Easy way to light LEDs

#1
If you need more voltage than the pin output supplies. You can easily light a White led from a picaxe running on 3 volts, for instance, with a simple voltage booster.

The circuit is called a blocking oscillator and has appeared under various guises. Search "joule thief."
http://www.emanator.demon.co.uk/bigclive/joule.htm

He shows the CT coil differently but it is immaterial how it is connected.
or
http://cappels.org/dproj/ledpage/leddrv.htm

The inductor is a ferrite core (not important -even a ferrite bead will work) wound with 30 turns center tapped. The core size is whatever will accommodate the wire you happen to have (enamel magnet wire - but any insulated wire will work)

The easiest way to wind the coil is to wind a bifilar coil by looping a length of wire then winding both coils simultaneously and then cutting the loop and phasing them start to finish using an ohm meter.

A 2N3906 NPN transistor will work fine and any transistor with a low current gain of ~100 will work.

The cap and 1N4148 aren't necessary for operation but improve efficiency and light output.

One caveat: Don't run the circuit without a load, since the output voltage can exceed 80 volts and eat the NPN transistor.

Check the circuit by connecting it to 1.5-3 V before connecting it to make sure it oscillates. If it doesn't oscillate you may have the inductor windings phased wrong.

The circuit can also be used as a boost supply for turning on power mosfets, or by adding a third winding to provide power as an isolated high side mosfet switch. In that case, use a zener or LEDs totaling ~10 volts drop.

I've even used it for powering a picaxe from a single 1.2 V nickel hydride cell and 3.2 volt zener shunt regulator - all under solar power - in that case the sink source of the picaxe is minimal so external switching transistors are necessary to switch loads and the filter cap has to be 10uf electrolytic.

More power can be obtained by lowering the 10 K resistor down to around 1K - but don't exceed the current limits of the picaxe.

You forum gurus: Is there any provision for posting GIF or JPG artwork? - my ascii schematic work sucks

+------------+
| |
| C| Ctr tap inductor
| C| See text
| C|
| +------- +VCC
| | (or picaxe pin)
.- C|
10K | | C|
| | C| 1N4148
'-' |
| +----->|----+----+
| | | |
| |/ | |
+ - - - -| 2N3906 V --- .1 uf cap
|> LED - ---
| | |
| | |
+-------- --+----+
|
=== (or picaxe pin)
GND

 

hippy

Technical Support
Staff member
#2
Flooby : Your ASCII art will show as intended when wrapped in {code} {/code} tags, but use square brackets not curly ones.
 
#3
<code><pre><font size=2 face='Courier'> +------------+
| |
| C| Ctr tap inductor
| C| See text
| C|
| +------- +VCC
| | (or picaxe pin)
.- C|
10K | | C|
| | C| 1N4148
'-' |
| +-----&gt;|----+----+
| | | |
| |/ | |
+ - - - -| 2N3906 V --- .1 uf cap
|&gt; LED - ---
| | |
| | |
+-------- --+----+
|
=== (or picaxe pin)
GND </font></pre></code>
 

Tom2000

Senior Member
#5
<i>&quot;Is there any provision for posting GIF or JPG artwork?&quot; </i>

Flooby,

Using this version of the software, not directly. You need to open a free account with one of the image hosting sites, such as <A href='http://photobucket.com/' Target=_Blank>External Web Link</a>

Post your image there, then post a link to said image in your message.

Hopefully the next version of forum software will allow display of images posted on free sites to be displayed directly in the messages.

Tom
 

boriz

Senior Member
#6
The original circuit (published in EPE) was called &#8216;1 volt LED&#8217;. As soon as I saw it, I new I had to build one. A couple of small mods and I built a great 4-LED torch that runs for around 10 hours constantly on 2 AAAs. It has served me well for many years now. I hacked the case of an old Pifco torch. One of those with the pointy MES bulb, the type that has a small built-in lens on the tip of the bulb. Here&#8217;s some pictures. These were taken using a cheap webcam, so pretty low quality. I was going through my 3D photography phase at the time.

Anaglyph images. You need red-blue 3D glases.
<A href='http://www.zen86415.zen.co.uk/ledtorch1_anaglyph.png' Target=_Blank>External Web Link</a>
<A href='http://www.zen86415.zen.co.uk/ledtorch2_anaglyph.png' Target=_Blank>External Web Link</a>

Stereo images. You use the cross-eye technique to view these. Cross your eyes and line up the white dots. When you have one dot in the middle, then the image is 3D.
<A href='http://www.zen86415.zen.co.uk/ledtorch1_stereo.png' Target=_Blank>External Web Link</a>
<A href='http://www.zen86415.zen.co.uk/ledtorch2_stereo.png' Target=_Blank>External Web Link</a>
 
#7
This circuit <A href='http://www.talkingelectronics.com/projects/PowerSupply5vSolar/PowerSupply5vSolar.html' Target=_Blank>External Web Link</a> can step 1.2V up to any desired voltage, just adjust the voltage divider going into the BC547. I've used these at 3V for leds, 5V for picaxes and 9V for radio transmitters. Occasionally the 547 dies - I found replacing it with a more robust 338 fixes the problem.

The nice thing about using one cell is that they don't mind being completely flattened. With 2 or more rechargeables in series one invariably goes flat before the others, gets reverse charged and then rapidly dies.
 

premelec

Senior Member
#8
I built the simple bead transformer step up some years ago and it works ok... however I find more interesting the new ICs which can start on .5 volts and run on as little as .3 volts - e.g. www.TI.com TPS61200. Their efficiency is better at higher input voltages - they can run off a single solar cell... two cells gives you a good efficient battery charger...

BTW I tested a single cell garden variety garden light step up unit and it came out about 60% efficiency input to output power.

Edited by - premelec on 02/09/2007 02:29:15
 
#9
The original circuit (published in EPE) was called &#8216;1 volt LED&#8217;.

Well I don't know about that. I imagine any number of people will have claimed the circuit by now.

In the dark ages, TV sets used vertical oscillators that were actually blocking oscillators. (tapped inductor that looked like a large/medium laminated transformer)

Back in the &quot;day&quot; we had to do a lot with a single toobe, we didn't have a gazillion transistors per millimeter. So blocking oscillators provided the vertical signal - the advantage was that they oscillated even when a synchronization signal wasn't present.

The CRT's of the time didn't have a separate circuit to blank them when the sweep stopped or slowed - so they'd burn a hole in the phosphors if the sweep stopped - picture toobe is dead.

In the old days the toobes supplying the vertical sync would get weak (or some component in the circuit change value) and the picture would roll vertically until the consumer adjusted the &quot;vertical hold&quot; control trying desperately to find the &quot;sweet spot.&quot;

I should say I worked in military electronics - and never ever replaced a Toobe - they where just that reliable. Consumer toobes and circuits sucked - military ones were indestructible.

The transistor oscillator can be improved with a cap across the resistor - for more power (but not necessarily with a picaxe because of current limitations)

In the day, we used germanium power transistors with 200 uf electrolytic caps across the 200 ohm base resistors to get 3KV out of audio plate transformers and make blue sparks with lots of power - not something a pic would take kindly to without a separate pass transistor.

I imagine the spark experimenters of the late 1800's and 1900's have had as much fun as electronics has been for me.

Read some old Maxwell - he's trying to explain inductors without knowing the word inductance, reactance, frequency, resistance - he understands it but tries to explain it with mechanical models - it is humbling to understand the giants of intellect that got us to this point.

&quot;If I have seen further it is by standing on ye shoulders of Giants.&quot; --Newton to Hooke, 5 Feb. 1676

The dark ages weren't that dark - human intelligence was as sharp during Homer's (and Christ's) time as today. Likely Abraham as well. Intelligence and politics/spin are two different things.

Lee DeForest had a blocking oscillator - but was too ignorant to understand it.

sorry for the politico/religious rant - just that engineers are bent on solving problems - not questioning whether the solutions actually do benifit mankind in the long term.
 
#10
A lovely rant Flooby.
I didn't really understand the subject title though.
Blacksmiths from aeons give the horseshoe a beating when cool(ish), they know it hardens it, but they didn't know why - according to my old Solid-State Physics prof.

Just think ; without Giants of Intellect, Scientist and Engineers you wouldn't have a thread to post on.
All great inventions can be abused.

Anyway, enough of that, as Hippy will get all excited and write a 100 line posting on &quot;Marxism and Its Effect on the Vertical Hold of My Television Set&quot;.
Talking of broken Radios, I must have a quick look at my wife's Bush.
 

premelec

Senior Member
#11
Going from whale oil lamps to white LEDs - in lighting we seem to be making some OK progress - without radioactive Welshbach [sp?] mantles just huge semiconductor plants.
 

premelec

Senior Member
#13
I was referring to the thorium in the gas mantles - my beam accelerator is kaput just now and I don't have the solid sources either - and that Cerenkov is just plain spooky... a bit of tritium with a phosphor is nice however - but the decay rate is a bit high...
 
Top