The principle of the design of high efficiency monolithic switching power adapter
Design high efficiency monolithic switchingpower adapter principles are as follows:
A universal principle.
Designed switching power supply adapter should work as far as possible in the case of the maximum duty cycle Dmax.
265V wide voltage range for the AC 85 to input the primary winding of the induction voltage Uor shall be as high as possible, can be selected within the range of 100 ~ 135V, to ensure that the AC input voltage is 85V when high-frequency transformer can transfer enough energy .
Second, the specific principles.
1 side of the circuit.
a) increasing the primary winding inductance (Lp), high-frequency transformer can operate in continuous mode. Chip switching power supply adapter and high-frequency transformer power losses are lower.
b) series with the input of a negative temperature coefficient the thermistor (NTCR), limiting the role of power is initially applied to the start of the cold, you should make it work as much as possible in the thermal state (low resistance state) to reduce thermistor power consumption. Rectifier bridge indicators set aside enough margin with a nominal rectified current must be greater than the rated current value, in order to reduce energy loss.
c) To correct estimation of the input filter capacitor, AC 85 ~ 265V input, output power per watt corresponds to capacity of 3uF, scale factor 3uF / W. 230V AC fixed voltage input scale factor for 1uF / W.
d) In order to improve the power adapter efficiency and reduce the cost, should be selected for low-power switching power supply chip.
2. High-frequency transformer.
a) In order to reduce the winding wire due to the skin effect and loss generated, it is recommended to use a multi-filar wound secondary windings.
b) low-loss core material suitable shape and correct winding method to minimize the leakage inductance. Under the conditions allowed in the installation space, and select the larger size of the core, helps to reduce the core loss.
Third, the secondary-side circuit.
(1) of the nominal current of the selected output rectifier at least continuous output current is typically 3 times. Recommend the use of forward power-down, Schottky diode reverse recovery time is very short.
2 in continuous mode, switching power adapter output filter capacitor on the AC current nominal value should be the pulsating current 1.5 to 2 times.