AN320 datasheet(11/13 Pages) STMICROELECTRONICS

Il numero della parte	AN320

Spiegazioni elettronici	In the field of parallel protection, the devices used have two main functions in transient operation

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Produttore elettronici	STMICROELECTRONICS [STMicroelectronics]

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11 / 13 page

AN320

Physical operation

Doc ID 5649 Rev 3

11/13

Figure 14.

Thyristor effect of the Trisil

As the avalanche current increases, this difference of potential can reach the threshold of

0.6 V, a value which is sufficient to create injection of electrons from the cathode towards the

P1 area and thus trigger thyristor N1 P1 N2 P2.

The electrons thus injected into P1 in fact will reach J2 by diffusion, and cross it under the

effect of the electrical field operating in the space charge of the reverse biased J2 junction.

In N2, the electrons help to reduce the potential of this area compared with P2 and as a

result inject holes from P2 towards N2. These holes travel in the reverse direction because of

their polarity. When they arrive at P2 they help to increase the potential of P1 with respect to

N1, this time resulting in the injection of electrons from N1 to P1.

The procedure is cumulative. The excess electrons in N2 and the holes in P1 will

compensate the fixed charges of the space charge and will thus suppress it. Junction J2 will

act as a forward biased junction and the voltage across the component will drop.

N++

P1 +

P2 +

J 2

J 1

N 2

J 3

()

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