Understanding the drivers for a flashlight

6 posts / 0 new
Last post
onehundredballs
Offline
Last seen: 1 month 5 days ago
Joined: 10/27/2019 - 04:55
Posts: 34
Location: Australia
Understanding the drivers for a flashlight

Hello all, I would like to ask those in the community who have experience with electronics how the drivers in flashlights work.

Specifically from taking power from the battery what steps does the driver do to that taken power to drive the LED?
Also, to regulate the light intensity is a constant voltage used with a variable current control or does something else occur.
I would ultimately like to understand the basic principles so that I can buy and use drivers myself for novelty LED’s and very small AUX lights.
How would you go about matching drivers to an LED you want to run?
I do have some understanding of electronics but would love to hear from those who know much more.
Cheers.

moderator007
moderator007's picture
Offline
Last seen: 8 hours 19 min ago
Joined: 12/23/2012 - 04:47
Posts: 3797
Location: North Carolina

Its a big subject and would take awhile to explain with all the different types of drivers but this thread should get you a basic undestanding of what the led needs and how the driver tries to regulate it.
http://budgetlightforum.com/node/74213
Leds need a supply voltage above their rated vf and a controlled current at or under their rated max current (which most can be pushed above their max rating).
The current determines the brightness but a led also has to have a associated voltage to run at that current with different types of leds having different needs.
That’s the reason these led test that are here on BLF are so valuable.
http://budgetlightforum.com/search?q_as=led%20test
We can see from the testing data exactly what voltage you must supply in order to run that led at a certain current to acheive the lumens your trying to target. Now its up to the driver design to accomplish this, usually by limiting the current to a set amount and varying the output voltage to acheive the set current. The driver has to be designed to accomplish the associated voltage by either buck or boost depending on the input volatge. The current is usually controlled by some type of current regulator IC or a regulated circuit. Then you also have linear drivers that control current by getting rid of the excess voltage from the supply by turning it in to heat.
Like I said its a big subject, I suggest to do some research and reading then if you have some questions we can gladly help.
There’s alot of good info on BLF about different types of drivers.

HarleyQuin
HarleyQuin's picture
Offline
Last seen: 4 months 2 weeks ago
Joined: 03/29/2013 - 04:47
Posts: 588

In this thread is a good summary about different driver types.
(Understanding the difference between Linear, Buck, Boost and Direct Drive drivers)

Especially with wight’s addition in post 56

Oshpark Boards:
HQ ProgKey: Universal Driver Programming Key . Boost: HQ 15mm/17mm programmable boost driver with ATtiny13A
46mm Triple-Channel: BLF SRK FET v3 . 17mm Linear: HQ10D / HQ4D / HQ4S . Contact Boards: 22/24/26mm

hiuintahs
Offline
Last seen: 6 days 11 hours ago
Joined: 06/15/2014 - 12:24
Posts: 144
Location: Utah

I’m sure you would find your answer if you search but the short answer is the driver is the electronic control circuitry between battery and LED to serve several purposes, namely the proper current and voltage to the LED. To understand why a driver is necessary is to understand that an LED is a diode with a forward voltage drop from anode to cathode when current is flowing and that voltage has to be reached otherwise no current flows and thus no light emitted. The typical LED has a forward voltage drop of around 3.0v before it begins to turn on and then once that happens, a very small increase in voltage takes it to its maximum limit with the risk of burning it out. Thus LED’s are best served via current control and not voltage control. The amount of current through an LED determines its brightness.

A good LED driver will basically be a small switching type of power supply that sources a fixed current depending on which mode you are in (low, med, or high), regardless of battery voltage (within reason of course). Since current is the determining factor in the circuit with it being the feedback mechanism in this power supply, the voltage will just go to whatever is needed to provide that current.

If the primary battery source voltage resides mostly below the 3.0v (single cell AA) then a boost type of driver is needed. If the battery voltage is above 3.0v (Lithium ion), then a buck type of driver is needed.

Summary:
1) LED is a diode that is best suited via current control.
2) Light output is proportional to current through the LED.
3) You can’t just put a battery voltage on the LED unless you are precisely right around the Vfwd of the LED. You can do that with a “fine” adjust of a bench power supply
4) Drivers boost or buck the battery voltage to the LED such that a constant regulated current flows.

Hope that helps in a few of words as possible without getting too technical.

Edit: I see that this was originally posted last year. Oh well, maybe if someone else comes across with the same question this can be useful.

Forsythe P. Jones
Offline
Last seen: 1 year 1 month ago
Joined: 08/15/2021 - 00:40
Posts: 413
Location: California

Let’s say you like watching movies: the adventure, the romance, the space battles, and so on. As you become a more experienced movie buff, you begin noticing and then studying how the film makers used lighting techiques, camera motions, musical cues and whatnot to make those movies keep you on the edge of your seat. And understanding the movie making process in turn deepens your appreciation of the movies themselves. You experience not only the hero’s dramatic close-up on the screen, but also the different tricks the director and cinematographer had to do to make that shot work exactly the way it did.

It’s the same thing with flashlights. After your 5th or 10th or 20th light, you are no longer buying them to find your way around in the dark or any other such practical purpose. You’re a flashaholic looking for new experiences, similar to being a movie buff. So of course understanding how the light makers solve the challenges that they face deepens your experience as a light buff.

I think that is a good enough reason to want to understand drivers, although thermals, materials, machining, batteries, leds, and these days software are also important. When I talk to non-flashaholics they can’t believe how much sophistication goes into making a light these days, with some of the best work being done by relative amateurs (modders here on BLF, etc.). But we here are all cognoscenti and that helps make things interesting.

YuvalS
YuvalS's picture
Offline
Last seen: 23 hours 16 min ago
Joined: 09/26/2018 - 10:39
Posts: 628

Have a look at this webpage, it helped me a lot when I started learning about drivers.
Deconstructing a flashlight | Deepak Kandepet

My FW repository

My BLF/OL contest entries: 7th 8th 9th | 10th |