- 日期: 2016-07-12
- 瀏覽次數: 1562次
Industrial power supply must meet some special requirements, such as low power consumption (to relieve the burden of chassis cooling), high power density (to reduce the space requirement), high reliability and high durability, and other unusual features in the normal power supply, such as easy to parallel, remote control, and some overload protection function, etc. At the same time, its demand for EMI and stability are more strict than other applications. Is analyzed in detail in this paper, a design example of 400 w power supply, explains the primary side and secondary side the use of the power module, and other methods to improve performance. In addition to improvements in electrical, module also adopts unified dimension, easy to achieve accurate compact mechanical design and to reduce installation and logistics costs. In fact, the two modules can have different rated power, so as to shorten the time to market. Power factor correction (PFC), with a bus or a DC link capacitor, for many different factors can't separate optimization is critical. Now, most of the power of active PFC circuit has been adopted, which boost converter, to ensure that the input current in phase with the input voltage, minimize the input sine wave distortion, and thus reduce conduction EMI, achieve wide input range (85 vac ~ 265 vac). Moreover, the boost converter Will adjust their own duty ratio according to the input voltage and input current, and capacitance of the bus voltage to 350 v to 400 v. However, if the raising of the pressure transducer is not active (for example in the start state), can the current flowing through the input rectifier, into the boost inductor and a diode, to empty bus capacitance, eventually produce a lot of surge current. To avoid this problem, need extra current-limiting circuit, otherwise could trigger a fuse of the grid. In high reliability or mission critical applications, the more strict requirements for maintaining time and saving electricity protecting, so bus capacitance must increase, the surge current become larger. In some cases, needs a NTC resistance, but in the "hot" (e.g., power), start the NTC is still very hot, can't provide protection. According to DIN EN - 61204 standard, test method for two cases: 70% of the rated input voltage, 20 ms. And 40% of the rated input voltage, 100 ms. The second case for there is no active PFC power is quite tricky. Pulse width modulation (PWM) is the main converter. The DC voltage is chopping as higher frequency square wave, so the use of smaller pressure device can switch to another voltage level and provide isolation. Not all topology using square wave duty ratio change, some topology USES frequency conversion, there is phase change between the two pulse sequence. This level mainly determine the efficiency of the converter and load regulation. Power converter efficiency is very important, first of all it related operating costs; The second is the chassis cooling must be put through to scatter in addition to the heat generated by the, The third is the hot components, the greater the more expensive, taking up space. These three factors and the service life of the power supply cost matters. Converter topology selection for both efficiency and radiation EMI is crucial, as the hard tend to switch the power switch, the dI/dt and dV/dt is very big, the higher current and voltage at the same time, this leads to production of large Numbers of switch frequency harmonic. Among various kinds of topology, harmonic resonance or quasi Boost topology are an advantage but more difficult to design, especially resonant topology, it is difficult to implement on the broad range of load. LLC topology is described below in wide load range limited switch frequency change and soft switch, it is easy to solve this problem. PWM level is at the heart of all necessary protection function. Under the condition of the current model converter, can protect voltage to the week deadline to avoid damage by most output problems, these problems are usually related to shut off the heat. Grade synchronous rectifier (SR) back to dc voltage ac voltage of the transformer. Because of low voltage electric current is often quite high, so the whole flow of transmission loss must be minimized. If use silicon PN junction diode can obtain the forward voltage of 0.7 V, the schottky diode can reach 0.4 V. To get a lower voltage level with the MOSFET, the voltage level by conduction resistance RDS (ON) and the output current, and the two cases are much lower than the last. But because the MOSFET is active device, therefore need a proper gate drive signal to complete, if the design is good, can greatly reduce the power consumption at this level, so as to further improve efficiency. In addition, the use of advanced low inductance packaging technology, design can also be very tight and durable.