JPH06175701A - Inductive load driving circuit - Google Patents

Abstract

PURPOSE:To provide an inductive load driving circuit which can quickly return an object to be driven by the inductive load by attenuating at a high speed the current flowing to the inductive load. CONSTITUTION:One of both ends of a solenoid 1 is connected to a power supply via a PNP transistor TR 1 and also grounded via a diode 2 set in the opposite direction. Meanwhile, the other end of the solenoid 1 is grounded via an NPN TR 2 and also connected to the power supply via a diode 1 set in the opposite direction. When a drive pulse having its modulated width is supplied, the TR 2 is turned on by a switch means. This means turns on the TR 1 when the drive pulses are continuously supplied at a interval smaller than the prescribed hour.

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 keyboard drive solenoid of an automatic piano.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing an example of the structure of a drive circuit of this type called a voltage control type drive circuit. In FIG. 4, 1 is a solenoid as an inductive load. One end of the solenoid 1 is connected to the collector of the NPN transistor TR4, and the other end is applied with the power supply voltage VO. A diode D3 is connected in parallel with the solenoid 1. This diode D3 is NP
This is provided in order to loop the current flowing in the solenoid 1 up to that time as a kickback current when the N transistor TR4 is switched from the ON state to the OFF state. The emitter of the NPN transistor TR4 is grounded, and the drive signal PWM is input to the base. This drive signal PWM is pulse width modulated by a pulse width modulation circuit (not shown) to a duty ratio corresponding to the target value of the current to be passed through the solenoid 1.

According to such a configuration, the drive signal PWM is N
By outputting to PN transistor TR4, NP
The ON / OFF switching of the N-transistor TR4 is repeated. While the NPN transistor TR4 is in the ON state, the NPN transistor TR4 is not supplied to the solenoid 1.
A voltage substantially equal to the power supply voltage V0 is applied via the.
Therefore, the current I1 flowing in the solenoid 1 increases according to the time constant determined by the inductance L.
Further, during this period, the current I1 flowing through the solenoid 1 passes through the NPN transistor TR4 as the current I2. Then, when the NPN transistor TR4 is switched to the OFF state, the current I1 which has been flowing in the solenoid 1 until then.
Is discharged as a current I3 through the diode D3, and the current I3
3 gradually decreases according to the time constant determined by the inductance L. In this way, an average current according to the duty ratio of the drive signal PWM flows through the solenoid 1,
As a result, the driven body (not shown) is driven by the magnetic field generated by the solenoid 1.

[0004]

By the way, as described above, in the conventional voltage control type drive circuit, since the diode D3 is connected in parallel to the solenoid 1, the drive signal PWM is generated.
Energy is efficiently transferred into the solenoid 1.
However, even if the supply of the drive signal PWM is stopped and the NPN transistor TR4 is turned off, the kickback current continues to flow in the solenoid 1 for a while, and the decay speed of the kickback current is slow, so that the driven body is not driven. There was a problem that the return was slow.

The present invention has been made under such a background and is capable of efficiently transmitting energy to an inductive load and at the same time by attenuating a current flowing through the inductive load at a high speed. It is an object of the present invention to provide a drive circuit for an inductive load that can quickly return a driven body driven by.

[0006]

A drive circuit for an inductive load according to the present invention comprises a first switch means inserted between one end of the inductive load and a power source, the other end of the inductive load and a ground wire. The second switch means interposed therebetween, the first diode for passing a current flowing from the other end of the inductive load to the power source, and the current flowing from the ground line to one end of the inductive load A second diode to be passed and a pulse-width-modulated drive pulse are input, and one of the first and second switch means is rendered conductive in accordance with the drive pulse, and the drive pulse is provided at intervals of a predetermined time or less. Only when it is continuously input, the first or second
Switch switching means for bringing the other of the switch means of (1) into a conductive state.

[0007]

The switch switching means brings the second switch means into the conducting state in accordance with the drive pulse and brings the first switch means into the conducting state only when the drive pulse is continuously input at intervals of a predetermined time or less. The operation of the present invention will be described below. According to the above configuration, when the drive pulse is turned on during the period in which the drive pulse is continuously input at the interval of the predetermined time or less, the first and second switch means are brought into the conductive state, and the power source → the first switch A current flows through a route of means → inductive load → second switch means → ground. When the drive pulse is turned off during this period, the second switch means is turned off, and a current flows through the path of power supply → first switch means → inductive load → first diode → power supply. When this drive pulse is not continuously input at an interval of a predetermined time or less, the first switch means is turned off, and as a result,
A current flows through a path of ground → second diode → inductive load → first diode → power supply. Since this current flows in the direction opposite to the direction from the power source to the ground, it is rapidly attenuated and the current value becomes zero.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing the configuration of a drive circuit for an inductive load according to an embodiment of the present invention. In this figure, the pulse-width-modulated drive signal PWM is supplied to the base of the NPN transistor TR2 via the resistor R9, and is also input to the low-pass filter LPF composed of the resistor R1 and the capacitor C1. The output signal of the low-pass filter LPF obtained from the resistor R1 and the capacitor C1 is input to the non-inverting input terminal of the comparator 2. Further, resistors R2 and R3 are inserted between the power source of the power source voltage V1 and the ground, and the voltage at the connection point of the resistors R2 and R3 is input to the inverting input terminal of the comparator 2 as a threshold level. There is. When the input signal from the low pass filter LPF exceeds this threshold level, the output signal of the comparator 2 becomes high level. The low-pass filter LPF and the comparator 2 determine whether or not the drive signal PWM is continuously input at intervals of a predetermined time or less, and when the drive signal PWM is continuously input at intervals of the predetermined time or less, the comparator 2 The output signal goes high. And the comparator 2
Output signal of NPN transistor T via resistor R5.
Supplied to the base of R3. A resistor R4 is inserted between the output terminal of the comparator 2 and the power supply terminal (power supply voltage V1).

On the other hand, one end of the solenoid 1 is connected to the collector of the PNP transistor TR1 and the other end is N.
It is connected to the collector of the PN transistor TR2.
Here, the power supply voltage V0 is applied to the emitter of the PNP transistor TR1, the emitter of the NPN transistor TR2 is grounded, and the power supply → PNP transistor TR1.
→ Solen 1 → NPN transistor TR 2 → Current flows through the route of ground. Further, one end of the solenoid 1 is also connected to the cathode of the diode D2, and the other end is also connected to the anode of the diode D1. The anode of the diode D2 is grounded, and the cathode of the diode D1 is connected to the power supply terminal (power supply voltage V0). Therefore, the diode D2 →
A regenerative current flows through the path of solenoid 1 → diode D1 → power supply. Further, a resistor R6 and a resistor R7 are interposed between the power supply terminal (power supply voltage V0) and the collector of the NPN transistor TR3, and NP
The emitter of the N-transistor TR3 is grounded. When the voltage at the connection point between the resistors R6 and R7 is applied to the base of the PNP transistor TR1 via the resistor R8 and the NPN transistor TR3 is turned on, P
The NP transistor TR1 is turned on.

According to such a configuration, the drive signal PWM
Is converted into a DC waveform by the low-pass filter LPF and input to the non-inverting input terminal of the comparator 2. Here, the duty ratio of the drive signal PWM exceeds a certain value (for example, a low value of about 3%), and the drive signal PW
While M is continuously input, the input signal to the comparator 2 exceeds a certain threshold and the output signal of the comparator 2 becomes high level. As a result, the NPN transistor TR3 and PNP transistor TR1 are turned on. During this period, when the drive signal PWM is at high level, the drive signal PWM passes through the resistor R9 and the NPN transistor T.
Applied to the base of R2, NPN transistor TR2 is turned on
State, and as a result, power supply → PNP transistor TR
A current I2 flows through a route of 1 → solenoid 1 → NPN transistor TR2 → ground. When the drive signal PWM goes low, the NPN transistor TR2 turns off.
Then, the kickback current I1 flows through the route of power source → PNP transistor TR1 → solenoid 1 → diode D1.

On the other hand, when the supply of the drive signal PWM is interrupted, the output signal of the comparator 2 becomes low level. In this case, the NPN transistor TR3 and PNP transistor TR1 are turned off. As a result, the current flowing through the solenoid 1 up to that point is the diode D2 →
It is returned to the power source as a regenerative current I3 via the path of solenoid 1 → diode D1.

This operation will be described below with reference to FIGS. 2 and 3.
Will be described in detail. First, assuming that the PNP transistor TR1 is turned off at a certain time t = 0 as shown in FIG. 3, at that moment, as shown in FIG. 2 (a), a current -V0 flowing from the ground side to the power source side. / RL (However,
RL causes the internal resistance of the solenoid 1) to flow to the solenoid 1.

Then, as indicated by the thick solid line C in FIG. 3, the current flowing through the solenoid 1 increases in accordance with the exponential curve of the time constant τ = L / RL, and the state of the drive circuit is as shown in FIG.
The stable state shown in (b), that is, the state in which the current V0 / RL flows from the power supply side to the ground side gradually shifts.

However, since the diodes D1 and D2 are interposed, the current flowing through the solenoid 1 is not positive,
The transient state ends when the current becomes zero. Here, the time from when the PNP transistor TR1 is turned off until the current flowing in the solenoid 1 becomes 0 is about 0.693τ, and the current of the solenoid 1 is cut off in an extremely short time.

A curve D in FIG. 3 shows a change in current flowing through the solenoid 1 in the case of the conventional voltage control type drive circuit for comparison. In this case, the current flowing through the solenoid 1 exponentially decreases toward the current value 0, and therefore does not become 0 completely even after the infinite time has elapsed. Further, in this embodiment, as described above, P
About 0.6 from the cutoff time t = 0 of the NP transistor TR1
After 93 τ seconds have passed, the current of the solenoid 1 is cut off. On the other hand, in the conventional voltage control type drive circuit, the current 0.37V0 / RL still flows through the solenoid 1 even at the time t = τ after the time t = 0.693τ.

[0016]

As described above, according to the present invention, the first switch means inserted between one end of the inductive load and the power source, and the other end of the inductive load and the ground line. Inserted second switch means, a first diode for passing a current from the other end of the inductive load to the power supply, and a first diode for passing a current from the ground wire to one end of the inductive load. The second diode and the pulse-width-modulated drive pulse are input, one of the first and second switch means is turned on in accordance with the drive pulse, and the drive pulse continues at intervals of a predetermined time or less. Since the switch switching means that brings the other of the first and second switch means into the conductive state only when being input is provided, the current flowing in the inductive load is attenuated at a high speed to thereby reduce the inductive load. Therefore there is an advantage that the return of the driven body to be driven can be performed quickly.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing an equivalent circuit in a process of shutting off a current of a solenoid 1 in the embodiment.

FIG. 3 is a waveform diagram showing a process in which the current of the solenoid 1 is cut off in the embodiment.

FIG. 4 is a circuit diagram showing a configuration of a conventional voltage control type drive circuit.

[Explanation of symbols]

1 ... Solenoid, D1, D2 ... Diode, TR1 ...
… PNP transistor, TR2, TR3 …… NPN transistor, 2 …… Comparator

Claims (1)

[Claims] 1. A first switch means interposed between one end of an inductive load and a power source, and a second switch means interposed between the other end of the inductive load and a ground wire.
Switch means, a first diode for passing a current from the other end of the inductive load to the power supply, a second diode for passing a current from the ground wire to one end of the inductive load, When a pulse-width-modulated drive pulse is input, one of the first and second switch means is turned on in accordance with the drive pulse, and the drive pulse is continuously input at intervals of a predetermined time or less. A drive circuit for an inductive load, further comprising: a switch switching means for bringing the other of the first and second switch means into a conductive state.