Comparison of BJT and MOSFET Astable Multivibrators: A Theoretical and Simulation Study for Teaching Fundamentals of Electronics

R. Długosz (Bydgoszcz Univ. of Science and Techn., Poland), A. Dąbrowski, P. Pawłowski (Poznan Univ. of Techn., Poland)

The paper presents a comparative analysis of an astable multivibrator realized with bipolar junction (BJT) or field-effect (FET) transistors used in teaching the fundamentals of electronics. Despite its simple structure, explaining its operating principle together with all essential aspects is not trivial. The astable multivibrator enables illustration of many key concepts required to understand electronics fundamentals: differences between bipolar and MOS transistors, controlling through current or voltage, operation of transistors in various modes, selection of bias resistors, positive feedback and oscillation conditions, capacitor behavior in pulse circuits, RC time constants, and digital circuit implementation principles. A progressive explanation of the circuit operation is proposed, which facilitates understanding and demonstrates engineering analysis using circuit decomposition and successive approximation techniques.