Preface.
The continuous miniaturization of electronic devices, especially computers, requires the size of the power supply to be miniaturized accordingly, thus switching power supplies began to replace the linear regulated power supplies characterized by bulky industrial frequency transformers, while the efficiency of the power supply was significantly improved. The reduction in the size of the power supply means that the heat dissipation capacity becomes worse, thus requiring the power consumption of the power supply becomes smaller, that is, the output power remains the same, the premise of the efficiency must be improved.
The power dissipation of the same volume of power supply is basically the same, therefore, to get greater output power, must improve efficiency, at the same time, high power efficiency can effectively reduce the stress of power semiconductor devices, which is conducive to improving their reliability.
Advances in power semiconductor devices: the fundamental of high-efficiency power conversion
The progress of power semiconductor devices, especially the progress of the PowerMOSFET leads to a series of progress in power conversion: PowerMOSFET's extremely fast switching speed, so that the switching frequency of the switching power supply from the bipolar transistor 20kHz to more than 100kHz, effectively reducing the volume of passive energy storage components (inductors, capacitors). Low-voltage PowerMOSFETs make low-voltage synchronous rectification a reality. The on-state voltage of the device is reduced from about 0.5V for Schottky diodes to 0.1V or even lower for synchronous rectifiers, increasing the efficiency of low-voltage rectifiers by at least 10%. The improved on-state voltage drop and switching characteristics of the high-voltage PowerMOSFETs have increased the primary efficiency of switching power supplies. The reduced power consumption of the power semiconductor devices also reduces the size of the heat sink and the overall machine.
There is an unwritten view in the power supply community that unregulated is more efficient than regulated, unisolated is more efficient than isolated, and narrow range input voltage is more efficient than wide range input. 97% efficiency is achieved with Vicor's 48V input power modules. AC input switching power supply requires power factor correction, as the power factor correction has a voltage regulator function, in the output ripple requirements are not high applications (such as the output connected to a battery or super capacitor), you can use power factor correction plus unregulated isolated converter circuit topology, foreign products in 1986, the efficiency reached more than 93%.
In the DC48V input voltage power supply module, the efficiency of more than 93% of the module almost invariably uses the front-stage voltage regulator, the rear stage does not regulate the isolation scheme, and the first stage output capacitor and the second stage output inductor eliminated, simplifying the circuit structure.
Many domestic switching power supplies are designed with relatively little attention to structural design, sometimes resulting in uneven temperature rise in various parts of the power supply, with some places overheating and others with almost no temperature rise, and even larger losses in the PCB. A good switching power supply should be a uniform distribution of components that generate heat on the PCB
on the PCB, and the temperature rise of the heating element is basically the same, the PCB should have the smallest possible loss, which is particularly important in the design of modular power supplies and Adapter with plastic housing.
Efficiency improvement at the same time: the power supply electromagnetic interference is reduced
Among the various losses in the switching power supply, the losses generated by electromagnetic interference, after a certain level of power efficiency will not be neglected. On the one hand, electromagnetic interference itself consumes energy, especially the improvement of power supply efficiency often requires soft switching technology or zero-voltage switching or zero-current switching technology (either specially set or inherent in the circuit itself), the application of these technologies to slow down the switching process of voltage, current change rate or eliminate the switching process, electromagnetic interference becomes very small, unlike conventional switching power supply circuit requires special settings to suppress Electromagnetic interference does not need to be specifically set up to suppress electromagnetic interference circuit (this circuit is the existence of losses).
Switching power supply into: the era of high efficiency power conversion
Careful analysis, high-efficiency power conversion seems to be very simple, and even some circuit topologies were introduced more than 20 years ago (such as two-stage conversion topology, as early as in the UNITRODE 82/83 data sheet ApplicationNote of AN19, TEK2235 oscilloscope also used this power conversion topology), but by the then Technology level, especially the limitations of people's awareness (always think that the efficiency of two-stage conversion is lower than single-stage, while in fact two-stage conversion can achieve the fact that inherent zero-voltage switching, single-stage conversion requires special additional circuitry and control methods) and has not been recognized and applied. The performance of the devices and the increased awareness have made the two-stage conversion one of the main ways of high-efficiency power conversion.
Conclusion
Now that advanced power semiconductor devices are readily available and advanced circuit topologies and control methods are being used for switching power supply design engineers and manufacturers, all that remains for them is to find ways to improve their technology while creating better application opportunities and market share.