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Low-voltage switchmode power LED supply circuit?

R

Richard Rasker

Jan 1, 1970
0
Hi all,

I'm playing around with a bunch of white power LEDs (the 3W version, with
0.7A current), and now I'm looking for an efficient step-down converter to
supply up to three of these from approximately 5V (four NiMH cells).

I designed stepdown converters before, but most of these were based on
regulator chips which required a rather higher supply voltage (e.g.
UC3842); also, they featured Schottky diodes to ground instead of a MOSFET,
which is less efficient. Last but not least, the output should be a
stabilized current, instead of a stabilized voltage.

Now before setting out and reinventing the wheel, I realized that there must
be countless suitable designs out there -- all those cheap LED torches must
have a built-in boost converter; also, every modern computer has several
low-voltage high-current switchmode step-down circuits.
So my question is if anyone could point out an actual circuit design, or at
least an SMPS controller chip capable of handling voltages as low as 3-4V.
I considered the good 'ole TL497, but that one has a minimum Vcc of 4.5V,
which is too close for comfort to the 5V battery voltage (I've had some
nasty latch-ups with that one, lacking an undervoltage lockout).

Thanks for any advice already, best regards,

Richard Rasker
 
H

Hammy

Jan 1, 1970
0
Hi all,

I'm playing around with a bunch of white power LEDs (the 3W version, with
0.7A current), and now I'm looking for an efficient step-down converter to
supply up to three of these from approximately 5V (four NiMH cells).

I designed stepdown converters before, but most of these were based on
regulator chips which required a rather higher supply voltage (e.g.
UC3842); also, they featured Schottky diodes to ground instead of a MOSFET,
which is less efficient. Last but not least, the output should be a
stabilized current, instead of a stabilized voltage.

Now before setting out and reinventing the wheel, I realized that there must
be countless suitable designs out there -- all those cheap LED torches must
have a built-in boost converter; also, every modern computer has several
low-voltage high-current switchmode step-down circuits.
So my question is if anyone could point out an actual circuit design, or at
least an SMPS controller chip capable of handling voltages as low as 3-4V.
I considered the good 'ole TL497, but that one has a minimum Vcc of 4.5V,
which is too close for comfort to the 5V battery voltage (I've had some
nasty latch-ups with that one, lacking an undervoltage lockout).

Thanks for any advice already, best regards,

Richard Rasker

NCP3065: 1.5 A Constant Current Switching Regulator for LEDs

You can get more then 1.5A by useing an external BJT,READ THE APP
NOTE.

3-40V IN.

Go to Onsemis site theres an excel spread sheet as well as example
desighns of most topologies including sepic.The controllers less then
two bucks in small quantity.

http://www.onsemi.com/PowerSolutions/product.do?id=NCP3065PG
 
R

Richard Rasker

Jan 1, 1970
0
NCP3065: 1.5 A Constant Current Switching Regulator for LEDs

You can get more then 1.5A by useing an external BJT,READ THE APP
NOTE.

3-40V IN.

Go to Onsemis site theres an excel spread sheet as well as example
desighns of most topologies including sepic.The controllers less then
two bucks in small quantity.

http://www.onsemi.com/PowerSolutions/product.do?id=NCP3065PG

OK, great, this is exactly what I need! Thanks for the tip-off!

Richard Rasker
 
H

Hammy

Jan 1, 1970
0
OK, great, this is exactly what I need! Thanks for the tip-off!

Richard Rasker

Given your input voltage range 3-5v if your planning on putting three
of you LED's in series depending on the voltage drop of your
particular LED's you may want a SEPIC converter there are two examples
of SEPIC'S under "Design Notes".

You can buy the controller here. As well as everything else you need.

http://www.newark.com

OR

http://www.digikey.com/

For coupled inductors try Busman's DRQ series.

http://www.cooperet.com/library/products/PM-4315 DRQ Series.pdf

COILCRAFT also sells prototype quantities.

http://www.coilcraft.com/
 
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