[vox-tech] ohms law

[Ted Deppner]

On Fri, Feb 02, 2007 at 12:34:26PM -0800, Jimbo wrote:
> drivability.  I have seen a few times that high resistance in the negative 
> leg of a circuit can take out components like computers, modules and even 
> not-so-complicated devices like bulbs and switches.  What I don't 

I have not seen what you're describing, however, I'll submit an idea as to
a possible reason.  Some DC things can be driven for voltage or for
current.  Data circuits like telephone service and T1 lines are current
driven rather than voltage driven.  That is, rather than supplying 12v
(for instance), they strive to provide a certain minimum amperage level.

Plain Old Telephone Service is actually a 600 milliamp circuit... whatever
the voltage needs to be to sustain that.  T1's will ramp voltage from the
double digits way up near 200 volts in order to drive electronics on the
far side.

It's also common in many DC power supply instances that you want a certain
amp load (charging batteries for instance), and the voltage can vary a bit
to achieve that.

So, if the circuit you're talking about is current driven rather than
voltage driven, it's entirely possible that in the presence of an
increased restance (load), the power supply ramps the voltage, possibly
overloading itself or other parts of the circuit path.

Lastly, many low power AC applications (possibly DC too) expect a certain
load expressed as impedance.  The supply side is expecting a 10k ohm
impedance load.  Depending on how the supply is architected a large
variance in that load can cause the supply side to inefficiently operate.
Common instances of this would be too many 8ohm speakers hanging off an
audio amplifier, or too many Y adapters off of a dvd player, tape deck,
vcr, etc.

I am not an expert on DC or AC, though I've tinkered a bit.  Please
forgive any inaccuracies and take what I've said as not definitive.

-- 
Ted Deppner
http://www.deppner.us/