How to design a simple and efficient switching pow

How to design a simple and efficient switching power supply

the rising global energy prices have made all walks of life have to seriously consider the issue of energy conservation. Among various energy-saving methods, improving the efficiency of switching power supply is an important means. Since the 80plus plan was put forward, the United States has launched 85pl plans for related production and manufacturing technologies us and 88plus, which will be implemented in a short time. Therefore, improving the efficiency of switching power supply as much as possible is the continuous goal of the power industry

in order to improve the efficiency of switching power supply, we must first understand the factors affecting switching power supply. Generally speaking, flyback and its derivative circuits have the lowest efficiency, and the efficiency of multipole transformation circuit topology is lower than that of single-stage transformation. Therefore, the above circuit topology should not be used in the application as far as possible

for forward power conversion, the larger the duty cycle, the higher the relative efficiency. Therefore, in the actual design, the duty cycle should be as large as possible. If the duty cycle is close to 1, it is the best

with the pressure of vehicle enterprises to reach the VOC national standard is not great, the switching frequency is getting higher and higher, and the switching loss is already a factor that cannot be ignored. Simple RCD buffer circuit is an important factor affecting efficiency. Therefore, using soft switching and zero voltage switching can effectively eliminate switching losses

when MOSFET with voltage level of 400-700v is applied, the conduction loss may account for two-thirds of the total loss. Therefore, trying to reduce the on resistance of MOSFET can effectively reduce the loss of MOSFET

based on the above factors, we propose a method to achieve high efficiency switching power supply by using pfc+ non regulated isolation converter combination. Mc33368 is used to realize PFC control, and irs2453 self oscillating full bridge converter is used for dc/dc conversion

because PFC has the function of voltage stabilization, in applications where the output voltage stability is not very high, the isolation transformation can not use the conventional PWM control mode, but the non PWM control mode with "100% duty cycle", which can improve the efficiency by 2% or more. The stability of output voltage can be achieved by the voltage stabilizing function of PFC link

in this way, the non regulated isolated converter can be regarded as a part of PFC, and PFC will become an isolated PFC. Because the isolated PFC has isolation function, voltage closing function and voltage stabilizing function, it becomes a real isolated switching regulated power supply

the maximum duty cycle obtained by using non PWM working mode can make the switch in the full bridge circuit turn on under "zero voltage", that is, to realize "zero voltage switching". This can improve the reliability of the circuit, further reduce the loss and improve the efficiency