6608a Led Driver

New on thissite sinceoriginal publication ofthis page in 2002:. Simplest LED Flasher Circuit (in the world? Be Careful About Peak CurrentA note of caution: These LEDs are comparatively expensive, so Isuggest putting a small resistor (1 to 10 Ohms) in series with thecathode of the LED and measuring the peak current as inferredfrom the IR drop using either a scope or a peak detection probe (asdescribed elsewhere in these pages) while testing this circuit to besure you don't exceed the Manufacturer's recommendations.

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In lieu ofspecific guidance from the manufacturer, for greater reliability try tokeep the peak current to half of the manufacturer's recommended maximum.OverviewA minimum number of parts yields a compact switching converterthat can provide sufficient voltage to drive white LEDs. The resultinglamp is much more efficient, in terms of lumen hours per pound ofbattery, than incandescent bulbs, and because the color of the light isdetermined by fluorescence of phosphors within the LED assembly, thecolor of the lamp does not change perceptibly as the battery runs down.As a result, very long battery life is achievable. This circuit issuitable for powering flashlights, emergency lighting, and otherapplications in which it is desirable to power white LEDs from one ortwo primary cell batteries using a low cost circuit.The CircuitThe circuit could not be simpler than this. The transistor, 1Kresistor and the tapped inductor form a blocking oscillator.

When thepower button is pressed, the transistor is biased on through the 1 kresistor. Voltage that appears from the tap on the inductor to thecollector causes the voltage on the 1K resistor to be even higher thanthe battery voltage, thereby providing positive feedback.

Also becausethere is voltage across the inductance between the tap and thecollector of the transistor, collector current increases with time(this is in addition to a starting value that relates to the currentsupplied to the base, but this part of the collector current is rathersmall. Because of the positive feedback the transistor stays saturateduntil something happens to change its base current.At some point the IR drop across the inductor from the tap tothe collector approaches the battery voltage (actually battery voltage- VCEsat). As this happens voltage is no longer induced in the windingfrom the tap to the 1k resistor and the base voltage starts to drop,and this forces the base voltage to go negative, thereby acceleratingthe switching off of the transistor.

Now, the transistor is off, butthe inductor continues to source current and the collector voltagerises.Quickly, the collector voltage gets high enough for the LED toconduct current, and it does for a little while, until the inductorruns out of current, then the collector voltage starts to ring towardground base voltage swings positive again, turning the transistor onagain for another cycle.The InductorIf you aren't designing this as part of a commercial product,you have a lot of latitude in the design of the inductor. The size ofthe core, its permeability, and its saturation characteristic (Physicaldimensions, u and Bs) determine how many amper-turns it can sustainbefore it saturates. If the core saturates before the IR drop from tapto collector approaches the battery voltage, the circuit will switchquickly anyway because saturating the core makes the coil look like aresistor and coupling between the collector half and the base half (theside with the 1k resistor) drops to very little, so the effect is thesame as the IR drop approaching battery voltage. The wire sizedetermines how many amps the circuit will dray (well, ok, milliamps)before the IR drop gets large enough for the circuit to switch.

Theinductance constant of the core (physical dimensions and u mostly)determine how man microseconds it takes the collector current to riseto the point the circuit switches off, and it also determines how longcurrent will be delivered to the LED when the transistor is off. Nearlyevery inductor parameter affects the performance of this circuit.I have made this with ferrite beads a few millimeters indiameter and toroid cores up to a few centimeters across (take a lookat the Rust Nail Inductor further down on this page). Here is thegeneral relationship between core size and characteristics:Large core: Easy to wind, lower frequency operation, higherpower.Small core: Harder to wind, higher frequency operation, lowerpower.How to get started: Get a transformer core, preferably ferrite,and wind 20 turns on it. Tap by pulling a short loop of wire off to theside, then continue winding another 20 turns.

Increase turns to lowerfrequency, decrease turns to increase frequency. I've used as little as10 turns, center tapped (5+5) and operated this at 200 kHz.

Experiment.Scroll down to the bottom of the page - the tiny ferrite core used inthe #222 bulb base run at about 200 kHz.A Circuit EnhancementThe neat thing about this circuit is that it has the bareminimum number of parts to do the job. The LED runs from pulsating DCand since its forward voltage is higher than the battery voltage, itdoes not interfere with the switching of the transistor. The drawbackis that the peak-to-average current of the LED is pretty high, it couldbe 3:1 or 5:1, depending on the circuit (mostly on the inductor andbattery voltage). Rusty NailNight LightThese blocking oscillator type power supplies work best withferrite cores, and sometimes they can be hard to locate.

Some readershave expressed anxiety over making inductors, and that isunderstandable since to many, inductors have an aura of mystery aboutthem.Just to prove that theseinductors aren't magic, or even that critical for that matter, I woundone on a rusty nail that I noticed laying beside theroadone day while waiting for a tow truck. It is a 2-1/2 inch (6.5 cm) longflooring nail, which serves as the inductor's core.The wire is a twisted pair of #24 solidcopper wire that I pulled from a length of CAT-5 (ethernet) cable,which is similar to the wire used to connect telephones insidebuildings.

I wound 60 turns of the twisted pair in about three layersaround the flooring nail, then I connected the start end of oneconductor tothe finish end of the other conductor and that made it into a 120 turncenter tapped inductor.I connected it to a 2N2222, a 1K resistor, a 1.5 volt penlight cell,anda white LED. Nothing happened. Then, I put a.0027 uf capacitor acrossthe 1 K resistor (it happened to be on the work bench) and the LED cameon. Sometimes you need.001 uf or so. The LED glows nicely and thecircuitdraws 20 milliamps fromthe AA cell.

The waveform on the oscilloscope looks terrible,but the point is that the circuit oscillated with even this rusty nail,and it boosted the output ofthe 1.5 volt AA cell to over 3 volts peak to drive the LED.Those who are familiar with some aspects of coil core selection wouldquickly point out that the eddy currents would be huge since iron has alow resistance compared to ferrite, or air for that matter, and thatthere would also likely be other types of large losses. The pointhere is not that you should run out and buy some flooring nails to makeLED lamps, but that this circuit was not 'designed', but was throwntogether and workedquite readily. If a rusty nail and some telephone wire is enough tolight up a white LED, then the inductor is not so critical. So, relax,go buy a ferrite core and get started on your project.(Above) Rust Nail Night Light.

This LED power supply was throwntogether in a few minutesusing scrap parts.Well, ok the LED itself was not really scrap.Common Sources for FerriteCoresWolfgang Driehaus from Germany wrote to point out that ferrite coresareused in compact fluorescent lamps, and he further stated that he hashadsuccess in making the cores work in this LED power supply circuit. Itwas only a day after receiving his email that I looked up at theceiling and saw some lamps that needed replacement. Here is what Ifound.Some compact florescent lamps from Sylvania had failed in my home.After buying new Philips lamps to replace them, I ventured into thegarage to take one of the Sylvania lamps apart. Sony dcr trv530 drivers for mac.

The first problem wasgetting to the electronics in the base of the lamps. In latercorrespondence, Wolfgang showed me that the base of the lamp can bepried open and the circuit board removed without having to break anyglass. Be careful not to break the glass tubes in the lamp, asthey contain mercury, which is toxic.Inside the base of the lamp, as Wolfgang Driehaus, Ifound three inductors with ferrite cores, as well as a pair of highvoltage transistors, a high voltage capacitor, and some otherpotentially useful components. The inductors were wound on three typesof cores, which are a bobbin core (left, covered in heat shrinktubing), a toroid core (center) and anE-E core, (right).I wanted to confirm the usefulness of the cores for myself, so Iremoved the existing windings from the bobbin and toroid cores. Icracked the E-E core in several places during the process of separatingit from the coilform, so I did not have achance to try it in the power supply circuit.On the bobbin core, I wound 50 turns of #32 magnet wire, pulled out acenter tap, and then wound another 50 turns. I connected this to a2N4401, a 330 Ohm base resistor, and a white LED, according to thecircuit at the top of this page.

When I connected a power supply set to1.5 volts, the LED lit up brightly. Ok, that is solid confirmation thatthe bobbin core from this particular Sylvania light works in thisapplication.On the toroid core, I wound 10 turns of #26 wire wrapping wire, pulledout a center tap, and wound another 10 turns. Connecting it in the samecircuit (2N4401, 330 Ohms, white LED) with a 1.5 volt power supply, Isaw that the LED lit up, but not as bright as with the bobbin core, butthen again, I had only put 20 turns on the toroid.So now we have a very common source of toroids. Compact florescentlamps are available in places, and as Wolfgang pointed out,they eventually wear out and need replacement.Another reader pointed out that another source of ferrite cores is theshielding beads used on computer peripheral cables. Thoseplastic-encased lumps on monitor, keyboard, and some USB cables areactually ferrite cores.

If you are about to toss an old keyboard intothe recycling bin, why not cut off that ferrite bead first? ChristianDaniel of Gernany wrote, noting that the shielding beads are not ideafor this kind of use, so you might want to try this last.Alternative Types of CoresIf you can't find a ferrite core, or even an old rusty nail, all is notlost. You can still make a pretty good white LED power supply by usinga non-magnetic core. It sounds like an oxymoron, but a nonmagetic corehas little effect on the magnetic flux from the windings, and thereforedoes not interact strongly with the circuit -it is there mainly toprovide mechanical support. Two experimenters have provided reports oftheir experiences with nonmagnetic cores, each with its uniqueattributes.The wood core inductorBill Levan in the United States came up with a wood core inductor.

Hiscircuit powers awhite LED from a 1.2 volt 700 milliamper-hour cell. Levan reportsthat he used the rusty nail night light circuit, but found that he didnot need the capacitor across the resistor. Levan's wood core is 5.08 cm x 12.7 mm x3.18 mm (2 inches x1/2 inch x 1/8 inch). The wire is 30 gauge solid conductor insulatedwire wrapping wire, Radio Shack #278-501.Wind 100 turns, pull out the center tap, then wind 100 turns more.

Intotal, there are 200 turns.You can contact Mr. Levan with questions about his wood core inductorand the circuit at the email address below.(The emailaddress isan image.)Air Core InductorAntonis Chaniotis in Greece converted his children's incandescent nightlight to use two LEDs in parallel, and increased battery life from onenight to about 30 hours of light over three nights.The LEDs, while emitting green light, are electricallysimilar to the white LEDs in the other circuits because, similar tomost white LEDs, the die emits ultraviolet light, which excites greenphosphors. Of course in the white LEDs, the phosphors emit white light.The large capacitor in the picture is 100 uf 25 volts, connected fromthe emitter of the transistor to the tap on the inductor, and it actsas a bypass capacitor to insure that the circuit sees a low impedancefrom the battery and switch. It may increase efficiency, especially asthe batteries runs down and the batteries' internal resistanceincreases.The base resistor is 10k, and the batteries is made of two 1.2 voltrechargeable cells in series.Mr. Chaniotis' analyzed the circuit with SPICE and confirmed hisfindings by experiment. Interestingly, his analysis showed that for hiscircuit theoptimum location for the tap is not in the center.The coil is a total of 35 turns 80 mm (3.2 inches) in diameter with nocore. Start by winding 14 turns, the start is the collectorwinding.

Pull out the tap for the battery connection, and then wind anadditional 21 turns for the base winding.Once, I made a similar coil for a different kind of application. I useda plastic food storage container from the kitchen as a coil form, thenafter winding, carefully slipped the coil off the container and heldthe wires together with tape. From the photograph, Mr. Chaniotiswrapped some wire around the bundle to hold it together.You can contact Mr. Chaniotis with questions about his air coreinductor and the circuit at the email address below.(The emailaddress is an image.)Solar Powered Garden LightThis simple flyback/blocking oscillator LED power supply was adapted toand built into solar powered garden light by a talented experimenter inthe United Statesknown as 'mrpiggss'. The method of switching the power supply offduring daylight hours, thus allowing the rechargeable cell to recharge,was taken from a circuit design by Nick Baroni, of Willetton,Washington, and published on the siliconchip.com.au website. Hereis the design from mrpiggss' workbench.The 1.5 volt cell used in this picture was replaced with a 1.25 voltnickel-cadmium cell.Actual values used in mrpiggss' circuit.Mr.

Baroni's original circuit used a BC547, but mrpiggss found that aBC547C (the version he bought) would work as Q1 but not Q2 (see 'A NoteOn Transistor Selection, below). In his version, mrpiggss used 2N4401transistors for both Q1 and Q2, to keep the bill of material as simpleas possible. He also noted that if R1 was 15k, the sunlightgatingfunction would be more sensitive, thus keeping the LED power supply offuntil it was darker than when R1 is 22k.The core for L1 came from ebay with no part number or supplier but itis the size of a penny and about 3mm thick.

The wire came in a 3 packof magnet wire from Radio Shack and and are pure copper. Beinggreenin color and 30 gauge, the wire is easy to handle and wind. The coreshave 40 turns, 20+20 (wind 20 turns, pull out the center tap, then wind20 turns more).

And removing the coating is easier than with reallythin wire. The insulation on this wire can just be burnt off with alighter, and it comes off just like magic. No scraping or sanding,although he use a small emery board to give it some tooth forsoldering.Another very nice method of removing the insulation from magnet wirecame from Christian Daniel of Germany: To quote his email:' Scratchingaway the insulation is difficult with thin wires, it's too easy to cutor weaken them. I prefer fine corund sanding paper.

Or - for very thinwires - I use an Asperin(R) pill and press the wire with the tinned hotsoldering tip on it: opacht! Put your eyes and nose away! The hotorganic acid destroys the insulation and it can be tinne nicely.'

The solar panel is a standard one-battery panel. It has no info on itbut puts out 1.5 volts in full sun.

No idea about the current rating.D1 can be nearly any silicon or germanium diode, provided it is ratedto handle the solar panel's output current into a short circuit. Formost of the panels used in garden lights, this means basically, anydiode you can buy. A low power Schottky or germanium diode would have alower forward voltage drop than a small signal silicon PN diode. The1N4001 series, as used by mrpiggss is a good choice as well because itslarge junction area results in a relatively low forward voltage drop.This is the 'circuit side' of the printed circuit board.The components are mounted on the opposite side. It should be noted thatthe basing for the transistors corresponds to the 2N4401, and NOT the BC547.mrpiggss' email address is ' thetraindork (at) gmail.com' -pleasenote that this email address needs to beretyped with '@' in place of (at). This is meant to stump spam robots,not people.ANote About Transistor SelectionThe transistor used in this circuit can be any one of a wide variety oftransistors.

I recommend trying the 2N4401, 2N3904, and 2N2222, listedin no particular order. Dariusz Flaga in Poland, noted that the BC338is popular in Europe and that its specifications, including voltage andcurrent ranting, and saturation characateristics, suggest that it is agood fit for this application.

Piggs in the U.S.A. (see the SolarPowered Garden Light, above), successfully used the BC547 on severalprototypes.You can even use PNP transistors, but if youdo, remember to reverse the battery and LED connections.

I havereceived email from a couple of project builders who used very highgain transistors and had trouble with their circuits. Transistors withhigh DC current gain (hfe) tend to switch slowly and may operateinefficiently or not at all. Stay away from the veryhigh-gain audio transistors in particular. The small capacitoracross the base resistor, as shown in the Rusty Nail Night Light canspeed up the transistor and make oscillation possible when you have lowa inductance inductor, or if the transistors are a little slow. Speedupcapacitors beyond.0033 uf (33000 pf) are probablyexcessive and may actually slow down the circuit by causing the base tobe over-driven. Bob Parrott's email address is: beep1952@hotmail.co.ukUtility Flashlight Using One Alkaline D CellBy: John S RohrerThis design is for a small flashlight that is reliable, manufacturableon a small scale, and which provides more than 100 hours of light from asingle alkaline D cell. Such a light would be suitable for emergencysituations.

The D cell is chosen because it is available worldwide.Alkaline D cell voltage starts at 1.6 volts (V), with most of the energyexpended at 1.2 V, and virtually no energy left at 1.0 V. For maximumlife, this design will function down to 1.0 V.White LEDs are more efficient than incandescent bulbs, more vibrationresistant, and last much longer.

A downside is the loss of the pleasingvisual spectrum of an incandescent bulb. LEDs are also chosen becausethe 5 millimeter (mM) or T-1 3/4 package is available with a narrow (15degree) viewing angle, eliminating the need for focusing reflectors orlens.

A 15 degree viewing angle illuminates a 1 foot diameter area 6feet away from the LED. This may seem small, but a beam covering a 2foot area would be only 1/4 as bright. So the choice is concentratedbrightness.Given that LEDs become less efficient at higher currents, the best wayto power an LED would be continuous direct current at about 60% of theLED maximum current. But the conversion from 1.5 V to 3.5 V requiresoscillation or pulsing. The pulsed drive should have as large a dutycycle as possible to reduce the peak currents versus the average currentin the LED, and thus maintain LED efficiency.There should be no perceptible flickering in the light output. So thepulse rate should be well above visual sensitivity, which is about 60times per second.Some transformers and ceramic capacitors are microphonic, convertingelectrical signals into audible ones.

Since noise is not desirable, thepulsing frequency also should be above the human audible range, which isroughly 20,000 times per second (Hz).An easily buildable flashlight implies common mechanical parts, with no machining.REASONINGAltho’ white LEDs require about 3.5 V to turn on, they are easilydestroyed if the voltage is forced higher. In the simplest circuits thatcan do the job, a single inductor stores energy in a magnetic field.The inductor energy is released as current to drive the LED, with thevoltage determined by the LED forward drop. The time required to storethe energy at the lower cell voltage is greater than the time to releaseit at the higher LED voltage; specifically, the storage time divided bydischarge time is proportional to the LED voltage divided by input(cell) voltage. This 3:1 to 4:1 ratio can be reduced by placing theinductor step-up voltage on top of the cell voltage, dropping the ratioto 2:1 to 3:1, but even this is less than 50% duty cycle for theLED. The problem can be eased by a tapped inductor (transformer),which decreases the time required to store the magnetic energy. Suchdesigns are common, yielding a simple circuit that supplies the neededcurrent during each charge-discharge cycle.The tapped inductor can also be employed as a transformer to providevoltage to drive an LED while magnetic energy is being stored in thetransformer magnetic field. Thus LEDs can be driven during energystorage and during energy release.

But the transformer output voltage isof opposite polarity for energy storage versus energy release. Using asingle LED implies diodes or transistors to steer the alternatingcurrent to it, but these would waste power. Two LEDs paralleled inopposite directions across the transformer output is more efficient. OneLED would be on while the other is off.If the transformer turns ratio is 4 to 1, then less than 1 volt canproduce enough voltage to drive an LED during energy storage.

This meansthat the LED powered by transformer action during energy storage willproduce light for cell voltage down below 1 V.IMPLEMENTATIONThe following schematic is the result of several 'Not that way!”experiences. For instance, transformer T1 is relatively expensive;however, when the assembly time and effort to produce a replacement areconsidered, it is a bargain.Circuit OperationWhen switch SW1 is turned on, DC current flows thru T1 winding 2-1-4-6and R3 to the parallel combination of DZ1 and Q1 base-R1. In otherdesigns, the current increases until limited by transformer saturation.This design has a specific current limit implemented by zener diode DZ1,transistor Q1, and the paralleled emitter resistance R1-R2.Forward-biased DZ1 has a higher voltage drop than the Vbe of Q1 becausethe junction doping for zener diodes raises the forward voltage dropover that of a comparable transistor base-emitter junction. This voltagedifference can be increased if a small area DZ1 is used with a largearea Q1. The difference can be 40 to 60 millivolts (mV). This differencecauses most of the R3 current to flow into the base of Q1, turning iton.As Q1 turns on, the voltage across winding 2-3 of T1 increases.Transformer action produces four times that voltage across winding3-1-4-6 and thus the LEDs. This drives Q1 on even harder thru R3 (andC2, which speeds the transition), until LED1 is turned on.

Now there is aconstant voltage momentarily across winding 2-3 while Q1 is saturated,and the current thru 2-3 increases at a rate determined by T1'sinductance. As the current increases, the voltage drop across R1-R2increases until that voltage plus Q1 base-emitter voltage begins toequal the drop across DZ1. This diverts more current into DZ1, limitingQ2 current. Measurements with an FMMT617 transistor, an R1-R2 emitterresistance of 0.5 ohm, and a FLZ5V1A zener diode yield a Q2 currentlimit of about 90 mA. This implies that the peak voltage across DZ1minus the voltage across Vbe1 is about 90 mV / 0.5 ohm = 45 mV.With a 1 to 4 reduction in current due to transformer action, the LED1peak current is 23 mA. Free download software reset printer epson t13.

Each LED is on for only part of a cycle, with thecurrent ramping approximately linearly (constant voltage) from zero topeak and back to zero during the 'on' time. So a 23 mA peak current withlinear current ramping averaged over a full cycle (0-23-0 mA)corresponds to an average current of about 6 mA per LED. The typicaloperating current of a 5 mM white LED is 10 mA.The DZ1 current limit stabilizes the light output versus cell voltage.However, the time to store this energy each cycle varies with the cellvoltage, so there is some brightness variation versus voltage due tothis.

But there is less variation than with no current limit. Thecurrent limit also prevents transformer saturation, which would lowerefficiency.As the current limit is reached, the 'rate of current increase' thru T1becomes zero, so the voltage across pins 3-6 drops to zero, as expressedin the equation dI/dT = V/L. This shuts Q1 off, and the magnetic energystored in the transformer produces a negative output voltage acrosspins 3-6, which powers LED2 until the energy stored in T1 inductance isdepleted.

Then R1 supplies base current to Q1 again, and the cyclestarts over.When the cell voltage drops below 3.6 V / 4 = 0.9 volts, there isinsufficient voltage to drive LED1, but the transformer still deliversenergy to LED2 on the second part of the cycle during the magnetic fielddischarge. This provides an end-of-battery-life indication as LED1 goesout but LED1 stays on.If Q1 is oscillating, it will continue to do so until the cell voltagedrops below 0.2 volt because transformer T1 steps that up to 0.8 volt,which is enough to turn Q1 on to start a new cycle. And current isdelivered to LED2 each cycle, altho' it dims considerably as the batteryvoltage drops. And because the cell will usually recover from 0.2 voltto above 0.7 volt with a little rest, it will produce some light from acell that would be totally dead in any other device.Note: A transformer's ability to hold a pulsed output voltage constantversus time is measured by its 'volt-microsecond' capability. Atransformer with a 50 V-uS rating can hold 4 volts for: 50 V-uS / 4 V =12.5 uS, which is the half-period of the 40 KHz operating frequency.C1 provides a low impedance across the D cell at higher frequencies.Prototypes have been built using a commonly available (Eagle Industries)plastic D cell battery holder with the printed circuit board mounted tothe battery holder. The shape of this assembly allows for convenientpositioning of the flashlight when it is set down, and it fits nicely inthe hand. The assembly does not break despite multiple 3 foot dropsonto concrete.The circuit draws about 80 mA at 1.6 V and 35 mA at 1.0 V.

A D celltypically stores 12 ampere-hours (AH), yielding about 200 hours of life.Eight hours use a day means 25 days of life.The brightness at 1.6 V decreases to about one-half at 1.2 V.CostsIn quantities of 100, the circuit board runs about $4.00, the switch$3.00, the transformer $2.70, the battery holder $1.00, withmiscellaneous parts adding another $3.00, for a parts total of $13.70.With this, all design goals have been met.John S Rohreroriginal 1Jun2011 last revision 19Feb2018 qMr. Rohrer's email address is jsmarohrer@fastmail.comDangerof EyeDamage From Visible Light Emitting DiodesContributors to This PageWhat started out as a simple web page to share a simple circuit thatallows white LEDs to be driven by a single 1.5 volt cell has grownbit-by-bit over the years to make it even more helpful toexperimenters.

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