This video by Sam Ben-Yaakov explains BJT filters and capacitance multipliers, focusing on their functionality and common misconceptions. The presentation begins with the limitations of a basic RC filter, which, while simple, suffers from efficiency issues due to voltage drops. To address these limitations, Saakov introduces a BJT-based filter, which uses a transistor to improve efficiency. The BJT filter allows for smaller capacitors and larger resistors without significant voltage drops. The filtering is achieved without affecting the DC component, making the circuit efficient and effective for applications such as smoothing rectified voltage. However, the video challenges the common labeling of BJT filters as “capacitance multipliers.” While the circuit exhibits some characteristics of capacitance amplification when viewed from the load side, Saakov argues that these features do not define the core filtering function of the circuit.
The second half of the video explores the true nature of capacitance multipliers, such as those involving operational amplifiers, and clarifies the confusion surrounding the terminology. Saakov provides examples of capacitance multipliers used to reduce impedance, but notes these circuits differ significantly from BJT filters. He critiques common misunderstandings in online resources, where BJT filters are mischaracterized as capacitance multipliers due to perceived similarities. Finally, the video concludes by emphasizing the importance of proper terminology and highlights the conditions under which BJT filters work effectively, noting their limitations with large ripple voltages and the need for higher DC drops in such cases.
Video content
Source: EPCI
