clever led driver
polop, Wed Jun 17 2009, 05:03PMHI there i have a p7 led (google it, there awsome) that requires a 2800mA constant current supply (Vf around 3.6v-4v). i know a resistor can work but drawing this kind of power, it would need to be huge!! i also know about the lm317 and its derivitive, but this is almost as inefficient as a resistor.
How could i make simply and cheaply some kind of switching supply that takes voltage from the 5-9v range and puts out 2-4.5v (Vout shifts in order to keep current regular)
You can buy circuit boards that do this that are specificaly designed for this led, that are also very cheap- but they only push 2A and seems a waste to underdrive such a brutal LED.
any ideas , cheap efficient small driver at 2.8A
Re: clever led driver
tobias, Wed Jun 17 2009, 07:33PM
Yeap..
You can try a ncp3063.. It's a DC/DC chip that has current limiting. But it can supply only 1.5 A without a driver.
Maybe you can find a way to use a FET after it to give you the power you need.
The IC is very cheap.. less then a buck.
Or a LM3401 (less then a buck too).
tobias, Wed Jun 17 2009, 07:33PM
Yeap..
You can try a ncp3063.. It's a DC/DC chip that has current limiting. But it can supply only 1.5 A without a driver.
Maybe you can find a way to use a FET after it to give you the power you need.
The IC is very cheap.. less then a buck.
Or a LM3401 (less then a buck too).
Re: clever led driver
Conundrum, Wed Jun 17 2009, 07:51PM
MC34063 in constant current mode? set the output voltage and cutoff resistor and test with a dummy load with similar Vdrop (several silicon diodes in series work well)
i'd also use a zener on the output just to be safe, set around 1V higher than the rated Vmax..
regards, -A PM me if you need any help with this
Conundrum, Wed Jun 17 2009, 07:51PM
MC34063 in constant current mode? set the output voltage and cutoff resistor and test with a dummy load with similar Vdrop (several silicon diodes in series work well)
i'd also use a zener on the output just to be safe, set around 1V higher than the rated Vmax..
regards, -A PM me if you need any help with this
Re: clever led driver
mikeselectricstuff, Wed Jun 17 2009, 11:31PM
Altjhough there are many switchmode buck reg chips that can be used for LEDs, by connecting their voltage feedback input across a current-sense resistor, however the typical 1.2v feedback voltage limits efficiency - there are a number of buck reg chips designed for LED apps, which have a much lower feedback voltage threshold - typically 0.2V. Most of the main semi mfrs have something in their range - I know Maxim have an external-FET part which should be easily scalable to larger O/P currents.
mikeselectricstuff, Wed Jun 17 2009, 11:31PM
Altjhough there are many switchmode buck reg chips that can be used for LEDs, by connecting their voltage feedback input across a current-sense resistor, however the typical 1.2v feedback voltage limits efficiency - there are a number of buck reg chips designed for LED apps, which have a much lower feedback voltage threshold - typically 0.2V. Most of the main semi mfrs have something in their range - I know Maxim have an external-FET part which should be easily scalable to larger O/P currents.
Re: clever led driver
wastehl, Thu Jun 18 2009, 03:10AM
There are IGBT gate driver chips that will handle this and give you the added capability of putting a simple pulser circuit on the enable line, useful for signaling, etc.
wastehl, Thu Jun 18 2009, 03:10AM
There are IGBT gate driver chips that will handle this and give you the added capability of putting a simple pulser circuit on the enable line, useful for signaling, etc.
Re: clever led driver
jonny5, Thu Jun 18 2009, 06:00AM
A Buck converter controlled by a 555 timer and a comparator?
The circuit uses a one-shot configured 555 timer and a comparator to implement a wacky controlled off-time buck converter.
6 VDC input, the LTspice simulation of the LED current:
12 VDC input, simulated LED current:
The simulation suggested that the 555 timer provided adequate gate drive at relatively low frequency (20KHz). Higher frequency operation could be obtained by decreasing the one-shot interval. This would permit the use of a smaller buck inductor and/or less current ripple. However, the 555 output might not be sufficient for high frequency switching. Perhaps a NPN/PNP voltage follower between the PMOS gate and the 555?
The voltage reference (150mV...really whatever you want) might be obtained via a voltage divider off of a linear regulator/zener/etc. Unfortunately, the comparator needs a (close to) rail-to-rail output and the ability to handle small input voltages (ie. voltage reference).
At high input voltages (15VDC and higher), the free-wheeling schottky diode dissipates a fair amount of power (over a watt)! Lower input voltages result in less average schottky diode current.
At low voltages (5VDC in the simulation) the switching frequency drops dramatically as the circuit attempts to maintain the desired LED current.
Overall, the circuit looks like it might drive a high-powered LED relatively efficiently. Of course, the only way to tell is to build the circuit and see. One more project to throw on the pile!
jonny5, Thu Jun 18 2009, 06:00AM
A Buck converter controlled by a 555 timer and a comparator?
The circuit uses a one-shot configured 555 timer and a comparator to implement a wacky controlled off-time buck converter.
6 VDC input, the LTspice simulation of the LED current:
12 VDC input, simulated LED current:
The simulation suggested that the 555 timer provided adequate gate drive at relatively low frequency (20KHz). Higher frequency operation could be obtained by decreasing the one-shot interval. This would permit the use of a smaller buck inductor and/or less current ripple. However, the 555 output might not be sufficient for high frequency switching. Perhaps a NPN/PNP voltage follower between the PMOS gate and the 555?
The voltage reference (150mV...really whatever you want) might be obtained via a voltage divider off of a linear regulator/zener/etc. Unfortunately, the comparator needs a (close to) rail-to-rail output and the ability to handle small input voltages (ie. voltage reference).
At high input voltages (15VDC and higher), the free-wheeling schottky diode dissipates a fair amount of power (over a watt)! Lower input voltages result in less average schottky diode current.
At low voltages (5VDC in the simulation) the switching frequency drops dramatically as the circuit attempts to maintain the desired LED current.
Overall, the circuit looks like it might drive a high-powered LED relatively efficiently. Of course, the only way to tell is to build the circuit and see. One more project to throw on the pile!
Re: clever led driver
Dr. Slack, Thu Jun 18 2009, 08:09AM
There are two alrternatives. Put something together yourself from an inductor, comparator and FET and learn about switching supplies. Or, obtain something ready made.
For ready made, I have always headed stright for the maxim-ic site, for two reasons. The first is they have a huge raft of parts. The second is that they have a policy of sampling, even to (especially to) amateurs, so there are no eithical problems about getting their standard two-off sample quantity for nothing.
I say "have always", because "progress" has meant that fewer and fewer new whizzy clever parts these days are available in a package that you can solder wires onto. Even if you can get fine wires onto the QTFN pads under a microscope, you still may have to get 1 watt out of the power pad in the middle, which is tough without a board. So increasingly my searches there start with DIP or SO package availability as the first criterion.
You can get a MAX16834 3A buck LED driver in an SO package. It needs an external switching FET (and of course an external inductor and a few Rs and Cs), but otherwise controls the whole driving job in one.
A MAX15037 is an internal switch buck 3A PSU, which can be configured for constant current output by returning the load current through a sense resistor to ground across its 0.6v Vsense feedback input, but it's in a TQFN, so nearly impossible to connect without a board.
Linear, TI, NatSemi (I think) and a few others all do LED drivers and PSUs as well. You may find better combinations of features with them. None are going to be more than $1 or $2, so if you have to buy from digikey, it's not going to break the bank.
Dr. Slack, Thu Jun 18 2009, 08:09AM
There are two alrternatives. Put something together yourself from an inductor, comparator and FET and learn about switching supplies. Or, obtain something ready made.
For ready made, I have always headed stright for the maxim-ic site, for two reasons. The first is they have a huge raft of parts. The second is that they have a policy of sampling, even to (especially to) amateurs, so there are no eithical problems about getting their standard two-off sample quantity for nothing.
I say "have always", because "progress" has meant that fewer and fewer new whizzy clever parts these days are available in a package that you can solder wires onto. Even if you can get fine wires onto the QTFN pads under a microscope, you still may have to get 1 watt out of the power pad in the middle, which is tough without a board. So increasingly my searches there start with DIP or SO package availability as the first criterion.
You can get a MAX16834 3A buck LED driver in an SO package. It needs an external switching FET (and of course an external inductor and a few Rs and Cs), but otherwise controls the whole driving job in one.
A MAX15037 is an internal switch buck 3A PSU, which can be configured for constant current output by returning the load current through a sense resistor to ground across its 0.6v Vsense feedback input, but it's in a TQFN, so nearly impossible to connect without a board.
Linear, TI, NatSemi (I think) and a few others all do LED drivers and PSUs as well. You may find better combinations of features with them. None are going to be more than $1 or $2, so if you have to buy from digikey, it's not going to break the bank.
Re: clever led driver
polop, Thu Jun 18 2009, 05:22PM
is the schottky diode need to be of any particular rating, for the 555 design ?
polop, Thu Jun 18 2009, 05:22PM
is the schottky diode need to be of any particular rating, for the 555 design ?
Re: clever led driver
GeordieBoy, Thu Jun 18 2009, 05:26PM
Schottky diode must block the full maximum supply voltage in reverse-bias, and be able to support the required output load current in forward conduction.
GeordieBoy, Thu Jun 18 2009, 05:26PM
Schottky diode must block the full maximum supply voltage in reverse-bias, and be able to support the required output load current in forward conduction.
Re: clever led driver
polop, Thu Jun 18 2009, 06:05PM
are these inductors alright?
they should i guess take the full current to the led. again 555 circuit
edit, i guess they are too low powered, winding my own i guess iis the best way i guess i have some torriodal cores from a psu, about 1cm diameter with perhaps a 4mm hole,
how critical is the exact inductance
polop, Thu Jun 18 2009, 06:05PM
are these inductors alright?
they should i guess take the full current to the led. again 555 circuit
edit, i guess they are too low powered, winding my own i guess iis the best way i guess i have some torriodal cores from a psu, about 1cm diameter with perhaps a 4mm hole,
how critical is the exact inductance
Re: clever led driver
jonny5, Thu Jun 18 2009, 06:56PM
The exact inductance isn't critical. More inductance reduces the current ripple, less inductance allows the use of physically smaller inductors. Less inductance (Buck inductor) increases the magnitude of the rate of current ramp (V = L * di/dt). Due to the constant off-time control, the circuit switches at a higher frequency for a smaller Buck inductance! Here's a sim of a 33uH inductor with 9 VDC IN.
Just a heads up: I have never built this circuit! The little experience I have had in electronics has taught me to be wary of simulations...they can't tell you everything. Real life is full of surprises...which makes it so much more interesting!
If you do build a variation of the 555-comparator circuit, let us know how it works!
Before I forget, the inductor shouldn't be allowed to saturate! The toroid power supply cores work nicely. Just remember that they decrease in inductance as the inductor current increases.
jonny5, Thu Jun 18 2009, 06:56PM
The exact inductance isn't critical. More inductance reduces the current ripple, less inductance allows the use of physically smaller inductors. Less inductance (Buck inductor) increases the magnitude of the rate of current ramp (V = L * di/dt). Due to the constant off-time control, the circuit switches at a higher frequency for a smaller Buck inductance! Here's a sim of a 33uH inductor with 9 VDC IN.
Just a heads up: I have never built this circuit! The little experience I have had in electronics has taught me to be wary of simulations...they can't tell you everything. Real life is full of surprises...which makes it so much more interesting!
If you do build a variation of the 555-comparator circuit, let us know how it works!
Before I forget, the inductor shouldn't be allowed to saturate! The toroid power supply cores work nicely. Just remember that they decrease in inductance as the inductor current increases.
Re: clever led driver
polop, Thu Jun 18 2009, 07:07PM
does the inductor need to take the full current of the led? if smaller inductance is better, and large is ok, can i use an arbetry amount there fore 20 or so 0.8mm diameter windings on the ~1cm toriod, a reasonable MOSFET, a reasonable schokkty diode, would that be a reasonable set of components?
. the other componants are non-changable and i have them already.
what components are the ones that sets the current output?
polop, Thu Jun 18 2009, 07:07PM
does the inductor need to take the full current of the led? if smaller inductance is better, and large is ok, can i use an arbetry amount there fore 20 or so 0.8mm diameter windings on the ~1cm toriod, a reasonable MOSFET, a reasonable schokkty diode, would that be a reasonable set of components?
. the other componants are non-changable and i have them already.
what components are the ones that sets the current output?
Re: clever led driver
ConKbot of Doom, Thu Jun 18 2009, 07:21PM
I have 5 of these badboys sitting next to me at the moment. I'm contemplating putting them into a maglight or something similar.(not all of them, though that would be awesome) I'd like to make my own driver, and I was too busy looking around at fancy switchmode converters and the like to think about a simple inductor and chopper circuit.
Given the fixed load of the circuit an inductor/chopper should be able to get a fairly high efficiency, correct?
I cant see the images here at work, but I'll come back to this at home, and maybe I can start messing with a driver circuit for one of these again.
ConKbot of Doom, Thu Jun 18 2009, 07:21PM
I have 5 of these badboys sitting next to me at the moment. I'm contemplating putting them into a maglight or something similar.(not all of them, though that would be awesome) I'd like to make my own driver, and I was too busy looking around at fancy switchmode converters and the like to think about a simple inductor and chopper circuit.
Given the fixed load of the circuit an inductor/chopper should be able to get a fairly high efficiency, correct?
I cant see the images here at work, but I'll come back to this at home, and maybe I can start messing with a driver circuit for one of these again.
Re: clever led driver
jonny5, Thu Jun 18 2009, 07:29PM
Indeed, the inductor carries the full LED current. As for using an arbitrary inductor...depends on how risky you wish to be! More turns on the core will increase inductance and simultaneously lower the peak saturation current. After all, only so much energy can be stored in the core before it saturates.
Since the 555 can't drive the PFET very hard, make sure that the PFET gate charge isn't too high! Otherwise, the switching losses may be significant.
The LED current is set by the reference voltage into the comparator and the voltage dropped across the current sense resistor. BY adjusting the voltage into the noninverting comparator input, the LED current can be changed. Good luck!
jonny5, Thu Jun 18 2009, 07:29PM
Indeed, the inductor carries the full LED current. As for using an arbitrary inductor...depends on how risky you wish to be! More turns on the core will increase inductance and simultaneously lower the peak saturation current. After all, only so much energy can be stored in the core before it saturates.
Since the 555 can't drive the PFET very hard, make sure that the PFET gate charge isn't too high! Otherwise, the switching losses may be significant.
The LED current is set by the reference voltage into the comparator and the voltage dropped across the current sense resistor. BY adjusting the voltage into the noninverting comparator input, the LED current can be changed. Good luck!
Re: clever led driver
polop, Thu Jun 18 2009, 08:25PM
ok ill go to maplin tommorow buy me a schottky diode and a decent mosfet. ill try this over the weekend
edit: that is a 50 milli ohm resistor yes, not a Megohm
and thats a 10uF electrolytic cap (there is no sign but large capacitance)
polop, Thu Jun 18 2009, 08:25PM
ok ill go to maplin tommorow buy me a schottky diode and a decent mosfet. ill try this over the weekend
edit: that is a 50 milli ohm resistor yes, not a Megohm
and thats a 10uF electrolytic cap (there is no sign but large capacitance)
Re: clever led driver
polop, Tue Jun 23 2009, 08:30PM
hello there
i have put the circuit together now but i cannot change the current, it is always 1 amp. i am varying the referance voltage from 0 to .5 and nothing changes.
test notes: if i take out the shottky diode it continues to work the same
inductor is 100uH, current is flowing through it to the led.
as far as i can se the circuit is wired as diagramed.
one thought, if the trig on the 555 is triggered by a low voltage, my comparitor when saturated low is still roughly 1.5 volts out, is that low engh?.
polop, Tue Jun 23 2009, 08:30PM
hello there
i have put the circuit together now but i cannot change the current, it is always 1 amp. i am varying the referance voltage from 0 to .5 and nothing changes.
test notes: if i take out the shottky diode it continues to work the same
inductor is 100uH, current is flowing through it to the led.
as far as i can se the circuit is wired as diagramed.
one thought, if the trig on the 555 is triggered by a low voltage, my comparitor when saturated low is still roughly 1.5 volts out, is that low engh?.
Re: clever led driver
jonny5, Tue Jun 23 2009, 09:20PM
The 1.5V minimum comparator voltage is probably OK. The following sim circuit
suggested that the 1.5V trigger voltage did indeed activate the 555 one-shot. Below is the simulated LED current at 9 VIN.
Unfortunately, the Schottky is an integral part of the Buck topology. As the P-FET turns OFF, the Schottly diode turns ON, allowing the inductor current to "free-wheel" during the switch OFF-time. Without the free-wheeling diode, the inductor current has no where to go! As such, the P-FET will experience a massive negative voltage spike! Unless the PFET is exceptionally rugged (dissipating the stored inductor energy via avalanche breakdown), the switch will fail. The following sim shows voltage peaking around -550V...which one would never see across an actual low-voltage PFET...yet one more example of simulation limitations.
Good luck!
jonny5, Tue Jun 23 2009, 09:20PM
The 1.5V minimum comparator voltage is probably OK. The following sim circuit
suggested that the 1.5V trigger voltage did indeed activate the 555 one-shot. Below is the simulated LED current at 9 VIN.
Unfortunately, the Schottky is an integral part of the Buck topology. As the P-FET turns OFF, the Schottly diode turns ON, allowing the inductor current to "free-wheel" during the switch OFF-time. Without the free-wheeling diode, the inductor current has no where to go! As such, the P-FET will experience a massive negative voltage spike! Unless the PFET is exceptionally rugged (dissipating the stored inductor energy via avalanche breakdown), the switch will fail. The following sim shows voltage peaking around -550V...which one would never see across an actual low-voltage PFET...yet one more example of simulation limitations.
Good luck!
Re: clever led driver
polop, Tue Jun 23 2009, 10:10PM
well i tested the mosfet it hafnt blow, i dont think it has turned off so there fore would not blow as current is just running through it and the inductor. therfore it is the current sencing that is not interuptinging th flow of current. pulling the trigger low with a wire turns the led off.
is there any simplifications that can be made to the circuit, like a simple transistor version or somthing
polop, Tue Jun 23 2009, 10:10PM
well i tested the mosfet it hafnt blow, i dont think it has turned off so there fore would not blow as current is just running through it and the inductor. therfore it is the current sencing that is not interuptinging th flow of current. pulling the trigger low with a wire turns the led off.
is there any simplifications that can be made to the circuit, like a simple transistor version or somthing
Re: clever led driver
jonny5, Wed Jun 24 2009, 07:07AM
Hi polop!
Simpler is almost always better. Here's an idea that uses a single comparator and the control loop phase-shifts to make a high powered LED driver:
The buck topology keeps relatively constant current through the high-powered LED (simulated by two smaller LEDs in parallel)by comparing the voltage dropped across the current-sense resistor to a regulated reference voltage. Since the rail-to-rail comparator output cannot drive the PFET gate directly, the totem-pole 2n3904/2n3906 pair source and sink the necessary gate currents to turn the switch on and off very quickly. Be careful with the phase shifts adding up around the control loop - the buck inductor, "output" 4.7uF capacitor, and low-pass filter off of the current-sense resistor all contribute to the total phase shifts. You might want to play around with a dummy load before risking the awesome LEDs!
Here's the simulated LED current:
I'm excited to try this circuit (have to find good LED's first)!
jonny5, Wed Jun 24 2009, 07:07AM
Hi polop!
Simpler is almost always better. Here's an idea that uses a single comparator and the control loop phase-shifts to make a high powered LED driver:
The buck topology keeps relatively constant current through the high-powered LED (simulated by two smaller LEDs in parallel)by comparing the voltage dropped across the current-sense resistor to a regulated reference voltage. Since the rail-to-rail comparator output cannot drive the PFET gate directly, the totem-pole 2n3904/2n3906 pair source and sink the necessary gate currents to turn the switch on and off very quickly. Be careful with the phase shifts adding up around the control loop - the buck inductor, "output" 4.7uF capacitor, and low-pass filter off of the current-sense resistor all contribute to the total phase shifts. You might want to play around with a dummy load before risking the awesome LEDs!
Here's the simulated LED current:
I'm excited to try this circuit (have to find good LED's first)!
Re: clever led driver
polop, Wed Jun 24 2009, 04:48PM
is there a chip that youguys would reccomend that does all the timing and things for me, ie the only components are the chip the inductor and the diode, that will regulate anywere between 0 and 3amps ? these solutions although they inerest me more, get me so fustrated because i do not have any equipment to dest them (apart from a hardly working ddm)
polop, Wed Jun 24 2009, 04:48PM
is there a chip that youguys would reccomend that does all the timing and things for me, ie the only components are the chip the inductor and the diode, that will regulate anywere between 0 and 3amps ? these solutions although they inerest me more, get me so fustrated because i do not have any equipment to dest them (apart from a hardly working ddm)
Re: clever led driver
Dr. Dark Current, Wed Jun 24 2009, 06:12PM
and
Dr. Dark Current, Wed Jun 24 2009, 06:12PM
polop wrote ...
is there a chip that youguys would reccomend that does all the timing and things for me, ie the only components are the chip the inductor and the diode, that will regulate anywere between 0 and 3amps ? these solutions although they inerest me more, get me so fustrated because i do not have any equipment to dest them (apart from a hardly working ddm)
National and Maxim have some, try here is there a chip that youguys would reccomend that does all the timing and things for me, ie the only components are the chip the inductor and the diode, that will regulate anywere between 0 and 3amps ? these solutions although they inerest me more, get me so fustrated because i do not have any equipment to dest them (apart from a hardly working ddm)
and Re: clever led driver
polop, Thu Jun 25 2009, 09:16PM
there is none that i can find that are easily solderable, all of them are in micro packages os are not capaple of driving a 2.8A led, any more for any more
polop, Thu Jun 25 2009, 09:16PM
there is none that i can find that are easily solderable, all of them are in micro packages os are not capaple of driving a 2.8A led, any more for any more
Re: clever led driver
lpfthings, Sun Jul 05 2009, 08:02AM
A bit late, but you can get a breakout board for the small packages. That will make them easier to work with. Are you thinking of turning it into a portable type thing? And I assume you mean the SSC P7 LED? I bought a torch from dealextreme.com for about $36US that uses the same LED, VERY bright!
lpfthings, Sun Jul 05 2009, 08:02AM
A bit late, but you can get a breakout board for the small packages. That will make them easier to work with. Are you thinking of turning it into a portable type thing? And I assume you mean the SSC P7 LED? I bought a torch from dealextreme.com for about $36US that uses the same LED, VERY bright!
Re: clever led driver
ConKbot of Doom, Mon Jul 06 2009, 08:49PM
I'm interested in something like this too, simple easy to make compact (SOT-5 or 6 comparator and drive transistors and a SOT223 or larger mosfet...) Definitely post your results, I'll do the same once I get around to making it.
ConKbot of Doom, Mon Jul 06 2009, 08:49PM
jonny5 wrote ...
Hi polop!
Simpler is almost always better. Here's an idea that uses a single comparator and the control loop phase-shifts to make a high powered LED driver:
The buck topology keeps relatively constant current through the high-powered LED (simulated by two smaller LEDs in parallel)by comparing the voltage dropped across the current-sense resistor to a regulated reference voltage. Since the rail-to-rail comparator output cannot drive the PFET gate directly, the totem-pole 2n3904/2n3906 pair source and sink the necessary gate currents to turn the switch on and off very quickly. Be careful with the phase shifts adding up around the control loop - the buck inductor, "output" 4.7uF capacitor, and low-pass filter off of the current-sense resistor all contribute to the total phase shifts. You might want to play around with a dummy load before risking the awesome LEDs!
Here's the simulated LED current:
I'm excited to try this circuit (have to find good LED's first)!
Hi polop!
Simpler is almost always better. Here's an idea that uses a single comparator and the control loop phase-shifts to make a high powered LED driver:
The buck topology keeps relatively constant current through the high-powered LED (simulated by two smaller LEDs in parallel)by comparing the voltage dropped across the current-sense resistor to a regulated reference voltage. Since the rail-to-rail comparator output cannot drive the PFET gate directly, the totem-pole 2n3904/2n3906 pair source and sink the necessary gate currents to turn the switch on and off very quickly. Be careful with the phase shifts adding up around the control loop - the buck inductor, "output" 4.7uF capacitor, and low-pass filter off of the current-sense resistor all contribute to the total phase shifts. You might want to play around with a dummy load before risking the awesome LEDs!
Here's the simulated LED current:
I'm excited to try this circuit (have to find good LED's first)!
I'm interested in something like this too, simple easy to make compact (SOT-5 or 6 comparator and drive transistors and a SOT223 or larger mosfet...) Definitely post your results, I'll do the same once I get around to making it.
Re: clever led driver
Avi, Thu Jul 16 2009, 04:27PM
I have one of these LEDs too.
I know LM317 is not the most efficient solution, but I tried it anyway, in-fact I tried up to 6 in parallel with a 0.47 ohm current adjust resistor.
from a rectified 12v source, i only obtained 2.2A, and less with less voltage input (still above 3v more then led drive voltage)
Avi, Thu Jul 16 2009, 04:27PM
I have one of these LEDs too.
I know LM317 is not the most efficient solution, but I tried it anyway, in-fact I tried up to 6 in parallel with a 0.47 ohm current adjust resistor.
from a rectified 12v source, i only obtained 2.2A, and less with less voltage input (still above 3v more then led drive voltage)
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