The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
From: "Phil Allison"
Subject: Re: Class B amplifiers: what are the large low-value resistors for?
X-Newsreader: Microsoft Outlook Express 5.50.4522.1200
Date: Thu, 14 Nov 2002 17:34:21 +1100
NNTP-Posting-Date: Thu, 14 Nov 2002 17:24:30 EST
Organization: Telstra BigPond Internet Services (http://www.bigpond.com)
"Paul Burridge" wrote in message
> The circuits I've seen for class b amps mostly seem to have two 0.25
> - 0.33 ohm resistors between the emitters of the output transistors
> concerned. Are they really necessary at all? And if I don't have these
> ultra-low values to hand, can I get away with 1ohm ones and what would
> be the effect on performance?
** They *are* necessary, with no emitter resistors the amp would
probably self destruct when it got hot by a process called "thermal
runaway" - kind of a vicious cycle that overheats the silicon.
Using 1 ohm resistors will reduce the available power - possibly
by a large factor if the amp has "VI limiting" built in - most do.
You may parallel connect several 1 ohms to get 0.33 or 0.25
ohms - that should work fine.
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup