Driver Questions for a Noob

[GVSS]

Not sure if this is the correct forum for this question, but I figured you guys would be able to help, or at least point me in the right direction.

I'm thinking of trying to build a bike light and I understand that you need a driver to power the led's, and that the driver delivers a constant current to the led.

What i don't understand is the voltage side of things. Most led's seem to have a voltage of 3.7 volts, but what voltage does the driver output. Does it output the same voltage it has coming in, or does it regulate the voltage to 3.7 volts automatically.

I get that a buck driver lowers voltage, and a boost driver increases voltage, but by how much, does it depend on the driver itself, ect.

This is the only part that seems to confuse me about the DIY route.

Not sure if this helps or not, but I'm thinking of modifying a p7 or mce flashlight and I'm thinking of replacing the stock driver with something better. I was planning on using between 2 to 4 18650 cells wired in parallel, would consider 2s2p if it would benefit in anyway.

and also, am i better using 2 drivers wired in series/parallel to give me a high/low mode?

I know these questions have probably been answered before but I've spent hours looking here and the MTBR.com diy light forum and haven't had much luck finding any answers.

Thanks in advance for the help!

 

[znomit]

:welcome:
Have you read the welcome mat?
Check it out and come back if you're still need answers.

 

[TexLite]

What i don't understand is the voltage side of things. Most led's seem to have a voltage of 3.7 volts, but what voltage does the driver output. Does it output the same voltage it has coming in, or does it regulate the voltage to 3.7 volts automatically.

I get that a buck driver lowers voltage, and a boost driver increases voltage, but by how much, does it depend on the driver itself, ect.

Hi GVSS, welcome to CPF.

A Constant Current driver driver does exactly what the moniker implies. It delivers a steady or constant current to the LED regardless of Vf (as long as the Vf is within operating or design parameters).

Lets say the driver is set to deliver 350mA. The Vf of LED's varies form one to another. A hypothetical forward voltage range for the LED's you will be driving varies from 3.3V-3.7V @ 350mA. Lets say three emitters, 3.3Vf, 3.5Vf, and 3.7Vf.

The driver would therefore output:
3.3V, 350mA for emitter #1.
3.5V, 350mA for emitter #2.
3.7V, 350mA for emitter #3.

The voltage would be equal to the forward voltage of the LED at the set output current.

and also, am i better using 2 drivers wired in series/parallel to give me a high/low mode?

I would use a single driver with multiple modes.

TaskLED builds excellent drivers, and The Sandwich Shoppe builds high quality drivers as well.

I know these questions have probably been answered before but I've spent hours looking here and the MTBR.com diy light forum and haven't had much luck finding any answers.

Thanks in advance for the help!

There is a lot of information out there and it can be difficult to sift through.

And as someone here recently pointed out, it can be even harder when you don't have an understanding of the terminology on the subject your looking for.

-Michael