JPS596448Y2 - voltage detector - Google Patents

Description

[Detailed description of the invention] This invention relates to a voltage detector that detects the presence or absence of voltage with high sensitivity.Even if there is a high-resistance coating on a conductor or other part to which voltage is applied, the probe is simply applied. The object of the present invention is to obtain a voltage detector that has high sensitivity so that detection can be performed by itself, is simple in construction, easy to assemble, and is suitable for miniaturization.

The present invention consists of a depression-type field effect transistor that has a case made of an insulating material, a probe whose tip protrudes from the case, and a gate connected to the probe through a high resistance. A transistor having a base connected to the drain of the transistor, a light-emitting diode connected in series with the emitter-collector path of the transistor, a DC power supply connected between the series circuit of the transistor and the light-emitting diode, and the DC power supply and the light-emitting diode. and a high resistance element whose connection point is connected between the probe and the source of the field effect transistor to connect the transistor and the light emitting diode so that the forward voltage generated between the light emitting diode The device is characterized in that a depletion type field effect transistor is biased near its cutoff state to obtain high sensitivity.

In the voltage detector of the present invention, a field effect transistor with extremely high input impedance is used as an active element, and by biasing this transistor near the cutoff state by the forward voltage of the light emitting diode, the high input impedance characteristic of the field effect transistor is improved. It maintains high sensitivity without loss, and does not require a special bias circuit, simplifying the structure.

An embodiment of the present invention will be described based on the drawings.

In Fig. 1, reference numeral 1 denotes a case to be held by hand, and this case 1 is connected to the ground via the user.A metal tube 2 is connected to the tip of the case 1, and a vinyl case is placed inside the metal tube 2. A cylindrical body 3 made of synthetic resin such as
A metal probe 4 is held by this cylindrical body 3.

The cylindrical body 3 constitutes a resistance, which will be described later, and has an extremely high resistance value.

The probe 4 is connected to an N-channel depletion field effect transistor (hereinafter referred to as FET) via a protective resistor 5.
(abbreviated as ) is connected to the gate of 6.

A light emitting diode 8 is connected between the source of this FET 5 and one pole 7 serving as a ground.

In addition, the drain of the FET6 is connected to a P
A current limiting resistor 11 is connected between the collector and emitter of the NP type transistor 9 and a ten pole 10, and is also connected to the light emitting diode 8.

Note that the resistor 12 and the capacitor 13 have equivalent values such as those of the human body.

Further, a resistor 14 having an extremely high resistance value is connected between the probe 4 and the single pole 7.

Further, reference numeral 15 denotes a conductive wire which is a voltage-tested portion and is covered with an insulator 16 .

In such a structure, when the case 1 is held and the probe 4 is brought into contact with the insulator 16, a signal voltage is generated at the gate of the FET 6 if a voltage is applied to the conducting wire 15.

That is, even if the resistance value of the insulator 16 is extremely high, there is a resistor 14 with a resistance value of the same level or higher.
A sufficient voltage can be obtained and FET 6 becomes conductive.

As a result, the drain current In, which becomes the base current 8 of the transistor 9, increases, and this drain current 2 increases.

A collector current 6 whose current value is multiplied by β flows through the light emitting diode 8, so the light emitting diode 8 emits light.

In addition, when no voltage is applied to the conductor 15, the FE
No voltage is applied to the gate of T5.

And ■ to 10 poles.

Since a voltage of C is applied, an extremely small drain current ■ is applied to FET6.

However, this drain current ID generates a voltage between the anode and cathode of the light emitting diode 8, and the FET is cut off.

The drain current at this time is ■.

In some cases, the light emitting diode 8 does not emit light.

Therefore, the present invention does not require a special bias circuit for biasing the FET, making the structure simple.

Further, since the voltage drop across the light emitting diode 8 has a value that biases the FET near its cutoff state, the detection sensitivity becomes extremely high.

As mentioned above, the present invention connects a probe with an extremely high resistance connected to the ground to the gate of an FET, and uses this FET to control the transistor of the amplifier circuit and energize the light emitting diode. Since the input impedance of the FET is extremely high, it is possible to obtain a sufficient signal voltage even if there is an insulator in the voltage section to be tested. Can be detected with high sensitivity.

Furthermore, since a light emitting diode is connected between the gate and source of the FET, the FET is biased near its cutoff state due to the voltage drop across the diode, resulting in high sensitivity, a reduced number of parts, and easy assembly.

Furthermore, by using a resin cylinder that holds the probe as a resistor with an ultra-high resistance value, it is possible to obtain a high resistance extremely easily.

In order to increase the sensitivity of an electroscope, it is known to use active elements with high input impedance, such as field effect transistors.

There are two types of field effect transistors: a compression type and an enhancement type, and the gate voltage versus source drain current characteristics of each type are shown by curves A and B in FIG. 3.

When such a transistor is used as an active element of a voltage detector, it is not necessary to apply a bias in the enhancement type, but it is necessary to apply a bias in the depletion type.

Therefore, in terms of circuit structure, an enhancement type that does not require a bias circuit is advantageous, but the rise of the characteristic curve is slow and the desired source-drain current does not flow unless the gate voltage increases to a certain extent, so the sensitivity is high. It won't happen.

On the other hand, depression. For Yon type, for example, the gate bias voltage is -V.

If it is set near the rising part of the characteristic curve A, a desired large source-drain current will flow even if the gate voltage increases slightly, and the sensitivity will be extremely high.

In the present invention, the depletion type field effect transistor 6 is used in consideration of the above-mentioned points, and the bias voltage -○ is extracted from the forward voltage of the light emitting diode 8, thereby eliminating the need to provide a special bias circuit, and thereby eliminating the need for a special bias circuit. It was possible to simplify something.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, in which Fig. 1 is a partially cutaway side view, Fig. 2 is a circuit diagram, and Fig. 3 shows gate voltage versus source of depletion type and enhancement type field effect transistors. 3 is a graph showing a pseudo drain current characteristic curve. 2...Metal cylinder, 3...Cylinder body, 4...
... Probe, 6 ... FET, 8 ... Light emitting diode, 9 ... Transistor (amplification circuit), 14 ... Resistor.

Claims (1)

[Scope of utility model registration request] A depletion type field effect transistor has a case made of an insulating material, a probe whose tip protrudes from the case, a gate connected to the probe through a high resistance, and a drain of the field effect transistor. A transistor having connected bases, a light emitting diode connected in series with the emitter-collector path of the transistor, a DC power supply connected between the series circuit of the transistor and the light emitting diode, and a connection point between the DC power supply and the light emitting diode. and a high resistance element connected between the probe and the probe, the source of the field effect transistor is connected to the connection point between the transistor and the light emitting diode, and a depletion type field effect is generated by the forward voltage generated between the light emitting diode. A voltage detector characterized in that a transistor is biased near its cutoff state to obtain high sensitivity.