Joule Thief

[Pirate88179]

Could it be some type of heat sink?

Do you mean something poured over a transistor?  This bump is only about .060" high off the board, not enough room to cover a chip or transistor I think.  Also, nothing on the other side of it on the board.  This really has me puzzled because it took time to place that there and, since these are made in China, I am sure there is nothing in there that is not needed.  It intersects with all of the traces on the board, hard to see that in the photos, sorry.

Your thought is a good one if they used some kind of very small, low profile chip.  Something like that might be buried under there.

  ***EDIT***  If there was a chip or something under there, we would see solder pins or something on the other side of the board right?  Nothing there at all.

Thanks,

Bill

[nul-points]

hi Bill

i think you'll find that there's a surface-mount chip (so no thro' holes!) under the blob - fairly standard practice for mass-produced low-cost boards

all the best
sandy

[resonanceman]

Hi Gary,  I have gotten a joule thief up to 350+v.  But how to charge up a large cap fast enough has been my issue.  I am trying to get the oscillations of the joule thief into another LARGER transformer.  A friend dropped of lots of electronics junk, and among that, there was several larger transformers.  I tried to get the oscillations of the joule thief into one of them today.  Not happening.  I can take the AA battery and tap on the primary coil, and see a fluctuation in the output/secondary.  But the pulse from a joule thief don't seem to doing anything.  I still have a few ideas to try, tomorrow. 

But getting a large cap charged up by starting with a high voltage power supply, and then turning it off when its up and running sounds interesting.  I have been using a bunch of 9v batteries to get high voltage.  Thanks for your help.  Please keep it coming.

Detrix

Detrix

From  my experience  a transformer that is  to large  acts like a choke...... you need  a stronger JT or a smaller transformer.


precharging   a cap may have some benifits.
JTs like high impedance....... charging  a  cap  from  zero starts out  looking like a dead short  to the JT
Charging  the cap to at least 3/4 of the  JT voltage  would allow the JT to   have a fairly high impedance load


gary

[Pirate88179]

hi Bill

i think you'll find that there's a surface-mount chip (so no thro' holes!) under the blob - fairly standard practice for mass-produced low-cost boards

all the best
sandy

Sandy:

Thanks for the tip.  Boy, it would have to be a really small chip to fit under there but, if this is the case, it would make sense.  Otherwise, why even have a board?  There are only 2 resistors mounted on the board and I guess you would not need to use a board just for that.

Thanks,

Bill

[kooler]

captain bill
the big green one is a inductor
and those transistors are covered in plastic
most cases there is two transistors and a resistor and or a small cap..
they cover them in plastic because the old solar lights the rain would kill the transistor till it dried out..
and the reason you don't see solder points is because that pcb is two layered and if you hold it up to the light
you can see the copper traces between layers

robbie