Classification of Switching Power Supplies, Detailed Explanation of AD/DC and DC/DC Power Supplies
Classification of Switching Power Supplies
People's field of switch power supply technology is to develop related power electronic devices while developing switch frequency conversion technology. The mutual promotion of the two promotes the development of switch power supplies towards light, small, thin, low noise, high reliability, and anti-interference with a growth rate of over two digits each year. Switching power supplies can be divided into two categories: AC/DC and DC/DC. DC/DC converters have now achieved modularization, and the design technology and production process have been mature and standardized both domestically and internationally, and have been recognized by users. However, the modularization of AC/DC, due to its own characteristics, encounters more complex technical and manufacturing problems in the process of modularization. The structure and characteristics of two types of switching power supplies are explained below.
DC/DC conversion
DC/DC conversion is the process of converting a fixed DC voltage into a variable DC voltage, also known as DC chopping. There are two ways in which choppers work: one is to keep the pulse width modulation mode Ts unchanged and change T (universal), and the other is to keep the frequency modulation mode T unchanged and change T (prone to interference). The specific circuits are divided into the following categories:
(1) Buck circuit - a buck chopper with an average output voltage Uo less than the input voltage Ui and the same polarity.
(2) Boost circuit - boost chopper, with an average output voltage Uo greater than the input voltage Ui and the same polarity.
(3) Buck Boost circuit - a buck or boost chopper with an average output voltage Uo greater than or less than the input voltage Ui, opposite polarity, and inductive transmission.
(4) Cuk circuit - a buck or boost chopper with an output average voltage Uo greater than or less than the input voltage UI, opposite polarity, and capacitor transmission.
Today's soft switching technology has made a qualitative leap in DC/DC. VICOR Company in the United States has designed and manufactured various ECI soft switching DC/DC converters with high output power of 300W, 600W, 800W, etc., corresponding power densities of (6, 2, 10, 17) W/cm3, and efficiency of (80-90)%. The RM series of high-frequency switching power modules using soft switching technology, newly launched by Japanese company NemicLambda, has a switching frequency of (200-300) kHz and a power density of 27 W/cm3. It uses synchronous rectifiers (MOS-FET instead of Schottky diodes), which improves the efficiency of the entire circuit to 90%.
2.2 AC/DC conversion
/DC conversion is the process of converting AC into DC, and the power flow can be bidirectional. The power flow from the power source to the load is called "rectification", and the power flow from the load back to the power source is called "active inverter". The AC/DC converter input is 50/60Hz AC power. Due to the need for rectification and filtering, relatively large filter capacitors are essential. At the same time, due to the limitations of standards (such as UL, CCEE, etc.) and EMC directives (such as IEC, FCC, CSA), EMC filtering and the use of components that comply with standards must be added to the AC input side, which limits the miniaturization of the AC/DC power supply volume. Additionally, due to the internal high-frequency, high-voltage The action of high current switches increases the difficulty of solving EMC electromagnetic compatibility problems, which puts forward high requirements for the design of internal high-density installation circuits. Due to the same reasons, high voltage and high current switches increase power consumption and limit the modularization process of AC/DC converters. Therefore, it is necessary to adopt power system optimization design methods to achieve a certain degree of satisfaction in its work efficiency.
AC/DC conversion can be divided into half wave circuit and full wave circuit according to the wiring method of the circuit. According to the number of power phases, it can be divided into single phase, three-phase, and multiphase. According to the working quadrant of the circuit, it can be divided into one quadrant, two quadrants, three quadrants, and four quadrants.
