brian
Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA
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 Posted: Mon Jul 10, 2006 4:00 am Post subject: LM-317 dimmer (was: Instrument Lighting) |
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The LM-317 is an adjustable *linear* voltage regulator. Think of it
as a power resistor that adjusts itself to always maintain the same
voltage at its output. By varying that voltage you can vary the
brightness of the lamps.
There is a drawback to this type of regulator; it must dissipate the
power represented by the voltage drop across the regulator (voltage
difference between the input and output). For example, if the input
is 14V and you have the output voltage set at about 50% (about 7
volts) for low-to-medium brightness for your lamps, and your lamps
draw about 1 amp, the regulator has to dissipate 7 watts ( [14V-7V] x
1A). Like the resistor it is going to get quite hot. You need to make
sure it has a good heat sink to get rid of the heat.
But if your lamp loads are low (perhaps you are using LED lighting)
then the LM-317 won't have to dissipate much power. It may be 30-year-
old technology but it does work pretty well.
This is where a variable switching regulator or a pulse-width-
modulator (PWM) is better. These devices dissipate very little heat
to achieve the same thing.
Brian Lloyd 361 Catterline Way
brian-yak AT lloyd DOT com Folsom, CA 95630
+1.916.367.2131 (voice) +1.270.912.0788 (fax)
I fly because it releases my mind from the tyranny of petty things . . .
— Antoine de Saint-Exupéry
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_________________
Brian Lloyd
brian-yak at lloyd dot com
+1.916.367.2131 (voice) +1.270.912.0788 (fax)
I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery |
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