I need help identifying a smd component

[DeltaFaya]

Hello,

I'm at work, and i have a task : someone gave me a small PCB and asked me to draw the schematic of it. The person who designed this PCB is not working anymore and he didn't left any single bit of information about that PCB.
So far, i've been able to understand, identify and draw pretty much everything, but i'm currently stuck : i can't identify this specific component (see picture). Even after searching with the marking on it, i can't find it's reference.

My guess is it is some kind of transistor, as it seems to be used to draw current for 4 LEDs. I draw the schematic linked to the component to help understand its role on the PCB :

So, if there is anyone who can work his magic to find that component, that would be awesome !

Thanks

 

[Grossel]

Can you at least figure what the circuit boards purpose ave being ?

Do you have reasons to think the LED's may have being used to detect light rather than emitting light ?

 

[sagor1]

It might, just might, be a 5C transistor, similar to a PBSS302NX. Seems like the same package, same pinouts as your diagram. Marking with W5C, the "W" means made in China according to this datasheet.

pbss302nx.pdf PDF datasheet. ALL TRANSISTORS DATASHEET. POWER MOSFET, IGBT, IC, TRIACS DATABASE. Electronic Supply. INNOVATION CATALOG. Service

 

[Nigel Goodwin]

Often SM device numbers are unidentifiable - but first off, what does the device do?, and specifically what do the LED's do?.

I'm presuming it's some kind of light or torch?, and the device is an NPN transistor switched ON via the 10K resistor (which I'd prefer to be considerably lower value), the 0.33 ohm is a current limiting resistor.

Assuming that's correct, it's pretty horribly and poorly designed - I'd short out the 0.33 ohm, lower the 10K considerably (depending on the current capability of the chip feeding it), and put a 0.68 ohm in series with each series pair of diodes.

 

[sagor1]

Often SM device numbers are unidentifiable - but first off, what does the device do?, and specifically what do the LED's do?.

I'm presuming it's some kind of light or torch?, and the device is an NPN transistor switched ON via the 10K resistor (which I'd prefer to be considerably lower value), the 0.33 ohm is a current limiting resistor.

Assuming that's correct, it's pretty horribly and poorly designed - I'd short out the 0.33 ohm, lower the 10K considerably (depending on the current capability of the chip feeding it), and put a 0.68 ohm in series with each series pair of diodes.

The PBSS302NX transistor seems to be a high gain/darlington (Hfe > 500 typical), so the 10k to base might be alright.

 

[Nigel Goodwin]

The PBSS302NX transistor seems to be a high gain/darlington (Hfe > 500 typical), so the 10k to base might be alright.

The issue then is the high Vbe, with a 3.3V chip feeding it you don't have much voltage over head.

 

[DeltaFaya]

I think Sagor1 is right about the PBSS302NX transistor, it fits quite well !

To give more information about the purpose of this PCB : it's a device supposed to detect neurotoxic gases, using light and liquid crystal. Some light is emitted using 4 LED, it goes throught a panel with some liquid crystal+some other chemical reacting to gases, and the residual light is collected with 4 photo-diode.
The DAC pin (pin 0) of the Seeeduino is used to drive and vary the intensity of the 4 LEDs using the NPN PBSS302NX transistor.
And we use 4 other pins of the Seeduino to "read" the 4 photo-diode (the 4 signals go throught a MAX9916 to amplify them).

This small device was a prototype, developped by a student for his PHD in optics.

 

[Nigel Goodwin]

So what happened to his thesis?, surely it was all clearly documented - or he was wasting his time

Incidentally, during my daughters Chemistry degree, they had to build an opamp circuit with an LDR, for measuring the amount of light passing through a liquid - sounds a similar-ish sort of thing.

 

[DeltaFaya]

So what happened to his thesis?, surely it was all clearly documented - or he was wasting his time

Surely, his thesis it quite well documented and i have it ! Unfortunatly, the electronic part of it wasn't relevent to figure in it. So, all i have about that device is only the description of its fonctions, but that's all.

This student was assisted by an electronical engineer who retired since. He designed and made that PCB but he wasn't know for being tidy and for keeping clean documentations about his work

I wont be able to get everything "right" (i probably wont be able to find the ref of the LEDs and photodiodes), but the closer i am, the better.

I am currently making the schematic on OrCAD Capture. Once i'm done, i'll post it here, so you'll have the full picture

 

[Nigel Goodwin]

Surely, his thesis it quite well documented and i have it ! Unfortunatly, the electronic part of it wasn't relevent to figure in it. So, all i have about that device is only the description of its fonctions, but that's all.

This student was assisted by an electronical engineer who retired since. He designed and made that PCB but he wasn't know for being tidy and for keeping clean documentations about his work

That's a shame - it wouldn't have taken much effort to add details of it to his thesis, presumably he must have had a reference to it?, but if that reference no longer exists it doesn't help.

Was it originally a 'one off' for his Phd?, and are you now wanting to manufacture a few of them?.

There are surprising crossovers between Chemistry and Electronics - in fact my daughter (with her Phd in Chemistry) works as a Technician at a University, for two different Physics based departments (plus her own research as well), but comes under the banner of "Electronics, Computing and Maths"