AN1966 datasheet(4/14 Pages) STMICROELECTRONICS

4 / 14 page

Overvoltage protection solution

AN1966

4/14

Figure 4. shows the characteristic of the TRIAC + Transil assembly. This is the case of a

600 V/12 A TRIAC protected by a 376 V Transil diode. (The dotted line in Figure 4. shows

the characteristic of the TRIAC alone).

Figure 4.

Characteristic of the TRIAC + Transil assembly

The advantages of this solution are the following:

●

The TRIAC will always operate within the voltage limits given by the manufacturer

(VDRM; VRRM or VDSM; VRSM) and thus far from the avalanche area. There is no more

risk of TRIAC failure

●

The TRIAC is turned on by a gate current which will ensure optimal di/dt conditions.

It should be noted that ST guarantees safe operation of their TRIACs even if the VDRM and

VRRM levels are exceeded by 100 V during less than 10 ms. This behavior is guaranteed by

the VDSM and VRSM parameters (refer to ST TRIAC datasheets). This allows an easier

choice of voltage protection.

Current (mA)

Voltage (V)

Transil

VBR

triac

VDRM

VDSM

-600 V

+600 V

-418 V

+418 V

triac

avalanche

zone

This current flows

through the gate

Current in the

turned on triac

AN1966 Datasheet(PDF) 4 Page - STMicroelectronics