JP2021197493A - Solenoid driving circuit - Google Patents

Abstract

To provide a solenoid driving circuit that can stabilize the heat generation of a solenoid coil and switching timing.SOLUTION: A solenoid driving circuit includes: a DC/DC converter 20 that has a voltage input terminal P1 connected to an external power supply 90 and a voltage output terminal P2 connected to a solenoid coil 100, has switching elements 22 and 25, and outputs a constant voltage relative to a fluctuating input voltage; and a timer circuit 30 that is connected to the voltage output terminal P2 of the DC/DC converter 20 and measures a time in which a voltage is output to the solenoid coil 100. A control unit 27 of the DC/DC converter 20 switches an output voltage of the DC/DC converter 20 to a voltage lower than the previous voltage on the basis of the state of a first switching timing determination terminal P3 when a predetermined time by the timer circuit 30 elapses from the start of energization of the solenoid coil 100.SELECTED DRAWING: Figure 1

Description

The present invention relates to a solenoid drive circuit.

As shown in FIG. 7, the solenoid drive circuit disclosed in Patent Document 1 includes a solenoid coil 200, an adsorption transistor 201, a holding transistor 202, a limiting resistor 203, and a timer circuit 204. The timer circuit 204 includes a capacitor 205 and a resistor 206. When the switch 207 is turned on, the adsorption transistor 201 and the holding transistor 202 are turned on, and a drive current is supplied to the solenoid coil 200 through the adsorption transistor 201. When a specific time elapses after the switch 207 is turned on, the suction transistor 201 is turned off by the timer circuit 204, and a holding current smaller than the drive current is supplied to the solenoid coil 200 through the holding transistor 202. In this way, power saving is realized by the combination of the timer circuit 204 and the limiting resistor 203, and after driving the plunger with a high current, the timer circuit 204 using the capacitor 205 passes the current path with the transistor 201 after a certain period of time. It is switched and the holding current is lowered.

Japanese Unexamined Patent Publication No. 2011-187520

However, in the solenoid drive circuit disclosed in Patent Document 1, since the current flowing through the solenoid coil 200 changes with the fluctuation of the supply voltage, for example, when the voltage is high, a large amount of heat is generated. Further, the timer circuit 204 is used to switch from the drive current to the holding current by the charging operation of the capacitor 205, but when the input voltage fluctuates, the charging speed of the capacitor 205 changes, so that the switching timing becomes unstable.

An object of the present invention is to provide a solenoid drive circuit capable of stabilizing the heat generation of the solenoid coil and stabilizing the switching timing.

The solenoid drive circuit for solving the above problems is a solenoid drive circuit that inputs an external power supply voltage to energize the solenoid coil for driving the electromagnetic valve, and the external power supply is connected to the voltage input terminal and the voltage output terminal. The solenoid coil is connected to the DC / DC converter, which has a switching element and outputs a constant voltage with respect to a fluctuating input voltage, and is composed of a resistor and a capacitor and is connected to the voltage output terminal of the DC / DC converter. A timer circuit for measuring the voltage output time to the solenoid coil is provided, and the DC / DC converter has a control unit for controlling a switching element of the DC / DC converter and switching connected to the timer circuit. It has a timing determination terminal, and the control unit predetermines the output voltage of the DC / DC converter based on the state of the switching timing determination terminal by the timer circuit from the start of energization of the solenoid coil. The gist is to switch to a lower voltage over time.

According to this, since the DC / DC converter can keep the output voltage constant even if the input voltage fluctuates, the voltage applied to the solenoid coil becomes stable against the fluctuation of the supply voltage from the external power supply. The heat generation of the solenoid coil can be stabilized. Further, by the control unit, the output voltage of the DC / DC converter based on the state of the switching timing determination terminal becomes lower than the voltage up to that point when a predetermined time elapses from the start of energization of the solenoid coil by the timer circuit. Can be switched to. At this time, even if the supply voltage fluctuates, the voltage applied to the timer circuit is constant, so that the charging speed of the capacitor is stable and the switching timing can be stabilized.

Further, in the solenoid drive circuit, the DC / DC converter may have a SEPIC circuit structure.
Further, in the solenoid drive circuit, it is preferable that the capacitor of the timer circuit has a discharge path formed via a diode.

Further, in the solenoid drive circuit, a diode for surge voltage countermeasures may be connected in parallel to the solenoid coil between the DC / DC converter and the solenoid coil.

Further, in the solenoid drive circuit, a diode for preventing erroneous wiring may be provided on at least one of the positive electrode line and the negative electrode line between the external power supply and the DC / DC converter.

According to the present invention, the heat generation of the solenoid coil can be stabilized and the switching timing can be stabilized.

The circuit diagram of the solenoid drive circuit in an embodiment. A schematic of a solenoid drive circuit to explain its operation. A schematic of a solenoid drive circuit to explain its operation. (A), (b), (c), (d) are time charts about the input voltage, the level of the first switching timing determination terminal, the output voltage, and the level of the second switching timing determination terminal. Explanatory drawing for explaining the level of the 2nd switching timing determination terminal, the level of the 1st switching timing determination terminal, and a mode. A circuit diagram of another solenoid drive circuit. A circuit diagram of a solenoid drive circuit for explaining background technology.

Hereinafter, an embodiment embodying the present invention will be described with reference to the drawings.
The solenoid drive circuit can be used for a pneumatic valve that drives and controls a pneumatic actuator (air operated valve, cylinder).

As shown in FIG. 1, the solenoid drive circuit 10 controls the flow of fluid by inputting an external power supply voltage to energize the solenoid coil 100 for driving the solenoid valve to perform the suction operation of the plunger of the solenoid valve. .. The solenoid drive circuit 10 is provided on the control board.

The solenoid drive circuit 10 includes a DC / DC converter 20 and a timer circuit 30. A voltage is applied to the solenoid coil 100 via the DC / DC converter 20.
The DC / DC converter 20 provided on the control board has a SEPIC (Single Ended Primary Inductor Converter) circuit structure. The DC / DC converter 20 includes a voltage input terminal P1, a voltage output terminal P2, a first switching timing determination terminal P3, a second switching timing determination terminal P4, and a ground terminal P5.

The DC / DC converter 20 includes a coil 21, a switching element 22, a capacitor 23, a coil 24, a switching element 25, a capacitor 26, a control unit 27, and a voltage sensor 28. The switching elements 22 and 25 are composed of, for example, MOSFETs.

The positive electrode of the external power supply 90 is connected to the voltage input terminal P1 of the DC / DC converter 20 via the switch 40, and the switch 40 is connected to the positive electrode line L1 between the positive electrode of the external power supply 90 and the DC / DC converter 20. It has a provided configuration. The switch 40 is driven by a control device (not shown). The negative electrode of the external power supply 90 is connected to the ground terminal P5 via the diode 41, and the negative electrode line L2 between the negative electrode of the external power supply 90 and the DC / DC converter 20 is provided with the diode 41 for countermeasures against erroneous wiring. It has become. In the diode 41, the anode is on the ground terminal P5 side and the cathode is on the negative electrode side of the external power supply 90. The diode 41 makes it possible to protect the DC / DC converter 20 from the reverse voltage due to incorrect wiring of the input voltage.

One end of the solenoid coil 100 is connected to the voltage output terminal P2 of the DC / DC converter 20, and the other end of the solenoid coil 100 is connected to the ground terminal P5.
In the DC / DC converter 20, one end of the coil 21 is connected to the voltage input terminal P1, and one electrode of the capacitor 23 is connected to the other end of the coil 21. A voltage output terminal P2 is connected to the other electrode of the capacitor 23 via a switching element 25. The connection point α in the middle of wiring connecting the coil 21 and the capacitor 23 is connected to the ground terminal P5 via the switching element 22. The connection point β in the middle of wiring connecting the capacitor 23 and the switching element 25 is connected to the ground terminal P5 via the coil 24. The connection point γ in the middle of wiring connecting the switching element 25 and the voltage output terminal P2 is connected to the ground terminal P5 via the capacitor 26. The voltage sensor 28 detects the output voltage Vout, which is the potential difference between the voltage output terminal P2 and the ground terminal P5.

The output voltage Vout detected by the voltage sensor 28 is sent to the control unit 27. The control unit 27 of the DC / DC converter 20 is connected to the gates of the switching element 22 and the switching element 25 of the DC / DC converter 20, and the control unit 27 controls the switching elements 22 and 25 on and off. Specifically, the duty ratio, which is the ratio of the on / off duration to one cycle in the on / off pulse train of the switching elements 22 and 25, is controlled.

The DC / DC converter 20 having a SEPIC circuit structure can output a constant voltage with respect to a fluctuating input voltage, and adjusts the duty ratio of the switching element 22 on the input side and the duty ratio of the switching element 25 on the output side. This adjusts the output DC voltage. Specifically, when the switching element 22 is on and the switching element 25 is off, the current due to the energy from the coil 24 flows through the switching element 22 and the capacitor 23, and the current due to the energy from the input voltage Vin flows between the coil 21 and the switching element. It flows through 22. Further, when the switching element 22 is off and the switching element 25 is on, a current flows from the coil 24 to the capacitor 26 and the solenoid coil 100 through the switching element 25, and a current from the coil 21 passes through the capacitor 23 and the switching element 25 to the capacitor 26. And flows to the solenoid coil 100. The output voltage Vout is adjusted by adjusting the duty ratio of the switching element 22 (duty ratio of the switching element 25).

Outside the DC / DC converter 20, a capacitor 50 is connected between the voltage output terminal P2 and the ground terminal P5. Further, a series circuit of the resistor 51 and the light emitting diode (LED) 52 is connected between the voltage output terminal P2 and the ground terminal P5. The light emitting diode (LED) 52 lights up when the solenoid coil 100 is energized (when a voltage is applied).

A diode 53 is connected between the voltage output terminal P2 and the ground terminal P5, and the anode of the diode 53 is on the ground terminal P5 side and the cathode is on the voltage output terminal P2 side. The diode 53 connected in parallel with the solenoid coil 100 can protect the DC / DC converter 20 from the surge voltage of the solenoid coil 100.

The timer circuit 30 is composed of a resistor 31 and a capacitor 32 connected in series, one end of the series circuit is connected to the voltage output terminal P2 of the DC / DC converter 20, and the other end is connected to the ground terminal P5. .. The timer circuit 30 makes it possible to measure the voltage output time to the solenoid coil 100.

The timer circuit 30, which is a series circuit of the resistor 31 and the capacitor 32, is connected in parallel with the solenoid coil 100.
The first switching timing determination terminal P3 of the DC / DC converter 20 is connected to a connection point a in the middle of wiring between the capacitor 32 and the resistor 31. The second switching timing determination terminal P4 of the DC / DC converter 20 is connected to the positive electrode of the external power supply 90 via the resistor 60 and the switch 40. When the switch 40 is closed, the external power supply voltage is applied to the second switching timing determination terminal P4 via the resistor 60 to bring it to the H level.

The connection point a in the middle of wiring connecting the capacitor 32 and the resistor 31 is connected to the voltage output terminal P2 via the diode 42 for discharging, and the capacitor 32 of the timer circuit 30 is connected to the capacitor 32 via the diode 42 with reference numerals L3 and L4. , L5, L6 have a configuration in which a discharge path to the ground terminal P5 is formed by the path shown in L6. The diode 42 has an anode on the capacitor 32 side and a cathode on the voltage output terminal P2 side.

The first switching timing determination terminal P3 and the second switching timing determination terminal P4 are connected to the control unit 27. When the level of the second switching timing determination terminal P4 rises to the H level, the control unit 27 sets the output voltage Vout of the DC / DC converter 20 to 5V at that timing (rising edge) and energizes (drives) the solenoid coil 100. Is supposed to start. Further, the control unit 27 sets the output voltage Vout of the DC / DC converter 20 based on the state of the first switching timing determination terminal P3 at the rising edge where the level of the second switching timing determination terminal P4 becomes H level. When a predetermined time elapses from the start of energization of the solenoid coil 100 to reach the threshold value of the level of the first switching timing determination terminal P3 by the timer circuit 30, the voltage is lower than the voltage up to that point (voltage corresponding to the adsorption current). It is possible to switch to (voltage corresponding to the holding current). Power consumption can be reduced by making the holding current that holds the position of the plunger smaller than the suction current corresponding to the plunger suction operation of the solenoid valve.

Next, the operation will be described.
FIG. 4A shows the transition of the input voltage Vin. FIG. 4B shows the transition of the level of the first switching timing determination terminal P3. FIG. 4C shows the transition of the output voltage Vout. FIG. 4D shows the transition of the level of the second switching timing determination terminal P4.

In FIGS. 4A, 4B, C, and 4D, the switch 40 is closed at the timing of t1 and the input voltage Vin is supplied to the DC / DC converter 20. Then, as shown in FIG. 4D, the second switching timing determination terminal P4 becomes H level. Using this as a trigger, the control unit 27 outputs 5V as the output voltage Vout of the DC / DC converter 20 as shown in FIG. 4C.

By setting the output voltage Vout of the DC / DC converter 20 to 5V, a plunger adsorption current flows through the solenoid coil 100 and the plunger adsorption operation is performed, as shown by the path Ru1 in FIG. Further, when the output voltage Vout of the DC / DC converter 20 is 5V, as shown by the path Ru2 in FIG. 2, a current flows through the resistor 31 in the timer circuit 30 to charge the capacitor 32.

The capacitor 32 of the timer circuit 30 is charged by the output voltage Vout of the DC / DC converter 20, and the level of the first switching timing determination terminal P3 rises as shown in FIG. 4 (b). As shown in FIG. 4C, the DC / DC converter assumes that the control unit 27 has changed from the L level to the H level at the timing of t2 when the level of the first switching timing determination terminal P3 reaches the threshold value. 3.3V is output as the output voltage Vout of 20.

That is, the control unit 27 sets the output voltage of the DC / DC converter 20 based on the state of the first switching timing determination terminal P3 for a time T1 (for example, 50 msec) predetermined by the timer circuit 30 from the start of energization of the solenoid coil 100. After that, it switches to 3.3V, which is lower than the previous 5V.

When the output voltage Vout of the DC / DC converter 20 becomes 3.3V, a plunger position holding current flows through the solenoid coil 100, and the plunger position is held. Further, by switching the output voltage Vout of the DC / DC converter 20 from 5V to 3.3V, it is possible to reduce the power consumption related to the driving of the solenoid valve while performing the adsorption operation of the plunger (power saving is achieved).

FIG. 5 shows a mode corresponding to the level of the second switching timing determination terminal P4 and the level of the first switching timing determination terminal P3.
As shown in FIG. 5, when the second switching timing determination terminal P4 is at L level and the first switching timing determination terminal P3 is at L level, the output voltage Vout of the DC / DC converter 20 is set to zero and no output is output. The shutdown mode (solenoid valve drive stop mode) is set. When the second switching timing determination terminal P4 is at H level and the first switching timing determination terminal P3 is at L level, the output voltage Vout of the DC / DC converter 20 is fixed to 5V in a 5V fixed mode. When the second switching timing determination terminal P4 is at H level and the first switching timing determination terminal P3 is at H level, the output voltage Vout of the DC / DC converter 20 is fixed to 3.3V in the 3.3V fixed mode. ..

As shown in FIGS. 4A, 4B, C, and 4D, when the switch 40 is opened at the timing of t3, the supply of the input voltage to the DC / DC converter 20 is stopped. Then, the output voltage Vout becomes zero, and the electric charge accumulated in the capacitor 32 of the timer circuit 30 is discharged via the diode 42 in the discharge path shown by the path Ru3 in FIG. Further, the second switching timing determination terminal P4 becomes the L level.

A surge voltage is generated when the energization of the solenoid coil 100 is stopped, a surge current flows through the diode 53 as shown by the path Ru4 in FIG. 3, and the surge voltage of the solenoid coil 100 is connected in parallel with the solenoid coil 100. The DC / DC converter 20 is protected by the generated diode 53.

In this way, since the DC / DC converter 20 can keep the output voltage constant even if the input voltage fluctuates, the voltage applied to the solenoid coil 100 is stable against the fluctuation of the supply voltage from the external power supply 90. However, the heat generation of the solenoid coil 100 can be stabilized.

Further, the control unit 27 sets the output voltage Vout of the DC / DC converter 20 based on the states of the switching timing determination terminals P3 and P4 to a time (startup time) predetermined by the timer circuit 30 from the start of energization of the solenoid coil 100. When T1 elapses, the voltage is switched to a voltage lower than the previous voltage. At this time, even if the supply voltage fluctuates, the voltage applied to the timer circuit 30 is constant, so that the charging speed (time to reach the threshold value) of the capacitor 32 is stable, and the switching timing can be stabilized.

In this way, it can be used as a power-saving free power supply circuit that can be used regardless of the power supply voltage.
Hereinafter, it will be described in detail.

By using the DC / DC converter 20 having a SEPIC circuit structure, the voltage applied to the solenoid coil 100 is stable, and the temperature rise of the solenoid coil 100 can be reduced. As shown in FIG. 4A, when the solenoid coil 100 is driven for a predetermined time (for example, 100 msec) as one cycle, when the supply voltage is high and the solenoid applied voltage is also high, the solenoid coil 100 is driven. The generated heat also increases and the solenoid coil 100 becomes hot, which makes it difficult to cool the solenoid coil 100 by the time of the next drive. On the other hand, in the DC / DC converter 20 as in the present embodiment, if the output voltage Vout is constant even when the input voltage Vin becomes high, the output voltage Vout of the DC / DC converter 20 even if the input voltage Vin fluctuates. Is fixed at 5V or 3.3V, and the heat generated in the solenoid coil 100 remains small and constant. As a result, the calorific value of the solenoid coil 100 can be kept constant, and the solenoid coil 100 can be cooled by the time of the next drive.

Further, since the output voltage of the DC / DC converter 20 is applied to the timer circuit 30 (resistor 31, capacitor 32), even if the supply voltage fluctuates (even if the input voltage Vin fluctuates), until the charging voltage reaches the threshold value. The time is constant, and the energization time of the adsorption current, that is, the start-up time can be constant. For example, the time T1 fixed at 5 V can be made constant (for example, 50 msec).

Specifically, the input voltage Vin is input to the DC / DC converter 20 via the switch 40, and 2.7 to 38 V is supplied as an input voltage to the DC / DC converter 20 from the DC / DC converter 20. 5V is output, and a voltage is applied to the solenoid coil 100 and the timer circuit 30 (resistor 31, capacitor 32). The capacitor 32 of the timer circuit 30 is charged, the charging voltage of the capacitor 32 rises, the voltage of the first switching timing determination terminal P3 of the DC / DC converter 20 rises, and the first switching timing determination terminal P3 When the level reaches the threshold, the output voltage of the DC / DC converter 20 is set to 3.3V.

In the solenoid drive circuit disclosed in Patent Document 1, since the current flowing through the solenoid coil 200 changes in response to fluctuations in the supply voltage, the current decreases as the voltage decreases, which may lead to malfunction of the plunger. In the present embodiment, the output voltage Vout of the DC / DC converter 20 is constant, the current flowing through the solenoid coil 100 does not decrease, and the operation of the plunger does not become defective. That is, even if the supply voltage fluctuates, the output voltage Vout of the DC / DC converter 20, that is, the voltage applied to the solenoid coil 100 can be kept constant, and malfunction of the plunger can be prevented.

According to the above embodiment, the following effects can be obtained.
(1) As a configuration of the solenoid drive circuit 10 for inputting an external power supply voltage to energize the solenoid coil 100 for driving the electromagnetic valve, the external power supply 90 is connected to the voltage input terminal P1 and the solenoid coil 100 is connected to the voltage output terminal P2. Is connected, has switching elements 22 and 25, and is composed of a DC / DC converter 20 that outputs a constant voltage with respect to a fluctuating input voltage Vin, a resistor 31 and a capacitor 32, and is a voltage output of the DC / DC converter 20. A timer circuit 30 connected to the terminal P2 and measuring the voltage output time to the solenoid coil 100 is provided. The DC / DC converter 20 includes a control unit 27 that controls the switching elements 22 and 25 of the DC / DC converter 20, a first switching timing determination terminal P3 that is connected to the timer circuit 30 and serves as a switching timing determination terminal. Has. The control unit 27 sets the output voltage Vout of the DC / DC converter 20 based on the state of the first switching timing determination terminal P3 when the time T1 predetermined by the timer circuit 30 elapses from the start of energization of the solenoid coil 100. Switch to a voltage lower than the voltage up to.

Therefore, by using a DC / DC converter 20 that outputs a constant voltage with respect to a fluctuating input voltage Vin and connecting a timer circuit 30 to the voltage output terminal P2 of the DC / DC converter 20, the heat generation of the solenoid coil 100 is stabilized. At the same time, the switching timing can be stabilized.

(2) Since the DC / DC converter 20 has a SEPIC circuit structure, it can be stepped up and down, and is practical.
(3) Since the discharge path (L3, L4, L5, L6) via the diode 42 is formed in the capacitor 32 of the timer circuit 30, the electric charge accumulated in the capacitor 32 can be removed at an early stage.

(4) Since the diode 53 for surge voltage countermeasures is connected in parallel to the solenoid coil 100 between the DC / DC converter 20 and the solenoid coil 100, surge voltage countermeasures can be taken.

(5) Since the diode 41 for countermeasures against erroneous wiring is provided in the negative electrode line L2 between the external power supply 90 and the DC / DC converter 20, countermeasures against erroneous wiring can be taken.
The embodiment is not limited to the above, and may be embodied as follows, for example.

〇 As a DC / DC converter with a switching element, we used a DC / DC converter with a SEPIC circuit structure that can handle boosting and stepping down so that the output voltage becomes constant even if the input voltage fluctuates. Instead, as a DC / DC converter with a switching element, even if a DC / DC converter that can handle the output voltage to be constant by boosting even if the input voltage fluctuates is used, the output is stepped down even if the input voltage fluctuates. A DC / DC converter that can handle constant voltage may be used.

〇 In FIG. 1, the DC / DC converter 20 has a second switching timing determination terminal P4 connected to the positive electrode of the external power supply 90 via the resistor 60 and the switch 40, but instead of this, FIG. 6 As shown in, this may be eliminated. That is, the control unit 27 of FIG. 1 has a second switching timing determination terminal P3 and a second switching timing determination terminal P4 as shown in FIGS. 4 (a), (b), (c), and (d). The elapse of a predetermined time T1 from the start of energization of the solenoid coil 100 was monitored by using the rising edge of the level of the switching timing determination terminal P4 as a trigger. Instead, as shown in FIG. 6, the control unit 27 is the first. When the charging potential of the capacitor 32 reaches the threshold value triggered by the fact that the level of the first switching timing determination terminal P3 starts to rise using only the switching timing determination terminal P3, it is determined that the predetermined time T1 has elapsed. You may.

〇 It is also possible to eliminate the discharge line of the capacitor 32 via the diode 42 for discharge in FIGS. 1 and 6, and the electric charge accumulated in the capacitor 32 can be removed regardless of the discharge line via the diode 42. For example, it is also possible to discharge through the resistor 31 and the solenoid coil 100.

〇 In FIGS. 1 and 6, a diode 41 for preventing erroneous wiring is provided in the negative electrode line L2 between the external power supply 90 and the DC / DC converter 20, but the positive electrode between the external power supply 90 and the DC / DC converter 20 is provided. A diode for measures against erroneous wiring may be provided on the line L1. In this case, the anode of the diode is on the positive electrode side of the external power supply 90, and the cathode is on the voltage input terminal P1 side of the DC / DC converter 20. In addition, diodes for countermeasures against erroneous wiring may be provided on both the positive electrode line L1 and the negative electrode line L2 between the external power supply 90 and the DC / DC converter 20. In short, a diode for preventing erroneous wiring may be provided on at least one of the positive electrode line L1 and the negative electrode line L2 between the external power supply 90 and the DC / DC converter 20.

○ The switching elements 22 and 25 may be configured by an IGBT or the like in addition to the MOSFET.

10 ... solenoid drive circuit, 20 ... DC / DC converter, 22 ... switching element, 25 ... switching element, 27 ... control unit, 30 ... timer circuit, 31 ... resistor, 32 ... capacitor, 41 ... diode for miswiring countermeasures, 42 ... diode, 53 ... diode for surge voltage countermeasure, 90 ... external power supply, 100 ... solenoid coil, L1 ... positive voltage line, L2 ... negative voltage line, P1 ... voltage input terminal, P2 ... voltage output terminal, P3 ... first switching Timing determination terminal, T1 ... predetermined time, Vin ... input voltage, Vout ... output voltage.

Claims (5)

It is a solenoid drive circuit that inputs an external power supply voltage to energize the solenoid coil for driving the solenoid valve.
A DC / DC converter that has a switching element and outputs a constant voltage with respect to a fluctuating input voltage, while an external power supply is connected to the voltage input terminal and the solenoid coil is connected to the voltage output terminal.
A timer circuit that is composed of a resistor and a capacitor, is connected to the voltage output terminal of the DC / DC converter, and measures the voltage output time to the solenoid coil.
Equipped with
The DC / DC converter is
A control unit that controls the switching element of the DC / DC converter,
The switching timing determination terminal connected to the timer circuit and
Have,
Based on the state of the switching timing determination terminal, the control unit sets the output voltage of the DC / DC converter from the voltage up to that point when a time predetermined by the timer circuit elapses from the start of energization of the solenoid coil. A solenoid drive circuit characterized by switching to a lower voltage. The solenoid drive circuit according to claim 1, wherein the DC / DC converter has a SEPIC circuit structure. The solenoid drive circuit according to claim 1 or 2, wherein a discharge path is formed in the capacitor of the timer circuit. The solenoid drive according to any one of claims 1 to 3, wherein a diode for surge voltage countermeasures is connected in parallel to the solenoid coil between the DC / DC converter and the solenoid coil. circuit. The invention according to any one of claims 1 to 4, wherein a diode for preventing erroneous wiring is provided on at least one of the positive electrode line and the negative electrode line between the external power supply and the DC / DC converter. Solenoid drive circuit.

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