Re: [CAD_CAM_EDM_DRO] Re: breakout board and diode question

The only problem with using diodes to protect the chip is that if the
chip power is off, all the signals are loaded by the chip, which the
diodes are trying to power. This could also cause erratic operation of
whatever is being driven by the chip. Analogy: The '541 is powered by
the PC, and you shut down the PC.

Regards,
JJ

On Saturday, Jan 31, 2004, at 21:37 US/Eastern, JanRwl@... wrote:

> In a message dated 1/31/2004 7:20:10 PM Central Standard Time,
> ja_erickson@... writes:
> did you ever build a breakout board that utilizes the 74LS541?
> do you have or know of any diagrams of how to build a breakout
> board using that octal driver, keeping in mind i'm not an E.E.
> but a really good assembler. haha
> I have. Tie each input-line to gnd. with a 4K7 resistor, then another
> 4ky
> resistor in series with each gate. Then tie each gate to +5 with a
> 1N4148, and
> from ground with another 1N4148. Total 16 diodes and 16 resistors.
> The first
> one ("to" +5) prevents the gate being forced higher than about +5.6
> VDC. The
> second one ("from" ground) prevents the gate input from going below
> about
> -0.6 VDC. These diodes WILL save your '541 if there are "electrical
> nasties"
> (bad emi, etc.), and in normal use, will have NO effect on signal
> (unless you
> have severe ringing, and then they will "help"). I have also added a
> couple of
> 74HC4538 monostables on the "pulse pins" to stretch the pulses to at
> least 2
> µS, when indicated; many stepper drivers will "ignore" input pulses
> shorter than
> 1µS or so.
>
> Jan Rowland
>
>
> [Non-text portions of this message have been removed]
>
>
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