Lighting fixtures based on LED strips are gaining more and more popularity over time and are successfully used for various purposes. Today they are used not only for decorating indoor and outdoor spaces, but also for arranging general lighting. In addition, they help to realize the idea of commercial lighting effects that draw attention to billboards and banners. The structure of the power supplies for the illuminators, designed for low voltage, includes transformers for 12 Volt LED strips (TP).
Features and characteristics of LED sources
Various samples of LED products differ in a number of features, the main ones of which are:
- directionality of the light flux;
- installation density;
- rated supply voltage;
- degree of protection.
According to the first indicator, well-known samples of LED devices are divided into front and end products. The most widespread are tapes with a frontal orientation and a scattering angle of about 120 degrees. Flexible stripes with a side light source are not so popular because they have a 90 degree corner radius.
The luminous flux from the LED strip is proportional to the number of emitting elements installed on it per one running meter. According to the existing classification, this number is selected from the following range: 30, 60, 90, 120 and 240 point units. The supply voltage for low-voltage tapes is either 12 or 24 Volts. Higher values are extremely rare.
Different brands of LED tapes differ in their protection against dust and moisture. The protection class is indicated on the product packaging as a combination of the letters IP followed by two numbers. The strip with open mounting of diode elements belongs to the IP20 class - there is no sealing at all. The most weatherproof tape has the highest grade, designated IP68.
How to choose the right TP for LED strips
The main working unit of the power supply unit (PSU) is a voltage converter that lowers the mains 220 volts to the desired value. Technical parameters, in accordance with which the transformer for LEDs is selected:
- the value of the voltage at the output of the device;
- the power that he is able to develop in the load;
- the degree of protection of the transformer against moisture.
The supply voltages for which the PSU is calculated are selected at the discretion of the user from a range of operating values of 12 and 24 Volts. The output power of the transformer built into it depends on the number of lighting elements connected to the unit. The degree of protection of the structure against moisture and dust is indicated in the same way as for LEDs (IP20-IP68) and is selected depending on the operating conditions.
Benefits of pulse transformers
When choosing a power source that is optimally suitable for use at home, it is necessary to take into account the following features of its components:
- A typical transformer for an LED strip is made, as a rule, in a pulse circuit.
- This approach allows you to reduce the size and weight of the power supply (UPS) itself.
- At the same time, the efficiency of the entire device as a whole is increased.
- To increase the efficiency of the UPS, an electronic circuit for generating the output voltage with overload protection allows.
Due to the advantages of pulse transformers, devices made on their basis have completely replaced obsolete analog samples.
UPS options
According to their design and performance, power supplies for LEDs are divided into the following types:
- compact power supply unit, similar in appearance to a charger for phones;
- a small-sized module placed in a rectangular oblong case;
- electronic ballast in a fully sealed box;
- a similar circuit housed in a standard size leaky casing.
The units have a small capacity (30-36 watts), but they are quite cheap. The modules are distinguished by a high power rating (up to 75 watts). Like the first samples, they are designed to work with decorative lighting, but unlike them, they have a higher cost.
Fully sealed electronic ballasts are designed for use in harsh climates. They are used to illuminate billboards and similar products on the street. Their non-hermetic counterparts, placed in a standard-sized case, are widely used in everyday life and in work offices. Among modern manufacturers of transformer power supplies, Russian companies MMP Irbis and IPS, as well as foreign companies Helvar and Mean Well (Taiwan), are especially popular.
Calculation of the power of the UPS transformer
The initial data for calculating the transformer for the UPS are the illumination parameters that are supposed to be achieved by this device. To successfully solve this problem, you will need to determine the length of the ribbon that provides the desired lighting effect. If we proceed from the fact that 60 standard diodes with a total consumption of 4.8 watts are placed on one of its meters, it is possible to calculate the total power by simply multiplying two known numbers. For these purposes, you don't even need a calculator, since all operations are easily performed in the mind.
If it took 10 meters of 60 LEDs to obtain a given level of illumination, the total power consumed by them will be 4.8x10 = 48 watts. Taking into account the small margin for this parameter, you should choose a power supply, the power of which is about 50-60 watts.
Features of transformers and their connections
When connecting power transformers, it is important to consider some of the subtleties of this procedure:
- it is undesirable to turn on the UPS without a load connected to it;
- first connect the LEDs, and then apply voltage to them;
- it is necessary to connect the LED strips taking into account the polarity indicated on the substrate.
Another feature of the procedure is the way the loads are connected (separate ribbons). Typical for them is the parallel connection to the UPS output block by means of a special adapter - its ends are soldered to the contact patch of the tape. However, if the total length of one strip exceeds 5 meters, it is allowed to use a series connection. In all other cases, such a connection cannot be called correct, since it will lead to a decrease in the brightness of the luminescence of the LED elements involved.
To connect an RGB strip to the power supply, you will need an additional module that controls the parameters of colored elements: their brightness and glow intensity. In addition, the device allows you to increase the load capacity of the UPS - it is used as a kind of amplifier.
Homemade transformer power supply unit for 12 volts
The self-manufacture of a transformer power supply for lighting tapes is easiest to consider using the example of an analog model, in which a typical stabilizer is involved. To assemble it, you will need the following components and parts:
- an inductive transformer that steps down the voltage from 220 to 15 volts alternating current;
- rectifier unit based on a diode bridge;
- several filter elements - capacitors with a capacity of at least 1000 μF;
- a conventional zener diode and a control transistor of an n-p-n structure;
- stabilizer microcircuit KREN8B, designed for an output voltage of 12 volts.
According to the scheme of a home-made power supply, the AC voltage reduced to the required level is rectified by a diode bridge, after which unnecessary harmonics are filtered out by means of capacitors. A constant voltage of 15-17 volts is then fed to the output microcircuit, where a stabilized voltage of 12 volts is formed.
Homemade PSU is limited in use and is more suitable for demonstration purposes. To efficiently supply power to a branched network of LED strips, you will need an industrial power supply with a set of additional functions.
