Now 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 shell.
Initially they were quite weak and expensive. But later, very bright white and blue diodes were released into production. By that time, their market price had declined. At the moment, there are LEDs of almost any color, which was the reason for their use in various fields of activity. These include lighting various rooms, backlighting screens and signs, use on road signs and traffic lights, in the interior and headlights of cars, in mobile phones, etc.
Description
LEDs consume little electricity, with the result that such lighting is gradually replacing pre-existing light sources. In specialized stores, you can purchase various items based on LED lighting, ranging from a conventional lamp and LED strip,ending with LED panels. They are all united by the fact that they require a current of 12 or 24 V to connect them.
Unlike other light sources that use a heating element, this one uses a semiconductor crystal that generates optical radiation when a current is applied.
To understand the schemes for connecting LEDs to a 220V network, you first need to say that it cannot be powered directly from such a network. Therefore, to work with LEDs, you must follow a certain sequence of connecting them to a high voltage network.
Electrical properties of LED
The current-voltage characteristic of an LED is a steep line. That is, if the voltage increases at least a little, then the current will increase sharply, this will lead to overheating of the LED with its subsequent burnout. To avoid this, you must include a limiting resistor in the circuit.
But it is important not to forget about the maximum allowable 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 220 volt network is alternating, and it will initially go in one direction and then back.
In order to prevent the current from moving in the opposite direction, the LED switching circuit should be as follows: a diode is included in the circuit. It will not pass reverse voltage. In this case, the connection must be parallel.
Another scheme for connecting the LED to the network 220volt is to install two LEDs back-to-back.
As for mains power 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 power dissipation will be approximately 3 watts. When a diode is connected in series, the power will be halved. The reverse voltage across the diode should be 400 V. When two opposite LEDs turn on, you can put two two-watt resistors. Their resistance should be two times less. This is possible when there are two crystals of different colors in one case. Usually one crystal is red and the other is green.
When a 200 kΩ resistor is used, a protective diode is not required, as the return current is small and will not destroy the crystal. This scheme for connecting LEDs to the network has one minus - the small brightness of the light 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 wasting electricity on heating the air with a limiting resistor. The capacitor does the job. After all, it passes alternating current and does not heat up.
It is important to remember that both half-cycles 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 another additional LED) in the opposite direction.parallel to the LED. Then he will skip the second half-period.
When the circuit for connecting the LED to the 220 volt network is turned off, voltage will remain on the capacitor. Sometimes even full amplitude at 315 V. This threatens with an electric shock. To avoid this, in addition to the capacitor, it is also necessary to provide a high-value discharge resistor, which, if disconnected from the network, will instantly discharge the capacitor. A small amount of current flows through this resistor during normal operation without heating 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 an alternating current circuit of at least 250 V, or 400 V.
The LED sequencing scheme involves the installation of a light bulb from several LEDs connected in series. For this example, one counter diode is sufficient.
Since the voltage drop across the resistor will be less, the total voltage drop across the LEDs must be subtracted from the power source.
It is necessary that the installed diode be designed for a current similar to the current passing through the LEDs, and the reverse voltage must be equal to the sum of the voltages on the LEDs. It is best to use an even number of LEDs and connect them back-to-back.
There can be more than ten LEDs in one chain. To calculate the capacitor, you need 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 the number of fallingvoltage across the capacitor.
LED connection errors
- The first mistake is when you connect an LED without a limiter, directly to the source. In this case, the LED will fail very quickly, due to the lack of control over the amount of current.
- The second mistake is connecting LEDs installed in parallel to a common resistor. Due to the fact that there is a scatter 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, due to which it may burn out. So when a single resistor is used, the LEDs must be connected in series. This allows you to leave the current the same when calculating the resistor and add the voltages of the LEDs.
- The third mistake is when LEDs that are designed for different currents are switched on in series. This causes one of them to burn weakly, or vice versa - to wear out.
- The fourth mistake is to use a resistor that doesn't have enough resistance. Because of this, the current flowing through the LED will be too large. Some of the energy, at an overestimated current voltage, is converted into heat, resulting in overheating of the crystal and a significant reduction in its service life. The reason for this is the defects of the crystal lattice. If the voltage is further increased and the p-n junction heats up, this will lead to a decrease in the internal quantum yield. As a resultthe brightness of the LED will drop and the crystal will be destroyed.
- The fifth mistake is turning on the LED at 220V, the circuit of which is very simple, in the absence of reverse voltage limitation. The maximum allowable reverse voltage for most LEDs is approximately 2V, and the reverse half-cycle voltage affects the voltage drop, which is equal to the supply voltage when the LED is off.
- The sixth reason is the use of a resistor whose power is insufficient. This provokes a strong heating of the resistor and the process of melting the insulation that touches its wires. Then the paint begins to burn and under the influence of high temperatures destruction occurs. This is because the resistor only dissipates the power it was designed to handle.
Power LED switching circuit
To connect powerful LEDs, you need to use AC / DC converters that have a stabilized current output. This will eliminate the need for a resistor or an LED driver IC. At the same time, we can achieve simple LED connection, comfortable system use and cost reduction.
Before you turn on powerful LEDs, make sure that they are connected to a power source. Do not connect the system to a power supply that is energized, otherwise the LEDs will fail.
5050 LEDs. Characteristics. Wiring Diagram
Low power LEDs also include surface mount LEDs (SMD). Most often they are used forbacklighting buttons in a mobile phone or for decorative LED strip.
5050 LEDs (body type size: 5 by 5 mm) are semiconductor light sources, the forward voltage of which is 1.8-3.4 V, and the direct current strength for each crystal is up to 25 mA. The peculiarity of SMD 5050 LEDs is that their design consists of three crystals, which allow the LED to emit multiple colors. They are called RGB LEDs. Their body is made of heat-resistant plastic. The diffuse lens is transparent and filled with epoxy resin.
In order for the 5050 LEDs to last as long as possible, they must be connected to the resistance ratings in series. For maximum reliability of the circuit, it is better to connect a separate resistor for each chain.
Schemes for switching on flashing LEDs
The flashing LED is an LED with an integral pulse generator built into it. Its flash frequency is from 1.5 to 3 Hz.
Despite the fact that the blinking LED is quite compact, it contains a semiconductor generator chip and additional elements.
As for the voltage of the blinking LED, it is universal and can vary. For example, for high-voltage it is 3-14 volts, and for low-voltage it is 1.8-5 volts.
Accordingly, the positive qualities of a flashing LED include, 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.
In separate types of flashingLEDs are built in about three multi-colored LEDs, which have different flash intervals.
Flashing LEDs are also quite economical. The fact is that the electronic circuit for switching on the LED is made on MOS structures, thanks to which a separate functional unit can be replaced with a flashing diode. Due to their small size, flashing LEDs are often used in compact devices that require small radio elements.
In the diagram, blinking LEDs are indicated in the same way as regular ones, the only exception is that the lines of the arrows are not just straight, but dotted. Thus, they symbolize the flashing of the LED.
Through the transparent body of the blinking LED, you can see that it consists of two parts. There, on the negative terminal of the cathode base, there is a light emitting diode crystal, and on the anode terminal, there is an oscillator chip.
All components of this device are connected using three golden wire jumpers. To distinguish a blinking LED from a normal one, just look at the transparent housing in the light. There you can see two substrates of the same size.
On one substrate is a crystal light emitter cube. It is made of rare earth alloy. In order to increase the luminous flux and focus, as well as to form the radiation pattern, a parabolic aluminum reflector is used. This reflector in the blinking LED is smaller in size than in the normal one. This is because in the second halfcase contains a substrate with an integrated circuit.
These two substrates are connected to each other by means of two golden wire bridges. As for the body of the blinking 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 located on the axis of symmetry of the body, it is necessary to use a monolithic colored diffuse light guide for the functioning of uniform illumination.
The presence of a transparent housing can only be found in flashing LEDs of large diameter, which have a narrow radiation pattern.
The flashing LED oscillator consists of a high-frequency master oscillator. Its work 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, divides the high frequency up to 1.5-3 Hz. The reason for using a high-frequency generator with a frequency divider is that the operation of a low-frequency generator requires a capacitor with the largest capacitance for the timing circuit.
Bringing the high frequency up to 1-3 Hz requires the presence of dividers on 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 master high-frequency oscillator, there is a protective diode and an electronic switch. Restrictivethe resistor is built into the flashing LEDs, which are rated for a voltage of 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 supply is reversed, a protective diode is required. It is necessary in order to prevent the failure of the microcircuit.
In order for the high-voltage flashing LEDs to work for a long time and go smoothly, the supply voltage should not exceed 9 volts. If the voltage rises, then the power dissipation of the blinking 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 he alth of a 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 0.25W.
Installation of LEDs
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 tip should not exceed 260 degrees.
When soldering, you can additionally use medical tweezers. Tweezers LEDis clamped closer to the body, due to which additional heat removal from the crystal is created during soldering. So that the legs of the LED do not break, they must not be bent much. They should stay parallel to each other.
In order to avoid overload or short circuit, the device must be equipped with a fuse.
Scheme for smooth turning on LEDs
The soft turn on and off LED scheme is popular among others, and car owners who want to tune their cars are interested in it. This scheme is used to illuminate the interior of the car. But this is not its only application. It is used in other areas as well.
A simple LED soft start circuit would consist of a transistor, a capacitor, two resistors and an LED. It is necessary to choose such current-limiting resistors that can pass a current of 20 mA through each string of LEDs.
The circuit for smoothly turning on and off the LEDs will not be complete without a capacitor. It is he who allows her to collect. The transistor must be p-n-p-structure. And the current on the collector should not be less than 100 mA. If the LED soft start circuit is assembled correctly, then, using the example of a car interior lighting, the LEDs will turn on smoothly in 1 second, and after the doors are closed, they will turn off smoothly.
Alternate switching on of LEDs. Diagram
One of the lighting effects using LEDs is turning them on one by one. It is called running fire. Such a scheme works from an autonomous power supply. For its design, a conventional switch is used, which supplies power to each of the LEDs in turn.
Consider a device consisting of two microcircuits and ten transistors, which together make up the master oscillator, control and indexing itself. From the output of the master oscillator, the pulse is transmitted to the control unit, which is also a decimal counter. Then the voltage is applied to the base of the transistor and opens it. The anode of the LED is connected to the positive of the power source, which leads to a glow.
The second pulse forms a logical unit at the next output of the counter, and a low voltage will appear on the previous one and close the transistor, causing the LED to turn off. Then everything happens in the same sequence.
