Offline green power control chip reduces standby power consumption

With the popularization of household appliances and audio-visual products, the widespread application of office automation and the continuous development of networking, more and more products have standby functions. While these new products greatly facilitate our lives, they also cause a lot of energy waste. According to a survey by the Organization for International Economic Cooperation, the energy consumed by countries due to standby accounts for about 3% to 13% of the total energy consumption. my country's standby energy consumption is even higher than the average level. Taking color TVs as an example, the test survey shows that the average level of standby power consumption of TVs in my country is 8.07W, of which color TVs with standby power consumption below 3W only account for 13.4% of the total number of color TVs tested, while those above 9W account for 34.8%. The US standard for standby power consumption of color TVs is no more than 3W. At present, the average standby energy consumption of urban households in my country has accounted for about 10% of the total household energy consumption, which is equivalent to each household using a 15~30W "eternal lamp". Standby energy consumption is like an invisible blood-sucking worm, which wastes energy and creates huge environmental pressure.

Analysis of the standby power consumption mechanism of switching power supply

At present, most electronic devices below 200W, such as power adapters, chargers, TVs and DVDs, etc., use offline flyback switching circuits to convert the 85V~275V AC power provided by the power grid into the DC voltage required by electronic devices. Under normal working conditions, the losses of the flyback switching power supply mainly include conduction loss and switching loss, as well as the loss of the control circuit. In standby mode, because the output current of the system is close to zero, the conduction loss can be ignored, and the switching loss and the loss of the control circuit become the main standby power consumption of the system. To reduce the standby power consumption, we should focus on reducing the switching loss and the loss of the control circuit. Figure 1, the main loss types of the flyback switching power supply in the standby state Figure 1 shows the main loss types of the flyback switching power supply in the standby state, among which MOSFET switching loss, gate-level drive loss, transformer core loss, output rectifier reverse recovery loss and buffer loss are all switching losses, while the loss of the control circuit is mainly manifested as the loss on the start-up resistor. Table 1 gives the approximate estimation formulas for these losses: Table 1 Estimation formulas for main power losses It can be seen that various types of switching losses are related to the switching frequency fsw, and reducing the switching frequency can reduce the switching losses. The loss of the starting resistor is directly related to the rectified DC bus voltage VDC and the resistance value RS. Under the working conditions of ensuring wide voltage input, the only way to reduce the starting resistor loss is to reduce the starting current and increase the starting resistor RS. There are currently two main standby energy-saving working modes: intermittent mode (skip cycle or burst mode) and frequency reduction mode (frequency reduction). Frequency reduction controls the switching frequency by detecting the output power. When the controller detects that the output power is less than the set critical value, the switching frequency decreases linearly with the output power to reduce the switching loss, so the standby power consumption can be reduced when the load is light or no load. Due to Therefore, reducing the switching frequency at a certain voltage may cause the problem of core saturation, which is the limitation of the frequency reduction technology. The basic idea of ​​the intermittent mode is that when the output power is less than the set critical value, the controller stops outputting the drive signal intermittently according to the output power size but keeps the switching frequency unchanged, which can greatly reduce the standby power consumption. The degree of reduction in standby power consumption depends on the length of the intermittent time. As shown in Figure 2, P1>P2>P3. ON Semi's NCP120x and BCD Semi's AP384xG are both typical intermittent PWM controllers. This technology can completely avoid the problem of core saturation under light load conditions. Figure 2, Schematic diagram of intermittent standby control The green power controller AP384xG is a "green power" controller produced by BCD Semi that is fully compatible with the industrial standard PWM controller 384x and has intermittent standby function. Figures 3 a and b show its internal circuit block diagram and pin arrangement diagram. Figure 3, internal block diagram of AP384xG From the internal circuit block diagram, it can be seen that the most obvious difference between AP384xG and the standard PWM controller 384x is that a controllable current source is added inside it. The comparison level of Pin CS is increased by charging the current source to realize the intermittent working mode under light load conditions to reduce standby power consumption. In order to further reduce standby power consumption and improve power efficiency, AP384xG is also specially designed with a low startup current circuit. The startup current is reduced from the typical 200uA to 40uA, which greatly reduces the loss on the startup resistor. At the same time, AP384xG also adds "pulse leading edge elimination technology", the so-called LEB function, which can avoid the interference of the sharp pulse generated by the discharge of parasitic capacitance when the power MOSFET is turned on to the current sampling signal. Table 2 shows the detailed differences between AP384xG and the standard PWM controller AZ384xA. It can be seen that the reduction of the chip's own working current can also reduce standby power consumption. Table 2. The main differences between AP384xG and AZ384xA In addition, AP384xG can provide a peak drive current of up to 1A to ensure fast turn-on and turn-off of the power MOSFET to meet high-frequency and high-power applications. This is something that many similar "green power" control chips cannot achieve. Due to the designer's special consideration of compatibility, AP384xG has the characteristics of being fully compatible with the standard PWM controller 384x, providing the so-called "Plug-and-Play" "green power" solution. Without modifying the original design, users can replace 3842/3/4/5 with AP3842/3/4/5G and adjust only a few resistance and capacitance parameters to make the power supply of the original design pass the energy-saving certification of "green power supply". Figure 4, Typical DVD power supply circuit diagram Figure 4 shows a typical DVD power supply circuit diagram. The figure points out that the only components that need to be replaced after replacing the original device with AP3842G are the starting resistor R3, the auxiliary coil power supply resistor R6, the dummy load R28 and the pin CS sampling resistor R10. Table 4 shows the comparison table of components before and after replacement. Table 4, comparison table of components before and after replacement Figure 5, power supply efficiency comparison curve before and after DVD power supply replacement Figure 5 shows the power supply efficiency comparison curve before and after DVD power supply replaces AP3842G. Figure a is the relationship curve between power supply efficiency and output current when the input voltage of the reference comparison chip system is 85V, 220V, and 265V before replacement, and Figure b is the power supply efficiency curve after using AP3842G. It can be seen that the full load efficiency of the power supply system has increased by nearly 10% before and after the replacement. Figure 6, the relationship curve between the standby power consumption and input voltage of the DVD power supply Figure 6 is the relationship curve between the standby power consumption and input voltage of the DVD power supply before and after the replacement. It can be seen that when the reference comparison chip is used, the standby power consumption of the DVD power supply has a large change in the entire wide input voltage, from 1.25W to 3.25W. After replacing with AP3842G, the standby power consumption of the DVD power supply is almost maintained at around 0.5W in the entire wide input voltage, and the energy saving effect is very obvious. Figure 7, the gate drive voltage waveform of the power MOSFET in the standby state before and after the replacement Figure 7 is the gate drive voltage waveform of the power MOSFET in the standby state before and after the replacement. It can be seen that the power supply controlled by AP3842G enters the intermittent working mode in the standby state.