【正文】 ng power supply can be divided into AC / DC and DC / DC two categories, AC / AC DC / AC, such as inverters, DC / DC converter is now modular design technology and production processes at home and abroad have already matured and standardization, and has been recognized by the user, but AC / DC modular, its own characteristics make the modular process, encounter more plex technology and manufacturing process. Hereinafter to illustrate the structure and characteristics of the two types of switching power supply. Selfexcited: no external signal source can be selfoscillation, pletely selfexcited to see it as feedback oscillation circuit of a transformer. Separate excitation: entirely dependent on external sustain oscillations, excited used widely in practical applications. According to the excitation signal structure classification。 shutdown, voltage, current) Voltammetric product / power device is power semiconductor devices on the loss. Compared with the linear power supply, the PWM switching power supply more efficient process is achieved by chopping, that is cut into the amplitude of the input DC voltage equal to the input voltage amplitude of the pulse voltage. The pulse duty cycle is adjusted by the switching power supply controller. Once the input voltage is cut into the AC square wave, its amplitude through the transformer to raise or lower. Number of groups of output voltage can be increased by increasing the number of primary and secondary windings of the transformer. After the last AC 18 waveform after the rectifier filter the DC output voltage. The main purpose of the controller is to maintain the stability of the output voltage, the course of their work is very similar to the linear form of the controller. That is the function blocks of the controller, the voltage reference and error amplifier can be designed the same as the linear regulator. Their difference lies in the error amplifier output (error voltage) in the drive before the power tube to go through a voltage / pulsewidth conversion unit. Switching power supply There are two main ways of working: Forward transform and boost transformation. Although they are all part of the layout difference is small, but the course of their work vary greatly, have advantages in specific applications. the circuit schematic The socalled switching power supply, as the name implies, is a door, a door power through a closed power to stop by, then what is the door, the switching power supply using SCR, some switch, these two ponent performance is similar, are relying on the base switch control pole (SCR), coupled with the pulse signal to plete the on and off, the pulse signal is half attentive to control the pole voltage increases, the switch or transistor conduction, the filter output voltage of 300V, 220V rectifier conduction, transmitted through the switching transformer secondary through the transformer to the voltage increase or decrease for each circuit work. Oscillation pulse of negative semiattentive to the power regulator, base, or SCR control voltage lower than the original set voltage power regulator cutoff, 300V power is off, switch the transformer secondary no voltage, then each circuit The required operating voltage, depends on this secondary road rectifier filter capacitor discharge to maintain. Repeat the process until the next pulse cycle is a half weeks when the signal arrival. This switch transformer is called the highfrequency transformer, because the operating frequency is higher than the 50HZ low frequency. Then promote the pulse of the 19 switch or SCR, which requires the oscillator circuit, we know, the transistor has a characteristic, is the baseemitter voltage is is the zoom state, These are the saturated hydraulic conductivity in the oscillatory state, then the operating point after a good tune, to rely on the deep negative feedback to generate a negative pressure, so that the oscillating tube onset, the frequency of the oscillating tube capacitor charging and discharging of the length of time from the base to determine the oscillation frequency of the output pulse amplitude, and vice versa on the small, which determines the size of the output voltage of the power regulator. Transformer secondary output voltage regulator, usually switching transformer, single around a set of coils, the voltage at its upper end, as the refer。s national economy. Developments and trends of the switching power supply 1955 . Royer (Roger) invented the selfoscillating pushpull transistor singletransformer DCDC converter is the beginning of the highfrequency conversion control circuit 1957 check race Jen, Sen, invented a selfoscillating pushpull dual transformers, 1964, . scientists canceled frequency transformer in series the idea of switching power supply, the power supply to the size and weight of the decline in a fundamental way. 1969 increased due to the pressure of the highpower silicon transistor, diode reverse recovery time shortened and other ponents to improve, and finally made a 25kHz switching power supply. At present, the switching power supply to the small, lightweight and high efficiency characteristics are widely used in a variety of puteroriented terminal equipment, munications equipment, etc. Almost all electronic equipment is indispensable for a rapid development of today39。 the other is the AC switching power supply. Introduces only DC switching power supply and its function is poor power quality of the original ecopower (coarse) such as mains power or battery power, converted to meet the equipment requirements of highquality DC voltage (Varitronix) . The core of the DC switching power supply DC / DC converter. DC switching power supply classification is dependent on the classifi