Electronics > Projects, Designs, and Technical Stuff

[LTSpice] Simulate Led Strip

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Zero999:

--- Quote from: lfaborges on August 09, 2020, 06:51:27 pm ---
--- Quote from: Zero999 on August 09, 2020, 05:56:02 pm ---
--- Quote from: lfaborges on August 09, 2020, 05:33:07 pm ---
--- Quote from: Jay_Diddy_B on August 09, 2020, 04:51:56 pm ---
--- Quote from: lfaborges on August 09, 2020, 02:19:56 pm ---What I've been doing is using a rectifier bridge and a capacitor, to try to light the LEDs. The problem is that the voltage has been below 12V.

The only thing I can't change about the project is the 2.8A current power supply

In the image, the green signal is the current source 2.8A and the blue signal is the measurement on the LED.

--- End quote ---

Are you measuring the voltage across D1, just the LEDs, or the voltage across C5?

The resistor R1, is part of the LED strip. Each three LED section of the strip has a 100 \$\Omega\$ resistor in series with three LEDs.

There will be voltage drop along the strip. This means if you feed the strip from one end the LEDs will be brighter at the end you feed than at the far end.

Please attach the .asc file to your posts.

You only need to run the simulation for 200ms, not 5 seconds.

Regards,
Jay_Diddy_B

--- End quote ---

I am measuring after the capacitor.

--- End quote ---
What voltage did you think you'll measure?

It's what you should expect. M = length = 176, which means R1's value is divided by 176, leaving only 0.57 Ohms, so most of the voltage drop will be due to the LEDs' forward voltage. If you set length to 1, the voltage will increase to 192V.

--- End quote ---

I expect 12V. I tested an LM7812, but the input voltage was low and the output resulted in approximately 8V. I thought about using a TRIAC or a Zener Diode if the voltage went up too much. But I can never find the perfect model to find 12V on the LED.

--- End quote ---
That's hardly surprising, since the LM7812 is only rated to 1A, it would have current limited.

ozcar:
As stated, the problem is how to drive exactly 528 of the LEDs from a 2800mA CC supply. As somebody already calculated each segment of strip (three LEDs) draws around 20.8mA, so 2800mA drives 2800/20.8 = 134 segments, or only 402 LEDs. 528 LEDs worth will light up, but will not be running at full brightness. Connected like that the choice is 402 LEDs at full brightness, or some larger number of LEDs with diminishing brightness of each LED as more are added.

The voltaqge range that the power supply can operate over was not specified. If it can output 24V (I would guess not), you could connect two lengths of strip, each with 402 LEDs, in series, but then you have 804 LEDs rather than the desired 528.

As a theoretical exercise, I suppose this could be an interesting challenge.

Myself, I would drive the strip from a 12V CV supply as the maker intended.

Zero999:

--- Quote from: lfaborges on August 08, 2020, 08:06:04 pm ---First thanks for everyone for the answers.

I need to make this led strip light up in a system that is powered by a constant current regulator (2.8A). I did some field tests and the input voltage was 7V.

I will still test the model proposed here in the forum and in the future I will give more answers.

--- End quote ---
Presumably your constant current regulator outputs DC? If so, then you made a mistake in your simulation by using an AC current source.

You need a constant voltage source, to power your LED strip. If it's 10W per metre and you're using 4.4m, then that's a total of 44W.

I = P/V = 44/12 = 32/3A

Swap the 2.8A constant current power supply for a 12V power supply rated to above 32/3A, so 4A or 5A will do.

lfaborges:

--- Quote from: Zero999 on August 10, 2020, 08:56:23 am ---
--- Quote from: lfaborges on August 08, 2020, 08:06:04 pm ---First thanks for everyone for the answers.

I need to make this led strip light up in a system that is powered by a constant current regulator (2.8A). I did some field tests and the input voltage was 7V.

I will still test the model proposed here in the forum and in the future I will give more answers.

--- End quote ---
Presumably your constant current regulator outputs DC? If so, then you made a mistake in your simulation by using an AC current source.

You need a constant voltage source, to power your LED strip. If it's 10W per metre and you're using 4.4m, then that's a total of 44W.

I = P/V = 44/12 = 32/3A

Swap the 2.8A constant current power supply for a 12V power supply rated to above 32/3A, so 4A or 5A will do.

--- End quote ---

The circuit in which I am going to install this LED, has this constant current source of 2.8A [AC]. So I said that it is something that I cannot change in the project.

Zero999:

--- Quote from: lfaborges on August 10, 2020, 11:54:34 am ---
--- Quote from: Zero999 on August 10, 2020, 08:56:23 am ---
--- Quote from: lfaborges on August 08, 2020, 08:06:04 pm ---First thanks for everyone for the answers.

I need to make this led strip light up in a system that is powered by a constant current regulator (2.8A). I did some field tests and the input voltage was 7V.

I will still test the model proposed here in the forum and in the future I will give more answers.

--- End quote ---
Presumably your constant current regulator outputs DC? If so, then you made a mistake in your simulation by using an AC current source.

You need a constant voltage source, to power your LED strip. If it's 10W per metre and you're using 4.4m, then that's a total of 44W.

I = P/V = 44/12 = 32/3A

Swap the 2.8A constant current power supply for a 12V power supply rated to above 32/3A, so 4A or 5A will do.

--- End quote ---

The circuit in which I am going to install this LED, has this constant current source of 2.8A [AC]. So I said that it is something that I cannot change in the project.

--- End quote ---
Then you're out of luck. The LED strip is completely unsuitable for your power supply  |O

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