ComputerVoltageSources

It is true that a TO-220 will allow us to more safely dissipate heat even if
we're not using all the current generating capability.

78L05 (296-1365-1-ND) in TO-92 package is 40 cents from Digi-Key
7805 (LM7805CT-ND) in TO-220 package is 48 cents from Digi-Key

Other parts sources may put the 7805 price at an advantage, as noted by
Grant.  It's worth it anyway for the "built in heatsink" from the larger
TO-220 package.

If I have time this weekend I'll do a preliminary schematic and PCB parts
placement for the LCD Support PCB and see what fits. 

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 Grant Richter
> 
> 
> 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).
> 
> 
> --- 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
> >