DocID024389 Rev 1

7/11

AN4275

Protection devices

3

Protection devices

The device used to protect against IEC 61000-4-5 is generally a clamping device located in

parallel with the circuit to be protected. This protection device limits the voltage to a

Figure 7 gives the I/V characteristics of a clamping device.

Figure 7.

I/V characteristics of a unidirectional clamping devices

equipment/circuit.

generated by the standard. It is worthless to choose a protection defined by a 10/1000 µs

surge (this surge is dedicated to telecommunication lines) when the standard requires to

comply with 8/20 µs.

ST has been specifying its protection devices with 10/1000 µs and 8/20 µs surges for years.

Trends toward optimized protection in cost and in size leads us to produce dedicated

protection devices specified according to IEC 61000-4-5.

lower than the maximum voltage the circuit can withstand.

direction and to a forward voltage on the other direction.

Bidirectional device must be used only if the application requires to accept a reverse plug-in

(on DC power lines) or if located on AC lines.

V

I

Off-state area

Working area

in case of

positive surges

Working area

in case of

negative surges