"Al" schreef in bericht
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In article ,
"petrus bitbyter" wrote:

".D.E" schreef in bericht
news:tHUSg.64297$5R2.18444@pd7urf3no...
I'm looking to add a mod to my pinball machine with a couple of led's
and
need to drop 6 volts dc down to 4.5 volts dc. Can anyone suggest which
resistor to use?

Thanks.

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No, due to lack of information. Suppose the LEDs do 4.5V when lighting,
what
current do they use? You'd realize that LEDs are current driven devices
so
the current can easily double while the voltage hardly changes.

petrus bitbyter



If your LED is specified at 10mA, then get two diodes whose forward
voltage is 0.75V at 10ma. Put them in series with your LED. If the
supply voltage goes up and the current goes up, the forward voltage of
the diodes will go up also thereby dropping more voltage across them.
Thus the dynamic resistance of the dropping diodes serves as a voltage
regulator. Really good diodes with a low dynamic resistance won't do.

Al

That diodes will work when you have a resistive load. But neither LEDs nor
other diodes behave like resistors. Once mo You need to regulate the
current, not the voltage. If the LED has been specified for 10mA at 4.5V
you'll need a series resistor of (6-4.5)/10=0.15k that's 150 Ohm. Most LEDs
are specified for 20mA or more. FAIK only low power LEDs require less.

petrus bitbyter