High Pitched Noise Coming From 2N5551 NPN Transistor - Page 1
Forum section: electronics / beginners

author: mojobojo
author_rank: Newbie
timestamp: November 14, 2013, 06:10:26 am
content: This is my first post so I figured I should say "Hi" first. I am a beginner to electrical engineering that has been lurking around the forums for a bit and finally made an account because I figured I could get an explanation to something strange I have encountered.Today I came across a circuit called a "Joule Thief". I figured it was simple enough for me to try with little equipment I have so I thought I would give it a shot. After a bit of tinkering I had finally got, to my amazement, an LED running off of some near dead batteries (to make sure it was not just the batteries powering the LED I made sure that they could not power the LED first). The result being a lit up led and a high pitched screeching noise coming from my transistor. First thing I did was touch the transistor to make sure it was not heating up. It seemed fine so I tried adding a 1k resistor to the base and that seemed to suppress the high pitched noise.What is causing the noise and is this damaging the transistor?Here is my circuit. There are 10 winds per wire around the ferrite bead and I am running it off of 1v. If I had a scope I would have taken some waveforms as well.Badly drawn schematic, pretty sure I drew it right.

author: madshaman
author_rank: Frequent Contributor
timestamp: November 14, 2013, 06:28:00 am
content: You're positive the noise isn't coming from your coil?

author: Dago
author_rank: Frequent Contributor
timestamp: November 14, 2013, 06:34:22 am
content: The noise is coming from your coil. It is caused when the system oscillates (like it should) and the windings constrict/move at the same frequency.

author: mojobojo
author_rank: Newbie
timestamp: November 14, 2013, 06:38:50 am
content: Quote from: madshaman on November 14, 2013, 06:28:00 amQuote from: Dago on November 14, 2013, 06:34:22 amI just double checked and it is coming from my coil. That makes sense, I can't believe I didn't think of that. Thank you.

author: BravoV
author_rank: Super Contributor
timestamp: November 14, 2013, 06:39:26 am
content: Either tighten your coil winding (rewind it from the start) , or dip the whole inductor into an epoxy or use a hot glue gun to secure and cover the windings, hopefully that will cure the whine. Works most of the times in my case.Also try move it into pcb or use direct point-to-point soldering (aka dead bug style) instead of doing it at breadboard, sometimes this will cure it too.I've played with this joule-thief for quite sometimes with so many variations while ago.

author: amyk
author_rank: Super Contributor
timestamp: November 14, 2013, 09:00:04 am
content: I've noticed that wirewound resistors and ceramic capacitors can produce whining noises in normal operation too.

author: richard.cs
author_rank: Super Contributor
timestamp: November 14, 2013, 01:32:27 pm
content: If it's an irritating squeel then you could always up the frequency and move it out of the audio band by taking a couple of turns off of your coil.

author: toxicnos
author_rank: Contributor
timestamp: November 15, 2013, 12:58:31 am
content: Yes i belive it is your coil as well. make sure the windings are tight,