[simpits-tech] 16 channel output board is done!

[Per Eriksson]

Long time lurker, first time poster...


> Leo Bodnar brought a good point to my attention yesterday.  While the
> UL2803 can indeed handle 500mA per channel max, that's not what the
> devices as a whole can sustain.
>
> I never thought to check, but the part has a max draw per channel of about
> 150mA if you're driving all 8 at the same time.  The Toshiba datasheet for
> the part I'm using states a max dissipation of 1.47W.  At 5 volts, that's
> only 294mA.  At the voltage I want to drive it at (24vDC), it's less than
> 100mA.
>

I've looked at the datasheet for ULN2803AP, because I assume that's the one
you're using. 1.47W is stated in the 'Maximum ratings', what most
manufacturers would call 'Absolute maximum'. I would not suggest using that
figure for calculating normal operational conditions. It will fail if used
at max rating, just not right away.

Also, I think you're using Vce when calculating power dissipation. Remember
to use Vce(sat) instead.

...

Just about every
> single digital output board that I've ever seen has _never_ mentioned this
> limitation.
>

Same observation here...

Back to my hole!

BR,
Per E
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