JPH0536979A - Surge protective element - Google Patents

Abstract

PURPOSE:To prevent an operation starting voltage from being increased more than a breakdown strength to contrive the improvement of the surge protection power of a surge protection element by a method wherein the element has a structure consisting of four layers of P1, N2, P3 and N4 layers and the N2 layer and the P3 layer, which are exposed, are respectively short-circuited with the P1 layer and the N4 layer by metallic electrodes. CONSTITUTION:A unidirectional thyristor consists of four layers of P1, N2, P3 and N4 layers from a circuit constitution to burden a reverse breakdown strength with diodes D1 and D2 and diodes D3 and D4 and one part of the N2, layer and one part of the P3 layer respectively penetrate the P1 layer and the N4 layer and are respectively exposed in the surface and rear of the thyristor. Moreover, the thyristor is formed into a reverse conduction type constitution, wherein these exposed parts are respectively short-circuited with the P1 layer and the N4 layer by metallic electrodes T1 and T2. A breakdown of the thyristor is set so as to begin when exceeding a mere yielding of a junction J2, that is, a breakdown voltage VB, of the junction J2, to break down a relation of VBO<VCL and to satisfy the relation of VBO=VCL. Provided that, the VBO is a breakdown strength and the VCL is an operating voltage. Thereby, the realization of an increase in a holding current is contrived and a protection power and a cut-off power can e improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surge protection element suitable for surge protection of a weak electric circuit such as a communication circuit.

[0002]

2. Description of the Related Art As a means for protecting a weak electric circuit such as a communication circuit from positive and negative surges, a surge protection element which is small and inexpensive and operates at high speed, for example, as shown in FIG.
There is known a bidirectional thyristor type surge protection device of V _BO ignition which is composed of five layers of P ₁ N ₁ PN ₂ P _{3 and has} the characteristics shown in FIG. 4 (b). This element Z is used by being connected between the lines L of the protected circuit G such as a communication circuit as shown in FIG. 4C, and the positive or negative surge voltage S ₁ that has entered the line L.
When S ₂ exceeds the withstand voltage V _BO of the element Z, it is turned on and a current is passed through the element Z so that a voltage higher than the withstand voltage V _BO is not applied to the protected circuit G. Further, when the current flowing through the element Z decreases and falls below the protection current I _H of the element Z, an operation for interrupting the follow current based on the DC power supply voltage E and the line resistance R to restore the normal state is performed.

[0003]

By the way, in order to perform a better surge protection element with such a surge protection element, it is required that the element has the following conditions. Withstand voltage V _BO is greater than DC power supply voltage E, that is, V _BO > E
While satisfying the conditions of, the protection capacity should be improved as small as possible. The holding current I _{H of the} element is I _H > E / R
While satisfying the above, try to improve the breaking ability by making it as large as possible. Large surge current capability. In order not to deteriorate the communication performance of the protection circuit which is the protected circuit G, the capacitance C of the element inserted between the lines L is minimized as shown in FIG. Withstand voltage V of element Z
_BO is V _BO = V _B (1-α) ^{1 /} , where V _B is the reverse breakdown voltage of the junction J ₂ or J ₃ in FIG. 4A and α is the current amplification factor of the constituent transistor N ₁ PN _2. ⁿ ………… (1) However, it is determined by n: 2-6. Therefore, the rising speed dV of the surge voltage
If / dt becomes large, the operation start voltage at the time of applying a surge is not determined by the withstand voltage V _BO , and the voltage higher than V _BO is outside V _CL 1
It becomes V _B. Therefore, in order to have good protection ability, V _BO =
Satisfy the relationship with V _CL . Is required. However, as is well known, for example, when the breakdown voltage V _BO is reduced, the electrostatic capacitance C of the element Z is increased. Depending on the structure of the bidirectional thyristor, it is not easy to satisfy the above conditions at the same time.

[Outer 1]

[0004]

SUMMARY OF THE INVENTION Among the above-mentioned requirements, the present invention aims to realize a withstand voltage (V _BO ) = operating voltage V _CL and an increase in holding current I _H , in particular, in order to realize protection ability and interruption ability. The purpose of the present invention is to present a surge protection element that is an improvement over the bidirectional thyristor type surge protection element.

[0005]

The objects of the present invention are achieved by the following means. That is, as shown in FIG. 1 (a), the diodes D which are in the forward direction with respect to the positive surge S ₁ respectively.
₁ and a one-way thyristor T and a diode D _{2 connected} in series to generate a positive surge current from the line connection terminals t ₁ to t.
A circuit that can run on a _2-way, a diode D ₃ whose forward directions becomes a series circuit of the one-way thyristor T and a diode D _4, the current due to the negative surge from the line connecting terminal t ₂ for a negative surge The circuit configuration is such that t ₁ flows in one direction. As a result, D ₁ , D ₂ and D ₃ , D ₄ are always applied to the unidirectional thyristor T when a positive or negative surge is applied.
So that each of the two diodes in
The reverse breakdown voltage of each diode makes it unnecessary for the unidirectional thyristor T to have a reverse breakdown voltage. From the above circuit configuration in which the reverse breakdown voltage is borne by the diodes D ₁ , D ₂ and D ₃ , D ₄ , the unidirectional thyristor T
As shown in FIG. 1 (b), it is composed of four layers of P ₁ N ₂ P ₃ N ₄ and part of the N ₂ layer and the P ₃ layer penetrates the P ₁ layer and the N ₄ layer to form the front and back surfaces. A reverse conduction type structure which is exposed and whose exposed portions are short-circuited by the metal electrodes T ₁ and T ₂ together with the P ₁ layer and the N ₄ layer is provided. And as is clear from the action described of the present invention one-way thyristor described below, mere breakdown breakdown of the junction J _2-way thyristor T, i.e. as starting when exceeding the breakdown voltage V _B of the junction J ₂ Since the relationship of V _BO <V _CL in the conventional element is broken and reverse breakdown voltage is not required, that is, reverse conduction is sufficient, it is possible to form the short gate structures F and H on the front and back surfaces. Therefore, the holding current can be increased to achieve the object.

[0006]

The unidirectional thyristor of the present invention operates as follows. That is, when a voltage is applied in the direction from the metal electrodes T ₁ to T ₂ of the unidirectional thyristor T via the diodes D ₁ and D ₂ in FIG. 1A, the unidirectional thyristor T shown in FIG. The forward junction J ₂ is reverse biased, and when the voltage reaches the breakdown voltage V _B of the junction J ₂ , currents I ₁ and I ₂ start to flow. These current components are P ₂ and P directly below the emitter.
The effective lateral resistance R _N R _P of _three layers, each of N ₂ layer and the P ₃ layer causes a voltage drop _{R N I 1, R P I} 2,
These voltage drops cause the junction J ₁ to be positively biased toward the left end and to the right end of the junction J ₃ . Then, when this bias voltage reaches about the positive-direction rising voltage V _D of the junction J ₂ J ₃ , holes and electrons are injected from the junctions J ₁ and J ₃ , respectively, and the state changes to the ON state.
On the other hand, when a voltage in the direction from the metal electrode T ₂ to T ₁ of the one-way thyristor T is applied via the diode D ₃ D ₄ in FIG. 1A, the one-way thyristor T in FIG. _It only shows a positive direction characteristic of ₂ . Further, when the on-state shifts to the off-state, the currents I ₁ and I ₂ decrease and the injection of the junctions J ₁ and J ₃ is stopped to turn off. Therefore, the characteristics of this one-way thyristor are as shown in FIG. From the above, the breakdown of the unidirectional thyristor T of the present invention is simply determined by the breakdown voltage V _B of the PN junction J ₂ , so that the breakdown voltage V _{BO is} the same as in the conventional device described above.
Between the operating voltage V _CL and the operating voltage V _CL is eliminated, and the problem of V _BO <V _CL is solved. At turn-off, the currents 1 ₁ and I ₂ are

[Equation 1] Since the injection of holes and electrons from the junctions J ₁ and J ₃ is stopped when the temperature falls below a certain level, the current I _H can be increased in the present invention, and the one-way thyristor of the present invention has a double-sided short gate structure. Therefore, the effect of increasing the holding current I _H is great. Further, since the surge current resistance can be determined by the effective area other than the short gate portion, if the area of the short gate portion is made small, there is no influence on the surge current resistance. Next, an embodiment of the one-way thyristor of the present invention will be described.

[0007]

2 (a) and 2 (b) are a plan view and an AA 'sectional view showing an embodiment of the unidirectional thyristor of the present invention manufactured by a diffusion method. In this example, a part of the N ₂ layer is penetrated through the P ₁ layer in the central portion to be exposed to the surface, and the exposed N ₂ layer and the P ₁ layer are short-circuited by the metal electrode T ₁ .
At two locations on the left and right ends, a part of the P ₃ layer penetrates the N ₄ layer and is exposed to the back surface, and the exposed portion of the P ₃ layer and the N ₄ layer are short-circuited by the metal electrode T ₂ . Short gate structure F in this case the front and rear surfaces, the holding current I _H as a large number of H is clear that becomes large, also the holding current as the distance between the short gate structure in the front and rear surfaces is small I _H
It is also clear that the increasing effect of Further, in order to realize stable turn-on, it is desirable that the turn-on is first performed in the central portion and gradually spreads over the entire periphery, which is the distance L ₁ in FIG. 2 (a).
And L ₂ should be L ₁ ≧ 2L ₂ . Figure 3 (a)
(B) is sectional drawing which shows the other Example of the one way thyristor of this invention. This example shows a short structure F on the front and back surfaces.
H is provided so as to face each other so that the same effect as that of the embodiment of FIG. 2 can be obtained, and the number, position, mutual arrangement, etc. of the short gate structures on the front and back surfaces are required such as the magnitude of the holding current. It can be arbitrarily selected according to the characteristics to be achieved. Also, the conductivity type of P ₁ N ₂ P ₃ N ₄ has been described above.
It goes without saying that the conductivity types may be reversed.

[0008]

As is apparent from the above description, according to the present invention, it is possible to provide a surge protection element for V _BO ignition having a high protection ability and a high interruption ability. It is very effective when used for surge protection.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a surge protection element of the present invention.

FIG. 2 is an explanatory diagram of an embodiment of the present invention.

FIG. 3 is an explanatory diagram of another embodiment of the present invention.

FIG. 4 is an explanatory diagram of a conventional surge protection element.

[Explanation of symbols]

Z surge protection element L line G protected circuit E DC power supply R line resistance D ₁ , D ₂ , D ₃ , D ₄ diode T one-way thyristor F, H short gate structure

Claims (1)

[Claims] [Claim 1] P ₁ N ₂ P ₃ N ₄ (N ₁ P ₂ N ₃ P ₄ )
4 layer structure of N ₂ (P ₂ ) layer and P ₃ (N ₃ )
Part of the layer penetrates the P ₁ (N ₁ ) and N ₄ (P ₄ ) layers to be exposed on the front surface and the back surface, respectively, and the exposure N
_{The 2} (P ₃ ) layer and the P ₃ (N ₃ ) layer are respectively formed together with the P ₁ (N ₁ ) layer and the N ₄ (P ₄ ) layer in a structure short-circuited by a metal electrode. Surge protection element that does.