Joule Thief

[TinselKoala]

Wow, 3 leds illuminated on that low voltage....nice work.  Just imagine what you might be able to do with some of these new hyperefficient smds?  Very impressive work TK.  Those leds were not just barely lit, they were all very bright and I know how hard that is to try to achieve.  I am thrilled to be able to light one led on .5 volts!

Great job,

Bill

I tested a bunch of transistors in that circuit for "start of oscillation" and "LEDs cut off" voltages, using a photocell to supply the voltage and a flashlight to control the illumination of the PV, and guess which transistor gave the lowest "off" voltage:

The very lowest was an unknown TO-92 plastic transistor marked "1802 N711" that cut out at 0.100 volts and started oscillating at 0.425 volts. But the next best was the venerable old 2n2222a in the metal can, with start at 0.420 V and cut out at 0.102 V !!
I tried all the usual suspects too, BC337-25, MPSA18 etc, fifteen different types in all. The BC337 is next best after the 2n2222a. But of course in other circuits the 2n2222a isn't the best choice.
The worst was 2n3904, with start at 0.491 and cutoff at 0.177.

ETA: I leave the thing sitting on the bench with the PV connected, and the voltage on the cap will slowly rise from the room lights. When it is between the "cutoff" and the "start" voltages the LEDs aren't illuminated because the oscillation hasn't spontaneously started. But if I "flick" the LED leads with a short piece of wire the oscillation starts and the LEDs come on, and drain the cap to the cutoff voltage over the span of several seconds.

[Pirate88179]

Can anyone recommend the type of diode I need for my ND1402 circuit?  Quoted below from the specs sheet:



'Diode

The diode is the main source of loss in dc-dc converters.  The most important parameters which affect their efficiency are the forward voltage drop and reverse recovery time...

...A Schottky diode with the following specs are recommended:

small forward voltage Vf < .3 volts
small reverse leakage current
fast recovery time/switching speed
rated current larger than peak inductor current
I rated > Ipk
reverse voltage larger than output voltage Vreverse > Vout"

I have not been able to located any diodes that come close to some of these specs.

Thanks for the assistance.

Bill

[SeaMonkey]

My favorite Schottky Diodes which suit most applications
are either 1N5819 or 1N5822.

[Pirate88179]

My favorite Schottky Diodes which suit most applications
are either 1N5819 or 1N5822.

Thank you, I appreciate the input.

Bill

[magpwr]

Can anyone recommend the type of diode I need for my ND1402 circuit?  Quoted below from the specs sheet:



'Diode

The diode is the main source of loss in dc-dc converters.  The most important parameters which affect their efficiency are the forward voltage drop and reverse recovery time...

...A Schottky diode with the following specs are recommended:

small forward voltage Vf < .3 volts
small reverse leakage current
fast recovery time/switching speed
rated current larger than peak inductor current
I rated > Ipk
reverse voltage larger than output voltage Vreverse > Vout"

I have not been able to located any diodes that come close to some of these specs.

Thanks for the assistance.

Bill

hi Pirate88179,

The fastest diode is the one with <1ns recovery time\mentioned as no recovery time in datasheet as sold in the ebay <$2usd-SDT12S60 INFINEON TO-220 Silicon Carbide Schottky Diode (It was the world first and fastest diode released years ago)

I would need to let the truth out.I think we all made a calculation mistake using the typical Schottky Diode eg:1N58XX series for the forever 3volt ou light.
Everyone then started using Schottky diode when we assume it was the best choice.I have this feeling using a fast response diode <50ns may solve the problem which some may argue.
The only details was not provided was the diode model/spec by the original circuit maker if i recall correctly.

I did some research and came across some research documents somewhere stating that Schottky Diode aren't really that fast it comes with reverse recovery time of around 300ns.Normally reverse recovery time will never be found in the datasheet for schottky diode which i don't understand why.

The primary advantage for the Schottky Diode is merely low voltage drop <0.7volts good enough for boost circuit running somewhere below <100khz.
If you take a look at those latest boost circuit running at around 400khz those are using better diodes.