how switching power supplies work

Switching power supply is the essence of an oscillation circuit, the conversion of electrical energy method is used not only in the power circuit, circuit in other applications are very broad, such as liquid crystal display backlight circuit, the fluorescent lamp. Switching power supply with a transformer with high rate, good stability, small size and other advantages compared. The disadvantage is that the power is relatively small, and the circuit to generate high frequency interference, transformer feedback oscillator circuit, can be bred occurred discipline of pulse current or voltage of the circuit called oscillation circuit, transformer feedback oscillator circuit is the circuitry that satisfied the conditions.

Switching power supply is divided into two forms, which are isolated and non isolated. According to the layout of the distribution of power distribution differences, can be divided into: positive and anti shock type two major categories. Flyback type means that the side of the original side of the transformer is stopped and the transformer can be stored. At the end of the primary side, secondary side conduction, energy is released to the load state of affairs, usual groovy flyback power supply tube, double tube not common. Is the original edge of the transformer in the original side of the side of the original side of the side of the side of the output voltage output to the load, energy through the transformer directly informed. According to the specification can be divided into general forward, including single forward, two transistorforward. Half bridge, bridge circuit belongs to forward circuit.

The forward and flyback circuits have their own characteristics. In the course of the planned circuit, it can be used to reach the optimal price ratio. As often as in small power can choose to use the anti shock. Slightly larger single acceptance is excitation circuit, medium power can accept double positive excitation circuit and half bridge circuit, low voltage acceptance push-pull circuit, and half bridge state of affairs similar. High power output, as usually adopt bridge circuit, low voltage may accept a push-pull circuit.

Flyback power supply because of its simple structure, saves a transformer and large volume of the inductor, and in the middle and small power supply get extensive application. Flyback power supply transformer leakage inductance is a very crucial parameters, due to the energy storage, the necessary transformer of flyback switching power supply, to get full use of the transformer core, usually to open air gap in the magnetic circuit, the target is transformation hysteresis curve of the core of the slope, the transformer to probably suffer large pulse current strike without as core into saturation nonlinear state, air gap in the magnetic circuit in high magnetoresistance state and in the magnetic circuit bred leakage magnetic far outweigh completely closed magnetic circuit.

As far as possible short pulse voltage connection, the input switch to the transformer line output transformer, rectifier to the adjacent line. The pulse current loop is small as small as the input filter capacitor is positive to the transformer to the switch tube to return the capacitor negative. Output unit of transformer output to rectifying tube to output inductance to the output capacitor return circuit transformer x capacitors to although even close to the switch power supply input end, the input line should stop and other circuit parallel, should be avoided. The Y capacitor should be arranged in the chassis grounding terminal or FG connection terminal. A total of inductance to be connected with the transformer to prevent magnetic coupling.

Output capacitor as usually accept two a near rectifier tube and the other should be close to the output terminal, can affect power output ripple index, two small capacitance and results should be better than a large capacity capacitor. Heating device to electrolytic capacitor and maintain a certain interval, in order to extend the service life of the whole machine, electrolytic capacitor is switch power life of the bottle neck, such as transformers, power tube, high power resistance and electrolytic link interval, between electrolysis is also required to set aside space for heat dissipation, conditional capacity allowed to install a fan or increase the exhaust hole.

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