AN1966

Overvoltage protection solution

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Overvoltage protection solution

The principle of the protection we propose here consists of turning on the TRIAC by the gate

as soon as the voltage across it exceeds a certain value. Such a principle can be easily

implemented with a low-cost circuit (see Figure 2. for schematic diagram). This circuit uses

a bidirectional Transil diode whose current/voltage characteristic is shown in Figure 3.

provides the TRIAC gate with current and turns it on (see Figure 4.). The TRIAC remains on

till the half cycle current passes through zero (see Figure 5.).

Figure 2.

Protection of the TRIAC by a bidirectional Transil diode

Figure 3.

Voltage-current characteristic of a Transil diode

Note:

tens of amperes, depending on the device part-number).

A2

A1

G

i

The triac is turned on by gate current (i) as soon as

voltage A2 has exceeded the voltage VBR of the Transil

Current

Voltage

IPP

IPP

VCL

VCL

-VBR

+VBR