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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