On Jun 29, 2008, at 7:01 AM, Tom=E1s =D3 h=C9ilidhe wrote:

> When I heard the term "push-pull driver", my first thought was that it
> was a driver that would provide a path to either Vcc or Ground  =

> depending
> on whether the input was high or low.

That's exactly correct.

>
> While I'm talking about drivers, does anyone know a very efficient
> driver that doesn't have considerable internal voltage drops?

For the sort of currents you're talking about for LEDs, you can look  =

at using logic-level "bus drivers" like 74xx240.  Exact current  =

depends on "xx", but a 74ac240 is spec'ed to provide +/-24mA on each  =

of 8 pins (with "abs max" being ~50mA per pin.)
The ~250mA on the low side is more of a problem.  There are dedicated  =

display drivers, but I guess there's a reason that discrete  =

transistors are so common in LED displays.

BillW


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