AN317 - APPLICATION NOTE

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It can be noted that Transil diodes withstand very

high transient overloads. For example, a diode in a

plastic case (DO-201) withstands an “I

A

This is due to the particular technology of Transils

in which the silicon chip is mounted between two

piston- shaped leads with very high thermal

capacity.

By

contrast,

the

current-handling

capability of a Transil in continuous operation is

similar to that of a diode in the same package.

TRANSILS

Case

DO-15

DO-201

R6

3

4.5

5

which do not result in the open-circuiting of a

TRANSIL diode previously destroyed by an

accidental overload.

PRACTICAL CONSEQUENCES

A. NON-REPETITIVE PULSE OVERLOADS

In pulse operation (duration 1 second) the electromechanical capacity of the case is very much higher than

that of the silicon chip (figure 1).

For example, if we consider the DO-201 case diodes of the “1.5 kW” series, the specifications of the

voltage). For the package, the value of “I

The risk of a TRANSIL diode becoming an open circuit after a pulse overload is thus negligible in practice.

The data in figure 1 thus enables the designer to check if his circuit falls within the absolute safety area.

B. PROTECTION DIODES AFTER A VOLTAGE

SOURCE

Transil diode whose silicon chip has been

destroyed is subjected to a current given by:

I

V

R

CP

=

In many cases this current can result in destruction

of the Transil diode contacts, i.e. an open circuit

which can have disastrous consequences.

To avoid this, it is necessary to add a device K

which breaks the circuit after the failure. This

device can be a fuse or a circuit-breaker. The data

in figure 1 and table 1 will enable the designer to

determine the fuse (or circuit-breaker) which will

break the circuit before the diode becomes an

open circuit.

CONCLUSION

The specification of the new I

TRANSIL diodes. It enables the designer to define his protection with absolute safety, a vital precaution

since the overloads encountered in practice do not always correspond with the standards. The building of

absolutely safe equipment enables the damage due to unforeseeable accidents to be limited, which is con-

sidered important by STMicroelectronics with our years of experience in the field of protection.