JPH0410722B2 - - Google Patents

Description

[Detailed Description of the Invention] () Technical Field The present invention relates to a coil current control device, more specifically, a coil circuit in which a coil is connected in parallel with a freewheeling diode, and a switch and a measuring resistor connected to the coil circuit. The present invention relates to a coil current control device which is opened when the current flowing through the coil exceeds a predetermined value by a switching means, and is closed again due to hysteresis characteristics, whereby the current flowing through the coil is turned on and off to perform clock control.

() Prior Art Conventionally, in order to control the current flowing through the coil, a measuring resistor is provided in the coil circuit, and a voltage proportional to the coil current is measured via the voltage drop caused by this resistor. A voltage signal is used to control the current flowing through the coil in this manner. Furthermore, it is known to perform this control using a clock. In this case, the coil will be bypassed by a freewheeling element, usually a diode or a corresponding thyristor. In this case, the coil current increases exponentially according to a time constant determined by the coil inductance and the measuring resistor, and when a predetermined threshold is reached, a switch in the coil circuit is opened, thereby The coil current again decreases according to an exponential function.
In conventional devices, the coil circuit is switched back on by passing a hysteresis feature with a predetermined time interval, resulting in a control operation that is periodically turned on and off and clocked. Such a device is described, for example, in US Pat. No. 3,575,154.

However, in conventional devices, the current value is fixed, so there is a problem that it is not possible to control the current value to various values.Also, in conventional devices, the number of circuit elements is small, which causes natural vibration. It has the disadvantage of being easy.

Another disadvantage of conventional devices is that when a switch is turned on and current flows through the coil again, a short current peak appears, which appears as noise, and this noise causes the switch to turn on and off unnecessarily. .

() Purpose Therefore, the present invention solves these conventional drawbacks, and provides a method for preventing the switch from being turned on and off unnecessarily and for accurately controlling the coil current over a wide range. The purpose of the present invention is to provide a coil current control device that is capable of controlling a coil current.

In order to achieve this object, the present invention includes a coil and a freewheeling element connected in parallel, a switch and a measuring resistor arranged in the coil circuit, and the switch and measuring resistor being connected to each other via a switching means. In the coil current control device, the switch is opened when a predetermined current value is exceeded, and is closed again after passing through a predetermined hysteresis, thereby controlling the current flowing through the coil on and off. consisting of a comparator for comparing the signal obtained via the measuring resistor with an adjustable threshold value, the comparator being connected via a delay element to a hysteresis switch, which controls said switch; The timing switch is controlled by the output signal from the hysteresis switch, and this timing switch controls the connection between the measurement resistor and the comparator, and when the switch is closed, the connection between the measurement resistor and the comparator is cut off for a short time. did.

() Effect As described above, in the present invention, the threshold value of the comparator that turns on and off the coil current can be adjusted.
The coil current can be controlled based on an arbitrary value, and the coil current can be controlled over a wide range. Further, in the present invention, a timing switch is provided, and this timing switch controls the connection of a coil current measuring resistor and a comparator that compares the coil current according to the output signal of the hysteresis switch, thereby turning the coil current on and off. When the switch is closed, the connection between the measuring resistor and the comparator is cut off for a short time, effectively blocking the short current peak noise that normally occurs when the coil current starts to flow again. Unnecessary turning on and off of the switch can be prevented, thereby making it possible to accurately control the current flowing through the coil.

() Examples The present invention will be described in detail below according to examples shown in the drawings.

In FIG. 1, the reference numeral 10 indicates a coil, and this coil is connected in parallel with a free wheel diode 11. In FIG. The coil 10 is connected via a switch 12 between the supply voltage U _O and earth, in which case a measuring resistor 13 is also connected to this coil circuit. The signal obtained from the measuring resistor 13 is connected to the inverting input terminal of a comparator, the non-inverting input terminal of which is applied with an adjustable predetermined threshold voltage U _S . The output of comparator 14 is connected via delay element 15 to the input of hysteresis switch 16, and switch 12 is controlled by the output of hysteresis switch 16. Furthermore, the measurement resistor 1 is set by the output of the hysteresis switch 16.
A timing switch 17 arranged at the connection from 3 to the comparator 14 is controlled. Such a coil 10 is, for example, an excitation coil used in a solenoid valve of an automatic transmission gear, or an ignition coil of an automobile.

When the threshold value U _S is set and the circuit starts operating by closing the switch 12, the current in the coil circuit follows an exponential function according to a time constant determined by the inductance of the coil 10 and the resistance value of the resistor 13. Rise. When the timing switch 17 is closed, a signal corresponding to the coil current is applied to the inverting input terminal of the comparator 14, which switches when its value reaches the threshold value _US . The output of the comparator 14 is applied to the delay circuit 15, and after a predetermined period of time has elapsed, the output of the comparator 14 is applied to the switch 12 via the hysteresis switch 16.
will be open. The coil current thereby decreases, comparator 14 reverses, and hysteresis switch 16 is returned via delay element 15, thereby causing switch 12 to close again. Threshold U _S adjusted in this way
The switch 12 is cut off for a predetermined time depending on the value of , the delay time of the delay circuit 15, and the width of the hysteresis switch 16, and the current flowing through the coil is turned on and off. In order to cut off the noise generated when the control switch 12 is closed again, the timing switch 17 is opened for a predetermined period of time when the hysteresis switch 16 returns and the switch 12 is closed.
The configuration is such that no signal is input to the

FIG. 2 shows a detailed circuit configuration of the block diagram shown in FIG. 1, in which the same parts as in FIG. 1 are given the same reference numerals.

In the embodiment shown in Fig. 2, the threshold value U _S is a variable resistor of 20
and the supply voltage U _B through a voltage divider consisting of a resistor 21
made from. The signal from the measuring resistor 13 is input to the comparator 14, so the signal from the measuring resistor 13 is input to the comparator 14.
The output of 4 generates a positive signal when the signal from the measuring resistor 13 becomes greater than this threshold.
A capacitor 25 connected to the output of the comparator 14 is charged via a resistor 23 and a diode 22. The voltage of the capacitor 25 determines the switching characteristics of the comparator 26 connected to the subsequent stage. This comparator is fed back by a diode 27, thereby forming a hysteresis switch. Comparator 2
The output of 6 is taken out from the terminal 28 and is also input to another comparator 29 via a resistor 30 and a capacitor 31. This comparator 29
The output signal of is connected to the non-inverting input terminal of the comparator 14 to which the signal from the resistor 31 is input. A signal obtained from an external switch can be input to terminal 28, thereby making it possible to interrupt this current control independently of the clock control. This is particularly advantageous when the coil is driven by a pulse modulated signal under control of a microprocessor.

When the voltage on capacitor 25 becomes greater than the threshold of comparator 26, its output shuts off (turns off) switch 12. switch 12
After the coil current is cut off by opening, the output of the comparator 14 is switched to the ground potential, so that the capacitor 25 is discharged via the resistor 24. The diode 22 functions to interrupt the coupling between the capacitor 25 and the resistor 23. When the voltage on capacitor 25 again falls below the lower threshold of comparator 26, switch 12 closes again. At the same time, the signal from the measuring resistor 13 is brought to the ground potential for a short time via the RC elements 30, 31 and the comparator 29, so that even if there is noise, it can be prevented from being applied to the input of the comparator 14. Normally, when a large coil current has to be switched, the free-wheeling diode 11 must be relatively large, and the charge in the pn junction region must first flow before the diode 11 shuts off, so that the current flows through the coil 10 again. When it flows, a short current peak appears, which appears as noise. Such noise can be blocked by the method described above.

FIG. 3 shows another embodiment for realizing the device of FIG. 1, in which the functions shown in FIG. 2 are combined, thereby reducing the number of circuit elements. be able to.

In the circuit of FIG. 3, input comparator 14 receives threshold value U _S via voltage divider 20,21.
The output of the comparator 14 is connected to a non-inverting input terminal of an operational amplifier 42 via a resistor 41 and to a power supply voltage U _B via a resistor 40.
The operational amplifier 42 is fed back via a capacitor 43, and a reference voltage U _R is applied to its non-inverting input terminal. This operational amplifier 4
The switch 12 is controlled by the output of the switch 2.

When the switch 12 is turned on, the current flowing through the coil 10 increases as described above. Measurement resistance 1
The voltage obtained from 3 is compared in a comparator 14 with a threshold value U _S . When the voltage across resistor 13 becomes greater than threshold U _S , comparator 14 switches to ground current. The voltage applied to the non-inverting input terminal of operational amplifier 42 then decreases according to an exponential function determined by resistor 41 and capacitor 43. When the voltage at the non-inverting input terminal of the operational amplifier 42 reaches the reference voltage U _R , the operational amplifier 42 is inverted, and the voltage applied to the non-inverting input terminal is moved largely in the negative direction as the capacitor 43 is charged. . The voltage across the non-inverting input terminal of operational amplifier 42 increases exponentially from this new value according to the value determined by capacitor 43 and resistors 40,41. When the voltage reaches the reference voltage again from below, the operational amplifier 42 is inverted again to its original state. This inversion causes the output voltage of the operational amplifier 42 to switch between a high level and a low level, thus turning the switch 12 on and off. In this way, on/off control is generated in which the off period of the switch 12 is determined substantially by each circuit element, and the on period is determined by the increase in the current flowing through the coil 10. If the coil is short-circuited, the current will be limited to a small value, so the circuit will be short-circuit safe.

Of course, the timing switch 17 can also be provided in the embodiment shown in FIG.

[Brief explanation of drawings]

The figures are all for explaining embodiments of the present invention. Fig. 1 is a block circuit diagram showing the principle configuration of the present invention, Fig. 2 is a more detailed circuit diagram of the circuit shown in Fig. 1, and Fig. 3 is a block circuit diagram showing the principle configuration of the present invention. FIG. 3 is a circuit diagram showing another embodiment of the present invention. 10... Coil, 11... Free wheel diode, 1
3...Measurement resistance, 14...Comparator, 15
...Delay circuit, 16...Hysteresis switch.

Claims (1)

[Claims] 1. A coil 10 and a freewheeling element 11 are connected in parallel, and a switch 12 and a measuring resistor 13 are further arranged in the coil circuit, and the switch and the measuring resistor are connected to each other via a switching means. Ori,
In this coil current control device, the switch 12 is opened when a predetermined current value is exceeded, and is closed again after a predetermined hysteresis, thereby controlling the on/off of the current flowing through the coil. It consists of a comparator 14 which compares the signal obtained via a resistor 13 with an adjustable threshold value Us, and the comparator 14 is connected via a delay element 15 to a hysteresis switch 16, by which said switch 12 is Also, a timing switch 17 is controlled by the output signal from the hysteresis switch 16, and this timing switch controls the connection between the measuring resistor 13 and the comparator 14, and when the switch 12 is closed, the measuring resistor and the comparator are connected. A coil current control device characterized by cutting off the connection for a short time. 2. The coil current control device according to claim 1, wherein the hysteresis switch 16 comprises a comparator 26 connected in feedback via a diode 27. 3 The hysteresis switch 16 and the delay element 1
5 comprises an operational amplifier 42 fed back by a capacitor 43; in this case, the capacitor 43 is charged and discharged according to the output signal from the comparator 14; Device. 4. The coil current control device according to any one of claims 1 to 3, wherein the coil 10 is an excitation coil of a solenoid valve of an automatic transmission gear of an automobile. 5. Claims 1 to 3, characterized in that the coil 10 is an ignition coil for an automobile.
The coil current control device according to any one of the preceding paragraphs.