Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

LED PWM + BUCK with constant current

Status
Not open for further replies.

bauerbach

Newbie level 3
Joined
Mar 19, 2007
Messages
3
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,283
Activity points
1,321
mc34063 led driver

I need to drive ~10 luxeon LEDs at 750-1000mA off the standard 12v current.

but when I use the various online calculators to find the resistor value, they all say I need a massive resistor for that current...

Ive been looking for formal drivers, but they all seem to be for AC input.

what are my options for driving these without overheating a resistor?
 

IanP

Advanced Member level 5
Joined
Oct 5, 2004
Messages
7,942
Helped
2,307
Reputation
4,616
Reaction score
531
Trophy points
1,393
Location
West Coast
Activity points
66,459
mc34063 led

Instead of power-wasting resistor(s) design PWM constant current source and drive LED(s) from there ..

Regards,
IanP
 

bauerbach

Newbie level 3
Joined
Mar 19, 2007
Messages
3
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,283
Activity points
1,321
constant current pwm

well that sounds great, but how do I do that?

Added after 13 minutes:

ok, I did some homework and found this while searching what you said

http://www.instructables.com/id/E0TL4RID3YEWIJMKVI/

seems very simple; my only question is that the Q2 mosfet says its the limiting factor, the unit they used there, how many LEDs could I support around 750mA? at 3.7volts each, I assume my best choice is to run them in series of 3 to maximize the native voltage. still then, what would such a circuit handle?
 

nguyennam

Advanced Member level 1
Joined
Sep 6, 2006
Messages
440
Helped
43
Reputation
86
Reaction score
14
Trophy points
1,298
Activity points
4,069
pwm constant current source

bauerbach said:
I need to drive ~10 luxeon LEDs at 750-1000mA off the standard 12v current.

but when I use the various online calculators to find the resistor value, they all say I need a massive resistor for that current...

Ive been looking for formal drivers, but they all seem to be for AC input.

what are my options for driving these without overheating a resistor?
You mean need to light 10 LEDs from car battery, right? And 10 LEDs at the same bunch, or several bunches? 1A max, OK, but how about the voltage drop and max current of each LED?

nguyennam
 

eziggurat

Full Member level 6
Joined
Feb 15, 2002
Messages
322
Helped
30
Reputation
62
Reaction score
18
Trophy points
1,298
Activity points
2,916
constant current source pwm

Can't you not use LEC driver chipset from Linear or National or Maxim? Also soanar.com.au sells an LED driver for Luxeon LEDs.
 

bauerbach

Newbie level 3
Joined
Mar 19, 2007
Messages
3
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,283
Activity points
1,321
led driver mc34063

Ill check those places out.

the LEDs are 1000mA max I think; Id be ok with 750mA even, but I want some headroom, 3.7volts each

it would be all of them together. and need to have 2 circuits, 1 to light them up at 750-1000mA and another for the dim lighting of maybe 250-350mA. Tail light application, so thats the need for 2 output levels. so either 2 circuits for each output, or a signal line that can change the constant current...

Added after 11 minutes:

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/5179

looking at that, I think it might be a real option, small, inexpensive and if I understand the specs right, I could put 2 of them in parralel, and by powering on the 2nd one, would double the brightness from 350mA to 700mA; is that right?

"Parallel Operation for LED Current > 350mA"
 

martingn

Member level 1
Joined
Mar 30, 2004
Messages
40
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,288
Activity points
381
mc34063a led

Hi All,

Any idea to implement Buck step-down constant current converter for LED supply (350mA-700mA) but with also PWM for dimmering?

It is suppose that there should be two frequencies involved... PWM (hundred of Hz) and Buck Switch ( KHz ).

Also PWM is modulating BUCK. How is the best way to achieve ?

Regards,

MArtin
 

martingn

Member level 1
Joined
Mar 30, 2004
Messages
40
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,288
Activity points
381
led pwm

I've found a MAXIM chip that does what I want. MAX16802.
 

nepoli

Newbie level 1
Joined
Nov 25, 2007
Messages
1
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,284
mc34063 350ma

i'm doing a research on lighting control using PWM so i need a buck converter for that.
plz help me in the design.
 

GelecG

Member level 1
Joined
Dec 1, 2006
Messages
35
Helped
3
Reputation
6
Reaction score
0
Trophy points
1,286
Activity points
1,466
pwm constant current

Hi Nepoli,

explain a lot.

search in www.educypedia.be and come back to talk more.

information of educy is very good for start a project.
 

PHARO

Newbie level 6
Joined
Nov 4, 2007
Messages
12
Helped
4
Reputation
8
Reaction score
4
Trophy points
1,283
Activity points
1,332
700ma current driver circuit

Hi,

Here is an Universal High-Energy LED Lighting System
 
  • Like
Reactions: mandoa

    mandoa

    points: 2
    Helpful Answer Positive Rating

PHARO

Newbie level 6
Joined
Nov 4, 2007
Messages
12
Helped
4
Reputation
8
Reaction score
4
Trophy points
1,283
Activity points
1,332
mc34063 pwm

Hi all!

Maxim ic: MAX774
 

martingn

Member level 1
Joined
Mar 30, 2004
Messages
40
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,288
Activity points
381
led pwm circuit

Pharo, thanks for this good info. Regards, Martin
 

PHARO

Newbie level 6
Joined
Nov 4, 2007
Messages
12
Helped
4
Reputation
8
Reaction score
4
Trophy points
1,283
Activity points
1,332
constant current led pwm

martingn,OK and here is a schematic with 5 Luxeon or same led's.It's very simple!
Regards,PHARO
 

martingn

Member level 1
Joined
Mar 30, 2004
Messages
40
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,288
Activity points
381
constant current pwm circuit

Pharo,
Could not open the last file. (0bytes)

Regards,
Martin

Added after 56 seconds:

Now I could!
Thanks!
Martin
 

PHARO

Newbie level 6
Joined
Nov 4, 2007
Messages
12
Helped
4
Reputation
8
Reaction score
4
Trophy points
1,283
Activity points
1,332
buck current source

Martin,

I try and download it now and it's OK.
You push "Download" button only.

Regards, PHARO
 

Status
Not open for further replies.
Toggle Sidebar

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top