This is a multi-part message in MIME format. ------=_NextPart_000_037E_01C13DEA.157C6500 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 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. ------=_NextPart_000_037E_01C13DEA.157C6500 Content-Type: image/gif; name="boost1.gif" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="boost1.gif" R0lGODlhIAHrAIAAAAAAAP///yH5BAAAAAAALAAAAAAgAesAAAL/jI+py+0Po5y02ouz3rz7D4bi SJbmiabqyrbuC8fyTNf2jef6zvf+DwwKh8Si8YhMKpfMpvMJjUqn1Kr1is1qt9yu9wsOi8fksvmM TqvX7Lb7DY/LaYBDHXGf63H5/P6f04fnFwBgSAiYSCKIl8CoCDlSh0j4GHnpMalQaYfpmblp2GiA +Gl6ipqqusra6vr6cQg7O3EoSgtpq7vL2+v7CwyMC6ebUjqcJmuMTLxyzHz2LCINTUYNcl0dlg2q vcbdAe7NJb5RPp51nqGOPsWLctsuxrksv+3oHPHMbk+Hn//gWLx+ROipuLaPoBGD9RwkVFjw30EI DyEKYQiPYgN+/xZdYDSRrZidgR17fFxUUsvJECRTVlk5zSUWg7Y2hZNphWankd1wStFJSqI5n+4k 1hSqgSNRHjpLKd259AlQSj2jNgFaaNDTp1b5IC3BtesNmLHCirVBFtvZjS2VUXA7KulXsGsX3PFj SV/QQRzSsqxr1G6FvFvn0gUMlepgqHvlxm2ImPAFyUMfZ0S81y+DuzYrM76MGW6ho7XatlxsGSRm JJpvrj7y7sTp1xFZmKXtMTfuhS9u74YM8PfF3sKH+JZwvDhK3RhEk1bel3nzxoahow6+7jN169MP ciWcPFfF0hsthBfsOmtndLNnOxR47vz6ygLlnRatz6n78hPDkf98Po5p+21GCX4a9cfdfwDm58iC BwKn3EC7mIeXSG9hB108sb3Vx4TXgWbdLb3Y1d5dG9binXwKieJLKAayOOKHYDloXzA23ohjjjru OAmMNd3YkW8+eqjVfT2eiJwxNJrHliJCmkikVgSSgqReSppVopMsdWgheVR2mSSC/umnJTYVLtnk SGhuhqE5+A3oxpMNGhhQJWuiB2FSAMLZhpxzxlcgn9XFVNZzgn6zJYmAKsqkmH0ReagafoZC4ZQy zohlbJF+aU2ibA42Xpiy3YnciJuC6YWKOnwX42g8vgorrFGoGoie+1TZnKnloBrQrF2wcyippXq4 qauNSvVrpaD/ZmphsepdugStXl042XbrdOmsOtK2eYU4wKY22Z7aVgvFtmihSC64yxaYLrXIkiOq lPzNFy6Zx7rrhLk1hERgqINSBF+76L67BUJs1ddrdyQKHO9VySbMKL2fnnuvw/A69J5iVu7LcLQP zxuxdhhTDK0S+voDcsjPDjzDuOV+jGe/Ij/YcscmwyzxnNY2HIPLBKuUMqMcnRwzyxYXHLSLShGd M81Hp9MewIWhXHISTPfmIELO/usozx6rFCuvVdvGodi8gf2i1NFRvfHOsJETdZ1T56qx1ynDd9+q OKsrr2PpVthvjkUjvPJoel9ctMoKV8x3em5bokmtiCf+p982/xf+l7qGui3D1TBIQ40s/AyddCyG Ra7m1ochXbqanEP89+k7Dv6pU4ez3rqxr098rZ3e4ot5Y3WTDPTIMs+cewu/N17bVa3uHjynzE9P ttGeqxWte8oYfHxcoE/b8PWmWw0OnbLbrr3k4efLGqD8uhg45TVbz/7Zjb4/bFs7LI98EeIzHi/8 yW1z+wPe/xwXhG9xLXqK0pBJDFi/evlOEoo7HYPyhznnqG5xTjvg2mInvMzBj3dNo9Sw1vMIc/EP esNRmO3GV0HolU97IkKh/Jazvqet64Yc7Bv13BelDGpHXytkoP+y80IYVrB8FMQH6lgowrYZsXn3 W+DYnAO8qv9kxopR7GAEj8WlDTIPLvEhVIOeZbYm5pAJHkyeW3ymxALST4dyPBgUS5gdHxSxjZar ox1Jh70HzpGNBwtbGpPnqqV18XZS5GMeeWgzOmltblpkpBfp2L+O8WqSH6yk+hqZr19syZCi9Iwn wZefQ2Kyj1/Km9w6iUBL2q0ogdQZJHXHSlP60Wg5IaXZ/DXCXApzLJfLBSLNx0tdylKKnvhexgBZ y13O0phuZNEj47hMpzXTeMdTYDSzCbtPhC5jmbxlMTkGwEuM047l5GIWP5lMJwWRb1ic5jCJF89E wORWGnOmGZlyzj2QBW+CSR8OAZpOff5LP3hLohoROrY/+MX/WwtSkSPd2c45aIYbJ1LVRamHR4la cYZvzBMq8wmI1hgOg4EKaTjByU11YjRY+qPOBj+aUYy+QaU+tGU/dQrSngVUDzxVGph+GlRzdm6o GgXqpTRRVKdyS5vUzOk1tyjVKbINpSJNag8Nd6arwhSRRM2qPb8Jz7OW1atMjWVamVnVO4p1dRB9 Z5kSQ0ZkvpSu0oTrXUO4M2+CqK9U/SsaRSZY2fwAjjL13ptGN1ViJjSlgQGmXx9K2L0alhGEiyha T6rWpnoPr6rbFk7latVmsHWyi3xrYRW6Ws9i07WahW1q2wrLsZIwElFl7WclK1vR3ta3swXtZSkb W7tiVrdKtJUDrlp70MzGdJtd4ytzXYpcky6XttPFhGkji8/QChS80AWucuOq2Ooa97XoVY16zctV 2w7WvYIM7nivhN9gfq5Yp7XalcQoNQXpFSTCGi4xfIngBCt4wa+yiirdpMEBYwrAOJHwoxjaMgpz 55QbvkeHo/FhEIe4DP0d8XtNjDsU95JHKm6xi1/cPhvBeMY0rrEen2fjHOt4x/stMY9/DOQgC3nI RC6ykY+M5CQreclMRkEBAAA7 ------=_NextPart_000_037E_01C13DEA.157C6500-- -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! 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