JPH07122424A - Drive circuit of electromagnet device - Google Patents

Abstract

PURPOSE:To stably maintain the specific value of a suction current and a hold ing current. CONSTITUTION:The conduction of a coil L of an electromagnet device is controlled by a switching element 1. A coil current is detected by a current detector 6 so as to amplify the detected output by an amplifier 12. The amplification factors of this amplifier 12 in the suction and holding times are converted into the outputs from a controller 4. The output from the amplifier 12 is amplified by the difference between the integrating output from an integrator 7 and the reference voltage using an error amplifier 8. The coil current is controlled at a specific value by controlling the on-term of the switching element 1 corresponding to the output from the error amplifier 8 using a PWM controller 9. The detection level of the coil current is converted by substituting the conversion of the amplification factors of the amplifier 12 in suction and holding times for the conversion of the reference voltage of the error amplifier 8. Through these procedures, the suction current and the holding current can be stably maintained at a specific value without being affected by the dispersion in DC voltage of the other circuits.

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 electromagnet device having a function of adjusting a coil current.

[0002]

2. Description of the Related Art As an electromagnet device, an iron core (fixed iron core) is used.
On the other hand, there is one that includes an electromagnet formed by winding a coil and an armature (moving iron core) that is provided relatively to the iron core and that is movable by the attraction force of the electromagnet. The electromagnet device includes a so-called solenoid in which an iron core is movably inserted inside the coil and the iron core is moved by energizing the coil, and a plunger or a contact is driven in conjunction with an armature. For example, an electromagnetic relay is also included.

By the way, in this type of electromagnet device, the armature is separated from the iron core when the coil is not energized (a gap (gap) between the armature and the iron core).
Are opposed to each other through). When the coil is energized, the armature is attracted to the iron core. Here, in a state where the armature and the iron core face each other with a gap in between, a large amount of electric power is required to attract the armature to the iron core. Then, as the gap between the armature and the iron core becomes smaller, the power required to attract the armature to the iron core becomes smaller at an accelerating rate, and in the state where the armature is attracted to the iron core, the required power is the most. Get smaller.

Here, after the armature is attracted to the iron core,
If the electric power before the adsorption is supplied as it is, the electric power is wastefully consumed and a problem such as heat generation of the coil occurs. Therefore, in this type of conventional electromagnet apparatus, a large amount of electric power is supplied (a large current is passed through the coil) until the armature is attracted to the iron core, and after the armature is attracted to the iron core, A driving method is adopted in which electric power capable of maintaining the state of attraction to the iron core is supplied (the current flowing through the coil is reduced).

FIG. 3 shows a drive circuit A of an electromagnet device which switches the current according to the state of attraction of this type of armature to the iron core. In this driving circuit A, and a state where the input voltage V _in is connected to the switching element 1 to control the coil current in the coil L in series across the input terminals to be applied to turn on the switching element 1 continuously, The coil current is controlled by intermittently switching on and off (so-called pulse driving). As the switching element 1, a MOSFET Q ₀ is used as shown in FIG.

That is, when a large amount of electric power is required to attract the armature to the iron core, the switching element 1 is continuously turned on to cause a large current to flow through the coil L, and after the armature is attracted to the iron core. , When supplying electric power capable of maintaining the state of attraction of the armature to the iron core, by intermittently turning on and off the switching element 1,
The current (effective current) flowing through the coil L is reduced.

The diode D ₀ connected in parallel to the coil L is a flywheel diode for absorbing the counter electromotive force generated in the coil L when the switching element 1 is off, and is a transistor instead of the diode. In some cases, a surge absorber, a Zener diode, or the like is used. The driving circuit A includes a regulated power supply unit 2 to create the power to each circuit to be described later from the input voltage, input the input voltage V _in is detected whether the voltage level that can supply sufficient current to the coil L Voltage detection unit 3 and input voltage detection unit 3
When it is detected that the input voltage V _in is a voltage level capable of supplying a sufficient current to the coil L, the control unit 4 that performs control for energizing the coil L, and the control of the control unit 4 And a drive unit 5 that drives the switching element 1.

[0008] Input voltage detector 3, More specifically, as shown in FIG. 4, constituted by a comparator 3a for comparing the reference voltage a voltage obtained by dividing the input voltage V _in min (forward voltage of the diode) There, when the divided voltage exceeds the reference voltage, that is, the input voltage V _in is at a voltage level capable of flowing sufficiently current to the coil L, the output becomes low level. The control unit 4 outputs a trigger signal composed of a negative polarity pulse signal having a constant pulse width in response to the fall of the output of the input voltage detection unit 3, and is composed of, for example, a monostable multivibrator.

The drive section 5 receives the trigger signal from the control section 4 and generates a high level output for a fixed time (for example, 100 msec). The monostable multivibrator 5a.
And an astable multivibrator 5b that generates a pulse signal with a constant cycle (for example, 20 to 50 kHz), a monostable multivibrator 5a, and an astable multivibrator 5
and an OR circuit 5c which takes the logical sum of the respective outputs of b.

In the drive unit 5, while the output of the monostable multivibrator 5a is at the high level, the output of the OR circuit 5c is also kept at the high level, whereby the switching element 1 is maintained in the ON state. . Therefore, current continuously flows through the coil L to the input voltage V _in is applied. When the output of the monostable multivibrator 5a changes to a low level, the output of the astable multivibrator 5b is output via the OR circuit 5c,
The switching element 1 is turned on and off. For this reason, a current flows intermittently in the coil L, and the coil current is suppressed to be small.

However, in the above-mentioned drive circuit A, the pulse width of the output of the astable multivibrator 5b and the pulse generation period are such that the current that holds the armature attracted to the iron core (hereinafter referred to as the holding current). It is necessary to set the value so that the power loss of the circuit element can be sufficiently reduced. However, since the pulse width of the output of the astable multivibrator 5b and the pulse generation period are fixed,
When the input voltage V _in changes, the holding current value changes accordingly, and it may not be possible to keep the power loss small.

Therefore, as an improvement on this point, a drive circuit A shown in FIG. 5 is provided. This drive circuit A
Then, instead of the drive unit 5 in the drive circuit of FIG. 3, a resistor R connected in series with the switching element 1 and the coil L is used.
A current detector 6 that detects the coil current from the voltage across both ends of ₀
An integrating unit 7 that integrates the output of the current detecting unit 3, an error amplifying unit 8 that outputs an error between the output of the integrating unit 7 and the reference voltage, and a pulse output according to the output of the error amplifying unit 8. For generating a pulse width (on-duty) of the pulse output and a so-called pulse width modulation (PWM) controller 9
And a reference voltage switching unit 10 that switches the reference voltage of the error amplification unit 8 based on the output of the control unit 4.

As shown in FIG. 6, the current detecting section 6 includes a resistor
R₀The amplifier 6a that amplifies the voltage across the
An amplified output is generated according to the current. The integrating unit 7 is
De D ₁, Capacitor C₁, And resistance R₁, R₂Using
Configured. The error amplification unit 8 includes a reference voltage and an integration unit 7.
Amplify the difference from the output and the error according to the difference
It is composed of an integrator 8a for integrating the amplified output. here
Instead of the integrating unit 7 and the error amplifying unit 8, the peak hole
Circuit and an error amplifier that does not have an integration function.
May be. The PWM control unit 9 is a triangular wave that generates a triangular wave.
Error amplification of the oscillator 9a and the output of the triangular wave oscillator 9a
It is composed of a comparator 9b for comparing with the output of the section 8
A pulse output whose pulse width changes according to the output of the difference amplification section 8
Generate force. The output of the PWM control unit 9 is, specifically,
When the output of the error amplifier 8 is large, the pulse
Outputs a pulse signal with a narrow pulse width.
It outputs a pulse signal with a wide width.

The control unit 4 is composed of the same control circuit 4a as the control unit 4 described in FIG. 3 and a monostable multivibrator 4b, and the output of the input voltage detection unit 3 falls to a low level. An output that is high level for a certain period from the time is generated. Then, the reference voltage switching section 10 outputs V _ref1 as the reference voltage of the error amplification section 8 when the output of the control section 4 is at the high level, and outputs V _ref2 when it is at the low level.

The operation of the drive circuit will be briefly described below.
The error amplifier 8 operates to find the difference between the coil current and the predetermined level and match the coil current to the predetermined level according to the difference. In other words, when the coil current exceeds the predetermined level, the pulse width of the pulse output is narrowed to decrease the coil current, and conversely, when the coil current decreases below the predetermined level, the pulse width is increased to increase the coil current. Let

When the armature is attracted to the iron core, that is, when the output of the monostable multivibrator 4b is at the high level, the reference voltage is set to V _ref1 and the coil current is higher than the predetermined level set by the reference voltage. Is small, the pulse width of the pulse output is widened, and a large current is passed through the coil L. After the armature is attached to the iron core, that is, when the output of the monostable multivibrator 4b becomes low level, the reference voltage is set to V _ref2 ,
The holding current is kept at a predetermined level with less power loss.

In the drive circuit A, the switching element 1 is pulse-driven even when the armature is attracted to the iron core. As a result, when the armature is attracted to the iron core, the current flowing through the coil L (hereinafter,
This current is also called a suction current) and is also kept at a predetermined level determined by the reference voltage V _ref1 . When an armature is attracted to an iron core, if an undesirably large attracting current is passed, for example, in the case of an electromagnet device having a movable contact driven integrally with the armature, the movable contact contacts the fixed contact. This is because the impact in the case of doing so becomes large, which causes problems such as contact wear and contact bounce. Further, even if there is a voltage drop caused by a large current flowing through the power cable, there is an advantage that it can be operated stably without being affected by the voltage drop.

FIG. 7 shows a drive circuit A having another structure capable of keeping the coil current constant even if the input voltage V _in changes. The specific circuit is shown in FIG. This drive circuit A
Then, in the case where the OR circuit 11 that takes the logical sum of the output of the control unit 4 (specifically, the monostable multivibrator 4b) and the output of the PWM control unit 9 is provided and the output of the monostable multivibrator 4b is at a high level. When the output of the monostable multivibrator 4b is at a high level, the output is applied to the gate of the switching element 1 via the OR circuit 11 to continuously turn on the switching element 1.
The switching element 1 is pulse-driven by the output of the WM control unit 9, and feedback control is performed to keep the coil current at a predetermined level determined by the reference voltage of the error amplification unit 8.

The configuration of the drive circuit A has an advantage that it is not necessary to switch the reference voltage of the error amplification section 8. However, in the case of the drive circuit A, the holding current although it constant regardless of the input voltage V _in, the suction current has the disadvantage that changes according to the input voltage V _in. Therefore, for example, in the case of an electromagnet device including a movable contact that is integrally driven with an armature, the impact when the movable contact comes into contact with the fixed contact is large, and a large current flows through the power cable. If there is a voltage drop,
There is a problem of being affected by it. Therefore, the drive circuit A in FIG. 5 is preferable.

[0020]

However, in the drive circuit A in FIG. 5 described above, the power supplied when the armature is attracted to the iron core (hereinafter referred to as "attraction") is absorbed by the armature to the iron core. When the supply power at this time (hereinafter, referred to as holding time) is considerably larger (for example, 10 times), the reference voltages V _ref1 and V _ref2 also need to be changed accordingly (for example, the reference voltage V _ref1 is set). It is necessary to select 10 V and the reference voltage V _ref2 to be 1 V). When the signal level is extremely changed as described above, the suction current and the holding current are set to desired levels due to the influence of the forward voltage error of the diode D ₁ and the DC voltage variation such as the offset voltage of the integrator 8a. There are cases where you cannot.

The present invention has been made in view of the above points, and an object of the present invention is to reduce the attracting current and the holding current even when the coil currents during the attraction and the holding are significantly different. An object is to provide a drive circuit for an electromagnet device that can stably maintain a predetermined value.

[0022]

In order to achieve the above object, the present invention comprises a switching element for controlling energization of a coil of an electromagnet device, and timer means for counting a certain time from the start of energization of the coil. Error detecting means for detecting coil current, amplifying means for amplifying output of the current detecting means and switching amplification factor according to output of the timer means, error for amplifying difference between output of amplifying means and reference voltage An amplifier means and a PWM control means for intermittently controlling the switching element to be turned on and off and controlling the on-period of the switching element in accordance with the output of the error amplifying means to control the coil current to a constant value. There is.

[0023]

The present invention has the above-mentioned configuration,
By switching the amplification level of the amplifying means during suction and holding to switch the detection level of the coil current, a predetermined current is maintained separately during suction and holding, and the reference voltage of the error amplifying means is held during suction. Eliminates the need to switch between time and time. In this way, by performing the switching control between the suction current and the holding current in terms of the AC voltage, even when the current values of the suction current and the holding current are significantly different, as in the case of switching the reference voltage, another circuit is used. The influence of the DC voltage variation of 1 is not affected, and the attracting current and the holding current are stably maintained at predetermined values.

[0024]

1 and 2 show an embodiment of the present invention. In this embodiment, the amplifier 1 is connected to the outputs of the current detector 6 and the integrator 7.
2 is provided, and the gain of the amplifying unit 12 is switched by the output of the control unit 4, and the switching control of the coil current between the suction and the holding is replaced with the switching of the reference voltage of the error amplifying unit 8 to detect the coil current. The feature is that it is performed by switching the output level.

The structure of the present invention will be described below with reference to FIG. 1 and FIG. 2 showing its specific structure. Driving circuit of the present embodiment also, as shown in FIG. 1, insert the switching element 1 to control the coil current in the coil L in series across the power input which the input voltage V _in is applied, the switching element 1 The pulse output from the PWM control unit 9 intermittently turns on and off. Then, in order to control the coil current to be constant at the time of attracting and at the time of holding, the resistor R ₀ connected in series with the switching element 1 and the coil L in the current detector 6
The coil current is detected from the voltage across both ends of the
Is integrated by the integrator 7, the error between the output of the integrator 7 and the reference voltage is amplified by the error amplifier 8, and the PWM controller 9 outputs the pulse output in accordance with the output of the error amplifier 8. Change the pulse width. That is, the feedback control is performed so that the coil current has a predetermined level according to the reference voltage of the error amplification unit 8. Since this point is the same operation as that described with the drive circuit in FIG. 6, detailed description thereof will be omitted.

In the present embodiment, the reference voltage of the error amplifying section 8 is constant, and the reference voltage is not switched between suction and holding, which is different from the drive circuit shown in FIG. That is, in this embodiment, the amplification unit 12 is provided between the current detection unit 6 and the integration unit 7.
Is provided and instead of switching the reference voltage of the error amplifier 8, the level of the detection output of the coil current is switched. The amplifier section 12, as shown in FIG. 2, there are constituted by an amplifier 12a for amplifying an output of the current detector 6, a switching element Q ₂ to which are connected between the input and the ground of the amplifier 12a , Switching element Q ₂
The on / off control of is performed by the control unit 4.

The control unit 4 includes a control circuit 4a and a monostable multivibrator 4 as in the drive circuit shown in FIG. 6 or 8.
The switching element Q ₂ is turned on and off by the output of the monostable multivibrator 4b. That is, when the switching element Q ₂ is turned on, the output of the current detector 6 is bypassed and is not input to the amplifier 12a, and the output of the amplifier 12a at that time is almost 0V.
When the switching element Q ₂ is off, the output of the current detector 6 is input to the amplifier 12a and the amplifier 12a
The output is appropriately amplified from.

A diode D ₂ is connected in parallel to the circuit composed of the amplifier 12a and the diode D ₁ connected to its output. This diode D ₂ works as follows. Now, when the switching element Q ₂ is on, the output of the amplifier 12a becomes almost 0V at that time, and the output of the current detection unit 6 is directly input to the integration unit 7 via the diode D ₂ . This is, so to speak, equal when the input is given to the integrator 7 through the amplifier 12a having an amplification factor of 1. When the switching element Q ₂ is off, the output obtained by amplifying the output of the current detection unit 6 by the amplifier 12a and the output of the current detection unit 6 are input to the integration unit 7. That is, the output of the current detector 6 is amplified through the amplifier obtained by adding 1 to the amplification factor of the amplifier 12a. In this way, the amplifier 1
There is no need to use a relatively expensive amplifier that can vary the amplification factor as 2a, and there is an advantage that the amplification unit 12 can be configured at low cost. However, it goes without saying that the amplification section 12 may be configured by using an amplifier whose gain can be varied.

In this embodiment, since the output of the astable multivibrator 4b is at a high level during suction, the switching element Q ₂ is turned on, and the integrating section 7 has the current detecting section 6
Is input via the diode D ₂ . At this time, the output of the integrating unit 7 becomes a level significantly lower than the reference voltage set in the error amplifying unit 8, and thus the output level of the error amplifying unit 8 increases. In this way, the error amplification unit 8
When the output of is large, the PWM control section 9 obtains a pulse output having a wide pulse width, the ON period of the switching element 1 becomes long, and a large current is passed through the coil.

In this case, it goes without saying that the coil current is kept constant by feedback control so that the reference voltage and the output of the integrator 7 coincide with each other. Thereby, for example, in the case of an electromagnet device including a movable contact that is integrally driven with the armature, the attracting current becomes larger than necessary when the armature is attracted to the iron core by the input voltage V _in , and the movable contact is increased. Does not increase the impact when it contacts the fixed contact. In addition, stable operation can be achieved without being affected by the voltage drop caused by the large current flowing through the power cable.

During holding, the astable multivibrator 4
Since the output of b becomes low level, switching element Q
₂ is turned off, and the output obtained by adding the output of the current detection unit 6 and the output amplified by the amplifier 12a via the diodes D ₁ and D ₂ is input to the integration unit 7. At this time, the output of the integrating section 7 becomes a level substantially equal to the reference voltage set in the error amplifying section 8, so that the output level of the error amplifying section 8 becomes small. Thus, when the output of the error amplification unit 8 is small, a pulse output with a narrow pulse width is obtained from the PWM control unit 9, the ON period of the switching element 1 is shortened, and the current flowing through the coil L is small. Suppressed.

During this holding, the holding current is kept constant by the feedback control. Here, since the holding current flowing in the coil L at this time is set to a value that does not cause power loss in a switching element or the like more than necessary, the drive circuit can be operated in a state with little power loss.
Further, in addition, if the holding current as described above is constant, even if there is variation in the input voltage V _in, the holding force of the armature of the core does not vary, the iron core of the armature It can be held stably.

Moreover, in the present embodiment, it is not necessary to change the current detection output by changing the amplification factor of the amplifying section 12 and change the reference voltage of the error amplifying section 8, so that the attracting current and the holding current are changed significantly. Even in this case, the attracting current and the holding current can be stably fixed at desired values. That is, in the present embodiment, since the switching control between the attracting current and the holding current is performed by AC voltage, even when the current values of the attracting current and the holding current are significantly different, the reference voltage is changed as in the case of switching. In addition, the attracting current and the holding current can be maintained at the predetermined values without being affected by the DC voltage variation of other circuits. Further, if the attracting current and the holding current are kept constant by switching the level of the current detection output as in the present embodiment, it becomes possible to perform the PWM control with substantially the same accuracy at the time of attracting and at the time of holding.

The circuit of FIG. 2 is provided with an AND circuit 13 which takes the logical sum of the output of the PWM control section 9 and the output of the input voltage detection section 3 so that the input voltage V _in causes a sufficient current to flow through the coil. PWM control unit 9 until the level reaches
However, the AND circuit 13 is not always necessary. By the way, as a method of switching the detection output level of the coil current, for example, switching the resistance value of the resistor R ₀ can be considered. However, in this type of electromagnet device, a large current of about 10 A flows during attraction, and in this case, the resistance R ₀ has an extremely low resistance value (for example, 0.2).
Ω) is required, and it is difficult to realize it by considering the ON resistance of the switching element or the ON resistance of the switching element Q ₀ when switching the resistance value using the switching element, for example. On the other hand, the amplifier 12 that amplifies the output of the current detector 6 as in the present embodiment.
If the method of switching the current detection output by changing the amplification factor of (3), it is possible to easily cope with the case of significantly switching the current flowing through the coil during suction and during holding.

[0035]

As described above, according to the present invention, the switching element for controlling the energization of the coil of the electromagnet device, the timer means for counting a fixed time from the start of energization of the coil, and the current detection for detecting the coil current. Means, amplifying means for amplifying the output of the current detecting means and switching the amplification factor according to the output of the timer means, error amplifying means for amplifying the difference between the output of the amplifying means and the reference voltage, and the switching element. A PW for controlling the coil current at a constant level by controlling ON / OFF intermittently and controlling the ON period of the switching element according to the output of the error amplifying means.
Since the M control means is provided, it is possible to switch the detection level of the coil current by switching the amplification factor of the amplifying means between the time of attraction and the time of holding, and to maintain the predetermined current individually during attraction and holding. Moreover, since it is not necessary to switch the reference voltage of the error amplification means between the time of attraction and the time of retention, it is possible to stably maintain the attraction current and the holding current at a predetermined value without being affected by the DC voltage variation of other circuits. You can

[Brief description of drawings]

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

FIG. 2 is a specific circuit diagram of the above.

FIG. 3 is a block diagram showing a circuit configuration of a conventional example.

FIG. 4 is a specific circuit diagram of the above.

FIG. 5 is a block diagram showing a circuit configuration of another conventional example.

FIG. 6 is a specific circuit diagram of the above.

FIG. 7 is a block diagram showing a circuit configuration of still another conventional example.

FIG. 8 is a specific circuit diagram of the above.

[Explanation of symbols]

A drive circuit L coil R ₀ resistance 1 switching element 4 control unit 6 current detection unit 7 integration unit 8 error amplification unit 9 PWM control unit 12 amplification unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideki Kurumi 1048, Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Works Co., Ltd.

Claims (1)

[Claims] 1. A switching element for controlling energization of a coil of an electromagnet device, a timer means for measuring a fixed time from the start of energization of the coil, a current detecting means for detecting a coil current, and an output of the current detecting means. And amplifying the difference between the output of the amplifying means and the reference voltage, and controlling the switching element intermittently on and off. A drive circuit for an electromagnet device, further comprising: PWM control means for controlling a coil current to a constant value by controlling an ON period of a switching element according to an output of the error amplification means.