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From: "Phil Allison"
Newsgroups: sci.electronics.design,sci.electronics.misc
References: <19ujtuc5hs95k7ofctv8shgklbrp2s4cmq@4ax.com> <7dkmtugumdu19uehuotn0408dkup3ed825@4ax.com>
Subject: Re: Class B amplifiers: what are the large low-value resistors for?
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Date: Wed, 20 Nov 2002 22:46:00 +1100
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"Paul Burridge" wrote in message
news:7dkmtugumdu19uehuotn0408dkup3ed825@4ax.com...
> On 19 Nov 2002 15:35:20 -0800, bigcat@meeow.co.uk (N. Thornton) opined
> thusly:
>
> >You say you have biasing / temp compensating there, yet its meant to
> >be class B: how is that so? For real class B you don't need to apply
> >any bias chain, so there should be no need for temp compensation.
>
> You certainly have to provide *drive current* to the bases and this is
> the chain through which it's provided. And with all due respect, your
> claim that class B doesn't require temp.compensation is at odds with
> everything I've thus far read on the subject in a number of books.
** Some temp compensation is needed to keep the OP stage in pure class
B *despite* large chip temp changes and hence Vbe changes.
The Crown DC300 A is a good example with 350 mV on the OP device
base-emitter junctions at idle and much less when really hot.
....................... Phil
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