An LED strip is a metallized base on which LEDs are located. On the inside, there is an adhesive surface, thanks to which the lighting can be fixed on furniture, walls, ceilings of rooms or facades of buildings. There are monochrome strips on which devices of one color are placed, and three-color or multi-color ones consisting of LEDs of 3 (RGB) and more colors. Due to the peculiarities of the operating principle of LEDs, they need appropriate power sources. Let’s consider how to choose a power supply unit for an LED strip.
Types of power supply units
A light-emitting diode is a device that begins to emit light under the action of a direct current passing through it. At the same time, there is a non-linear relationship between current and voltage, which can lead to the burning of LEDs even in the event of a small voltage surge in the network. To avoid this and limit the amount of current consumed, resistors are added in series to the LED chain, and power comes from a power supply unit with a stabilized output voltage of 12 or 24 V.
According to the principle of operation, power sources for LED strips are divided into transformer and pulse.
The transformer power supply unit consists of a step-down transformer, diodes for rectifying the sinusoidal current, a smoothing filter and a voltage stabilization circuit.
- the simplicity of the circuit
- junction to the secondary circuit with a 220 V network.
- low efficiency,
- significant dimensions and weight of the block (this is directly affected by the bulky transformer).
A more modern switching power supply unit includes a circuit that converts the oscillations of the 50 Hz frequency network into a higher frequency of about 30 kHz. Thanks to this, the dimensions and weight of the pulse transformer are sharply reduced, and its efficiency increases. The presence of a transformer allows such a unit to be disconnected from the power supply network. On the other hand, a pulsed power supply is more expensive than a transformer due to the use of a larger number of electronic components.
Sometimes a transformerless power supply scheme is used to save money. In this case, lowering the voltage from 220 V to the operating voltage is carried out using a capacitor connected in series. Usually, the use of such a scheme is not recommended, since it does not have a disconnection of the circuit of the LED strip with the power network, which can lead to a high voltage shock when reinstalling the strip with the network on. In addition, such a scheme is poorly protected against network surges and overvoltages.
Depending on the operating conditions, power supply units are divided into the following types:
- in a protective jacket;
- sealed in a plastic case;
- sealed in a metal case.
Blocks of the first type are intended for installation in a dry room with a low level of dust and humidity. They have a degree of protection IP33 or lower. Such a block is a printed circuit board installed in a metal casing with perforations. This casing protects the circuit from mechanical influences, but does not protect against moisture and dust. Units with a capacity of more than 300 W can be provided with forced ventilation in the form of a fan. Installed only in industrial premises.
Blocks of the second type can be installed in wet and dusty places. They have an IP67 degree of protection. The difference between such blocks and metal blocks is their lower weight and greater compactness.
The power supply units of the third type are designed for outdoor use. Therefore, in addition to good protection against moisture and dust (IP67), they have a strong aluminum case. Thus, they are protected from external mechanical factors.
How to choose
The power supply unit for the tape is selected taking into account:
- degree of protection of the block.
The operating voltage of LED strips can be 12 or 24 V. Accordingly, the power supply unit can be designed for one or another voltage.
The next parameter is power. To determine it, the consumed power of the tape (Rpml) is calculated:
Rpml = Ruml * L, – where Ruml is the specific power of the tape, W / m, L is the length of the tape, m.
The power of the power supply is equal to Rpml increased by 25%.
Depending on the place of installation, the type of PSU protection is selected – in a casing, hermetic plastic or hermetic metal.
For example, you need to buy a power supply unit for an SMD 3528 type tape 8 m long, installed on the street. For this tape, the specific power is equal to 4.8 W / m. The power consumed by the tape will be equal to 38.4 W. Taking into account the reserve, the power of the power supply unit is 48 W. From the tables and catalogs, you can choose the appropriate power supply unit of the Arlight company, type ARPV-LM24050. This power supply has an output voltage of 24 V, output power of 48 W, protection class IP67.
Sometimes a unit for changing the brightness (dimmer) or a color change controller is included in the power circuit of the LED strip. The power consumption of these devices should also be taken into account when determining the power of the power source.
To connect the tape to the power supply unit, its terminals are soldered or connected to the corresponding terminals or connectors of the unit. At the same time, the polarity must be taken into account. If the polarity is incorrect, the tape will not work and may fail.
The connection of the three-color tape is made using a special RGB controller. This controller has three pins for the number of flowers and one pin for ground. The wire from each color of the RGB tape is connected to the corresponding output of the controller. The ground wire of the tape connects to the ground of the controller. The additional power consumed by the controller is usually close to 5W.