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 the manufacturer indicates 300V 15A on the case. The maximum current through the amplifier should be limited to the maximum current of the connector - 15A, and only if you are sure of the quality of the connectors. What does it mean? The photo below shows the result of load testing of this connector. The current was only 4.2 A !!!!!

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I showed the results of similar tests of other connector types in a separate post.
LED strip/lights connectors and maximum currents
https://teardownit.com/posts/led-strip-lights-connectors-and-maximum-currents
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You must avoid disconnectable connectors if you need to get more than 10A of current out of your amplifier. Only large connectors with screws can be used.

The wiring diagram of this amplifier:

Galvanic isolation

Another problem you may encounter is not included in the documentation either. To understand this problem, I must disassemble the amplifier and draw a wiring diagram. I will disassemble a good amplifier, for example.

The wiring diagram:

The input signal goes to the opto-isolators, and the phototransistor controls the output transistors, pulling their gates to +5/12/24V. The solution has an undoubted advantage - the control and output circuits are connected optically, but not electrically! In addition, the opto-isolator requires a current of a few mA to operate, and random induced noise will not cause false triggering. Galvanic isolation is widely used in industrial electronics; inputs and outputs are isolated via opto-isolators.

Now, I'm going to disassemble a low-quality amplifier.

The wiring diagram:

What do we see? The input signal goes through a 10k resistor to the comparator input. The galvanic isolation between input and output is missing! Moreover, the huge input resistance of the comparator makes it very sensitive. Such amplifier circuitry will laugh at us - in the second or third stage, the amplifier will trigger randomly. The LED strip works like a giant antenna, receiving a 60 Hz feed from the power grid when there is no input signal (or the lights are off).

For example, a compact Noname RGBW strip amplifier has a full decoupler (sold on Amazon and Aliexpress). This surprised me a lot:

Using amplifiers without galvanic isolation is a test of luck for the user. The devices may operate normally but pick up power line noise depending on the weather, moon phase, cloud color, etc.

How can you determine galvanic isolation in an amplifier without disassembling the device? It is easy. With a multimeter, you need to measure the resistance between V+ input and V+ output. The resistance should be infinite.

Performance issues

The use of opto-isolators is one of many prerequisites for good work. Simple opto-isolators have a low operating frequency limit. The problem is not present when using RGB controllers with low PWM frequency (hundreds of Hertz). But that low frequency is itself a problem for humans. It is the flickering of light that damages our eyes.

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More details in a separate post:
Shelly RGBW2 controller and Shelly Duo RGBW bulb. Dangerous light pulsations.
https://teardownit.com/posts/shelly-rgbw2-controller-and-shelly-duo-rgbw-bulb-dangerous-light-pulsations
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A low-quality amplifier will add distortion if the PWM frequency is increased to a safe level (1250-1500 Hz). You will see these distortions as a change in the brightness and hue of the light in the LED strip before and after the amplifier. Manufacturers know how to solve this problem. I disassembled an amplifier labeled "high speed":

The wiring diagram:

The device uses high-speed 6N137 optoisolators with logic output. The amplifier is galvanically isolated and does not ruin the colors with insufficient speed.

The device performs well at 200 Hz PWM frequency and 20 kHz (!!) PWM frequency, with little distortion:

The problem can be seen in another amplifier with conventional opto-isolators. It works at a PWM frequency of 200 Hz. At 20 kHz, there is no signal at the output. The output signal is distorted to the point of inoperability - the output keys do not have time to open at a frequency of a few kHz. The input signal (inverse) is shown in yellow, the output signal in blue:

Manufacturing quality

Sometimes, inside the device housing, I can see the horror, hell, and pain of an electronic engineer. Anyone can understand why a device works poorly and does not work for long.

An example of one of the RGB amplifiers:

Unwashed flux, single-sided PCB (to reduce cost). The heat from the field-effect transistors is dissipated onto the board tracks and overheats the switches. Rudimentary landing places for opto-isolators are on the board, but the tracks on the board will not allow us to use them! /facepalm/

Conclusions

Unfortunately, the price and quality of LED amplifiers have little correlation. You can pay dearly for junk, but a cheap, no-name amplifier will be a great device. Only by reviewing the internals can you understand the quality of the product.

• Do not trust the maximum current indicated on the housing. Disconnectable terminals provide a total device operating current of less than 15A. Screw terminals can provide a maximum device current of 10-30 Amperes (according to terminal manufacturers' documentation).
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• If you don't want to have problems with strange behavior of LED amplifiers, you need to use amplifiers with galvanic isolation. This property is not shown in the specifications or in the documentation. The only way to determine this without disassembling the housing is to measure the resistance between V+ input and V+ output.
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• Quality RGB controllers have a high PWM frequency, but poor RGB amplifiers introduce distortions in color and brightness. You should look for devices that explicitly state "high speed."