Technical Approaches for Power Consumption Reduction in High-Power Switching Power Supplies
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 presents new challenges for power design engineers.
Analysis of Power Consumption of Switching Power Supply
To reduce standby losses and improve standby efficiency of switch mode power supplies, it is necessary to first analyze the composition of switch mode power supply losses. Taking flyback power supply as an example, its operating losses are mainly manifested as MOSFET conduction loss and MOSFET conduction loss
In standby mode, the main circuit current is low, the MOSFET conduction time ton is small, and the circuit operates in DCM mode, so the related conduction losses, secondary rectifier losses, etc. are small. At this time, the losses are mainly composed of parasitic capacitance losses, switch overlap losses, and starting resistance losses.
Switching overlap loss, PWM controller and its starting resistor loss, output rectifier tube loss, clamp protection circuit loss, feedback circuit loss, etc. The first three losses are directly proportional to frequency, that is, directly proportional to the number of device switches per unit time.
Methods to Improve the Standby Efficiency of Switching Power Supply
According to the analysis of losses, cutting off the starting resistor, reducing the switching frequency, and decreasing the number of switches can reduce standby losses and improve standby efficiency. The specific methods include: reducing the clock frequency; Switching from high-frequency working mode to low-frequency working mode, such as switching from quasi resonant (QR) mode to pulse width modulation
For flyback power supply, the control chip is powered by the auxiliary winding after startup, and the voltage drop across the starting resistor is about 300V. Set the starting resistance to 47k Ω and consume nearly 2W of power. To improve standby efficiency, the resistance channel must be cut off after starting. TOPSWITCH, ICE2DS02G has a dedicated startup circuit inside that can turn off the resistor after startup. If the controller does not have a dedicated startup circuit, a capacitor can also be connected in series with the startup resistor, and the losses after startup can gradually decrease to zero. The disadvantage is that the power supply cannot restart automatically, and the circuit can only be restarted after disconnecting the input voltage and discharging the capacitor.
