Trisil characteristics

AN320

6/13

Doc ID 5649 Rev 3

1.4

The ability of semiconductor components to withstand high currents in transient operation is

limited for pulses longer than 10 ns by a second breakdown due to heat. This phenomenon,

although not destructive, is considered as the normal utilization limit in so far as the behavior

of the component depends on the external circuit.

The temperature rise within the semiconductor is thus the parameter which defines the

behavior of the component and its capacity to withstand current surges. It is given by

Equation 1:

Equation 1:

With

●

●

●

●

●

This equation clearly shows the advantage of the Trisil. A decrease in the voltage across its

terminals enables it to conduct a much higher current than the avalanche diode for the same

junction temperature. Since the voltage to be taken into consideration for the calculation is

that in the conducting state, the permitted current levels in transient operation are

independent of the avalanche voltage and the guaranteed values are identical for all the

types of a given series (see Figure 8).

Figure 8.

Comparison of the limited transient currents for a Transil and a Trisil in

the similar cases (SMB).

The maximum junction temperature taken into account in transient operation is not that

given in the catalogues (junction temperature in operation or in storage) but corresponds,

with a certain safety margin, to the second breakdown due to thermal causes, i.e. about

350-400 °C.

This high current capacity can be applied in AC operation at the 50 Hz industrial frequency

(see Figure 9), which is particularly interesting in telephony where equipment should be

protected against overvoltages resulting from accidental coupling of the telephone line with

VBR(V)

IPP(A)

Trisil

8/20µs

Transil

8/20µs

Trisil

10/1000µs

Transil

10/1000µs

0

20

40

60

80

100

120

140

160

50

100

150

200