JP2006351910A - Solenoid driving circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve by a simple circuit configuration without using any light emitting diode a method for shortening the attenuating time of the reverse electromotive current generated in a solenoid coil, when so applying pulses to the solenoid coil used in an electromagnetic pump, etc. as to drive it. <P>SOLUTION: A switching element 3 whose ON/OFF is performed by a desired pulse input voltage is so connected with an end of a solenoid coil 1 as to constitute a solenoid driving circuit for generating intermittently a magnetism in the solenoid coil 1, and a diode 2 for preventing the reverse current of the solenoid coil 1 is connected in series with the switching-element side of the solenoid coil 1. Thereafter, a nonpolar electrolytic capacitor 5 connected in series with a resistor 4 is connected in parallel with the solenoid coil 1 and with the diode 2 for preventing the reverse current of the solenoid coil 1. Further, a flywheel diode 6 is connected in parallel with the resistor 4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a solenoid drive circuit that shortens the decay time of an induced electromotive current generated in a solenoid coil when the solenoid coil used in an electromagnetic pump or the like is driven by applying a pulse.

  In the DC pulse drive of an electromagnetic pump or the like that operates using the magnetic force obtained by energizing the solenoid coil, the counter electromotive current energy generated by cutting off the current of the solenoid coil having inductance is generally shown in FIG. As in the circuit shown, the transistors and the like are protected by commutating to the flywheel diode D and consuming it as Joule heat.

  In this case, the decay time of the counter electromotive current Ib is several ms or more in the case of an electromagnetic pump, and the current becomes zero with a relatively long time constant. Therefore, when the drive cycle is 20 ms or less, the back electromotive force decay time, that is, the current fall time of the electromagnetic pump drive current Ic is inconvenient, such as a decrease in output due to a delay in recovery of the plunger of the electromagnetic pump. The long decay time of the back electromotive current Ib causes an excessive temperature rise in the solenoid coil. FIG. 7 shows current waveforms at various points in the circuit diagram of FIG.

Patent Document 1 describes a technique for shortening the above-described counter electromotive current decay time. That is, as shown in FIG. 8, most of the back electromotive current generated in the solenoid coil SC when the transistor Tr is cut off instantaneously charges the electrolytic capacitor C through the resistor R1 as the current Ie in the figure. The charged electric charge of the electrolytic capacitor C is gradually discharged as the current Ig flowing through the LED through the resistors R1 and R2 according to the time constant of the resistors R1 and R2. FIG. 9 shows current waveforms at various points in the circuit of FIG.
JP2002237374

  The back electromotive current almost instantaneously flows as the current Ie for charging the electrolytic capacitor C at the moment when the transistor Tr is cut off, so it is confirmed that the fall decay time of the drive current If flowing in the solenoid coil SC is quickly attenuated. it can.

  However, in the circuit shown in FIG. 8, if the current flowing through the solenoid coil increases, the generated back electromotive current also increases. Therefore, the capacity of the electrolytic capacitor C shown in FIG. 8 increases and the charge charge also increases. The light emitting diode that discharges the electric charge needs to be discharged within the “maximum pulse forward current value”. For that purpose, a plurality of circuit units including the light emitting diode LED, the protection diode D2, and the resistor R2 need to be connected in parallel. Will arise.

  As a specific example, FIG. 10 shows a circuit example in which a solenoid coil having a DC resistance of 0.9Ω and an inductance of about 3 mH is driven by a DC 12V power source. In the circuit of FIG. 10, the capacitance of the capacitor C is 1000 μF, and when charging through the resistor R1, the resistor R1 is 10Ω in order to keep the capacitor C within the allowable ripple current range. When the duty ratio for energizing the solenoid with this circuit constant is about 40%, a current of about 70 mA flows through each of the infrared light emitting diodes LED1 and LED2. FIG. 11 shows the voltage waveform at both ends of the solenoid coil.

  As can be seen from FIG. 11, the back electromotive voltage reaches near -70V, and the collector voltage of the transistor Tr viewed from the ground side is about 80V. This voltage needs to be lower than the maximum open-base emitter-collector collector voltage VCEO, but in general, a transistor that drives a solenoid coil with a large current at a low driving voltage has a low VCEO. It is desirable that the current is not more than three times the driving voltage.

  Specifically, in the circuit example shown in FIG. 10, in order to lower the impedance of the back electromotive circuit unit, the resistance is changed from 10Ω to 3Ω as in the circuit example shown in FIG. To reduce the current, the capacitor capacitance is changed from 1000 μF to 4700 μF. The voltage waveform at both ends of the solenoid coil at this time is shown in FIG. The back electromotive force is reduced to about -40V, but increases slightly from 70 mA to 100 mA for the infrared diode. However, the capacitor capacity of 4700 μF is relatively large, and the current flowing into the 100 mA infrared light emitting diode is also equal to the maximum rated value.

  Accordingly, the present invention seeks to achieve a method for shortening the decay time of the generated back electromotive current without using a light emitting diode and with a simple circuit configuration.

  A solenoid drive circuit according to the present invention is a solenoid drive circuit in which a switching element that is turned on and off by an input voltage of a desired pulse is connected to one end of a solenoid coil, and the solenoid coil generates magnetism intermittently. A backflow prevention diode is connected in series on the switching element side, and a non-polar electrolytic capacitor connected in series with a resistor is connected in parallel to the solenoid coil and the backflow prevention diode, and a flywheel diode is connected in parallel to the resistance. (Claim 1).

  As a result, a forward drive current Ij flows through the solenoid coil when the transistor is turned on, and at the same time, a current Ik that charges the nonpolar electrolytic capacitor flows through the power-type resistor. This current Ik charges the power-type resistance side of the non-polar electrolytic capacitor with a positive charge and charges the counter-power-type resistance side (the collector side of the transistor) with a negative charge.

  Next, when the transistor is shut off, the counter electromotive current Ii that is generated reversely charges the nonpolar electrolytic capacitor in the direction of the power type resistance from the counter power type resistance side. Shorter. Therefore, the fall decay time of the solenoid coil drive current Ij is accelerated.

  As described above, according to the present invention, the non-electrolytic capacitor connected in parallel to the solenoid coil is charged positively on the power-type resistance side and negatively charged on the anti-power-type resistance side when the transistor is turned on. Since the power type resistance side is negatively charged and the counter power type resistance side is positively charged at the time of OFF, the decay time of the back electromotive current can be extremely shortened.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a circuit diagram of the present invention, FIG. 2 shows voltage waveforms at various locations, and FIG. 3 shows current waveforms at various locations. In FIG. 1, the solenoid coil 1 is used in a stepping motor, an electromagnetic coil, or the like. Hereinafter, the solenoid coil 1 will be described with an example employed in an electromagnetic pump. One side of the solenoid coil 1 is a diode 2 that prevents backflow. And connected to the collector side of the transistor 3 as a switching element.

  A series circuit of a power-type resistor 4 and a nonpolar electrolytic capacitor 5 is connected in parallel to the solenoid coil 1 and the backflow preventing diode 2. Further, a flywheel diode 6 is connected in parallel to the resistor 4.

  Now, when the transistor 3 is turned on, a forward drive current Ij flows through the solenoid coil 1, and at the same time, a current Ik for charging the nonpolar electrolytic capacitor 5 flows through the power type resistor 4. This current Ik charges the Z side of the non-polar electrolytic capacitor 5 to a positive charge and the Y side to a negative charge.

  Next, when the transistor 3 is shut off, the counter electromotive current Ii generated by the counter electromotive force charges the non-polar electrolytic capacitor 5 from the Y side to the Z side. Since the electrolytic capacitor 5 was charged in the reverse direction and the charge was reversely charged, the back electromotive current was discharged through the nonpolar capacitor 5 from the viewpoint of charge transfer.

  The decay time of the discharge current, that is, the back electromotive current Ii is extremely short as shown in FIG. Therefore, the fall decay time of the solenoid coil drive current Ij is faster than Ic of FIG. In addition to defining the charging / discharging time of the non-electrolytic capacitor, the power-type resistor 4 lowers the impedance between + Vs and Y to reduce the sum of the counter electromotive voltage and the drive DC voltage Vs, that is, (X) and FIG. 2 is a resistance necessary for preventing the transistor 3 from being destroyed by limiting the Vp-p indicated by (Y) of 2 so as not to exceed the rated value of the “base open emitter grounded collector maximum voltage” VCEO of the transistor 3.

  In FIG. 4, as the values of the elements constituting the circuit of the present invention, the solenoid coil 1 has a DC resistance of 0.9Ω, an inductance of 3 mH, the capacitance of the nonpolar electrolytic capacitor 5 is 470 μF, and the power-type resistor 4 is 100Ω. FIG. 5 shows the voltage waveform at both ends of the solenoid coil 1 when the energization condition for the solenoid coil 1 is 40% as in the case described above, but the back electromotive force is within -30V. This is because the generation of the back electromotive force can be reduced with fewer parts than the circuit example using the conventional LED shown in FIG. 12, and at the same time, the capacitance of the capacitor is greatly reduced. The inventive back electromotive force circuit is advantageous.

It is a circuit diagram which shows the Example of this invention. It is a pulse waveform at the X, Y and Z points. It is a current waveform of Ih, Ii, Ij, and Ik. In the circuit diagram of this invention, it is the circuit diagram which showed the concrete value to the solenoid coil, resistance, and a nonpolar electrolytic capacitor. It is a voltage waveform which appears on both ends of the solenoid coil same as the above. It is a general circuit diagram of a conventional example. It is a current waveform of Ia, Ib, and Ic. 1 is a circuit diagram of a first embodiment disclosed in Patent Document 1. FIG. It is a current waveform of Id, Ie, If, and Ig same as the above. It is a circuit diagram of the 2nd example shown in patent documents 1. It is a voltage waveform which appears on both ends of the solenoid coil same as the above. In the circuit diagram of the 2nd Example shown by patent document 1, it is a circuit diagram which showed the specific value of each element to comprise. It is a voltage waveform which appears on both ends of the solenoid coil same as the above.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solenoid coil 2 Diode 3 Transistor 4 Power-type resistance 5 Nonpolar electrolytic capacitor 6 Flywheel diode

Claims (1)

In a solenoid drive circuit that connects a switching element that is turned on and off by an input voltage of a desired pulse to one end of the solenoid coil, and intermittently generates magnetism in the solenoid coil,
A backflow prevention diode is connected in series to the switching element side of the solenoid coil, and a non-polar electrolytic capacitor connected in series with a resistor is connected in parallel to the solenoid coil and the backflow prevention diode. A solenoid drive circuit characterized by connecting foil diodes in parallel.

Images