Joule Thief 101

[tinman]

 author=picowatt link=topic=8341.msg478352#msg478352 date=1458842767]

I thought you two were "discussing" whether or not decreasing the base resistance increased the collector (and L1) current or just produced additional waste heat in the base resistor.  Perhaps I misunderstood.  As I said, I have no dog in this hunt.

My claim is that an increase in current flow through L2 will increase the magnetic field strength in the core. As we now know that the current flow dose indeed increase as we reduce the base resistance in L2,and we know that the LED puts out more light when we reduce the base resistance,then how can that not mean that the magnetic field strength has increased in the core?.
The only way to get more light output from the LED is an increase in magnetic field strength in the inductor,and this can only happen when we increase the current flowing through L2and the base of the transistor. So how MH can say that increasing the current flow through L2 dose not increase the magnetic field strength in the inductor is beyond me

This would of course depend on whether Q1 is fully saturated at both the lower and higher base resistance. 
Measuring Vce and Ic at the two base resistances should help clarify is Q1 is fully saturated (turned on) at both base resistance values or is turned on harder with one more than the other.

Oh-dont go there with MH. There is no such thing as switching on the transistor harder in the JT circuit.

It is late here now,so i will get to those test as soon as i can PW.


Brad

[MileHigh]

You are going to drag him down with you,and the outcome will be he leaves because of your lying ways.

LOL

Look at post #1210, PW was courteous enough to find the reference for you.

Oh-dont go there with MH. There is no such thing as switching on the transistor harder in the JT circuit.

Put your brain in gear and read PW's quoted text again.  Plus I made a fairly detailed posting about the same subject.

[Magluvin]

Guy shows output of microwave transformers set up with and without a capacitor. With capacitors, resonance is just above 50hz.


https://www.youtube.com/watch?v=XlG4NyQf3T0

Mags

[SeaMonkey]

Put your brain in gear and read PW's quoted text again.  Plus I made a fairly detailed posting about the same subject.

There is no such thing as switching on the transistor harder in the JT circuit.

Whenever a Power Transistor such as the 2N3055 is used in a
switching circuit there is always the possibility of driving the
transistor into (a) non-saturation, (b) soft-saturation or
(c) hard-saturation.

Hard saturation is preferred since it will result in best circuit
efficiency, providing it is accomplished without excessive (just
enough) base drive.  The drawback of Hard-Saturation is
charge-storage within the base region which slows turn-off
unless some means of applying momentary reverse-bias across
the base-emitter junction is incorporated to speed up turn-off.

The base drive winding of the Joule Thief transformer will normally
accomplish that to some degree.  Placing a speed-up capacitor
across the base-drive-resistor will assure that the reverse bias
impulse is sufficiently strong to make a difference.

By the way, most transistors will operate reasonably well in
their inverse mode where it is "upside-down" in the circuit.
The Emitter is connected as the Collector and the Collector
is connected as the Emitter.  Current gain is not good in
this configuration but that it does work is sometimes made
use of in exotic circuits.

[picowatt]