LED strip amplifier / LED amplifier / RGB amplifier. Features, problems, choice.

What is the difference between LED strip amplifiers, LED amplifiers, and RGB amplifiers?

Only in words and channels.

• LED strip amplifier is a general definition.
• An LED amplifier usually refers to a single-channel device that operates with a white light strip. Another name is the DC amplifier.
• WW LED Amplifier is a dual channel device for warm and cool white light temperature strips.
• An RGB amplifier is a three-channel device that produces red, green, and blue color strips.
• The RGBW amplifier is a four-channel device for red, green, and blue color strips, with additional white LEDs.
• The RGBWW amplifier is a five-channel device for red, green, and blue color strips, with additional warm and cool white LEDs.

Why do you need LED amplifiers?

Conductors always have resistance. Imagine we want to install an LED strip around a 500-square-foot room (16*32 feet). We need 96 feet of LED strip, and it is impossible (!) to connect it to the power supply at one point (!). Why?

For example, a strip has a power consumption of 3 watts/foot (a 16-foot reel has a power rating of 48 watts and a current of four amps at 12V). A 16-foot strip comprises 96 sections (cut lines) of two inches each. Each strip section will have an internal conductor resistance of 0.005-0.02 Ohms, depending on the manufacturing quality. The total native resistance of the strip is 0.48 to 2.8 Ohms. The supply voltage drop for the last sections of the strip will be 2 - 7.7 V. The voltage across the last sections of the strip will be 10 - 4.3 V. This is very low!

When all three channels are on, we will clearly see the difference in brightness between the beginning and end of a 16-foot strip. For an RGB strip, it will look like a color change. The start of the strip will be white, and the end of the strip will be yellow.

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Details are in my earlier post:
Effect of reducing the LED strip supply voltage on the light emitted
https://teardownit.com/posts/effect-of-reducing-the-led-strip-supply-voltage-on-the-light-emitted
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Several solutions to the power problem exist for a long line of LED strips. The first option is to install a thick power cable next to the entire LED strip and connect it to the strip several times every 10-20 feet. For example, a 4*14 AWG cable. The solution is excellent and reliable but expensive.

The second option is the use of an LED strip amplifier. The device is a set of transistor keys for powering a powerful load controlled by a special signal. LED amplifiers allow us to use multiple power supplies, synchronizing powerful loads with a control signal. We don't need to run four thick conductors along the entire length of the RGB strip, but just install a few power supplies and amplifiers every 10-20 feet. We can also combine power supply options depending on the situation.

We will also need an RGB amplifier to connect more loads (LED strips) to the RGB controller output than it supports/allows. For example, the RGB controller is designed for a 100W load, but we want to connect 300W LED strips.

So, what can go wrong with such simple devices? When choosing from catalogs and online stores, you will see only two significant characteristics - operating voltage (5/12/24V), maximum output current, and the number of channels - three for RGB and four for RGBW. However, my experience has shown that not everything is shown in the documentation.

Lying about the maximum current

Amplifiers are DC-powered, and when all channels are switched on, the total current of all channels flows through the common power wire (5/12/24V). Therefore, the maximum total current through the amplifier is critical. Since we are describing an electrical circuit, it is crucial to know how strong the weakest link is.

Let's take a look at such an amplifier.

In the housing and documentation, the maximum current through the amplifier is 24A. But! The device uses disconnectable connectors, which...

Finding branches using a reflectometer

As you know, a data cabling system consists of different segments. To connect them all and bring the data connection to the end user, it is necessary to make a certain number of crossings. Often, staff forgets to disconnect "old" lines. As a result, over time, parallel branches appear, and their presence can have a detrimental effect on the quality of services.

BRANCHES AS A SOURCE OF PROBLEMS

Parallel branches can make it difficult to serve clients and ensure system functionality. With the introduction of digital systems, the search for parallel branches becomes an increasingly important task since they negatively affect the operation of digital transmission systems and, even if in most cases they are relatively short in length, nevertheless lead to significant problems. The bramch creates a second path for digital signals transmitted on the main line, which travel along the branch and are reflected from its open end. Reflected signals (echoes) enter the main line, where they are mixed with "good" digital signals and negatively affect the quality of the transmitted data. Therefore, to ensure correct operation of the digital line, the branches must be disconnected completely.

When connecting to analog lines, branching also creates problems. For example, if there is a fault on such a branch, it may show itself in the form of a decrease in the quality of the transmitted signal.

Finally, unknown branches can affect the accuracy of diagnostic equipment, for example, when measuring cable capacitance and estimating the distance to a break using a capacitive bridge. An unknown branch increases the combined capacitance of the cable pair and causes a measurement error: for the tested pair, the calculated length will be greater than the actual length.

It is very important to have full information about all the parallel branches available on the line in order, if necessary, to select the correct algorithm for troubleshooting and eliminating the problem.

SEARCHING FOR THE LOCATION OF THE BRANCH CONNECTION

The capacitive bridge is the device most often used to measure the length of a cable that is open at the far end. Unfortunately, it only allows one to estimate the total length of a cable pair, including all parallel branches.

Using multi-function devices (combining a capacitive and resistive bridge), it is possible to calculate the length of the branch cable due to the ability to compare the length values obtained from measuring the cable capacitance and the resistance of the loop.

Pic main_img_p7621_thumb.png

In this case, an OTDR is the most optimal and, moreover, the only device that allows one to find the locations of branching, measure the lengths of the branches, and determine the distance to them.

However, in practice, cable analyzers that combine the functions of a reflectometer and a multi-function instrument are more convenient. The implementation of two measurement methods (reflectometric and bridge) in one device allows for comparison of the results obtained for more accurate fault localization.

The classic branch reflectogram is similar to the one for testing a damaged cable, the only difference being that the reflection of the signal from the branch is a straight line rather than a curve.

As an explanation, let's look closely at the reflectograms for an open-ended cable section without a branch and a cable section with one (it is located at a distance of 3385 ft). The corresponding measurement results using a capacitive bridge were transferred to the reflectometer for direct comparison and accounted for. Note how the presence of a branch affects the measurement results of a capacitive bridge—in particular, how the cable section with a branch distorts the pulse reflected from the open end of the cable at a distance of 6500 feet. This occurs because part of the energy of the reflectometer signal was lost passing through the branch. The ideal way to view these graphs simultaneously is to use a dual-channel OTDR...

Power control unit for testing

Scheme

Element functions:

• J1 - AC grid input 
• J2 - oscilloscope connection, current monitoring
• J3 - output for power supply under test
• SW1 - circuit sensitivity switch for measuring Inrush current
• SW2 - zero-cross switching on and off
• SW3 - instant switching on and off for inrush current measurements
• T1 - current transformer, 10A, 1:1000
• U1 - Solid State Relay, zero-cross, controlling voltage 90–250 VAC

AC-synchronized switching on and off

If the device requires zero-cross on-off switching, the operator should use SW2, while SW3 should be open. In this case, the SW1 should be switched to the lower position according to the diagram. Then, 10A of the grid current will correspond to the connector J2 voltage equal to 1V.
In synchronous mode, the on state of SW2 corresponds to a continuous mode; the value of the source current can be easily measured by briefly connecting the ammeter to the output terminals of SSR U1 without changing the position of the switches. With this measurement method, the ammeter does not risk being overloaded by the shock current of turning on the device.
Asynchronous switching on and off
When measuring INRUSH CURRENT, the operator should reduce the sensitivity of the current measurement circuit (upper position for SW1 on the diagram), open SW2, and use SW3 to turn on the device. In this case, 10A of grid current will correspond to a voltage at connector J2 equal to 0.1V.
Since powering on will be accidental relative to the source phase, the measurement procedure should be repeated several times (at least ten). Only then can the maximum and average values for the INRUSH CURRENT be reliably determined.

Assembly

The described power control unit was assembled on a breadboard with a 0.1-inch pitch; the look of the unit is shown in the photos below:

On view 1 of the power control unit in the foreground, one can find the terminals for connecting the source and the device under test, switch SW2, and current transformer T1:

Power control unit view 2:

Power control unit view 3 shows the current sensitivity switch SW1 and connector J2:

Usage example

For example, if one uses the device to test a power supply, then with an oscilloscope, one can determine the following characteristics of the unit:

• INRUSH CURRENT
  Peak input current at full load
  
• POWER FACTOR
  Power factor of AC mains draw (usually listed if there is a PFC in the supply) https://en.wikipedia.org/wiki/Power_factor
  
• SETUP TIME
  Time to set up from the moment of applying the input voltage until the output voltage reaches 90% of the rated level at 100% load.
  
• RISE TIME
  Time for the output voltage to rise from 10% to 90% of the nominal level.
  
• HOLD UP TIME
  Time to keep operating at 100% load from the moment the input voltage is turned off until the output voltage drops to 90% of the rated level.
  
• FALL TIME
  The output voltage decay time is 90% to 10% of the nominal level.
  

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Done.
Best regards.