Technical methods for reducing power consumption of high-power power sources
With the increasing importance of energy efficiency and environmental protection, people have higher expectations for the standby efficiency of switching power supplies. Customers require power supply manufacturers to provide power products that meet green energy standards such as BLUEANGEL, ENERGYSTAR, and ENERGY2000. However, the EU requires switching power supplies with rated power of 0.3W-15W, 15W-50W, and 50W-75W to have standby power consumption less than 0.3W, 0.5W, and 0.75W, respectively, by 2005.
At present, when most switching power supplies switch from rated load to light load and standby mode, the power efficiency drops sharply, and the standby efficiency cannot meet the requirements. This poses new challenges for power design engineers.
Power consumption analysis of switching power supply
To reduce the standby loss of switching power supplies and improve standby efficiency, the first step is to analyze the composition of switching power supply losses. Taking flyback power supply as an example, its operating loss is mainly manifested as: MOSFET conduction loss MOSFET conduction loss
In standby mode, the main circuit current is small, the MOSFET conduction time ton is very small, and the circuit operates in DCM mode, so the related conduction losses and secondary rectifier losses are small. At this time, the losses are mainly composed of parasitic capacitor losses, switch overlap losses, and startup resistance losses.
Switch overlap loss, PWM controller and its starting resistor loss, output rectifier loss, clamp protection circuit loss, feedback circuit loss, etc. The first three losses are proportional to frequency, that is, they are proportional to the number of device switches per unit time.
Methods to Improve the Standby Efficiency of Switching Power Supplies
According to the loss analysis, cutting off the starting resistor, reducing the switching frequency, and reducing the switching frequency can reduce standby loss and improve standby efficiency. The specific methods include: reducing the clock frequency; Switch from high-frequency working mode to low-frequency working mode, such as switching from QuasiResonant (QR) mode to Pulse Width Modulation (PWM), and switching from Pulse Width Modulation to Pulse Frequency Modulation (PFM); BurstMode.
Cut off the starting resistor
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. Set the starting resistance value to 47k Ω and consume nearly 2W of power. To improve standby efficiency, the resistance channel must be cut off after startup. TOPSWITCH and ICE2DS02G have a dedicated starting circuit inside, which can turn off the resistor after starting. If the controller does not have a dedicated starting circuit, capacitors can also be connected in series with the starting resistor, and the loss after starting can gradually decrease to zero. The disadvantage is that the power supply cannot restart itself, and the circuit can only be restarted after disconnecting the input voltage and discharging the capacitor.
