Automobile has become an indispensable means of transportation for people to travel, and it is the daily work of engineers to select high reliability capacitors for automotive electronic equipment. First of all, we must clearly understand the technical parameters and performance characteristics of each capacitor with different specifications. Secondly, we must select the most cost-effective and reliable solution according to the environment and special application scenarios of automotive electronics.
The application of capacitors in automotive electronics can generally be summarized into the following six application areas:
Power system control: motor, transmission and emission control. Nowadays, the vigorous development of electric vehicles has increased many new opportunities for power conversion and control electronic equipment.
Vehicle control: anti lock braking, active suspension, traction control, power and four-wheel drive steering.
Safety, comfort and convenience: airbag actuator, anti-collision, temperature and humidity control, cruise control and anti-theft.
In car entertainment system
Driver information display and audible warning system
Diagnosis and maintenance
So how to choose the appropriate capacitor according to the main working environment and application fields of the car? In general, most capacitors fall into one of two basic structural categories: electrostatic (polymer film and ceramic capacitors) and electrolytic (tantalum and aluminum) capacitors. Electrostatic capacitors are nonpolarized devices, which usually exhibit very low equivalent series resistance (ESR) and impedance. Electrolytic capacitors usually have higher capacitance values but are polarized.
tantalum electrolytic capacitor
Tantalum electrolytic capacitor is generally a chip device with rated voltage from 2.5VDC to 63VDC, and 125V axial lead is used. Note: In order to obtain the highest reliability, the actual applied voltage of solid tantalum capacitors is derated to 50% of the rated voltage, and tantalum polymer and wet bulk axial tantalum capacitors are derated to 80%.
Tantalum electrolytic capacitors have very stable electrical characteristics as time and temperature change
The maximum capacity of chip tantalum capacitor is 2200 μ F. The maximum capacity of axial wet block tantalum capacitor can reach 10000 μ F。
Surge test/screening and larger chip enclosure size (low ESR value and large capacitance value).
Typical failure rates under normal voltage derating service conditions are 5FIT to 15FIT (failures per billion hours).
Aluminum electrolytic capacitor
The rated voltage of the chip type aluminum electrolytic capacitor is from 6.3VDC to 450VDC, and the large tank type aluminum capacitor has a higher voltage.
The temperature grade is 85 ℃, 105 ℃ or 120 ℃.
The maximum capacity of chip type aluminum capacitor is 10mF.
No surge current screening is required.
The aluminum electrolytic capacitor has a natural wear mechanism, and its service life under fully rated voltage and maximum temperature conditions will be limited to 5000 hours. If the rating is reduced to 80% of the rated voltage, the service life can be extended twice.
The rated voltage of ceramic capacitor ranges from 6.3VDC to 5000VDC (100V or less for most applications); The voltage does not need to be derated, but the voltage coefficient of the capacitor must be considered. When working at or near the rated voltage, the effective capacitance value of multilayer ceramic capacitor (MLCC) may lose up to 40%.
The working temperature of ceramic capacitor can exceed 150 ℃.
No polarization (it can be charged with large current during high-speed insertion).
Ceramic capacitors have very low ESR and DC leakage current.
Typical failure rate is less than 1FIT; The typical failure mode is short circuit or parameter drift.
Polymer film capacitor
Rated voltage from 16VDC to 2000VDC; No derating is required.
The maximum operating temperature of most polymer film capacitors is 105 ℃ (PPS capacitors are 125 ℃).
Ultra low ESR and DC leakage current
Typical failure rate is less than 5FIT; Typical failure modes are open circuit or parameter drift.
The surface mounted products are limited in automotive applications.
It is not always easy to determine which capacitor type is best suited for a given application. In addition to the above parameters, performance and other factors, it is also important to comprehensively consider the cost, size and manufacturability.