Vehicle power supply environment analysis and power supply selection

As cars are equipped with more and more electronic devices, their reliability and comfort have been greatly improved. But when you are enjoying the comfort of the car, do you know that the electronic devices in the car are enduring a devilish EMC environment? Therefore, it is necessary to add an isolated power supply to the front end of the on-board electronic devices to isolate the harsh interference and avoid damage to the electronic devices.

The development of automobiles has brought great convenience to life. Cars equipped with a large number of electronic devices have also greatly improved their reliability and comfort. While you are enjoying the comfort of the car, do you know that the electronic devices in the car are enduring a devilish power consumption environment? Selecting an isolated power supply for the front end of the electronic devices in the car can block the harsh interference at the front end of the electronic devices to avoid damage to the electronic devices.

The actual input voltage waveform of the power supply will be bad due to the start-up of the internal combustion engine, disconnection of the inductive load, sudden interruption of the parallel load current, etc. The ISO7637-2 standard simulates the input voltage waveform under bad conditions, and some of the worst waveforms are listed below.

Pulse 1: A transient pulse caused by disconnection of power from an inductive load

Table 1 Pulse 1 parameter table

From the data in Table 1, we can see that a voltage of -100V can be induced on a 12V power supply line, and a voltage of -600V can be induced on a 24V power supply line. If there is no isolated power supply and EMC filtering circuit at the front end of the electronic equipment, the subsequent MCU, LCD, audio and other parts 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 wiring harness inductance

Table 2 Pulse 2a parameter table

Pulse 2b: A momentary pulse generated by a DC motor acting as a generator after the ignition circuit is disconnected

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: Instantaneous pulse (positive pulse) generated during the switching process

Table 5 Pulse 3b parameter table

Pulse 4: Voltage drop due to energizing the starter motor of an internal combustion engine

Table 6 Pulse 4 parameter table

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

Table 7 Pulse 5b parameter table

Here we recommend the E2405ASBD-20W power module, with an ultra-wide input voltage range of 6V~63V and an output of 5V/4A. 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, it can make the subsequent electronic equipment work stably and reliably. E240512ASDD4-20W, ultra-wide input voltage range of 6V~63V, dual output of 5V/3A and 12V/0.4V. The main regulated 5V output can power the MCU, LCD and other parts, and the auxiliary unregulated 12V can power the audio and other parts.

ZLG Zhiyuan Electronics Vehicle Power Module