Development Trend of Switching Power Supply Technology
The development direction of switching power supply is high frequency, high reliability, low consumption, low noise, anti-interference and modularization. Because the key technology of switching power supply is light, small and thin is high frequency, so the major foreign switching power supply manufacturers are committed to synchronously developing new high-intelligence components, especially to improve the loss of the secondary rectification device, and in the power iron Oxygen (Mn? Zn) materials to increase scientific and technological innovation to improve the high magnetic performance at high frequency and large magnetic flux density (Bs), and the miniaturization of the device is also a key technology. The application of SMT technology has made great progress in switching power supplies. Components are arranged on both sides of the circuit board to ensure that the switching power supply is light, small and thin. The high frequency of switching power supply will inevitably innovate the traditional PWM switching technology. The soft switching technology of ZVS and ZCS has become the mainstream technology of switching power supply, and the working efficiency of switching power supply has been greatly improved. For high reliability indicators, switching power supply manufacturers in the United States reduce the stress on devices by reducing the operating current and junction temperature, which greatly improves the reliability of the products. Modularization is the general trend in the development of switching power supplies. Modular power supplies can be used to form distributed power supply systems, and N+1 redundant power supply systems can be designed to achieve capacity expansion in parallel mode. Aiming at the disadvantage of high operating noise of the switching power supply, if the high frequency is pursued alone, the noise will also increase accordingly, and the use of partial resonant conversion circuit technology can theoretically achieve high frequency and reduce noise, but some There are still technical problems in the practical application of resonant conversion technology, so a lot of work still needs to be carried out in this field to make this technology practical. The continuous innovation of power electronics technology makes the switching power supply industry have broad development prospects. In order to speed up the development of my country's switching power supply industry, we must take the road of technological innovation, walk out of the road of joint development of industry, education and research with Chinese characteristics, and contribute to the rapid development of my country's national economy.
The Method of Improving the Standby Efficiency of Switching Power Supply
cut start
For the flyback power supply, the control chip is powered by the auxiliary winding after startup, and the voltage drop on the startup resistor is about 300V. Assuming that the starting resistance is 47kΩ, the power consumption is nearly 2W. To improve standby efficiency, this resistor channel must be cut off after start-up. TOPSWITCH, ICE2DS02G has a special start-up circuit inside, which can turn off the resistor after start-up. If the controller does not have a special start-up circuit, a capacitor can also be connected in series with the start-up resistor, and the loss after start-up can gradually drop to zero. The disadvantage is that the power supply cannot restart itself, and the circuit can only be started again after disconnecting the input voltage to discharge the capacitor.
reduce clock frequency
Clock frequency can be ramped down smoothly or abruptly. Smooth decline means that when the feedback exceeds a certain threshold, the clock frequency is linearly decreased through a specific module.
switch working mode
1. QR→pWM For switching power supplies working in high-frequency mode, switching to low-frequency mode during standby can reduce standby loss. For example, for a quasi-resonant switching power supply (working frequency of several hundred kHz to several MHz), it can be switched to a low-frequency pulse width modulation control mode pWM (tens of kHz) during standby. The IRIS40xx chip improves the standby efficiency by switching between QR and pWM. When the power supply is under light load and standby mode, the voltage of the auxiliary winding is small, Q1 is turned off, and the resonance signal cannot be transmitted to the FB terminal. The FB voltage is lower than a threshold voltage inside the chip, and the quasi-resonance mode cannot be triggered, and the circuit works at a lower frequency. PWM control mode. 2. pWM→pFM For switching power supplies that work in pWM mode at rated power, the standby efficiency can also be improved by switching to pFM mode, that is, fixing the on-time and adjusting the off-time. The lower the load, the longer the off-time and the higher the operating frequency. Low. Add the standby signal to its pW/ pin, under rated load conditions, the pin is high, the circuit works in pWM mode, when the load is below a certain threshold, the pin is pulled low , the circuit operates in pFM mode. Realizing the switching between pWM and pFM also improves the power supply efficiency during light load and standby state. By reducing the clock frequency and switching the working mode, the standby operating frequency can be reduced, the standby efficiency can be improved, the controller can be kept running, and the output can be properly regulated in the whole load range. Responds quickly even when the load surges from zero to full load and vice versa. The output voltage drop and overshoot values are kept within the allowable range.
Controllable Pulse Mode
(BurstMode) controllable pulse mode, also known as skip cycle control mode (SkipCycleMode), refers to a certain link of the circuit controlled by a signal with a period larger than the clock period of the pWM controller when it is under light load or standby conditions, so that the pWM The output pulse is valid or invalid periodically, so that the efficiency of light load and standby can be improved by reducing the number of switches and increasing the duty cycle at a constant frequency. This signal can be added to the feedback channel, pWM signal output channel, the enable pin of the pWM chip (such as LM2618, L6565) or the internal module of the chip (such as NCp1200, FSD200, L6565 and TinySwitch series chips).
