Re: Car Batteries

On 2008-02-02, Don Foreman <dforeman@xxxxxxxxxxxxxxxxxxxx> wrote:
On Sat, 02 Feb 2008 01:09:12 -0500, clare at snyder.on.ca wrote:

Because a Zener only STARTS to conduct above a certain voltage. Zener
regulators are GENERALLY shunt regulators. The load is in series with
a low value, high power resistor, and the zener goes across the load
in such a manner as to short excess voltage to ground, causing the
voltage drop across the resistance to absorb/regulate to the zener
resistance.
Diodes in SERIES are generally used for minor voltage adjustment (not
regulation) with the forward drop of various diodes generally running
in the 0.64 volt range for silicon diodes, Schottky diodes drop
significantly less, Germanium diodes significantly more.

Actually -- germanium diodes significantly *less* -- as is
supported by the site which you point out below. Germanium diodes at
about 200 mV forward drop, Silicon diodes at about 700 mV forward drop.
(Actually, I had remembered germanium as being closer to 150 mV, but
haven't checked one in years.

See: http://www.kpsec.freeuk.com/components/diode.htm if you don't
want to take my word for it.

By the way, what business are you in?
25+ in the automotive, and almost as long now in computer electronics.

[ ... ]

A Zener would indeed provide a fairly constant drop and they are
sometimes used that way. This wouldn't be a regulator, just a drop
that is fairly constant over a reasonable range of load currents. The
output would not be regulated, but it would be reduced by a fairly
constant amount.

The problem here is that a 12V automotive system goes through a
wider voltage swing than a 6V one does, and if you are using a zener in
series, (assuming that the load draws enough to get past the knee of the
zener's curve) you will wind up with more voltage swing at the 6V load,
by subtracting something approaching a constant from the 12-14V swing of
the charging system and battery.

Enjoy,
DoN.

--
Email: <dnichols@xxxxxxxxxxx> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
.

Relevant Pages

  • Re: Selenium rectifier question
    ... 2.8X of the voltage for the peak to peak from the AC. ... You should find out the required current needed for the supply load. ... diodes should be rated to at least 3X the required current at minimum. ... This would allow for 900 Watts maximum load at 1000 Volts. ...
    (sci.electronics.repair)
  • Re: Diodes on Cathode?
    ... It is NOT a damn zener - you clot - the voltage limiting effect works by ... I like to see a pair of Zobels beginning to load the output tubes at ... I have often included the anode to 0V diodes to limit transformer ... say 100 ohms, for where the load might normally be 16 ohms. ...
    (rec.audio.tubes)
  • Re: Switching Regulator for Audio Amplifier
    ... with regulators, switching supplies and the like, the effort should go into ... components that had sufficient head room for any voltage I desired, ... And that is exactly what my PS was supplying ... It was under heavy load that two of the devices failed. ...
    (sci.electronics.design)
  • Re: 13.8V high current power supply
    ... gutsy dummy load or antenna to dump 100W into, ... When the 60 HZ wave drops, the diodes drop out of conduction and the filter ... cap is now supplying *all* the load current...and the voltage drops in the ... Since this is a full wave rectifier if we had ideal diodes they would be ...
    (rec.radio.amateur.homebrew)
  • Re: Matching to the impedance of an alternator.
    ... Being able to tune that capacitance as load ... dynamo speed change could be nice. ... The original objective is to down convert the voltage so the current draw ... thereafter - in the absence of solid state switching regulators; ...
    (sci.electronics.design)