# LED PWM + BUCK with constant current

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#### bauerbach

##### Newbie level 3
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

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
constant current pwm

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

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?

Matuuuch

### Matuuuch

points: 2

#### nguyennam

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
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
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...

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
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
led pwm

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

#### nepoli

##### Newbie level 1
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
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
700ma current driver circuit

Hi,

Here is an Universal High-Energy LED Lighting System

mandoa

### mandoa

points: 2

mc34063 pwm

Hi all!

Maxim ic: MAX774

#### PHARO

##### Newbie level 6
constant current buck

Luxeon led driver with MC34063. 12V DC input

points: 2

### shahidali55

points: 2

#### martingn

##### Member level 1
led pwm circuit

Pharo, thanks for this good info. Regards, Martin

#### PHARO

##### Newbie level 6
constant current led pwm

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

Matuuuch

### Matuuuch

points: 2

#### martingn

##### Member level 1
constant current pwm circuit

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

Regards,
Martin

Now I could!
Thanks!
Martin

#### PHARO

##### Newbie level 6
buck current source

Martin,

Regards, PHARO