Voltage Regulator - ( 12vdc down to 3.0 and 1.5 vdc)

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bhickeys Associate Join Date: Mar 2007 Posts: 31	Voltage Regulator - ( 12vdc down to 3.0 and 1.5 vdc) 01/09/2008 3:02 PM
	What I'm trying to accomplish is reducing 12 VDC (automotive application) down to 1.5VDC in one application for LED's and again an other 12VDC to 3.0 VDC. I know I can through the use of a 220 resister and a 5.1 volt zener diode reduce the 12vdc to 5.1, but how do you reduce the voltage even further for the above mentioned. The smallest zenor diode I found is 5.1 volts. Brian
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JohnDG Guru Join Date: May 2006 Location: Reading, Berkshire, UK. Going under cover. Posts: 9684 Good Answers: 468	#1 Re: voltage regulator- ( 12vdc down to 3.0 and 1.5 vdc) 01/09/2008 3:24 PM
	If you just want to light the LEDs, you don't need a zener diode - just insert a series resistor to bring the current from the 12V supply down to an appropriate level. For most LEDs (except blue), the LED will drop about 1.5V, so you've got 10.5V left. For, say, 10mA, you'd need a 1K resistor. Blue LEDs drop about 3 volts, so you're left with 9V. Again, for 10mA, use the nearest resistor you can find to 9K - no need to be too fussy. 1K would still give you 9mA! Remember that the automotive supply will be a bit over 14V when that engine's running (but can vary all over the place depending on electrical load (heaters & lights)). For your 3V supply, zeners are readily available from 2.4V up. Go to a component supplier (e.g. http://uk.rs-online.com/) and search. __________________ "Love justice, you who rule the world" - Dante Alighieri
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Sniccus Power-User Join Date: Mar 2007 Location: Northeast Pennsylvania, USA Posts: 173	#3 In reply to #1 Re: voltage regulator- ( 12vdc down to 3.0 and 1.5 vdc) 01/09/2008 10:38 PM
	Yes, you are right about the resistors for the LED application, I use them a lot. I use them on 24 vac in air conditioning systems for custom status panels. Actually, for most JUMBO size LED's, a 1.2KΩ - 1.5kΩ series resistor works well. ( A 1k makes them too bright and can burn them out.) __________________ Unless you're the lead dog on the sled, the view is always the same....
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bhankiii Guru Join Date: Sep 2006 Location: El Lago, Texas, USA Posts: 2639 Good Answers: 65	#2 Re: voltage regulator- ( 12vdc down to 3.0 and 1.5 vdc) 01/09/2008 4:24 PM
	What you want is a LM317 linear voltage regulator. By setting two resistor values you can get any voltage out from 1.2V up to about 2V less than your input, 10V in your case. They are easy to use and come in a wide variety of packages and current ratings.
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Emjay4119 Guru Join Date: Dec 2005 Location: Queensland Coalfields Australia. Posts: 697 Good Answers: 11	#4 Re: Voltage Regulator - ( 12vdc down to 3.0 and 1.5 vdc) 01/10/2008 10:12 PM
	The current issue of Techonline has a very good article on LED lighting and the issues including voltage level changing. The article is from Maxim electronics. There are also resources available from National semiconductor, International rectifier etc. I viewed these resources also via Techonline. We used to use series resistors once but unless this is for a one off application where efficiency doesn't count it is obsolete.
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Haajee Guru Join Date: Feb 2006 Posts: 1758 Good Answers: 6	#5 Re: Voltage Regulator - ( 12vdc down to 3.0 and 1.5 vdc) 01/10/2008 11:12 PM
	1. Do you need for one LED 1.5V; LED needs nearly 1.8V to work. 2. Why not use CC LED? 3. There are Voltage converters of all sizes & Power ratings for downward convertion. Look for you requirements.
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MUKULMAHANT Guru Join Date: Dec 2006 Location: Long.92E,Lat.26N Posts: 1336 Good Answers: 14	#6 Re: Voltage Regulator - ( 12vdc down to 3.0 and 1.5 vdc) 01/27/2008 5:35 AM
	4 silicon diodes(1 amp rated is fine) in series will give FORWARD DROP of about 2.0 V. If you connect this 2V TO BASE OFA Silicon NPN Transistor- you get 1.5V at emitter. Feed 12V thro' dropper resistor such that Collector has 4>5 volts.( can be down to 2.5 V) This is how I would have done 30 years back. I guess it will work also today.
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bhankiii (1); Emjay4119 (1); Haajee (1); JohnDG (1); MUKULMAHANT (1); Sniccus (1)

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