Technical methods for reducing power consumption of high-power switching power supply
As energy efficiency and environmental protection become increasingly important, people have higher and higher expectations for the standby efficiency of switching power supplies. Customers require power supply manufacturers to provide power supply products that comply with green energy standards such as BLUEANGEL, ENERGYSTAR, and ENERGY2000. The EU's requirements for switching power supplies are accurate: by 2005, the standby power consumption of switching power supplies with rated powers of 0.3W~15W, 15W~50W and 50W~75W must be less than 0.3W, 0.5W and 0.75W respectively.
At present, when most switching power supplies transfer from rated load to light load and standby state, the power efficiency drops sharply, and the standby efficiency cannot meet the requirements. This poses new challenges to power supply design engineers.
Switching power supply power consumption analysis
To reduce the standby loss of the switching power supply and improve the standby efficiency, we must first analyze the composition of the switching power supply loss. Taking a flyback power supply as an example, its operating losses mainly include: MOSFET conduction loss MOSFET conduction loss
In the standby state, the main circuit current is small, the MOSFET conduction time ton is very small, and the circuit works in DCM mode, so the related conduction loss, secondary rectification loss, etc. are small. The losses at this time are mainly caused by parasitic capacitance losses and switching losses. It consists of overlap losses and starting resistor 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, proportional to the number of times the device switches each time. Unit of time.
Methods to improve the standby efficiency of switching power supply
According to the loss analysis, it can be seen that cutting off the starting resistor, reducing the switching frequency, and reducing the number of switches can reduce standby losses and improve standby efficiency. Specific methods include: reducing the clock frequency; switching from high-frequency operating mode to low-frequency operating mode, such as switching from quasi-resonant mode (QuasiResonant, QR) to pulse width modulation (PulseWidthModulation, PWM), switching from pulse width modulation to pulse frequency modulation ( PulseFrequencyModulation). , PFM); Controllable pulse mode (BurstMode).
Cut off the starting resistor
For a flyback power supply, the control chip is powered by the auxiliary winding after startup, and the voltage drop across the startup resistor is approximately 300V. Assuming a startup resistor value of 47kΩ, the power dissipation is close to 2W. In order to improve standby efficiency, the resistor channel must be cut off after startup. TOPSWITCH, ICE2DS02G has a special startup circuit inside, which can turn off the resistor after startup. If the controller does not have a dedicated starting circuit, you can also connect a capacitor in series with the starting resistor, and the loss after starting can be gradually reduced to zero. The disadvantage is that the power supply cannot restart itself. The circuit cannot be restarted until the input voltage is disconnected and the capacitor is discharged.
