Definition To be called a Joule Thief I think a circuit needs to be able to start when it's input voltage is below 1.0 Volt. That's because one volt is one of the definitions of a dead single cell battery. So if a circuit can start up on less than that it's stealing energy that would have been thrown away if the 'dead' battery was put in the hazardous waste. The lower the starting voltage the more energy a circuit is capable of stealing.
But coupled with low starting voltage a circuit needs to have enough output current to do something useful, like lighting a LED or powering something useful. For example there are some MOSFETs that can be used to make a multivibrator that will start at 0.16 Volts, but if it can't drive anything that circuit is not a Joule Thief. A blocking oscillator is a circuit that can be made into a Joule Thief by selecting parts that allow low voltage starting and is the most common circuit.
Most inverter circuits will not start at low enough voltages to be called a Joule Thief. The Joule Thief is very similar to the Flyback Converter but it does not have metallic isolation between the input and output. The Forward Converter is more efficient than the Flyback Converter.
Low voltage driven oscillator circuit, John E. Bohan, Jr (Honeywell), Mar 29, 1988, 331/117.00R, 331/117.0FE, 331/185, 331/66- will start and run from a PowerPile thermoelectric generator (i.e.
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Starts around 0.1 Volts) Self-energizing Burner Control System for a Fuel Burner, John E. Bohan, Jr (Honeywell), Sep 29, 1987, 431/59, 431/90, 331/66, 137/66, 431/42 - complete circuit including the oscillator. EEVblog #664 -LTC3108 data sheet has info for 100:1 transformer suppliers. Honeywell Powerpile 750 mV thermopile (see my for output data) Alternatives or additions to Blocking Oscillator (flyback oscillator) There are some circuits used with very small solar cells to power motors that make use of a voltage detector IC such as the Panasonic MN1381, Maxium MAX8212, Microchip TC54, etc. These CMOS circuits close a switch to ground when the voltage falls below some minimum voltage (they come in many voltages or allow setting the trip point with external resistors).
This way an energy storage capacitor can be charged by the very small solar panel then discharged into the load. An example is the. Miller Solar Engine The Panasonic poly crystal solar cell generates electricity even when it's cloudy. The motor runs once every six minutes for about six seconds. When in direct Sun the motor runs for about six seconds with a pause of a few seconds. Note: the business card size assembly instructions were for a different version MSE and incorectly showed the two TO-92 components with the flats up.
You can see (click photo for a larger version) that the diagram on the board shows the flats down. The Brown are based on a blocking oscillator that's modified to use less power, prolong battery life. Note an induction coil generates a back EMF or kick when it's drive current is interrupted.
Automobile spark ignition engines use 'spark coils' to step up the vehicle low voltage DC to many kilovolts to fire the spark plugs. Solar Path Lights 12 June 2013 - Got a Solar Path Light form Home Depot (bar code: 22) for $2.88 and took it apart. It contained: AA battery rated at 250 mAh (tested 269 mAh) QX5252E TO-94 (4 lead) IC 100 uH inductor (Red, Black, Brown, Gold = 200 uH 5%) 45 x 45 mm solar panel Open Circuit Output Voltage: 2.6 LED, warm white, with long leads (i.e. Very weak if no heat sinking) PCB about 1/4' x 1' Solar Path Light schematic with QX5252E The QX5252F is in a different package and has an additional terminal for a CdS photo resistor to allow setting the turn off and turn on brightness. QX5252 Waveform at Lx (between L and LED) with LED On (Solar Panel in dark). From - The Channel 1 yellow icon at left is at 0 Volts with a scale of 1 Volt/square. The negative going spike goes to - 480 mV The positive spike is at +4.12 V.
Frequency 101 kHz The flat bottom is at 0 Volts (FET On - charging inductor) A little over 2 uS on time. Opened Rayovac and Energizer 9V battery showing AAAA cells. Note the energizer has loose AAAA cells, but their polarity is backwards, i.e. Point is negative. There's three jumpers in the energizer base each connecting 2 cells. The snaps on the Energizer are not on the center line, but are offset 0.5mm. A cleaver way to lower the cost, i.e.
No Nickel tabe & no welding. You also can remove individual cells. If you look at the schematic you can see it matches the PCB. Walmart IDC IDC577105 (Westinghouse) Path Lights for less than $1 The solar panel on this unit is 30mm x 30mm, smaller than the 45mm x 45mm panel op the Home Depot light. This light has the QX5252E mounted as a Chip On Board ( on the back of the PCB.
The battery is a 2/3 AA size and is rated 150 mAh, the lowest capacity I've seen. I wonder how long and how bright this light is? 100 uH inductor.
Comparing the Home Depot and Walmart solar path lights The Home Depot on the left is a warmer light. My has not arrived, expect it tomorrow. This is a hand held 2.5 second exposure @ ISO 1000 The mode of operation is not a classical Joule Thief, but rather an Induction Coil. The energy stored in an inductor is given by: Energy equals one half the product of the inductance and the current squared. When the Sun is shining the solar panel charges the battery because the voltage on the SBat terminal is higher than on the Bat terminal. Note: the battery voltage is much less than the forward voltage of the LED so only a very small current flows through the LED and inductor during charging.
Note: the QX5252 terminal Lx is open during charging. At night the voltage at the solar panel drops below the battery voltage enabling the light circuit. The FET turns on shorting out the LED and connecting the battery and inductor in series, thus charging the inductor. When the inductor is fully charged the voltage at the Bat terminal has dropped from about 1.4 V to zero at which point the FET turns off. When the FET opens the inductor generates a voltage kick that's added to the battery voltage to turn on the LED for a very short time. The voltage (with no load) is equal to the inductance times the rate of change of the current.
After the inductor is out of energy no current flows through the inductor or LED. If it's still dark the cycle starts over. This Solar Path Light retailed for $2.88 at Home Depot meaning that it is a very low cost product. This circuit is lower in cost than one that uses a two winding transformer like the classical Joule Thief. Another way they get the cost low is using a way undersized battery, i.e. I'm guessing that inside the AA case is really a AAAA battery , see the photo above of opened Rayovac and Energizer 9V batteries showing the 6 AAAA cells inside. Battery Size Capacity mAh Chemistry Weight Oz Solar 250 mAh AA 269 Ni-Cad 0.5 Energizer AA 3100 Alkaline 0.8 Imedion AA 2100 Ready to Use Ni-MH 1.0 Energizer AAAA 600 Alkaline 0.2 Note: capacity based on 25 mA load.
Wiki lists the capacity of the AAAA Ni-MH as 325 to 500 mAh so the 'Solar' brand battery has low capacity even for a AAAA size, i.e. It's very cheap. I upgraded my Solar Path Light by installing the Imedion Ready To Use battery which should increase the 'hours of operation' from the sticker value of 1 hour to at least 8 hours. Model LZ3W/LZ6W An Intermatic (Malibu) 600 mAh Ni-Cad that's totally dead. This unit is still functional, both battery and electronics, but the top black plastic is turning to dust. Old Unit with Discrete Parts Top Old Unit with Discrete Parts Bottom This may be the circuit in one of the old patents. 23 July 2013- 7 out of 7 of these that were not working after installing a new battery were fixed by using a small file to clean the positive battery contact and the positive end of the battery, then putting a small dab of Silicon grease on the positive end of the battery.
The idea is that the Silicon grease will keep out the battery fumes that are making a very poor connection. To test this just put a small screwdriver blade between the battery positive end and the light battery contact with the solar panel down and shielded from light. If the LED lights then that's the problem. These have battery date codes of 2009 (it's June 2013) and are either dead or nearly dead. To open place a knife blade gently between the black top and the narrow clear plastic ring and gently pry.
If it does now separate a little move a little and try again. After a few tries you will be able to remove the top without any new damage (the Sun has already done a lot of damage). Remove the old battery and install a fresh high capacity Ni-MH cell. The removed batteries were: Malibu 600 mAh Ni-Cad (65 each) Solar 1500 mAh Ni-MH - still working Hampton Bay 800 mAh Ni-Cad - still working 6 of 8 batteries dead - all Malibu 600 mAh 6 of 8 of the electronics units still light the LED when the solar cell is face down on a table (in the dark) and 1.3 VDC is applied to the battery terminals.
1 electronics still works even thought the surrounding black material has crumpled into dust. It may be transplanted into a mechanically good but electrically dead unit. Need to check the solar cells as a couple of them look like they may be dead.: 5041952 Control circuit for a solar-powered rechargeable power source and load - uses a 1767 filament lamp 5086267 Control circuit for a solar-powered rechargeable power source and load - uses a 1767 filament lamp 5221891 Control circuit for a solar-powered rechargeable power source and load - uses a 1767 filament lamp The IC is a Chip On Board so it's not at all clear how the circuit works, but it does have a 2 lead axial inductor like the unit above. History I started looking into a Blocking Oscillator as one way to power a High Brightness LED from a single cell battery (Alkaline, Ni-MH or a No.
The early work is on the web page. But it's getting more involved so am starting a new page.
Blocking Oscillators are also used in many other applications. For example if you remove the LED and replace it with a series connected high voltage diode and capacitor and add a third winding with many turns you can generate high DC voltages like used for. With the 7 turn coil unit if the LED is removed the T1B pulse is about 85 volts. The blocking oscillator is also used in some sea mines to power a. They can also be used to drive a piezo disk.
Use a blocking oscillator to generate the flash High Voltage. Working with the Fair-Rite toroid in 43 and 73 material everything seemed to work. The transformer is wound on a toroid of the same type as used to wind. But the 85 material (square B-H) did not. To investigate why a working unit using 73 material was measured again. I suspect that a different winding is needed with the 85 material. Fig 1 Schematic Working 73 material parts: Core: Fair-Rite Transistor: SA1805 LED: LTW-77HC4 R1: 1k Supply Voltage 0.64 Volts.
Fig 2 Base Waveform closed loop Fig 3 Waveform at junction of T1A-1 & R1 Fig 4 Collector waveform self oscillating. Fig 5 Emitter Current Emitter current measurement was made by inserting a 10 Ohm resistor between the emitter and ground. This radically changed the operating parameters of the circuit. But you can see that the current is rising during the LED off time. In this case the voltage across 10 ohms gets to 320 mv or the current gets to 32 ma. Notice that in this case the current has a linear ramp back to zero lasting about 1 us, i.e.
That's the LED on time. Then there's a delay of about 3+ us before the linear ramp up in collector current. Flagiusz sent me an improvement: 'You can speed up transistor switching time by adding capacitor (ca.
1nF) parallel to R1 resistor.' Royer Inverter This is a circuit that uses push-pull transistors to drive a transformer. Used to Zero Voltage Switching Electrical inverter circuits, Westinghouse Electric Corp, 1957-02-26 - Magnetic flux swings from positive saturation to negative saturation This design depends on a saturable core material, i.e. With a rectangular B-H curve (Fig 2 on sheet 1). EBay search term: 'High Voltage Boost Converter ZVS' - not Royer see on it. Just a boost converter eBay search term: '40W DC-AC inverter 12V to 220V' - this is a Royer with a choke on the input - there are also 150W and 500W versions (eBay item 92, YouTube - note 20 kHz, NOT 60 Hz Magnetic coupled transistor oscillator, Westinghouse Electric Corp,1959-12-01 - a Joule Thief version of the Royer - Magnetic flux swings from starting point to positive saturation and back.
Google Group - to promote circuits that work on dead single cell batteries. Experimenter's PCB Motivated by the at the Mendocino County Museum on 25 May 2013 I'm designing a Printed Circuit Board that will allow changing all the components without soldering. It will have a AA battery holder mounted on the board with solder pads to add an external battery instead of using the on board AA. In a like manner it will be possible to solder wires for a external LED. If you are interested in buying one of these printed circuit boards either as a kit to be soldered or already assembled. This is a Joule Thief made from the schematic above just to try some parts.
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This is one way to experiment, but requires more experience than a purpose built board that has component markings. Parts used for this prototype: Transformer core: Fair-Rite 9.65mm OD, 5mm ID, 73 material T1 & T2 windings: 10 Turns of 24 AWG magnet wire (about 5' for each winding) R1: 1 k Ohm Q1: Fairchild KSD5041, NPN transistor made for use in for High Voltage generation from one AA battery. This circuit will start at 0.5 Volts so can be powered by 'dead' flashlight batteries, i.e. The battery doesn't work in the application but will power this circuit. D1: Warm White LED from Electronic Goldmine Stock No. Warm White simulates a filament lamp or kerosene lamp and is a lot more pleasing to the eye than the 'white' LEDs that have a lot of blue content. The beta version has two socket configurations for Q1, one has the lead order E C B and the other E B C to match the two most common lead arrangements on TO-92 outline transistors.
R1, Q1 and the LED have sockets so the components can just be pushed in. The transformer has screw terminals for all four wires. Test points for Vb and Vc, wires can be soldered to make it easier for test leads. Provision for soldering wires for an external battery marked +. An external LED can be used by plugging wires into the LED socket.
Beta Silk Screen layer 28 May 2013 - The PCB, sockets & AA Battery holder have arrived and been assembled. Waiting for the two dual terminal strips for holding the transformer wires. The LED is connected across the transistor Collector - Emitter junction so the collector voltage shown in Fig 4 is the same as the LED voltage. Since the power supply is a single cell with a voltage between near zero and 1.5 Volts some boost is needed to light the white LED (Vf nominal 3.4 Volts).
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The boost comes from the collapsing magnetic field in T1. Then the transistor is turned on and the collector to base voltage is very low (32 mV in Fig 4). The current in T1B starts ramping up until either the transistor saturates or the core saturates or maybe both are happening.
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When the rate of increase of T1B current decreases that generates a voltage in T1A that turns off the transistor. To estimate the collector current using the value of collector voltage. The LED all by itself is measured first: V I P 2.28 1 2 2.94 10 29 3.00 15 45 3.06 20 61 3.11 25 78 3.15 30 95 Core Current For making calculations relating to the toroid the current through the coil is needed.
May 8 2008 (05/08/08) Triad CST206-3A 300T current transformer on order. Expect by end of May. Joule Thief circuit w/ Current Transformer Fig 6 Current Transformeer to measure Emitter (Collector) Current Fig 7 Emitter Current Waveform Current Transformer Using the Fair-Rite 73 material transformer used above with two windings of 59 turns each with the center tap where the power supply was connected not used. To calibrate a single wire was passed through the center and driven by the HP 33120 with a 10 V pk-pk square wave.
Since it has a 50 Ohm internal impedance the calibration current is 200 ma. The scope displays 171 mv so the cal factor is 1.17 Volts/Amp. This plot is not showing a linear ramp down from the peak current but instead a step. That may be because this is not an optimum current transformer.
3 Nov 2011 - Note: The output of a current transformer needs to have a resistive load since it's output is a current, not a voltage. By choosing the load resistor you can end up with a 'nice' Volts/Amp conversion constant. That's probably why the output looked wrong. The current transformer is NOT DC coupled. The DC level will average to zero. The vertical channel has zero volts offset and is 100 mv per division.
During the LED off time the current through T1B and the transistor C-E junction ramps up until the transistor is turned off. That transition is the trigger point at the left edge of the scope. Immediately after the transition the transistor current is zero which allows setting the DC levels on the waveform. Adding 75 mv gives the DC levels. 0 ma at the left edge and ramping up to 180 ma. Hcore = (0.4. PI.
Turns. Current)/ (effective length of core) Hcore = (0.4. 3.14. 7.18) / 2.18 =0.726 Oe The power supply is showing a current of 74 ma. The emitter current does not include the LED current so a seperate measurement was made of the total current which turns out to have the same peak to peak value but looks more like a sawtooth (does not have as pronounced a flat part). A linear ramp from zero current to 180 ma has an average value of 90 ma. But this is over 32 us and the other 5 us of the period there is no current so the average current would be 32/(32+5).
90 = 77 ma which is pretty close to the meter reading of 74 ma. R1 sets the base drive. Decreasing R1 increases the transistor base and collector currents and more coil current means a brighter LED. As R1 is inecreased a point is reached where the LED is no longer on. At this point the circuit is still oscillating but the peak voltage at the LED (same as the collector voltage) is just below the LED turn on voltage. Q1 There are a number of special requirements for this transistor.
First off it must operate with low voltages. Most transistors are specified to work with a collector voltage around 10 V but in order for the oscillator to start this transistor needs to have decent beta and low Vces with maybe 30 milli volts on the collector. Depending on the circuit values the size of the reverse bias spike on the base emitter junction might kill some transistors. A work around is to add a zener diode to protect the transistor. If high voltages are involved the collector breakdown voltage needs some headroom. This is the first time I've used Spice, a general-purpose circuit simulation program for nonlinear dc, nonlinear transient, and linear ac analyses. It came from UC Berkeley.
I'm using the free version from Technology called. It has a a couple dozen NPN transistors built in. After trying all the transistors (and adding the ZTX690B) here are some results along with the spice model parameters. Note the energy stored in the inductor (that's needed to light the LED) is directly proportional to 1/2. L. I^2. So doubling the current does much more good than doubling the inductance.
The point where the current ramp up stops iscontrolled by the transistor parameters. Fig 8 Gummel-Poon schematic The model is a 'T' configuration.
So RC gets added to RE for the collector emitter junction. In the data below the ZTX1048 has RC and RE values that are 50 to 300 times lower than those for the 2N2222.
That alone may explain why it will allow more current to flow. 4 Ohms for RC + RE for the 2N2222 which limits the current to 1 Volt / 4 = 250 ma peak less than 125 ma for a ramp. 0.032 Ohms for RC + RE for the ZTX1048 plus the 0.030 in the inductor and battery total 0.062 Ohms for a current of 16 Amps peak. So something else is the limiting factor. By trying all the transistors some worked much better than others.