JPS6323875Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is intended to prevent damage and deterioration of circuit elements (particularly semiconductor active elements such as ICs and transistors) due to discharge current caused by internal discharge of a cathode ray tube and fluctuations in ground potential. Regarding the protection circuit around the cathode ray tube.

In cathode ray tubes, discharge may occur between the electrodes due to dust entering the tube or scratches on the electrodes.

The area where this type of discharge is most common is between the focus electrode and the high-voltage electrode, and it has been confirmed that during discharge, a discharge current of several 100 A flows from the focus electrode to the ground circuit in a period of several 100 nanoseconds. High-energy pulses (several tens of nanoseconds) are applied to semiconductor components in a short period of time due to electromagnetic induction caused by currents.
is applied, resulting in fatal damage.

This point will be explained with reference to FIG. 1, which shows the connection relationship between the cathode ray tube 2 including the electron gun 1 and its surrounding parts, and FIG. 2, which shows an equivalent circuit diagram at the time of interelectrode discharge.

Now, as in the above example, if a discharge occurs between the focus electrode G ₄ and the high voltage electrodes G ₃ and G ₅ ,
The electric charges accumulated in the high-pressure capacitance C formed by the interior carbon coating 4 and the exterior carbon coating 5, which are respectively coated on the inner and outer surfaces of the cone portion leading to the funnel portion 3 of the cathode ray tube 2, are G ₅ , G ₃ electrode → G ₄ electrode → Spark gap 6
→A discharge occurs along the route of the ground terminal 7, and a large current path is formed momentarily. Note that 8 indicates an anode electrode to which high voltage Hv is applied.

Furthermore, the digital processing circuits often used in recent television sets are prone to malfunction due to pulse noise, and therefore require a sufficient protection circuit. A method of increasing the resistance of the interior carbon coating 4 has been considered as a method of suppressing the discharge flow during the discharge inside the cathode ray tube. However, in this method, the capacitance for applying high voltage (several hundred PF) is a distributed capacitance with the entire surface of the interior carbon coating as a positive pole, so current flows with low resistance from the capacitance near the high voltage electrode _G5 , and the pulse width Although it becomes narrower, the rising current value hardly decreases, and the ground potential fluctuates depending on the impedance of the ground circuit that it passes through.

Furthermore, as shown by the dotted line in FIG. 2, it is possible to insert a resistor 9 in series with the ground terminal 7 to reduce the discharge current, but in that case, the ground side electrode 10 of the spark gap 6 The drawback remains that the potential does not drop much.

Furthermore, _in consideration of this point, as _shown by the dotted line in FIG. resistance 1
It is also possible to insert a resistor 2 or 13, but this not only increases the manufacturing cost of the cathode ray tube 2, but also has the disadvantage that it cannot be applied to a cathode ray tube that does not have such a built-in resistor. It was done. Furthermore, in the event that the resistor is destroyed or disconnected, the resistor alone cannot be replaced and the cathode ray tube must be replaced.

The present invention was devised in view of the various drawbacks of the conventional examples.

Hereinafter, the present invention will be explained with reference to FIGS. 3 to 6. Figure 3 shows an electron gun 1 implementing the present invention.
4 shows the connection relationship between the cathode ray tube 2 including the cathode ray tube 2 and its surrounding parts, and FIG. 4 shows an equivalent circuit diagram at the time of interelectrode discharge. 5 and 6 show an embodiment of the present invention.

For convenience of explanation hereinafter, common reference numerals are given to the same components in each drawing of FIGS. 3 to 6.

Now, in the cathode ray tube 2, high voltage electrodes G ₃ ,
If a discharge occurs from G ₅ to the focus electrode G ₄ , the charge accumulated in the capacitance C formed between the inner and outer carbon coatings 4 and 5 of the cone portion of the cathode ray tube 2 will be transferred to the inner carbon coating 4 . → High voltage electrodes G ₅ , G ₃ → Focus electrode G ₄ → Focus stem pin 18 → Socket 15 of cathode ray tube socket 14 → Focus external protruding terminal 16 of the socket
→Resistor R→Spark gap 6→Earth terminal 7
→ Earth load G → Discharge occurs through the route of the exterior carbon coating 5, which is the negative electrode of the capacitor C. Therefore, since the discharge current flows through the resistor R connected in series with the discharge circuit, it is sufficiently attenuated, and at the same time, the high frequency component of the discharge flow flows through the earth lead G. The induced rise in the potential of the ground terminal 7 is also suppressed to a small level by the resistor R. Comparing this point between the conventional example and the present invention, it is found that 450A without the resistor R
While a discharge current of about
In the case of 20KΩ, the discharge current will be about 1A, which is significantly reduced. Also, the potential of the ground terminal 7 is the resistor R
If there is no resistor, it is 12.8Kv, and if the resistor R is 20KΩ, it can be significantly reduced to 1.2Kv.

It should be noted that the insertion position of the resistor R must be limited to between the focus external projecting terminal 16 provided in the socket 14 and the spark gap 6. If you only want to reduce the discharge current, you can insert a resistor R in series from the spark gap 6 to the ground terminal 7 or the ground lead G, but in that case, the impedance of the focus lead wire 17 should be In the latter case, the impedance on the ground terminal 7 side increases significantly, which is dangerous.In the latter case, not only the impedance on the ground side increases, but also the potential on the ground terminal 7 increases when a discharge occurs. , the ground potential of the signal system connected to the terminal also rises, which adversely affects the IC of the circuit. Furthermore, if a resistor R is inserted between the spark gap 6 and the focus lead wire 17, it cannot be expected to have the effect of suppressing the problematic discharge current, but if a certain resistance is inserted on the focus voltage supply circuit side, There is nothing different about it.

In FIG. 5 showing an embodiment of the present invention, a focus external projecting terminal 16 protruding from a socket 14 integrated on a printed circuit board 20 has a resistor R connected thereto without being relayed to the printed circuit board 20. One end of the spark gap body 6' is connected to the ground terminal 7 on the printed circuit board 20, and the other end is connected to the other end of the resistor R and the focus lead wire 17. The connection point (hereinafter referred to as point A) between the lead terminal of the resistor R, one end of the spark gap body 6', and the focus lead wire 17 is also the fifth point.
As shown in the figure, the focus lead wire 1 is not relayed to the printed circuit board 20.
7 is gripped by a band 19 glued to the socket 14. By not relaying anything other than the ground terminal 7 of the spark gap body 6' to the printed circuit board 20 in this way, the printed circuit board 2
This prevents electrical discharge to the parts and circuits on the 0.
Furthermore, if the focus external protruding terminal 16 and the point A portion of the socket are covered with an insulator, an even more insulating effect can be obtained.

FIG. 6 is also an embodiment of the present invention, but compared to the embodiment of FIG. It is fixed by a provided band 19. In this embodiment, it is also conceivable to attach an insulating cover that completely covers the resistor R, the spark gap body 6, and the point A portion.

When implementing the present invention, only the focus spark gap [the spark gap located between the focus electrode _G4 and the ground terminal 7] is provided externally together with the resistor R as shown in FIGS. 5 and 6, and other The spark gap (for example, the spark gap between the electrodes G ₁ , G ₂ , etc. and the ground terminal 7) may be disposed within the cathode ray tube socket 14.

According to the cathode ray tube peripheral protection circuit in which this invention has been implemented, even if the current limiting resistor R is damaged, only that resistor R needs to be replaced. It has the effect of preventing component destruction and digital circuit malfunction, making it possible to produce extremely reliable products.

[Brief explanation of drawings]

Fig. 1 is a connection diagram of a cathode ray tube and a conventional peripheral circuit, Fig. 2 is an equivalent circuit during tube discharge in a conventional example, Fig. 3 is a connection diagram of a cathode ray tube and a peripheral circuit of the present invention, and Fig. 4 is a connection diagram of a cathode ray tube and a peripheral circuit of the present invention. FIGS. 5 and 6, which are equivalent circuit diagrams at the time of internal discharge when the cathode ray tube peripheral circuit is used, show perspective views of the cathode ray tube peripheral circuit in which the present invention is implemented. 2... Braun tube, 6... Spark gap,
14...Cathode ray tube socket, 16...External protruding terminal for focus, 20...Printed circuit board, G ₄
...Focus electrode, R...resistance.

Claims (1)

[Scope of utility model registration request] A terminal led out so as to protrude outward from the cathode ray tube socket into which a stem pin connected to the focus electrode of the cathode ray tube is fitted, and a spark gap whose one lead terminal is connected to the ground foil of the printed circuit board integrated into the cathode ray tube socket. and a current limiting resistor connected between the other lead terminal of the spark gap and the external protruding terminal of the socket.