Re: power supply mods


"John Popelish"
Phil Allison wrote:


** Beware - the " Sample Power supply 1 " schem will simply not work.

It might, if the positive and negative supply currents vary
only a small fraction of the total current if the LED
current passes through both regulators. But I can't see how
the LED current returns to the negative supply at all.

The data ***:
http://www.intersil.com/data/fn/fn3082.pdf
shows the digital ground (the negative rail for the LED
switches) connecting to pin 27 but the schematic shows pin
27 connected only to a capacitor. And this is what is shown
on the data *** as a typical ICL7107 design. WTF?


** Looks like misprint in figure 8, pin 27 should be labelled as pin 21.

The -5 volt supply needs only small current, hence the simple inverter schem
to derive it from the +5 volt one.



....... Phil


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