Please help someone who knows nothing

[serpa4]

Hello. First time here and posting.
I purchased an LED array to use in place of my incandescent light bulbs in my motor home. The incandescent lights use 1.5 amps each and the LED array only used 150 milliamps. Here is a description of the array:
25 led High Powered SMT Array Outfitted with 25 of the latest SMT High Powered LEDs. Designed especially for overhead lighting & angled sockets & applications requiring a lot of light.
Flexible wires to base allows the to be adjusted to any angle
25 Led array measures 38mm x 38mm x 10mm thick
The problem with LEDs in motor homes is that they are either:
1) Not bright enough
2) Too blue in color
3) Short lived due to high charge rates of the batteries. My on board charger will put out up to 14.5 - 15 volts.

I have found this array to be white and bright, but it’s not regulated. I have looked at a lot of 3-pin 12vdc regulators online, but most have a very high drop out voltage, like 1 to 1.5 volts. This doesn’t work since I often see 11 volts or sometimes 10.8 with very low batteries while camping. Then you throw in the voltage drop, and the LEDs are extremely dim or don’t light at lower voltages due to dropout. This LED array does work fine at 10.5 volts and is pretty bright.


I think this project would be exactly what I need.
http://www.drbob.net/project/powersupply/linear/12v1alvdfxd/index.html
It’s a 12 volt regulator with only .1 volt drop. So, even with a dead battery of 10.8 volts, the led with the regulator’s dropout voltage (.1volts) would leave the array with 10.7 volts. I have tested the array at 10.7 volts and it works fine and is still bright. I need the regulator to be small to fit inside the lamp enclosure in my motor home. It took me 2 days to figure out what 12vdc regulator I needed (didn’t work). I know nothing about electronics at all. I don’t know how to read the diagram or what parts to buy since I don’t even know what they do. Please help if possible. For example, the schematic shows a LM324 with 3 lines coming out of it. I looked at the schematic for the LM324A and it shows 14 pins. I have no clue on how to wire this. What is + and what is - and what is the line coming out of the point of the LM324 schematic? Then there is another triangle in the center of the regulator schematic and I don’t know what that is or how to wire it. There is also an IRF9520 in the regulator schematic. I looked at the data sheet on an IRF 9520 and it shows a D/G/S. I don’t know what goes to Gate, Source, and Drain. Can someone tell me something like the “drain goes to R5 (3.3K resistor) or what ever? I cannot find a 25uF 16WV anywhere on line. Where would I get one? Also, the parts list and schematic doesn’t match. The schematic shows a 25uF 16WV capacitor but it is not listed on the parts list. The parts list shows a 25 uF 50WV electrolytic capacitor but it isn’t show on the schematic.

Anyone have a minute to tell me how to build this item? It would greatly help me. Thank you.
I have a bread board, multi meter, and a variable DC power supply. I have very very basic knowledge on electronics.
Links:
LED array (25 led High Powered SMT Array - Outfitted with 25 of the latest SMT High Powered LEDs )
http://autolumination.com/otherleds.htm
Dr Bob’s project: Low dropout voltage regulator. His email is not working.
http://www.drbob.net/project/powersupply/linear/12v1alvdfxd/index.html

 

[saeed_pk]

Hello,
You got a very serious problem. your incandescent lights use 1.5 amps now
you have 25 LED's 150 mA each so u should have

150×25=3750 mA or 3.75 A

See if your Source( Battery) does not give such a big current. this condition arises when you connect them in parallel.
you have to make some series parallel combination to drive
one more thing you can do
connect a 150Ω resistor with each LED and connect them in parallel Do not change
the voltage otherwise u might have dimmed output .

 

[House_Cat]

saeed_pk-
Your analysis is completly incorrect. The LEDs would not be in parallel, they would be in series - the total current is therefore 150ma as serpa4 has stated.

serpa4 -
The triangle symbol in the schematic denotes an "Operational Amplifier" which is a basic building block for many different types of electronic circuits. If you take a look at a data sheet for the 14pin device, you will see the same schematic symbol used in a top view of the physical chip (see https://www.onsemi.com/pub/Collateral/LM324-D.PDF ). The pluses and minuses are clearly marked.

Note that there are four of the amplifiers in the same package - your circuit only needs to have two of the four connected. You can pick any two that are the most convenient for you to wire. Pin 4 and pin 11 (VCC and VEE) are the power supplies for the chip that are shown in the schematic as straight lines coming out of the top and bottom of the triangle symbol. VCC is the positive supply and VEE goes to ground (the negative supply).

For the IRF9520 field effect transistor (FET), G, D, and S stand for GATE (G), DRAIN (D), and SOURCE (S). If you look at the data sheet from the Harris Semiconductor databook (see **broken link removed** ), you will see a diagram for the FET that uses the same schematic symbol as your reference schematic. The source (S) is the top line, the gate (G) is the middle line that connects to R4, and the drain (D) is the bottom line that connects to R5.

Observe that Bob's project photos show a large aluminum heat sink as part of the construction. That is because this circuit will get hot while it's in use. Without some way to remove the heat from the immediate location of the chips, the heat would destroy the circuit within a short time.

Be sure to read Dr Bob's article carefully. The output voltage is controlled by the ratio of R2 To R3, and his example is set for a 6volt output from the first stage. That 6 volts is then amplified to 12 volts in the following stage, so the regulator output is 12 volts with 15 volts input. If your input falls below 12 volts, there will be no regulation. If you want a constant 11 volt output, you'll need to adjust the values of R2 and R3 slightly to change the output of the first stage to 5.5 volts instead of 6. This could be accomplished by replacing the fixed resistors with an 8K potentiometer - that would make the regulator adjustable.

The 25uf capacitor in the parts list will work in the circuit. "WV" stands for working voltage. A 50WV capacitor can tolerate a higher working voltage than the minimum 16WV shown in the schematic. Any capacitor with a working voltage rating higher than 16WV will work in the circuit shown - you could use 20WV, 25WV, 35WV, etc. Note that the higher the working voltage, the larger the physical size of the capacitor will be.

Since you are being brave and venturing into a project with very little knowledge, you may have some failures. Use a fuse in series with the supply to your little circuit so any mistakes are less likely to wipe out all your parts. A blown fuse is a minor annoyance while you are learning, and it beats having to replace a bunch of burned out semiconductor parts.

 

[serpa4]

Wow, thank you so much for your time. Yes, the total array is 150 milliamps. I have another question if you please:
You said:
That 6 volts is then amplified to 12 volts in the following stage, so the regulator output is 12 volts with 15 volts input. If your input falls below 12 volts, there will be no regulation. If you want a constant 11 volt output, you'll need to adjust the values of R2 and R3 slightly to change the output of the first stage to 5.5 volts instead of 6. This could be accomplished by replacing the fixed resistors with an 8K potentiometer - that would make the regulator adjustable.

The array is designed for 12 volts max. As far as I know, running at a lower voltage is fine, but with a dimmer output. If my camper battery drops below 12 volts and the LED is output is lower, that is fine. I don't need to have the 11 volts increased to 12 volts. I have tested the LEDs down to 10.5 volts and they make enough light. What I'm trying to protect the array from is too much voltage. With my solar panel, voltage at the battery can be 15 volts.

Added after 1 minutes:

P.S. what size fuse do you reccomend? I will try to gather parts tomorrow from the electronics store.

I have found the schematic of the LM324-D and FET that you showed. I see it is clearly labeled for both devices!!! Thank you. Your instructions are very clear.

It looked like the heat sink was used for the entire componet, regulator and power supply. Looking at his photos on page 5, he has audio video cables adn other wires going into the box. I was figuring since I only needed 150 millamps of power and no power supply, video cables, etc. that he has shown I would just put in in a heat shrink tube and put it inside the overhead light enclusure.

Why is he going from a 6 volt output and amplifying to 12 volts? Is there an advantage to this? Is there an advantage to your suggestion on regulating to 11 volts?

It looks like there is a descrepency on the parts list vs schematic. The schematic show R4 to be 10K ohms while the parts list shows R1, R3-R6 all as 3.3K ohms. Do you know if it should be 10K or 3.3K ohms resistor? Thank you.

Ultimately, I want any voltage 12-15 volts to be reduced to 12 volts and anything under 12 volts just be what it is. Are you suggesting this device can amplify my dead battery of 10.8 volts up to 12 volts?

What is your guess on the power consumption of this regulator? I don't want to remove the 1.5 amp incandescent light and replace with a 150 milliamp LED and a 1.5 amp draw regulator. That would defeat my purpose of saving battery power. My camper has 100 amp hours of power. If I go camping and use the interior lights for 3 hours at 1.5 amps x 2 lights in each fixture x 3 days = 27 amp hours removed from my battery just for lights and still have heater, refrigerator, radio, etc. With the 150 milliamp LED 3 x .150 x 2 x 3 = only 2.7 amp hours used!!! This is a very large savings. My children always leave the lights on also.

Should I attempt to make a circuit board like he did? Looks complicated adn I have no clue how to accomplish it. Do these things come in a kit that makes it easy to design and make? How does one go about making a pattern on the circuit board? Is a program used?

Thank you, your knowledge and time is appreciated.

 

[House_Cat]

Wow! Lots of questions.

No, you can't boost your 10.8V battery to 12v with this circuit. The amplification from first stage to second is just how the circuit is designed to work. You can't get more out of it than the maximum voltage that is applied to the circuit overall.

All I meant was the output of the circuit will "droop" as the supply voltage drops below 12V. Your stated goal should be satisfied.

Whenever you drop voltage across a circuit, whether it is a simple resistor or a regulator, there is power dissipated in the circuit. That power is the voltage dropped across the circuit times the current through the circuit (P=IE). In your case it's going to be roughly worst case 3volts x .175amps = 150 milliwatts. That's OK without a heat sink as long as there is some ventilation. Even 150mw is going to heat up if it is in a tightly closed can without any air circulation. If you look at the data sheet, the operational amplifier chip is rated up to +70C (158F). As long as it stays below that temperature in the worst case for your camper operation, you should be OK (do you camp in the desert?) The device that is going to generate the most heat is the FET output stage of your regulator. The zener diode is running at low current (about 1ma), and the operational amplifier runs at less than 1ma. The FET has the voltage drop across its source to drain impedance, so it gets rid of the excess energy in the form of heat. I'm guessing you will probably be OK without a heat sink for your application unless the fixture gets excessively heated by the sun on the shell of your motor home during operation.

I would suggest at most a 0.5amp fast acting fuse while you test your circuit - that's 3 times what your circuit should be drawing in operation. I haven't done the calculations, but that shouldn't blow while your 25uf filter capacitor is first charging through the FET when you power up. The inrush current to your filter will be the worst normal current flow. Once the capacitor charges, the current should settle out to just a couple of milliamps over your 150ma LED demand.

No, you don't have to make a printed circuit. Point-to-point wiring on a perf board should be fine in this application. Learning how to make a PCB should come once you've gained a bit more knowledge of basic electronics. It's not hard, but there are things to learn about proper layout of components, and chemical processing is required. It takes a bit of practice to get it all right.

 

[serpa4]

Thanks for all the help. I will post my success or failure.

 

[Meridian]

Hello,
You got a very serious problem. your incandescent lights use 1.5 amps now
you have 25 LED's 150 mA each so u should have

150×25=3750 mA or 3.75 A

... I thought he was refering to the led 'array' being 150mA...

 

[serpa4]

I didn't find all the exact parts.
I went with a 22uf 16wv capacitor insted of 25uf
The FET was a little different. Not sure what, but the guy at the electronics store said it should work.
Got it all wired on my bread board and SUCCESS!!!!
Very good success actually.
I have about .05 volt drop!!!
The LED array and regulator together draws 170 mah at `4.5 volts and less at lower voltages.
Its regulated to 12.24 volts. Not sure where the .24 volts came from, o-well all is very good. The LED array is extreamly bright and runs perfect at 10.5 volts. I cannot tell the difference really between 10.5 and 12.24 volts.
Thank you very much for everyones assistance. I'm letting it sit running for a few hours to ensure the components dont get too hot before I transfer it all to the circuit board thing and solder it all up.
Wow, this is cool.