Technical method of reducing power consumption of high power switching power supply
At present, when most switching power supplies are switched from rated load to light load and standby state, the power supply efficiency drops sharply and the standby efficiency cannot meet the requirements. This poses a new challenge to power supply design engineers.
Power consumption analysis of switching power supply
In order to reduce the standby loss of switching power supply and improve the standby efficiency, the composition of switching power supply loss should be analyzed first. Taking the flyback power supply as an example, its working losses are mainly as follows: MOSFET conduction loss.
In the standby state, the current of the main circuit is small, the ON time of MOSFET is small, and the circuit works in DCM mode, so the related conduction loss and secondary rectifier loss are small. At this time, the loss is mainly composed of parasitic capacitance loss, switch overlap loss and starting resistance loss.
Switch overlap loss, PWM controller and its starting resistance loss, output rectifier loss, clamp protection circuit loss, feedback circuit loss, etc. Among them, the first three losses are proportional to the frequency, that is, to the switching times of the device per unit time.
Methods of improving standby efficiency of switching power supply
According to the loss analysis, cutting off the starting resistor, reducing the switching frequency and switching times can reduce the standby loss and improve the standby efficiency. The specific methods are: reducing the clock frequency; Switch from high-frequency working mode to low-frequency working mode, such as QuasiResonant mode (QR) to PulseWidthModulation (PWM), and pulse width modulation to PulseFrequencyModulation (PFM); Controlled BurstMode.
Cut off the starting resistance
For the flyback power supply, the control chip is powered by the auxiliary winding after starting, and the voltage drop of the starting resistor is about 300V V. Let the starting resistance be 47kΩ, and the power consumption is nearly 2W. To improve the standby efficiency, the resistance channel must be cut off after starting. TOPSWITCH, ICE2DS02G has a special starting circuit inside, which can turn off the resistor after starting. If the controller does not have a special starting circuit, a capacitor can also be connected 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, and the circuit can only be started again after the input voltage is disconnected and the capacitor is discharged.
