JPH064105A - Driving circuit for inductive load - Google Patents

Abstract

PURPOSE:To provide the driving circuit for the inductive load which is simple in constitution and exactly and speedily responds to a current command. CONSTITUTION:One end of a solenoid 1 is grounded through an NPN transistor(TR) 2 and also connected to a power source reversely through a diode 3 and the other end of the solenoid 1 is connected to the power source through a PNP TR 13 and also grounded reversely through a diode 14. Further, this circuit is provided with a comparator 20 which compares the value of the current flowing to the solenoid 1 with the command and a flip-flop 21 which is reset when the comparator 20 detects the current which flows to the solenoid 1 reaches the command, and the ON/OFF states of the NPN TR 2 and PNP TR 13 are switched with the output signal of the flip-flop 21.

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 an inductive load, and more particularly to a driving circuit suitable for driving a hammer driving solenoid of an automatic piano.

[0002]

2. Description of the Related Art FIG. 6 is a circuit diagram showing the structure of a drive circuit of this type, which is called a voltage control type drive circuit. In FIG. 6, 1 is a solenoid as an inductive load. One end of the solenoid 1 is connected to the collector of the NPN transistor 2, and the power supply voltage V is applied to the other end. A diode 3 is connected in parallel with the solenoid 1. The diode 3 is provided to loop the current flowing through the solenoid 2 up to that time as a kickback current when the NPN transistor 2 is switched from the ON state to the OFF state. The emitter of the NPN transistor 2 is grounded, and the drive signal PWM is input to the base via the resistor 4. 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 this structure, an average current according to the duty ratio of the drive signal PWM flows through the solenoid 1, and the magnetic field generated by the solenoid 1 drives the driven body (not shown).

FIG. 7 is a circuit diagram showing a structure of a conventional drive circuit called a current feedback drive circuit. In this current feedback drive circuit, a detection resistor 5 for detecting a current flowing through the solenoid 1 is interposed between the emitter of the NPN transistor 2 and the ground.
The connection point between the detection resistor 5 and the emitter of the NPN transistor 2 is grounded via the feedback resistor 6 and the capacitor 7 in series. Then, these feedback resistor 6 and capacitance 7
The voltage at the connection point is fed back to the non-inverting input terminal of the comparator 8. Here, the non-inverting input terminal of the comparator 8 is grounded via the resistor 10. On the other hand, at the inverting input terminal of the comparator 8,
An energization amount designation signal M corresponding to the target value of the current to be passed through the solenoid 1 is input via the resistor 9. Also, the comparator 8
A feedback resistor 11 is inserted between the output end of the above and the inverting input end. A triangular wave signal A output from a triangular wave generating circuit (not shown) is input to the non-inverting input terminal of the comparator 12.
The output signal of the comparator 8 is input to the inverting input terminal of the comparator 12 as a threshold value for determining the level of the triangular wave signal A. The output signal of the comparator 12 is supplied to the base of the NPN transistor 2 via the resistor 4.

With such a configuration, the comparator 12 functions as a pulse width modulation circuit and outputs a drive signal (pulse width modulation signal) having a duty ratio according to the output signal level of the comparator 8. This drive signal is sent to the NPN via the resistor 4.
It is supplied to the base of the transistor 2. As a result, a current flows through the solenoid 1 and a voltage corresponding to this current is generated across the detection resistor 5. A voltage obtained by smoothing the voltage across the detection resistor 5 is fed back to the non-inverting input terminal of the comparator 8. Here, when the voltage fed back to the non-inverting input terminal of the comparator 8 is higher than the level of the energization amount designating signal M input to the inverting input terminal, the level of the output signal of the comparator 8 rises.
As a result, the duty ratio of the drive signal output by the comparator 12 decreases, and the current flowing through the solenoid 1 decreases. Conversely, when the feedback voltage to the non-inverting input terminal of the comparator 8 is lower than the level of the energization amount designating signal M, the level of the output signal of the comparator 8 decreases and the drive signal output by the comparator 12 The duty ratio of is increased. As a result, the current flowing through the solenoid 1 increases. As a result of such negative feedback control being performed, a current corresponding to the energization amount designation signal M is passed through the solenoid 1.

FIG. 8 is a circuit diagram showing a configuration of a current feedback type drive circuit using a conventional full bridge circuit. In the current feedback drive circuit shown in FIG. 7 described above, the solenoid 1
One end of is connected to the collector of NPN transistor 2,
In addition, the power supply voltage V is directly applied to the other end. However, in the drive circuit shown in FIG. 8, the other end of the solenoid 1 is connected to the collector of the PNP transistor 13. In the PNP transistor 13, the power supply voltage V is applied to the emitter and the collector is the diode 1
4 is grounded in the opposite direction. Further, resistors 15 and 16 and an NPN transistor 17 are inserted in series between the power supply and ground, and the voltage at the connection point of the resistors 15 and 16 is applied to the base of the PNP transistor 13. In addition, at the base of the NPN transistor 17,
The pulse-width-modulated drive signal output from the comparator 12 is applied via the resistor 18. The other configurations are similar to those of the current feedback type drive circuit shown in FIG.

According to this structure, both the NPN transistors 2 and 17 and the PNP transistor 13 are in the ON state while the level of the drive signal output from the comparator 12 is high. Therefore, during this period, one end of the solenoid 1 is grounded through the NPN transistor 2 and the other end is P
It is connected to the power supply through the NP transistor 13. As a result, power source → PNP transistor 13 → solenoid 1 →
A current flows through a path of NPN transistor 2 → detection resistor 5 → ground. Then, when the level of the drive signal output from the comparator 12 becomes low level, the NPN transistor 17, the PNP transistor 13, and the NPN transistor 2 are all turned off, and the current flowing in the solenoid 1 up to that point is It is returned to the power supply through a path formed between the power supply and the ground, that is, diode 14 → solenoid 1 → diode 3.

[0008]

The voltage control type drive circuit described above has a problem that the response to the drive signal is slow. On the other hand, according to the current feedback type drive circuit shown in FIGS. 7 and 8, the above-described negative feedback control is performed, so that the current flowing through the solenoid 1 can quickly reach the target value. However, in the case of the current feedback type drive circuit, there is a problem that the responsiveness is not good when the NPN transistor 2 is in the OFF state. That is, in the current feedback drive circuit, the NPN transistor 2 is OF
When in the F state, as shown in FIG.
A loop circuit is formed by short-circuiting both ends of the diode 3 by a diode 3 (not shown in FIG. 9). The current flowing through the solenoid 1 until then circulates in the loop circuit (hereinafter, this current is referred to as a loop current) and is gradually attenuated. In this case, the decay rate of the current circulating in the loop circuit is determined by the inductance L of the solenoid 1.
And the internal resistance R _L. In the case of the current feedback type drive circuit shown in FIG. 7, this attenuation speed is slow and it has not sufficiently met the demand for high responsiveness. This problem also applies to the voltage-controlled drive circuit.

According to the drive circuit shown in FIG. 8, when the NPN transistor 2 is turned off, the solenoid 1
Since a voltage having a polarity opposite to that applied before is applied to the solenoid, the current flowing in the Solenoid 1 is suddenly reduced to 0.
Can be However, this drive circuit
As shown in FIG. 8, there is a drawback that the number of parts is large and the configuration is complicated. Further, in both of the current feedback type drive circuits shown in FIGS. 7 and 8, the voltage across the detection resistor 5 is fed back to make the average value of the current flowing through the solenoid 1 match the target value. . However, the loop current flowing through the solenoid 1 does not flow through the detection resistor 5 when the NPN transistor 2 is in the OFF state.
As described above, in the case of the current feedback type drive circuits shown in FIGS. 7 and 8, only the current subtracted from the loop current out of the total current flowing through the solenoid 1 is fed back, so that accurate current feedback control is not performed. There was a problem. FIG. 11 shows the relationship between the current target value and the average current actually flowing in the solenoid 1 in the Stanchi drive circuit and the current feedback drive circuit. In the figure, the maximum value of the current target value and the maximum value of the current flowing through the solenoid 1 are each set to 100%, and the relationship between the two is shown. As shown in this figure, the current flowing through the solenoid 1 is not directly proportional to the current target value, but is proportional to the target power 1/2. Further, both the current feedback type drive circuits shown in FIGS. 7 and 8 have a problem that a triangular wave generation circuit is required.

The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to provide a drive circuit for an inductive load, which has a simple structure and responds accurately and at high speed to a target current value.

[0011]

According to the present invention, there is provided current detecting means for detecting a current flowing through an inductive load, first switch means interposed between one end of the inductive load and a ground wire, and Second switch means inserted between the other end of the inductive load and the power supply, a first diode for passing a current from one end of the inductive load to the power supply, and the inductive load from the ground line. A second diode that allows a current to flow to the other end of the first diode and the first diode at the predetermined cycle interval.
And a control means for turning on the second switch means and turning off the first and second switch means when the current value matches the target value.

[0012]

According to the above construction, the first and second switch means are turned on every predetermined period, and the route of power supply → second switch means → inductive load → first switch means → ground is established. An electric current flows. When this current matches the target value, the first and second switch means are turned off.
As a result, ground → second diode → inductive load → first
The current flows through the path of the 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.

[0013]

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. This drive circuit
A comparator 20 and an SR flip-flop 21 are added to the configuration shown in FIG. 8, and comparators 8 and 12, resistors 6, 8 to 11 and a capacitor 7 are deleted. Other configurations are similar to those of the drive circuit shown in FIG. 8 described above. However, this drive circuit does not require a triangular wave generation circuit unlike the current feedback drive circuit shown in FIGS. 7 and 8. In the comparator 20, the energization amount designation signal M is input to the inverting input terminal, and the voltage at the non-grounded end of the detection resistor 5 is input to the non-inverting input terminal. The SR flip-flop 21 is set by the drive pulse P generated every predetermined period, and the comparator 2
It is reset when the output signal of 0 rises. The Q output signal of the SR flip-flop 21 passes through the resistors 4 and 18, respectively, and the NPN transistors 2 and 17
Is input to each base.

According to this structure, when the SR flip-flop is set by the drive pulse P and its Q output signal rises, the NPN transistor 17 and PNP are set.
The transistor 13 and the NPN transistor 2 are all turned on, and the power source → PNP transistor 13 → solenoid 1 → as in the case of the drive circuit shown in FIG.
A current flows through a path of NPN transistor 2 → detection resistor 5 → ground. A voltage proportional to this current is detected by the detection resistor 5 and input to the non-inverting input terminal of the comparator 20.

When the voltage detected by the detection resistor 5 matches the target value, the output signal of the comparator 20 rises and the SR flip-flop 21 is reset. As a result, the NPN transistor 17 and the PNP transistor 1
3 and the NPN transistor 2 are all turned off, and the current flowing in the solenoid 1 up to that point is returned to the power source through the route of diode 14 → solenoid 1 → diode 3.

This operation will be described below with reference to FIGS. 2 and 3.
Will be described in detail. First, as shown in FIG. 3, at a certain time t = 0, the PNP transistor 13 and the NPN transistor 13
If the transistor 2 is turned off, at that moment, as shown in FIG. 2 (a), the current -V / _RL (where _RL is the internal resistance of the solenoid 1) flowing from the ground side to the power source side is the solenoid. Flows to 1.

Then, as indicated by a 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 / R _L , 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 V / _RL flows from the power supply side to the ground side gradually shifts.

However, since the diodes 3 and 14 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 13 and the NPN transistor 2 are 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 changes in the current flowing through the solenoid 1 in the case of the voltage control type drive circuit and the current feedback type drive circuit described above 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 the present embodiment, as described above, from the cutoff time t = 0 of the PNP transistor 13 and the NPN transistor 2 to about 0.69.
The current of the solenoid 1 is cut off after 3τ seconds have elapsed. On the other hand, in the voltage control type drive circuit and the current feedback type drive circuit, the current 0.37V / RL still flows through the solenoid 1 even at the time t = τ after the time t = 0.693τ. As described above, according to this embodiment, the current of the solenoid 1 can be rapidly cut off.

Further, according to the present embodiment, the PNP transistor 13 and the NPN transistor 2 are shut off when the value of the current flowing through the solenoid 1 matches the target value. Therefore, as shown in FIG. On the other hand, a pulse current having a maximum value that matches the target value can be passed. Here, the cycle of the pulse current matches the cycle of the drive pulse P supplied to the SR flip-flop 24. Therefore, according to this embodiment, as shown in FIG. 5, the relationship between the target value of the current to be passed through the solenoid 1 and the value of the current actually flowing through the solenoid 1 can be made proportional.

[0021]

As described above, according to the present invention, the current detecting means for detecting the current flowing through the inductive load and the first switch interposed between one end of the inductive load and the ground line. Means, a second switch means interposed between the other end of the inductive load and a power supply, a first diode for passing a current flowing from one end of the inductive load to the power supply, and a ground wire When the second diode that allows a current to flow to the other end of the inductive load and the first and second switch means are turned on at the predetermined cycle interval, and the current value matches the target value, Since the control means for turning off the first and second switch means is provided, it is possible to realize a drive circuit for an inductive load that has a simple structure and that responds accurately and at high speed to a target current value. The effect of being able to There is.

[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 waveform diagram illustrating the operation of the example.

FIG. 5 is a diagram showing a relationship between a target value of a current to be passed through a solenoid 1 and a current value actually flowing through a solenoid 1 in the embodiment.

FIG. 6 is a circuit diagram showing a configuration of a conventional voltage control type drive circuit.

FIG. 7 is a circuit diagram showing a configuration of a conventional current feedback drive circuit.

FIG. 8 is a circuit diagram showing a configuration of a current feedback type drive circuit using a conventional full bridge circuit.

FIG. 9 is a circuit diagram showing an equivalent circuit in the process of shutting off the current of the solenoid 1 in the conventional voltage-controlled drive circuit.

FIG. 10 is a diagram illustrating the operation of a conventional current feedback type drive circuit.

FIG. 11 is a diagram showing the relationship between the target value of the current to be passed through the solenoid 1 and the value of the current actually flowing through the solenoid 1 in the conventional current feedback drive circuit.

[Explanation of symbols]

20 ... Comparator, 21 ... SR flip-flop, 1 ...
Solenoids, 2, 17 ... NPN transistors, 13 ...
… PNP transistors, 3, 14… Diodes.

Claims (1)

[Claims] 1. A current detecting means for detecting a current flowing through an inductive load, and a first interposing member between one end of the inductive load and a ground wire.
Switch means, a second switch means interposed between the other end of the inductive load and a power supply, a first diode that allows a current flowing from one end of the inductive load to the power supply, and the ground. A second diode for passing a current flowing from the line to the other end of the inductive load, and the first and second switch means in the ON state at the predetermined cycle interval, and the current value matches the target value. A drive circuit for an inductive load, comprising: a control means for turning off the first and second switch means in this case.