Power adapter features
The power adapter has high efficiency, the circuit has perfect protection measures (covering overcurrent, overvoltage, and overtemperature). The power supply has built-in over-short protection. When the load is short-circuited or the load is too heavy, the product will automatically protect it. Is a super reliable power supply.
Light weight and easy to carry, replacing traditional transformers. Power products are divided into two categories: indoor use and outdoor use. Outdoor use products are sealed and sealed, waterproof and moisture-proof, suitable for various environments; easy to install, can be hung or placed on supporting objects; indoor use The product mechanism has no waterproof function and is only suitable for indoor installation.
The traditional energy-consumption linear voltage regulator power adapter actually stabilizes the voltage of the load by changing the energy consumption components in series or parallel in the load circuit. When the load voltage increases, the equivalent resistance of the energy dissipating circuit increases, so that the voltage on the load decreases; on the contrary, when the load voltage decreases, the resistance energy consumption is reduced, and the load voltage is increased. Because the energy dissipation circuit works in the linear region within the voltage regulation range, 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, so it is also called a linear regulated power adapter , Or relative to the current digital circuit, it can also be called an analog regulated power adapter;
The switching power supply and the adapter are both switching power supplies, and are composed of a high-frequency switching tube and its control circuit. The adapter power supply is a regulated switching power supply, and the switching power supply charger has a floating charging function. The voltage increases as the current decreases, and then there is only voltage and no current.
The energy consumption of the energy-consumption regulated power adapter is necessary and unavoidable, because the voltage regulation process is realized by the amount of energy consumption. Because of this, the wider the voltage regulation range of this regulator, the greater the input / output voltage The larger the difference, the greater the energy consumption, which is obvious. 220V city power rectifies and outputs 300V DC power. It is impossible to output stable 5V, 12V low voltage DC power through this type of regulator. The energy-consuming low-voltage output voltage regulator must be used in conjunction with the power frequency transformer, which causes the size and weight of the voltage regulator to increase, and also adds additional losses (copper and iron losses of the transformer).
The efficiency of filtering is greatly improved, which greatly reduces the capacity and volume of the filtering capacitor. The working frequency of the switching power adapter is currently 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 higher; even if capacitor filtering is used after half-wave rectification, The efficiency is also increased by 500 times. Under the same ripple output voltage, when a switching power supply is used, the capacity of the filter capacitor is only 1/500 to 1/1000 of the filter capacitor in a linear regulated power supply.
The advent of switching regulators has completely changed the concept of voltage regulators. As the name suggests, the switching regulator uses continuous switching to turn continuous DC power into intermittently powered pulses, and then uses energy storage filter elements to turn discontinuous pulses into continuous DC power. Switching regulators use an output stage to repeatedly switch between “on” and “off” states to produce an output voltage with energy storage components (capacitors and inductors). Its adjustment is realized by adjusting the switching timing according to the feedback sample of the output voltage. As long as the on / off time ratio is controlled, the output voltage can be changed, and then the on / off action time is controlled by the change of the output voltage to stabilize the output voltage. Obviously, if the on / off has ideal characteristics in 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 300V DC voltage to 5V, eliminating the need for a power frequency transformer, which is one of the biggest advantages of the power adapter. The current power adapter has a maximum efficiency of 95% and a power-volume ratio of 3.2W / cms. Compared with an energy-consuming regulator with the same output power, the consumption of non-ferrous metal materials is reduced by more than 90%. At present, there are many types of power adapters, and the performance gap is huge, but each has its own advantages and special areas, so it is difficult to compare specific data with energy-consuming regulators. This book will introduce the characteristics and application areas of each special-purpose power adapter. The problems with the 1 and 2 power adapters and the current solutions
Books on power adapters published in previous years, when referring to power adapters, always list a series of shortcomings specific to energy-consuming regulators. But with the rapid development of power adapter technology, these shortcomings have been continuously improved by new technologies and devices.
Increased switching frequency
In power adapters, increasing the switching frequency can be more conducive to exerting advantages and more effectively suppress ripple. However, until the 1980s, the operating frequency of power adapters mostly did not exceed 40kHz, generally 15-25kHz. To increase the frequency of the power adapter, the first problem encountered is limited by the switching speed of the switch. Power adapter with bipolar switch tube, which
When the PN junction is conducting in the forward direction, the carriers continue to diffuse to the opposite region, so that the carriers in the opposite region have a considerable amount of storage. When the reverse voltage is added, the charge stored in the switch will continue to diffuse while the holes and electrons recombine, and the switch will not turn 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 switching tube current has begun to decrease. When the switch is turned off, the emitter and collector junctions are reverse biased, there are no free electrons in the base region of the transistor, and the collector current is zero. If the forward-bias voltage of the emitter junction is above 0.7V, the forward-bias voltage first charges the capacitor of the emitter junction and gradually cancels the electric field in the PN junction before starting to emit electrons to the base region. Therefore, the whole process causes the transistor to conduct for a delay time. After the electrons are emitted to the base region, within the length of the base region, it diffuses toward the collector region, while recombining with the holes disappears. In this process, a certain number of electrons are stored in the base area, and finally the density corresponding to the required collector current is reached, and then the switch is turned on. The time this process takes is called the pulse rise time. In addition, the bipolar transistor has a pulse fall time. It can be seen that the switch formed by the bipolar triode is not ideal, and the rise time and storage effect all form switching losses. The higher the operating frequency, the closer the rise time and storage time are compared to its period, the greater the loss, and it is even too late to turn off before the next cycle arrives, causing continuous conduction and damaging the switch. Although the current switching tube manufacturing process makes the base region thinner and reduces such losses, the switching frequency of the bipolar transistor is still difficult to exceed 40kH. .
At present, this problem is solved due to the development of Schottky diodes and field effect switches. Schottky diodes use the energy barrier between metal and semiconductor contacts to form a rectifying effect, and their forward characteristics are better than PN junction diodes. It has a small forward voltage drop, and even when used for maximum rectified current, the forward voltage drop is only at o. 3 a o. Within 5V. The ordinary diodes are between 0.7-1V. In addition, Schottky diodes conduct electricity through majority carriers and have no storage effect. Their 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 is a voltage control device. It does not contain minority carriers, so there is no storage time for minority carriers. Its turn-off time can be as small as tens of ns, which is 10 times smaller than a bipolar transistor the above. At present, Schottky diodes are used for pulse rectification, and field-effect transistors are used as switching devices for general civil power adapters , and their operating frequencies are at 200 kHz. The US military power adapter module has enabled the switching frequency to reach more than 4MHz. Increasing the switching frequency first reduces the volume and quality of the power adapter significantly. A modular power adapter with a working frequency of 4.4MHz, an output power of 160W, a volume of only 1lem ~ 5emXlcm, and a mass of less than 150g. In addition, the increase of the switching frequency also provides favorable conditions for the reduction of the ripple output. High-frequency ripple can obtain smaller ripples through simpler filters.
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|| Release time: 2019.09.03 Source: Power adapter manufacturers|
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Dongguan Qiqi Industrial Co., Ltd. specializes in producing: power adapters , chargers, LED drive power supplies, car chargers, switching power supplies, etc ...