Looking to drop 6 volts dc to 4.5 volts dc
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Posted by .D.E on September 28, 2006, 2:41 pm
Please log in for more thread options 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. -- _____________________________ Later. Have a better one. D.E. To email me back, remove "forget.the.spam" | ||||||||||||||||||||||
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Posted by Rich Grise, Plainclothes Hippi on September 28, 2006, 2:45 pm
Please log in for more thread options On Thu, 28 Sep 2006 18:41:29 +0000, .D.E wrote: R = (Vsupply - Vled) / Iled Good Luck! Rich | ||||||||||||||||||||||
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Posted by petrus bitbyter on September 28, 2006, 4:29 pm
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> 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. > > -- > _____________________________ > Later. > Have a better one. > D.E. > To email me back, remove "forget.the.spam" > 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 | ||||||||||||||||||||||
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Posted by Al on September 29, 2006, 8:46 am
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> > 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. > > > > -- > > _____________________________ > > Later. > > Have a better one. > > D.E. > > To email me back, remove "forget.the.spam" > > >
> 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 | ||||||||||||||||||||||
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Posted by petrus bitbyter on September 29, 2006, 4:07 pm
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>
>> > 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. >> > >> > -- >> > _____________________________ >> > Later. >> > Have a better one. >> > D.E. >> > To email me back, remove "forget.the.spam" >> > >>
>> 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 more: 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 | ||||||||||||||||||||||
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> need to drop 6 volts dc down to 4.5 volts dc. Can anyone suggest which
> resistor to use?
>