Varicap diode #question

[M0BSW]

I have a circuit which states varicap diode its code is 1n4004, I looked it up and it says silicon regulator diode, well that 's not a varicap diode is it.

[electronics man]

do you have a schematic?

[SeanB]

It can be used as a varicap diode, as a varicap diode is a regular diode that is specced to have the quoted values of reverse bias capacitance on the junction. A typical signal diode has low capacitance, 3-4pF, and a power diode has higher.

Typically 8-15pF at 4v according to this datasheet.

http://www.diodes.com/datasheets/ds28002.pdf

If you want higher use a larger power diode, but YMMV. Leakage current as well will be a lot higher. Up to 50uA while a varicap can be a lot lower.

[edpalmer42]

Check out these pages for info on using regular diodes as varactor (varicap) diodes:

http://www.hanssummers.com/varicap/varicaporig.html
http://www.hanssummers.com/varicap/varicapled.html

Ed

[T3sl4co1l]

Beware that 1. no one publishes data on the Q factor of junction capacitance, because they don't need to, and 2. probably because they don't want to anyway.  Schottky diodes, for instance, are oft quoted as saving reverse recovery losses; but the capacitance is so large (and probably lossy -- I wish I had numbers), they can actually perform worse in some circuits.

Tim

[Tac Eht Xilef]

Beware that 1. no one publishes data on the Q factor of junction capacitance, because they don't need to, and 2. probably because they don't want to anyway.

About 10~15 years ago I compared the Q factor as varicaps on various power diodes I had lying around. I don't remember the exact diodes I used (certainly 1N400x, as well as others including some weird unmarked ones from my telco days & various stud rectifiers), and I definitely don't remember the exact numbers, but they were surprisingly comparable to typical low capacitance / low C_R varicaps. Even more surprisingly, devices of the same type were fairly consistent across batches & manufacturers. I wouldn't use them for front-end tuning, but they were certainly good enough for tuned oscillators and filters at a pinch.