What is the principle of 12V low voltage light strip and how to calculate the power?

2024/04led strip light source

In addition to high-voltage light strips that can be connected to 220V mains power, there is another type of LED light strips, which are low-voltage light strips. Low voltage, as the name suggests, is an LED light strip whose input voltage is DC12V, or 24V (of course there are also 36V and 48V, which may be less).

The benefits of low voltage light strips are:

It is safe to use, there is no risk of electric shock even if it touches the light strip.
It can be cut into any 5cm or 10cm section, suitable for DIY usage scenarios of different lengths.
It has more functions than high-pressure lamps, such as RGB phantom effects, color temperature conversion, and even running water and horse racing effects.
Easy to match the power supply. No professional knowledge is required, just understanding the power and voltage will make a perfect match.
Since there are many benefits, let’s understand the principle and how to calculate its power.

12V low voltage light strip principle
The principle of 12V low voltage light strip is actually relatively simple. We know that the voltage of SMD LED lamp beads is generally between 3-4V. When we connect three SMD LED beads in series, we can get a voltage drop of about 9-12V.

Next, we connect many sections of circuits with 3 lamp beads in parallel, and we can get a very long LED low-voltage light strip. In other words, we can use a 12VDC constant voltage power supply to power LEDs.

12V low voltage LED light strip

There are a few things to note here:

1. The voltage of each LED lamp bead is actually different. However, by screening out lamp beads that are particularly close to the voltage, we can get a relatively stable voltage drop lamp strip. For example, we all choose LED lamp beads between 3.0-3.1V to make light strips. Knock on the blackboard! ! Some low-priced LED light strips do not strictly select the voltage range of the LED lamp beads. Therefore, use not only affects the stability, but also causes inconsistent color temperature and brightness.

2. If you understand the volt-ampere characteristics of LEDs, you will know that when the voltage is greater than the LED operating voltage, such as above 5V, the current allowed to pass through the LED lamp beads will become very, very large. The passage of large current will cause the LED lamp bead chip to burn out due to high temperature. Therefore, we cannot directly string 3 LED lamp beads together. What to do?

SMD chip resistors, as a current limiting function, appear on LED light strips. By the way, the small black dots on the low-voltage lamp strip besides the LED lamp beads are chip resistors with fixed resistance. With the existence of these resistors, even if the output voltage of the constant voltage driver fluctuates, the LED lamp beads will not be burned out at once, and they play a role in protecting the lamp beads.

The resistance values of different chip resistors directly affect the current flowing through this string of LED lamp beads. In other words, the power and brightness of the LED strip are also determined by the resistance values of these resistors.

3. Because each string of 3 SMD LED lamp beads, plus a chip resistor, forms a small circuit. Then we connect countless of these small circuits in parallel to get a long light strip. That’s why low-voltage light strips can be cut at will. After cutting, although the lengths are different, because the input voltage remains the same, the same driving power supply as before can still be used.

How to calculate the power of 12V LED light strip?
Okay, we know that the voltage of the 12V LED strip is 12VDC, so how to calculate its power?

From the above we can know that the chip resistor determines the current of each string, that is, each LED. Let's take the 12V low-voltage light strip with SMD2835 specification as an example. Assume that the resistance of the resistor is set at: limiting the current of each string of LED lamp beads to 30mA; the rated voltage of a single 2835 SMD lamp bead is 60mA. Why should it be set at What about 30mA? Because on the premise of ensuring brightness, the lower the current, the more helpful it is to reduce the heating of the lamp beads, improve the luminous efficiency, and extend the service life of the lamp strip.

Now we can calculate the power of each strip.

Power (W) = Voltage (V) x Current (A) That is: Power = 12V x 30mA = 0.36W.

Suppose also that our one-meter light strip has 120 SMD 2835 lamp beads, so there are 120/3=40 strings connected in parallel. The power of the one-meter light strip is: 0.36W x 40 = 14.4W .

If there are only 60 lamp beads per meter, there are 60/3=20 lamp beads, and the power of this lamp strip is: 0.36W x 20 = 7.2W.

Full roll of 12V low voltage LED strips

The light strips on the market all say 14.4W per meter, are they actually available?
There are many types of LED light strips on the market, and they are all mixed up. Whether the nominal power is the same as the actual one requires careful identification.

Generally speaking, as a manufacturing company, the early low-voltage SMD5050 light strips basically read: power < 14W/M. This means that the power per meter will be less than 14W. This makes people ambiguous. If you make 3W per meter, it is still less than 14W. Even if you achieve 12W, it will still be less than 14W. There is no difference between 3W per meter and 12W per meter. The brightness is definitely different.

Qualified LED light strip manufacturers will write out the accurate power consumption of LEDs, for example: power 12W/m. Through the product label, we can calculate the power supply matching the light strip that is suitable for our specific length.

Of course, it is not ruled out that there are false marks, including light strips and power supplies. How to tell the difference?

Here I will explain to you how non-professionals, without professional instruments, can tell whether the light strip is good or bad, or whether the power is high enough.

First, let’s look at how many SMD lamp beads there are in the next meter. The more lamp beads, generally the higher the power. Generally, the number of lamp beads per meter is 60, 90, 120, 180, 200, or even 240. The more lamp beads, the greater the power and brightness will naturally be.
We can also look at the thickness of the flexible version of the light strip. Flexible board is a flexible and bendable circuit board. Thanks to the characteristic of flexibility, LED low-voltage light strips are used in such a wide range of scenarios. Under the white (and also yellow) insulation layer on the flex plate is the copper skin. Copper is used to carry current. We know that the greater the power, the greater the current required. If the flexible plate only has copper on one side, then the power of this light strip will not be very high. On the contrary, if there are copper sheets on the upper and lower sides of the flexographic plate, and the copper sheet is thicker, then the power of this light strip will be greater.
Turn on the power to see the brightness. The higher the brightness, the greater the power generally speaking.
The above are a few ways to distinguish the power of light strips through visual inspection without using a power meter or professional instruments. I hope it can help everyone.

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