Need Help Identifying this Part (Zener Diode)

[bigwave]

This little fella (D1 in the attached diag.) marked "33 8J" was installed between Vcc=3.3v and an IR photo sensor (QRE1113) output using a 51k pull-up resistor. Output feeds a GPIO pin input on a Nordic-semi SOC module.  It's probably a 3.3v zener but it would be good to know for sure.  I hunted for the symbol and codes but was unsuccessful - maybe "F" for "Fairchild"?.  D2 is a lot smaller and both seem just for transient and input protection. [It's off a Wahoo Kickr Core trainer, if you're curious].

Thanks,
Dave

[ArdWar]

LF for Littelfuse, they're well known for making circuit protection so it's very likely a TVS diode.

Although considering the implementation I wonder why are they using TVS there, and using it in such way. Feels like rather weird even for a bodge.

[floobydust]

I find it as Littelfuse TVS SMF3.3 a 3.3V clamp, with no capacitance spec. relevant to the high value 51k resistor in your circuit. Not sure of the speeds here.
There may be ESD discharges with a moving wheel and this is for coverage.

[bigwave]

LF for Littelfuse, they're well known for making circuit protection so it's very likely a TVS diode.

Although considering the implementation I wonder why are they using TVS there, and using it in such way. Feels like rather weird even for a bodge.

Thanks.  I thought it a bit odd as well.  The sensor is on a pigtail about 6cm away from Zeners on the main board-- I thought maybe they had some spurious power supply injection during testing -- this trainer has a pretty beefy stator with the sensor nearby.

-Dave

[bigwave]

I find it as Littelfuse TVS SMF3.3 a 3.3V clamp, with no capacitance spec. relevant to the high value 51k resistor in your circuit. Not sure of the speeds here.
There may be ESD discharges with a moving wheel and this is for coverage.

Thanks!   Yah, quite possibly it's for discharge given the proximity to the back-emf stator (maybe inductive noise) -- sample rate is less than 2kHz. The 51k does not seem typical for this sensor - the few other sensor projects I've seen using this BJT photocell typically use 10k with the LED biased at 100 ohm. (you can buy the thing from sparkfun with/without a cap.  I think the larger collector resistance is there to drive down Vce and put the zero (low) side value closer to ground.  The pin-out for the soc gives Vzero-Digital as up to .3xVcc max (3.3v).

-Dave
[I miss through-hole! :-) ]