With a small amount of additional circuitry, these devices can be used in circuits subject to transients higher than 36 V. Use only zener diodes or zener-type transient absorbers (sometimes referred to as transzorbs). Any other type of transient absorber has an unacceptable time delay. Start by adding a pair of resistors as a working impedance for the zener diode, as shown in Figure 8-4. Keep these resistors as small as possible, preferably 10 Ω or less. Larger values can be used with an additional induced error resulting from a reduced signal that actually reaches the device input pins. Many applications are satisfied with a 10-Ω resistor along with conventional zener diodes of the lowest power rating available because this circuit limits only short-term transients. This combination uses the least amount of board space. These diodes can be found in packages as small as SOT-523 or SOD-523.

Figure 8-4 Transient Protection