Jump to content
Electronics-Lab.com Community

The capacitance of the varicap


Recommended Posts

The varicap is a special diode that which changes its capacity according to DC voltage applied to it in reverse manner, that is when high DC => low capacitance and vice versa, I think this is OK.
Now, looking to Fig.varicap (FROM: http://hem.passagen.se/communication/bug_rf.html), the varicap is BB149A, this varicap (according to its datasheets) has acapacitance of more than 20pF for DC votage less than 1VDC.
Lets assume for a moment that its capacitance is 20pF. As seen in the Figure, this BB149A is connected to other capacitors,i.e. 3.9pF & 15pF and the three elements with L1 combine an LC circuit.
My question is: What is the equivalent capacitance of the three
mentiond above with explination about series or parallel.



Link to comment
Share on other sites

I'm not going to tell you the answer but I'll tell you how to figure it out.

Capacitors in series:
Ctotal = 1 / (1/C1 + 1/C2+ 1/C3)

Capacitors in  parallel:
Ctotal = C1 + C2 + C3

If you need more help then don't be afraid to ask.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Create New...