When we want to operate a LED lamp, in most cases, our LED light source works directly from the 230 Volt AC mains. That is, we screw it into the socket, turn on the light, and it works.
As with halogen bulbs, in certain cases, it is more practical or safer to use low-voltage bulbs. These are most commonly seen as 12 Volt bulbs in furniture lighting, desk lamps, and Christmas lights. This is also true for LEDs. There are LEDs that operate on 5, 12, or 24 Volt DC, some that can use both DC and AC, and some that can only be operated with 12 or 24 Volt AC.
Additionally, it is necessary to mention that there are LEDs that require constant current power supplies. That is, the LEDs are connected in series, so the power supply outputs a voltage depending on the number of LEDs connected in series, and the light output of the LEDs can be adjusted by the regulated current. But this is another area; this article is about the power supply of low-voltage LEDs connected in parallel to replace halogens.
Let’s start with the shorter information.
- If a LED can operate with both DC and AC, always use DC, as this eliminates the possibility of flickering that can occur with AC use.
- There might be 12 Volt LEDs that are dimmable using phase-cut dimming. These are conventional (but modern and not 20-year-old) wall dimmers. Phase-cutting can only be done with AC. So, if we want to dim a 12 Volt LED with phase-cut dimming, we can only use a transformer that provides an AC output (iron core transformer, toroid transformer yes, never a halogen electronic transformer), because it will also work with DC, but only at maximum brightness and we won’t be able to reduce the brightness.
- However, if a LED only operates with AC, which can also be 12 or 24 Volts, it will not work with DC. This is because these LEDs are generally continuous color-changing RGB LED lamps, and the color-changing rhythm is provided by the 50Hz frequency of the mains AC. Without AC, there is no color change either.
Beyond all this, most low-voltage LEDs require 12 Volt DC, but there are also some that require 24 or 5 Volt DC.
Options According to Application Location and Mode:
There are power supplies for operating LEDs called adapters, LED drivers, and transformers (iron core transformers).
- The adapter is like a phone charger, so it has a plug (with a plug). For lower power units, the plug is built into the power supply housing, while for higher power (and heavier) units, it is mounted on a floating cable. The 12 Volt output is also a longer cable, with a so-called DC Jack connector at the end. It is advisable to buy an adapter for those who want to install LED strips themselves (not as professionals) and thus provide power from an existing outlet. The disadvantage is that we will have free-hanging wires, which we cannot always hide, but in return, we get a simple implementation method. But such an adapter can also be used for 12 Volt LED desk lamps or other 12 Volt spotlights installed later.
- A more aesthetically pleasing solution is if we can hide the power supply. These are the power supplies called LED drivers. These either have a short pair of wires sticking out, or none at all, but instead have a terminal strip on the box where the wires can be connected. These LED drivers can be permanently connected to the home electrical network and can be hidden, in simpler cases, on top of a tall cabinet, in a cavity made from a piece of furniture board, above a suspended ceiling, or in a suitably large built-in wall mounting box. There are primarily two types, waterproof and non-waterproof (naturally, they come in various water and dust resistance levels in terms of IP protection).
- Non-waterproof ones are mostly in perforated metal housings, but there are also closed plastic housings that are dust-protected, or plastic housings with grilles. The ones with grilles are cheaper, but this also means that the heat generated is dissipated by the air, so they cannot be placed in a completely sealed narrow space, as this would result in the power supply overheating and failing. Additionally, the terminals of these power supplies are exposed, so the installation location must be determined by an electrical professional, as the exposed wire connections must be placed in a safe location where they cannot be touched during everyday use, ensuring safety and protection.
- Waterproof power supplies are recognizable by being completely sealed, either with a solid metal heatsink or a closed plastic housing. These types dissipate the heat generated during operation through their surfaces. They can be installed more safely since they have shorter pieces of wire sticking out, and these wires can be insulated. The waterproofing is a broad category; some types can be used continuously underwater (IP68), while others are only protected against splashing water and heavy rain (IP65 protection).
- Iron-core transformer, though any of the above may contain an iron-core transformer, the essence of the name is that it contains nothing else, meaning it outputs AC. These can also be found in waterproof and non-waterproof versions.
- Non-waterproof can be as simple as an exposed toroid coil, thus requiring an electrical professional for safe installation to ensure safety and accident prevention, and there are also more closed plastic-housed versions where the terminals for connecting the wires are in a place covered by a plastic lid.
- Waterproof power supplies typically have IP68 protection, meaning they can be used continuously underwater up to the depth specified by the manufacturer. This necessity mainly targets the design of color-changing step-proof, fountain, garden pond, or swimming pool LED RGB lighting.
- IMPORTANT: No LED can be used with the so-called “halogen electronic transformer” designed to output AC for halogen light sources! During the transformation, harmonics can appear on the AC waveform, which the LED electronics cannot filter out, thus quickly damaging the LED. This is not the fault of the halogen electronic transformer, as this does not cause problems with a filament, but simply because it was not designed for LEDs, just as LEDs were not designed for it.
It is also important to know that various safety electronics can be built into the power supplies, depending on the power supply. The most common are:
- Short-circuit protection. If the output wire pair is accidentally shorted, the power supply will not burn out but will shut off. The power supply will work again once the short circuit is removed.
- Overload protection. It specifies up to what percentage above the nominal load it can operate and for how long before it shuts down, to prevent power supply failure.
- Wide input voltage range. Ensures a stable output despite potential fluctuations in the network voltage.
- Input overvoltage protection.
- Output voltage adjustment within a certain range, allowing the power supply voltage to be tailored to specific needs.
- Output noise suppression, ensuring the DC is true direct current without any ripple.
- Of course, we cannot expect any of these additional protections from a power supply that consists solely of an iron-core transformer.