Another 2 transistor 1.5v circuit

[koala]

Right I found this one on EDN, anyone got any comments? It looks promising.


Voltage-to-current converter drives white LEDs

 

[MrAl]

Hello again,

Hi nukiez, and thanks for the circuit!

I did a quick analysis on it, and found that although it
does work it looks like it doesnt regulate very well and
the efficiency will be around 60% or maybe less.

For a 1.5v input i got the circuit to output 20ma
(although peak current was wayyyy high (120ma peak) )
by juggling some values around a bit.
At 1.4v input, the output current went down to 15ma.
At 1v input, there was negligible output current.
This is why i think this has the worst regulation i've
seen so far :-)

Very interesting circuit though, and perhaps there is a
small modification that will improve the regulation?
I invite everyone to look for one...

Thanks again.

BTW, if you examine the Brinkmann circuit on my home page
you will see that this circuit is the exact same circuit
(if you remove R1) only reversing the polarities and
swapping PNP for NPN and vice versa :-)

Good luck with your LED circuits,
Al

 

[koala]

I am not a engineer or anything but I learn my electronics though hobby so I can't give any comments. I digged up the circuit from the web. Yes we are all looking for the 'efficient' circuit /ubbthreads/images/graemlins/smile.gif. 60% is really all right for a circuit which doesn't have any 'IC' in it. I am planning to mod a maglite solitate to a single led light. Anyone knows the average efficiency of an ARC-AAA?

Thanks for the input appreciate it.

 

[GWO]

Have you seen the patent filed by CMG Equipment? It lays claims on a two transistor step-up circuit. I'm no patent lawyer, but this reads as if they have claims on all battery powered LED flashlights. I also know that some patents would never hold up in court. I'm curious what you guys think of it.

Patent number: 6,366,028

Patent artwork (from patent search). You'll have to copy/paste this to get it to work:
http://patimg1.uspto.gov/.piw?Docid=06366028&homeurl=http%3A%2F%2Fpatft.uspto.gov%2Fnetacgi%2Fnph-Parser%3FSect1%3DPTO1%2526Sect2%3DHITOFF%2526d%3DPALL%2526p%3D1%2526u%3D%2Fnetahtml%2Fsrchnum.htm%2526r%3D1%2526f%3DG%2526l%3D50%2526s1%3D6,366,028.WKU.%2526OS%3DPN%2F6,366,028%2526RS%3DPN%2F6,366,028&PageNum=&Rtype=&SectionNum=&idkey=350175768832

 

[koala]

Ok that's a long URL! You can learn alot of stuff from patents! They even list you the parts! Ok can someone please tell me why I couldn't view the pages 1-8? All I can see is the top and left frame. The middle is blank. /ubbthreads/images/graemlins/frown.gif

EDIT: Ok I got it now, install TIFF plugin!

 

[Ty]

[ QUOTE ]
GWO said:
Have you seen the patent filed by CMG Equipment?

[/ QUOTE ]

From the patent attorneys I've dealt with in previous jobs, you can patent almost anything. Patents are supposed to cover new ideas that would not be obvious to practitioners in the field, but this doesn't stop much. I doubt the idea of an LED flashlight was new and original at the time that was filed, and is actually relatively obvious, IMHO. I'd guess it would afford some protection if some company makes almost exact copy knock-offs, but otherwise it probably isn't that useful. However, I am not a patent attorney, so don't really know anything /ubbthreads/images/graemlins/smile.gif

As far as the circuit, the basic astable multivibrator used has been around since the vacuum tube days. Replacing one of the load resistors with an inductor is a neat twist, but probably not the first time this has been done. Running the LED directly off the stepped-up current pulses without any sort of current regulation is either elegant simplicity (if the characteristics of the coil and rest of the circuit are designed to limit the LED current pulses to a safe level), or profoundly poor design (if not) /ubbthreads/images/graemlins/wink.gif