​Electronic equipment, especially computers and miniaturization, request the volume of power supply with the miniaturization, and switching power supply started to replace is characterized by heavy power frequency transformer of linear regulated power supply, a considerable improvement of power efficiency at the same time. The decrease of the volume of power supply means that the heat capacity of variation, and therefore requires the power the power consumption of small, namely on the premise of the output power is constant, efficiency must be raised.

High efficiency power conversion: switching power supply design goal

The same volume of the power the power dissipation of basic same, therefore, to get more power output, must improve the efficiency, at the same time, high power efficiency can effectively reduce the stress of the power semiconductor devices, to improve its reliability.

The wastage of the switch power supply are mainly: passive component loss and active element wear and tear

Switching loss has been confused with switching power supply designers, because of the power semiconductor devices in the process of switch, the device on at the same time there are current, voltage, thus inevitably exist switch loss, if the switch power supply switch tube and the output rectifier diodes can achieve zero voltage switch or zero current switch, its efficiency can be improved obviously.

Switching process caused by the switching loss will be roughly 5% ~ 10% of total input power, greatly reduce or eliminate the loss can be to improve the efficiency of switching power supply by 5% ~ 10%. Is the most effective method of soft switch technology or zero voltage switch or zero current switching technologies.

In many of the soft switch scheme, practical full bridge converter with high power, usually adopts the phase shifting zero voltage switch control

Way, this way of control requirements in the primary side need to attach a stream inductance to ensure that in the condition of zero voltage switch tube conduction, due to the RMS current through the larger, the additional inductor will fever (although much smaller than that of the RC buffer circuit), which is not used in low voltage power transformation.

The characteristics of passive lossless snubber circuit is not to undermine the conventional PWM control modes, simple design/debug. In spite of this, passive lossless snubber circuit and quasi resonant/zero voltage switch works also has some disadvantages, such as can only achieve soft switch off and not good for the flyback converter in the large load range. Soft switch in the active clamp is to improve the efficiency of single pipe is/flyback effective method, the original patent restrictions have now failure, can be widely used.

The progress of power semiconductor devices: high efficiency power transformation

The progress of power semiconductor devices, especially PowerMOSFET triggered a power transformation of a series of progressive: PowerMOSFET extremely fast switching speed, the switch frequency of switch power supply from a bipolar transistor more than 20 KHZ to 100 KHZ, effectively reduce the numerous sources of energy storage device (inductance and capacitance) volume. Suit low synchronous rectifier PowerMOSFET make to become a reality, the device of conduction voltage from 0.5 V to schottky diode, even lower down to 0.1 V of synchronous rectifier, the low voltage of the rectifier efficiency increased at least by 10%. High-pressure PowerMOSFET conduction of pressure drop and the characteristics of the switch is improved and improve the efficiency of the primary switch power supply. Power semiconductor devices to reduce the power consumption of the radiator and a decrease in the volume of the whole machine.

Power industry have an unwritten views: no voltage is more efficient than regulated, not isolation is more efficient than isolation, narrow range of input voltage is higher than wide range input efficiency. Vicor 48 v input power module efficiency reached 97%. Ac input switching power supply to power factor correction, due to the power factor correction has voltage stabilizing function, the application of the output ripple requirements is not high, such as the output with the battery or super capacitor), can be used in a power factor correction and not the isolation converter circuit topology, in 1986, the existing products abroad, the efficiency more than 93%.

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