[NSRCA-discussion] Regulators and heat

[John Pavlick]

Guys,
 Some more interesting things about regulators. There are basically two
types of regulators: linear or "shunt" type and switchers. Each has
advantages and disadvantages. Most people are familiar with the linear type.
They get warm when they have to dissipate power. That's why it's not a good
idea to use a 3S Li pack with a linear regulator. The excess voltage is
absorbed by the regulator and makes it get warm. In a switcher, the
regulator actually varies the duty cycle (ON vs. OFF time) to regulate the
voltage. Here's the cool part (pun intended) it doesn't give off much heat
because it's not shunting the current, it just turns off when the voltage
gets too high. It has an inductor and a diode so the output doesn't turn
off, just the current draw from the battery. The other neat thing about a
switcher is this. If you use a 3S 730mAh pack, you'll actually draw less
current than if you used a 2S pack. Why? It's a complicated procedure
involving lasers... No, not really but it's a little hard to explain in a
few words. Take my word for it, it's true. Now before you go out and buy a
magic switcher, there is a downside. Actually there are a few. First, a
switching regulator circuit requires more parts than a linear regulator
circuit. More parts = more weight. Weight is bad. The other problem is
"noise". The regulator turns the power on and off and this can create havoc
with your radio. There are a few good switching regulators for R/C use so it
is possible to use one, but you have to be very wary of the potential for
noise.
 Matt mentioned a linear regulator that Ed built for him. He may not have
mentioned that this regulator has an adjustable output and it's very light.
By having an adjustable output, you can buy one regulator and set it to what
you prefer. You don't need to buy another regulator if you want to run on
5.6V now and then 6V later for example. The other cool thing about having an
adjustable output is if you run 2 packs w/ 2 regulators in parallel. You can
fine tune the voltage output so that both packs are supplying power or you
can favor one of the packs by setting the regulator on the other pack lower.
Ed chose the linear topology for reliability and "clean" output. Because
it's a linear type it does generate heat, but for the power that's required
to run the equipment in a pattern plane, it's not even breaking a sweat if
you run a 2S Li pack.

John Pavlick
http://www.idseng.com

--
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.1.394 / Virus Database: 268.9.0/368 - Release Date: 6/16/06