Switching power supply
Switching power supply can be divided into two categories of AC/DC and DC/DC, DC/DC converter is now modular, and the design technology and production process at home and abroad have been mature and standardized, and has been recognized by the user, but the modularity of the AC/DC, because of its own characteristics make the modularization of the process, encountered a more complex technology and technology Manufacturing problems. The following two types of switching power supply structure and characteristics are described.
2.1 DC/DC converter
DC/DC converter is to convert a fixed DC voltage into a variable DC voltage, also known as DC chopper. Chopper works in two ways, one is the pulse width modulation method Ts is unchanged, change the ton (general purpose), the second is the frequency modulation method, the ton is unchanged, change the Ts (prone to interference). Its specific circuit consists of the following categories:
(1) Buck circuit - buck chopper, its output average voltage Uo is less than the input voltage Ui, the same polarity.
(2) Boost circuits - boost choppers, whose output average voltage Uo is greater than the input voltage Ui, with the same polarity.
(3) Buck-Boost circuits - Buck or Boost choppers, whose output average voltage Uo is greater or less than the input voltage Ui, with opposite polarity and inductive transfer.
(4) Cuk Circuit - Buck or Boost Chopper, whose output average voltage Uo is greater or less than the input voltage Ui, with opposite polarity and capacitive transfer.
Today's soft-switching technology makes a qualitative leap in DC/DC, the U.S. VICOR company designed and manufactured a variety of ECI soft-switching DC/DC converter, its maximum output power of 300W, 600W, 800W, etc., the corresponding power density of (6, 2, 10, 17) W / cm3, the efficiency of the (80-90) %. Japan's NemicLambda's latest introduction of a soft-switching technology of high-frequency switching power supply module RM series, its switching frequency (200-300) kHz, power density has reached 27 W/cm3, using synchronous rectifier (MOS-FET instead of Schottky diode), is the entire circuit efficiency increased to 90%.
2.2 AC/DC converter
AC/DC converter is to convert AC to DC, the power flow can be bidirectional, power flow from the power supply to the load is called "rectifier", power flow from the load back to the power supply is called "active inverter". "The input of AC/DC converter is 50/60Hz alternating current, because it must be rectified and filtered, so relatively large filter capacitors are essential, and because of safety standards (such as UL, CCEE, etc.) and EMC directives (such as IEC, FCC, CSA), the AC input side must be added to the EMC filtering and the use of components that comply with safety standards, which limits the number of components that can be used in the AC/DC converter. Safety standards components, which limits the miniaturization of the AC/DC power supply volume, in addition, due to the internal high-frequency, high-voltage, high-current switching action, making it more difficult to solve the EMC electromagnetic compatibility problem, but also on the internal high-density installation circuit design puts forward high requirements, due to the same reason, high-voltage, high-current switching makes power supply operating consumption increases, limiting the AC/DC converter The modularization process, therefore, must use the power system optimization design method in order to make its work efficiency to reach a certain degree of satisfaction.
AC/DC converter can be divided into half-wave circuits and full-wave circuits according to the wiring of the circuit. According to the number of power supply phases can be divided into single, three-phase, multi-phase. According to the circuit operating quadrant can be divided into one quadrant, two quadrant, three quadrant, four quadrant.
Module power supply
Module power supply advantages
● Simple design. Only one power supply module with a small number of discrete components is required to obtain a power supply.
● Shorten the development cycle. Modular power supply is generally available with a variety of input and output options. Users can also repeat the iteration or cross iteration, constitute a building block type combination of power supply, to achieve multiple inputs and outputs, greatly reducing the prototype development time.
● Flexible changes. If you need to change the design of your product, simply convert or parallel connect another suitable power module.
● Low technical requirements. Modular power supplies typically come with standardized front ends, highly integrated power modules, and other components, making power supply design easier.
● Modular power supply shell has a heat sink, heat sink and shell of the trinity of structural forms, the realization of the modular power supply conduction cooling method, so that the power supply temperature value tends to minimize. At the same time, but also endowed with a modular power supply gold and jade packaging.
● High-quality and reliable. Modular power supplies are generally fully automated production, and with high-tech production technology, so the quality is stable and reliable.
● Wide range of applications: modular power supply can be widely used in aerospace, locomotive and naval vessels, military industry, power generation and distribution, post and telecommunications, metallurgy and mining, automatic control, household appliances, instrumentation and scientific research and experimentation, and other social production and life in various fields, especially in the field of high-reliability and high-tech plays an irreplaceable important role.
The role of the module power supply
1, the output voltage adjustment
For TRIM or ADJ (adjustable) output pin module power supply products, through the resistance or potentiometer on the output voltage within a certain range of adjustment, the general adjustment range of ± 10%.
For TRIM output pins, the center of the potentiometer is connected to the TRIM, in all +S, -S pins of the module, the other two ends were connected to the +S, -S. There is no +S, -S, will be connected to the two ends of the corresponding output of the main circuit, respectively, the positive and negative poles (＋S connected to +Vin, -S connected to -Vin). When there is no +S, -S, the two ends are connected to the corresponding main output positive and negative (+S to +Vin, -S to -Vin), and then adjust the potentiometer. Potentiometer resistance value generally choose 5 ~ 10kΩ is more appropriate.
The ADJ output pins are divided into the input side of the regulation and output side of the section. The output side regulation is the same as the TRIM pin. Input side adjustment can only upwardly adjust the output voltage, at this time, one of the potentiometer will be connected to the center, the other end is connected to the ground of the input.
2, the input protection circuit
General modular power products have built-in filters to meet the general power application requirements. If you need a more demanding power system, you should increase the input filter network. LC or π-type networks can be used, but care should be taken to choose as small an inductor and as large a capacitor as possible.
In order to prevent the input power transient high voltage from damaging the module power supply, it is recommended that users connect a transient absorbing diode to the input and use it in conjunction with a fuse to ensure that the module is within a safe input voltage range. In order to reduce ****module noise, you can increase Y (Cy) capacitance, generally choose a few nf high-frequency capacitors. r for the fuse, D1 for the protection diode, D2 for the transient absorption diode (P6KE series).
3, remote control on/off circuit
The remote control switching operation of the module power supply is carried out through the REM terminal. There are two general control modes:
(1) REM is connected to -VIN (reference ground) and remotely switched off, requiring VREF<0.4V. REM is suspended or connected to +VIN, and the module operates, requiring VREM>1V.
(2) REM is connected to VIN and remotely switched off, requiring VREM<0.4V, REM and +VIN connected to the module work, requiring VREM>1V. REM suspended, remote shutdown, the so-called "suspended shutdown" (-R).
If the control is to be isolated from the input, an opto-coupler can be used as a means of transmitting the control signal.
4, the combination of modules
(1) Parallel expansion. Parallel connection of the output of the same module can make the output capacity, but the output voltage of the parallel module should be adjusted more consistently to ensure that the relative equalization of current, while avoiding unnecessary oscillation. For modules with larger current outputs, the lead resistors can also be carefully designed to equalize the current. Modules connected in parallel in this way should not be more than two. At the same time, if one of the module output is faulty, the entire system will not work properly. Parallel expansion connection circuit RL for the load.
(2) Redundant hot backup parallel connection. Will be the same module output through the diode after parallel connection can make the output capacity to enhance the reliability of the power system. In principle, if with the corresponding output alarm circuit, the module will be placed on the bus that can be removed, so that the failure of the module can be replaced in a timely manner. With this method of parallel connection of the module, there is no volume limit. d is generally Schottky diode.
(3) Series expansion. The output of the same module in series, the output voltage can be multiplied, the power is also increased accordingly, and the output of the series must be connected to the diode for protection.
5, the backup use of ringing
Ringing generator is mainly used for telephone exchanges to provide ringing telephone users, generally used in the bias state. Bias can be divided into positive and negative bias. In order to improve the reliability of the ringing system, it is necessary to back up the ringing stream.
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