> On 23 Aug 2017, at 15:07, dwight <[email protected]> wrote: > > > The regulator needs about 2.5 to 3 volts head room. The circuit is what is > often called a boost circuit. If my calculations are right, it should produce > about 15.5 to 16V on C10. This gives the regulator enough over voltage to > work as a regulator. If the supply you have is not regulated it won't be able > to be used directly. > TR2 and L1 transformer form an oscillator. When TR2 conducts, it causes a > field to build up in L1. When TR2 turns off, the field in L1 tries to > collapse. The voltage build up until the diode conducts charging C10. This is > often called fly-back. Coils like to keep conducting at a constant rate. > Since TR2 turns off, the coils voltage will continue to rise until it finds a > path to send the current ( the diode ). > When the voltage gets high enough across the resistor divider, R16/R15, TR3 > turns off. This removes the bias needed to turn on TR2, shutting down the > oscillation. > If the voltage on C10 drops to the point that TR3 conducts, the oscillation > will start again, boosting the voltage on C10 again. > Dwight
That’s brilliant, thanks Dwight! — Adrian/Witchy Binary Dinosaurs - Celebrating Computing History from 1972 onwards > > From: cctalk <[email protected] > <mailto:[email protected]>> on behalf of Adrian Graham via cctalk > <[email protected] <mailto:[email protected]>> > Sent: Wednesday, August 23, 2017 12:33:44 AM > To: General Discussion: On-Topic and Off-Topic Posts > Subject: Re: A little power circuit explanation please > > > > On 23 Aug 2017, at 00:49, Rob Doyle via cctalk <[email protected] > > <mailto:[email protected]>> wrote: > > > > It's a little switching power supply. It steps up the 9V input voltage to > > something a few volts greater than 12V to feed the 12V regulator. > > > > If your 12V is correct, it is probably working. > > > > This is from 2 months ago but I was puzzling over the 12V circuit in this > particular machine and also maybe suffering from a red herring since the PSU > I was using is from a ZXSpectrum+2 which is an unregulated 12-14V lump so the > coil was already being fed 12V. > > A > > > Rob. > > > > On 8/22/2017 4:30 PM, Adrian Graham via cctalk wrote: > >> Hi folks, > >> Failing Atari PSU aside I remembered a question I had ages ago but never > >> posted about the power circuit of another 80s home micro, the Enterprise > >> 64. This machine is powered by a 2A 9V unregulated PSU and internally > >> there’s a pair of 7805s and a 78L12 to smooth things out. > >> There’s also a small transformer coil in there too (L1 on the following > >> schematic) and I’m not entirely sure what it’s for. Here’s the schematic > >> of the original circuit, any enlightenment gratefully received since I > >> have an Enterprise 64 with a dead coil :) > >> http://www.binarydinosaurs.co.uk/ep64PowerRegulators.png > >> <http://www.binarydinosaurs.co.uk/ep64PowerRegulators.png> > <http://www.binarydinosaurs.co.uk/ep64PowerRegulators.png > <http://www.binarydinosaurs.co.uk/ep64PowerRegulators.png> > > > >> Cheers! > >> — > >> Adrian/Witchy > >> Binary Dinosaurs - Celebrating Computing History from 1972 onwards > > >
