Isolating +5V DC power

Isolating +5V DC power

Post by Ryan de Jonckheer » Sun, 01 Dec 2002 02:48:35



I am working on a system with distributed power.  +5V will be
distributed to a number of modules along a backplane.  The unregulated
source will be a 6V SLA battery and will be regulated to +5V by a buck
converter.  I would like to be able to isolate each module in the system
to prevent transient effects from microprocessors, crystals, etc... from
affecting other modules in the system.  The max current draw that I am
designing for is 1A, although if it ever actually reaches that level,
I'll be disappointed and probably will redesign for lower power
consumption.  The big kicker is I would like to do this cheaply ($10 for
a DC-DC converter for each module is not cheap in my mind).  I have an
idea of how to go about this, but would like to hear comments on how
effective or feasible this proposal is.  Essentially, here is what I am
thinking, any comments are welcome.  I am going to try and simplify the
drawing some so only the additional discrete components will be shown.

             +--------------+
             | Buck         |
             | Converter    |
    +--------| In        Out|---+----------------+----- +5 + 1Vd
    |        |      GND     |   |                |
    |        +--------------+   +-|>|--+--- V1   +-|>|--+--- V2
    -                |            D2   |           D3   |
   --- +6V          _|_                |                |
    |              _\_/_  D1          === C1           === C2
    |                |                 |                |
   _|_              _|_               _|_              _|_
    _                _                 _                _

D1 is a 1N4004 to raise the output of the buck converter 1
                voltage drop (Vd)
D2, D3 are 1N4004 to isolate the power supplied to each module
C1, C2 are electrolytic filter capacitors
V1, V2 are the +5V that each module would see

Sorry about the bad ascii art.  I really don't know too much about power
distribution, but I would like to try and eliminate (or significantly
lower) the noise that I've seen on the power lines resulting from
switching in the the digital circuitry.

Ryan

 
 
 

Isolating +5V DC power

Post by Alan Hooke » Sun, 01 Dec 2002 08:18:01


If I was really worried about noise spinning about the system, I would:
1) Replace the diode with a either a small resistor (say 1 to 10 ohms,
but dropping say 0.1 volts max at full current into the board) or better
still, a small ferrite bead with a few turns squeezed into it.
2) Use say 10uf 25V for the electroytic, but add a 0.1uf ceramic in
parallel.

Alan *
__________________________________________________________________________


> I am working on a system with distributed power.  +5V will be
> distributed to a number of modules along a backplane.  The unregulated
> source will be a 6V SLA battery and will be regulated to +5V by a buck
> converter.  I would like to be able to isolate each module in the system
> to prevent transient effects from microprocessors, crystals, etc... from
> affecting other modules in the system.  The max current draw that I am
> designing for is 1A, although if it ever actually reaches that level,
> I'll be disappointed and probably will redesign for lower power
> consumption.  The big kicker is I would like to do this cheaply ($10 for
> a DC-DC converter for each module is not cheap in my mind).  I have an
> idea of how to go about this, but would like to hear comments on how
> effective or feasible this proposal is.  Essentially, here is what I am
> thinking, any comments are welcome.  I am going to try and simplify the
> drawing some so only the additional discrete components will be shown.

>              +--------------+
>              | Buck         |
>              | Converter    |
>     +--------| In        Out|---+----------------+----- +5 + 1Vd
>     |        |      GND     |   |                |
>     |        +--------------+   +-|>|--+--- V1   +-|>|--+--- V2
>     -                |            D2   |           D3   |
>    --- +6V          _|_                |                |
>     |              _\_/_  D1          === C1           === C2
>     |                |                 |                |
>    _|_              _|_               _|_              _|_
>     _                _                 _                _

> D1 is a 1N4004 to raise the output of the buck converter 1
>                 voltage drop (Vd)
> D2, D3 are 1N4004 to isolate the power supplied to each module
> C1, C2 are electrolytic filter capacitors
> V1, V2 are the +5V that each module would see

> Sorry about the bad ascii art.  I really don't know too much about power
> distribution, but I would like to try and eliminate (or significantly
> lower) the noise that I've seen on the power lines resulting from
> switching in the the digital circuitry.

> Ryan

--

 
 
 

1. FS: 5V DC/DC power supply PCB great for mobile robotics

I have 18 DC/DC power supplies I'd like to sell at pretty much cost.
I got a great deal on the PCB's and I'd like to sell what I don't
need.

The DC/DC converter PCB is designed around the Datel UWR-5.2/1500-D5
DC/DC converter.  The power supply can use a variety of input voltages
and supply +5.2 volts at 1.5 amps.  The power supply was designed in mind
of a single battery powering both the motors and the electronics of a
mobile robotics platform.  The isolated DC/DC converter and a large
inductor at the input should keep any unwanted motor noise out of
sensitive electronics.  All that is needed for operation is a battery
and a power switch.

For a picture and a manual of the power supply goto:

Picture, 32K JPEG
www.elnet.com/~gad/PwrSupplyA.jpg

Manual, 70K PDF
www.elnet.com/~gad/DCtoDC_Rev1.pdf

I'm asking $35 each for them.  The Datel converters alone cost over $40
new.  Like I said above, I'm not making much if any $$$ on these.  I'd
just like to get them out of my projects drawer and see them put to good
use.  I'l split shipping.

If interested contact me by email

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