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How do I exend supply range of LM317 for CC mode?

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Actually I think I have found a partial answer - a floating LM317 regulator with a zener between it's input and output
I remember a specific failure mode on the "floating" 317 circuits with HV involved. There's usually some capacitors some where and at turn on they can force too much voltage across the LM317. Remember having this argument with the marketing idiots at NSC. I wanted to take the "HV floating" apps off the data sheet but nobody ever listened.
 
I remember a specific failure mode on the "floating" 317 circuits with HV involved. There's usually some capacitors some where and at turn on they can force too much voltage across the LM317. Remember having this argument with the marketing idiots at NSC. I wanted to take the "HV floating" apps off the data sheet but nobody ever listened.
Hy bounty,

Nice to see some posts from you again.

I found the same problem that you state with the LM317/LM337 and other floating high, voltage-circuits. They are OK on paper in a steady state condition but get killed at turn on and turn-off. Spikes from the mains supply can also kill them. The other thing that is needed is a rectifier diode from the LM317 Input to Output terminals to prevent reverse voltages.

We had an equipment with a floating arrangement that had a high failure rate in the field, and I just could not convince the design authorities what the problem was. Instead they came up with all sorts of band aid remedies. This went on for some time and of course there was plenty of hot air, reports and studies but in the end, after a touch of heat from the MD, they simply changed the failing pass transistor for a high voltage version and the equipment never failed again.:arghh:

spec
 
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The one I linked to has a zener between input and output to protect against exactly this. It also has a zener between output and adj but no one on stackexchange is sure what it's for.
Speaking of zeners...
I've been playing some more with the limiting circuit I linked to in #5, in LTSpice. Big difference between using 1n... series zeners and using bzx... series zeners. The bzx series need more current...
I'll try building it on my next day off. Sorted out an ancient mosfet and ancient bc238 for it.
 
is there a reason why you cant put the 66 LED's in parallel? .. the 317 TO-3 version is a current beast.
this would allow dividing the voltage fluctuation issues on input side to more manageable scenario
 
Because then I would need a low voltage supply, not much of a problem in its own right, but the led's would need current balancing resistors - which means extra parts, extra soldering, and wasted power.
 
I've built a working supply now. Thanks for all the help and suggestions everybody!
I went with the switching voltage limiter after all.
So far I have built 1 board with 1 1/2 of the LED strings on it, (ie, a complete 66, plus 33) still got 99 to solder. Still waiting for the 10uF capacitors to arrive in the post, but it's working ok without. Also need to build input filter for the circuit. Tried it with a dummy load to get the full current.
Running it off an isolation transformer at the moment.
Schematic attached.
 

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  • Schematic_Design__led-driver_sch_Linux-generated_files.pdf
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Neat design and well drawn schematic. I hope the circuit proves to be reliable.

spec
 
Thanks :)
Me too. But everything was cheap or free and it will only run for short amounts of time, so I'll probably never find out if it's unreliable!
 
Because then I would need a low voltage supply, not much of a problem in its own right, but the led's would need current balancing resistors - which means extra parts, extra soldering, and wasted power.

while those points do hold merit,
my concern is based in what ive seen in the industry with series LED lighting, since i own a repair shop-
if one goes out, your customer will be calling you, or a repair tech- since the string will be dead. your saving grace may be the intermittant usage of this circuit
best of luck,
jim
 
Back before mass market LED's came down into the price range I found fitting I built a number of LED lights with large numbers of small LED's in series like you are doing.

The simplest and most durable LED driver circuits I found were nothing more than a capacitively coupled design with a large value capacitor on the LED side of the bridge rectifier to keep the LED side voltage stable during short power transient events.

The next best hybrid that had actual active current limiting was that circuit but with a standard LM317 set up as a CC regulator, like what you are doing, where the capacitive impedance of the input was set up to provide minimal to no active voltage drop across the LM317 at normal live voltages. That worked well too and had high overall efficiency in normal working conditions.
 
while those points do hold merit,
my concern is based in what ive seen in the industry with series LED lighting, since i own a repair shop-
if one goes out, your customer will be calling you, or a repair tech- since the string will be dead. your saving grace may be the intermittant usage of this circuit
best of luck,
jim
Sorry Jim, this is a project for me to use for myself! There is no customer.
Though it's a good point to remember in case I ever do anything like this for someone else!
 
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Lots of UV - makes your eyes go funny! The couple of odd placed LED's are due to the geometry of the perf boards, though it should work perfectly well without them. I wanted to check voltages before messing with the numbers. Only the resistors get hot, nothing else.
Exposed a test piece of dry film very effectively. Waiting for a timer to arrive in the post so I can do calibrated exposures.
I made a (not very good) deep box that the array sits at the bottom of it. Haven't had time to try making any boards with it yet.
glowing.jpg supply.jpg
 
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Back before mass market LED's came down into the price range I found fitting I built a number of LED lights with large numbers of small LED's in series like you are doing.

The simplest and most durable LED driver circuits I found were nothing more than a capacitively coupled design with a large value capacitor on the LED side of the bridge rectifier to keep the LED side voltage stable during short power transient events.

The next best hybrid that had actual active current limiting was that circuit but with a standard LM317 set up as a CC regulator, like what you are doing, where the capacitive impedance of the input was set up to provide minimal to no active voltage drop across the LM317 at normal live voltages. That worked well too and had high overall efficiency in normal working conditions.
I actually thought about using series capacitor supplies, before I decided I wanted something more regulated. I was going to use just the LM317's + resistors, until I discovered the variance in mains voltage (and of course Mike pointed out the variance in LED voltage)
 
I actually thought about using series capacitor supplies, before I decided I wanted something more regulated. I was going to use just the LM317's + resistors, until I discovered the variance in mains voltage (and of course Mike pointed out the variance in LED voltage)

Yea back when I was playing with that stuff I started out over engineering things as well but the more I experimented with it the more it became obvious that LED's are pretty forgiving little devices when put together in large numbers. :cool:

Most of what I used had either 20 or 30 ma ratings but proved to be able take substantially more than that for short periods without any degree of diminished performance which thus ruled out the need for precision voltage and current regulation.

As far as longevity of operation went the simpler minimal component and regulation based designs lasted way longer than the fancy designs that had active voltage and current control designed into them. there was simply less power end components to fail for any number of reasons. ;)
 
Neat design and well drawn schematic. I hope the circuit proves to be reliable.

spec
I second that too. Very well laid out perf-board construction.

When I've worked with UV lights, I also found that my eyes get irritated and wobbly.
I ignore whether long term exposure could burn your retina or not. But for safety, I bought some inexpensive yellow-colored sunglasses with at least UV-A protection rating.
 
Just made a "do nothing" test board with it. After about 10 attempts to get the process right, I got:
thinnest track: 5mil
smallest gap between tracks: 5mil
smallest hole in pad: 10mil (I did a 5 mil one but it it didn't etch. I think I didn't clean the unexposed film in the sodium carbonate long enough)
finest detail: target shaped pad with 3mil detail. One of the arms has gone
fine gap between large areas: I did a ground plane, then the board outline, then spare copper outside the outline. So the gap is 5mil. It got partly filled on one side but that might have been a sharpie accident where I covered the spare copper around the test area.

Mounted the board in a cutout in some cardboard before putting it through the laminator. All previous attempts were using a clothes iron, which had worked well when I made my first board to test the film a while ago. Exposed on top of my UV box for 23 elephants (since I don't have a timer yet). The film is a bit wrinkly so the iron didn't work so well this time.

Only using a single transparency - I know a lot of people recommend a double layer. Maybe I'll need it for bigger boards
.test-board.jpg
 
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