Capacitance multiplier A capacitance design gned ed to mak make a capacitance multiplier multiplier is desi capacitor function like a capacitor that is much larger. This can be achieved in at least two ways. •
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An active circuit, circuit, using a device such as a transistor or operational operational amplifier amplifier
which in turn is about 2–3 V less than VS (when loaded). Larger values of R1 (and C1) reduce the output ripple to almost negligible levels. levels. On the downside downside this causes the output output to rise rise slow slowly ly towa towards rds the requi required red value value (espe(especially when the load is connected), due to the larger time constant of R1 and C1.
A passive circuit, using autotransformers using autotransformers.. These are typicall typically y used for for calibrati calibration on standard standards. s. The General General Radio / IET labs 1417 is one such example.
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Capacit Capacitor or multipli multipliers ers make make low-f low-freq requenc uency y filter filter and longlongduration timing circuits possible that would be impractical with actual capacitors. capacitors. Another application application is in DC power suppli supplies es wher wheree very very low low rippl ripplee volta voltage ge (un (unde derr load) load) is of paramo paramount unt import importanc ance, e, such such as inclass-A in class-A amplifiers.
Operati Operationa onall Amplifi Amplifier er based
Vi
Vo
R2 R1 C1
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Trans Transis isto torr based based
0V
+ -
Vs
OP
R1 C1
A basic capacitance multiplier.
Q
R2 0V
Here, Here, the capac capacita itanc ncee of capac capacito itorr C1 is multip multipli lied ed by the ratio of resistances C = C1 * R1 / R2, if looking into the Vi node. Vo
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Autotra Autotransf nsform ormer er based
These achieve achieve a high accuracy accuracy (approximatel (approximately y 0.25%) at large values of capacitance (e.g. 1 F), by multiplying the capacitance of a lower value precision capacitor by the use of two transformers.
A basic capacitance multiplier.
Here the capacitance of capacitor C1 is multiplied multiplied by the transistor’s current gain (β). R1 and C1 form a low-pass filter and help smooth any ripple in VS. R1 supplies the charging current as well as thetransist thetransistor’ or’ss (denot (denoted ed by Q) base base curre current. nt. R2 is theload on the circuit. circuit. Without Without Q, R2 would would be the load on the capacitor and C1 would have to be very large to maintain low ripple ripple.. With Q in place, place, the loading imposed imposed upon C1 is simply the load current reduced by a factor of β. Conversely, C1 appears “multiplied” by a factor of β to the load.
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Note that this circuit is not a voltage regulator, since the output voltage varies directly with the input VS. The output voltage is about 0.65V less than the base voltage,
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Capacitance multiplier for power supplies on ESP web-site Capacitance multiplier ( multiplier (OpAmp OpAmp)) Java Java Appl Applet et that sho shows ws an anim animated ated capa capacita citance nce multiplier Transistor capacitance multiplier with design details
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IET Labs 1417 FOUR-TERMINAL CAPACITANCE STANDARD
REFERENCES
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Text and image sources, contributors, and licenses
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Text Capacitance multiplier Source: https://en.wikipedia.org/wiki/Capacitance_multiplier?oldid=712827433 Contributors: Theodore Kloba, Rohitbd, Tabby, Bluebot, Zidane tribal, Homer Landskirty, Alecjw, Addbot, Yobot, GrouchoBot, Malmo1 and Anonymous: 10
Images File:Cap-mult-op.svg Source: https://upload.wikimedia.org/wikipedia/commons/a/ac/Cap-mult-op.svg License: CC-BY-SA-3.0 Contributors: i saw it here and made a Qucs file out it with 3 colors; i think there is no copyright (or so) on that idea, although i would have needed some time to get it... :-) (author: Michael Margraf) Original artist: Homer Landskirty (
talk) File:Cap-mult-q.svg Source: https://upload.wikimedia.org/wikipedia/commons/d/dc/Cap-mult-q.svg License: CC-BY-SA-3.0 Contributors:
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Cap-mult-q.png Original artist:
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Cap-mult-q.png
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