# How to decipher zener diode encoding?

I'm new to electronics and I'm trying to reverse engineer the circuit board in an R/C car. I've come across a diode and it is labelled...

C3V3
5T


1) I assume 3V3 means 3.3V, but what do the C and 5T mean?

2) Is the black stripe on the input or output side?

3) Is there a dead giveaway letting me know this is a "zener" diode? I ask because I've been web searching and all results turn up as a zener diode.

• A close-up photo of the board would be good. – gwideman Apr 17 '14 at 22:55
• I cannot attach photos, I don't have a high enough rating... However, this is strictly a diode we are talking about. – Zak Apr 17 '14 at 23:31
• The appearance of the diode, the typeface used, possible confusion over characters and possibly even the surrounding components, would give a clue as to what this is. For example, "5T" could actually be "ST", a manufacturer of diodes. – gwideman Apr 17 '14 at 23:34
• Maybe you could post a photo to somewhere you do have access to? – gwideman Apr 17 '14 at 23:35
• @gwideman It very well could be ST in a block style font. Also, I've been looking for photos and I can't find one to save my life. – Zak Apr 17 '14 at 23:37

Tentative answer.... iterating as OP adds more details...

... and adding details from the datasheet found by @Shantam

• 3V3 -- a zener of 3.3V
• C -- tolerance, probably 5%
• Stripe indicates cathode end of a diode. That's the end to which the arrow in the symbol points.
• ST -- SGS Thomson
• Can you address why it should be obvious it is a "Zener" diode? – Zak Apr 18 '14 at 0:25
• @Zak Because of the 3V3 marking. The forward/reverse bias voltage drop of most "regular" diodes is not a determining factor of their application, whereas Zeners are used exclusively for over-voltage protection or voltage regulation. – Shamtam Apr 18 '14 at 0:44
• I imagine something like this is what you're looking at: datasheets360.com/pdf/-2117927204213530624 – Shamtam Apr 18 '14 at 0:46
• @Shantam Score! That's exactly what I was suspecting, but didn't find. – gwideman Apr 18 '14 at 0:48
• @Zak Judging by the notes under the Electrical Characteristics table, the 'C' is an indication of tolerance on the voltage characteristic, since 'B' is shown to indicate +/-2%, and 'A' indicates 1%. 'C' is probably 5% -- the VZT/IZT column (probably should be VZT @ IZT) shows 3.1 to 3.5V for the 3V3. onsemi.com/pub_link/Collateral/AND8250-D.PDF shows a nice zener graph. – gwideman Apr 18 '14 at 1:00