Communication Switching Power Supply technology was introduced to China in the 1980s and is now widely used in the field of communications. Since the performance of the communication switching power supply directly affects the reliability of the communication system, it is particularly important to correctly judge the advantages and disadvantages of the communication power supply. It is obviously not enough to measure the advantages and disadvantages of the switching power supply only from the input and output characteristics of the power supply. It should also start from the following aspects.
One power device
The communication switching power supply technology belongs to the power electronic technology, which uses a power converter for power conversion, and thus it is easy to infer the approximate development date of the product from the type of the power device. We know that high-power silicon rectifiers and thyristors appeared in the 1960s; thyristors, giant power transistors (GTRs) and gate-turnable thyristors (GTOs) for high-power inverters were produced in the 1970s; Power FETs (MOSFETs) appeared in the 1980s; insulated gate bipolar transistors (IGBTs) were the devices that appeared in the 1990s.
It should be noted here that the power FET is significantly reduced in switching time due to unipolar multi-sub-conductivity, so it is easy to achieve a switching operating frequency of 1 MHz. However, in order to increase the device blocking voltage, the power FET must widen the drift region of the device. As a result, the internal resistance of the device increases rapidly, the on-state voltage drop of the device increases, and the on-state loss increases. An insulated gate bipolar transistor is similar in structure to a power FET, except that the insulated gate bipolar transistor adds a P+ substrate to the N+ substrate (drain) of the N-channel power FET. The improvement of the collector of the gate bipolar transistor) makes the insulated gate bipolar transistor have a series of outstanding advantages: forward bias, high input impedance, low on-resistance, high withstand voltage, and large safe working area. And high switching speed.
Looking at the package of the power device can also easily distinguish the advantages and disadvantages of the communication power supply. The die is soldered directly to the substrate to improve heat dissipation and reduce parasitic inductance, capacitance and thermal resistance. Products that are not directly soldered to the substrate are inferior.
Two circuit principle
1 depends on whether it uses hard switching technology or soft switching technology. Various lossless snubber circuits composed of LC passive components and fast recovery diodes change the switching transition process of the switching transistor, so that the switching voltage and current changes are not abrupt (ie hard switching) but are slowly changing (ie soft) Switch), thereby significantly reducing the switching loss of the power device, increasing the switching frequency of the system, reducing the volume and weight of the converter, reducing the output ripple of the system, and overcoming the sensitivity of the conversion circuit to parasitic distribution parameters, reducing The switching noise of the system broadens the frequency band of the system and improves the dynamic performance of the system.
2 depends on whether it uses variable frequency control (PFM) or constant frequency control (PWM). Constant frequency control (also known as phase shift control) is better than inverter control. Phase-shift control full-bridge conversion circuit, combining the advantages of constant-frequency control technology and soft-switching technology, realizes constant-frequency control in a wide range, realizes large-scale stepless adjustment of output voltage or current, and realizes in the instant of commutation of power devices Zero voltage switching for commutation.
3 power factor correction technology can suppress the grid side harmonic current, reduce reactive power, thereby improving the power factor, while reducing the noise and pollution generated by the high-order harmonics of the power supply, achieving energy-saving purposes.
4 Load current sharing is a key technology that reduces the output imbalance of the module parallel and makes the system redundant and fault-tolerant, making it easy to form a large-capacity communication power system. At present, there are mainly droop (Drop) current sharing method, master slave (main slave) current sharing method, average current (average current) current sharing method, external current sharing controller (external controller) current sharing method, maximum current automatic (highest Current) current sharing method. The maximum current automatic current sharing method can not only realize the automatic current sharing of the power module, but also realize the redundancy of the power module. The exit and increase of the power module do not affect the normal operation of the system, the open circuit, the short circuit of the current bus and the module Damage will not affect the normal operation of other modules in the system.
Three protection and lightning protection measures
In addition to overvoltage, undervoltage, phase loss, overcurrent, short circuit, overload, overheating, we usually want the protection function provided by the equipment, but also need to know whether there is battery monitoring and charging current limiting function. Whether to use imported brand-name lightning protection components (such as OBO, DEHN, FURSE, etc.) is also the basis for ensuring reliable and stable system in the future.
Four alarm functions
When the system works to reach the preset alarm level or the system fails, the monitoring module not only emits an audible and visual alarm, but also actively dials the fault content to the central station or the higher-level office, and automatically calls the BP machine or mobile phone specified in advance. For unattended communication stations, this is an important basis for measuring power quality.
Five monitoring interface
The use of computer technology to realize the telemetry, remote control and remote signaling functions of communication power can improve the maintenance and management quality of the system, reduce the maintenance cost of the system, and improve the overall work efficiency. Therefore, having a remote communication interface is the minimum requirement for communication power. Similarly, the type of interface also reflects the level of power supply technology from one side. In general, the Ethernet interface is superior to the RS485 interface, and the RS485 interface is superior to the RS232 interface.
Six electromagnetic compatibility
This is one of the most overlooked aspects. Due to the increasing capacity of switching power supplies, the harmonic pollution generated by them has seriously affected other power loads (mainly electronic equipment) of the power grid. Therefore, in foreign countries, especially Europe and the United States, New industrial standards have been established for the electromagnetic compatibility of electrical equipment, which makes us aware of the characteristics of the selected power input and output filters and the reasonableness of the shielding structure. Does not meet the CISPR 22 and CISPR 24 standards.
Although communication switching power supply technology is a multi-disciplinary edge technology involving power electronics, semiconductor devices, integrated automatic control, computer (microprocessor) technology and electromagnetic technology, as long as you master some background knowledge and basic principles, It is not difficult to grasp the judgment of the performance of the switching power supply.
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