Understanding the difference between Linear, Buck, Boost and Direct Drive drivers

Flashlight Modding and DIY Parts
8

Nice explanation, I think it is a good introduction for folks who are new to building flashlights, but I guess someone who is completely new to this should judge that :-)

Thanks for the write-up!

9

I don’t, it’s a in-depth subject.

If you want to redo it with less text that’d be cool but I urge you leave everything already up. Make a new post with the shortened version, you should never remove reference material.

10

I did also do an article about it a couple of years ago (Date says 2010): http://lygte-info.dk/info/DriverTypes%20UK.html

11

Thanks for the support guys! I see that somebody already linked to my topic so I’m happy. :slight_smile:

12

I somehow never found this article on your website, even though I looked through it many times.
Anyway, I added a link to your article at the bottom of the OP.

13

That article was only posted on CPF and I wanted to update it before posting it on my website, but has never gotten around to do that. Maybe you can use some ideas from it (I might still update it and post it sometime in the future).

14

Lagman, you may consider going a little more in-depth on the PWM section and go into duty-cycle some.

15

Thanks for taking the time to put all this great information together.

16

I might do a separate in depth topic on this. I don’t want this to be so long that it scares newbies.

On a side note, I have a doubt about my title. Would it be better to say:
“Understanding the difference between Linear, Buck, Boost and Direct Drive drivers”
Instead of:
“Understand the difference between Linear, Buck, Boost and Direct Drive drivers”
?

17

Yes, not really wrong as is but adding “ing” wouldn’t hurt, no ones going to complain tho.

*native speaker but not an English teacher or anything

18

So both are correct but the one with “ing” sounds better?

19

Nice summary, i like it.

20

applaud the topic: it’s an instruction, ‘do this’ (works fine in your title, as “you can do this”)
applauding the topic: it’s a description, ’we are doing this” (also works fine in your title)

21

Thank you! In that case I think I’ll put “Understanding” as it fits better what I intended to say.

22

Nice, simple explanation.

When I was working with buck and boost circuits we simply called them DC-DC inverters which was basically just an oscillator (square or sawtooth) driving a toroidal transformer and operated at 20khz and above if I remember correctly. It’s been many, many years.
Higher frequencies allowed smaller components but usually lower efficiencies. That’s part of the buck/boost drivers used here.
You have to have AC, in one form or another, to transform voltage, so DC-DC converts DC to AC, changes voltage up or down, then converts to DC again.

The L/C portion in these drivers looks like part of the regulation circuit and operates at audible frequencies.
Your explanation is a lot easier to understand.

What we, the end user, care about is:

  1. Voltage range usable for input.
  2. Usable voltage and current out and stability.
  3. Overall efficiencies at various voltage/current levels.
  4. What driver to use in which situation.

That you describe very well.

Thanks for an excellent article.

23

Excellent Resource !
Thanks for this, it’s possibly the most valuable post in the last month.
:slight_smile:

24

Thanks, This is all new to me. Maybe this could be the first in a new sub-section of basic information for newbies. Now that I have a super nice light it might be good to understand more.

25

Thanks for sharing this lagman. I know how to swap drivers but I really don’t understand how these drivers differ from one another - until I read this.

I was also somewhat ‘relieved’ because the driver of the BLF Starry Light flashlight I bought through group buy failed and I replaced it with a Nanjg 105c driver. I now feel safer using the light with 4 AA NiMH because its total voltage of 4.8 volts when fully charged is way below the 6 volt limit of the 7135 chip. :slight_smile:

26

There is also a power and temperature limit on the 7135 chip and this is usual reached way before the 6 volt limit. Luckily the chip will protect itself and just reduce the current when it gets to hot.

27

Basically you are wasting the power of one AA battery into the driver. Not the most efficient solution but it should work as long as the driver doesn’t overheat.
If you want to reduce heat losses you could use a dummy AA cell to reduce the voltage a bit. That would make your light a 3xAA light. :slight_smile:
The light should be as bright. Maybe that it will start reducing current a bit earlier at the end of discharge though. 7135 chips start reducing current about 0.2V above the LED voltage.