Just a few observations, please nobody get offended. Specially Harry who is a kick ass
musician, top notch engineer and all around fine fellow.
1. The Basic Atom Pro data sheet doesn't list the current draw. But the Basic Atom 28M is
listed at 5 ma.
2. Everything on the board runs on +/- 15 volts (op-amps, DACs, voltage references,
indicator LEDs etc.) except the processor and Speakjet chip.
3. The processor carrier board has a built in 5 volt regulator. It says it is limited to +12
volt input, but that is because it is a surface mount LM2936MM-5.0 SOIC-8 with no
heatsink (look at the schematic in the data sheet). It is in the files section Basic Arom Pro
24M.pdf Notice the cute charge pump they used to get a negative voltage for the RS-232
output to use from the RS-232 input negative voltage.
4. A 78L05LCZ in a TO-92 is overkill for the 20 ma. or so actually needed for both chips
but a generic 7805 in a TO-220 is less expensive (God Bless Capitalism).
5. A fully expanded PSIM with input pots, MIDI interface, DIN interface and Speakjet chip
with 36 dB octave reconstruction filter draws 110 ma from the +15 volt supply and 20 ma.
from the negative supply (I just measured it on mine). That includes whatever the 5 volt
regulator is drawing. So (0.11+0.02 = 0.13) amps times 15 volts = 1.95 watts for the total
assembly. 30 ma is used just for the LEDs.
--- In ComputerVoltageSources@yahoogroups.com, harrybissell <harrybissell@...> wrote:
>
> OK lets do the math (check my figures)
>
> 78L05 has "100mA with suitable heatsink" and with short leads
> to a PCB... 160C/W junction to ambient. Max junction temp is 125C
>
> .016A x 10V (voltage drop) = .16W x 160 = 25.6C rise over ambient.
>
> Even with a 25C ambient this is going to run HOT. You will not want
> to touch it...
>
> OK, we can use the 7805 which is MUCH better (and bigger).
>
> If you are assuming two PCBs thats not a problem... as long as the
> connector between the boards does not get silly. Still, two PCB
> will double the cost. Best to avoid that if possible.
>
> H^) harry
>
> John Loffink wrote:
> >
> > Dave has proposed testing the actual LCD as his experience is that
> > much less
> > current is required for the backlight than specified. A 78L05 is
> > specified
> > to handle 100 mA. I'd recommend derating of 60%, for 60 mA.
> > Backlight
> > specification was 160 mA, Dave has run a similar one at 16 mA with
> > good
> > results.
> >
> > I'm ordering one myself tonight.
> >
> > Regardless, there's tons of room on the LCD Support PCB, 30 x 85 mm,
> > assuming it mounts parallel to the LCD assembly using standoffs. We
> > could
> > fit a T-220 7805 or LM341 if needed.
> >
> > John Loffink
> > The Microtonal Synthesis Web Site
> > http://www.microtonal-synthesis.com
> > The Wavemakers Synthesizer Web Site
> > http://www.wavemakers-synth.com
> >
> > > -----Original Message-----
> > > From: ComputerVoltageSources@yahoogroups.com
> > > [mailto:ComputerVoltageSources@yahoogroups.com] On Behalf Of
> > harrybissell
> > > Sent: Tuesday, March 14, 2006 10:46 PM
> > >
> > > I suggest a big wish list, then pare down to the amount that
> > > will fit on the PCB size you want without making the
> > > density too high.
> > >
> > > Really high density will amke the layout hard, possibly
> > > affect yeild and the ability of some folks to successfully
> > > complete the project.
> > >
> > > I'm all for incorporating a good feature set, but its for sure
> > > that 'creeping featurism' will set in if we're not careful.
> > >
> > > The 78L05 is very unlikely to support the requirements of the LCD
> > > backlight.
> > >
> > > I'm agreeing if you just want the 5V for the LCD itself... the 78L05
> > > will handle that.
> > >
> > > (maybe I'm not up to speed yet, there are only a couple hundred
> > posts
> > > not counting files etc... :^)
> > >
> >
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