LED Photo studio strobe

I did not look at the datasheet for your LEDs but three white LEDs in series without a current-limiting resistor might need 12.3V or more to have the very high current that you want.
As they warm up their current will increase which might destroy them.

I think the resistors are 15 ohm, not 150.

If you built it on a breadboard it may just be contact resistance. I would expect it to be a little low at 12 volts since the target is probably 300ma max @ 14 volts.

using the factory setup, can you measure the voltage across a few of the LEDs and the resistor while powered directly off you 12 volt supply and the voltage of the supply. I'm working on some ideas I have.

I think I like this idea. Lots of people don't like parallel LEDs, but I do it all the time and haven't had a problem yet. Other wise put a LM317 at the end of every string, .12 US each for the .1 amp TO92 style

kinarfi
Unloaded source - 12.08V
Under load source voltage - 11.95V
Voltage on resistor - 2.45V
Voltage on LED1 - 3.2V
Voltage on LED2, 3 - 3.14V

You have a soft spot for LM317, right? The IRFZ44N has plenty of load current to play around, it is rated at 49A and I really have to make use of them otherwise I will be stuck with them.

PS: I also have some 2N7000 and a couple of LM317 so I can try your schematic. Either way, I have to shunt all resistors and the give it a try.

One thing to look at in the spec sheets is the Rds on, the 2N2000, 2N7002 has a Rds of 5 to 7.5, bad, yourIRFZ44N has an Rds = 17.5mΩ, good, forget about the 2n7002, it was just a number I knew, use your IRFZ44N. When it comes to current manipulation, I like devices that have a feed back like the LM317 & LT1270A, 1.25v, so to have a current of xxx ma, you divide 1.25v by xxxma and you have the resistance needed for that current. If you have the overhead voltage to work with, they're great, they're cheap too. For you project, your power supply is very close to the minimum, IMHO.

Nedix said:

kinarfi
Unloaded source - 12.08V
Under load source voltage - 11.95V - 2.45 = 9.5v
Voltage on resistor - 2.45V÷150=16.33333333333333333333333333333 ma
Voltage on LED1 - 3.2V
Voltage on LED2, 3 - 3.14V average around 3.18 x 3 = 9.54 v

You have a soft spot for LM317, right? The IRFZ44N has plenty of load current to play around, it is rated at 49A and I really have to make use of them otherwise I will be stuck with them.

PS: I also have some 2N7000 and a couple of LM317 so I can try your schematic. Either way, I have to shunt all resistors and the give it a try.

Click to expand...

Is there an a voltage adjustment pot on your power supply? If so you may want to boost it to 13 or 14v. The LM317 wants a little over 2 volts, if I remember correctly.

What do you need these figures for? Yes, the power supply has a little trim and I can go up to 13 something V.

My bad. I read you post as .3 amps per string for some reason. Kinarfi is trying to understand where your problem lies. Seems he has it. The voltage drop across your diodes is about 3.18 volts each at 16.3 ma. So for 3 about 9.54 volts. Then at 16.3 ma the 150 ohm resistor drops about 2.45 volts which adds up to your supply voltage. (+/-) 261 ma per panel (16 strings of 3 in series)
So you have 2 choices.
You can raise your supply voltage to lets say 13 volts. This will make the drop across the diodes go up just a little - lets say to 3.2 volts. Now we have 9.6 across the diodes and 3.4 across the resistor. your current should now be about 22.6ma each string or 362ma.
The other alternative is to make the resistor smaller and still run at 12 volts. Lets say we make it 130 ohms. So we have 12 - 9.6 or 2.4 volts across 130 ohms for a current of 18.5 ma per string or 295 ma. per panel.
I still can't figure out why the current wasn't higher with all 5 panels. It might be your power supply drops a bit or there is a big range in the panels.

Option one, 1 LM317 per panel, option 2, 1 small LM317 per string, option 3, all panels in series and use a LT1270A and put all panels in series. You'll need a 100v cap and an inductor.
PM coming.


In spice, if you have a component and put M=2 next to it, it means you have 2 in parallel, I thought N meant series, but spice isn't recognising it. What is correct letter