Constant current driver for high-intensity LEDs

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1

The JunkJam project I’m working on is going to be building a
dragonfly, using a mirror ball cut in half for the eyes. This will be
used in daylight, so I’m thinking of using high-intensity LEDs shining
at the mirror ball to mimic the iridescence of a real dragonfly’s
eyes. The LEDs I’m considering are these:

http://www.ebay.co.uk/itm/Y-4x-10W-RGB-High-Power-LED-Lamp-bulb-Light-Bright-/330721383428
http://www.ebay.co.uk/itm/10w-RGB-LED-High-Power-Led-Light-Energy-Saving-Lamp-Cup-/200741718216
http://www.ebay.co.uk/itm/9W-RGB-LED-HIGH-FLUX-POWER-UK-BASED-red-green-blue-each-3W-6-LEG-not-1W-10W-/300691137009

These all need 700mA - 1000mA forward current so I’m looking for
advice on how best to provide that - the power source will be a 12V
car battery. Each RGB needs to be PWM’d as well, so I’m looking at
supplies capable of driving a segment (R, G & B) from each of the 2
LEDs. I found a circuit on Instructables:

I’m wondering if that circuit looks OK, or if there’s a better way of doing it?

Ta,

Alan Burlison

2

The JunkJam project I’m working on is going to be building a
dragonfly, using a mirror ball cut in half for the eyes. This will be
used in daylight, so I’m thinking of using high-intensity LEDs shining
at the mirror ball to mimic the iridescence of a real dragonfly’s
eyes. The LEDs I’m considering are these:

http://www.ebay.co.uk/itm/Y-4x-10W-RGB-High-Power-LED-Lamp-bulb-Light-Bright-/330721383428
http://www.ebay.co.uk/itm/10w-RGB-LED-High-Power-Led-Light-Energy-Saving-Lamp-Cup-/200741718216
http://www.ebay.co.uk/itm/9W-RGB-LED-HIGH-FLUX-POWER-UK-BASED-red-green-blue-each-3W-6-LEG-not-1W-10W-/300691137009

These all need 700mA - 1000mA forward current so I’m looking for
advice on how best to provide that - the power source will be a 12V
car battery. Each RGB needs to be PWM’d as well, so I’m looking at
supplies capable of driving a segment (R, G& B) from each of the 2
LEDs. I found a circuit on Instructables:

http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/step8/a-little-micro-makes-all-the-difference/

I’m wondering if that circuit looks OK, or if there’s a better way of doing it?

Ta,

You could make a small improvement by changing the non-mosfet transistor
for a OP-AMP and reduce the value of the sense resistor (you’ll dump
more power from the mosfet though).

Either than or go find a chip to do it.

Ben Dooks bjdooks@googlemail.com http://www.fluff.org/ben/

3

You could use something like this

http://uk.farnell.com/xp-power/ldu2430s700-wd/led-driver-dc-dc-20w-wired/dp/
1961528-----Original Message-----
From: hacman@googlegroups.com [mailto:hacman@googlegroups.com] On Behalf Of
Alan Burlison
Sent: 23 April 2012 14:10
To: hacman@googlegroups.com
Subject: [HACMan] Constant current driver for high-intensity LEDs

The JunkJam project I’m working on is going to be building a dragonfly,
using a mirror ball cut in half for the eyes. This will be used in
daylight, so I’m thinking of using high-intensity LEDs shining at the mirror
ball to mimic the iridescence of a real dragonfly’s eyes. The LEDs I’m
considering are these:

http://www.ebay.co.uk/itm/Y-4x-10W-RGB-High-Power-LED-Lamp-bulb-Light-Bright
-/330721383428
http://www.ebay.co.uk/itm/10w-RGB-LED-High-Power-Led-Light-Energy-Saving-Lam
p-Cup-/200741718216
http://www.ebay.co.uk/itm/9W-RGB-LED-HIGH-FLUX-POWER-UK-BASED-red-green-blue
-each-3W-6-LEG-not-1W-10W-/300691137009

These all need 700mA - 1000mA forward current so I’m looking for advice on
how best to provide that - the power source will be a 12V car battery. Each
RGB needs to be PWM’d as well, so I’m looking at supplies capable of driving
a segment (R, G & B) from each of the 2 LEDs. I found a circuit on
Instructables:


little-micro-makes-all-the-difference/

I’m wondering if that circuit looks OK, or if there’s a better way of doing
it?

Ta,

Alan Burlison

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4

You could make a small improvement by changing the non-mosfet transistor
for a OP-AMP and reduce the value of the sense resistor (you’ll dump more
power from the mosfet though).

I thought an op-amp needed both a + and - supply to work, or am I confused?

Either than or go find a chip to do it.

Any suggestions?

Alan Burlison

5

Alan,

Times have moved on…there are now what’s known as single supply op
amps which can and do work from 0v and a positive rail.

Regards

AlexOn 23 April 2012 17:01, Alan Burlison alan.burlison@gmail.com wrote:

You could make a small improvement by changing the non-mosfet transistor
for a OP-AMP and reduce the value of the sense resistor (you’ll dump more
power from the mosfet though).

I thought an op-amp needed both a + and - supply to work, or am I confused?

Either than or go find a chip to do it.

Any suggestions?

–
Alan Burlison

–
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To post to this group, send an email to hacman@googlegroups.com.
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6

You could use something like this

http://uk.farnell.com/xp-power/ldu2430s700-wd/led-driver-dc-dc-20w-wired/dp/
1961528

I’d need 6 of them I think as they only go up to 1A output, which
would make them too pricey. Plus I’m wondering how I’d get the 0 -
1.25V PWM control signal out of a 5V AVR - would a simple voltage
divider work?

Alan Burlison

7

Times have moved on…there are now what’s known as single supply op
amps which can and do work from 0v and a positive rail.

Ben was saying that an op-amp would drop more power with an op-amp, as
I expect each channel to draw up to around 2A that might be an issue I
think, although I expect I’ll probably have to have a humongous
heatsink for the LED anyway:

http://www.ebay.co.uk/itm/1pcs-Aluminium-heatsink-cooling-plate-10w-10watt-high-power-led-light-lamp-/330721375507

Alan Burlison

8

You could make a small improvement by changing the non-mosfet transistor
for a OP-AMP and reduce the value of the sense resistor (you’ll dump more
power from the mosfet though).

I thought an op-amp needed both a + and - supply to work, or am I confused?

Nope, you can run them single supply. I’ve made a constant-current sink
with a single supply op-amp.

Either than or go find a chip to do it.

Any suggestions?

Ben Dooks bjdooks@googlemail.com http://www.fluff.org/ben/