4 types of capacitor for filtering applications in switch mode power supply systems
Aluminum electrolytic capacitors
For a long time, power system designers have been using aluminum electrolytic capacitors to filter the input and output of switch mode power systems. These capacitors provide excellent capacitance per unit volume and are inexpensive. The high CV of aluminum electrolytic capacitors is achieved by depositing a thin layer of dielectric material on the etched aluminum metal foil. The excellent capacitance density and relatively low cost of these capacitors make them a popular choice for SMPS filtering applications.
Tantalum capacitors provide a high level of capacitance, and they are commonly used in SMPS filtering applications. Tantalum capacitors have highly porous anodes that provide a large dielectric surface area, and therefore have an extremely high CV density. Compared with aluminum electrolytic capacitors, these capacitors have better performance characteristics and are suitable for filtering applications in switching power supply systems. However, the cost of producing these capacitors is higher than the cost of aluminum electrolytic capacitors.
A variety of dielectric materials can be used to design ceramic capacitors. The choice of material depends mainly on the required performance characteristics. The impressive performance characteristics of ceramic capacitors make it a suitable choice for input and output filtering in SMPS systems. Ceramic discs and multilayer ceramic capacitors (MLCC) are used for SMPS filtering. Although ceramic disc capacitors are stable over a wide temperature range and are suitable for applications requiring high voltage ratings, many manufacturers have switched to multilayer ceramic capacitors due to their CV density.
Film / foil and metallized film capacitors have impressive self-healing properties. Most film capacitors use polypropylene or polyester dielectric materials. Polyester is easily available and has a high dielectric constant. On the other hand, polypropylene has a lower dissipation factor. Polyester-based film capacitors are mainly used for applications requiring high volumetric efficiency, while polypropylene-based capacitors are mainly used for high current DC and high voltage / high frequency AC applications.
The performance and reliability of the switching power supply system depends largely on the input and output filter capacitors. The types of capacitors commonly used in SMPS for filtering applications include aluminum electrolytic capacitors, tantalum capacitors, film capacitors and ceramic capacitors.
SWITCH MODE TRANSFORMERS
Switch mode transformers (also called switch mode power transformers and SMPS transformers) are used in regulated power supplies and have the function of boosting or stepping down voltage or current, and / or are provided between the input and output terminals of the switch mode Isolated Power. On the primary side of a switch-mode transformer, the duty cycle (on-time) of the input voltage waveform changes (switches) to provide a constant output voltage under varying load conditions.
A metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a field-effect transistor (FET with an insulated gate) where the voltage determines the conductivity of the device. It is used for switching or amplifying signals. The ability to change conductivity with the amount of applied voltage can be used for amplifying or switching electronic signals. MOSFETs are now even more common than BJTs (bipolar junction transistors) in digital and analog circuits.
A diode is defined as an electronic component that conducts current in only one direction (as long as it operates within a specified voltage level). The ideal diode will have zero resistance in one direction and infinite resistance in the opposite direction.