Strange idea..
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From: Jan Panteltje on 11 Jul 2010 15:09 It was hot today, again,. very hot, 34 C inside (no aircos here), http://panteltje.com/panteltje/view_sensors.php so I switched everything off - that did not help- , so sat down and switched on the old soldering iron. What I wanted to do was make a more efficient power regulator for my 3.3V in the LED controller... that is a LM317 regulating 12.5V down to 3.3V at about 200 mA. Say 2.5 W, and the box got so hot that it did not melt, but melted some plastic thing that I had on top of it... Very strange, well that LM317 is about 65 C / W without heatsink so go figure, you can bake eggs on it. Anyways I did the old LC oscillator thing with a BC547 and a toroid (any toroid), and a second winding for the 3.3 V and a Schottky diode. Works perfectly, stays stone cold (well also 33 C hehe). But then this toroid is rather big, and started thinking why not up the frequency and use air core? Say 30 MHz... Then started thinking, hey why not use stripline and go to 900MHz, it is a class C oscillator (sine ) after all. The missing piece is a suitable diode that does 200 mA at 1 GHz? Any suggestions? Anybody tried a stripline voltage converter yet?
From: Tim Williams on 11 Jul 2010 15:35 "Jan Panteltje" <pNaonStpealmtje(a)yahoo.com> wrote in message news:i1d4ti$aqq$1(a)news.albasani.net... > What I wanted to do was make a more efficient power regulator for my 3.3V > in the LED controller... that is a LM317 regulating 12.5V down to 3.3V at about 200 mA. Give this a try: http://webpages.charter.net/dawill/tmoranwms/Circuits_2010/CC_Buck.png Requires a feedback winding, which isn't saying much; traces on the PCB would suffice. I've also been playing with this recently. Pretty much ideal behavior in just six transistors (no feedback winding). Who even needs a UC3842? http://myweb.msoe.edu/williamstm/Images/Discrete_Boost.png With current instead of voltage feedback, and a secondary, it would work fine for LEDs on any combination of voltage. > Anyways I did the old LC oscillator thing with a BC547 and a toroid (any toroid), > and a second winding for the 3.3 V and a Schottky diode. > Works perfectly, stays stone cold (well also 33 C hehe). That can be a tricky approach. If you do a stupid blocking oscillator thing, http://webpages.charter.net/dawill/tmoranwms/Elec_IndHeat1.gif with a tuned load, then you get into conduction angle, bias and quenching problems. The ratio of power output to resonant VAs to excess transistor capacity is ugly, so if you want more than a watt, you already need big power transistors (i.e., no 2N4401's). Put half and half together, and you get the equally stupid chopper thing, which looks like a multivibrator, but maybe isn't (since timing comes from the tank, you don't need RCs). This time, at least, it saturates in both directions, so you can drive low Q loads, and maybe biasing is a little easier. The amazing thing is, the stupid chopper is only one inductor away from a surprisingly smart Royer oscillator. With 180 degree conduction angle, a Royer is very efficient, has little switching loss, and uses most of the VA capacity of your transistors. The downside is, the tank looks like a capacitor against the series inductor, so you can get overshoot, necessitating excess voltage ratings on your transistors, and you need a big fat inductor, presumably high enough inductance that current varies less than maybe 20% during a cycle (i.e., a half cycle, because you get sine wave cusps at the CT). > But then this toroid is rather big, and started thinking why not up the > frequency and use air core? Because, coupling stinks. And if you use a resonant tank to compensate for stray L and C, then you don't have regulation, you get an impedance match system. So the whole thing gets a bit uglier. On the plus side, if you're only ever driving the same LED, you only need to match for one load. > Say 30 MHz... Then started thinking, hey why not use stripline and go to 900MHz, > it is a class C oscillator (sine ) after all. > The missing piece is a suitable diode that does 200 mA at 1 GHz? > Any suggestions? > Anybody tried a stripline voltage converter yet? AFAIK, LEDs look like capacitors in the MHz, and probably make excellent bypass capacitors in the 100s. And in turn, in the 1000s, they probably look like hunks of wire, i.e., inductors. So you'll need SMT diodes if you want to drive them with AC, if they even go that fast. LEDs are junction diodes, so they'll be a lot slower than schottkies, but not nearly as slow as silicon, since they're made of the same things as fancy RF parts, i.e., GaAs, InP, etc. As far as I know, they look ideal up to a few MHz, so they're at least that much better than Si junction diodes. I don't think class C is a good idea, because you can't cover the range of input and output voltages and currents while maintaining high efficiency. Class C is what, 80% tops? At this voltage, a proper synchronous MOSFET switching circuit will top 90%. What you lose in physical size you make up for in power savings -- you'll probably spend as much circuit area on heatsinking and resonators as you will on a controller. You could certainly look at using the same transistors for switching at maybe 1/10th the frequency, or less, but good luck finding a controller that will do it -- you're pretty much stuck rolling your own (not a bad idea... if you can sell 100k of them) or doing it all discrete (= way bigger than either). Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: John Larkin on 11 Jul 2010 16:42 On Sun, 11 Jul 2010 14:35:32 -0500, "Tim Williams" <tmoranwms(a)charter.net> wrote: >AFAIK, LEDs look like capacitors in the MHz, and probably make excellent bypass capacitors in the 100s. And in turn, in the 1000s, they probably look like hunks of wire, i.e., inductors. So you'll need SMT diodes if you want to drive them with AC, if they even go that fast. > >LEDs are junction diodes, so they'll be a lot slower than schottkies, but not nearly as slow as silicon, since they're made of the same things as fancy RF parts, i.e., GaAs, InP, etc. As far as I know, they look ideal up to a few MHz, so they're at least that much better than Si junction diodes. I've measured various small LEDs that have capacitances from about 5 to around 100 pF. There doesn't seem to be a predictor for that. LEDs also show step-recovery-diode like charge storage, so are probably not good RF rectifiers. Skyworks makes cute little (as in, you-can-barely-see-them-SC79) schottkies that run around 0.25 pF, and they are *very* fast. Probably not very good at 200 mA. Some early "switching" power supplies were LC oscillators followed by rectifiers, toobs yet. John
From: Jan Panteltje on 11 Jul 2010 17:09 On a sunny day (Sun, 11 Jul 2010 14:35:32 -0500) it happened "Tim Williams" <tmoranwms(a)charter.net> wrote in <c2p_n.27729$3%3.25068(a)newsfe23.iad>: >"Jan Panteltje" <pNaonStpealmtje(a)yahoo.com> wrote in message = >news:i1d4ti$aqq$1(a)news.albasani.net... >> What I wanted to do was make a more efficient power regulator for my = >3.3V >> in the LED controller... that is a LM317 regulating 12.5V down to 3.3V = >at about 200 mA. > >Give this a try: >http://webpages.charter.net/dawill/tmoranwms/Circuits_2010/CC_Buck.png >Requires a feedback winding, which isn't saying much; traces on the PCB = >would suffice. Thank you Tim, it is a LED controller, but the 3.3V is for the 3 micros (PICs) and the Ethernet chip :-) >I've also been playing with this recently. Pretty much ideal behavior = >in just six transistors (no feedback winding). Who even needs a UC3842? >http://myweb.msoe.edu/williamstm/Images/Discrete_Boost.png >With current instead of voltage feedback, and a secondary, it would work = >fine for LEDs on any combination of voltage. > >> Anyways I did the old LC oscillator thing with a BC547 and a toroid = >(any toroid), >> and a second winding for the 3.3 V and a Schottky diode. >> Works perfectly, stays stone cold (well also 33 C hehe). > >That can be a tricky approach. If you do a stupid blocking oscillator = >thing, >http://webpages.charter.net/dawill/tmoranwms/Elec_IndHeat1.gif >with a tuned load, then you get into conduction angle, bias and = >quenching problems. The ratio of power output to resonant VAs to excess = >transistor capacity is ugly, so if you want more than a watt, you = >already need big power transistors (i.e., no 2N4401's). I think in the long ago past we had a discussion about the meaning of 'blocking oscillator'. Although the diagram of mine looks the same, and CAN be used as a blocking oscillaor, it is not... it is a simple class C sine wave oscillaor. ------------------- +12.5 | | Scottky 6k8 |------ ------- a k ----> +3.3 |___ ||( | ( | | | ||( 10t === ( === | 1t ) ||( | 150 nF ( --- | | | ----- --------------| | | c | --- - b /// === e BC547 | 1u | /// /// The waveform at the collector looks like a pure sinewave, except the bottom is flat, where the transistor switches on. >Put half and half together, and you get the equally stupid chopper = >thing, which looks like a multivibrator, but maybe isn't (since timing = >comes from the tank, you don't need RCs). This time, at least, it = >saturates in both directions, so you can drive low Q loads, and maybe = >biasing is a little easier. > >The amazing thing is, the stupid chopper is only one inductor away from = >a surprisingly smart Royer oscillator. With 180 degree conduction = >angle, a Royer is very efficient, has little switching loss, and uses = >most of the VA capacity of your transistors. The downside is, the tank = >looks like a capacitor against the series inductor, so you can get = >overshoot, necessitating excess voltage ratings on your transistors, and = >you need a big fat inductor, presumably high enough inductance that = >current varies less than maybe 20% during a cycle (i.e., a half cycle, = >because you get sine wave cusps at the CT). > >> But then this toroid is rather big, and started thinking why not up = >the >> frequency and use air core? > >Because, coupling stinks. And if you use a resonant tank to compensate = >for stray L and C, then you don't have regulation, you get an impedance = >match system. So the whole thing gets a bit uglier. But I do not need regulation, as the 12.5 V comes from an external switchmode. I would need some regulation if I connected it to a full 12V battery, In the long ago past I cheated with this system by adding a series regulator on the input, it dropped only a little bit of voltage so got hardly warm :-)
From: Tim Williams on 12 Jul 2010 03:39
"Jan Panteltje" <pNaonStpealmtje(a)yahoo.com> wrote in message news:i1dbul$ljg$1(a)news.albasani.net... > I think in the long ago past we had a discussion about the meaning of > 'blocking oscillator'. > Although the diagram of mine looks the same, and CAN be used as a blocking > oscillaor, > it is not... it is a simple class C sine wave oscillaor. > > ------------------- +12.5 > | | Scottky > 6k8 |------ ------- a k ----> +3.3 > |___ ||( | ( | > | | ||( 10t === ( === > | 1t ) ||( | 150 nF ( --- > | | | ----- --------------| > | | c | > --- - b /// > === e BC547 > | 1u | > /// /// That's a blocking oscillator, operated in a non-blocking mode. Assuming "blocking" refers to "it's not always oscillating". With big C on the load, when the "flyback" is done discharging through the load, voltage goes down around zero (or +V at the collector), but because of the capacitor, it undershoots, which forward biases the transistor again. Resonant or quasi-resonant circuits are hard to make blocking; if you underbias them, then you'll get squegging instead. The trick then is to make C small enough so the RC time constant roughly matches the LC time constant, so the squegging rate is close to the cycle rate and it runs as a throttled sinewave oscillator. I made a blocking oscillator for a high voltage supply, http://webpages.charter.net/dawill/tmoranwms/Circuits_2010/Tubescope_Supply.png which, due to the large capacitance of the HV winding, runs in a resonant mode, with slightly clipped peaks due to the diodes. > But I do not need regulation, as the 12.5 V comes from an external > switchmode. > I would need some regulation if I connected it to a full 12V battery, > > In the long ago past I cheated with this system by adding a series > regulator on > the input, it dropped only a little bit of voltage so got hardly warm :-) LDOs can be very handy for cleaning up ridiculously noisy SMPS. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms |