Post by thread:[EE:] simple step-up SMPS challenge

Hi Vasile, how about a challenge, for a simple step-up circuit to power a 4v to 5v PIC from a 1.5v battery, or even a 1.2v NiCd cell. I know chips are available to do this, but with price and availability problems. A cheap 2-transistor circuit that does this (and regulates ok) would be very useful. So, who can suggest a super cheap circuit that does this: * 2 or 3 cheap transistors * ONE standard pre-wound cheap inductor * ok for 1.1v input (discharged NiCd cell) * 4v or 5v output, reasonable regulated * cheap total parts cost and small size * decent efficiency Maybe a simple boost or buck-boost circuit? Similar to the high-gain self oscillating things that Russell and myself have been playing with? :o) -Roman Vasile Surducan wrote: {Quote hidden}> > The easyest way is to built a two coil inductance ( terminals > a,b,c). Supply the coil at terminal "b" with 1,5 or 3V. At terminal > "a" one FET or mos-FET transistor with small r-DS and V-GS, connected with > drain. Source to ground , gate to a simple oscillator ( could be a > positive feedback self oscillator, but then instead of a simple inductance > will be a transformer ). At terminal "c" you'll have a magnified > oscillation voltage. Rectifying with fast swiching diodes and filtering > will gave you 5V. Negative stabilisation feedback is not necessary for > small loads. > Computing the wrapping wire numbers using Faraday's law. > > Cheers, Vasile > > On Tue, 11 Sep 2001, Octavio P Nogueira wrote: > > > What about the opposite? > > >From 1.5V or 3V to 5V? > > I know there are several IC doing that > > but here in Brazil it's not that easy to get them. > > > > Friendly Regards > > > > Octavio Nogueira > > =================================================== > > spam_OUTnogueiraTakeThisOuTpropic2.com ICQ# 19841898 > > ProPic tools - low cost PIC programmer and emulator > > http://www.propic2.com > > =================================================== > > > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

Roman, a cheap step-up with ordinary transistors from 1.1 V is a real challenge ! You need very small VCE if you think to bipolar transistors, but I think bipolars can't be used here. Even serious circuits like LT 1930 ( 1Amp ) running at 1...2MHz have a minimum 2.6V input voltage. About efficiency, I think 60% will be pretty good. But I preffer to design a little expensive circuit than to have problems with sorting transistors for high-est gain. Vasile On Wed, 12 Sep 2001, Roman Black wrote: {Quote hidden}> Hi Vasile, how about a challenge, for a simple > step-up circuit to power a 4v to 5v PIC from > a 1.5v battery, or even a 1.2v NiCd cell. > > I know chips are available to do this, but > with price and availability problems. > A cheap 2-transistor circuit that does this > (and regulates ok) would be very useful. > > So, who can suggest a super cheap circuit that > does this: > * 2 or 3 cheap transistors > * ONE standard pre-wound cheap inductor > * ok for 1.1v input (discharged NiCd cell) > * 4v or 5v output, reasonable regulated > * cheap total parts cost and small size > * decent efficiency > > Maybe a simple boost or buck-boost circuit? > Similar to the high-gain self oscillating things > that Russell and myself have been playing with? > :o) > -Roman > > > Vasile Surducan wrote: > > > > The easyest way is to built a two coil inductance ( terminals > > a,b,c). Supply the coil at terminal "b" with 1,5 or 3V. At terminal > > "a" one FET or mos-FET transistor with small r-DS and V-GS, connected with > > drain. Source to ground , gate to a simple oscillator ( could be a > > positive feedback self oscillator, but then instead of a simple inductance > > will be a transformer ). At terminal "c" you'll have a magnified > > oscillation voltage. Rectifying with fast swiching diodes and filtering > > will gave you 5V. Negative stabilisation feedback is not necessary for > > small loads. > > Computing the wrapping wire numbers using Faraday's law. > > > > Cheers, Vasile > > > > On Tue, 11 Sep 2001, Octavio P Nogueira wrote: > > > > > What about the opposite? > > > >From 1.5V or 3V to 5V? > > > I know there are several IC doing that > > > but here in Brazil it's not that easy to get them. > > > > > > Friendly Regards > > > > > > Octavio Nogueira > > > =================================================== > > > nogueiraspam_OUTpropic2.com ICQ# 19841898 > > > ProPic tools - low cost PIC programmer and emulator > > > http://www.propic2.com > > > =================================================== > > > > > > > -- > > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > > email @spam@listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email KILLspamlistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body > > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

This is going to be fun. Definitely doable. The biggest challenge is STARTING oscillation reliably at low voltages. Once started the output voltage can be used for bias supplies etc. The important parameter is saturation voltage. This can be well under 0.1 volts with a bipolar at low current. Efficiencies are not going to be marvellous. Silicon Chip magazine December 2000 did a single cell to white LED converter. This uses 4 transistors and could use less. They use a basic cross coupled astable multivibrator driving a buffer which drives the pulsed coil. Output rings till the LED absorbs the available energy, This could easily be adapted to a higher voltage design. 3 x BC548, 1 x BC337, 1 diode, 1 inductor, 3 caps, 6 resistors. Runs on under 1 volt. No efficiency stated. 220 uH inductor (custom wound). Runs at 11 KHz. Easily adapted. I calculate power at about 50 mW input with values used. (0.5 L I^2 f) ipk = 220 mA. (They claim 64 mW output power which appears wrong). ie 10 mA at 5 v at 100% efficiency. This sounds about right for a LED (maybe a bit low). This could obviously be increased.. I could (probably) do this with a self oscillating design with 2 transistors (regulated) or one transistor with questionable regulation and a multiwinding inductor. Depends on the value of using an off the shelf 1 winding inductor. Note that the relatively high currents here make the inductor more demanding than for the recent buck designs (saturation of core and losses). Roman ? More anon. Russell McMahon _____________________________ {Quote hidden}> Roman, a cheap step-up with ordinary transistors from 1.1 V is a real > challenge ! You need very small VCE if you think to bipolar transistors, > but I think bipolars can't be used here. > Even serious circuits like LT 1930 ( 1Amp ) running at 1...2MHz have a > minimum 2.6V input voltage. > About efficiency, I think 60% will be pretty good. > But I preffer to design a little expensive circuit than to have problems > with sorting transistors for high-est gain. > Vasile > > On Wed, 12 Sep 2001, Roman Black wrote: > > > Hi Vasile, how about a challenge, for a simple > > step-up circuit to power a 4v to 5v PIC from > > a 1.5v battery, or even a 1.2v NiCd cell. > > > > I know chips are available to do this, but > > with price and availability problems. > > A cheap 2-transistor circuit that does this > > (and regulates ok) would be very useful. > > > > So, who can suggest a super cheap circuit that > > does this: > > * 2 or 3 cheap transistors > > * ONE standard pre-wound cheap inductor > > * ok for 1.1v input (discharged NiCd cell) > > * 4v or 5v output, reasonable regulated > > * cheap total parts cost and small size > > * decent efficiency > > > > Maybe a simple boost or buck-boost circuit? > > Similar to the high-gain self oscillating things > > that Russell and myself have been playing with? > > :o) > > -Roman > > > > > > Vasile Surducan wrote: > > > > > > The easyest way is to built a two coil inductance ( terminals > > > a,b,c). Supply the coil at terminal "b" with 1,5 or 3V. At terminal > > > "a" one FET or mos-FET transistor with small r-DS and V-GS, connected with > > > drain. Source to ground , gate to a simple oscillator ( could be a > > > positive feedback self oscillator, but then instead of a simple inductance > > > will be a transformer ). At terminal "c" you'll have a magnified > > > oscillation voltage. Rectifying with fast swiching diodes and filtering {Quote hidden}> > > will gave you 5V. Negative stabilisation feedback is not necessary for > > > small loads. > > > Computing the wrapping wire numbers using Faraday's law. > > > > > > Cheers, Vasile > > > > > > On Tue, 11 Sep 2001, Octavio P Nogueira wrote: > > > > > > > What about the opposite? > > > > >From 1.5V or 3V to 5V? > > > > I know there are several IC doing that > > > > but here in Brazil it's not that easy to get them. > > > > > > > > Friendly Regards > > > > > > > > Octavio Nogueira > > > > =================================================== > > > > spamBeGonenogueiraspamBeGonepropic2.com ICQ# 19841898 > > > > ProPic tools - low cost PIC programmer and emulator > > > > http://www.propic2.com > > > > =================================================== > > > > > > > > > > -- > > > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > > > email TakeThisOuTlistservEraseMEspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body > > > > -- > > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > > email RemoveMElistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body > > > > > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listservEraseME.....mitvma.mit.edu with SET PICList DIGEST in the body > > > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservmitvma.mit.edu with SET PICList DIGEST in the body

Russell McMahon wrote: > > This is going to be fun. > Definitely doable. > > The biggest challenge is STARTING oscillation reliably at low voltages. > Once started the output voltage can be used for bias supplies etc. Good point. Multivibrator type design would be a good place to start, using one side as the power driver. If the other side could be adapted to control the regulation, excellent, but even a third transistor for regulator control would be ok. > The important parameter is saturation voltage. This can be well under 0.1 > volts with a bipolar at low current. > Efficiencies are not going to be marvellous. Sure, I got 19mV Vce (from a larger transistor), there may be some issues finding the right small package bipolar transistor. But once found, if it is a common type of transistor the circuit would fulfil the requirements of being super cheap... {Quote hidden}> Silicon Chip magazine December 2000 did a single cell to white LED > converter. This uses 4 transistors and could use less. They use a basic > cross coupled astable multivibrator driving a buffer which drives the pulsed > coil. Output rings till the LED absorbs the available energy, This could > easily be adapted to a higher voltage design. 3 x BC548, 1 x BC337, 1 > diode, 1 inductor, 3 caps, 6 resistors. Runs on under 1 volt. No efficiency > stated. 220 uH inductor (custom wound). Runs at 11 KHz. Easily adapted. > > I calculate power at about 50 mW input with values used. (0.5 L I^2 f) ipk = > 220 mA. (They claim 64 mW output power which appears wrong). > ie 10 mA at 5 v at 100% efficiency. This sounds about right for a LED (maybe > a bit low). This could obviously be increased.. > > I could (probably) do this with a self oscillating design with 2 transistors > (regulated) Ooh! You are on! Let's see the circuit. :o) > Depends on the value of using an off the shelf 1 > winding inductor. Note that the relatively high currents here make the > inductor more demanding than for the recent buck designs (saturation of core > and losses). > Russell McMahon I think the off the shelf inductor is fairly vital in the challenge, simply because if the thing is to be practical you need to be able to make them cheap and in quantity. Anyone can build one if time and cost are no problem, using specialty wound toroids that take 1 hour to wind or $4 chips. Being able to use it in a small or medium sized run would give many options for a small PIC product. Especially low current devices like 10mA or 20mA etc. -Roman -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservEraseMEEraseMEmitvma.mit.edu with SET PICList DIGEST in the body

Hi Vasile, small Vce is possible with cheap bipolar transistors, at low currents anyway. The main use for this would be to use a D cell or C cell (etc) battery to power your PIC product, instead of a 9v battery. So the 5v output current needed would only be low, for most of my projects 5mA to 20mA is plenty. -Roman Vasile Surducan wrote: {Quote hidden}> > Roman, a cheap step-up with ordinary transistors from 1.1 V is a real > challenge ! You need very small VCE if you think to bipolar transistors, > but I think bipolars can't be used here. > Even serious circuits like LT 1930 ( 1Amp ) running at 1...2MHz have a > minimum 2.6V input voltage. > About efficiency, I think 60% will be pretty good. > But I preffer to design a little expensive circuit than to have problems > with sorting transistors for high-est gain. > Vasile > > On Wed, 12 Sep 2001, Roman Black wrote: > > > Hi Vasile, how about a challenge, for a simple > > step-up circuit to power a 4v to 5v PIC from > > a 1.5v battery, or even a 1.2v NiCd cell. > > > > I know chips are available to do this, but > > with price and availability problems. > > A cheap 2-transistor circuit that does this > > (and regulates ok) would be very useful. > > > > So, who can suggest a super cheap circuit that > > does this: > > * 2 or 3 cheap transistors > > * ONE standard pre-wound cheap inductor > > * ok for 1.1v input (discharged NiCd cell) > > * 4v or 5v output, reasonable regulated > > * cheap total parts cost and small size > > * decent efficiency > > > > Maybe a simple boost or buck-boost circuit? > > Similar to the high-gain self oscillating things > > that Russell and myself have been playing with? > > :o) > > -Roman -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservspam_OUTKILLspammitvma.mit.edu with SET PICList DIGEST in the body

Hello Roman, There was also a one-cell LED flashlight in Electronics Design about a month ago. It uses 2 transistors and a simple inductor. They mentioned in the text that another transistor could be added to get some regulation. I would send the ckt but its at home just now. I have tried the ckt but it appears to be touchy, I didnt have exact resistor values and had a hard time getting it to go. But the leading indicators are that it is possible to torture this ckt into an SMPS. I will send ckt later. Alice {Quote hidden}> Hi Vasile, small Vce is possible with cheap > bipolar transistors, at low currents anyway. > The main use for this would be to use a D cell > or C cell (etc) battery to power your PIC > product, instead of a 9v battery. So the > 5v output current needed would only be low, > for most of my projects 5mA to 20mA is plenty. > -Roman > > > Vasile Surducan wrote: > > > > Roman, a cheap step-up with ordinary transistors from 1.1 V is a real > > challenge ! You need very small VCE if you think to bipolar transistors, > > but I think bipolars can't be used here. > > Even serious circuits like LT 1930 ( 1Amp ) running at 1...2MHz have a > > minimum 2.6V input voltage. > > About efficiency, I think 60% will be pretty good. > > But I preffer to design a little expensive circuit than to have problems > > with sorting transistors for high-est gain. > > Vasile > > > > On Wed, 12 Sep 2001, Roman Black wrote: > > > > > Hi Vasile, how about a challenge, for a simple > > > step-up circuit to power a 4v to 5v PIC from > > > a 1.5v battery, or even a 1.2v NiCd cell. > > > > > > I know chips are available to do this, but > > > with price and availability problems. > > > A cheap 2-transistor circuit that does this > > > (and regulates ok) would be very useful. > > > > > > So, who can suggest a super cheap circuit that > > > does this: > > > * 2 or 3 cheap transistors > > > * ONE standard pre-wound cheap inductor > > > * ok for 1.1v input (discharged NiCd cell) > > > * 4v or 5v output, reasonable regulated > > > * cheap total parts cost and small size > > > * decent efficiency > > > > > > Maybe a simple boost or buck-boost circuit? > > > Similar to the high-gain self oscillating things > > > that Russell and myself have been playing with? > > > :o) > > > -Roman > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email EraseMElistservspamspamBeGonemitvma.mit.edu with SET PICList DIGEST in the body > > > -- _______________________________________________ FREE Personalized E-mail at Mail.com http://www.mail.com/?sr=signup Talk More, Pay Less with Net2Phone Direct(R), up to 1500 minutes free! http://www.net2phone.com/cgi-bin/link.cgi?143 -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

Yes, you have right, I had thought to large current. Thanks also to Octavio which is thinking to the piclist people. Vasile On Thu, 13 Sep 2001, Roman Black wrote: {Quote hidden}> Hi Vasile, small Vce is possible with cheap > bipolar transistors, at low currents anyway. > The main use for this would be to use a D cell > or C cell (etc) battery to power your PIC > product, instead of a 9v battery. So the > 5v output current needed would only be low, > for most of my projects 5mA to 20mA is plenty. > -Roman > > > Vasile Surducan wrote: > > > > Roman, a cheap step-up with ordinary transistors from 1.1 V is a real > > challenge ! You need very small VCE if you think to bipolar transistors, > > but I think bipolars can't be used here. > > Even serious circuits like LT 1930 ( 1Amp ) running at 1...2MHz have a > > minimum 2.6V input voltage. > > About efficiency, I think 60% will be pretty good. > > But I preffer to design a little expensive circuit than to have problems > > with sorting transistors for high-est gain. > > Vasile > > > > On Wed, 12 Sep 2001, Roman Black wrote: > > > > > Hi Vasile, how about a challenge, for a simple > > > step-up circuit to power a 4v to 5v PIC from > > > a 1.5v battery, or even a 1.2v NiCd cell. > > > > > > I know chips are available to do this, but > > > with price and availability problems. > > > A cheap 2-transistor circuit that does this > > > (and regulates ok) would be very useful. > > > > > > So, who can suggest a super cheap circuit that > > > does this: > > > * 2 or 3 cheap transistors > > > * ONE standard pre-wound cheap inductor > > > * ok for 1.1v input (discharged NiCd cell) > > > * 4v or 5v output, reasonable regulated > > > * cheap total parts cost and small size > > > * decent efficiency > > > > > > Maybe a simple boost or buck-boost circuit? > > > Similar to the high-gain self oscillating things > > > that Russell and myself have been playing with? > > > :o) > > > -Roman > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email spamBeGonelistservSTOPspamEraseMEmitvma.mit.edu with SET PICList DIGEST in the body > > -- http://www.piclist.com hint: To leave the PICList KILLspampiclist-unsubscribe-requestspamBeGonemitvma.mit.edu

Mark Skeels wrote: {Quote hidden}> > > > Silicon Chip magazine December 2000 did a single cell to white LED > > > converter. This uses 4 transistors and could use less. They use a basic > > > cross coupled astable multivibrator driving a buffer which drives the > pulsed > > > coil. > > I used a astable multivibrator to drive a voltage doubler circuit. I had to > add a JFET as a buffer to the output because it drew too much current and > messed up the duty cycle. > > But, I'm thinking of going to some sort of inverting logic gate oscillator > because it costs us about $.06 to put down each smt component. > > There were 10 components for the multivibrator and JFET buffer in the > original design. I think I could use a hex inverter and parallel the left > over inverters at the output, like, say, a 4049. I'd use this to drive the > doubler network. I need to generate roughly 5 or 6 mA at the output. It runs > at about 10KHz; the frequency and voltage outputs are not critical. > > Of course, this is unregulated. I needed it to generate a higher dc voltage > to drive an op amp driving P-channel fets so that I could turn them off all > of the way. Hi Mark, this is interesting, using a hex inverter or other logic chip, but surely this will be limited to applications that step up from 5v to higher voltages? Not for 1.1v to 5v application? -Roman -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-requestEraseMEmitvma.mit.edu

Here is another I've looked into. archives.e-insite.net/archives/ednmag/reg/1998/021698/04di.htm (about halfway down page, look for '5 to 24V switcher') It's 5V to 24V, and regulated. It runs fine as speced, could it be tortured to go to 1.5V supply? I don't know enough to recalculate the resistors to drop the input voltage down, but would truly appreciate someone explaining (slowly, in words of just a few syllables) how to do such a redesign. I imagine the tricky part is getting the regulator transistor to work with the low voltage headroom, since it has to share the headroom with the second half of teh oscillator. That's where my 2 neurons finally gave out. alice {Quote hidden}> The circuit looks simple enough, i'm not > convinced that it can be converted to > regulate and give top performance but it's > a good starting point. Thanks! > -Roman > > > > Octavio P Nogueira wrote: > > > > This circuit is at > > www.e-insite.net/ednmag/index.asp?layout=article&articleId=CA90758&pu > > bdate=07/05/2001 > > > From: "Alice Campbell" <TakeThisOuTelectrifriedKILLspamspamGEOLOGIST.COM> > > > > There was also a one-cell LED flashlight in Electronics Design about a > > month ago. It uses 2 transistors and a simple inductor. They mentioned in > > the text that another transistor could be added to get some regulation. I > > would send the ckt but its at home just now. I have tried the ckt but it > > appears to be touchy, I didnt have exact resistor values and had a hard time > > getting it to go. But the leading indicators are that it is possible to > > torture this ckt into an SMPS. I will send ckt later. > > -- > http://www.piclist.com hint: To leave the PICList > .....piclist-unsubscribe-requestRemoveMEmitvma.mit.edu > > > -- _______________________________________________ FREE Personalized E-mail at Mail.com http://www.mail.com/?sr=signup Talk More, Pay Less with Net2Phone Direct(R), up to 1500 minutes free! http://www.net2phone.com/cgi-bin/link.cgi?143 -- http://www.piclist.com hint: To leave the PICList RemoveMEpiclist-unsubscribe-requestspamBeGonemitvma.mit.edu

part 1 2135 bytes content-type:text/plain; (decoded 7bit) Here's a bare bones circuit for people to criticise unmercifully and hopefully improve. Any resemblance to other circuits living or dead is only partially coincidental. It's a truly horrible circuit. But a simpler one would be hard to think of.. Versions of it work over limited voltage ranges. It could be worked on to make it operate for a given load range and 1.0 to 1.5 volt operating range. It may be fatally flawed. Testing really wants a variable voltage supply as it is possible to get versions which start only over a limited voltage range and operate over a wider but still restricted range. Attempst to operate from a battery during development may lead to the cct never starting. Whether it can be made flexible enough I leave as an exercise for the student :-) Try R2 = R3 = 1k, R1 = 3k3, R4 = 10k for starters. This is kin to the 2 transistor LED driver of the other day and suffers similar defects (and a few of its own). Switching off of Q2 (main switch) is is controlled by R1 not providing enough current to hold the transistor in saturation. Not nice. D1, D2 provide enough isolation to hold Q1 off when Q2 is on and its base is at Vbe above gnd. As Ic Q2 rises it comes out pf saturation when Icq2 > betaQ2 x (Vin-0.6/R1) (approx ;-)) Collector of Q2 rising takes d2 d1 R2 highand turns Q1 on which clamps Q2 off. L rings to deliver power via D3 to load. R4. Having load voltage high helps efficiency due to drop across D3. A LED load can be connected across L1 as per previous circuit BUT better efficiency is obtained with LED from Q2 collector to ground as then the battery provides part of the LED voltage directly. Using a small 100 uH inductor efficiency was poor. At Vin = 2 voltsIin = 43.4 mA, Rload = 10K, Vout was 15.7V for an efficiency of 35%. Not good. This circuit (or a properly behaved variant) MAY be suitable for eg a 12v programming supply from eg 5 volts. I would prefer a driven switch using eg a multivibrator - one more transistor but much more designable. Fun though. Bed time here. (and then some) regards Russell McMahon part 2 2050 bytes content-type:image/gif; (decode) part 3 154 bytes -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Russell McMahon wrote... >Here's a bare bones circuit for people to criticise unmercifully and >hopefully improve. >Any resemblance to other circuits living or dead is only partially >coincidental. > >It's a truly horrible circuit. [description snipped] Yep, it is indeed horrible. As Olin has pointed out, it can't oscillate. You'd be better off with a classic blocking oscillator. That reminds me of a story. Years ago, I worked at a place where we made propane igniter modules for portable heater/dryers used by the telephone companies when servicing underground cable vaults. These modules used three windings on a saturable core, in an oscillator circuit that contained a transistor, two or three resistors, a capacitor and (IIRC from a quarter-century ago) a diode. The primary winding connected between VCC (a 1.5V cell) and the collector of the switch transistor; a secondary winding, with somewhat fewer turns, provided regenerative base drive to the transistor; and the third winding generated the output to a HV rectifier diode and a 5nf, 10KV capacitor. The transformer for this particular unit looked like a TV flyback transformer with a serious attitude problem, and it REALLY packed a wallop. With 1.5 VDC in, we got about 7000 volts out. At one point in our blind quest to wring more profit out of this little monster, we got a brilliant idea: why not use this same circuit design to make a high-efficiency cattle prod (our plant was just outside of Denver, Colorado, near the stockyards)? The idea of an "efficient" stock prod sounds odd, I suppose, but most stock prods of the time used a high-voltage generator based on a magnetic vibrator (sort of like the old Model T Ford spark coils) and were horribly inefficient. The batteries, so the stockyard folks told us, only lasted but a few minutes and all the yardhands walked around with their pockets bulging with flashlight batteries. Our little gadget could go on and on for hours on a single "D" cell, giving off a fat, juicy quarter-inch spark and a loud "SNAP!" every couple of seconds. So we really thought we had something. Anyhow, we whipped up a couple of prototypes and primed Earle, the sales guy, to go out and do some field tests. The next day, Earle went off to the stockyards dressed in about $500 worth of hand-tooled leather dudewear from L.L. Bean and a brand-new Stetson, cattle prods tucked under his arm. The poor guy came back a few hours later- dripping wet, covered with big brown splotches and smelling like a cow that's just suffered a HORRENDOUS case of diarrhea. Seems old Earle had violated the cardinal rule of dealing with cattle: never, never, NEVER stand directly behind a cow for an extended period of time. Feed cattle are bred for beef quality, disease resistance and the ability to gain a lot of weight in all the right places in a short period of time when fed an unlimited supply of grain. They are **NOT** bred for either intelligence or good anal sphincter control. Being mammals, they do occasionally sneeze- and when a cow sneezes, stuff likely as not comes flying out both ends of the cow. So, one simply does not tarry behind a cow. Ever. The way Earle told it, he drove out to the feedlot and got permission from the shift boss to go into one of the pens and run a few experiments. He took the stock prods, let himself into the pen, and went looking for a victim. He settled on one particular beast that was busily munching its way through a feed-trough full of corn, and quietly snuck up directly behind it. Planting his shiny leather L.L.Bean boots firmly in the dirt, he pushed the "ON" button and held it in to let the prod build up a good, hefty charge. Then, with a decisive lunge worthy of D'Artagnon, he thrust the business end of our prototype straight into the cow's backside. Bad move. Old Earle thrusted alright, but the cow didn't give him a chance to parry; the result was spectacular. "That damned cow didn't just crap me," Earle said later. "The ass end of that thing f***ing DETONATED! I jabbed and then my whole world turned brown! Covered with cowshit, and now they're mad at me down at the yard because it took 'em an hour to catch the cow and get it calmed down again." Seems there aren't really any good engineering guidelines on how much electrical energy is required to get a feed cow's undivided attention without also sending the cow into an all-out, bellowing panic. Some things in engineering are simply not on the datasheet, and this was one of them. Anyhow, eventually the thing worked just fine after we cut the number of turns on the output secondary by half and reduced the output capacitance to only a couple hundred picofarads; Earle said the cow just grunted, raised its head out of the feed trough, and started slowly shambling away. Perfection is sweet. Anyhow, Russell, try a blocking oscillator design. They can be made to work nicely on a very low supply voltage. If all you want out of the thing is 5 volts or so, there's no need for a third output winding like we had. Just use the primary. DD -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

part 1 6627 bytes content-type:text/plain; (decoded 7bit) > > Here's a bare bones circuit for people to criticise unmercifully and > > hopefully improve. > > I've only looked at the schematic and not your description. But c'mon > Russel! Just a few brain cells in gear before fingers in motion would save > the rest of us save a lot of time. This circuit is stable and won't oscillate > because you've got two inverting stages tied in a ring with DC paths, which > makes a flip-flop. Olin, OK - that's merciless criticism as requested :-). I'm sorry that your brain cells and my moving fingers don't reach the same conclusion. This is a real working circuit. I didn't get this circuit just from a "thought experiment" or a SPICE model. I thought from what I'd written that it was clear that this was a real working circuit, albeit a flawed one, but obviously I should have made this clearer, somehow. As noted, it was offered as a starting point and a demonstration of the basic elements of such a circuit . You will note that I gave some efficiency figures at the bottom of the post and I made some practical comments about it working over various voltage ranges with various parameters. I also provided a specific set of resistor values in the text under which I did some measurements. (I said : "Try R2 = R3 = 1k, R1 = 3k3, R4 = 10k for starters".) I didn't put these on the diagram because, as I noted, this is not a nice circuit as it stands, different values will be required depending on load and Vin etc and, as I noted, I was offering it as a basis for possible development for those who may want to play with it. . Putting it more clearly, hopefully: I drew this circuit up essentially as shown. I then built it, This circuit is working on my workbench. The results given were measured with standard test equipment. I monitored waveforms with an oscilloscope. It oscillates very well when it is in oscillation. The circuit works over only a limited input voltage range. The starting voltage range is within but less than the operating voltage range. As noted, I do not suggest this as a final circuit. Something may be able to be made from this circuit. It MAY take a very simple change (made possibly with lots of development effort) to make it much more useable. As to mechanism of operation - > As Vin goes up when power is turned on, Q2 will go on via R1 and keep its > collector low, thereby preventing Q1 from ever going on. If R1 is low > enough Vin will continue to drain thru L1 and Q2 forever or until something > fries The mechanism by which Q2 comes out of saturation and causes switching was briefly covered in my original text. This is a fairly common and very time honoured means of causing switching transition in simple low power, power conversion oscillators. As I noted, it relies on the beta (current gain) of Q2 and is therefore not a nice method. Again: - Q2 turned on by R1. - Q1 turned off by R3 and not enough voltage from Vin to turn it on due to D1,D2 and then R2/R3 divider. - Q2 collector current via L1 increases (i ~- Vt/L) - Q2 collector current driven by Iba2 x Beta q2 via R1. - As current ramps up a point is reached where Icq2 exceeds beta x Ibq2 and Q2 will start to come out of saturation. - At this stage L1 attempts to maintain the peak current flow while Q2 is reducing its ability to handle this. Vq2 will start to rise regeneratively. At this stage it still has drive via R1. - When (IF) Vcq2 rises high enough to start to turn off Q1 the process becomes fully regenerative and Q2 is shut off completely. This happens about when (Icq2 - 2 x 0.6) x R3/(r2+r3)m = 0.6 volts ie when Q2 collector voltage - the 2 diode drops of D1,D2 divided by R2, R3 reach 0.6 volts approx and turn on Q1. Clearly this is not a very nice process and the range of input voltages which it works over are affected strongly by component values and Q2 beta. Nothing will "fry" as long as the circuit is "designed". ie Icq2 max does not saturate L1. R1 is dimensioned to cause beta starving of drive to Q2 at designed peak current. Beta of Q2 is known (or its range). I'll say again as I said in the last post (not in exactly these words). - not a nice circuit - not a final circuit - has possibilities - works in practice - flaws make other circuits more attractive - may be redeemable. - interesting to note its existence. - may have applications for simple higher voltage tasks eg 5 to 12 volts. I also replaced D1,D2 with a 5v zener and got some interesting results but that's another story. Having such a simple WORKING circuit to look at allows people to examine and understand the mechanism of oscillation. More complex circuits which have been "optimised" for practical use hide the core processes and are hard for beginners (or experts ;-) ) to understand. This circuit is fundamentally the same as the EDN circuit forwarded by Alice a few days ago but its operation is much easier to understand. For that reason alone it is potentially valuable even if it is never used in this form. Roman has suggested (offlist) an emitter resistor for Q2 to stabilise oscillation. As shown there is NO explicit voltage regulation but this could easily be added in rudimentary form with a zener from Vout to left hand end of R2 or (probably better here) a zener across the output. Power output can be adjusted by varying R1 to limit Icq2 peak appropriately. When there is no load this does go into a self limiting mode as Q1 is held off longer under the larger inductive decay time but this is not a controlled method of voltage limiting (Vout about 25 volts for Vin = 2 volts under that condition in one arrangement). >(can't tell since you didn't provide component values). If R1 is too > high to keep Q2 saturated, then Q1 might (again, no component values) turn > on, turning Q2 off. Once that happens it will stay that way until power is > removed. This is the key point. The rise in Vcq2 due to inductive ringing of L1 causes Q1 to turn on and regenerative turnoff commences. Very nice and square waveform at Cq2 over a limited Vin range. > At most one single brief pulse will be delivered to the output > each time power is applied. This is probably true for Vin outside the working range The circuit is dependant on Vin being neither too high nor too low. I can think of several possible ways of improving it but they will have to wait a while. Roman may turn it into a work of art in the meantime :-) regards, Russell McMahon. part 2 2050 bytes content-type:image/gif; (decode) part 3 154 bytes -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

>Here's a bare bones circuit for people to criticise unmercifully and >hopefully improve. ... >It's a truly horrible circuit. // Yep, it is indeed horrible. As Olin has pointed out, it can't oscillate.You'd be better off with a classic blocking oscillator. // But, it does oscillate ! (Maybe not in SPICE?). That is an actual working circuit that I have shown. See my other two posts for comments and mechanism of oscillation. As I noted there - this is a bare bones idea starter that shows how simple (and horrible ;-) ) such things can get. I have no problems with using blocking oscillators or their variants. Roman, who proposed this challenge, wanted, if possible, a single winding design so that cheap off the shelf inductors could be used. I mentioned recently that I have a very nice forward converter design but that it uses 3 windings. Being a forward converter it does not have the stored energy limitations of the typical small blocking oscillator designs. This allows better power transfer per core volume. Fwd converters have their own limitations but can be excellent in some applications. I'll wait until I've trialled a working version at 0.9 - 1.5 volt in and 5v in before I give details. Long ago we built many of these in a number of forms. Vin was typically, 12, 24 and 50 volts. Various outputs. Some with regulation. Interesting design. Stay tuned. Russell McMahon -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Russell McMahon wrote: {Quote hidden}> You will note that I gave some efficiency figures at the bottom of the post > and I made some practical comments about it working over various voltage > ranges with various parameters. I also provided a specific set of resistor > values in the text under which I did some measurements. (I said : "Try R2 = > R3 = 1k, R1 = 3k3, R4 = 10k for starters".) I didn't put these on the > diagram because, as I noted, this is not a nice circuit as it stands, > different values will be required depending on load and Vin etc and, as I > noted, I was offering it as a basis for possible development for those who > may want to play with it. > . > Putting it more clearly, hopefully: > > I drew this circuit up essentially as shown. > I then built it, > This circuit is working on my workbench. > The results given were measured with standard test equipment. > I monitored waveforms with an oscilloscope. > It oscillates very well when it is in oscillation. > The circuit works over only a limited input voltage range. > The starting voltage range is within but less than the operating voltage > range. > As noted, I do not suggest this as a final circuit. > Something may be able to be made from this circuit. > It MAY take a very simple change (made possibly with lots of development > effort) to make it much more useable. And a VERY functional way of designing something. :o) {Quote hidden}> As to mechanism of operation - > > > As Vin goes up when power is turned on, Q2 will go on via R1 and keep its > > collector low, thereby preventing Q1 from ever going on. If R1 is low > > enough Vin will continue to drain thru L1 and Q2 forever or until > something > > fries > > The mechanism by which Q2 comes out of saturation and causes switching was > briefly covered in my original text. This is a fairly common and very time > honoured means of causing switching transition in simple low power, power > conversion oscillators. As I noted, it relies on the beta (current gain) of > Q2 and is therefore not a nice method. > > Again: > > - Q2 turned on by R1. > - Q1 turned off by R3 and not enough voltage from Vin to turn it on due to > D1,D2 and then R2/R3 divider. > - Q2 collector current via L1 increases (i ~- Vt/L) > - Q2 collector current driven by Iba2 x Beta q2 via R1. > - As current ramps up a point is reached where Icq2 exceeds beta x Ibq2 and > Q2 will start to come out of saturation. > - At this stage L1 attempts to maintain the peak current flow while Q2 is > reducing its ability to handle this. Vq2 will start to rise regeneratively. > At this stage it still has drive via R1. > - When (IF) Vcq2 rises high enough to start to turn off Q1 the process > becomes fully regenerative and Q2 is shut off completely. > This happens about when > (Icq2 - 2 x 0.6) x R3/(r2+r3)m = 0.6 volts > > ie when Q2 collector voltage - the 2 diode drops of D1,D2 divided by R2, > R3 reach 0.6 volts approx and turn on Q1. > Clearly this is not a very nice process and the range of input voltages > which it works over are affected strongly by component values and Q2 beta. > > Nothing will "fry" as long as the circuit is "designed". ie Icq2 max does > not > saturate L1. R1 is dimensioned to cause beta starving of drive to Q2 at > designed peak current. Beta of Q2 is known (or its range). > Having such a simple WORKING circuit to look at allows people to examine and > understand the mechanism of oscillation. More complex circuits which have > been "optimised" for practical use hide the core processes and are hard for > beginners (or experts ;-) ) to understand. > This circuit is fundamentally the same as the EDN circuit forwarded by Alice > a few days ago but its operation is much easier to understand. For that > reason alone it is potentially valuable even if it is never used in this > form. > > Roman has suggested (offlist) an emitter resistor for Q2 to stabilise > oscillation. This would increase stability and provide some relief from changes in Vbe and Beta with each device. {Quote hidden}> As shown there is NO explicit voltage regulation but this could easily be > added in rudimentary form with a zener from Vout to left hand end of R2 or > (probably better here) a zener across the output. Power output can be > adjusted by varying R1 to limit Icq2 peak appropriately. > This is the key point. > The rise in Vcq2 due to inductive ringing of L1 causes Q1 to turn on and > regenerative turnoff commences. > Very nice and square waveform at Cq2 over a limited Vin range. > > > At most one single brief pulse will be delivered to the output > > each time power is applied. > > This is probably true for Vin outside the working range > The circuit is dependant on Vin being neither too high nor too low. > I can think of several possible ways of improving it but they will have to > wait a while. > > Roman may turn it into a work of art in the meantime :-) Sorry I've been away for a few days riding my motorcycle but I am keen to have a fiddle. :o) Apart from the emitter resistor already mentioned, I can see some benefits from adding a capacitor B-E on Q1, this could help tune the circuit when matched with the performance of the inductor at set currents, and may help oscillation over a slightly larger current/voltage range than you are getting now. I think the main issue will be regulaton, and how cheaply and simply it can be added, since you have already proven that the circuit works and has an acceptable efficiency for a quick nasty prototype. -Roman > --------------------------------------------------------------- > > Name: boost1.gif > Part 1.2 Type: GIF Image (image/gif) > Encoding: base64 -- http://www.piclist.com hint: To leave the PICList TakeThisOuTpiclist-unsubscribe-requestspammitvma.mit.edu

part 1 6666 bytes content-type:text/plain; (decoded 7bit) ******** Before we start: ************ - This is a REAL operating circuit. - This circuit DOES oscillate (& very well) in practice *. - It IS possible to describe a formal feedback mechanism and mode of operation. OK WHAT IT DOES: 1 cell to LED driver or Low voltage to higher voltage step up or Flasher With minimal parts count. I suspect this wins the minimum component count with a single winding inductor as per Roman's spec. I put this under the above heading as in some ways it's a continuation of that theme. It also addresses the LED torch and LED from 1 cell applications. I expect that Roman & Alice will have lots of fun further developing this circuit, Jinx will use it in 3 unexpected applications in the next two weeks and xxx & yyy will have lots of fun "commenting" on it :-). This is based on a very time honoured flasher circuit which I have used for other applications.in the past. This is as stripped down as it seems to be possible to get it with an inductor added to provide voltage step up. Adding some components (typically 1 or 2 resistors) alters and may improve performance. Other applications might be a voltage step up for eg 5 --> 12v for programming, solenoid drive as per Jinx's recent application, RS232 supply etc. I haven't optimised this or measured efficiencies but as shown it has a remarkably square drive waveform and may even be somewhat efficient. OUTPUT As shown the inductor "rings" when Q1 is turned off delivering NEGATIVE output below ground. To reverse the circuit to supply positive output above Vin swap Q1 and Q2 types and swap ground and Vin connections. LOAD To use as a voltage supply replace the LED with a diode and filter capacitor. Usually only a single LED would be used. LED1 is driven solely by the flyback voltage LED2 sees" both flyback voltage and input voltage. Arrangement 2 is more efficient as the input voltage is added to the flyback and this part of the supplied voltage is essentially "100% efficient" The LED1 arrangement has the advantage that if Vin exceeds LED normal forward voltage somewhat (say up to 5 volts) the LED will still operate at less than destruction current. Efficiency will suffer in this mode but we now have a LED that will operate from Vin = 0.7 volts to Vin = ??? When operated with only an inductor as load (no LED) my example rings to about 25 volts limited (probably) by L1 to C1 ratio and scope and stray capacitive loading. A LED which will not "glimmer" whatsoever when connected to a single cell can be run across the whole cell operating range. COMPONENT VALUES I have not shown component values (but see example below) as performance is immensely affected by component choice. The circuit is reasonably "designable" but the operation is surprisingly tricky considering the component count. Rather than play with this further I thought I would release it to the eager masses (well, Roman and Alice anyway :-) ) as they are much more likely to extend and optimise it than I am at present. EXAMPLE: Single no-name brand le Clanche AA cell (standard penlight battery) half flat. V = 1.2 volt L1 = 330 uH miniature choke ** R2 = 1M C1 = 100 pF Fosc approx 10 kHz HP high brightness Red LED I_Battery approx 4 mA Surprisingly bright. ** - Dick Smith Electronics R5234 A slightly physically larger 2.5 mH inductor gives somewhat brighter output at somewhat increased current. I gain the impression that the higher inductance is more efficient (as would be expected). CAPACITOR I have shown C1 as an electrolytic to denote polarity. When used for a continuous supply (as here) the cap will be so small that a non electrolytic will invariably be used. When used as a flasher (see below) an electrolytic may be appropriate. VARIATIONS. This circuit can be extended and amended vastly. A few guidelines: Placing a resistor "R1" in series with C1 will have a significant effect on discharge times (as it removes the Q2 Vbe clamp effect on the capacitor). Placing a resistor between Q2 collector and Q1 base (try 1K to start) will affect discharge and on cycle times. This circuit delivers a negative voltage relative to ground. A mirror image circuit may be built by swapping Q1 with Q2 and ground with Vin to make a circuit providing voltage ABOVE Vin. L1 may be altered significantly, varying energy storage for a given frequency. Changing frequency will affect energy delivered and therefore LED brightness (or available output power) Adding resistors to alter mark space (charge discharge) will affect power delivered. . OPERATING VOLTAGE Oscillation starts at about 0.65 volts but with components shown above doesn't give notable LED brightness till about 0.8 to 0.9 volts in. More is better. Output waveform squares up nicely by Vin = 0.8 volt or so. EFFICIENCY Doesn't look marvellous. Didn't do formal tests but some rough measurements suggest well under 50% efficiency !!!! If so, should be able to be improved substantially, at cost of extra complexity. . REGULATION No ! :-) If used as a voltage supply I suspect that a simple zener and series R connected from output to an appropriate transistor base will allow the oscillator to be disabled when desired Vout is reached. Given the power levels involved a simple shunt zener may be better and easier. If low power maintenance of a voltage is desired then the zener scheme would allow the oscillator to "burst" as required to maintain voltage. FLASHER When C is made large (say 1 uF range) the frequency of operation will be so low that individual output pulses will be individually distinguishable. In this case, provided the energy in the inductor is adequate, the LED 'flashes". The design will need to be arranged to provide requisite energy. WORTHWHILE? Possibly not - but it's fun. A simple 2 transistor cross coupled multivibrator would use a few more parts but be rather more designable. Probably worth a look though. SO OK - over to Roman, Alice, Jinx, ... - any other improvers out there ??? regards Russell McMahon _______________________ * For oscillation the current in R2 *Beta Q1 x Beta Q2 MUST be lower than the load current. This means that it will stop oscillating when the load resistance is increased above this level. The low resistance inductor load generally meets this requirement. part 2 1637 bytes content-type:image/gif; (decode) part 3 136 bytes -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservEraseMEmitvma.mit.edu with SET PICList DIGEST in the body

Extract from some offlist correspondence: > Things were slow today so I soldered up your circuit - bingo! Very > interesting combination of r-c relaxation oscillator and saturating inductor. > > A junk box toroid started things off; then I found a Coilcraft smd 68uH > part and tried it. It pulled about 6mA @ 1.0 volts. Then I played around > with the r-c values and finally tried removing the led and replacing it > with a diode/cap to see what sort of negative bias supply could be made. > That one wasn't as encouraging but it was all fun to do. Note that when the inductor "rings" it is driving the timing capacitor and there is going to be an LC energy storage transfer / resonance effect. This is not the primary timing mode of the oscillator proper but will interact. The peak voltage that it will ring to will be affected by, amongst other things, the ratio of L to C - I mentioned this in passing in my original post. By decoupling the inductor from the oscillator proper you would remove this interaction. The easiest ay to do this would be to add another transistor as the inductor driver. This adds minimal complexity but two more components. By now we have 3 transistors and some other circuit may begin to commend itself. Still fun though. After a little playing I was getting about 25 volts peak when the inductor was rung without a LED. As resonant energy storage is proportional to L, C, i^2 and V^2 then increasing the inductor by N willincrease the capacitive peak voltage by N^0.5 IF the peak inductor current is the same. (If increasing L by a factor of N caused the peak current to drop to 1/Nth (as it may) then the overall energy storage may drop with increasing inductance due tot eh I^2 term). As I noted, this circuit is "designable" but has many complex and not initially evident interactions. Chances are that some basic experimenting will reveal a lot more about what "really" happens with changes than any amount of modelling. Russell -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservEraseMEspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

I tried out Russell's circuit, mainly out of curiosity. It works quite well, but aside from the novelty, I did not need a method to light an LED from a single cell. But it *is* interesting... The best LED drive seems to be to connect the LED from the output to the supply, as Russell mentioned. Also, since NPN's are typically faster than PNP's, I reversed the topology and achieved faster switching times. This improves efficiency slightly and I think allows for higher voltages to be produced. So if you have a handful of old alkaline batteries sitting around waiting to be disposed of, you can squeeze every last electron out them and have a bunch of blinking LEDs decorating your lab in the dark. In practical terms, aside from LED's, there is a good use for this circuit. There have been several requests on the piclist for power supply circuits so if you want one to play with, this is a good one as it is very low power and won't likely let out the magic smoke from inside the parts. And it's a lot safer than, say, offline switchers. Finally, if one needs to power up a pic circuit from a single cell (key fob transmitter, rtc, etc.), you could do a lot worse than to try this out. With the led removed, it's not too hard to get 5 or 6 volts out of it. And since pic's can be made to run down to around 3 volts, it should do nicely to power them. Tom M. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads