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Article: Capacitor amplifier reduces ripple without dc loss.
- Article from:
- EDN
- Article date:
- June 6, 1996
- Author:
CopyrightCOPYRIGHT 1996 Reed Business Information, Inc. (US). This material is published under license from the publisher through the Gale Group, Farmington Hills, Michigan. All inquiries regarding rights should be directed to the Gale Group. (Hide copyright information)
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Filtering out power-supply ripple usually requires large capacitors. However, an active circuit can boost the effectiveness of small capacitors as ripple filters: The trick is to avoid introducing dc loss.
Filter capacitors reduce ripple in power-supply circuits or provide pulse energy at a constant dc voltage. In both applications, there is fundamental conflict. The circuit needs constant voltage, but capacitor energy-storage and -delivery capability is a function of capacitance and of voltage-change squared. To achieve a low-ripple output, therefore, the circuit needs a large, costly capacitance.
Early attempts to use active circuits to reduce capacitor size ...