and the ground, resistors 15 and 16
An NPN transistor 17 is interposed in series, and a voltage at a connection point between the resistors 15 and 16 is set to the PNP transistor 1.
3 is applied to the base. The retriggerable monostable multivibrator 20 is driven by the drive pulse PWM and outputs a control pulse OUT. Here, the pulse width of the control pulse OUT has a constant value longer than the cycle of the drive pulse PWM. Accordingly, the retriggerable operation is performed by the monostable multivibrator 20 during a period in which the drive pulse PWM is continuously supplied at regular intervals. Therefore, the control pulse OUT is output as a temporally continuous high-level signal. FIG. 2 shows this state. This control pulse OUT is NP via the resistor 18
It is supplied to the base of the N transistor 17.

With this configuration, during the period in which the drive pulse PWM is supplied, the control pulse OUT is generated, so that both the NPN transistor 17 and the PNP transistor 13 are turned on. When the level of the drive pulse PWM becomes high, the NPN transistor 2 is turned on, and the current i flows through a path of power supply → PNP transistor 13 → solenoid 1 → NPN transistor 2 → ground. Next, when the drive pulse PWM goes low, the NPN transistor 2 is turned off. As a result, the current i flowing through the solenoid 1 at that time gradually attenuates while circulating through the closed loop including the diode 3, the PNP transistor 13 and the solenoid 1. The above operation is performed during a period in which the drive pulse PWM is continuously supplied, and a temporally pulsating current i flows through the solenoid 1 as shown in FIG. Further, the average value of the current i is proportional to the pulse width of the drive pulse PWM.

When the supply of the driving pulse PWM is interrupted, the NPN transistor 2 is turned off. Further, as shown in FIG. 2, at a time delayed by the pulse width of the control pulse OUT from the time when the driving pulse PWM is finally supplied , the output of the monostable multivibrator 20 is used.
Since a certain control pulse OUT falls, the NPN transistor 17 and the PNP transistor 13 are turned off. That is, the drive pulse is set for a predetermined time (control pulse
OUT pulse width)
NPN detected by monostable multivibrator 20
Transistor 17 and PNP transistor 13 are OF
The state becomes the F state. Thus, a monostable multivibrator
20 indicates that the drive pulse has not been supplied for a predetermined time or more.
Function as state detecting means for detecting the state. Note that FIG.
Has a drive pulse period of 62.5 μS and a control pulse OU
Control pulse OU when pulse width of T is 100 μS
The waveform of T is illustrated. Thus, the PNP transistor 13 and the NPN transistor 2 are both turned off.
When the state is reached, the current i that has been flowing through the solenoid 1 up to that point is: diode 14 → solenoid 1 → diode 3
Is returned to the power supply via the path. The current i increases according to the exponential curve, and the drive circuit gradually shifts to a stable state, that is, a state where the current i flows from the power supply side to the ground side. However, diodes 3 and 1
4, the transient state ends when the current becomes zero. As described above, when both the PNP transistor 13 and the NPN transistor 2 are turned off,
Since the voltage between the power supply and the ground is applied in a direction opposite to the direction of the current i flowing through the solenoid 1, the current of the solenoid 1 is cut off in a very short time.

<Second Embodiment> Next, a second embodiment of the present invention will be described. In this embodiment, the circuit shown in FIG. 3 is used in place of the monostable multivibrator 20.
This circuit is a combination of a down counter and an AND gate. In the down counter, a predetermined count value, for example, 100 is set by the rise of the drive pulse PWM. After that, the down counter
The countdown is performed according to the clock pulse output from the ND gate, and a high-level signal is output until the count value becomes zero. This output signal is used as the control pulse OUT. The AND gate is provided with a control pulse OUT and a clock CL supplied at predetermined intervals.
The logical product with K is supplied to the down counter as the clock pulse. Of course, the period of the clock CLK (for example, 1
MHz) is shorter than the period of the drive pulse PWM. In the case of the first embodiment, a time constant circuit for determining the pulse width of the control pulse OUT output from the monostable multivibrator is required. However, in this embodiment, such a time constant circuit is unnecessary. Further, since the time constant circuit is not used, there is no variation in the pulse width of the control pulse OUT due to the time constant, and a stable operation can be obtained.

[0012]

As described above, according to the present invention, the first state which is interposed between one end of the inductive load to be driven and the ground line and turned on by the pulse width modulated drive pulse is provided. Switch means; a first diode for passing a current from one end of the inductive load to a power supply;
A second diode for passing a current flowing from the ground line to the other end of the inductive load, state detecting means for detecting that the drive pulse has not been supplied for a predetermined time or more, and interposed between the end and the power supply, provided a second switch means for the driving pulse is set to OFF state when it is detected that is not supplied for a predetermined time or more by the state detecting means, the predetermined time ,Previous
Since the drive pulse period is longer than the above-described drive pulse period, the kickback current of the inductive load can be quickly released when the drive pulse stops.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a drive circuit for an inductive load according to a first embodiment of the present invention.

FIG. 2 is a waveform chart for explaining the operation of the embodiment.

FIG. 3 is a circuit diagram illustrating a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing a configuration of a conventional driving circuit.

FIG. 5 is a diagram showing a relationship between a target value of a current to flow through the solenoid 1 and a current value actually flowing through the solenoid 1 in the same drive circuit.

FIG. 6 is a waveform diagram showing a temporal change of a current at the time of interruption in the same drive circuit.

[Explanation of symbols]

20 monostable multivibrator, 1 solenoid, 2,17 NPN transistor, 13 PNP transistor, 3,14 diode.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-224597 (JP, A) JP-A-58-97817 (JP, A) JP-A-62-7400 (JP, A) 7142 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G05B 11/28 G05B 11/36 507 G10F 1/02 H02P 8/00 H02M 7/42-7/98 H02P 6 / 00-6/02 H02K 41/00-41/06 H01F 7/18

Claims (1)

(57) [Claims] 1. A first switch means interposed between one end of an inductive load to be driven and a ground line, and turned on by a pulse width-modulated drive pulse, and a power supply from one end of the inductive load. A first diode for passing a current flowing to the other end of the inductive load from the ground line; and a second diode for passing a current flowing to the other end of the inductive load, and detecting that the driving pulse is not supplied for a predetermined time or more. a state detection unit that, the interposed inductive load at the other end and the power supply between, the said drive pulse by said state detecting means is an OFF state when it is detected that is not supplied for a predetermined time or more 2. The inductive load driving circuit according to claim 1, wherein the predetermined time is longer than the driving pulse period .