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A article to let you thoroughly understand the power adapter.

A article to let you thoroughly understand the power adapter.

Update Time:2019-05-14
Power adapter is a power supply conversion device for small portable electronic devices and electronic appliances. It is generally composed of components such as a casing, a transformer, an inductor, a capacitor, a control IC, and a PCB.

What is a power adapter?
Power adapter is a power supply conversion device for small portable electronic devices and electronic appliances. It is generally composed of components such as a casing, a transformer, an inductor, a capacitor, a control IC, and a PCB. Its working principle is converted from an AC input to a DC. Output; according to the connection method can be divided into wall-mounted and desktop. Widely used in security cameras, set-top boxes, routers, light bars, massage instruments and other equipment.

The power adapter is also called an external power supply. It is a power supply voltage conversion device for small portable electronic devices and electronic appliances. It is commonly found in small electronic products such as mobile phones, liquid crystal displays and notebook computers.

The structure of the power adapter
The DC/DC converter is used for power conversion, which is the core part of the power adapter, in addition to startup, overcurrent and overvoltage protection, noise filtering, etc. The output sampling circuit (R1, R2) detects the output voltage change, and Compared with the reference voltage U, the error voltage is passed through an amplification and pulse width modulation (PWM) circuit, and then the driving circuit controls the duty ratio of the power device to achieve the purpose of adjusting the output voltage.

The DC/DC converter has various circuit forms, and a commonly used PWM converter with a working waveform of a square wave and a resonant converter with a working waveform of a quasi-sinusoidal wave are commonly used.

For a series linear regulated supply, the transient response of the output to the input is primarily determined by the frequency characteristics of the regulator. However, for a resonant regulator with a quasi-sinusoidal waveform, the transient change of the input is more represented at the output. While increasing the switching frequency, the transient response of the power adapter can also be improved due to the improved frequency characteristics of the feedback amplifier. The load change transient response is mainly determined by the output LC filter characteristics, so the transient response characteristics can be improved by increasing the switching frequency and reducing the output filter LC product.

Main categories of power adapters
The power adapter can be divided into AC/DC and DC/DC. The DC/DC converter as the secondary power supply has been modularized, and the design technology and production process have been matured and standardized at home and abroad, and have been obtained. User approval. However, the primary AC/DC, due to its own characteristics, has encountered more complicated technical problems and process manufacturing problems in the process of modularization. The structure and characteristics of the two types of power adapters are described below.

DC/DC type power adapter
DC/DC type power adapter converts fixed DC voltage into variable DC voltage, also known as DC chopper. 斩L.DCDC type power adapter wave filter works in two ways: First, pulse width modulation T does not change, change the frequency modulation mode t (general); second, the frequency modulation mode t does not change and changes T (easy to generate interference). The specific circuit has the following types

1Buck circuit—buck chopper, whose output average voltage Uo is smaller than the input voltage UD, and the polarity is the same;

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

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

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

Today's soft-switching technology has made a qualitative leap in DC/DC converters. VICOR Power Adapters of the United States has designed a variety of ECI soft-switching DC/DC converters manufactured by capacitor transmission. The maximum output power is 300W, 600W, 800W. Etc., the corresponding power density is 6.2W/cm3, 10W/cm3, 17W/cm3, and the efficiency is 80%~90%. The latest RM series of high frequency power adapter module adopting soft switching technology by Nemic Lambda of Japan, 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 overall circuit efficiency to 90%.

Power adapter AC/DC converter
The AC/DC converter converts the alternating current to direct current, and its power current flow direction can be bidirectional. The transformation of the power current to the load is called "rectification", and the power current is transmitted back to the power supply by the load called "active inverter". AC/DC converter input is 50/60Hz AC, which must be rectified and filtered. Relatively large filter electrolytic capacitors are indispensable. At the same time, due to safety issues, such as UL, CCEE standards and EMC directives (such as IEC, FCC, CSA), AC input must be EMC filtered and use components that meet safety standards, thus limiting AC / DC The volume of the power supply is further miniaturized. In addition, due to the internal high-frequency, high-voltage, high-current switching action, it is more difficult to solve the EMC electromagnetic compatibility problem, and it also puts high requirements on the design of the internal high-density mounting circuit. For the same reason, high voltage . The high current switch increases the operating loss of the power supply and limits the modularization of the AC/DC converter. Therefore, the power system optimization design method must be adopted to achieve a certain degree of satisfaction in working efficiency.

AC/DC converter can be divided into half-wave circuit and full-wave circuit according to the circuit connection mode; according to the control characteristics of the circuit, it can be divided into three categories: uncontrollable, semi-controlled and full-controlled; , three-phase and multi-phase; according to the circuit working quadrant can be divided into one quadrant, two quadrant, three quadrant and four quadrant.

Advantages of the power adapter
1. Small size and light weight. The switching power adapter does not use a bulky power frequency transformer. Since the power dissipation on the switching MOS tube is greatly reduced, a large heat sink is omitted. For these two reasons, the switching power adapter is small in size and light in weight.

2. Low power consumption and high efficiency. In the switching power adapter circuit, the switching MOS transistor is excited under the excitation signal, and it alternately operates in the on-off and off-on-conduction state, the conversion speed is fast, the frequency is generally above 50 kHz, in some advanced switches. In the power line, it can be hundreds or nearly mega Hz. This makes the power consumption of the switching MOS transistor small, the efficiency of the power supply can be greatly improved, and the efficiency can reach 90%.

3. The efficiency of filtering is greatly improved, so that the capacity and volume of the filter capacitor are greatly reduced. The operating frequency of the switching power adapter is basically working above 50kHz, which is more than 1000 times that of the linear regulated power adapter. This makes the filtering efficiency after rectification almost 1000 times. Even after half-wave rectification and capacitor filtering, The efficiency has also increased by 500 times. At the same ripple output voltage, when using a switching power supply, the capacity of the filter capacitor is only 1/500 to 1/1000 of the filter capacitor in the linear regulated power supply.

4. Wide voltage regulation range. The output voltage of the switching power adapter is regulated by the duty cycle of the excitation signal, and the change in the input signal voltage can be compensated by frequency modulation or widening. In this way, when the voltage of the power frequency grid changes greatly, it can still ensure a relatively stable output voltage. Therefore, the switching power supply adapter has a wide voltage regulation range and the voltage regulation effect is very good. In addition, methods for changing the duty ratio include pulse width modulation type and frequency modulation type. The switching regulator power supply not only has the advantage of wide voltage regulation range, but also has many methods for realizing voltage regulation. Designers can flexibly select various types of switching power supply integrated circuit chip solutions according to the requirements of practical applications.

Power adapter development trend
At present, the power adapter on the market utilizes power electronics technology to control the output voltage by adjusting the ratio of the turn-on and turn-off time of the switching transistor, and using the power semiconductor device as a switch to adjust the output voltage.

The first stage of the development of China's power adapters was before 1976, which was the initial stage of the development of China's switching power supply and power adapter industry. The relevant power supply technologies are not mature, and there is no systemization and standardization.

External power supply was mainly based on linear power supply before the 1980s. The biggest disadvantage of linear power supply is that it is larger in size and weight than the power adapter, and the efficiency is low, but the advantage is stable operation and simple circuit, but it is particularly bulky, rough and inconvenient to carry.

So in the mid-1980s, Toshiba of Japan took the lead in using switching power supply technology for the external power supply of notebooks. Its pioneering work opened a new page in the history of power adapter development in the world, and became the world's first independent notebook power adapter. Because the power supply of the switching power supply technology is externally placed, the notebook does not need to consider the heat generated by the power conversion to gather in the notebook itself, and the power adapter is convenient to carry, thereby effectively improving the commercialization and popularization of the notebook computer. It has been used today.

Since Toshiba has turned on the notebook power supply to fully realize the switching power supply, the notebook manufacturers have taken the lead in completing the computer power generation. In the 1990s, the power adapter has been widely used in various electronic and electrical equipment, program-controlled switches, communication, power detection equipment power supply and Control device power.

The power adapter is generally composed of a pulse width modulation (PWM) control IC and a MOSFET, and is one of the representative of the current regulated power supply.

In 1989, China's standardized power supply production enterprises have grown to 171, with more than 340 product specifications and an annual output of more than 600,000 power supplies.

At this stage, with the gradual rapid development of the power industry, the vast number of power technology workers urgently need to break the original closed state and understand the outside world. Since the mid-1970s, power technology personnel spontaneously organized technical exchanges. In 1978, the first national power technology exchange seminar was held. In 1983, the China Power Supply Society was established. In 1986, it was approved by the State Science and Technology Commission.

In the late 1990s, a series of standards in Europe regarding power conversion efficiency and standby power consumption pushed the power adapter to an unreachable height. The high frequency of the power adapter makes it develop direction, the high frequency makes the switching power supply miniaturized, and the power adapter enters a wider range of applications, especially in the high-tech field, which promotes the miniaturization of high-tech products. Lightweight. In addition, the development and application of power adapters are of great significance in terms of energy conservation, resource conservation and environmental protection.

In 2001, Apple developed a stylish and lightweight power adapter, which pushed the power adapter to another new peak. The power adapter was brought to the light and stylish direction, so the appearance of the power adapter no longer felt like The previous appearance was a single and less aesthetically pleasing impression.

Shenzhen Lianyunda Electronics Co., Ltd. was founded in 2006, a professional manufacturer of safety power. The main research and development production and sales of various types of power adapters, switching power supplies, battery chargers, and has world certification. Standardize and improve internal quality control, so as to continuously improve product quality standards and provide quality products and services to our customers.
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