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Old 09-04-2010, 06:53 PM #17
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Default Re: Looking for general help in understanding regulator design

so one thing im hearing is that i'd be better off trying an adjustable voltage regulator like an LM317 instead of the fixed 5V.

i also need to re-do the equation and add RL=2.6ohm. i am not sure if this would be correct tho, the Io current value in the datasheet seems to only depend on the value of R1, RL is shown as variable (i think that's what the arrow across it means...)

speaking of the supply output, it's rated for 10.6V and 1.32A. however, I know i'm getting >12V from it, so the current could also be different. i have another one from GF's scanner ( ) that I plan on trying as well. is there a way to measure "hot" resistance of a lightbulb, i dont think i can let the whole circuit run and just measure across its terminals?

i am leaving for Connecticut with the GF and will only be back late on sunday. i feel bad for everyone giving me advice and not posting anything back but monday is a holiday so i'll be able to try your suggestions then!


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Old 09-04-2010, 06:59 PM #18
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Default Re: Looking for general help in understanding regulator design

We will still be here to help. The bulb is still lit in the picture, so that it might have an effect depending on the exact wiring. Yes the LM317 would probably be a better choice. I don't mind helping. I'm a bit rusty, but it's like riding a bike You don't forget how.
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Old 09-04-2010, 10:55 PM #19
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Default Re: Looking for general help in understanding regulator design

Quote:
is there a way to measure "hot" resistance of a lightbulb
Not really, but you can calculate it if you know the current through it and the voltage across it, voltage/current = resistance.
Another way would be if you are lycky enough to have the power written on the bulb, voltage*voltage/power = resistance. **
The actual resistance at your operating temperature will be somewhere between the 2,6 Ohm measured cold and resistance at nominal voltage and power output.

** E.g if it was 12V 5W would give 12*12/5 = 28,8 Ohm
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Old 09-05-2010, 12:21 PM #20
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Default Re: Looking for general help in understanding regulator design

Keep in mind that bulbs filaments resistance is always more low, when it's cold, and increase when it turn incandescent ..... there are special instruments, for measure this, but the better way is still the current system.

Measure the resistance in cold state with a multimeter, then use a power supply that can be used as current source (or one that have a current limiter), an amperometer and a voltmeter ..... place the amperometer in serie with the bulb, and the voltmeter directly in parallel to the bulb ..... start with current at zero, increase it until the filament just start to become dark orange, and note the current and voltage ..... do the same for a current that glow the filament approximatively half the full luminosity, and then with the current at full luminosity ..... then divide the voltage on the bulb for the related current, and you have the resistance of the filament in that condition.

These 4 readings are enough for give you an approximative resistance curve (ofcourse, more measures you take, more your curve is precise, but if you want just to have an indication and not a lab graphic, 4 or 5 measures are usually enough ..... if instead you want a more precise curve, you can take a measure each, say, 100mA, or 50mA, and draw a precise curve at the end of the serie)

If you don't have a power supply that let you set the current steps, you can proceed the same, just increasing the voltage slowly, keeping an eye on the amperometer ..... means, doing it manually, using the amperometer in the circuit for stop when the current reach the level you want for each reading.
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Old 09-05-2010, 12:58 PM #21
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Default Re: Looking for general help in understanding regulator design

I just checked the Data Sheet on the LTC4054...

I would go that route for charging Li-Ion batteries...

http://www.datasheetcatalog.org/data...y/405442xf.pdf

It is a much simpler circuit and the Data Sheet has
application notes and drawings...

If Li-Ion batteries are not monitored correctly and
are over charged and they over heat.. they could
catch fire or even explode..


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Old 09-05-2010, 01:24 PM #22
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Default Re: Looking for general help in understanding regulator design

Sorry lasersbee, your link lost the final "f"

http://www.datasheetcatalog.org/data...y/405442xf.pdf
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Old 09-05-2010, 02:00 PM #23
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Default Re: Looking for general help in understanding regulator design

Lightbulbs make shitty test loads for anything, as described above.

For a constant voltage source they start out as a near short circuit, so it has to be able to source a lot of current to get the filament warm. Once its warm, they're fine.

Current sources don't like lightbulbs at all - they tend to burn them out if they can source enough voltage to do so. If they don't, it will work fine regardless of lamp temperature, but you can use a monkey wrench as a test load for a current source too
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Old 09-05-2010, 02:24 PM #24
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Default Re: Looking for general help in understanding regulator design

Quote:
but you can use a monkey wrench as a test load for a current source too
Certainly, just remember the diodes to ensure a forward voltage.
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Old 09-05-2010, 03:10 PM #25
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Default Re: Looking for general help in understanding regulator design

Quote:
Originally Posted by HIMNL9 View Post
Sorry lasersbee, your link lost the final "f"

http://www.datasheetcatalog.org/data...y/405442xf.pdf
.... Thanks HIMNL9.....Fixed...
Not enough coffee this morning....


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Old 09-07-2010, 01:51 PM #26
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Default Re: Looking for general help in understanding regulator design

I got one of those breadboards, sure they are convenient, but also a bit confusing.
I did not look carefully enough at the hole line-up and were arrogant enough to go strait to diode.
Fortunately it was only a 300mW red that got exposed to 12V direct drive.

I have soldered together a test load, with wires tinned for breadboard, now.
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Old 09-08-2010, 01:59 AM #27
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Default Re: Looking for general help in understanding regulator design

Toke, I know what you meant by confusing oh, I hope your Red is OK!

Trip to CT turned out to be very productive - I borrowed a Fluke 79-III I also changed input power supplies, the new one puts out 15.83V. The combination of these two factors now produces consistent results that match calculated!

First, the RL value. Using the basic circuit from Fig.13 and measuring with the Fluke, RL=4.96V/0.355A=14ohm. Why not 5.0V? Measured temp of the heatsink with an IR thermometer at 65C. From the datasheet Vo reduces by 1.1mV for each 1C from 25C. 5.0-(65-25)*1.1=4.96, love it when numbers line up so nicely

Second, Fig.14 circuit. Using 3 random R1 values I had in the board. I measured Id=0.003A.
R1=10.2, Vxx=4.37, Io=0.431, measured Io=0.468A (VL=9.15, RL=19.55)
R1=20, Vxx=5.02, Io=0.254, measured Io=0.270A (VL=2.118, RL=7.84)
R1=217, Vxx=5.06, Io=0.026, measured Io=0.035A (VL=0.083, RL=2.37)

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Old 09-08-2010, 02:01 AM #28
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Default Re: Looking for general help in understanding regulator design

Well Done Comradmax!!

Congrats!
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Old 09-08-2010, 03:41 AM #29
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Default Re: Looking for general help in understanding regulator design

Sounds like great progress.

(My diode died, another died when I tried to cram a ground down LM317 and resistors into a too narrow host, something must have shorted, 3 left. At >$5 at GB this is not too sad.)
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Old 09-08-2010, 03:59 AM #30
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Default Re: Looking for general help in understanding regulator design

Toke at least They weren't 445nm or 405nm. Cramming is only good for exams and not electronics IMO.
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Old 09-08-2010, 05:58 PM #31
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Default Re: Looking for general help in understanding regulator design

i had some phone meetings at work, so there was time to make these
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Old 09-27-2010, 02:53 PM #32
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Default Re: Looking for general help in understanding regulator design

I'd like to resurrect this thread because yesterday I managed to make my first linear driver, make my first laser, then kill my first laser

I took what I had already:
* battery: 9V
* V-reg chip: LM78L05
* resistors: 2x 100Ohm 1/4W
* capacitors: 1uF, 0.1uF
* Aixiz: stock acrylic
* LD: extracted from PHR-803T sled

Using 5 diodes for my test-load I got a 4.2V drop and found the reistor value to set 70mA current. I didnt have 50Ohm, so I used 2x100, this gives me 1/2W rating on them as well. This powered on my PHR and it looked great, beam and color look much better than my 405nm $9 pointer! I think this is also due to higher power output making the beam more visible Focused laser lit a match's head in 5s, and this was when I got greedy... I replaced the 50Ohm with 33Ohm without using the test-load, thinking it would result in 100mA, but it actually went up to 140mA! LD must have died instantly, live and learn

Disappointed I went on to solder a version that fits inside Aixiz. The idea is to have just 2 wires coming out that I connect to a switch and battery. I tested current and it gives the same 70mA, but I will have to extract another PHR and try the whole thing soldered up in the module. It doesnt look like anything is shorting to the case, but I will wrap the driver in electrical tape for good measure anyway.

Total cost in parts for this project is ~$15, I plan to put this inside a mini-altoids box (Altoids Gum) with a momentary push-button on top Thanks again to people that help, and for all those great threads I found with search
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