How to design a charger voltage regulator for portable electronic devices is discussed in this circuit design example. The circuit is designed with two operational amplifiers, a pair of P-channel JFET transistors and one P-type MOSFET or PMOS transistor at the output. For more examples see • Electrical Engineering... . How the battery charger is working and what are the roles of electronic components are analyzed and discussed in this video. There are two main stages in this circuit. The first stage is a precise bandgap stage that uses two Junction Field Effect Transistors and one op amp to realize a precise 2.5 volt voltage reference at the input of the power stage. Temperature compensation is achieved by a compensating current source IPTAT with a positive temperature coefficient current proportional to absolute temperature of the transistor junction. The potentiometer R1 can be adjusted to make sure the nominal voltage at room temperature is 5 volt at the output of this circuit. There are many choices for power PMOS transistor. As an example IRF9530 p-type MOSFET from Vishay Semiconductor is available from electronic component distributors like Mouser. A combination of Op Amp negative feedback and virtual short, Pinch-off voltage difference for the p-channel JFET transistors (due to intentional difference in their channel implants) and Kirchhoff circuit laws is applied to analyze this circuit and compute the output voltage formula and temperature compensation components.
4 окт 2024
