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From: "Spehro Pefhany"
Subject: Re: Mixed Voltage TTL design
User-Agent: tin/pre-1.4-19990216 ("Styrofoam") (UNIX) (Linux/2.2.14 (i586))
Date: Tue, 03 Sep 2002 18:45:03 GMT
NNTP-Posting-Date: Tue, 03 Sep 2002 14:45:03 EDT
In sci.electronics.design Eric Simmerman wrote:
> I'm designing a TTL circuit to interface with a I/O circuit that runs
> at 12 volts. I've got experience with logic design, but this is out of
> my area of expertise. I was thinking of slapping a voltage regulator
> circuit in to use the 12volt VCC to provide power to my 5-volt TTL
> components, but I don't know the best way to boost my 5-volt outputs
> back up to 12 volts (I have 6 outputs). I also don't know if this is
> the best general approach. Can anyone point me in the right direction?
> This has to be a fairly common problem right?
By "TTL" can we assume you mean 5V HCMOS?
What do your outputs have to do? Sink current? Source current? Both?
Resistive load? Inductive load? How much current?
For outputs that sink current and when a volt or so of Vce(on) is okay,
you can use an inexpensive darlington array with integrated flyback
diodes. Integrated source drivers are also available, but more expensive.
You can also use NPN transistors with base resistors, or "digital
transistors" that have built-in resistors (also available in duals),
adding external flyback diodes if required.
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