JPH0127286Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) The present invention relates to an electrostatic breakdown prevention circuit that is optimal for use in electronic circuits that use elements with low electrostatic withstand voltage such as MOS and LSI.

(Prior Art) Generally, active elements such as CMOS/LSI and FET are easily damaged by static electricity, so a circuit to prevent static electricity damage is essential for circuits using these types of active elements.

Therefore, conventionally, as shown in Figure 1, the input terminal IN
A capacitor C is inserted between the ground side terminal E of the electronic device and the GND of the electronic device case to bypass static electricity, thereby preventing the electrostatic damage described above.

However, in the conventional device described above, the ground side terminal E and the ground point E ₁ (in audio circuits, single point grounding is common in order to maintain characteristics)
The impedance Z that the earth wire E ₂ has,
A large loop was formed by the capacitor C and the chassis, and there was a possibility that oscillation or ringing would occur. Further, when the above-mentioned conventional technology is applied to a digital circuit, there is a problem that malfunction occurs due to oscillation or the like. Note that EQ indicates an equalizer, M indicates a muting circuit, and A indicates a main amplifier.

(Purpose of the invention) This invention eliminates the drawbacks of the conventional ones mentioned above,
It is an object of the present invention to provide an electrostatic damage prevention circuit that can not only accurately remove harmful static electricity but also has no risk of adversely affecting electronic circuits.

(Structure of the invention) The electrostatic damage prevention circuit according to the invention is designed to prevent electrostatic damage that should be inserted between the ground side terminal of the input end of an electronic circuit using an element with low electrostatic withstand voltage and the casing of an electronic device. The electrostatic damage prevention circuit is characterized in that two unidirectional elements are connected in parallel so that they have opposite polarities.

(Example) A second example of the electrostatic damage prevention circuit according to the present invention is shown below.
The explanation will be made based on the drawings and FIG. 3, and the same parts as those explained in FIG. 1 will be given the same reference numerals and the explanation thereof will be omitted.

In the figure, 1 indicates the entire electrostatic damage prevention circuit, which includes two unidirectional elements, diodes D ₁ and D ₂ in the illustrated example.
are connected in parallel so that they have opposite polarity,
One end thereof is connected to the ground side terminal E of the input terminal IN of the electronic circuit 2, and the other end thereof is connected to the electronic device case GND.

To explain an example of its operation in the above configuration, first, when high voltage static electricity is induced in the ground side terminal E and the voltage exceeds the threshold level of the diodes D ₁ and D ₂ , the impedance of the diode D ₁ or D ₂ increases. decreases rapidly, and harmful static electricity is absorbed into the GND side of the electronic device housing. Therefore, active elements in the electronic circuit 2, such as FETs used in the equalizer EQ, can be protected from electrostatic damage. In addition, if high voltage static electricity is not induced in the ground side terminal E, the diode D ₁ ,
Since D ₂ is in the off state, no loop is formed and there is no possibility of any adverse effect on the electronic circuit 2.

FIG. 3 shows another embodiment, in which two input terminals IN ₁
and IN ₂ , and the ground wire E ₂ is connected to Z ₁ , Z ₂ ,
If static electricity is induced in the input terminal IN ₁ or IN ₂ when the electrostatic breakdown prevention circuits 3 and ₄ according to the present invention are not installed, the impedance will be reduced due to the _above impedance. As a result, high voltage is induced at points _{P1 and P2} , and current flows from point _P2 through the muting circuit M and the muting drive circuit F in the _Z4 direction or toward the power source, destroying the element. However, as shown in the diagram, the diode
The static electricity can be eliminated by providing an electrostatic breakdown prevention circuit ₃ consisting of D 3 and D 4 and an electrostatic breakdown prevention circuit ₄ consisting of diodes D ₅ and D ₆ on the _P1 point side and the _P2 point side, respectively. It can be absorbed into the GND side of the electronic device case.

(Effects of the invention) According to the electrostatic breakdown prevention circuit according to the invention, static electricity induced on the input end side of an electronic circuit can be appropriately absorbed, and elements in the electronic circuit can be protected. Of course, it does not create harmful feedback loops in the electronic circuit.
There is no risk of oscillation or malfunction, especially
It is ideal as an electrostatic damage prevention circuit for electronic circuits using CMOS, LSI, etc.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an application example of a conventional electrostatic damage prevention circuit, and FIGS. 2 and 3 are circuit diagrams showing an embodiment of the electrostatic damage prevention circuit according to the present invention. 1, 3, 4...Electrostatic breakdown prevention circuit, 2...Electronic circuit, _D1 to _D6 ...Diode as a unidirectional element.

Claims (1)

[Scope of Claim for Utility Model Registration] An electrostatic damage prevention circuit to be inserted between the earth side terminal of the input end of an electronic circuit using an element with low electrostatic withstand voltage and the casing of an electronic device, The electrostatic breakdown prevention circuit is characterized in that two unidirectional elements are connected in parallel so that they have opposite polarities.