A major challenge in automotive design is to protect electronic components - such as control units, sensors, and entertainment systems - from damaging reverse voltages, voltage transients, electrostatic discharge (ESD), and noise that occur on power lines. Rectifiers are the ideal solution for power line protection in automotive electronics, and there are several important parameters to consider for these applications, including forward current, repeated reverse voltage, forward inrush current, and melting speed.
    Test conditions and application parameters for automotive electronic equipment
    The basic circuit for polarity protection is shown in Figure 1. Circuit (A) provides polarity protection only, while circuit (B) provides load drop suppression in addition to polarity protection.
    The following is a definition of the main parameters to consider when selecting a power line polarity protection diode for automotive applications.
    Maximum repetitive reverse voltage (VRRM)
    The maximum repetitive reverse voltage is the maximum voltage that the diode can withstand in the 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.ACH in Japan, and the peak voltages for these tests are shown in the table below.
    According to the above test conditions, the VRRM of the diode used for power line protection should be 300 V-400V for 12V power lines and 600V for 24V power lines.
    Forward current (IF (AV))
    The forward current specified in the product description usually refers to the maximum average forward current that the diode can withstand in the forward bias state under the thermal limit conditions of the package. This parameter is related to the current consumption of the circuit in operation.
    The forward current capacity will vary with the junction temperature of the diode, as shown in Figure 2. Other relevant parameters include thermal resistance (indicated by symbols such as RqJC, RqJA, RqJL, and RqJM).
    Forward Inrush Current (IFSM)
    The forward surge current specified in the product introduction refers to the maximum peak current that the diode can withstand in the forward bias state within the specified time and pulse condition range. This rating is limited by the thermal capacity of the diode.
    The forward inrush current specification relates to two main operations, and the ISO-16750-2 and JASO D001-94 automotive standards contain tests that simulate both operations. The first operation is to protect the circuit from the high current that occurs during load drop conditions. The tests that simulate the second operation are ISO-7677-2 Pulse 2a and 3b, which consist of 50 ms and 100 ms pulse widths with 2Ω and 50Ω line impedances, respectively. This is a relatively small energy value compared to the forward inrush current under load drop test conditions.
    Simulation tests for load drop suppression include ISO-16750-2 tests A and B, JASO standard type A and D, and other tests.
    In this case, a high surge current flows through the polarity protection diode, and a high enough forward surge capacity is required to avoid failure. The following formula can be used to estimate the surge current value in the load drop suppression test:
    Ipeak = (Vpeak -- VFd-Vclamping)/(Ri + Rzd)
    Vpeak: surge voltage Vclamping voltage VFd: positive voltage drop of the polarity protection diode Ri: line impedance Rzd: resistance of the clamping component
    Electrostatic Discharge (ESD)
    Electrostatic discharge will affect the working stability and reliability of on-board electronic modules during their service life.
    ISO-10605 and JASO Standard 5.8 specify test conditions for this parameter.
    Non-repeating avalanche Energy (EAS)
    The non-repetitive avalanche energy of the diode is the maximum energy that the diode can absorb in the bias state in order to prevent the circuit from being affected by the induced transient recoil voltage or the induced high reverse voltage from the motor and solenoid. There is currently no automotive standard for this parameter.
    Temperature conditions for automotive electronic systems and components
    JASO regulates the operating temperature range from -40oC to + 100oC depending on the location of the car's electronic systems and components, such as in the trunk, engine, and elsewhere.
    When designing the electronic unit for automotive use, consideration should be given to protecting the electronic unit from penetration or induction transient energy from the induction unit and the shock of the reverse electrical connection. Transient energy is generated by spark plugs and motors that drive wipers, brakes, door locks, and other components. Also consider electrostatic discharge from people and car interiors.