Transient voltage suppressors (TVS) for automotive electronic protection: Page 4 of 4

March 31, 2011 //By Soo Man Kim
Transient voltage suppressors (TVS) for automotive electronic protection
A major challenge in automotive design is protecting electronics – such as control units, sensors, and entertainment systems – against damaging surges, voltage transients, ESD, and noise that are present on the power line. Transient voltage suppressors (TVS) are ideal solutions for automotive electronic protection and have several important parameters for these applications, including power rating, stand-off voltage, breakdown voltage, and maximum breakdown voltage. Following are definitions for these parameters.
8: Reverse bias status

Secondary Protection of the Automotive Power Line

The primary target of protection circuits in automotive systems is high surge voltages, but the clamped voltage is still high. Secondary protection is especially important in 24- V powertrains, such as found in trucks and vans. The main reason for this is the maximum input voltages for most regulators and dc-to-dc converter ICs for automotive applications are 45 V to 60 V. For this kind of application, using secondary protection, as shown in Figure 9, is recommended.

Figure 9: Secondary protection circuit

Adding resistor R onto the power line reduces the transient current, allowing smaller power-rating TVSs as the secondary protection. Current requirements for microprocessor and logic circuits in electronic units are 150 mA to 300 mA, and the minimum output voltage of a 12-V battery is 7.2 V at - 18 °C, or 14.4 V for a 24-V battery under the same conditions. In a 24-V battery under the above conditions, the supply voltage at a 300-mA load is 8.4 V at R = 20 Ω, and 11.4 V at R = 10 Ω at a minimum voltage of 14.4 V (24-V battery voltage in - 18 °C).

VL = (Vmin ⁄ ( Vmin IL)) × (( Vmin IL) – R)

VL: Voltage to load

Vmin: Minimum input voltage

IL: Load current

R: Resistor value

Power rating of R = I2R

This supply voltage is higher than the minimum input voltages for most voltage regulators and DC/DC converter ICs.

About the author:

Soo Man (Sweetman) Kim is Senior Application Manager for Vishay Intertechnology, Inc.

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