Could some electronics guru please shed some light on this ? Several Web sites(please check list below) have schematics and flashy color photographs of single white led light powered off a single 1.5 Volt AA battery.
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As most of these are very simple, I have simulated a number of them with SPICE, but none of them produce the advertised results. What is the mystery ? Some even have supposed oscilloscope traces !! Any thoughts hints would be helpful. Thanks in advance.
snipped-for-privacy@gmail.com wrote in news: snipped-for-privacy@googlegroups.com:
This class of single transistor blocking oscillator boost converter designed to drive a LED from a single cell is colloquially known as a "Joule Thief". Searching for that term with the keywords 'SPICE simulation' will find many simulations of varying degrees of accuracy. The basic circuit is pretty forgiving, and can easily be got working with junk-box parts which accounts for its popularity.
If the simulation doesn't model non-ideal behaviour of key components to a reasonable level of accuracy, it will *NOT* produce realistic results. Have you accounted for the cell's internal resistance, the resistance of the transformer primary, transformer core saturation, the LED's junction capacitance and the transistor's gain falling at high collector currents?
Post your simulations (preferably in LTSPICE format) and the observed results you are trying to match up with and chances are, someone will point out what you've missed.
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You can see an explanation of this sort of circuit at
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I suspect that your SPICE simulations may not have worked, because you may have modeled the inductor as a normal "theoretically perfect" one (which is linear). The joule thief circuit depends pretty heavily on the fact that it uses an inductor with significant amounts of nonlinearity in its behavior - the ferrite core of the inductor saturates at sufficiently high current levels.
Dear electronic idiot: learn to read and understand a schematic! If you claim that your SPICE "simulation" did not work,then that indicates your ignorance in electronics.
Yes, I agree totally that unless the non-linearities in the key inductor behavior are modeled correctly, the SPICE simulation would work. As for the transistor, I have used the standard SPICE model for 2N4401. The diode has not yet been inserted. I was just trying to see if the oscillations could be simulated first. Unfortunately, I use HSpice at work, and Ngspice at home(the simulations were done in my spare time), both of which use text based source files as input, as opposed to LTSpice's GUI based format.
Dear electronic genius, pray pass on some of your deep and profound knowledge in the subject, so that guys like me can read and understand schematics correctly.
unfortunately (for you) LTSpice has become the lingua franca for sharing simulations in this newsgroup, mainly because the price is right *1, it'll run on anything *2 and it's easier to use than ms-paint *3
The save format is an ASCII *4 netlist with some embedded GUI layout information, it can run other ASCII netlists.
*1 Free download
*2 Well, anyting with an x86 cpu - it runs OK in wine, and whatever it is that recent macs use to run windows apps
*3 if your goal is drawing electronic schematics
*4 If you tell it to use 'u' for micro, there's a checkbox somewhere,else Windows-1252.
Well, The source file is below. It runs on Ngspice-26. The inductor is non-ideal, and the model for white light LED is also includ ed. As shown below, I have tried to measure current and voltage, and hence the three current measurement nodes. The circuit is a minor variation of one I saw at one of the Web sites I referred to, in my initial post.
Ngspice is completely free, and has its own users' and developers forums on SourceForge. Though initially developed for Unix-like and Linux platforms, precompiled binaries are available for Windows -- no issues at all. No need to install Wine, Linux/Unix is its native environment. Output files can be plotted with Excel or OpenOffice or Gnuplot. The text based input makes it very easy to include special models -- about 2 years ago, I had to do a lot of work with the sub-micron MOSFET models from UC Berkeley(BSIM 4.6) -- all I had to do was have an .INCLUDE statement in my source files.
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