High power switch mode power consumption reduction engineering approach
With the growing importance of energy efficiency and environmental protection, people expect more and more high standby efficiency of switching power supply, customers require power supply manufacturers to provide power supply products to meet the BLUEANGEL, ENERGYSTAR, ENERGY2000 and other green energy standards, and the European Union on the switching power supply to **: By 2005, the rated power of 0.3W~15W, 15W~50W and 50W~75W switching power supplies need to be less than 0.3W, 0.5W and 0.75W, respectively. 50W and 50W~75W switching power supply, standby power consumption should be less than 0.3W, 0.5W and 0.75W respectively.
Most of the current switching power supply from the rated load into the light load and standby state, the power supply efficiency drops sharply, standby efficiency can not meet the requirements. This presents a new challenge to power supply design engineers.
Switching power supply power consumption analysis
To reduce switching power supply standby loss and improve standby efficiency, we must first analyse the composition of switching power supply loss. In the case of a flyback power supply, for example, its operating losses are mainly manifested as follows: MOSFET conduction loss MOSFET conduction loss
In the standby state, the main circuit current is small, MOSFET conduction time ton is very small, the circuit works in the DCM mode, so the related conduction loss, secondary rectifier loss is small, at this time, the loss is mainly composed of parasitic capacitance loss and switching overlap loss and start-up resistance loss.
Switching overlap loss, PWM controller and its starting resistance loss, output rectifier loss, clamping protection circuit loss, feedback circuit loss. The first three losses are proportional to the frequency, that is, with the number of device switches per unit of time is proportional.
Improve the standby efficiency of switching power supply methods
According to the loss analysis, cut off the starting resistance, reduce the switching frequency, reduce the number of switching can reduce standby loss, improve standby efficiency. Specific methods are: reduce the clock frequency; switch from high-frequency operating mode to low-frequency operating mode, such as quasi-resonant mode (QuasiResonant, QR) switching to pulse width modulation (PulseWidthModulation, PWM), pulse width modulation switching to pulse frequency modulation (PulseFrequencyModulation, PFM); switchable power supply standby efficiency. PFM); Controllable pulse mode (BurstMode).
Cutting 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. To improve the standby efficiency, the resistor channel must be cut off after startup, and the ICE2DS02G has a dedicated startup circuit to turn off the resistor after startup. If the controller does not have a special start-up circuit, you can also start the resistor in series with a capacitor, the loss after the start can be gradually reduced to zero. The disadvantage is that the power supply can not restart itself, only disconnect the input voltage, so that the capacitor discharge to start the circuit again.
