JP2007180864A - Current control circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate an effect of a supply voltage on a current control circuit that can output two different voltages on the basis of the supply voltage and control a current flowing to a load by a duty ratio of these two voltages. <P>SOLUTION: A current control circuit 16 comprises an oscillation circuit 20, and the oscillation circuit comprises an astable multivibrator using an operational amplifier 22. A supply voltage Vp or a voltage reflecting the variance of the supply voltage Vp is supplied to the operational amplifier 22 as the supply voltage. During oscillation, the connection point of a resistor Rt and a capacitor Ct connected in series is connected to the minus terminal of the operational amplifier 22, and a connection point between one end of a resistor Rf with the output voltage Vo of the operational amplifier 22 applied to the other end and one end of a resistance Rs with the prescribed voltage Vz applied to the other end is connected to the plus terminal of the operational amplifier 22. Therefore, the oscillation circuit 20 itself has characteristics of reducing the duty ratio as the supply voltage Vp rises, and increasing the duty ratio as the supply voltage lowers. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a current control circuit for controlling a current flowing through a load such as an electromagnetic switching valve or a solenoid of an electromagnetic switch.

  An electromagnetic switching valve will be described as an example. Conventionally, in an electromagnetic switching valve, a spool that is slidably inserted into a body and is biased to a neutral state by a spring is excited via a push pin by excitation of an electromagnetic solenoid. The flow path is switched by pressing and moving.

  As a conventional solenoid drive circuit and current control circuit for driving such an electromagnetic solenoid, the one shown in FIG. 7 is known. A switching element SW is connected in series to the electromagnetic solenoid 1, and a switching control signal from the current control circuit 4 is applied to the gate of the switching element SW. As shown in FIG. 8, when the excitation command input from the outside is turned ON, a switch control signal that is turned ON while the excitation command is ON is output from the current control circuit 4, and the rated solenoid current by the power supply voltage is output. When the excitation command is turned off, the switch control signal from the current control circuit 4 is turned off. A varistor 2 as a surge absorber is connected in parallel to the electromagnetic solenoid.

  However, in the circuit shown in FIG. 7, the rated solenoid current by the power supply voltage continues to flow even after the spool switching is completed. Since the current required to maintain the switching state against the urging force of the spring against the spool may be smaller than the rated solenoid current at the time of switching, if the rated solenoid current continues to flow even after the switching is completed, However, most of the heat is dissipated as Joule heat, resulting in a waste of power consumption.

  In order to avoid such a problem, in the driving circuit proposed in Patent Document 1, as shown in FIG. 9, an electromagnetic solenoid 1 and a first switching element SW1 are connected in series between both terminals of a power source, and the electromagnetic A series circuit of a reflux diode 6 and a second switching element SW2 and a surge absorber 2 are connected to the solenoid 1 in parallel. The current control circuit 4 controls ON / OFF of the first switching element SW1 and the second switching element SW2, and as shown in FIG. 10, while the excitation command is ON, the second switching element is turned ON and the excitation is performed. The first switching element is kept ON until the switching by the spool is completed after the command is turned ON, and then the first switching element is turned ON / OFF at a predetermined cycle until the excitation command is turned OFF. Controls the current flowing through the electromagnetic solenoid.

  As a result, until the switching is completed by the movement of the spool, a rated current is passed through the electromagnetic solenoid 1 to obtain an exciting current for driving the spool, and after the switching is completed, the spool is held at a sufficient solenoid attracting force to keep the switching state. The current flowing through the electromagnetic solenoid 1 is reduced by switching control so that the current becomes the current. At this time, during the time when the voltage application to the electromagnetic solenoid 1 is turned off by the switching control, the current due to the magnetic energy stored in the solenoid 1 is caused to flow to the solenoid 1 via the return diode 6. When the excitation command is turned off, the return circuit via the return diode 6 is cut off, and the current due to the magnetic energy stored in the solenoid is absorbed by the surge absorber 2 so that no response delay occurs. Thus, according to the configuration of Patent Document 1, power consumption can be reduced.

JP 2001-132866 A

  By the way, when the power supply voltage fluctuates, the holding current fluctuates accordingly, and depending on the magnitude of the fluctuation, the holding current becomes too low to hold the solenoid sufficiently, and switching failure occurs. There is a problem that it may occur.

  For example, when a plurality of electromagnetic switching valves are controlled to ON / OFF at a unique timing by a common power supply voltage, when one electromagnetic switching valve is in a holding state, This may occur when the switching valve is turned on.

  Or, as another example, when a battery is used as a power source, the output voltage of the battery is high immediately after charging (higher than the rated voltage) and gradually decreases over time. It is done. In this case, the full output immediately after charging is a wasteful consumption of power and accelerates battery consumption.

  In general, as a conventional solution to power supply voltage fluctuations, it is conceivable to perform PWM control such as detecting and feeding back a holding current and controlling the pulse width. Since it is necessary to provide a current detection circuit and a PWM control arithmetic circuit for each, there is a problem that the configuration becomes complicated, and the occurrence of failure is high in quality and is expensive.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a current control circuit that is not affected by the power supply voltage in the case where the current flowing through the load is controlled by the duty ratio of the voltage.

In order to solve the above-mentioned problem, the invention according to claim 1 of the present invention enables two different voltages Voh and Vol to be oscillated and output based on the power supply voltage Vp, and the duty ratio Rd = tvoh / ( tvoh + tvol), (tvoh: output duration of Voh, tvol: output duration of Vol, | Voh |> | Vol |), a current control circuit for controlling the current flowing through the load,
The oscillation circuit has a characteristic that the duty ratio decreases as the power supply voltage Vp increases and the duty ratio increases as the power supply voltage Vp decreases.

According to the second aspect of the present invention, two different voltages Voh and Vol can be oscillated and output based on the power supply voltage Vp, and the duty ratio of the two voltages Rd = tvoh / (tvoh + tvol), (tvoh: output duration of Voh, In the current control circuit that controls the current flowing through the load according to tvol: Vol output duration, | Voh |> | Vol |)
The oscillation circuit has a characteristic that the duty ratio Rd changes so that the fluctuation ratio of the equivalent applied voltage Ve≡Vp · Rd becomes smaller than the fluctuation ratio of the power supply voltage Vp.

  According to a third aspect of the present invention, the oscillation circuit according to the first or second aspect comprises an astable multivibrator using an operational amplifier.

  According to a fourth aspect of the present invention, the oscillation circuit according to the third aspect is composed of an astable multivibrator using an operational amplifier, and the operational amplifier uses the power supply voltage Vp or the fluctuation of the power supply voltage Vp as the power supply voltage. A reflected voltage is supplied, and at the time of oscillation, a connection point between a resistor Rt and a capacitor Ct connected in series is connected to the − side terminal, and an output voltage of the operational amplifier is applied to one end of the + side terminal. A connection point between the other end of Rf and the other end of resistor Rs to which a predetermined voltage Vz is applied is connected to one end.

  According to a fifth aspect of the invention, the ratio of the resistance values of the resistor Rf and the resistor Rs according to the fourth aspect is such that the fluctuation ratio of the equivalent applied voltage Ve = Vp · Rd is within a desired range with respect to the fluctuation ratio of the power supply voltage Vp. It is characterized by being set to.

  According to a sixth aspect of the present invention, the oscillation circuit according to any one of the first to fifth aspects oscillates when the power supply voltage Vp> the predetermined voltage Vz is satisfied, and the two voltages Voh and Vol are alternated. When the power supply voltage Vp <predetermined voltage Vz is satisfied, the oscillation is stopped and only Voh is output.

  A seventh aspect of the invention is characterized in that the predetermined voltage Vz according to any one of the fourth to sixth aspects is generated by a reference voltage circuit including a Zener diode ZD.

  The invention according to claim 8 is characterized in that the reference voltage circuit according to claim 7 can selectively output any one of a plurality of predetermined voltages.

  The invention according to claim 9 is characterized in that the power supply voltage according to any one of claims 1 to 8 is a battery voltage.

  According to a tenth aspect of the present invention, there is provided a current control circuit according to any one of the first to ninth aspects of the holding current that needs to flow through a load in order to maintain the movable member at a position that resists the restoring force. It is a circuit for this.

  An eleventh aspect of the invention is characterized in that the tenth aspect is a circuit for a holding current of an electromagnetic solenoid of an electromagnetic switching valve.

  According to the first aspect of the present invention, the oscillation circuit itself has the characteristic that the duty ratio decreases as the power supply voltage increases and the duty ratio increases as the power supply voltage decreases. Regardless of voltage fluctuations, the current flowing through the load can be corrected to be substantially equal. Since the change of the duty ratio by the oscillation circuit itself is used, complicated feedback control can be eliminated, the circuit configuration can be simplified, and can be achieved at low cost.

  According to the second aspect of the invention, the oscillation circuit itself has the characteristic that the duty ratio Rd changes so that the fluctuation of the equivalent applied voltage Ve≡Vp · Rd becomes smaller than the fluctuation of the power supply voltage Vp. Regardless of fluctuations in the power supply voltage, the current flowing through the load can be corrected to be substantially equal. Since the change of the duty ratio by the oscillation circuit itself is used, complicated feedback control can be eliminated, the circuit configuration can be simplified, and can be achieved at low cost.

  According to the third aspect of the present invention, the circuit configuration can be simplified without using special parts by using an astable multivibrator using an operational amplifier as a circuit having the above characteristics.

  According to the invention described in claim 4, as the power supply voltage of the operational amplifier, the power supply voltage Vp or a voltage reflecting the fluctuation of the power supply voltage Vp is supplied, and the voltage between the output voltage and the predetermined voltage is applied to the + side terminal of the operational amplifier. By feeding back the voltage divided by the resistor Rs and the resistor Rf, contrary to the common sense that the equivalent applied voltage increases as the power supply voltage rises, it can be set to a substantially constant equivalent applied voltage.

  According to the fifth aspect of the present invention, by appropriately setting the ratio of the resistance Rf and the resistance Rs, it is possible to easily design so as to satisfy the required fluctuation ratio of the equivalent applied voltage.

  According to the sixth aspect of the present invention, it is possible to save power consumption when the power supply voltage is high by oscillating when the power supply voltage is high and not oscillating when the power supply voltage is low.

  According to the seventh aspect of the invention, the predetermined voltage can be easily generated by the Zener diode, and when the power supply voltage Vp becomes smaller than Vz, the predetermined voltage is not applied and the oscillation is stopped. become able to.

  According to the eighth aspect of the invention, fine control can be performed by selectively outputting any one of a plurality of predetermined voltages.

  According to the ninth aspect of the present invention, by applying the present invention to a battery voltage that changes over time, the influence of the change over time can be mitigated.

  According to the invention of claim 10, the present invention is not a circuit for moving the movable member, but a circuit for holding current that needs to flow through a load to maintain the movable member in a position against the restoring force. Can be applied as

  According to the invention described in claim 11, the present invention can be applied as a circuit for the holding current of the electromagnetic solenoid of the electromagnetic switching valve.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an example of a block diagram of a circuit including a current control circuit according to the present invention for flowing a current through a load.

  In FIG. 1, the load is a solenoid 10, and a solenoid drive circuit 12 is connected to the solenoid 10. The solenoid drive circuit 12 can be, for example, the solenoid drive circuit of FIG. 9 as shown in FIG. 7 or Patent Document 1, and is supplied with a power supply voltage Vp. The solenoid drive circuit 12 includes a current control circuit 14 for controlling the excitation current of the solenoid, a current control circuit 16 for controlling the holding current according to the present invention, and an input signal processing circuit 18 for issuing a command signal. The signal is input through the gate circuit.

  The current control circuit 14 is a one-shot circuit that outputs a rectangular wave signal that is ON for a predetermined time when the excitation command is turned ON. This predetermined time is the time required for the spool, which is a movable member, to move and complete switching if it is an electromagnetic switching valve.

  The current control circuit 16 comprises an oscillation circuit, and has a characteristic that its duty ratio changes depending on the power supply voltage, as will be described in detail below. By adding the outputs of the current control circuit 14 and the current control circuit 16 by an OR circuit or the like, a switch control signal as shown in FIG. 10B is generated.

  FIG. 1 is an example in which a solenoid 10 is used as an electromagnetic solenoid of an electromagnetic switching valve. Corresponding to the plurality of solenoids 10, a solenoid drive circuit 12, a current control circuit 14, and an input signal processing circuit 18 are provided. However, since the current control circuit 16 is common, the current control circuit 16 is in a state where the power supply voltage is likely to fluctuate due to the influence of ON / OFF of each electromagnetic switching valve.

  FIG. 2 is a detailed circuit diagram of the current control circuit 16 according to the present invention, which is composed of an astable multivibrator 20 using an operational amplifier as an oscillation circuit.

  In the figure, the astable multivibrator 20 includes an operational amplifier 22, and a power supply voltage Vp that is not a constant voltage but can be varied is supplied as the power supply voltage of the operational amplifier 22. In this case, not the power supply voltage Vp itself but a voltage reflecting fluctuations in the power supply voltage Vp such as a voltage proportional to the power supply voltage Vp may be supplied. A connection point between the resistor Rt and the capacitor Ct of the series circuit 24 including the capacitor Ct and the resistor Rt is connected to the negative terminal of the operational amplifier 22. The connection point between the resistor Rs and the resistor Rf is connected to the + side terminal of the operational amplifier 22. The output voltage Vo of the operational amplifier 22 is applied to one end of the resistor Rf. A Zener diode ZD constituting the reference voltage circuit 26 is connected to one end of the resistor Rs, and a predetermined voltage Vz is applied to the power supply voltage Vp that can vary. Therefore, the positive side terminal of the operational amplifier 22 is positively fed back a voltage obtained by dividing the voltage between the output voltage Vo and the predetermined voltage Vz by the resistor Rs and the resistor Rf.

  The operation of the above astable multivibrator will be described as follows. The voltage Vt at the connection point between the resistor Rs and the resistor Rf is

となる。ここで、

とおいた。

It becomes. here,

It was.

  When the output of the operational amplifier 22 is Vo = Voh, that is, when it is saturated in the direction of discharging current, the capacitor Ct is being charged, and the voltage Vt at the connection point between the resistor Rs and the resistor Rf is (1) From the formula

となり、オペアンプ２２の出力が、Ｖｏ＝Ｖｏｌのとき、つまり、電流を吸い込む方向で飽和しているときは、コンデンサＣｔから放電中であり、抵抗Ｒｓと抵抗Ｒｆとの接続点の電圧Ｖｔは、（１）式より

When the output of the operational amplifier 22 is Vo = Vol, that is, when it is saturated in the direction of sucking current, the capacitor Ct is discharging, and the voltage Vt at the connection point between the resistor Rs and the resistor Rf is From equation (1)

となる。

It becomes.

となる。ここで、τ≡Ｃｔ・Ｒｔであり、Ｖｃｌは発振が持続しているときのＶｃの最小値で、充電の初期値となる。また、放電中は、 When the voltage of the capacitor Ct is Vc (t), during charging,

It becomes. Here, τ≡Ct · Rt, and Vcl is the minimum value of Vc when oscillation continues, and is the initial value of charging. During discharge,

となり、Ｖｃｈは発振が持続しているときのＶｃの最大値で、放電の初期値となる。

Vch is the maximum value of Vc when oscillation continues and becomes the initial value of discharge.

  Since the output of the operational amplifier 22 is inverted when Vc = Vt, Vcl = Vtl and Vch = Vth.

となるので、この式を変形すると、充電時間ｔｃは、

で求められる。ここに、（２）、（３）式を用いて、Ｖｔｈ、Ｖｔｌを消去して整理すると、 If the charging time until the voltage of the capacitor Ct becomes Vch is tc,

Therefore, when this equation is transformed, the charging time tc is

Is required. Here, using the equations (2) and (3), if Vth and Vtl are deleted and arranged,

となる。

It becomes.

  Similarly, when the discharge time until the voltage of the capacitor Ct becomes Vcl is td,

となるので、この式を変形すると、放電時間ｔｄは、

Therefore, when this equation is transformed, the discharge time td is

となる。ここに、（２）、（３）式を用いて、Ｖｔｈ、Ｖｔｌを消去して整理すると、

It becomes. Here, using the equations (2) and (3), if Vth and Vtl are deleted and arranged,

となる。

It becomes.

であり、デューティ比Ｒｄは、Ｒｄ＝ｔｃ／Ｔであるから、 The oscillation period T is

Since the duty ratio Rd is Rd = tc / T,

となる。上記式からＲｄは、時定数τには無関係であることが分かる。

It becomes. From the above equation, it can be seen that Rd is independent of the time constant τ.

  As shown in FIG. 1, an equivalent applied voltage that is substantially applied to the solenoid 10 that is supplied with the power supply voltage Vp and whose supply is controlled by the duty ratio Rd of the current control circuit 16 is Ve = Rd × Vp.

  Since the power supply voltage of the operational amplifier 22 is under the fluctuation of the power supply voltage Vp, Voh is affected by the power supply voltage Vp and has a value slightly smaller than the normal power supply voltage Vp, while Vol is hardly affected by the power supply voltage Vp. . Further, the operational amplifier 22 is fed back to the + side terminal with a voltage obtained by dividing the voltage of the output voltage Vo (Voh, Vol) and the predetermined voltage Vz by the resistor Rs and the resistor Rf, and one end of the resistor Rs. Since a predetermined voltage Vz that does not depend on the power supply voltage Vp is applied, the duty ratio Rd = tvoh / (tvoh + tvol), (tvoh = tc: output duration of Voh, tvol = td under the influence of the fluctuation of the power supply voltage Vp. : Output duration time of Vol). Specifically, the duty ratio decreases as the power supply voltage Vp increases, and the duty ratio increases as the power supply voltage decreases. At this time, the oscillation frequency also changes. This characteristic is achieved by the astable multivibrator 20 itself without the need for feedback control of a detection value such as an external current value. Therefore, if this characteristic is used, the power supply can be configured with a simple configuration without using any special components. It is possible to cancel the voltage Vp so that the equivalent applied voltage Ve has a fluctuation rate smaller than the fluctuation rate of the power supply voltage Vp.

  Furthermore, by selecting k within a suitable range, it is possible to set so that the variation of the equivalent applied voltage Ve = Rd × Vp with respect to the variation of the power supply voltage Vp falls within a predetermined range.

  Here, in order to qualitatively see the relationship between the value of k and the duty ratio Rd, and the relationship between the value of k and the equivalent applied voltage Ve, Vp = Vps (1 + ΔVp) (Vps: reference voltage (or rated voltage)). For convenience, it is assumed that Voh = Vp−a · Vps, Vol = b · Vps, Vz = c · Vps, and using equation (8), Vp / Vps is set for various k (0 <k <1). When a graph with the duty ratio Rd as the vertical axis is drawn on the horizontal axis, the result is as shown in FIG. 3A. Ve / Ves (Ves is Ve when Vp = Vps) is plotted with Vp / Vps as the horizontal axis. When the graph with the vertical axis is drawn, it is as shown in FIG. 3B. In preparing the graph of FIG. 3, for parameters a, b, and c, (a) is c = 0.4, that is, Vz = 0.4 Vps, and (b) is c = 0.6, that is, Vz. = 0.6 Vps, a = 0.04, b = 0.03. In an actual general operational amplifier, as described above, Voh is about 1 V lower than the power supply voltage supplied to the operational amplifier, and Vol has a substantially constant value almost independent of the power supply voltage supplied to the operational amplifier. However, even if it approximates to Voh = Vp−a · Vps and Vol = b · Vps as in the above equation, the tendency does not change.

  3A shows that the duty ratio Rd tends to decrease and increase in the opposite direction with respect to the increase and decrease of the reference voltage (rated voltage) Vps of the power supply voltage Vp. From FIG. 3B, the reference voltage of the power supply voltage Vp can be seen. It can be seen that the fluctuation ratio of the equivalent applied voltage Ve to the reference equivalent applied voltage Ves can be reduced with respect to the fluctuation ratio of (rated voltage) Vps. By setting k to a desired range (for example, around 0.9 or 0.9 or more), the equivalent applied voltage Ve can be hardly changed. Therefore, by selecting Rs and Rf so as to satisfy the required allowable fluctuation range, a circuit that satisfies the specifications can be designed.

  The above example is an example corresponding to the power supply voltage fluctuation at any time of the current control circuit 16, but the present invention oscillates the duty ratio according to the power supply voltage when the power supply voltage is higher than a predetermined value, It is also possible to use it so as not to oscillate within a predetermined value range.

  In this case, the circuit configuration of FIG. 2 is not changed, but the value of Vz is set to be the predetermined value. When Vp> Vz, the equivalent circuit of FIG. 2 is expressed as shown in FIG. 4A, and the current control circuit 16 oscillates with a duty ratio that depends on the magnitude of the power supply voltage Vp. On the other hand, when Vp <Vz, the equivalent circuit of FIG. 2 is expressed as shown in FIG. 4B, and Vt> Voh is always satisfied, and oscillation stops.

  According to this, for example, as shown in FIG. 5, when the power supply voltage Vp is a battery voltage that tends to decrease with time, the power supply voltage Vp oscillates in a range larger than the predetermined voltage Vz. When the power supply voltage Vp decreases and becomes lower than the predetermined voltage Vz, the oscillation stops. Therefore, if the predetermined voltage Vz is set to the rated voltage, it oscillates to save power consumption when the power supply voltage Vp is equal to or higher than the rated voltage, and full output when the power supply voltage becomes lower than the rated voltage. And will be able to.

  FIG. 6 shows an example of a current control circuit having still another oscillation circuit 20-1 according to the present invention. In this example, the reference voltage circuit 26-1 can output a plurality of predetermined voltages Vz. This is different from the previous embodiment. Specifically, the reference voltage circuit 26-1 has Zener diodes Vz1 and Vz2 having different voltages and a switch S1, and switches between the predetermined voltage Vz1 and the predetermined voltage Vz2 by a switching signal.

  By appropriately setting and switching the values of the predetermined voltage Vz1 and the predetermined voltage Vz2, finer control can be performed. For example, the reference duty ratio can be changed by switching between the predetermined voltage Vz1 and the predetermined voltage Vz2. Alternatively, the oscillation can be stopped by the predetermined voltage Vz1 and the oscillation can be generated by the predetermined voltage Vz2, or vice versa. Further, in combination with the control of FIG. 5, it is possible to control the duty ratio to be changed by the predetermined voltage Vz2 while setting the threshold for the temporal change of the power supply voltage Vp of FIG. 5A to Vz1. .

The present embodiment has the following effects.
-The power supply voltage can be corrected with a simple configuration and can be realized at low cost.
-The allowable range for use with respect to the rated voltage of the power supply can be expanded. If the voltage allowed for use is set lower, the holding current must be set higher in advance, which will impair the energy saving effect, and conversely, if the holding current is lowered, the allowable range of the voltage used will be narrowed. In the present invention, such a problem can be eliminated.
Since the current value to the load is controlled by the voltage duty ratio, the same current control circuit can be used for different power loads if the rated voltage is the same. For example, even in an electromagnetic switching valve, there are a plurality of types of solenoids having different values of required excitation current and holding current depending on the valve size. However, since the same duty ratio control can be applied, there is one solenoid for these solenoids. The current control circuit can be used in common, and the cost can be reduced.

  In the above example, the current control circuit for the solenoid in the electromagnetic switching valve is taken as an example. However, the present invention is not limited to this, and can be applied to any load that requires current control. is there. For example, even in the case of an electromagnetic switch, it is preferable that the holding current is lower than the exciting current in order to prevent the coil from burning and heat generation. However, as such a holding current control circuit, the current control circuit of the present invention is used. Is applicable.

It is an example of the block diagram of the circuit for supplying an electric current to load including the current control circuit of this invention. It is a circuit diagram of the current control circuit of the present invention. It is a graph showing the change of the duty ratio with respect to the fluctuation | variation of the power supply voltage according to the value of k = Rf / (Rs + Rf). It is a graph showing the fluctuation | variation of the equivalent applied voltage with respect to the fluctuation | variation of the power supply voltage according to the value of k = Rf / (Rs + Rf). 2A is the equivalent circuit of FIG. 2 when Vp> Vz, and FIG. 2B is the equivalent circuit of FIG. 2 when Vp <Vz. It is a waveform diagram of an output voltage and an equivalent applied voltage when the power supply voltage Vp decreases with time. FIG. 6 is a circuit diagram of still another current control circuit according to the present invention. It is a circuit diagram showing the solenoid drive circuit and current control circuit for driving the electromagnetic solenoid of the conventional electromagnetic switching valve. FIG. 8 is a waveform diagram of an excitation command, a switch control signal, and a solenoid current of the circuit of FIG. It is a circuit diagram showing the solenoid drive circuit and current control circuit for driving the electromagnetic solenoid of another conventional electromagnetic switching valve. FIG. 10 is a waveform diagram of an excitation command, a switch control signal, and a solenoid current of the circuit of FIG. 9.

Explanation of symbols

10 Solenoid (load)
16 Current control circuit 20 Astable multivibrator (oscillation circuit)
22 Operational amplifier 26 Reference voltage circuit Rs, Rf Resistor ZD Zener diode

Claims (11)

Two different voltages Voh and Vol can be oscillated and output based on the power supply voltage Vp, and the duty ratio of the two voltages Rd = tvoh / (tvoh + tvol), (tvoh: output duration of Voh, tvol: output duration of Vol, In the current control circuit for controlling the current flowing through the load by | Voh |> | Vol |),
A current control circuit having an oscillation circuit that has a characteristic that the duty ratio decreases as the power supply voltage Vp increases and the duty ratio increases as the power supply voltage Vp decreases. Two different voltages Voh and Vol can be oscillated and output based on the power supply voltage Vp, and the duty ratio of the two voltages Rd = tvoh / (tvoh + tvol), (tvoh: output duration of Voh, tvol: output duration of Vol, In the current control circuit for controlling the current flowing through the load by | Voh |> | Vol |),
A current control circuit comprising an oscillation circuit having a characteristic that the duty ratio Rd changes so that the fluctuation ratio of the equivalent applied voltage Ve≡Vp · Rd is smaller than the fluctuation ratio of the power supply voltage Vp.   3. The current control circuit according to claim 1, wherein the oscillation circuit is composed of an astable multivibrator using an operational amplifier.   The oscillation circuit is composed of an astable multivibrator using an operational amplifier, and the operational amplifier is supplied with the power supply voltage Vp or a voltage reflecting the fluctuation of the power supply voltage Vp as its power supply voltage. The connection point of the resistor Rt and the capacitor Ct connected in series is connected to the terminal, and the predetermined voltage Vz is applied to the other end and one end of the resistor Rf in which the output voltage of the operational amplifier is applied to one end thereof. The current control circuit according to claim 1, wherein a connection point with the other end of the resistor Rs is connected.   5. The ratio of the resistance values of the resistor Rf and the resistor Rs is set so that the fluctuation ratio of the equivalent applied voltage Ve = Vp · Rd with respect to the fluctuation ratio of the power supply voltage Vp falls within a desired range. The current control circuit described.   The oscillation circuit oscillates when the power supply voltage Vp> the predetermined voltage Vz is satisfied, and outputs two voltages Voh and Vol alternately, and stops the oscillation when the power supply voltage Vp <the predetermined voltage Vz is satisfied. 6. The current control circuit according to claim 1, wherein only Voh is output.   The current control circuit according to claim 4, wherein the predetermined voltage Vz is generated by a reference voltage circuit including a Zener diode ZD.   8. The current control circuit according to claim 7, wherein the reference voltage circuit can selectively output any one of a plurality of predetermined voltages.   The current control circuit according to claim 1, wherein the power supply voltage is a battery voltage.   10. The current control according to claim 1, wherein the current control is a circuit for a holding current required to flow through the load in order to maintain the movable member at a position against a restoring force. circuit. The current control circuit according to claim 10, wherein the current control circuit is a circuit for holding current of an electromagnetic solenoid of the electromagnetic switching valve.

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