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Power adapter features

Power adapter features
The power adapter has high efficiency, the circuit has perfect protection measures (including overcurrent, overvoltage and overtemperature), the power supply has built-in short-circuit protection, when the load short-circuit or overload, the product will automatically protect. Is a super reliable power supply.
Light weight, easy to carry, replace the traditional transformer. Power supply products are divided into indoor use and outdoor use of two categories of products, outdoor use of products with closed irrigation, waterproof and moisture-proof, suitable for a variety of environments; Easy to install, can be suspended or flat on the supporting object; Indoor use of the product mechanism is not waterproof function, only suitable for installation indoors.
The traditional energy-consuming linear voltage-stabilizing power adapter, in fact, stabilizes the voltage of the load by changing its energy consumption through the energy-consuming components in series or parallel in the load circuit. When the load voltage increases, the equivalent resistance of the energy dissipation circuit increases and the load voltage decreases. On the contrary, when the load voltage is reduced, the resistance energy consumption is reduced and the load voltage is increased. Because the energy dissipation circuit works in the linear region within the stable voltage range, and the voltage drop within this range is proportional to the increase of the input voltage and inversely proportional to the increase or decrease of the load current, it is also known as the linear regulated power supply adapter, or compared with the current digital circuit, it can also be called the analog regulated power supply adapter.
Switching power supply and adapter are switching power supply, which are composed of high frequency switching tube and its control circuit. While the adapter power supply is a stable switching power supply, the switching power charger has the function of floating charge, the voltage is increased with the decrease of the current, to the voltage but no current.
The energy consumption of the energy-dissipation stabilized voltage supply adapter is necessary and inevitable, because the voltage stabilizing process is realized through the energy consumption. Therefore, it is obvious that the wider the voltage stabilizing range is, the larger the input/output pressure difference is, and the greater the energy consumption is. It is impossible for 220V mains power to output 300V dc after rectifying. It is also impossible for such regulators to output stable 5V and 12V low-voltage dc. The energy-consuming low-voltage output voltage regulator must be used together with the power-frequency transformer, which increases the volume and weight of the voltage regulator and also increases the additional loss (copper loss and iron loss of the transformer).
The efficiency of filtering is greatly improved, and the capacity and volume of filtering capacitance are greatly reduced. At present, the operating frequency of the switching power adapter is basically above 50kHz, which is more than 1000 times of that of the linear stabilized power adapter, which makes the filtering efficiency after rectification almost improve 1000 times. Even with half - wave rectification and capacitor filtering, the efficiency is improved by 500 times. At the same ripple output voltage, when switching power supply is used, the capacity of the filter capacitor is only 1/500 ~ 1/1000 of the filter capacitor in the linear regulator power supply.
The appearance of switch voltage regulator has completely changed the concept of voltage regulator. As the name suggests, switching voltage stabilizer is through switching action, make continuous direct current into intermittent power supply pulse, and then through energy storage filter elements, the discontinuous pulse into continuous direct current. Switching regulators use an output stage, repeatedly switching "on" and "off" states to produce an output voltage in conjunction with energy storage components (capacitors and inductors). Its adjustment is realized by adjusting the switching timing according to the feedback sample of output voltage. As long as the on/off time ratio is controlled, the output voltage can be changed, and then the on/off time can be controlled through the change of the output voltage to make the output voltage stable. Obviously, if the on/off characteristics are ideal during this process, there should be no loss, and the switching time ratio can vary widely. Therefore, it is also possible for the switching regulator to directly output the 300V dc voltage regulator to 5V, eliminating the need for power frequency transformers, which is one of the greatest advantages of the power adapter. Current power adapters have reached the highest efficiency of 95%, power volume ratio up to 3. 2W/CMS, compared with the energy dissipation voltage regulator with the same output power, the consumption of nonferrous metal materials is reduced by more than 90%. At present, there are many kinds of power adapter with great performance difference, but each has its own advantages and special fields, so it is difficult to compare the specific data with the energy dissipation stabilizer. This book introduces the features and application areas of each power adapter for a specific purpose, problems with 1,2 power adapters, and current solutions
Books published in the past few years on power adapters have always included a list of specific shortcomings relative to energy-dissipating regulators. However, with the rapid development of power adapter technology, these shortcomings are constantly improved by new technologies and devices.

Increase in switching frequency
In the power adapter, increasing the switching frequency can be more beneficial to play the advantages, and more effective to suppress the ripple. However, until the 1980s, the operating frequency of the power adapter did not exceed 40kHz in most cases, generally ranging from 15 KHZ to 25kHz. The first difficulty in increasing the frequency of the power adapter is limited by the switching speed of the switch tube. With a bipolar switch tube power adapter, the

PN junction in the positive guide, the carrier continuously to the other region diffusion, so that the other region carrier has a considerable number of storage. When the reverse voltage is added, the charge stored in the switch continues to spread while the hole recombines with the electron, and the switch will not be cut off until the stored charge disappears. At the end of the storage time, a few of the excess carriers near the PN junction have disappeared, and the current of the switching tube starts to decrease. When the switch tube is cut off, the emitter junction and collector junction are reverse biased, there are no free electrons in the triode base area, and the collector current is zero. If the transmitting junction positive deviation voltage reaches 0. Above 7V, the positive bias voltage first charges the capacitor of the emitter junction, gradually cancels the electric field in the PN junction, and then starts to emit electrons to the base region. Therefore, the whole process enables the transistor to conduct with a delay time. After the electron is emitted to the base area, within the distance of the base area, one side is diffused towards the collector area and the other side is combined with the hole and disappears. In this process, a certain number of electrons are stored in the base area, and the current density of the collector is finally reached to make the switch tube work. The time taken up by this process is called the pulse rise time. In addition, the bipolar transistor has pulse drop time. It can be seen that the switch composed of bipolar triode is not ideal, and the rise time and storage effect all form switch loss. The higher the working frequency is, the closer the rising time and storage time are compared with the cycle, the greater the loss will be. It is even too late to turn off before the next cycle, causing continuous conduction and damage to the switch tube. Although the current switching tube manufacturing process makes the base area thinner and reduces such losses, the switching frequency of bipolar triode is still difficult to break 40kH.
At present, this problem has been solved by the development of schottky diode and field effect switch. Schottky diode USES the energy barrier between metal and semiconductor to form rectifying effect. It has a small forward pressure drop, even for the maximum rectified current, which is only o. 3 o. Less than 5 v. Ordinary diodes are all at 0. Between 7-1 v. In addition, schottky diodes conduct electricity through most carriers, have no storage effect, and the reverse recovery time is two orders of magnitude faster than ordinary diodes, and one order of magnitude faster than fast recovery diodes.
The field effect switch tube is a voltage control device, does not contain a few carriers, there will be no minority carrier formation of the storage time, the shutdown time can be small to dozens of ns, than the bipolar triode 10 times smaller than. Currently, schottky diode is used as pulse rectifier and field effect tube as general civilian power adapter for switching devices. The operating frequency is 200kHz and up to daggers. The u. s. military power adapter module, the switch frequency has reached more than 4MHz. With the increase of switching frequency, the volume and quality of the power adapter are greatly reduced. The modular power adapter with a working frequency of 4.4mhz has an output power of 160W, a volume of only 1lem~5emXlcm, and a mass of less than 150g. In addition, the increase of switching frequency also provides a favorable condition for the decrease of ripple output.
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