Metallized axial film capacitors are a kind of component made of two pieces of conductors close to and insulated from each other for storing electric charge, which is mainly used in circuits such as tuning, filtering, coupling, bypassing and energy conversion. According to the dielectric material used in capacitors, they are mainly divided into ceramic capacitors, aluminum electrolytic capacitors, film capacitors and tantalum electrolytic capacitors. According to the China Electronic Components Association (CECA) cited by Wisdom Research Consulting, the market size of ceramic capacitors, aluminum electrolytic capacitors, film capacitors, and tantalum electrolytic capacitors accounted for 49%, 29%, 8%, and 7% of the market size of capacitors, respectively.
Metallized Axial Film Capacitors: The First Choice for High Voltage and High Reliability in the Capacitor Family
Metallized axial film capacitors are capacitors that utilize a plastic film as the dielectric. The origin of the technology is the paper capacitor, which was invented in the second half of the 19th century. This is a capacitor in which paper impregnated with oil and paraffin is inserted into aluminum foil and rolled into a roll. Instead of metal foil, metal is vaporized directly onto the paper and rolled into a type called MP capacitors. Film capacitors, along with ceramic capacitors, aluminum electrolytic capacitors, and tantalum capacitors, are the main members of the current family of capacitors.
Metallized axial film capacitors were developed in the 1930s. Although they are difficult to miniaturize compared to laminated ceramic chip capacitors, they are used in home appliances, automotive electronics, industrial equipment, and power electronics due to their high insulation resistance and excellent reliability. Film capacitors are as important in analog circuits (including power) as MLCCs in digital circuits, and this has led to the growth of film capacitors in the power era.
Metallized axial film capacitors are broadly classified into foil electrode type and evaporated electrode type (metallized thin film type) according to the method of forming the internal electrodes, and into wound, laminated, inductive, and non-inductive types according to the structure. Foil electrode type film capacitors use metal foil (aluminum, tin, copper) overlaid with plastic film and wound to form a capacitor. The internal electrodes are attached with wires to become inductive type capacitors, while the terminal electrodes are mounted with wires or terminals to become non-inductive type capacitors, which have a small inductance component and excellent high frequency performance.
The evaporation electrode type capacitors have internal electrodes formed by evaporating metal (aluminum, zinc, etc.) on plastic film, and are non-inductive type capacitors with end-face electrodes. Compared with the foil electrode type, the evaporation electrode type can be miniaturized, and can be further divided into the winding type and the laminated type in terms of processing methods.
Vaporized electrode type metallized axial film capacitors are characterized by high reliability and self-healing electrodes. When a voltage is applied to a weakly insulating area of the film, the surrounding vaporized film oxidizes instantly, restoring the insulating properties of the capacitor. In applications where reliability is important, vapor-deposited electrode type film capacitors are further enhanced by manufacturing methods such as split vapor deposition and addition of a fusing section. In addition to the electrodes and manufacturing method, the material properties of the dielectric also make a difference in the performance of film capacitors.
New demand catalyzes boom, metallized axial film capacitors meet high speed development
Widely used in motor control, power conversion, UPS (Uninterruptible Power Supply) and other fields, inverters are electronic devices that convert low-voltage (12V/24V/48V, etc.) DC power into 220V AC power. Film capacitors have the advantages of high voltage, high capacity and high reliability in power circuits, which determines their indispensable position in inverters.
Home Appliances: Terminal Growth Slows, Demand Remains Steady
Large household appliances such as refrigerators, washing machines, air conditioners need to drive large motors, in the motor, control circuits and frequency conversion circuits kind of metallized axial film capacitors play different roles, according to the different functions can be divided into three main categories:
- EMI Suppression: In addition to the power supply, the EMI Suppression is also used at the input and output of the inverter circuit, both of which act as EMI suppressors to prevent component damage;
- DC link: Acts as a low-pass filter to suppress fast transient currents and smooths the output voltage to keep the DC bus voltage within the permissible range;
- AC film capacitors: are used in induction motor drive control circuits, where a capacitor is needed to switch the motor in the desired direction by phase shift when the induction motor is started.
For appliances that consume a lot of power, such as refrigerators, washing machines, and air conditioners, if the frequency of the power supply can be adjusted according to the operating status of the appliance, the power consumption can be reduced and the life of the appliance can be extended. Frequency converters consist of rectifier, filter, inverter, brake and drive units that control AC motors by changing the frequency of the motor’s operating power supply. The current in the inverter circuit is converted from AC to DC to AC, and film capacitors are required for EMI suppression at both the input and output points. Therefore, the demand for metallized axial film capacitors in home appliances depends on the overall shipment of home appliances and the penetration rate of inverter appliances.
Lighting: Energy efficiency drives up LED penetration, replacing demand for fluorescent lamps
Metallized axial film capacitors are mainly used in ballasts for fluorescent lamps and high intensity discharge lamps such as high pressure mercury, high pressure sodium and metal halide lamps in the lighting industry. Film capacitors are mainly used in fluorescent lamps for two types of functions: one is inside the starter for EMI suppression during induction, and the other is between the line and neutral for power factor correction.
As the concept of energy saving spreads globally, the penetration of LED lighting is increasing rapidly, especially its luminous efficacy compared to fluorescent lamps is significantly enhanced. Traditional compact fluorescent lamps have a luminous efficacy of around 60lm/W, halogen lamps less than 20lm/W, and incandescent lamps with an efficiency of 13lm/W already account for less than 5% of the total, while residential LED lighting has already exceeded 100lm/W and has been progressing at the rate of 6lm/W-8lm/W per year since 2010, with the top technologies already capable of achieving 210lm/W.
In LED lighting, since ballasts are not required, capacitors are primarily used in the drive circuit to smooth and minimize ripple from the power supply, help avoid flicker and eliminate overheating, and improve the life of the fixture. Therefore, the growth of LED lighting will reduce the need for film capacitors in fluorescent lamps. At present, the cost of film capacitors in LED driving power is higher than that of aluminum electrolytic capacitors, so many products with high price sensitivity and low service life requirements choose to use aluminum electrolytic capacitors. From the film capacitor leading enterprises lighting business related revenue trends, lighting field overall demand for metallized axial film capacitors in a slow decline.
New Energy Vehicles: Indispensable Capacitive Products in the Mobility Revolution
The application of metallized axial film capacitors in the field of new energy vehicles is mainly divided into three parts: inverters for new energy vehicles, on-board chargers (OBCs) and supporting charging piles. The core of a new energy vehicle is the “three electrics”, and the inverter belongs to the electric drive system. Its function is to convert the high voltage DC output from the power battery or storage battery into three-phase AC with variable current and frequency for the motor to run, in order to control the vehicle’s driving speed. When braking, the inverter can rectify the three-phase AC current into DC current to charge the power battery. The presence of an inverter makes electric/hybrid vehicles start faster.
Inverters are mainly composed of power modules, microcontrollers, gate drivers, current sensors, position sensors and so on. According to Infineon’s estimation, the cost of power devices in new energy vehicle inverters accounts for about 40% of the cost, which is the highest value; the cost of capacitors used for AC filtering accounts for about 16% of the cost, which is the second most valuable part after the power devices.
Metallized axial film capacitors in OBCs are mainly EMI capacitors, DC-Link capacitors & buffer capacitors, resonant capacitors, power factor correction (PFC), etc. Similar to inverters, DC-Link capacitors & buffer capacitors are also used in OBCs. Similar to inverters, DC-Link capacitors have the highest value because of their highest capacitance, reaching hundreds of dollars, while EMI capacitors, resonance capacitors and PFC capacitors have capacitance values of a few tens of nF, which are cheaper per unit. In addition, film capacitors are also used in DC-DC converters, which step down the power of the power battery pack to provide low-voltage power equipment such as instrumentation, wipers and lights, and at the same time charge the low-voltage battery.
As for charging piles, according to different charging methods, they can be divided into AC charging piles and DC charging piles. Among them, AC charging pile connects OBC to charge the power battery, adopts conventional voltage and small power, usually called “slow charging”, and is mostly used in residential areas, public parking lots and shopping malls, etc., with lower cost; DC charging pile adopts high-voltage and high-power to directly charge the power battery pack, and is usually called “fast charging”. DC charging pile adopts high voltage and high power to charge the power battery pack directly, which is usually called “fast charging”, and is mostly used in operating vehicle power stations and fast charging stations, etc., with a higher cost.
