Classification, structure and characteristics of power adapters

　　The power adapter is a product that we can often use in our lives, but do you know? Its classification, structure and characteristics are quite complicated. If you are interested, follow the power adapter manufacturer to learn about it!

　　1. Self-excited

　　The self-excited power adapter uses a regulator tube and a switching transformer auxiliary winding to form a positive feedback loop to realize self-excited oscillation and stabilize voltage output. Since the regulator tube of the self-excited power adapter doubles as an oscillator tube, there is no need to set up a special oscillator. The pulse signal is formed by self-oscillation, which is a non-fixed frequency pulse signal, which changes with the input voltage and load. The frequency is higher at light load, lower at heavy load, and intermittent oscillation occurs at no load.

　　The self-excited power adapter itself has a certain self-protection function. Once the load is too heavy, it will inevitably destroy the feedback condition and stop the oscillation, thereby protecting the power adapter. Because of its high peak current and large ripple current, especially poor stability during high-power and high-current operation, it is mostly used in low-power applications below 60W.

　　2. Other aggressive

　　The adjustment tube of the other-excited power adapter circuit does not participate in the oscillation process of the excitation pulse, and a special oscillator generates the pulse to control the adjustment tube. For example, the commonly used integrated circuits UC3842, NCP1200, TL494 and other integrated controllers can output PWM pulses with adjustable duty cycles. Nowadays, many integrated controllers can automatically raise and lower the switching frequency according to the output power, so as to maintain excellent power conversion efficiency under different load conditions.

　　Because the integrated controller integrates the protection circuit, control circuit, oscillation circuit and feedback signal detection circuit on the same chip, it has good anti-interference performance, simple circuit and powerful functions, and can complete oscillation, voltage stabilization, overcurrent, overvoltage and Protection functions such as undervoltage are incomparable to discrete power adapters, so they have become more and more widely used in recent years.

　　3. DC/DC power adapter

　　The DC/DC power adapter transforms a fixed DC voltage into a variable DC voltage, also known as a DC chopper. Chopping L. There are two working methods for the DCDC power adapter: one is the pulse width modulation method If T does not change, change the frequency modulation method t (general); second, if the frequency modulation method t does not change, change T (easy to cause interference). The specific circuits are as follows

　　①Buck circuit-step-down chopper, the average output voltage Uo is less than the input voltage UD, and the polarity is the same in and out;

　　②Boost circuit—boost chopper, the average output voltage Uo is greater than the input voltage UD, and the polarity is the same in and out;

　　③Buck-Boost circuit step-down or step-up chopper, the average output voltage Uo is greater than or less than the input voltage

　　④ Cuk circuit—buck or boost chopper, the average output voltage Uo is greater than or less than the input voltage UD, the polarity is reversed, and the inductance is transmitted.

　　Today's soft-switching technology has made a qualitative leap in DC/DC converters. The American VICOR Power Adapter Company has designed a variety of ECI soft-switching DC/DC converters. The maximum output power is 300W, 600W, and 800W. The corresponding power density is 6.2W/cm3, 10W/cm3, 17W/cm3, and the efficiency is 80%~90%. Japan Nemic Lambda Corporation recently launched a high-frequency power adapter module RM series using soft switching technology. The switching frequency is 200~300kHz, the power density has reached 27W/cm3, and the synchronous rectifier (mos-fet instead of Schottky diode) is used to increase the efficiency of the entire circuit to 90%

　　4. Power adapter AC/DC converter

　　The AC/DC converter converts AC to DC, and its power current flow can be bidirectional. The conversion of power current to the load is called "rectification", and the transfer of power current from the load back to the power source is called "active inverter". The AC/DC converter input is 50/60Hz alternating current, which must be rectified and filtered. Relatively speaking, a relatively large filter electrolytic capacitor is essential. At the same time, due to safety issues, such as UL, CCEE and other standards and EMC directives (such as IEC, FCC, CSA), AC input must be added EMC filtering and use of components that meet safety standards, which limits the volume of AC/DC power supply to be further miniaturized. In addition, due to the internal high frequency, The high-voltage and high-current switching action makes it more difficult to solve the EMC problem, which puts high demands on the design of the internal high-density mounting circuit. For the same reason, the high-voltage and high-current switching makes the power supply work loss Increased, limiting the process of AC/DC converter modularization. Therefore, it is necessary to use the power system optimization design method to make its work efficiency reach a certain degree of satisfaction

　　AC/DC converters can be divided into half-wave circuits and full-wave circuits according to the wiring method of the circuit; according to the control characteristics of the circuit, they can be divided into three types: uncontrollable, half-controlled and full-controlled; according to the number of power phases, they can be divided into single-phase ､Three-phase and multi-phase; according to the working quadrant of the circuit, it can be divided into one quadrant, two quadrants, three quadrants and four quadrants

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