JPH0442616Y2 - - Google Patents

Description

[Detailed explanation of the idea] [Industrial application field]

The present invention relates to a circuit for detecting the cutoff current of a solenoid valve, and in particular, the solenoid valve is connected in series with a detection resistor through a switching element, and the cutoff current is detected by the detection resistor. Regarding a detection circuit.

[Summary of the idea]

The present invention connects a detection transistor in parallel with the switching element, connects the base of this transistor to the opposite terminal of the solenoid valve, and connects the collector of this transistor to the connection point between the switching element and the detection resistor. When the current to the solenoid valve is cut off, a surge current flows through the detection resistor, thereby reliably detecting demagnetization of the solenoid valve.

[Conventional technology]

A conventional solenoid valve drive circuit is constructed as shown in FIG.
I was trying to connect it. and diode 4
is connected in parallel with coil 1, and when switching transistor 2 is turned non-conductive,
A surge voltage generated in the coil 1 causes current to be returned to the power source via the diode 4.

[Problem that the invention attempts to solve]

The drawbacks of such conventional solenoid valve drive circuits are:
No surge current flows through the detection resistor 3 connected in series with the switching transistor 2. That is, when the switching transistor 2 is cut off, the surge current flows through the diode 4 to the power supply side, so that no surge current flows through the resistor 3 at all. Therefore, according to such a conventional circuit, a potential difference is not generated in the detection resistor 3 due to the surge current, making it impossible to detect the shutoff of the solenoid valve using the surge current. Therefore, the conventional circuit has the disadvantage that it cannot reliably detect de-energization of the solenoid valve. The present invention was developed in view of these problems, and detects the shutoff operation of a solenoid valve by effectively utilizing the surge current generated in the coil that constitutes the solenoid valve when the solenoid valve is demagnetized. It is an object of the present invention to provide a cut-off current detection circuit for a solenoid valve.

[Means to solve the problem]

The present invention provides a circuit in which a solenoid valve is connected in series with a detection resistor via a switching element, and a detection transistor is connected in parallel with the switching element in a circuit in which a cut-off current is detected by the detection resistor. The base of the detection transistor is connected to the opposite terminal of the electromagnetic valve, and the collector of the detection transistor is connected to the connection point between the switching element and the detection resistor.

[Effect]

Therefore, according to the present invention, when the switching element is cut off and the coil of the electromagnetic valve is demagnetized, the detection transistor is turned on by the back electromotive force, and a surge current flows through the transistor to the detection resistor. Therefore, the surge current creates a potential difference in the detection resistor, making it possible to reliably detect the shutoff of the solenoid valve.

【Example】

The present invention will be explained below with reference to an illustrated embodiment.
FIG. 1 shows a cutoff current detection circuit for a solenoid valve according to an embodiment of the present invention, in which a coil 10 constituting the solenoid valve is connected in series with a switching transistor 11; A detection resistor 12 is connected to the terminal. and the above switching transistor 1
The detection transistor 13 is connected in parallel to the transistor 1. Note that the switching transistor 11 is composed of an NPN transistor, whereas the detection transistor 13 is composed of a PNP transistor. Moreover, the base of the detection transistor 13 is connected to the power supply terminal 14 on the opposite side of the coil 10. In the above configuration, when a current is passed through the control terminal 15 to the base of the switching transistor 11, the transistor 11 becomes conductive, thereby exciting the coil 10. In other words, the solenoid valve 10 is energized. Next, when the base current to the control terminal 15 is cut off, the switching transistor 1
1 becomes non-conducting, thereby demagnetizing the coil 10 and deenergizing the solenoid valve. When demagnetizing the coil 10, this coil 10
A back electromotive force is generated, and the voltage at the negative terminal becomes higher than that at the positive terminal. That is, a surge voltage is generated in the coil 10. This coil 1
A surge voltage of 0 causes a base current to flow from the emitter to the base of the transistor 13, thereby making the PNP transistor 13 conductive. Therefore, the surge current accompanying the back electromotive force generated in the coil 10 flows from the coil 10 to the detection resistor 12 through the emitter and collector of the transistor 13. Therefore, this detection resistor 1
A potential difference is generated between both ends of the solenoid valve 2, and this potential difference makes it possible to detect the shut-off state of the solenoid valve.

[Effect of the idea]

As described above, the present invention connects a detection transistor in parallel with the switching element that controls the solenoid valve, connects the base of the detection transistor to the opposite terminal of the solenoid valve, and connects the collector of the detection transistor to the switching element. It is connected to the connection point between the element and the detection resistor. Therefore, with such a configuration, when the solenoid valve is cut off, the detection transistor is turned on by the back electromotive force generated in its coil, and a surge current flows through the transistor to the detection resistor.
It becomes possible to reliably detect the shutoff of the solenoid valve. Moreover, since the current due to the surge voltage is directly supplied to the detection resistor by the detection transistor without passing through the switching element, the surge voltage is not applied to the switching element, or the current is not applied to the switching element suddenly. No current associated with surge voltage flows, thereby making it possible to prevent deterioration of the switching element and extend its life. In addition, since the current associated with the surge voltage is not supplied to the switching element, the switching element will not malfunction.
The desired operation will be performed accurately.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a cut-off current detection circuit for a solenoid valve according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional cut-off current detection circuit for a solenoid valve. In addition, in the symbols used in the drawings, 10...Solenoid valve (coil), 11...Switching transistor, 12...Detection resistor, 13...Detection transistor, 14...Power terminal, 15...Control terminal , is.

Claims (1)

[Scope of Claim for Utility Model Registration] In a circuit in which a solenoid valve is connected in series with a detection resistor via a switching element, and the detection resistor is used to detect a breaking current, a detection resistor is connected in parallel with the switching element. connecting a transistor, and connecting the base of the detection transistor to the opposite terminal of the solenoid valve;
A cutoff current detection circuit for a solenoid valve, characterized in that a collector of the detection transistor is connected to a connection point between the switching element and the detection resistor.