This is a multi-part message in MIME format. ------=_NextPart_000_0254_01C27D56.741E56C0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Challenge: Convert low voltage DC such as battery or 3v or 5v rail to "somewhat higher" dc voltage at modest power levels for e.g. processor operation, FET gate drive, LED drive, Op-Amp supply, Programmer Vpp supply, and more. Somewhat over a year ago I proposed a design challenge for a simple circuit to step up low voltages to somewhat higher ones for a range of applications. I believe there was and is a demand for such capability and that such a circuit may even provide functionality not readily achieved with available ICs. While there was some initial response to this challenge it died an early death, probably due to the events of September 11th. I'd like to re-propose it and suggest a range of applications and target parameters. Those interested are welcome top redefine the targets more broadly or into several categories if felt desirable. I have a specific prospective application in mind for my own use (4v to 12v converter for FET gate drive) but this is only one of many possible applications. I also would like a low cost, compact, efficient white LED driver that provides essentially constant output and reliable starting over a full range of single cell voltages (<0.9V - > 1.5V) Ideally a single core design will allow a variety of input and output voltages and power levels with suitable simple component changes. Low cost, (non)complexity, efficiency, low parts count, gee-whiz factor, single inductor, ... all score brownie points. Target power level is modest and will vary somewhat with application. e.g. a white LED may require 10 to 20 mA at 3v, A FET gate supply a few mA at 12v, an opamp supply 1 to 10 mA at 12v, a processor 5 to 20 mA at 3v to 5v etc. Target efficiency is "as high as possible and as low as appropriate". e.g. a design that rings an inductor and uses a clamp zener to dissipate any surplus energy would have poor efficiency at less than full power output but such an approach may well be acceptable in many applications. A highly desirable aim is use of a single inductor with a single winding although multi winding inductors or multiple inductors may well be acceptable. (Single winding inductors at this power level are widely available and low cost). Lowest possible starting and operating voltage is a desirable aim although the importance of this will vary with application (e.g. a 3v processor supply to 12v FET drive application only requires that the circuit start and run properly on the 3v supply.) A "run the 1.5v cell utterly dry" design will ideally run on under 0.9v and will hopefully also start on less than a volt. Number and type of active devices is "free" although obviously the less the better commensurate with meeting other design aims. I anticipate that most designs would use one to 3 transistors although more may be appropriate. Use of an IC may be appropriate, although this may limit lower starting and operating voltage. That said, a 4069 CMOS inverter IC has a minimum Vdd of 3 volt (but you will almost certainly need at least 1 transistor as well to allow "flyback" voltage to be used). Low cost is desirable although the real cost of a given design will vary with use - e.g. a commercial product will consider PCB area and component installation costs. Too complex a design will be beaten in cost and simplicity by commercial alternatives. Few ICs aim at the very low power / low voltage / low cost market so there is a niche. The ability to start and run at voltages under 1 volt would place the design in a relatively exclusive club. _______________ As my initial contribution to this challenge I submit my comments and circuit from a year ago for a white (or other) LED driver circuit (led1cel2.gif), plus a modified version of this designed to produce a positive output voltage and allow higher input voltages (smps512.gif) While I have named the diagrams SMPS512 it in fact has NO means of regulation shown and no RC component values shown. R2 is added to the LED flasher version to increase Q2 turn on time during the inductor drive pulse and R3 is added to stop Q2 trying to apply full supply to Q1 base :-). NB - neither of these circuits is optimal. *** THE CIRCUIT DOES OSCILLATE *** The circuit has been built and tested in practice. This is not a paper only dream. (Hopefully that makes it clear enough :-) The above added because this circuit not surprisingly attracts detractors due no doubt to its interesting mechanism of operation. I imagine (but have not yet tested) that a zener from point g to point c would provide regulation of sorts. When out exceeded approx Vin + Vzener - 0.6 Q2 would be held off. This has the disadvantage of reducing Vout with decreasing Vin - less of a problem for Vout >> Vin. In most applications an output zener shunt regulator would suffice. Brief description of operation. NB R1 is sized large enough to NOT be able to support max drive required by Q2 to keep Q1 turned on at peak inductor current. !!!!!!!!!! It's function is to START on drive and possibly provide timing. R2 small wrt R1 Letters a to h refer to equivalently labelled points on circuit diagram. Startup. Q1, Q2 off. c, f at Vin as C1 uncharged. C1.c charges downwards via R1. Q2 turned on via R1+R2 when b reaches approx Vin-0.6 (setting lower bound on starting voltage). Q2 turning on turns on Q1 via R3. Q1 turning on pulls f and therefore c low via C1, turning Q2 harder on causing regenerative turn on. c now increases as C1 charges via base Q2, Current increases in L (approx a ramp) As drive to Q1 DECREASES as C1 charges, drive to Q2 (BetaQ1 x !bq1) decreases until current in L cannot be supported by Q2. As current in Q2 prevents current ramp up in L field starts to collapse and inductor starts to 'ring". f rising increases c further adding to regenerative turn off. f will ring either to - limit set by load - limit set by clamp output zener (not shown) - limit set by LC in tank cct (as no C across L c is only parasitic and small) - reverse breakdown Q2 be junction (R2 reduces this prospect) In practice the first two effects are most likely unless there is no load at all. With f held high c will now start downwards due to R1 (something like bricklayer and barrel story :-) ) This will be hastened with increasing load as f will decay sooner. Voltage at c will sooner or later reach starting point and cycle repeats. Notes: - R2 & R3 are refinements from LED driver version but don't alter basic mode of operation. - R1 size and Q2 beta are important factors in achieving turnoff. - IF L saturates it should do so not too far below the R1-Q2beta limit or there will be large unproductive current spikes in Q1 collector/inductor. Saturation is not necessary but provides another rmeans of triggering regenerative turnoff/ring phase. Efficiency is not liable to be fantastic but Roman can probably tweak it to get 80% plus :-) ++++++++++++++++++++++++++++++++++++++++++++++ LED flasher / driver FROM LAST YEAR ******** 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 e.g. 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. ---------------------------------------------------------------------------- ---- ------=_NextPart_000_0254_01C27D56.741E56C0 Content-Type: image/gif; name="led1cell2.gif" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="led1cell2.gif" R0lGODlhuQC8AIAAAAAAAP///yH5BAAAAAAALAAAAAC5ALwAAAL/jI+py+0Po5y02ouz3rz7D4bi SJbmiabqyrbuC8fyTNf2jef6zvf+DwwyACIAMWGMHJHGpKFZWTqkQiX1cw1kkYvscTusjsBM59OM 8ELUiiWZe0Zrqe40uvmG5bXdw5U91SVX94Dnd5gGx/eEuOh4s+dlqJhY2NfWGMa4ednoNvmoE9lJ mqlJiZhHGFqZKAUoKjcE5UdbSydbZob3uTe3O/vXZusrZnyMnKy8zNzs/AwdLT1NXW19jZ2tvc1d U9x9/Q1OLT4uXW7+LGurnovBjswLLc9Bn8yLn6+/z9/v/w8woL14oJoNzHDwGDyD7i4sjEcuBLod E39UPMXsYg+N/5iccaQoUR1CeOwK/rLzUIIkYZZQxdm1ruEYhJ5McVrVygLLRzI52WS16NVPEhVX vYE1VEnHUKqW5qzp9ETRkg1yIb2FzyVOoFoF0bH5cUJRqFVdskp58iyfry2f+iT7FsXYmz+FkuqJ suPOsmbZsGUxddCdkia/lCPyB3HeQLp6wcSFtshGh0l1igRp2e27yznQXaXsUZTXnGCKCYyMGVKw W3HNBgOoEEfpx3i5evUnJp+3qk6yrqHwz7VqzS3I0NL9Wyy/Up2FrzCexLdS4Pr4pm4NuFB01My1 J4QTFovzFEe3b45icrXs8XK9X/RcO+3wyu291wO9hvtIwVv+vv9QFR9jr223XHFkIRWeelGNtkF5 vfWD3UytIWjCdwBy5Flycj3UH3sanAZhg/gJWCFQpXm4n1X5YTgiYwmC55x/ZSw4hTsX3peZFS+2 4hiFnbwizonuiZjjis0RJ6RY1vGmGE1F1higCjImFSSJDE6EZUauJamSlcNs1WWLsSFpSpVLMhjh mUouMyVri4Wp5ptp0gjnPSh+2Baa9BE3nTJthpTnjHTe2V1uhJ7npZuD7pmooXyKp6Gghc4ZKUSP euDLSo2yyOahYsbZJ6OVjikqnmsWGdaOBl7agZmZhadqdqziSJ1DCcb6nKdPKqfci7hKqWsUHzZ0 HKB+SlfCR/v/BAsqqTqC2axkIPwqa5jQYiSVsVqS+EWp1M4KHGcYdUtpqbRiKm5jm1w7qbSQGpQn ubYtqm2r6Tolr2m5TutRgPmeKpVVUcp3T3qasEsvpoUZPCCbIILycMQST4xcwfoF5S15C1/8y8Cx 6OsIyBtqSt235IUbMsAxZBjamggzy++udrqcMQ0sw0tzuTpnK7Ol1tY8w83b/qwzx8l+6vOzjH5X Lco4B2z0GIfdK3XURAnb8sjzhdopsOvV2fXJX3Pt575bB1q212c3+qXJSEu4drSSHim2Dd+Y5rHa 9e3mdEtu94xexTtXOPWoou3H5OA8q9xu3Fb0OjZKAim+sk6H/+V9dGOwOco40XyT/RoPdyM6b9NQ qoT53oaT/TfbkkeS+uJoE0xnqnJfyHAqooNO+6PKzuL6S0yX/nmzKTVF5KS4C25u5bPH0Tjlg0qy YoHNOx/tQiKTLhx0wTnbLkl9v23cgLgZU/7p179XUGSJnYZ+8MS8Lfvz4I9XLP0lgp129FC895/O JY09ueNf3VaHPhsZKXlm411uDHYjBh7QgVWg2PAEKDXAVRCCCzRVAym4wQ7ZR4ITtN+EIKYi7CWO hCW8XXfkdQYZRNCDppPfC8sUtCE5yQXbe+EgcChD+8yFhxic0I9gZi/1ZSmABtSMXxKmui+tTw/j a1uPFIVFJv8qiHhI5B4CpzGbP0WvCIXTRhiXkr4agjAIJPmhng5BLC1WMX50eQvJ2jZGuM2Rc1e5 W3papytAumsv4BKcIMHVxRw2qTJ4m18QNchGO+anV4tUYRGFEB2slAdyNtPfNtCSvxxCEhzLQuT+ sJYOL8rxkqkMnt5Y2UpsUXGUscxj/ZpYS1e28Iu5tOUp9+iDjUlumJo04QdxOZk6muiGK1zZwKwm ypQl6jPCcybHLvgxuwhiGOGzoDe9yUf6+IhJsWtQAdVVwQMxc0/QnFbeDjks/hDzJVCEZy+JeM9s 2DOfx+TnOfwZDoBaY58CrUfECorQhCp0ocKzHkMfCtGItrIXlBKtqEUvasZyYnSjHO2oRz8K0pDS oAAAOw== ------=_NextPart_000_0254_01C27D56.741E56C0 Content-Type: image/gif; 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