On the CVS board, we have to have control of power supply sequencing to prevent blowing
up the expensive DAC chip (see the datasheet). The +5 and Vref supplies HAVE to come
up AFTER the +/- 15 volts. And they can NOT stay on if the 15 volts goes away even for a
few milliseconds. The only way to assure this is to derive these supplies from +15 supply
and minimize the energy stored in capacitors after the 5v regulator.
You have to double check your power supply sequencing, otherwise magic smoke will
appear. On multi supply devices, there are substrate diodes connecting 5 and 15 volts that
don't appear on the schematic. If the 15 volts supply fails or is temporarily shorted, but
not the 5 volt supply, this can reverse bias substrate diodes and blow metal vapor all over
the inside of a chip.
For an LCD display board. I sure hope the 200 ma backlight connector is on a seperate pad
from the main 5 volt so the wires can be run seperately. A display module probably
doesn't need 15 volts at all.
But we will have to consider the case where 5 volts is on but either the +15 or -15 volt
supply is off. We don't want the LCD module supplying destructive currents BACK to the
CVS in a fault condition.
--- In ComputerVoltageSources@yahoogroups.com, "Larry T." <larry@...> wrote:
>
> If you only want to supply pads, thats okay, but PLEASE supply the
> pads, polyswitches and diode locations for all 3 voltages. It should
> be very easy to make all of the boards switch between using the +15
> w/a regulator and using +5 direct by choosing between the regulator
> and parts or the polyswitch and parts. I will point out that more and
> more +5v components are showing up in our analog systems and probably
> has a lot to do with MOTM moving to a 6 pin conector and a 3 voltage
> supply.
>
> Larry T.
>
> --- In ComputerVoltageSources@yahoogroups.com, Harry Bissell Jr
> <harrybissell@> wrote:
> >
> > Damn good idea.
> >
> > The polyswitch fuses can also improve on-card
> > power supply filtering (by being slightly resistive)
> > and cause a softer start on the power supply.
> >
> > H^) harry
> >
> > Grant Richter <grichter@> wrote: Here is a practical idea.
> >
> > You have three pads labeled +V, Ground and -V. These go to
> resetable polyfuses and
> > 1N4001 diodes to protect the circuitry in case the 12 year old
> science fair student hooks
> > something up wrong.
> >
> > direct link to schematic:
> > http://www.blacet.com/techPS.gif
> >
> > From John Blacets fine technical page.
> >
> > http://www.blacet.com/tech.html
> >
> > Then the end user can wire up ANY kind of connector he wants to
> hook up to those three
> > pads.
> >
> > The 1/3 square inch of board spaced used can substitute for the 2
> square inches of board
> > space it would take to support every possible connector type that
> will probably change or
> > go obsolete anyway, and who has all the mechanical drawings need
> to make the custom
> > PC board connector footprints? And who is going to take
> responsibility for everything
> > being correct with each connector type, and what if the
> manufacturer changes the pinout
> > or adds something new??????
> >
> > Just take an existing "fill in the blank" system power cable, chop
> one end off and solder
> > the appropriate three wires to the three pads on the CVS board and
> be done with it.
> >
> > --- In ComputerVoltageSources@yahoogroups.com, "John Loffink"
> <jloffink@> wrote:
> > >
> > > Good point. Here's what could be supported based upon PCB
> stuffing options:
> > >
> > > Synthesizers.com 6 pin 0.100"
> > > MOTM/Blacet 4 pin 0.156" add 5 V regulator
> > > MOTM 6 pin 0.156"
> > > Modcan 3 pin 0.156" add 5 V regulator
> > >
> > > Any others?
> > >
> > > 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.
> > > >
> > > > I would like to suggest that, if at all possible, we include
> both the
> > > > Blacet/MOTM 4 pin +/-15v power connector. and the Synthesizers.com
> > > > +5/+/-15v 6 pin connector. The board could allow for the
> optional +15
> > > > to +5 regulators when using the 4 pin connector. Some of us
> already
> > > > have +5 in our systems, and generally, no matter how much
> ANYTHING you
> > > > come up with will use (short of a room heater), the +5v supply is
> > > > never anywhere near being used to it's rated output. I note
> that some
> > > > of the newer MOTM boards also use a seperate +5v supply.
> > > >
> > > > I bring this up in part because of the LED/LCD/VFD
> discussions, and
> > > > partly because the MPU in consideration has requirements for
> +5v, and
> > > > I really don't want to add more +15 to +5 regulators to my already
> > > > stressed out +15v supply, when I have 4-6A of un-touched +5 just
> > > > sitting around asking to be used.
>