Nowadays, LED lighting has become very popular . The thing is that this lighting is not only powerful enough, but also cost-effective. LEDs are semiconductor diodes in an epoxy sheath.
Initially, they were quite weak and expensive. But later very bright white and blue diodes were released into production. By then, their market price had fallen. At the moment, there are LEDs of almost any color, which served as the reason for their use in various fields of activity. These include the illumination of various rooms, the illumination of screens and signs, use on road signs and traffic lights, in the passenger compartment and headlights of cars, in mobile phones, etc.
LEDs consume little power, as a result of which such lighting gradually replaces pre-existing light sources. In specialized stores you can buy various items, which are based on LED lighting, starting from a conventional lamp and LED strip, ending with LED panels. They are all united by the fact that their connection requires a current of 12 or 24 V.
Unlike other light sources that use a heating element, a semiconductor crystal is used here, which generates optical radiation under the influence of current.
To understand the schemes for connecting LEDs to a 220V network, you first need to say that he will not be able to feed directly from such a network. Therefore, to work with LEDs, you must follow a certain sequence of connecting them to the high voltage network.
Electrical properties of the LED
The current-voltage characteristic of the LED is a cool line. That is, if the voltage increases at least a little, the current will increase sharply, this will entail overheating of the LED with its subsequent burnout. To avoid this, it is necessary to include a terminating resistor in the circuit.
But it is important not to forget about the maximum permissible reverse voltage of LEDs of 20 V. And if it is connected to a network with reverse polarity, it will receive an amplitude voltage of 315 volts, that is, 1.41 times more than the current one. The fact is that the current in the network at 220 volts is alternating, and it will initially go one way, and then back.
In order to prevent the current from moving in the opposite direction, the circuit for turning on the LED should be as follows: the diode is connected to the circuit. He will not miss the reverse voltage. In this connection must necessarily be parallel.
Another scheme for connecting an LED to a 220 volt network is to install two on-parallel LEDs.
As for the power supply from the network with a quenching resistor, this is not the best option. Because the resistor will give off strong power. For example, if you use a 24 kΩ resistor, then the dissipation power will be about 3 watts. When you turn on the diode in series, the power will decrease by half. The reverse voltage on the diode should be 400 V. When two counter LEDs turn on, two two-watt resistors can be supplied. Their resistance should be half as much. This is possible when two crystals of different colors in the same case. Usually one crystal is red, the other is green.
In the case when a 200 kΩ resistor is used, the presence of a protective diode is not required, since the reverse current is small and will not cause crystal destruction. This circuit for connecting LEDs to the network has one minus - the small brightness of the bulb. It can be used, for example, to illuminate a room switch.
Due to the fact that the current in the network is alternating, this avoids unnecessary waste of electricity for heating the air with the help of a limiting resistor. The capacitor copes with this task. After all, it passes alternating current and does not heat up at the same time.
It is important to remember that both half-periods of the network must pass through the capacitor in order for it to pass alternating current. And since the LED conducts current only in one direction, it is necessary to put a conventional diode (or even an additional LED) counter-parallel to the LED. Then he will miss the second half-cycle.
When the circuit for connecting the LED to the 220 volt network is turned off, the voltage will remain on the capacitor. Sometimes even the full amplitude is 315 V. This threatens with a shock. To avoid this, in addition to the capacitor, it is necessary to provide also a discharge resistor of a large nominal value, which, if disconnected from the network, will instantly discharge the capacitor. Through this resistor, during normal operation, an insignificant current flows that does not heat it.
To protect against pulsed charging current and as a fuse, we put a low resistance resistor. The capacitor must be special, which is designed for a circuit with an alternating current of at least 250 V, or 400 V.
The LED sequential switching scheme involves the installation of a bulb of several LEDs connected in series. For this example, one counter diode is enough.
Since the voltage drop across the resistor will be less, the total voltage drop across the LEDs must be taken from the power source.
It is necessary that the installed diode be rated for a current similar to the current passing through the LEDs, and the reverse voltage should be equal to the sum of the voltages on the LEDs. It is best to use an even number of LEDs and connect them counter-parallel.
There can be more than ten LEDs in one string. To calculate the capacitor, it is necessary to subtract from the amplitude voltage of the network 315 V the sum of the voltage drop of the LEDs. As a result, we find out the number of voltage drop across the capacitor.
LED connection errors
- The first error is when they connect an LED without a limiter directly to the source. In this case, the LED will very quickly fail, due to the lack of control over the current value.
- The second error is the connection to the common resistor of the LEDs installed in parallel. Due to the fact that there is a spread of parameters, the brightness of the LEDs will be different. In addition, if one of the LEDs fails, the current of the second LED will increase, because of which it can burn out. So when a single resistor is used, it is necessary to connect the LEDs in series. This allows you to leave the current unchanged when calculating the resistor and add the voltage of the LEDs.
- The third error is when the LEDs, which are designed for different currents, turn on in series. This becomes the reason that one of them will burn weakly, or vice versa - to work for wear.
- The fourth mistake is the use of a resistor that has insufficient resistance. Because of this, the current flowing through the LED will be too large. Some part of the energy, when the voltage is too high, is converted into heat, as a result of which the crystal overheats and significantly reduces its service life. The reason for this is defects in the crystal lattice. If the voltage increases even more and the pn junction heats up, this will lead to a decrease in the internal quantum yield. As a result, the brightness of the LED will drop, and the crystal will undergo destruction.
- The fifth error is the inclusion of an LED in 220V, the circuit of which is very simple, in the absence of reverse voltage limitation. The maximum permissible reverse voltage for most LEDs is approximately 2 V, and the reverse half-cycle voltage affects the voltage drop, which is equal to the supply voltage when the LED is locked.
- The sixth reason is the use of a resistor whose power is insufficient. This provokes strong heating of the resistor and the melting process of the insulation, which concerns its wires. Then the paint begins to burn and under the influence of high temperatures, destruction occurs. This is because the resistor dissipates only the power for which it was designed.
Power LED circuit
To connect high-power LEDs, you need to use AC / DC converters, which have a stabilized current output. This will help to abandon the use of a resistor or integrated circuit driver LEDs. At the same time, we can achieve a simple connection of LEDs, comfortable use of the system and lower costs.
Before turning on high-power LEDs, make sure that they are connected to a power source. Do not connect the system to a power supply that is energized, otherwise this will result in failure of the LEDs.
LEDs 5050. Specifications. Inclusion circuit
Low power LEDs also include SMDs. Most often they are used to illuminate buttons on a mobile phone or for decorative LED strip.
5050 LEDs (case size: 5 by 5 mm) are semiconductor light sources with a direct voltage of 1.8-3.4 V, and a direct current per crystal of up to 25 mA. The peculiarity of SMD 5050 LEDs is that their design consists of three crystals, which allow the LED to emit several colors. They are called RGB LEDs. Their case is made of heat-resistant plastic. The dispersion lens is transparent and coated with epoxy.
In order for the 5050 LEDs to work as long as possible, they must be connected to the resistance values in series. For maximum circuit reliability, it is best to connect a separate resistor to each circuit.
Wiring Diagrams for Flashing LEDs
A flashing LED is an LED in which an integrated pulse generator is integrated . The frequency of flashes he has is from 1.5 to 3 Hz.
Despite the fact that the flashing LED is quite compact, the semiconductor chip of the generator and additional elements are contained in it.
As for the voltage of the flashing LED, it is universal and can vary. For example, for high-voltage it is Z-14 volts, and for low-voltage it is 1.8-5 volts.
Accordingly, the positive qualities of the flashing LED can be attributed, in addition to the small size and compactness of the light signaling device, also a wide range of permissible voltage. In addition, it can emit various colors.
About three multi-colored LEDs with different flash intervals are embedded in certain types of flashing LEDs.
Flashing LEDs are also quite economical. The fact is that the electronic circuit for turning on the LED is made on MOS structures, so that a separate functional unit can be replaced with a blinking diode. Due to their small size, flashing LEDs are often used in compact devices requiring small radio elements.
In the diagram, blinking LEDs are denoted in the same way as ordinary ones, the only exception is that the arrow lines are not just straight, but dashed. Thus, they symbolize the blinking of the LED.
Through the transparent housing of the flashing LED, it can be seen that it consists of two parts. There, on the negative terminal of the cathode base, there is a crystal of a light emitting diode, and on the anode terminal there is a generator chip.
All the components of this device are connected with the help of three golden wire jumpers. To distinguish a blinking LED from a normal one, just look at the transparent case in the light. There you can see two substrates of the same size.
On one substrate is a crystal cube of the light emitter. It consists of a rare earth alloy. In order to increase the luminous flux and focusing, as well as to form a radiation pattern, a parabolic aluminum reflector is used. This reflector in a blinking LED is smaller in size than in a regular one. This is due to the fact that in the second half of the case there is a substrate with an integrated circuit.
Between themselves, these two substrates communicate with the help of two golden wire jumpers. As for the housing of the flashing LED, it can be made of either light-diffusing matte plastic or transparent plastic.
Due to the fact that the emitter in the blinking LED is not on the axis of symmetry of the case, for the functioning of uniform illumination it is necessary to use a monolithic color diffuse fiber.
The presence of a transparent housing can only be found in flashing large-diameter LEDs that have a narrow radiation pattern.
The high-frequency master oscillator consists of a flashing LED generator. Its operation is constant, and the frequency is about 100 kHz.
Along with the high-frequency generator, a divider on logic elements also functions. He, in turn, carries out high frequency division to 1.5-3 Hz. The reason for the joint use of a high-frequency generator with a frequency divider is that for the low-frequency generator to work, a capacitor with the largest capacity for the timing circuit is required.
Bringing a high frequency to 1-3 Hz requires the presence of dividers on the logic elements. And they can be quite easily applied to a small space of a semiconductor crystal. On the semiconductor substrate, in addition to the divider and the master high-frequency generator, there is a protective diode and an electronic key. The limiting resistor is built into the flashing LEDs, which are designed for voltage from 3 to 12 volts.
Low voltage flashing LEDs
As for the low-voltage flashing LEDs, they do not have a limiting resistor. When the power is reversed, a protective diode is required. It is necessary in order to prevent the failure of the microcircuit.
To ensure that the operation of high-voltage flashing LEDs is long-term and uninterrupted, the supply voltage should not exceed 9 volts. If the voltage increases, the dissipated power of the flashing LED will increase, which will lead to heating of the semiconductor crystal. Subsequently, due to excessive heating, degradation of the flashing LED will begin.
When it is necessary to check the serviceability of the flashing LED, in order to do this safely, you can use a 4.5 volt battery and a 51 ohm resistor connected in series with the LED. The power of the resistor must be at least 0.25 watts.
Installation of LEDs is a very important issue for the reason that it is directly related to their viability.
Since LEDs and microcircuits do not like static and overheating, it is necessary to solder parts as quickly as possible, no more than five seconds. In this case, you need to use a low power soldering iron. The temperature of the sting should not exceed 260 degrees.
When soldering, you can additionally use medical tweezers. With tweezers, the LED is clamped closer to the case, due to which, when soldering, an additional heat removal from the crystal is created. So that the legs of the LED do not break, they need to be bent slightly. They must remain parallel to each other.
In order to avoid overload or short circuit, the device must be equipped with a fuse.
LED smooth switching circuit
The scheme of smooth on and off LEDs - popular among others, it is interested in car owners who want to tune their cars. This scheme is used to illuminate the interior of the car. But this is not its only application. It is used in other areas.
A simple scheme for smoothly turning on the LED should consist of a transistor, a capacitor, two resistors and LEDs. It is necessary to select such current-limiting resistors that can pass a current of 20 mA through each chain of LEDs.
The scheme of smooth on and off LEDs will not be complete without the presence of a capacitor. It is he who allows her to collect. The transistor must be a pnp structure. And the current on the collector should not be less than 100 mA. If the scheme for smoothly turning on the LEDs is assembled correctly, then, for example, the interior lighting of a car will have a smooth turn on of the LEDs for 1 second, and after closing the doors, a smooth turn off.
Alternately turn on the LEDs. Scheme
One of the lighting effects with the use of LEDs is their alternate inclusion. It is called running fire. Such a circuit works from autonomous power. , .
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