[FARC] Voltage booster?

[m.e.whitmore at comcast.net]

Phil,

I may have stumbled on a solution to your problem. Yesterday I didn't notice the first link
in your email and went to the second one. I did a PSpice simulation and could not get it to
not work. With what I learned today I think I can go back and make it not work.

Looked at the first link today and decided to build one. The only LEDs I have are red so I
connected two in series and measured 3.2 volts forward drop at 1 mA. My core is an unknown
with 16 turns of bifilar magnet wire. The resulting inductor measures 26uH at 1.8mHz.
Transistor is a 2n390? (can't read the last digit)but checks out as NPN. Connected the LEDs
with the cathode on the collector of the transistor.

I am always cautious about hooking up a new circuit to a battery with no current limit so I
powered it up from a bench supply set at 1.3 volts. LEDs lit but not brightly. Hooked up Fluke
DVM to measure input current. 42mA but the LEDs did not light. Put 150u capacitor across the
input and the LEDs came back on. Hooked up scope and saw 30V positive (WRT the cathods)spikes
spaced at 646nS or about 1.5m spikes per second. These spikes were reverse biasing the LEDs.
The forward bias of approximately 4V had about a 10% duty cycle with zero volts for the rest
of each cycle.

My conclusion is that the inductance of the meter leads tends to kill the oscillations. I will
confirm this with the simulation later. There was still oscillation but not strong enough to
forward bias the LEDs. A 0.01u cap works just as well as the 150u to effectively remove the inductance.

Decided to turn the LEDs around and see how that worked. Much better, duty cycle now about
26% at 172nS and LEDs are at least 3db brighter.

If you just happened to hook up your "joule theif" with a bench supply using long
leads like I did, that may be why it did not work. Other than that, bad transistor,
emitter/collector reversed, bad Led, really dead battery, cracked or high loss core,
wiring error are the only other things that I can think of.

Happy New Year to all

Regards,
Mark



 
----- Original Message -----
From: "Philip Karras" <ke3fl at yahoo.com>
To: "ccarc" <k3pzn-list at mailman.qth.net>, "Mid Atlantic" <madxra at madxra.org>, "Frederick AmateurRadioClub" <farc at mailman.qth.net>
Sent: Monday, December 30, 2013 6:49:15 AM
Subject: [FARC] Voltage booster?

Has anyone built one of these? I've been trying but have yet to get it working. It such a simple circuit I can't believe I can't get it working or figure out what I'm doing wrong!

See the Instructable called, "Making A Simple Joule Thief (made easy), by ASCAS" : (They call this circuit a "Joule Thief" because you seem the steal energy from a "dead" battery)
http://www.instructables.com/id/Making-A-Simple-Joule-Thief-made-easy/

Any ideas about how to get this to work would be appreciated.

I'm using a 3-Volt white LED, and green core from a dead CFL, and about 20 turns of double wire.

Another I've come across is the Supper Joule Thief, "Make a SUPER Joule Thief Light! by clevelandstorms" at
http://www.instructables.com/id/Make-a-SUPER-Joule-Thief-Light/

Perhaps I should give that one a try instead.

73 de KE3FL,
Phil
AEC Carroll County
OES, ORS, & VE
http://cs.yrex.com/ke3fl
Karras' Corner: http://blog.solidsignal.com/content.php/1005-karras-corner
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