12V voltage regulators

[30boat]

I need some voltage regulators to use with the led bulbs I just bought.What type should I get?
I saw that Maplin sells them but I don't know wich ones to order.
Thanks

 

[William_H]

Now presumably you mean you want to drive actual LED (bulb).
They require a current regulator and usually drop about 2.5 volts per bulb.
The characterisitc of a LED is that at voltage less than its required voltage it will draw no current. When the required voltage is reached the current increases dramatically to destruction.
A simple ressitor is effective in that as the current drawn rises so the resistor reduces the voltage. However as you are probably aware a ressitor with one LED bulb on 12v is OK the increase in current from 12v to 14v is not so great. However this resistor will waste about 4 times as much pwer as the LED uses. If you put 3 or 4 bulbs in series then the current change between 12v and 14v is huge.

So you need a current regulator or a voltage regulator and series resistor.
A voltage regulator reducing the battery input to 9volts would be OK down to a fairly flat ships battery. You could then have 3 bulbs in series with pewrhaps a 50 ohm resitor for 50 ma bulbs. A 12v regulator will drop several volts internally so won't work with less than 14v input.

Or you could set up a regulator like a LM317 as a current regulator. This requires a resistor which will drop 1.25 volts at the required current but will in addition lose another 2 volts or so in the regulator so limiting you to 2or 3 bulbs in series.
You could use one of the computer regulators with 18v output but this would be poor efficiency unless you fed a lot of LEDs with it. ie 6 strings of 6 in series.
Most proper LED lamps will have purpose designed switch mode power supply current regulated with pulsed current to feed many LED bulbs in series.
Have a look at Maxim site for chips available.

Is this what you were asking? PM me if you wish for further details. olewill

 

[marno]

Someone on the forums put me onto an LM2940, they drop about .5 of a volt at maximum current (1 amp) http://www.rapidonline.com/productinfo.a...;catref=82-0846 I use them with my LEDs. I also use a capacitor as per http://www.reuk.co.uk/LM2940-12V-1A-Low-Dropout-Regulator.htm
Sorry about all the long links.

 

[Ruffles]

Don't you need a current regulator for an LED? My involvement in electronics ended before high power LEDs were invented but surely you need something like this:
http://www.national.com/pf/LM/LM3402.html

The MR16 LED replacements are really remarkably good value. They convert 12v AC OR DC to a carefully regulated current (not voltage). They do this extremely efficiently using a bit of capacitance and inductance and a few 100kHz. All for a couple of quid including the LEDs.

An old fashioned voltage regulator wastes power by a controlled voltage drop across a semiconductor. Not the done thing these days.