Blocking bad interference, vehicle power supply environment analysis and power selection strategy

As cars develop and install more and more electronic devices, their reliability and comfort have also been greatly improved. But when you enjoy the comfort of the car, you know that the electronics on the car are enduring a demonic EMC environment. Therefore, it is necessary to add an isolated power supply to the front end of the in-vehicle electronic device to block the bad interference and avoid damage to the electronic device.

The development of the car has brought great convenience to life. The reliability and comfort of the car with a large number of electronic devices has been greatly improved. When you enjoy the comfort of the car, you know that the electronic devices in the car are enduring a demonic environment. The use of an isolated power supply for the front end of the electronic device of the car can block the harsh interference at the front end of the electronic device to avoid damage to the electronic device.

Due to the ignition of the internal combustion engine, the inductive load disconnection, the sudden interruption of the parallel load current, etc., the actual input voltage waveform of the power supply is poor. The ISO7637-2 standard simulates input voltage waveforms under harsh conditions. Some of the worst waveforms are listed below.

Pulse 1: Instantaneous pulse due to power supply disconnection from inductive load

Table 1 Pulse 1 parameter table

From the data in Table 1, it can be seen that the voltage of -100V can be induced on the 12V power supply line, and the voltage of -600V can be induced on the 24V power supply line. If the front end of the electronic equipment does not have isolated power supply and EMC filter circuit, the latter stage Parts of the MCU, LCD, audio, etc. may be damaged.

Pulse 2a: A transient pulse caused by a sudden interruption of current in a device connected in parallel with the device under test (DUT) due to harness inductance

Table 2 Pulse 2a parameter table

Pulse 2b: a transient pulse generated by a DC motor used as a generator after the ignition circuit is switched off

Table 3 Pulse 2b parameter table

Pulse 3a: transient pulse (negative pulse) caused by the switching process

Table 4 Pulse 3a parameter table

Pulse 3b: transient pulse generated by the switching process (positive pulse)

Table 5 Pulse 3b parameter table

Pulse 4: Voltage drop due to powering up the starter motor of the internal combustion engine

Table 6 Pulse 4 parameter table

Pulse 5b: The alternator is generating a charging current, and a load-dump transient pulse occurs when the discharged battery is disconnected, provided that the alternator has an automatic protection function.

Table 7 Pulse 5b parameter table

The E2405ASBD-20W power module is recommended here, with a wide input voltage range of 6V~63V and 5V/4A output. As long as a small amount of EMC filter circuit is added to the input end of the power module, it can have good EMC anti-interference ability. When the line voltage fluctuates greatly, the latter electronic equipment can work stably and reliably. E240512ASDD4-20W, 6V~63V ultra-wide input voltage range, 5V/3A and 12V/0.4V dual output. The main circuit voltage regulator 5V output can supply power to the MCU, LCD and other parts, and the auxiliary circuit unregulated 12V can supply power to the audio and other parts.

ZLG Zhiyuan Electronic Vehicle Power Module