# Need Help with 12V LED

Hi, I am new to forum and know very little on electricals and electronics.

Now i have a few OSRAM Ostar 12V LEDs (https://goo.gl/04rrZy) with heatsink which i am working with as a hobby. Power source is a car battery. Here i list all my query one by one

1. As per the datasheet of this LED, it say the working forward current is between 50 ~ 1500 mA. But when i connect this LED directly to Power Source without any resistance in circuit, it draws only 490 mA of current. But how to make it to draw around 1 A of current so that i could get a better brightness?
Note: after going through a few articles i came to know a constant current circuit is available which supplies a constant current irrespective of voltage variation. In that case can i make a circuit with a output of 1A and supply to this LED so that it is forced with a 1A current in it?

2. Another trial requires me to connect two of these 12V LED in series. But my source is just a 12V (13.5v to be precise) car battery. Is it possible to make any circuit so that i can power up this series connection. Here also i needed the LEDs to draw a 1A of current.

3. In another case i have a 6V LED (https://goo.gl/h3YLxP). So what kind of a circuit should i make for it to be powered up by the same 12 v battery and make the led to draw around 500mA of current.

I hope the post is easy to understand. Sorry for my english as terms used as i am not an expert in electricals.

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Hi,

With that constant current stuff you are already going on the right direction.
Indeed, what you need is a 'boost' or 'step-up' type 'LED driver'. That will be able to supply a constant current, at different (both higher/lower) voltage than the source.
Since it's a hot topic, with those words you will find many home projects, integrated circuits, AppNotes.

Mohammed Suhail
The data sheet for the 12V LED shows it is simply 4 LEDs in series, so each has the typical ~ 3V forward voltage.

As Rive pointed out - these are not meant to be driven directly from a voltage source. In some cases (6V LED from a ~ 12V source), you could just use a series resistor ( R ohms = (Vsource minus Vled) divided by LEDcurrent ), but that wastes some energy ((Vsource minus Vled) * LEDcurrent) which you may or may not care about. But generally, you will want an active circuit to convert the battery voltage to a current source for the LEDs.

Seek out application notes on using that part on a car battery.

Mohammed Suhail
thanks for all your suggestion, so i shall try to make a constant current circuit. But my point 2, requires 2 led in series which makes it 24V, how can i power up the led of 24V from a 12V source.

A 'boost' type LED driver will just increase the voltage on the LEDs to the point that exactly the pre-set current will flow.

Of course there are limits, but two 12V LED from 12V source will be OK.

The more problematic one is the 6V LED. Boost drivers are not very good when the output voltage is around or below the input voltage. You might need to use some more LEDs in series or pick a buck-boost type driver.

Last edited:
CWatters
Homework Helper
Gold Member
Why do they have to be in series?

Why do they have to be in series?
that is how the circuit is available.

Can someone please share me a circuit diagram for me which would give a constant current of 1) 1A current and 2) 500mA of current on a 13.5V input. Please

CWatters
Homework Helper
Gold Member
Have a look on ebay for something like a...

DC-DC Constant Current Boost (or step up) LED Power Supply Driver module

They appear to be available for under \$10.

These convert the 12V into a variable voltage at a constant current. The current can usually be set by adjusting a potentiometer. Ask seller if it meets the spec you need eg

Input: 12-14V (wider range is available).

Output:
Voltage: 12V to 30V? (you need at least 28.2V for two LED in series)
Current: Constant current adjustable up to at least 1A.

Power: >30W (It appears you need at least 28W but 100-150W modules appear to be available at same price).

Some have a minimum current setting. eg you can't adjust the current below this minimum value. Typically it's 200mA but check this is ok for you.

If you get one capable of more than 1A set the current to it's lowest value before powering it up! Perhaps test it using a cheap 12V car light bulb before using the expensive LED?

Consider putting a fuse in series with the input.