Mystery SOT323F

dot as positive
dot as negative
The X axis is the measurement, the Y axis is the voltage supplied, starting at .10v and ending at 2v increasing by .1v. The blue line is supplied voltage, red line is measured voltage. I set up the SOT in line with a 1ohm resistor attached before the positive lead of the bench power supply. The first graph shows when the positive lead from the power supply is connected to the side with the dot, the other graph is when negative is connected to the side with the dot. I’ve had it suggested that this component is a TVS diode, I don’t know what it is or how to order one. Any information is appreciated

circuit-20211211-0251
This is the circuit i pulled the SOT from. It’s marked as a diode, I don’t know the polarity but i’m guessing it’s a zener because on the PCB it’s marked with a ‘z’. the line that leads away from the zener connects to the ground pins of the IC it’s connected to (nRF51822) and the 2.1v comes from the same IC’s GPIO pin.

Hi user86,

Kindly provide a few more bits of information:

  1. Did you measure the shown curves while the component was mounted on the PCB or was it removed before?
  2. Do you have a photo of the device (preferably while mounted on the board, showing also the neighbourhood)?

Cheers,
heke, AsamaLab

  1. I attached the component to a breakout board so i could solder to it easier. The board has no other components on it.
  2. Yeah, please see attached


Based on the position in the PCB assembly, I believe they are used as transient suppressors to protect the rest of the circuit from static zaps by humans through the push buttons via the two signal wires connecting the PCBs.

If this is correct, then simply removing them from the circuit will make the whole system start working again (just be careful not to static zap the buttons with the protectors missing).

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Based on the application, part marking and SOD-323 package type I think what you have is a TVS diode made by the company Leiditech,
Mfg PN: SD05C

This is a jelly bean type part, we have the same package type under the similar part numbers from companies like Semtech

https://www.digikey.com/short/5jw8q208

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That’s the jelly bean part I’ve designed into nearly all my product designs with input switches and a microcontroller. :+1:

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