Electronics > Beginners
Need trouble shooting help (pics)
billbyrd1945:
"Transistors do not "hold a charge" like that."
I didn't mean to imply that. I suspected the 5v wall wort (or is it "wart") was responsible. And even if it is, I'm fine with that. I'm sure the YouTuber didn't intend for anyone to think of unplugging a transformer as a switch in itself. I'm tickled that merely disconnecting the 12VDC (or the 5V wire) provides instant on and off. It's working perfectly and drawing 0.056 AMPS. Finished project photo attached. Thanks to everyone! This means a lot to me!
alsetalokin4017:
Beautiful! I like the way you used the dowels to hold the connecting posts. All you need now is to find a little 3-prong socket connector so you can easily change transistors to see how different ones behave, and a 10k potentiometer to substitute for the fixed resistor. The idea is to find the greatest resistance that will still allow enough current through to turn on the transistor fully.
I found an ideal "socket" for a transistor on the end of a little cable I scavenged from a discarded CRT television that I found on the roadside. The blue screw blocks from Vellemann are ideal for mosfets in the TO-220 or TO-247 style packages. (The smaller ones need legs bent a bit, the larger ones are exact fit without bending.)
alsetalokin4017:
--- Quote from: Richard Crowley on February 23, 2019, 10:38:35 pm ---
--- Quote from: billbyrd1945 on February 23, 2019, 09:31:13 pm ---...discharge the transistor with my fingers...
--- End quote ---
Transistors do not "hold a charge" like that. Certainly not for low-voltage DC circuits such as yours.
(snip)
--- End quote ---
Actually it would be more correct to say that "BJTs don't hold a charge like that." Mosfets, which are charge-actuated devices, can and do hold a gate charge, staying 'on' (for Nch types) as long as that charge persists. It can indeed be charged or discharged with a finger!
(the finger charge demonstration action happens after about 5 minutes in)
(Looks like the narrator was confused about lowside/highside switch arrangements, but never mind that.)
But of course bipolar junction transistors don't work like this.
billbyrd1945:
Too cool! That (one with a pot and connectors) will be my next project. Still going to keep this one for posterity.
billbyrd1945:
"Transistors do not "hold a charge" like that."
I misunderstood you. I thought you were referring to my thoughts about the wall wart retaining some energy. In reality, you were telling me that the finger shorting doesn't work on BJTs. Uh... yep, I stepped in it again. I had been watching vids about MOSFETS and forgot that I had changed my focus to the transistor project. So I don't know why there was some kind of state change when I did it. Hmm. I probably did something else at the same time and got confused.
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