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[DPRG] increased output drive by CMOS and TTL devices

Subject: [DPRG] increased output drive by CMOS and TTL devices
From: Tom Gralewicz mot at ieee.org
Date: Tue Jun 26 14:17:51 CDT 2001

I think the problem with paralleling TTL is that you have bipolar 
transistors.  You can't directly parallel these since variables in voltage 
drop across different transistors can make one pull the full current while 
the other does nothing.  Usually when paralleling bipolar transistors you 
put a small resistor in series with output of each one to allow current 
sharing.  With TTL it is generally a bad idea to parallel them, you are 
better off using a driver chip.


At 10:10 AM 6/26/01 -0500, you wrote:
>I've seen this done in a number of cases. The only problem you might run
>into is that the two devices are not going to switch at exactly the same
>time, possibly resulting in a very short rail to rail connection. The end
>result of this is a spike on your 5V rail. For hobby projects and such, you
>are probably fine. I would not do it however on a production unit.
>
>Rick
>
>
>-----Original Message-----
>From: dprglist-admin at dprg.org [mailto:dprglist-admin at dprg.org]On Behalf
>Of Ben Strednak
>Sent: Monday, June 25, 2001 4:58 PM
>To: dprglist at dprg.org
>Subject: [DPRG] increased output drive by CMOS and TTL devices
>
>
>Hi folks.
>
>According to Forrest Mims, in his Engineer's Notebook, you can tie together
>the outputs of a CMOS IC to increase the amount of current the IC can source
>and sink.  For example, Mims uses a 4011 (quad nand gate), and connects all
>of the inputs of two gates to one another.  He then connects the two outputs
>to each other.  Can you do the same thing with TTL ICs and get the same
>effect?  More specifically, a 74LS04?
>
>Ben
>
>
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Tom Gralewicz
mot at ieee.org

Midwest Computer Recyclers
www.dead-computers.com
(414) 541-1716



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