Design And Implementation For Switching Mode Power Supply Of Multiple And Adjustable Outputs

Compared with linear power supply,Switching Mode Power Supply(SMPS) has many significant advantages such as higher efficiency, smaller volume and high stability,which is used widely. This thesis designs and implements a multiple-output SMPS with an adjustable output for an induction heating system. It includes several constant outputs and an adjustable output, the output voltage of the constant output are +5V, +15V, +18V; and the output range of the adjustable output is 17V~28V.The power supply design topology selected for this thesis is flyback converter which requires simple peripheral circuit and suits for medium power level. Pulse width modulation(PWM) chip UC3842 is used to get compact circuit which use fewer elements and cost less. The three isolated output +5V, +15V, +18V are realized by using two or more output windings. Although this way may have the problem of cross-adjustable accuracy, the power supply meets the requirement demanded by induction heating system. For the adjustable output,a potentiometer is used to adjust the output voltage over a wide range. The adjustable section also uses flyback converter and UC3842. The fundamental principle of adjustable output is regulating the sampling voltage by a potentiometer, then duty ratio of the output pulse changed by the feedback loop. Power supply for UC3842 is usually provided by an auxiliary winding. This method may cause shortage of power supply for UC3842 when the duty ratio is too small. To provide sufficient power supply for UC3842, the +18V of multiple-output section is used in the adjustable section. As the maximum power dissipation of UC3842 is 1W, the +18V output can be used for other load.Through debugging, measurement results show that the power supply meets the requirement demanded by the induction heating system. In addition, the output voltage levels of the SMPS developed in the thesis are at the power supply levels of common electronic systems. Thus the SMPS in the thesis can be used as debugging power supply in laboratory. The working frequency of the induction heating system is very high, and is easy to be affected by electronic systems operating at close frequency,for example SMPS. To reduce the parasitic effect of the high frequency and avoid Electromagnetic Interference(EMI) of the induction heating system and other electronic system, Electromagnetic Compatibility(EMC) is considered in the process of PCB layout and routing. In the debugging of SMPS, problems such as shortage of power supply with auxiliary winding, severely damage of electronic component in the moment of power on, noise of the transformer and big ripple of output voltage, etc.,are considered. The thesis analyzed those problems specifically and proposed solutions.