JP2585925Y2 - Grounding device for high voltage supply line - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grounding device for a high-voltage supply line which, when an overcurrent flows in a high-voltage supply line for supplying a high voltage to an electrostatic coating machine or the like, releases the overcurrent to the ground.

[0002]

2. Description of the Related Art A grounding device of this type is provided with a semiconductor switch in a grounding circuit for connecting a high-voltage supply line for supplying a high voltage to an electrostatic coating machine and the ground, and usually has a non-grounding circuit. By maintaining the conductive state and short-circuiting the ground circuit when an overcurrent is detected to detect an overcurrent, the residual charges are instantaneously discharged to prevent the occurrence of a spark. A thyristor is used as a switching element of a semiconductor switch, and in a device to which a high voltage of several tens of kV is applied as in an electrostatic coating machine, a potential applied to each thyristor is reduced to increase a high voltage. A large number of thyristors are connected in series so as to withstand the load.

[0003]

However, since the thyristor has a low input impedance, a large drive current is required to correctly operate as a switch.
Therefore, a power supply device having a large capacity must be used, and there is a problem that equipment costs increase. In addition, when a large number of thyristors are connected in series as described above, even if a rated drive current is applied to each thyristor, there is a variation in each of them, so that it is difficult to drive all of them simultaneously. there were.

[0004] Accordingly, the present invention has a technical problem to operate all switches connected in series simultaneously and reliably without using a special power supply device, and to instantaneously short-circuit a ground circuit. And

[0005]

According to the present invention, a plurality of short-circuiting semiconductor switches are connected in series to a ground circuit connecting a high voltage supply line to which a predetermined high voltage is supplied and a ground. The semiconductor switch has a source terminal and a drain terminal of a field effect transistor serving as a switching element connected to a high voltage side and a ground side of the ground circuit, and has a non-conductive bias between the source terminal and the drain terminal. A resistance, a conduction bias resistance and a high resistance are connected in series, and a contact between the non-conduction bias resistance and the conduction bias resistance is connected to a gate terminal. A capacitor charged by a voltage equal to or higher than the threshold voltage of the field effect transistor due to the voltage drop effect of Sa is the source terminal of the field effect transistor via a light receiving element to be connected during reception of the signal light emitted from the control light emitting section - characterized in that connected between the gate terminal.

According to the present invention, the field effect transistor is normally in a non-conductive state, and when a predetermined high voltage is applied to the high voltage supply line, the voltage drop effect of the non-conductive bias resistance and the conductive bias resistance is obtained. The capacitor is charged with a voltage higher than the threshold voltage generated by the above. Then, for example, when an overcurrent flows in the high-voltage supply line, the light emitting element for control of each semiconductor switch irradiates a signal light to the light receiving element, whereby the light receiving element becomes conductive and at the same time, a threshold from each capacitor. Since a voltage equal to or higher than the value voltage is output and applied between the source terminal and the gate terminal of each field effect transistor, the source terminal and the drain terminal are brought into conduction. Therefore, when an overcurrent flows through the high-voltage supply line, the ground circuit is turned on, so that the residual charge remaining in the high-voltage supply line can be instantaneously released to the ground, and the occurrence of spark can be prevented.

Next, when the discharge of the capacitor is completed, the voltage higher than the threshold voltage is not applied between the source terminal and the gate terminal from the capacitor, so that the supply of the high voltage to the high voltage supply line is turned off. In this case, the source terminal and the drain terminal of the field effect transistor become non-conductive, and the ground circuit is cut off. Then, after confirming safety, start supplying high voltage to the high voltage supply line.
Charging of the capacitor is started again. Since the field effect transistor serving as a switching element has high impedance, it can be reliably operated with a small current output from a capacitor, and simultaneously irradiate the light receiving element of each semiconductor switch connected in series with signal light. By
All the semiconductor switches can be operated simultaneously and reliably.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a circuit diagram showing a main part of a grounding device according to the present invention, and FIG. 2 is a flow sheet showing an electrostatic coating device using the grounding device.

The grounding device according to the present invention provides a high voltage supply for applying a high voltage of, for example, −50 kV from the high voltage generator 2 to the electrostatic coating machine T disposed opposite to the grounded work W. A grounding circuit 5 is connected between the line 3 and the ground 4, and the grounding circuit 5 accommodates, for example, ten semiconductor switches 1, 1,. ing.

In each of the semiconductor switches 1, 1..., The source terminal 7 S of the field effect transistor 7 serving as a switching element is connected to the high voltage supply line 3 side of the ground circuit 5, and the drain terminal 7 D is connected to the ground circuit 5. It is connected to the earth 4 side. A non-conducting bias resistor R ₁ , a conducting bias resistor R ₂ and a high resistor R ₃ are connected in series between the source terminal 7 S and the drain terminal 7 D.
The contact of the non-conductive bias resistor R ₁ and the conductive bias resistor R ₂ is connected to the gate terminal 7G.

The non-conductive bias resistor R ₁ and the conductive bias resistor R ₂ are connected to the respective resistors R ₁ and R _2.
A capacitor 10 charged with a voltage equal to or higher than the threshold voltage of the field-effect transistor 7 due to the voltage drop effect of is connected in parallel to form a power supply circuit 8. The power supply circuit 8 is connected to a source terminal 7S-gate terminal 7G of the field effect transistor 7 via a light receiving element 9 which is turned on when receiving the signal light emitted from the control light emitting section 12.
Connected between them.

In this example, ten semiconductor switches 1 and 10 are connected to a ground circuit 5 having a potential difference of 50 kV applied to both ends.
Are connected in series, the potential difference applied to both ends of each semiconductor switch 1 is 5 kV. Here, the resistance values of the resistors R ₁ , R ₂ , and R ₃ are 200 kΩ and 500 k, respectively.
If Ω and 500 MΩ are selected, the voltage drop at each of the resistors R ₁ and R ₂ is about 2 V and about 5 V, respectively. When the field effect transistor 7 having the threshold voltage V _T = 5 V is used, when the light receiving element 9 is in a non-conductive state,
A non-conductive bias of about 2 V is applied between the S-gate terminal 7G, the non-conductive state is maintained between the source terminal 7S and the drain terminal 7D, and 2 + 5 =
A voltage of 7 V is applied to charge.

The control light emitting unit 12 for irradiating the light receiving element 9 with signal light includes, for example, an overcurrent detector 13 provided in the high voltage generator 2 when an overcurrent flows through the high voltage supply line 3. , A light source (not shown) such as a flash is turned on to output a signal light, and the signal light is applied to the light receiving element 9 via the optical fiber 14. Therefore, the light source can be provided outside the coating booth, and there is no danger of igniting the organic solvent or the like in the atomized state.

The light receiving element 9 conducts only while the control light emitting section 12 is irradiating the light receiving element 9 with the signal light, and the voltage output from the capacitor 8 is applied between the source terminal 7S and the gate terminal 7G. Applied, the source terminal 7S-
Since the connection between the drain terminals 7D is conducted, the semiconductor switch 1 is turned on. When the discharge of the capacitor 10 is completed or the irradiation of the signal light to the light receiving element 9 is stopped, the light receiving element 9 is turned off and the source terminal 7S
Since no voltage is applied between the gate terminal 7G and the source terminal 7S-drain terminal 7D is turned off, the semiconductor switch 1 is cut off.

The above is an example of the configuration of the present invention, and its operation will be described next. First, in a normal state, the signal light is not irradiated to the light receiving element 9 and while the light receiving element 9 is in a non-conductive state, the capacitor 10 of the power supply circuit 8 is connected to the non-conductive bias resistance R ₁ and the conductive bias resistance R _2. Is charged at a voltage (7V) higher than the threshold voltage V _T = 5V.

When the overcurrent detector 13 detects an overcurrent at which there is a danger of spark discharge due to an abnormal approach between the electrostatic coating machine T and the workpiece W, first, the high-voltage generator 2 is turned off. At the same time, a signal light such as a flash is output from the overcurrent detector 13 and irradiates the light receiving elements 9 of the respective semiconductor switches 1, 1,... Via the optical fiber 14, whereby all the light receiving elements 9 are simultaneously driven. It becomes conductive. Therefore, all the semiconductor switches 1 interposed in the ground circuit 5
The capacitor 10 is discharged, between the source terminal 7S- gate terminals 7G of the field effect transistor 7, and a voltage higher than the threshold voltage V _T is applied, between the source terminal 7S- drain terminal 7D is rendered conductive at the same time As a result, the ground circuit 5 is short-circuited, so that the residual charge remaining in the high-voltage supply line 3 and the electrostatic coating machine T is instantaneously discharged to the ground 4, and a spark discharge between the electrostatic coating machine T and the workpiece W is generated. Can be prevented beforehand.

Since each semiconductor switch 1 uses a field effect transistor 7 having a relatively high impedance as a switching element, it can be reliably operated by a small drive current of the capacitor 10 or the like.

[0018] When the discharge of the capacitor 10 is completed, since the light receiving element 9 is turned off, the voltage applied between the source terminal 7S- gate terminal 7G becomes below the threshold voltage V _T, the source Terminal 7S-Drain terminal 7
D is in a non-conductive state, and the ground circuit 5 is cut off.
Therefore, in this state, if the safety is confirmed and the high voltage generator 2 is turned on again, a high voltage can be applied to the electrostatic coating machine T.

[0019]

As described above, according to the present invention, a high-impedance field-effect transistor is used as a switching element, and it operates reliably with a small current output from a photovoltaic cell or a capacitor. There is an effect that the circuit is small and can be reliably operated with a small drive current. In addition, since the field effect transistor is short-circuited by simultaneously irradiating the light receiving element of each semiconductor switch with the signal light, even when a large number of semiconductor switches are connected in series to the ground circuit. Has the effect that they can be operated simultaneously and reliably. In addition, for capacitors, the voltage higher than the threshold voltage of the field effect transistor can be charged by the high voltage applied to the high voltage supply line during normal operation. And the field effect transistor can be operated with the voltage output from the capacitor.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a main part of a grounding device according to the present invention.

FIG. 2 is a flow sheet showing an electrostatic coating device using the grounding device according to the present invention.

[Explanation of symbols]

1 ··· Semiconductor switch 3 ··· High voltage supply line 4 ··· Ground 5 ··· Ground circuit 7 ··· Field effect transistor 7G ··· Gate terminal 7S ··· Source terminal 7D ... Drain terminal R ₁ ... Non-conducting bias resistor R ₂ ... Conducting bias resistor R ₃ ... High resistance 9 ... Light receiving element 10 ... Capacitor 12 ... Emission for control Department

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-119321 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H03K 17/10 H03K 17/687

Claims (1)

(57) [Scope of request for utility model registration] A ground circuit (5) for connecting a high voltage supply line (3) to which a predetermined high voltage is supplied and a ground (4),
A plurality of short-circuiting semiconductor switches (1, 1...) Are connected in series, and the semiconductor switch (1) has a source terminal (7S) and a drain terminal (7D) of a field-effect transistor (7) serving as a switching element. A non-conducting bias resistor (R ₁ ), a conducting bias resistor (R ₂ ) and a non-conducting bias resistor (R ₁ ) are connected between the source terminal (7S) and the drain terminal (7D) of the ground circuit (5). A high resistance (R ₃ ) is connected in series, and a contact between the non-conductive bias resistor (R ₁ ) and the conductive bias resistor (R ₂ ) is connected to a gate terminal (7G); ₁ ) and the conduction bias resistor (R ₂ ), the capacitor (10) charged with a voltage equal to or higher than the threshold voltage of the field effect transistor (7) due to the voltage drop effect of the resistors (R ₁ , R ₂ ). ) Are connected in parallel, said capacitor (10) Is a light-receiving element (9) that becomes conductive when receiving signal light emitted from the control light-emitting unit (12).
A grounding device for a high-voltage supply line, which is connected between the source terminal (7S) and the gate terminal (7G) of the field effect transistor (7) via a gate.