A major automotive design challenge: choosing automotive power line polarity protection diodes

A major challenge in automotive design is to protect electronic components such as control units, sensors, and entertainment systems from destructive reverse voltages, voltage transients, electrostatic discharge (ESD), and noise that appear on power lines interference. Rectifiers are ideal solutions for automotive electronic power line protection. There are several important parameters to consider for these applications, including forward current, repeated reverse voltage, forward surge current, and melting speed.

Automotive electronic equipment test conditions and application parameters

The basic circuit used for polarity protection is shown in Figure 1. Circuit (A) only provides polarity protection, while circuit (B) provides load dump suppression in addition to polarity protection.

Figure 1: Basic polarity protection circuit

The following is the definition of the main parameters that need to be considered when selecting a power line polarity protection diode for automotive applications.

Maximum Repeated Reverse Voltage (VRRM)

The maximum repetitive reverse voltage is the maximum voltage that the diode can withstand in reverse bias mode. In reverse bias mode, the leakage current flowing through the diode generates heat in the diode junction and causes thermal runaway. Tests that simulate this condition include ISO-7637-2 pulse 1 and 3a in the United States and JASO D001-94 standard type B and E.Each in Japan. The peak voltages of these tests are shown in the following table.

Table 1: ISO-7637-2 and JASO D001-94 standard VRRM