Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Mon, 12 May 2003 15:24:00 -0400
Message-ID: <redirect-2345101@logan.com>
Reply-To: "Dan Schaefer" <dfs155@earthlink.net>
From: "Dan Schaefer" <dfs155@earthlink.net>
Subject: Re: voltage regulators
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I don't agree that a "linear" regulator is "preferable" over a switching,
pulse-width modulator type for the following reasons:

1. By definition, a linear regulator utilizes a continuously variable
voltage drop across itself to control the field current supplied to the
alternator. Due to good ol' Ohm's Law (Voltage [E] x Current [I]= Watts
[P]). Watts (power) developed across the regulator will manifest itself as
Heat. Depending on how much power dissipated by it's function, a linear
regulator may need cooling to keep it alive.

2. Also by definition, switching regulators switch the field voltage full
"On" or full "Off" at a fairly high rate with the ratio of On to Off
continuously adjusted to provide the average field current required over
time. Except for the extremely small period of time when the regulator is
actually switching and the slight voltage drop while "On", there is full
voltage across the device at zero current or nearly zero voltage at
whataever current is required. Bottom line, the switcher exhibits very low
dissipation (high efficiency) and in the same application as the linear,
will remain cool.

3. The voltage output from the alternator does not swing abruptly due to the
field switching as the inductance of the field cannot allow the current to
change rapidly regardless of the method used to regulate. All switchers
include a "free wheeling" or "fly-back" diode across the output that allows
the field current to continue to flow during the "Off" period due to the
energy stored in the field inductance.

4. The battery is always required to filter the noise put out by the
alternator regardless of whether you have a linear or switching regulator. A
major source of noise that the battery must absorb is due to the fact that
the raw output from the alternator is a relatively high (and variable)
frequency AC that must be converted to DC by the rectifiers (diode pack), in
turn producing a very high ripple voltage. So, the battery acts as a huge
filter capacitor for the ripple voltage regardless of the type of regulator
used.

OK, class dismissed.

Dan Schaefer