Emitter / Collector pins proper connection in the 1.2 kit

Get help and show off your TV-B-Gone kit!

Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.
Locked
User avatar
madlynxx
 
Posts: 2
Joined: Fri Feb 10, 2023 12:20 pm

Emitter / Collector pins proper connection in the 1.2 kit

Post by madlynxx »

Hello everybody,

Sorry if this newbie question has already been adressed somewhere in this forum.

Slight confusion here: on the PCB of Adafruit's 1.2 kit (blue version), the "EBC" marking next to the 4 PN2222A locations suggests that emitter pins are connected to the cathodes of the 4 IR LEDs. In the official schematic (tvbgone3sch.png) however, PN2222A collectors are (with emitters connected to ground).
Screenshot.png
Screenshot.png (502.3 KiB) Viewed 1287 times
All reproductions I have been making with various LED models (including the fantastic Osram SFH4544), connecting collectors to cathodes, work very well.

Just to remove any ambiguity about the PN2907A + 4 PN2222A combo, can anyone definitely confirm that NPN transistors' collector pins should connect to LEDs cathodes, emitter pins to ground, as shown in the schematic?

Thanks a lot!

User avatar
dastels
 
Posts: 15608
Joined: Tue Oct 20, 2015 3:22 pm

Re: Emitter / Collector pins proper connection in the 1.2 kit

Post by dastels »

Yes, with an NPN transistor the collector connects to the LED cathode, emitter to ground That lets the transistor switch current flow through the LED on/off.

Why do the PCB markings suggest that the emitters are connected to the cathodes?

Dave

User avatar
madlynxx
 
Posts: 2
Joined: Fri Feb 10, 2023 12:20 pm

Re: Emitter / Collector pins proper connection in the 1.2 kit

Post by madlynxx »

Thank you Dave for you answer.

About the "EBC" marking in the picture above, possibly a misreading on my part (as it's possibly not meant to indicate the PN2222A mounting orientation). Associated with the transistor TO-92 shape marking next to it, it suggests that the provided PN2222A have a "CBE" pinout, which is not very common, hence my question.

I may push the interpretation a little to far :)

Anyway, thanks for the collector / cathode connection confirmation!

User avatar
dastels
 
Posts: 15608
Joined: Tue Oct 20, 2015 3:22 pm

Re: Emitter / Collector pins proper connection in the 1.2 kit

Post by dastels »

OK. Yeah, that is odd. It should be CBE if it's referring to the transistor pins. Even so it's completely unnecessary since the outline is there.

Dave

Locked
Please be positive and constructive with your questions and comments.

Return to “TV-B-Gone Kit”