Hi everyone! Eh, I guess I joined the forum a fair few months ago now but despite the odd comment, never really introduced myself or for that matter, got around to posting any of the questions I meant to ask
So for the "introduction" part: I did a tiny bit of electronics when I was also tiny (one or two trivial LED things, and something out of a kit) and later studied it a little in A-Level Physics classes at 6th-Form College (age 17ish), but up until about 2 years ago, most of my life I've mostly just been programming rather than having anything to do with electronics. In those past 2 years OTOH I've read a lot, experimented a bit, and made a few circuits. But no blue smoke yet! I'm much more happy with DC stuff than AC (aside from op-amps, which I like), and I think I'm pretty comfortable with any DC-related terms and concepts I can think of.
So yeah, that's me, hello, etc Anyway, to business! One thing I've been wrestling with over the past N months is the issue of a power supply for a simple, modular PIC programmer circuit I've been designing and building.
Yes, of course the 5V supply is easy with 7805s or my little SMPSU brick. But programming (most) PIC chips also needs a "VPP" voltage of 13V, give or take a bit. And though I have another, fairly hefty PSU brick that can give about 16V open-circuit, or about 15V or so with a very small load (the brick is labelled as 13V at 2A IIRC), there was an issue of sorting out a workable regulator to get 13.3V or so with the potentially low headroom: I think it'd be too tight for an LM317 and I'm wary of my own design for a "low-dropout" style regulator as I'm not sure if it might oscillate. And I currently am quite hard-up so I'm quite strongly against the idea of buying any more bits if I can possibly avoid it!! I already have like £300 worth of parts from last year, that ought to be plenty
Anyway. Yesterday it struck me: I have that 5V SMPSU (seems reasonably regulated), which would be fine for most of the circuit; what if I just stuck an 8.4V or 9V PP3 battery on top of that?! AFAIK that SHOULD give a pretty reliable 13.4V (with an optional diode), unless there's something I'm missing. The diagram attached shows what I mean, if it's not glaringly obvious. It should need NOTHING I don't already have AFAIK, it seems so quick and simple, I could probably just use my breadboard even. And I wouldn't have to worry about calibrating the voltage with my skewed voltmeter (no, it's not quite broken enough to deserve replacing)
That'd be a lot of problems solved. And yet, "If something sounds too good to be true, it probably is", "things are rarely that simple", and the idea reminds me of those vague mysterious warnings we used to get about not mixing different brands of battery or whatever, so I'm feeling very paranoid. WILL this work as I hope? The VPP line doesn't need much current except perhaps in transients but I feel like I might be missing something. And is it SAFE? I have this image of the battery bursting into flames for some reason Sorry for the post length BTW, I expected lots of "You should just..." comments otherwise
View attachment psu_and_battery.pdf
So for the "introduction" part: I did a tiny bit of electronics when I was also tiny (one or two trivial LED things, and something out of a kit) and later studied it a little in A-Level Physics classes at 6th-Form College (age 17ish), but up until about 2 years ago, most of my life I've mostly just been programming rather than having anything to do with electronics. In those past 2 years OTOH I've read a lot, experimented a bit, and made a few circuits. But no blue smoke yet! I'm much more happy with DC stuff than AC (aside from op-amps, which I like), and I think I'm pretty comfortable with any DC-related terms and concepts I can think of.
So yeah, that's me, hello, etc Anyway, to business! One thing I've been wrestling with over the past N months is the issue of a power supply for a simple, modular PIC programmer circuit I've been designing and building.
Yes, of course the 5V supply is easy with 7805s or my little SMPSU brick. But programming (most) PIC chips also needs a "VPP" voltage of 13V, give or take a bit. And though I have another, fairly hefty PSU brick that can give about 16V open-circuit, or about 15V or so with a very small load (the brick is labelled as 13V at 2A IIRC), there was an issue of sorting out a workable regulator to get 13.3V or so with the potentially low headroom: I think it'd be too tight for an LM317 and I'm wary of my own design for a "low-dropout" style regulator as I'm not sure if it might oscillate. And I currently am quite hard-up so I'm quite strongly against the idea of buying any more bits if I can possibly avoid it!! I already have like £300 worth of parts from last year, that ought to be plenty
Anyway. Yesterday it struck me: I have that 5V SMPSU (seems reasonably regulated), which would be fine for most of the circuit; what if I just stuck an 8.4V or 9V PP3 battery on top of that?! AFAIK that SHOULD give a pretty reliable 13.4V (with an optional diode), unless there's something I'm missing. The diagram attached shows what I mean, if it's not glaringly obvious. It should need NOTHING I don't already have AFAIK, it seems so quick and simple, I could probably just use my breadboard even. And I wouldn't have to worry about calibrating the voltage with my skewed voltmeter (no, it's not quite broken enough to deserve replacing)
That'd be a lot of problems solved. And yet, "If something sounds too good to be true, it probably is", "things are rarely that simple", and the idea reminds me of those vague mysterious warnings we used to get about not mixing different brands of battery or whatever, so I'm feeling very paranoid. WILL this work as I hope? The VPP line doesn't need much current except perhaps in transients but I feel like I might be missing something. And is it SAFE? I have this image of the battery bursting into flames for some reason Sorry for the post length BTW, I expected lots of "You should just..." comments otherwise
View attachment psu_and_battery.pdf
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