On Thu, 23 Jul 2009 06:49:21 -0700 (PDT), fungus <openglMYSOCKS@artlum.com> wrote:>On Jul 23, 2:26�pm, default <defa...@defaulter.net> wrote: >> On Thu, 23 Jul 2009 04:20:21 -0700 (PDT), fungus >> >> <openglMYSO...@artlum.com> wrote: >> >> PS >> >> Another possibility is the choice of a poor core material. �You may >> have something that has too low permeability for this application. �If >> that's the case, a few more turns of wire may make a difference. >> (like 30-40 turns instead of 10-20) >> >> Check out this site, he's got some better drawings and circuit >> variations: >> >> http://cappels.org/dproj/ledpage/leddrv.htm#Rusty_Nail_Night_Light > >There's an interesting bit at the bottom which says: > >"I was intrigued with getting the BC107 to run and added a small >capacitor (22nF) across the base resistor to 'kick-start' the >oscillations.Called a 'speed-up' capacitor. For a short time, it acts as a short circuit across the resistor. And in this case, it will dramatically increase your BJT dissipation due to substantially increased base current for a short time near the early on-time. If it is anything near 1000's of pF, anyway. (22nF is way, way too much, I think.)>It worked so well - with various transistors and coils that I was >further intrigued to see how much I could increase the resistor value >- hence the 20k trimpot. (The 22nF also got over the problem of the >oscillator failing when I tried to add an ammeter in the battery >circuit). > >I found it would continue to oscillate right up to 20k ohms and this >also had the effect of reducing the supply current (osc only) from >90mA to 800microamps - very important if using batteries."The amount of delivered power to the LEDs goes down. In other words, at some point it is a bad idea because of the transistor's increased dissipation. You made me curious enough to try a simulation with 200uH on each half of the transformer, a 2N2222 BJT, a 1N5819 freewheeling diode, 10uF output cap (across the 6 LEDs with Vfwd=3, Ron=12.6), and 3 fresh batteries. The Spice results look like: Battery C BJT LEDS 436mW 0pF 28mW 19.9mA 428mW 22pF 16mW 20.0mA 425mW 220pF 19mW 19.7mA 392mW 2.2nF 50mW 16.5mA 173mW 22nF 142mW 0.0mA So battery power does go down. But BJT power goes up and they eventually cross and the whole endevour is a waste. In other words, the BJT starts eating up all the power and eventually eats up everything there is. If you look at the above closely, there does seem to be a small range of values that work well. Say up to a few hundred pF in the example case I let Spice run on. Everything depends, though. So mileage may vary. Jon
Joule Thief - still not working....
Started by ●July 23, 2009
Reply by ●July 23, 20092009-07-23
Reply by ●July 23, 20092009-07-23
On Thu, 23 Jul 2009 04:20:21 -0700 (PDT), fungus <openglMYSOCKS@artlum.com> wrote:>I just got some proper parts to start making joule thieves but I'm >still >having problems. > >The circuit is this: http://www.artlum.com/jt/joulethief.gif > >Except I have R1 and L1 one the other way around (as in the original >web page at http://www.emanator.demon.co.uk/bigclive/joule.htm ) > >The problem is that my transistors keep on overheating and dying. >Why should this be? I'm using a 2N2222 in metal can (as shown here >http://en.wikipedia.org/wiki/2N2222 ). These can switch at hundreds >of megahertz so I don't think it's because of slow switching. > >I measured the current at point X and it seems high - over 100mA. >Could this be the cause of the overheating? Even if it isn't the >problem >it seems wasteful. I tried putting in a resistor there but the circuit >shuts down. >. >I also tried a honking big "high speed switching" transistor pulled >out of a PSU but it made the LEDs go very dim. > >Any ideas?That's a horrible circuit. Too many conflicting parameters depend on the value of R1. A proper blocking oscillator uses an RC time constant to set the rep rate, and a separate resistor to limit the base current. ftp://jjlarkin.lmi.net/BlockOsc.JPG John
Reply by ●July 23, 20092009-07-23
On Thu, 23 Jul 2009 06:49:21 -0700 (PDT), fungus <openglMYSOCKS@artlum.com> wrote:>On Jul 23, 2:26�pm, default <defa...@defaulter.net> wrote: >> On Thu, 23 Jul 2009 04:20:21 -0700 (PDT), fungus >> >> <openglMYSO...@artlum.com> wrote: >> >> PS >> >> Another possibility is the choice of a poor core material. �You may >> have something that has too low permeability for this application. �If >> that's the case, a few more turns of wire may make a difference. >> (like 30-40 turns instead of 10-20) >> >> Check out this site, he's got some better drawings and circuit >> variations: >> >> http://cappels.org/dproj/ledpage/leddrv.htm#Rusty_Nail_Night_Light >> > >There's an interesting bit at the bottom which says: > >"I was intrigued with getting the BC107 to run and added a small >capacitor (22nF) across the base resistor to 'kick-start' the >oscillations. >It worked so well - with various transistors and coils that I was >further intrigued to see how much I could increase the resistor value >- hence the 20k trimpot. (The 22nF also got over the problem of the >oscillator failing when I tried to add an ammeter in the battery >circuit). > >I found it would continue to oscillate right up to 20k ohms and this >also had the effect of reducing the supply current (osc only) from >90mA to 800microamps - very important if using batteries." > >... >Core material and number of turns will affect the frequency of oscillation and that can affect power dissipation. As frequency goes up (fewer turns or less permeable core) the transistor may get warmer due to core losses and storage time (staying on when it should be off for a few nano to microseconds - doing it more often). Then there's D8. That should be a high speed diode not a run of the mill 60 Hz rectifier. A cheap 1N4148 or 1N914 switching diode will be good enough for LEDs - they switch very fast and can tolerate 100 milliamps and up to 100 Volts (manufacture specs may vary, but that's a general idea of what they are rated at). The cap across the resistor is, in my opinion, a good idea as long as you don't get too carried away. (and .022 uf sounds a little high - but a lot depends on how fast it is running too) It serves to drive the transistor harder when the initial switching occurs and that is a good thing. The base emitter dissipation will rise - but the emitter - collector voltage should go down (and that usually accounts for more dissipation since the current is much higher there). You want it to switch fast and not dilly-dally in the linear region. (all other things being equal . . . ) --
Reply by ●July 23, 20092009-07-23
On Thu, 23 Jul 2009 09:24:55 -0700, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:>On Thu, 23 Jul 2009 04:20:21 -0700 (PDT), fungus ><openglMYSOCKS@artlum.com> wrote: > >>I just got some proper parts to start making joule thieves but I'm >>still >>having problems. >> >>The circuit is this: http://www.artlum.com/jt/joulethief.gif >> >>Except I have R1 and L1 one the other way around (as in the original >>web page at http://www.emanator.demon.co.uk/bigclive/joule.htm ) >> >>The problem is that my transistors keep on overheating and dying. >>Why should this be? I'm using a 2N2222 in metal can (as shown here >>http://en.wikipedia.org/wiki/2N2222 ). These can switch at hundreds >>of megahertz so I don't think it's because of slow switching. >> >>I measured the current at point X and it seems high - over 100mA. >>Could this be the cause of the overheating? Even if it isn't the >>problem >>it seems wasteful. I tried putting in a resistor there but the circuit >>shuts down. >>. >>I also tried a honking big "high speed switching" transistor pulled >>out of a PSU but it made the LEDs go very dim. >> >>Any ideas? > >That's a horrible circuit. Too many conflicting parameters depend on >the value of R1. A proper blocking oscillator uses an RC time constant >to set the rep rate, and a separate resistor to limit the base >current. > >ftp://jjlarkin.lmi.net/BlockOsc.JPGWould you care to provide some sample values and analyze that circuit for us? I see the RC node moving towards a bias point, but not really setting the frequency at which the BJT goes on and off. But I haven't sat down more than to glance over it, yet. Jon
Reply by ●July 23, 20092009-07-23
"fungus" <openglMYSOCKS@artlum.com> wrote in message news:ddeb7f42-6adb-4135-8544-a913ef763879@e27g2000yqm.googlegroups.com...>I just got some proper parts to start making joule thieves but I'm > still > having problems. > > The circuit is this: http://www.artlum.com/jt/joulethief.gif >Start with the original circuit, and get it to work on one battery. http://cappels.org/dproj/ledpage/leddrv.htm#Rusty_Nail_Night_Light then go from there to what you want to do.
Reply by ●July 23, 20092009-07-23
On Thu, 23 Jul 2009 19:04:43 GMT, Jon Kirwan <jonk@infinitefactors.org> wrote:>On Thu, 23 Jul 2009 09:24:55 -0700, John Larkin ><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: > >>On Thu, 23 Jul 2009 04:20:21 -0700 (PDT), fungus >><openglMYSOCKS@artlum.com> wrote: >> >>>I just got some proper parts to start making joule thieves but I'm >>>still >>>having problems. >>> >>>The circuit is this: http://www.artlum.com/jt/joulethief.gif >>> >>>Except I have R1 and L1 one the other way around (as in the original >>>web page at http://www.emanator.demon.co.uk/bigclive/joule.htm ) >>> >>>The problem is that my transistors keep on overheating and dying. >>>Why should this be? I'm using a 2N2222 in metal can (as shown here >>>http://en.wikipedia.org/wiki/2N2222 ). These can switch at hundreds >>>of megahertz so I don't think it's because of slow switching. >>> >>>I measured the current at point X and it seems high - over 100mA. >>>Could this be the cause of the overheating? Even if it isn't the >>>problem >>>it seems wasteful. I tried putting in a resistor there but the circuit >>>shuts down. >>>. >>>I also tried a honking big "high speed switching" transistor pulled >>>out of a PSU but it made the LEDs go very dim. >>> >>>Any ideas? >> >>That's a horrible circuit. Too many conflicting parameters depend on >>the value of R1. A proper blocking oscillator uses an RC time constant >>to set the rep rate, and a separate resistor to limit the base >>current. >> >>ftp://jjlarkin.lmi.net/BlockOsc.JPG > >Would you care to provide some sample values and analyze that circuit >for us?No, too much work. I see the RC node moving towards a bias point, but not really>setting the frequency at which the BJT goes on and off. But I haven't >sat down more than to glance over it, yet. >In general, "on" pulse width is set by the volt-second saturation of the inductor (although a small value of C can make it shorter.) Base current is limited by R2 (the one connected to the base.) While the transistor's on, the base current charges up the cap, and that charge will back-bias the transistor until R1 recharges the cap back up to +0.7 volts, at which it fires again. Something like that. Try R1=1K, R2=100 C=100nF as very rough starting points. A lot depends on the inductor. It won't Spice unless the model includes inductor saturation. It's probebly easier to use a Tiny Logic schmitt-trigger oscillator to drive the transistor, and just use a single-winding inductor. Blocking oscillators are tricky. John
Reply by ●July 23, 20092009-07-23
On Thu, 23 Jul 2009 13:23:15 -0700, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:>On Thu, 23 Jul 2009 19:04:43 GMT, Jon Kirwan ><jonk@infinitefactors.org> wrote: > >>On Thu, 23 Jul 2009 09:24:55 -0700, John Larkin >><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: >> >>>On Thu, 23 Jul 2009 04:20:21 -0700 (PDT), fungus >>><openglMYSOCKS@artlum.com> wrote: >>> >>>>I just got some proper parts to start making joule thieves but I'm >>>>still >>>>having problems. >>>> >>>>The circuit is this: http://www.artlum.com/jt/joulethief.gif >>>> >>>>Except I have R1 and L1 one the other way around (as in the original >>>>web page at http://www.emanator.demon.co.uk/bigclive/joule.htm ) >>>> >>>>The problem is that my transistors keep on overheating and dying. >>>>Why should this be? I'm using a 2N2222 in metal can (as shown here >>>>http://en.wikipedia.org/wiki/2N2222 ). These can switch at hundreds >>>>of megahertz so I don't think it's because of slow switching. >>>> >>>>I measured the current at point X and it seems high - over 100mA. >>>>Could this be the cause of the overheating? Even if it isn't the >>>>problem >>>>it seems wasteful. I tried putting in a resistor there but the circuit >>>>shuts down. >>>>. >>>>I also tried a honking big "high speed switching" transistor pulled >>>>out of a PSU but it made the LEDs go very dim. >>>> >>>>Any ideas? >>> >>>That's a horrible circuit. Too many conflicting parameters depend on >>>the value of R1. A proper blocking oscillator uses an RC time constant >>>to set the rep rate, and a separate resistor to limit the base >>>current. >>> >>>ftp://jjlarkin.lmi.net/BlockOsc.JPG >> >>Would you care to provide some sample values and analyze that circuit >>for us? > >No, too much work.Hmm. Just to goose things along, for the joule thief circuit I get something like this for the frequency: (Vbattery - Vsat) * (Vout + Vfreewheeldiode - Vbattery) f = ------------------------------------------------------- Ic_peak * L_collector * (Vout + Vfreewheeldiode - Vsat) Ic_peak may require an iteration or two with a datasheet to approximate. I just go in with an assumed Ic, look up a beta estimate for that on one curve and then grab the Vbe estimate from another curve, and apply them into: Ic_peak = beta*(Nratio*(Vbattery - Vsat) + Vbattery - Vbe))/Rbase That Ic_peak is then used to repeat the process. When it settles, I've usually got a reasonable figure that I can use to compute 'f'. (Nratio is the turns ratio, usually just 1.) I tend to use Vsat=0.2V. If your suggestion is so nicely designable, can't you at least provide an approximate equation?>>I see the RC node moving towards a bias point, but not really >>setting the frequency at which the BJT goes on and off. But I haven't >>sat down more than to glance over it, yet. > >In general, "on" pulse width is set by the volt-second saturation of >the inductor (although a small value of C can make it shorter.)So in your circuit case, it does depend on saturation of the core. What would happen in an air core case?>Base >current is limited by R2 (the one connected to the base.) While the >transistor's on, the base current charges up the cap, and that charge >will back-bias the transistor until R1 recharges the cap back up to >+0.7 volts, at which it fires again. > >Something like that. > >Try R1=1K, R2=100 C=100nF as very rough starting points. A lot depends >on the inductor. It won't Spice unless the model includes inductor >saturation.Yes. I gather.>It's probebly easier to use a Tiny Logic schmitt-trigger oscillator to >drive the transistor, and just use a single-winding inductor. Blocking >oscillators are tricky.Single BJTs are cheap and, if you saw one of the web sites mentioned some time back in the related thread, you'd have seen that the whole thing is tiny enough to place inside a small flashlight bulb base. ... Since you write, "That's a horrible circuit. Too many conflicting parameters depend on the value of R1. A proper blocking oscillator uses an RC time constant to set the rep rate, and a separate resistor to limit the base current," shouldn't it be the case that you can tell me how to compute the frequency with ease? Isn't that the entire point of saying all that? Or did I miss your point, here? Jon
Reply by ●July 23, 20092009-07-23
On Jul 23, 5:13=A0pm, Jon Kirwan <j...@infinitefactors.org> wrote:> > ...a 'speed-up' capacitor. > ... > You made me curious enough to try a simulation with 200uH on each half > of the transformer, a 2N2222 BJT, a 1N5819 freewheeling diode, 10uF > output cap (across the 6 LEDs with Vfwd=3D3, Ron=3D12.6), and 3 fresh > batteries. =A0The Spice results look like: > > Battery =A0 =A0 C =A0 =A0 =A0 BJT =A0 =A0 =A0 LEDS > =A0436mW =A0 =A0 =A00pF =A0 =A0 28mW =A0 =A0 19.9mA > =A0428mW =A0 =A0 22pF =A0 =A0 16mW =A0 =A0 20.0mA > =A0425mW =A0 =A0220pF =A0 =A0 19mW =A0 =A0 19.7mA > =A0392mW =A0 =A02.2nF =A0 =A0 50mW =A0 =A0 16.5mA > =A0173mW =A0 =A0 22nF =A0 =A0142mW =A0 =A0 =A00.0mA > > So battery power does go down. =A0But BJT power goes up and they > eventually cross and the whole endevour is a waste. =A0In other words, > the BJT starts eating up all the power and eventually eats up > everything there is. >Ok, that's scary. I'll stick to playing with the number of turns of wire for a while. I'm going to try a ferrite rod instead of a ring because they're much quicker to add and remove wire (and you can even do it while the circuit is running!)
Reply by ●July 23, 20092009-07-23
On Jul 23, 4:36=A0pm, "petrus bitbyter" <pieterkraltlaatdit...@enditookhccnet.nl> wrote:> The diode you added makes things worse.... >Wasn't me that added it...> So you need to move the diode. Place it between R1 and the base of the > transistor.I'll try that, thanks.> Next step is adding more turns to the coil as others stated already. Gues=s> you will need 1.5-2 times the original number of turns. >Yes, this seems to be the place to experiment.
Reply by ●July 23, 20092009-07-23
