ComputerVoltageSources

It would be better to adapt a hot plug type controller based upon +/- 15V
power and FET to the task than a relay, but even that is going to extremes.
I am not proposing this.

Don't you hate it when manufacturers make vague warnings about claims, then
don't characterize them fully?

I looked back at the TI DAC7614P that I recommended, and it is +/-5V or +5V
only.  Consequently it doesn't have the power sequencing problem of the
Analog Devices part.  But it introduces a new one, requiring precision
amplification to generate 10 volt outputs with 12 bit accuracy.  I think
Grant said he was going to op amp buffer the DAC outputs anyway.  12 bit
resolution over 10 volts is about 0.24% accuracy. Scaling using 0.1%
Precision resistors should do it.  These are 96 cents each from Mouser.  We
need two for each DAC output.  So, $8 in resistors, but the 16 pin DIP
DAC7614P is only $16.43 from Digi-Key, not $44.93 like the DAC8420FP.  Net
savings is about $20.

You could try matching batches of 1% resistors with a DMM, but a typical 4
digit DMM only has absolute accuracy of 1%. You really need a 5-6 digit DMM
for matching to this precision.  I have one, but realize that most DIYers
don't.

John Loffink
The Microtonal Synthesis Web Site
http://www.microtonal-synthesis.com
The Wavemakers Synthesizer Web Site
http://www.wavemakers-synth.com


> -----Original Message-----
> From: ComputerVoltageSources@yahoogroups.com
> [mailto:ComputerVoltageSources@yahoogroups.com] On Behalf Of Larry T.
> 
> Would it be possible to use a small pc mounted relay to
> connect/disconect the +5 and Vref based on +15 being present?  That
> way loss of +15 protects the part?  In which case +5 being from +15
> makes no difference.
> 
> Larry T.
> 
> --- In ComputerVoltageSources@yahoogroups.com, "Grant Richter"
> <grichter@...> wrote:
> >
> > The note on power supply sequencing is on page 12 of the
> DAC8420_a.pdf file.
> >
> > They say it can take some milliseconds of fault condition, but not
> how many.
> >