Design Of Digitally-controlled Adjustable DC Power Supply

Adjustable DC power supply is one of the basic and indispensible instruments in thecircuit experiments. It is widely used in experiment teaching. While the knob-regulatedlinear power supply, which is mostly used is bulky, inefficient and hardly achieves anaccurately adjustment. To resolve these weakness, in this paper, a digitally-controlledadjustable power supply is designed in which a microchip is used as the control core, Thedesign process is as follows:Firstly, the advantages and disadvantages of switched mode power supply and linearpower supply are analyzed. Analyzing the problems existed in nowadays power suppliesused in experiment teaching, a design proposal is expounded, in which, a microchip is usedas the control core, pre-regulator switched power supply is combined with linear regulatedpower supply with the two output voltages controlled one by one.Secondly, in the system aspect, a scheme of the combination of flyback topology andcontrol chip TOPSwitch-GX is selected as the pre-regulator switched power supply whilethe one of the combination of adjustable regulator LM317and negative feedback circuit isselected as linear regulated power supply. The two output voltages are controlled by themicrochip digitally and synchronously.Thirdly, in the circuit aspect, modules of the two are designed and analyzed in detail.In the pre-regulator switched power supply, the isolated circuit which consists of precisionvoltage reference TL431and linear optocoupler PC817is mainly designed, the operatingprinciples of the clamp buffer circuit and the selection standards of the RC parameters isanalyzed in detail. While in the linear regulated power supply, the implementation ofnegative feedback controlled circuit whose reference voltage is given by the microchip isexpounded. In addition, the high frequency transformer is designed.Fourthly, the overall proposal and the software program of the single-chip digitalcontrol module.is introducedFinally, a power device is made, each performance is tested in detail. The results showthat the performances of this device basically achieve the design requirements, it has a goodapplication value.