Super capacity
A supercapacitance is an elementary electronic circuit which is a form of impedance converter . The application is in the area of analog low-pass filters . The circuit was presented in 1969 by LT Bruton as part of the Bruton transformation (FDNR technique). In this transformation, frequency- independent ohmic resistances become linear frequency-dependent capacitors and capacitors become supercapacitors whose purely real impedance depends on the square of the frequency .
The circuit consists of two operational amplifiers , two capacitors and three ohmic resistors that determine the specific value of the supercapacitance. For a simplified representation, a special symbol with the designation D is usually used in circuit diagrams , as shown in the adjacent figure.
The value of the real impedance at connections 1 and 2 of a supercapacitor is:
with the value and dimension for D , which is determined by the passive components of the circuit as:
The two resistors with the designation R have no influence on the value of D , but they must have the same values. In practical filter circuits, all three resistors are usually chosen with the same value.
literature
- Lutz v. Wangenheim: Active Filters and Oscillators . 1st edition. Springer, 2008, ISBN 978-3-540-71737-9 .
Web links
- G. Krucker : Active filters based on LC structures (PDF; 162KiB) March 23, 2003. Retrieved February 18, 2011.
Individual evidence
- ^ LT Bruton: Network Transfer Functions Using the Concept of Frequency Dependent Negative Resistors , IEEE, Circuit Theory, 1969, issue CT-16, pages 406 to 408