Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Potential Controlled Variable Capacitor
Name: Walter
Status: student
Grade: 9-12
Location: MA 
Country: N/A
Date: 4/27/2005

I am looking for a kind of variable capacitor, which can be controlled by voltage applied on it, and whose capacitance range can reach to 1nF-20nF. I knew that varactor diode is controlled by voltage, but its value range is 100-800pf, which is not I want.

The use of Diodes as capacitors is the only means I am aware of in current use as voltage controlled capacitors. Still, the values you desire are close enough in range to what you can get that a work around is available.

Wire 10 Varactor Diodes in parallel with each other, and you will accomplish the same result. for a 500 pF Diode, ten of them equate to 5 nF. It is not the simplest, cheapest, nor most compact means of accomplishing this goal, but it is the only means that comes to mind. I will include the formulas for adding capacitance just to post them in a logical place, though I am sure with the question you are asking, you are already well aware.

Capacitors in series with each other. (end to end)

1/C1 + 1/C2 = 1/Ct (where Ct is the total achieved capacitance)

Capacitors in parallel with each other. (Side by Side)

C1 + C2 = Ct

Ryan Belscamper

Click here to return to the Engineering Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory