Design Of Multi-output Constant Current Source Based On Power Distribution Control Strategy

Flyback converters are widely used in multi-output applications due to their advantages of simple topology,low cost,and small size.In the multi-output flyback converter,the traditional single closed-loop control only feedback regulates the main circuit,and the auxiliary circuit is not controlled,so it leads to the problem of cross regulation rate.At present,the cross regulation rate has been improved very well in the case of multi-channel constant voltage output,However,the problem of cross regulation rate has not been effectively solved in the multi-output constant current source.In order to improve the cross regulation rate of the multi-output constant current source,a detailed theoretical analysis of the energy transfer during the operation of the flyback converter is carried out,and a strategy based on power distribution control is proposed to predict the expected output power of the power supply.According to the control strategy,the expected input power of the power supply is reasonably distributed to each output,and the cross regulation rate is fundamentally solved.The specific implementation method is as follows,Firstly,the designed multi-output flyback converter is guaranteed to work in the Discontinuous conduction mode,According to the expected output current value and real-time load value of each channel,the total expected power of the multi-channel output is calculated,and combined with the principle of energy conservation,the total expected input power is obtained;Secondly,the precise conduction time of the main switch and each output rectifier switch can be derived using the energy transfer in Discontinuous conduction mode.The total input power of the power supply can be controlled by controlling the conduction time of the main switch of the flyback converter.The total input power can be It is reasonably distributed by controlling the on-time of the output rectifier switch tube so that the total output power of the power supply is equal to the total input power,and each channel can obtain the desired power,thereby obtaining the desired output current.The multi-output constant current source based on this control strategy has the advantages of low cross regulation rate,individually controllable output current and high power supply stability.According to the design requirements,select appropriate circuit parameters and simulate the proposed control strategy in the Saber software environment.It can be seen that under this control strategy,the cross regulation rate of the multi-output constant current source is within 2%,consistent with theoretical analysis.Using TMS320F280049C as the main control platform,prototypes were produced and hardware tests were conducted.The experimental results show that the cross regulation rate of the three outputs is less than 2%,and the output current accuracy and load adjustment rate have reached the research goals.