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Switching Mode Power Supply中文版
Latest developments in switching power supply technology
2018-11-09      Browse times: 4278

1 synchronous rectification technology
         Since the birth of synchronous rectification technology in the late 1990s, it has made important contributions to the 
improvement of switching power supply efficiency.Xian. The current synchronous rectification scheme using IC control 
technology has been widely accepted by R&D engineers. The newly listed high-end switching power supply has almost 
no work without synchronous rectification technology. 
         Now the synchronous rectification technology is trying to realize ZVS and ZCS mode. Synchronous rectification. 
Since the release of ZVS synchronous rectification technology by Galaxy in 2002, it has been widely used. This method 
of synchronous rectification technology subtly links the pulse signal of the secondary side synchronous rectification with 
the primary side PWM pulse signal. Up, its rising edge leads the rising edge of the primary PWM pulse signal, and the 
falling edge hysteresis realizes the US mode operation of the synchronous rectification MOSFET. The latest dual-output 
PWM control IC has almost added to the control logic. The secondary side implements the US synchronous rectification 
control terminal. For example: Linear-Tech's LTC3722, LTC3723, INTERSIL's ISL6752, etc. These ICs not only solve the 
soft switching of the primary side power MOSFET, And focus on solving the US-side synchronous rectification of the 
secondary side. With these ICs, the DC/DC converter has a total conversion efficiency of 9 4% or more.
         In an asymmetric switching power supply circuit topology, especially for a good positive or positive active clamp 
circuit,In the synchronous rectification of the secondary side, in order to realize the synchronous rectification of the ZVS 
mode and eliminate the loss caused by the conduction loss and the reverse recovery time of the MOSFET body diode, 
Texas Instruments | Instrument Company's latest patented technology "pre-detection gate drive technology" A large number 
of digital control technologies have been added to the control chip. The birth of the control chip UCC27228 of the forward 
circuit synchronous rectifier has brought the efficiency of the forward circuit to an unprecedented high efficiency. After 
matching the active clamp technology of the primary side, this is made. The latest circuit mode not only achieves the 
soft-switching ZUS mode of the primary side, but also solves the core reset and energy feedback, reduces the voltage 
stress of the power MOSFET, and achieves the synchronous rectification of the ZVS optimal state of the secondary side. 
The medium and small power DC/DC converters using these two technologies have an efficiency of over 94% and a power 
density of more than 200 W per cubic inch.2 Best Primary PWM Control IC.
         Active clamp technology has lasted for more than ten years. Since the release of VICOR's patented technology in 2002, 
the new active clamp control ICs released by various companies have been born like mushrooms, giving users the fullest. 
Choice. TI, which holds the early active clamp control technology, not only maintains the original UCC3580 series, but also 
newly developed the UCC2891-94 with superior performance. It uses current-mode control and combines high-side clamps 
and Low-side clamps are two control schemes that give new control techniques. ONSEMI has first introduced the NCP1560 
control chip with low-voltage (100 V) active clamps, followed by active clamps for high-voltage applications. Control chip NCP
1280. It not only solves the requirements of LCD TV, plasma TV power supply, but now it is used as the main control PWM IC 
for the next generation fanless PC power supply. It can be seen how beautiful the future market prospect of this technology is. 
National Semiconductor Corporation The 5000 series has an active clamp control IC, the model is LM5025. Even the unknown 
Semtech company also gives the active clamp control chip, the model is SC4910. The conductor company has invested in this 
kind of control chip, and it is by no means rich or nowhere to spend. There is a huge market opportunity behind it. Until 
recently, TI's new active clamp control IC UCC2897, Active-clamped PWM control has been perfected. National 
Semiconductor has just introduced the LM5034, an active-clamp active-active control IC that can be interactively operated, 
which does not increase the input filter capacitor. In this case, the output power is doubled, enabling the active clamp 
technology to reach a power level of 1 kW. The Taiwanese company has given the cheapest active clamp control ICSD7558 
and SD7559, which greatly reduces the The cost of using source clamp technology.
         The full-bridge phase-shifting ZVS soft-switching technology, which is familiar and commonly used in the field of 
high-power, has contributed to the efficiency of high-power switching power supplies. It has also been greatly developed 
in the past 10 years. From TI's UC3875 to UCC3895, from Ling The company's LTC1922 to LTC3722 have added 
technology to adaptively detect the operating state of the power MOSFET, thereby more accurately adjusting the switching 
time to achieve the ZVS state, making the full-bridge phase shifting technology reach its peak. In particular, the LTC3722 
control IC has been greatly reduced. The inductance and volume of the resonant inductor reduce the boundary conditions of 
the non-ZVS operating state, reduce the loss of duty cycle, etc. However, today, when synchronous rectification technology 
is widely used, it cannot achieve the best US synchronous rectification. Because the full-bridge phase-shifting circuit is 
essentially asymmetric, it cannot achieve full ZVS synchronous rectification. Although TI engineers have made great efforts, 
it gives the synchronous rectification scheme in the circuit that is turned on. Half of the turn-off process is hard-switched, so 
the efficiency is always inferior to the synchronous rectification of the ZVS mode of the symmetrical circuit topology.
          In the field of making high-power switching power supplies, the latest technological achievements should be the latest 
PWM from INTERSIL.The symmetrical full-bridge US control IC, model number is ISL6752. It solves the problem that the four 
MOSFET switches that control the primary side are in the US working state, and can accurately give the synchronous 
rectification of the control secondary side to the ZUS working state. Drive signal. Here we can spend some extra ink: The 
ISL6752 controls a symmetrical full-bridge circuit. The upper left and upper right switches of the four arms operate at 50% 
duty cycle, and the pulse width is not modulated. The lower left and lower right switches use pulse width modulation to adjust 
the pulse width to control the output voltage. It can accurately control the on and off of the relevant pulse and its delay time, 
so that the parasitic parameters can be used to achieve the full use. The US soft switch of the bridge 4 power MOSFETs 
maintains the highest conversion efficiency of the primary side. In addition, it also gives the synchronous rectification drive 
signal of the secondary side. This drive signal can be adjusted in the primary side control IC relative to the PWM. The lead or 
delay of the pulse, thereby overcoming the delay caused by the transmission of the signal to the secondary side, so that the 
synchronous rectification of the secondary side always maintains the switching state of the ZVS at any duty cycle, ensuring 
synchronous rectification High efficiency. The IC has maintained such a low price, almost phase shift control IC cheaper than 
any one of the full-bridge.The conversion efficiency is achieved with a 400 W DC/DC converter made with this IC and an 
excellent power MOSFET.95%.
          For low-power switching power supplies, the PWM control IC of the flyback converter is still used, but it must be able 
to solve the synchronous rectification control method of the secondary side. ONSEMI's NCP1207 and NCP1377 are still in the 
high-voltage AC/DC field. The latter. If you can match the synchronous rectifier control IC UCC27226 of TI's flyback converter, 
it can make them a nearly perfect high-efficiency power supply. In the flyback converter control IC in the low-voltage DC/DC
field, Linear-Tech's LTC3806 is superior. The LTC3806 not only controls the PWM, but also gives accurate secondary 
synchronous rectification drive signals. It is a masterpiece of low-voltage low-power power control ICs.
           In summary, we can give the best control method and optimal circuit topology that can be selected in today's switching 
power supply design.The high power should be full bridge ZVS plus secondary side US synchronous rectification, the typical 
control IC is ISL6752; medium power to low power should be active clamp forward conversion ZVS soft switch with secondary 
side pre-check side gate drive technology Synchronous rectification; and low power should be a quasi-resonant flyback 
converter with synchronous rectification.
           Recently, in the power supply of LCD TVs, more asymmetric half-bridge ZVS technology is used. In TV systems, there 
are many analog circuits and small signal processing circuits. It is hoped that the dv/dt and dil dt in the power supply are 
smaller. Well, the switching elements in the asymmetric half-bridge circuit just work in this state, which is the best price-
performance circuit for the TV system of about 200W. The current control IC already has ST company's L6598, Philips' 
TEA1610, ONSEMI's NCP1395. Their performance is basically the same, there are some subtle functional differences.
Of course, there is no absolute limit here, but there should be a corresponding best choice under different conditions.
3 VICOR's latest technology
           VICOR's new MHz-rated operating frequency, 1000 W per cubic inch of ultra-high power density PRM (pre-regulated)
The DC/DC of the module) and VTM (Voltage Conversion Module) is still the pinnacle of today's power technology. It has f
or the first time increased the power density of the module's power supply to 1000 W per cubic inch, truly miniaturizing the 
power supply. Significance.However, VICOR's PRM technology and products are still not completely cleared to the market. 
Only VTM can enter the market in batches, but its technical direction is correct. In fact, PRM plus VTM is a group of regulated 
power supplies, which is essentially US SYNQOR company's patent - cascading technology; its first stage is used for voltage 
regulation, and the second stage is used for isolation and voltage transformation.
            The author recently improved the thinking mode of PRM, and separated the Buck-Boost in PRM. I chose Buck 
at the end and Boost at the end. When I selected Buck, I used the pre-check side-gap drive control technology with 1 
MHz operating frequency. Drop the input voltage to a certain intermediate voltage, and then add VTM to form a set of 
high power density power supply. When Boost is selected, the input voltage is raised to a certain level by using the 
synchronous Boost control technology of 1 MHz operating frequency. A higher intermediate value, plus VTM also constitutes 
a set of high power density power supplies.
             The advantage of VTM lies in the breakthrough technical thinking mode. The comprehensive promotion of this way 
of thinking is still difficult in China.Difficult, but also a long time to develop. This must have sufficient risk investment 
mechanism, but also have a long-term vision from the government to the enterprise, do not invest a little money and look 
forward to immediate results. VIGOR VTM has 3 patent technologies, everyone Knowing that the more patented projects are, 
the easier it is to break through. Many patented technologies are those who think of it, and we have to wait ten years before 
using this technology.4 Rapid development of non-isolated DC/DC technology
              In recent years, non-isolated DC/DC technology has developed rapidly. Due to the current load of a set of electronic 
equipment or electronic systems, the power system is required to provide multiple voltage levels. For example, a desktop PC 
requires +12V, +5. V, +3.3 V, -12V four voltages and standby +5 V voltage. On the motherboard, it requires 2.5 V, 1.8 V, 1.5 V 
or even 1 V. For this reason, it is impossible to give a set of AC/DC. With so many voltage outputs, and most of the low-voltage 
supply currents are large, many non-isolated DC/DC converters have been developed, which can be basically divided into two 
categories. One is the internal power-switching device. DC/DC converter. Another type of DC/DC controller that does not 
require a power switching device that requires an external power MOSFET. According to the circuit function, there is a Buck 
with buck; Boost with boost; Buck-Boost or SEPIC capable of step-down; IN-VERTOR with positive pressure to negative 
pressure. Among them, the most popular, the fastest growing Buck is Buck. According to the output current, there are 
single-phase, two Phase and multiphase; the control mode is mainly PWM,and a small part is PFM.
               Among the non-isolated DC/DC conversion technologies, TI has pre-checked side-gate drive technology from TI, 
which uses digital technology.Control synchronous Buck, DC/DC converter with this technology can achieve conversion 
efficiency up to 97%,of which TPS40071 is its representative product. Boost boost mode also appears the use of MOSFET 
instead of diode synchronous Boost works. In the field, the efficiency is greatly increased, and efforts are being made to 
further eliminate the conduction and reverse recovery loss of the body diode of the MOSFET.
               In the Buck-Boost circuit, the monolithic integrated IC is currently only the Liner-tech LTC3443, which is the most 
ideal product. It is the most similar to VIGOR's PRM, and the conversion efficiency is also high, reaching 95%, just work. 
The voltage is still relatively low, only 6V. With the advancement of IC manufacturing technology, the operating voltage of 
this circuit will gradually increase to 20V, 40V, 60V, or even 100V. At this time, the complete monolithic IC produces "PRM" 
"It is perfect."5 Major breakthroughs in PFC technology
               At the APEC meeting held in the United States in March 2006 and the PICM meeting in Shanghai, China, engineers
 proposedPFC circuit technology without rectifier bridge, and has been quickly put into practical use. It uses two inductors, 
two power MOSFETs, two fast recovery diodes to form the PFC boost circuit, which works in 50% of the half cycle, thus 
eliminating The rectifier bridge that causes power consumption, especially at the low end of the input voltage, that is, the 
AC 90V input, the efficiency is increased by up to 1.5 percentage points. Since the input and output of this circuit have 
no co-location, the voltage is input. The detection brings trouble. The IR 1150S, designed and manufactured by American 
IR Company using the patented ONE SYCLE technology, just eliminates the detection of the input voltage. Therefore, the 
IR1150S becomes the most convenient control IC for making the rectifierless PFC. This working mode circuit increases the 
efficiency of PFC by more than one percentage point. Engineers interested in this technology can pay attention to relevant 
reports.