Re: How would one use NPN transistors only?
From: Fred Bloggs (nospam_at_nospam.com)
Date: 06/11/04
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Date: Fri, 11 Jun 2004 15:23:39 GMT
Rick wrote:
> Jim Thompson <thegreatone@example.com> wrote:
>
>>See "MC1554-AudioPowerAmp.pdf" on the S.E.D/Schematics Page of my
>>website.
>
>
>
> Don't see how this can work - the output stage's darlington has its
> base and emitter clamped to almost the same voltage by the two
> diodes connected to pin 8; it won't conduct.
>
Well- that's the point- the pull-up Darlington is cut-off by the
conduction of the pull-down Darlington...the idea , for the output at
least, is borrowed from the earlier totem-pole output drive
architecture. The diode with anode to pull-up Darlington base is a
virtual reflection of the output node voltage to the base-node, ensuring
0V combined 2x Vbe drop, and therefore cut-off, whenever the diode at
pull-down Darlington collector conducts.
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