LEDs have great advantages compared to conventional incandescent lamps and fluorescent lamps, thanks to which they are increasingly used in lighting equipment. Most LED lamps are equipped with a power circuit and can be connected directly to a network with a voltage of 220 V, but there are also models whose operating voltage must be 12 or 24 V. For these, power supply units for LED lamps are provided, which are included in the set or purchased separately.
Features of the power supply of LEDs
To understand the features of the power supply of LED lamps, it is necessary to take into account the features of the operation of LEDs.
As you know, an LED is an electronic device with a semiconductor pn junction, which emits light energy when a current passes through this junction. As the amount of light energy passes through the current transition increases. At the same time, a lot of heat begins to be released for each LED when the current increases too much, which leads to the burning of the device. Therefore, the amount of current flowing through the LED must be limited.
In the simplest case, a resistor connected in series with an LED serves as such a limiter. This limiting scheme is often used in LED strips. The disadvantage of such a scheme is the power consumption of the resistor itself.
LED lamps
The composition of a regular LED lamp with an E27 base includes the following elements:
- LED chip;
- diffuser;
- printed circuit board;
- radiator;
- Power Supply;
- plinth.
Although the efficiency of LEDs is quite high, a fairly significant part of the energy supplied to them is converted into heat. Therefore, a radiator is used to dissipate this heat in the lamp.
To provide power in LED lamps, a circuit including a bridge rectifier and the simplest filter consisting of a capacitor and a resistor is used. To reduce the voltage, a resistor or capacitor is connected in series with the rectification circuit.
The values of the resistor and capacitor for the MR-16 lamp are 1.6 kΩ and 0.8 μF, respectively.
This is a simplified circuit that works in network conditions without voltage spikes or surge impulses. If such a lamp is screwed into an unstable network, it can soon be expected to burn out earlier than the term of operation set according to the nomenclature. Also, the disadvantage of such a scheme can be called the presence of current pulsation, which, taking into account the low inertia of LEDs, leads to pulsation of light, that is, the quality of lighting deteriorates.
Power supply units
Special power supply units for LED lamps help to improve the quality of lighting and increase the power of LEDs. There are transformer and pulse power supplies, as well as drivers.
Power supply units of the first and second type are devices used to obtain a stabilized voltage.
The transformer unit consists of the following elements:
- step-down transformer;
- rectifier;
- filter;
- stabilizer.
With the help of a transformer, the voltage of 220 V is reduced to a working voltage of 12 or 24 V. After rectification with the help of power diodes connected according to the bridge circuit, the voltage is supplied to the smoothing filter, and then to the stabilizer.
Pros:
- simplicity of the scheme;
- junction with a 220 V network;
- can work in idle mode
Cons:
- large weight and dimensions;
- low efficiency;
- overload intolerance.
The operating frequency of the pulsed power supply unit is higher than that of the transformer, so the transformer built into it has a higher efficiency and less weight. Like the previous option, it provides a connection to the 220 V network. The disadvantage is the intolerance of idling and overloads.
The driver is a pulse source of stabilized current, the main elements of which are:
- accumulative throttle;
- transistor key;
- key management scheme.
The operating frequency is 30-50 kHz. The voltage on the LED changes according to the readings of the current in the circuit.
A feature of drivers is the presence of non-sinusoidal currents at its input, which is due to the pulsed nature of its operation. Therefore, high-quality drivers have a two-stage circuit. The first stage is designed to filter the input signal, and the second stage is to provide the specified stabilized current.
The main parameter of the driver is the value of the stabilized current. This means the following. Let there be a driver with a current of 300 mA and a power of 10 W. When an LED with a current of 300 mA and a voltage of 3 V is connected to its output, a current of 300 mA will flow through the LED. The output voltage of the driver will be 3 V. When connecting 2-phase devices in series to the driver, the output voltage will be 6 V, and the current will remain equal to 300 mA. When the next device is connected, the current will remain the same, although the voltage at the output of the driver will increase to 9 V. That is, in any case, the driver maintains the specified current value.
There are quite powerful drivers. For example, the JNY-JC30W driver for a 30-watt LED floodlight produces an output current of 900 mA at an output voltage of 21-40 V.
Choice of power option
If the lamps illuminate a room that does not require a special quality of light, then it is quite possible to use transformer-type or pulse-type power supply units. In this case, light pulsations due to voltage surges will not be particularly noticeable.
In the case when a high-quality light stream is required, as well as if this lamp consumes a lot of power, then it is recommended to use a driver.
The location of the lamp also affects the choice of power supply units. In particular, it affects the degree of protection. In a living room, it should be lower, and in an aggressive environment with dust, moisture, the requirements will be higher.
Rating of power supply unit
When choosing a power supply unit, you must first evaluate the power of the lamp. The power of the power supply unit should be greater than the power consumed by the light source, and it is better if this power has a margin of 20-30%.
When buying LEDs, it is necessary to immediately select a suitable power supply unit for them. At the same time, it is necessary to take into account the supply current and the voltage on the LED. For example, a white LED with a current of 300 mA has a voltage drop of 3-3.4 V, that is, the power required for it is approximately 1 W.
It follows that a driver with a current of 300 mA and a power of 10 W is suitable for an LED lamp with 10 white LEDs.
And in a lamp with red LEDs at a current of 300 mA, 15 LEDs can be installed. After all, the voltage drop on such an LED is only 1.8-2.0 V. And the required power for a red diode is approximately 0.6 W.