Driver facts by Jinks.

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Driver facts by Jinks.

Post by PESCA » 06 Jan 2013, 13:06

Jinks wrote:Hi Paul

Does the LED look like this?

If it does, it is a Cree XR-E led ( the Q5 stands for the brightness bin the led is from within the XR-E family)

The XR-E Q5 has a maximum drive current of 1 amp and a forward voltage of 3.7V at this amperage.

A fully charged 18650 battery is 4.2v, so direct driving the led will cause it to draw way more than 1 amp until the voltage of the battery drops nearer to the forward voltage of the LED. Direct driving is quite common within the flashlight modding community, where 'over driving' LED's is common practice. But to do this you need bloody good heat sinks (usually custom made out of copper) and good thermal transfer between the LED, heat sink and torch body.

There are 4 common types of torch LED drivers, these being Buck, Boost, Linear Regulator, and Buck-Boost.

Buck Driver- Allows you to use multiple batteries such as 2,3 or 4 18650 cells in series, the driver will drop the voltage and regulate the current for the led. It is no good for a single 18650 cell, as the battery voltage will need to be at least 0.5v over the forward voltage of the LED for the driver to operate efficiently. You could use a buck driver in your torch, and use two cr123 batteries instead of a single 18650.
Example of a single mode buck driver

Boost Driver- A Buck in reverse, allows the led to be powered from a single AA or AAA battery, the driver will boost the voltage.

Linear Regulator- These drivers have have current regulating AMC7135 chips on the board, the chips are wired in parallel and each one is rated at 350ma, so for a 1 amp LED, you will need a driver with 3 chips (1050ma).
These are ideal to use with a single 18650 battery, as when the battery is fully charged, the excess voltage will be burnt of as heat, as the battery voltage drops nearer the LED forward voltage, less heat will be produced and the driver will become more efficient. When the battery voltage drops below the forward voltage, the driver will go into direct drive, and the LED will dim, warning you of a low battery. Normally, these drivers have a maximum input voltage rating of about 4.5V, as any more will generate too much heat and blow the chips. The drivers are also available with single and multi modes
One like this would suit your needs ... -5v-127687

Buck-Boost Driver Does the same as a buck and boost driver in one package, very efficient drivers but good ones are expensive

So in short, the type and number of batteries you want to use will determine whether you need a buck, boost or linear driver, and then you need to choose a driver within that type with the correct current rating for your LED, and the number of modes you need. Simples ;)

Use this database to help you find drivers ... erlist.php

And have a read through this site for more info, there is a section on drivers on the site

Hope this Helps