> After brief thought the BooBu converter evolved. > ... > It may even work (although I haven't tried it yet). > ... > do note its "thought experiment" status (and > it's 12:30am here and I'm going to bed and ..... > ... > The circuit will definitely need work > ... > Components values where shown should be ignored! > ... > I have taken some liberties in simplification > ... Frankly Russel, this is getting a bit tedius. I certainly don't want to discourage the exchange of ideas here, but at least a modicum of brain in gear before fingers in motion would be a small courtesy to everyone else. As has become obvious over the last week or so, most people on this list are not electronics experts and certainly not switching power supply experts. They are trying to learn this stuff and mostly have no good way to tell for themselves whether a circuit is a good design or some flaky hairbrain scheme that plays fast an loose with the laws of physics cooked up in a sudden flash of inspiration while watching TV, talking on the phone, and munching on junk food all at the same time. I am also dismayed to see this circuit is based on your earlier one that several people pointed out had shortcomings. Yes I know it works in your particular instance, but I would never commit such a thing to production. I don't want to rehash all that, so I'll briefly comment on this new circuit. > Initial turnon is by RBUK2 biasing Q2 and Q4 on. And therefore Q3. > LH end of L will rise to Vin. I assume the "LH" end is the one connected to Q3? The other end of LBUK1 is held low by Q4 being on. > C2 will charge via R1. It would be nice if you used consistant and short names for parts. Having RBUK1, R1, C2, CBUK2 is a pain. > When Vc2 exceeds Vzener_Z1 then Q1 will be turned on as before. > Q1 on will turn Q2 & Q4 off and L will "ring" and deliver power to output. Not for long (see below), and assuming it doesn't enter linear operation. Once again I see no hysteresis. You are counting on high gain and phase shift to produce oscillation, but that is left wide open to part variations. Can you prove (and I don't mean by example) this will always oscillate? > The RH end of R1 will be at ground during ringing cycle and C2 will > discharge. Now the Q3 end of LBUK1 is called "RH"?!! Please take a little care. Make up decent names, define them, and stick to them consistantly. > I have shown D2 allowing this discharge but on reflection a resistor in > series with D2 is probably needed or some other means to prevent immediate > discharge of C2 - needs thought. Not much. A resistor dissapates power and isn't needed as long as D2 can handle the maximum current of LBUK1 - which of course needs to be calculated as part of the design. > Regardless, when Vc2 reduces Q1 will turn > off initiating another turn on cycle. I'm going to stop here because going further is wasting time. Too many things are major screwed up here. For one thing, LBUK1 is still fully charged at this point. Remember, Q1 turned on because the voltage on C2 just reached a threshold. Since there is no hysterisis, Q1 will turn off shortly after C2 goes below this threshold. In boost mode, the collector of Q3 will be "regulated" to this threshold level, DBUK2 never conducts, LBUK1 will keep charging until something fries, ... I could go on, but this is getting pointless. ******************************************************************** Olin Lathrop, embedded systems consultant in Littleton Massachusetts (978) 742-9014, olin@embedinc.com, http://www.embedinc.com -- 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