Those searching for practical knowledge on electrical circuits and LED component wiring should start with this tutorial. It’s more than possible that you’ve already read this Wikipedia page on series and parallel circuits, as well as a few other Google search results on the topic, and are still unsure or want more particular information regarding LEDs. We’ve gathered and prepared all the key materials needed to assist you to comprehend the idea of electrical circuits and their link to LEDs after years of delivering LED education, training, and presenting the electronic circuit concept to clients.
First and foremost, don’t allow electrical circuits and wiring LED components to intimidate or perplex you; appropriately connecting LEDs may be simple if you follow this guide. Let’s start with the most fundamental question:
What type of circuit should I use?
If given the option, the most efficient approach to operate high-power LEDs is to utilize a series circuit with a constant current LED driver. A series circuit ensures that each LED receives the same amount of current. This implies that each LED in the circuit will have the same brightness and that no one LED will need more current than the others. When each LED receives the same amount of current, problems like thermal runaway are reduced.
Don’t worry, parallel circuits are still a viable alternative and are frequently utilized; we’ll go over them later.
The current in a series circuit follows one path from start to end, with the Anode (positive) of the second LED linked to the Cathode (negative) of the first. This is sometimes referred to as “daisy-chained” or “looped“. An example may be seen on the right: To wire a series circuit like the one shown, connect the positive output of the driver to the positive of the first LED, then connect the negative of that LED to the positive of the second LED, and so on until the circuit reaches the last LED. Finally, the last LED connection connects the LED’s negative to the constant current driver’s negative output, forming a continuous loop or daisy chain.
Here are a few bullet points for reference about a series circuit:
- The same current flows through each LED.
- Varying voltages across each LED is okay.
- If one LED fails, the entire circuit won’t work.
- Series circuits are easier to wire and troubleshoot.
- The total voltage of the circuit is the sum of the voltages across each LED.
Powering a Series Circuit:
The loop notion is no longer a difficulty, and you could probably figure out how to wire it, but how about powering a series circuit?
“The overall voltage of the circuit is the sum of the voltages across each LED,” says the second bullet point above. This implies you must provide at least the total of each LED’s forward voltages. Let’s have a look at this using the same circuit as before, but this time assuming the LED is a Cree XP-L operated at 1050mA with a forward voltage of 2.95V. The total forward voltage of these three LEDs is 8.85Vdc. As a result, the minimum necessary input voltage to drive this circuit is 8.85V.
Because these power modules might alter their output voltages to fit the series circuit, we advised utilizing a constant current LED driver from the start. Because the forward voltages of LEDs change as they heat up, it’s critical to employ a driver that can alter its output voltage while maintaining the same output current. Check out this page for more information about LED drivers. However, it’s critical to ensure that your driver’s input voltage can generate an output voltage equal to or greater than the 8.85V we calculated before.
Some drivers require a modest increase in input to accommodate for the driver’s internal circuitry (the BuckBlock Driver requires a 2V overhead), while others offer boost (FlexBlock) capabilities that allow you to input less.
Hopefully, you will be able to locate a driver that will allow you to complete the LED circuit with the diodes in series, but some conditions may make this difficult. Sometimes the input voltage is insufficient to power several LEDs in series, or there are too many LEDs to have in series, or you want to keep LED driver costs down. Here’s how to comprehend and construct parallel circuits for any reason.
Powering Parallel Circuits:
Parallel circuits get the same voltage for each LED as a series circuit, and the total current to each LED is equal to the total current output of the driver divided by the number of parallel LEDs.
Don’t worry, we’ll show you how to build a parallel LED circuit here, which should help tie everything together.
In parallel circuits, all positive connections are linked together and returned to the LED driver’s positive output. In contrast, all negative connections are tied together and returned to the driver’s negative output. Take a look at the illustration on the right.
Each LED would get 333mA in the example with a 1000mA output driver; the total output of the driver (1000mA) is divided by the number of parallel circuits (3).
Here are a few bullet points for reference about parallel circuits:
- The voltage across each LED is the same
- The total current is the sum of currents through each LED
- The total output current is shared through each parallel circuits
- Exact voltages are required in each parallel circuit to help avoid current hogging
Now let’s combine them to create a Series/Parallel Circuits:
series/parallel circuits, as the name indicates, incorporate parts from both circuits. Let’s start with the circuit’s series section. Let’s assume we want to operate 9 Cree XP-L LEDs at 700mA apiece at 12Vdc; each LED’s forward voltage at 700mA equals 2.98Vdc. The second rule from the series circuit bullet points demonstrates that 12Vdc is insufficient to power all nine LEDs in the series (9 x 2.98= 26.82Vdc). However, 12Vdc is sufficient to power three in-series devices (3 x 2.98= 8.94Vdc). And, according to rule 3 of the parallel circuits, the total current output is divided by the number of parallel strings.
So, if we use a 2100mA BuckBlock with three parallel circuits of three LEDs in series, the 2100mA is split by three, and each series receives 700mA. This is demonstrated in the sample image.
This LED circuit planning tool will assist you in deciding the circuit to utilize when creating an LED array. It provides you with various series and series/parallel circuit alternatives to choose from. Your input voltage, LED forward voltage, and the number of LEDs you want to utilize is all you need to know.
The downfall of multiple LED strings:
When running parallel and series/parallel circuits, keep in mind that if a string of LEDs burns out, the LED/string will be removed from the circuit, and the excess current load that was flowing to that LED will be divided among the others.
With bigger arrays, this isn’t a big problem because the current is scattered more evenly, but what about a circuit with just two LEDs/strings? The current would then be increased for the remaining LED/string, which might be more than the LED can manage, resulting in burnout and the destruction of your LED! Always keep this in mind, and attempt to put up a system that won’t harm all of your LEDs if one of them burns out.
Another potential issue is that the forward voltage tolerance of LEDs from the same production batch (same binning) might be as much as 20%. When different voltages are applied to different strings, the current is not distributed evenly. Thermal runaway occurs when one string draws more current than another, causing the overdriven LEDs to heat up and their forward voltages to vary more, resulting in more uneven current sharing.
Many circuits set up like this have worked effectively in the past, but caution is advised. A fantastic article on ledpixeltm.com provides further information on this topic and solutions to help avoid it (current mirror).
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