# help building a circuit



## krogerssolar (Jan 8, 2009)

has any one built at circuit to drop track or battery voltage down to around 5 volts or 3 volts for led and some sound units without putting other on board bats to control leds


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## Greg Elmassian (Jan 3, 2008)

it's called a voltage regulator... they have them at radio shack with a circuit, 3 terminals, input, output ground. 

If you are running it from track, you need to put a full wave bridge from the rails to the output... so reversing the track polarity still gives you same plus and minus... then into the regulator, and your 5 volts out. Harder to find 3 volt regulators. 

Realize you need to put a heat sink on the regulator if you are running any kind of current... 

If you need more help, please give more information, what track voltage, how many leds, what sound board, etc. 

Regards, Greg


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## Totalwrecker (Feb 26, 2009)

sure they have.... 
I'm getting ready to use a 5v regulator for some lights off a battery pack no circuit tho'. 18v to the reg and 5 v out 
Others will mention resistors and fancier things.... 
Back in January there was a thread on using leds for lighting, many good tips offered there. 

John


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## krogerssolar (Jan 8, 2009)

Greg the load wont be much i'm looking at a one install with about two leds powering a micro cpu to control a flashing program the other install would be about 4 to 8 leds for steady and maybe flashing if i can make the right circuit i found plans online but i don't think it works ill have to grab my readable voltmeter and see what its putting out the regulator i have is a input of 36 out is 5+ and the voltage would be around 24 volts. this is the site that i tried http://www.eidusa.com/Electronics_Voltage_Regulator.htm


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## Michael Glavin (Jan 2, 2009)

The 78XX series voltage regulator(s) noted at the link you provided (and by Greg) is an industry standardized component and will work great for you application. 

MAX voltage input is 36V, output is variable upon the unit chosen. 

A full wave bridge rectifier is a MUST as noted previously. 

If you can't find a 3V regulator a resistor in line with the LED(s) will suffice prior to the LED and after the regulator. 

Michael


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## Dan Pierce (Jan 2, 2008)

And with the voltage regulator, do not forget the small bypass caps to suppress oscillation and the large input capacitor for non battery inputs to keep the output stable for intermittent track power. 

Specs can be found at www.nsc.com for the 7805/LM7805. 

For 3 volts to over 20 volts, there is the adjustable LM317 for 1.5 amps, LM350 for 4 amps, and LM338 for 5 amps. 

These are available for high prices at the shack, but digi-key is a better place to get lots of variety and better prices.


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