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Author Topic: LM107 OpAmp & LM338 Voltage Regulator  (Read 27542 times)

Dave_W_Cooksey

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LM107 OpAmp & LM338 Voltage Regulator
« on: June 01, 2009, 09:05:39 PM »
Hi i need:

1- LM107 Op-Amp
2- LM338 Voltage Regulator
1- 2 Watt Reostat

if any one has these items for sale let me know please

David
« Last Edit: June 02, 2009, 12:39:07 AM by Dave_W_Cooksey »

TinselKoala

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Re: LM107 OpAmp & LM338 Voltage Regulator
« Reply #1 on: June 02, 2009, 09:13:20 PM »
Hi i need:

1- LM107 Op-Amp
2- LM338 Voltage Regulator
1- 2 Watt Reostat

if any one has these items for sale let me know please

David

The 338 comes in either the TO-3 case (LM338K) or the TO-220 package (LM338T). Which do you need?

DigiKey lists the LM338K for $32.37 ea. and the LM338T for $2.70 ea.
Both are rated 5 amps, so unless you really need the TO-3 package for some reason, the TO-220 will really save some bucks.

The LM107 is available in a can or a DIP, and crosses to (LM107H) MC1741, and (LM107L) MC174. Do you need a specific package, or will either one do? Do you need the freq-compensated version?

And generally when ordering Rheostats one would like to know the Resistance rating as well as the power handling capacity.

poynt99

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Re: LM107 OpAmp & LM338 Voltage Regulator
« Reply #2 on: June 03, 2009, 05:24:20 AM »
There are much better pin for pin replacements (dozens) for the old LM107 / MC1741. Why would you want this one specifically? What is your application?

Buy the LM338T from Digikey as TK suggested.

.99

Dave_W_Cooksey

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Re: LM107 OpAmp & LM338 Voltage Regulator
« Reply #3 on: June 03, 2009, 05:26:14 PM »
Hi guys here is the drawing i am trying to put together
i found this drawing on the net and wanted to build it,
yes i am looking for those TO-220's

Nothing even mentioned about the input voltage was included
w/ the drawing.

What im trying todo is be able to light up 2- M16 12V 55Watt
Lights

55 watts / 12v = 4.583 amps * 2 = 9.166 amps

For the LM107 i was thinking the 8 pin model
Need a LM107H,  MC1741, or MC174

Reostat  2watt 2K

« Last Edit: June 04, 2009, 01:26:32 AM by Dave_W_Cooksey »

derricka

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Re: LM107 OpAmp & LM338 Voltage Regulator
« Reply #4 on: June 04, 2009, 02:19:43 AM »
This circuit appears to be an adjustable voltage regulator, with a set 10 Amp limit.  If you just want to power a pair of lights, from mains power, this circuit alone is not enough (you would still need an unregulated DC power supply to feed this circuit). But unless you require adjustable brightness, or extreme brightness stability, this circuit is both overkill, and waste-full.  If you just need basic illumination, all you need is a transformer, 12 VAC output rated at 12 Amps (or more)  M-16 halogen bulbs don't mind AC.  Another option is to use a small switching power supply (available from many lighting shops), intended to power 12V Halogen bulbs. These are small, light, and highly efficient.

TinselKoala

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Re: LM107 OpAmp & LM338 Voltage Regulator
« Reply #5 on: June 04, 2009, 03:44:35 AM »
I agree. That's a screwy circuit to use for the stated application, unless there's something you aren't telling us.

Plus to get 20 volts out you'd have to put 21 or 22 volts in, and that's close to or above the rating for the op-amp, as far as I can tell.

If you are looking just for controllable power for illumination using those bulbs, you should look for SCR or Triac or MOSFET based lamp dimmer or motor control circuits. The components are cheap and the circuits are efficient.
Here's a link to one I found. To get more output power you can just duplicate the output stage and parallel it to the pulse generator stage.
http://www.ctshooter.com/dimmer.html
The most expensive component is the box.

poynt99

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Re: LM107 OpAmp & LM338 Voltage Regulator
« Reply #6 on: June 04, 2009, 06:04:42 AM »
Dave,

That drawing is taken right from the specification sheet, but there is no description of the circuit.

Do you need to vary the output voltage for dimming?

Assuming that circuit works alright, a suitable and available replacement for the LM107 might be the LM318. It is a much faster op-amp, but speed is not required for this application. One small drawback is a 4mV offset voltage, vs. 1.5mV with the LM107. It is good up to +/- 20V though, so only a couple volts less than the LM107. The LM318 is cheap at under $2.

.99

Dave_W_Cooksey

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Re: LM107 OpAmp & LM338 Voltage Regulator
« Reply #7 on: June 04, 2009, 06:10:09 AM »
Hi TK the output would be only 12 volts which the lights need
and not 20 volts.

If you guys know of a simple circuit that can handle the lights
please post a drawing of it.

David

derricka

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Re: LM107 OpAmp & LM338 Voltage Regulator
« Reply #8 on: June 04, 2009, 12:20:54 PM »
Lighting4Art.com sells a 75 watt electronic switching transformer for $19.50 which would power one 55 watt bulb. They also sell a 150 watt transformer which would power two of your bulbs for $63
Input is 120 volts for these transformers.
Hookup is easy, two wires in, two wires out.
(Cannot be used with 120volt dimmers- 12volt dimmers ok)

http://www.lighting4art.com/shop1.asp?group=ETX

http://www.translitesonoma.com/pdfs/Transformers/PS-LVT-0207.pdf

poynt99

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Re: LM107 OpAmp & LM338 Voltage Regulator
« Reply #9 on: June 04, 2009, 02:41:38 PM »
Dave,

Whether you need dimming or not is an important question before we continue. If not, you're off to the races with something simple. If yes, then that's a slightly different story.

The 150W transformer derricka suggested might be the best solution, however I have not been able to find a diagram for how to hook up a dimmer, nor what to use for it. It does come with a diagram apparently. It's cheaper here....only $40:
http://www.lightology.com/index.cfm/method-light.store_profile/sku-1244XF-LVT1511-ELEAC-ALST/dept-Power%20Supply/szdept_label-

A bit of a diagram here:
http://www.lightsearch.com/Lightech2006/pdf/LVT-151%20AC.pdf

.99

TinselKoala

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Re: LM107 OpAmp & LM338 Voltage Regulator
« Reply #10 on: June 05, 2009, 12:55:49 AM »
Dave, did you take a look at the link I posted earlier? The circuit there is cheap, small, reliable, and you can also use it to control DC motor speed. (It's a basic PWM power supply).
If you don't get the fancy box and knob, the parts will cost you under 10 dollars, so you can make one for each lamp and still spend less than the cost of that transformer.
The diagram is about halfway down, and there's clear explanations of how and why it works.

http://www.ctshooter.com/dimmer.html

derricka

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Re: LM107 OpAmp & LM338 Voltage Regulator
« Reply #11 on: June 05, 2009, 06:02:01 AM »
Hi Dave,
I have looked over Tinsel Koala's dimmer circuit, and it appears to be a great choice to go with the power supply I recommended earlier.
The MOSFET will need to be upgraded if you want to dim two 50 watt bulbs together, so let me know if you intend to do this.

If you really didn't want to spend any time soldering parts together, you could consider the lighting4art.com C150 magnetic transformer rated at 150 watts. This one is a bit bigger, heavier and more expensive ($108.19), than the power supply I suggested, but will work with industry standard 120 volt dimmers. I should warn you that 120 volt dimmers usually flicker at low brightness levels.  The circuit suggested by TK should do a better job, as it operates at a higher frequency, but if you want to use TK's circuit, use the electronic supply I suggested before.