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1、Switching Power Supply Switching power supply is a voltage conversion circuit, the main work is the step-up and step-down, are widely used in modern electronic products. Always work because the switching transistor in the on and off state, so called switching power supply. Switching power supply in
2、real terms is an oscillator circuit, the conversion of electrical energy not only used in power circuit, the circuit in other applications are also common, such as LCD backlight circuits, such as fluorescent lamps. Switch the source compared with the transformer high efficiency, good stability, smal
3、l size and other advantages, disadvantages is the relatively small power, and high-frequency interference on the circuit, circuit complexity, such as easy maintenance.Talking about switching power supply before you familiar with the feedback oscillator circuit transformer, can produce a regular puls
4、e current or voltage of the circuit is called oscillation circuit, transformer feedback oscillator circuit is able to meet these conditions the circuit; it in the basic amplifier circuit with a feedback loop composed of C2, L1 election to form a parallel resonant frequency circuit, the instantaneous
5、 power in the circuit turn-VT, this time in the C2, L1, composed of parallel resonant circuits have a very rich harmonic, when the plus parallel resonance frequency and the natural frequency of the same circuit, the circuit to enter a state of oscillation, and VT through L3 feedback to further enlar
6、ge the base, and ultimately the formation of a regular pulse current or voltage output to the load RL. Switching power supply is around the transformer and the feedback oscillator circuit design, but the basis of the original increase in the number of protection and control circuits, analysis of our
7、 oscillation circuit can be used to analyze the method of switching power supply.Switching Power Supply vibration by way of sub-swing can be divided into self-excited and it excited the two, since there is no need for plus-excited self-oscillation signal source, since the excitation can see it as a
8、feedback oscillator circuit transformer, and it is excited is totally dependent on the outside to maintain the oscillation, in the practical application of self-excitation of a comprehensive range of applications. According to the structure of incentives signal classification; can be divided into pu
9、lse-width-modulated pulse amplitude modulation and two pulse-width-modulated signal to control the width, that is, frequency, pulse amplitude modulation control signal of the magnitude of the role of the two the same so that oscillation frequency is maintained at within a certain range, to the effec
10、t of voltage stability. Winding transformer can be divided into three types in general, a group involved in the primary winding of the oscillation, a group is to maintain the oscillation of the feedback winding, there is a group of the load windings. Household appliances used in switching power supp
11、ly,after the AC to 220V bridge rectifier, converted into about 300V DC, filter into the transformer is added after the switch to high-frequency oscillations of the collector, feedback winding back to the base to maintain the oscillation circuit, load sensor windings of the electrical signal, by rect
12、ification, filtering, the DC voltage regulator has been to provide power to the load. Winding in the provision of electric power load, but also take up the capacity of voltage stability, the theory is then a circuit voltage output voltage sampling devices to monitor the output voltage changes, timel
13、y feedback to adjust the oscillation frequency oscillator circuit to achieve the voltage stability The purpose of the circuit in order to avoid interference, the feedback voltage to the oscillator circuit will be isolated optocoupler. Most switches have a standby power circuit, switching power suppl
14、y in standby mode still oscillating, but the frequency of normal working hours than lower.Some switching power supply are complex, numerous components, many protection and control circuit, in the absence of technical support, maintenance is a headache with the matter. I face this kind of situation i
15、s, first of all, I will find the switch and its participation in the external oscillation circuit, it separated from the circuit to see if it met the conditions for oscillation, such as detection bias and whether it is normal, whether positive feedback failure, as well as its own switches, switching
16、 power supply has very large protection, after exclusion of the prosecution and load control and protection circuit.the control circuit while output from the sample, with the set standards, then controlled inverter, change its frequency or pulse width output achieve stability, on the other hand, according to test data provided by the circuit by circuit protection identification, Control circuit for the unit for various protection measures. SMPS developments and trends in the United Stat
