Very often a situation arises when you need to connect an LED to 220 volts. For this, there are special circuits that allow you to make a backlight in a switch or an indicator for household appliances. As a rule, when calculating, the mains voltage is taken based on the amplitude value, and the current passing through the LED should be 30% lower than the nominal one.
LED power calculation
When a constant voltage is used to power an LED, the circuit is connected in series with it. To calculate its resistance, a special formula is used:
Where Upit is the supply voltage, Usd consists of the sum of the voltage drops for each LED, and Inom.sd is the rated current of the resistor. Thus, the formula allows you to determine the resistance with a sufficient degree of accuracy.
Powering diodes from alternating mains voltage has its own characteristics. Here there are high voltage pulses that are applied to the LED in reverse polarity. At this time, the pn junction of the LED is closed, and the current value is zero. The entire mains voltage is applied to the LED chip, while its permissible reverse voltage is only 30-60 V. Thus, AC wiring circuits must limit the forward current and the applied reverse voltage.
Options for connecting LEDs to the network
In the first, most common option, an LED, a diode and a resistor are used for connection. The LED has low power and its reverse voltage exceeds 350 volts. The resistance of the resistor is calculated using the formula given above. To reduce heat, the resistor value can be increased, although this will result in some reduction in light brightness. Several LEDs are connected in series, observing polarity.
There is a second option for how to connect an LED to 220 volts. To reduce the heat generation of the elements present in the circuit, instead of a resistor, you can use it, which is a reactance.
In addition, the resistance can be composite when a resistor and a capacitor are involved. This pair acts as a current-limiting combined resistance. To make the LED glow brighter, the capacitance of the capacitor is increased. The number of LEDs in the circuit can be increased, while the parameters of the circuit elements do not change.
To connect an LED to a 220V AC network, the circuit uses specialized power supplies, which are called LED drivers. Its main technical parameters are current and power. For correct connection through the driver, a fixed or adjustable output current can be used. If you are designing Ice lighting, then it will be much more convenient with a regulator. Typically, ice chips are connected to the driver in series, which allows you to get almost the same current through each component of the circuit. The main disadvantage of such a chain will be the failure of the entire circuit if at least one LED burns out. The driver design can be different, from a simple design based on a quenching capacitor to an advanced one with almost zero ripple coefficient.
The operating principle of most of the considered schemes for connecting LEDs to a 220V network is approximately the same. They limit the current and cut off the reverse wave of alternating voltage. Since most LEDs are afraid of high reverse voltage, a blocking diode is used in the circuits. The latter is IN4004 - it is designed for voltages above 300 volts. If you need to connect many light-emitting components to 220V, you should connect them in series.
The amateur radio designs discussed below can be used in the manufacture of homemade color and music devices, various signal level indicators, smooth switching on and off of lighting, etc.
An example of such inclusion is a typical LED strip with a voltage of 220 volts. It has 60 light-emitting semiconductor LEDs connected in series, which are powered by a rectifier (typical). The disadvantage of this connection scheme to 220V is strong light pulsations.
In this diagram for connecting an LED to 220V, excess voltage is cut off using a capacitor, which is selected based on the reference parameters of the LED current. Resistor power from 0.25 W or higher. The capacitor must be at least 300 volts. The value of the zener diode should be taken a little higher than the supply voltage of the LED, for example, at 5 volts, the domestic zener diode KS156A is perfect.
The circuit works as follows: when the 220V power is turned on, capacitor C1 begins to charge, while from one half-wave it is charged directly, and from the other through a zener diode. As the voltage across the capacitor increases, the zener diode increases its internal resistance, thereby limiting the charging voltage of the capacitor. This circuit is used in the case of powering LEDs with a high operating current - from 20 mA or more.
A typical example of such a design is . The plate with LED components should be installed on the heat sink and a stabilizer placed nearby. If the driver is of poor quality, the light will flicker at a frequency of about 100 Hertz. Such prolonged pulsations can cause irreparable harm to the health of humans or pets.
For LEDs connected to a 220 volt circuit, when creating lamps, you should always try to reduce the level of ripple due to their negative impact on the human visual system. It all depends on the frequency: the lower it is, the more noticeable the pulsation is to the eye. At frequencies above 300 Hz, the pulsations are completely invisible and therefore safe for the eyes.
But pulsations at frequencies of 60-80 Hz and even 100-150 Hz are practically not perceived visually, but they cause increased eye fatigue and, with prolonged exposure, can also impair vision.
Below we will look at diagrams on how to turn on an LED in a 220-volt network to reduce ripple. To do this, the easiest way is to connect a smoothing capacitor in parallel with the light-emitting component.
Table - Dependence of the current through the LEDs on the capacitance of the ballast capacitor.
As soon as power is supplied to the flashing LED circuit, capacitor C2 begins to charge through resistor and diode D1. The constant voltage coming from the capacitor periodically opens, causing the LED to light up briefly. The flash frequency of the latter is set by the capacitance of the capacitor, and the brightness of the flashes by the resistance of the resistor.
Resistance R1 is designed to dampen the amplitude of current surges that occur: at the moment of selecting the brightness of the glow with the SA1 toggle switch, at the moment of connecting to a 220V alternating voltage network and during charging of capacitors. Capacitor C4 is used to reduce voltage ripple after rectifying the alternating voltage, thus reducing the risk of damage to the LEDs when powered from a 220V network.
One of the important issues when working with LEDs is its connection to an AC and high voltage network. It is known that an LED cannot be powered directly from a 220 V network. How to properly assemble the circuit and provide power to solve the problem?
Electrical properties
To answer the question posed above, it is necessary to study the electrical properties of the LED.
Its current-voltage characteristic is a steep line. This means that when the voltage increases even by a very small amount, the current through the emitting semiconductor increases sharply. An increase in current leads to heating of the LED, as a result of which it can simply burn out. This problem is solved by including a limiting resistor in the circuit.
The LED has a low reverse breakdown voltage (about 20 volts), so it cannot be connected to a 220 volt AC network. To prevent current flow in the opposite direction, it is necessary to include a diode in the circuit or turn on a second one opposite the first LED. The connection must be parallel.
So, we know that any circuit for connecting an LED to a 220 volt network must contain a resistor and a rectifier, otherwise power will be impossible.
Why is such a scheme needed? First of all, for the design of the network indicator. An LED light can be an excellent indicator to help determine whether an electrical appliance is plugged in or not. It is added to the circuit of switches and sockets to easily find them in the dark.
Such an indicator begins to glow at a voltage of just a few volts. At the same time, it consumes a minimal amount of electricity due to the low (several miles of amperes) current.
Which resistor should I use?
To select the optimal resistor resistance, you need to use Ohm's law.
R=(Ugrid-Ul.)/Il.nom.
Suppose we took a red LED for the indicator with a nominal current value of 18 mA and a forward voltage of 2.0 Volts.
(311-2)/0.018=17167 Ohm=17 kOhm
Let's explain where the number 311 comes from. This is the peak of a sine wave along which the voltage in our network changes. Without going into the realm of mathematics with all its calculations, we can simply say that the peak voltage is 220 * √2.
Sometimes there are circuits that do not have a rectifying diode. In this case, the resistance must be increased several times in order to reduce the current and protect the indicator light from burning out.
Elementary circuit of a current indicator
What is needed to make the simplest indicator, which is powered from a 220 volt network? Here is the list:
- a regular indicator LED of any color you like;
- resistor from 100 to 200 kOhm (the higher the resistance, the less brightly the light bulb will glow);
- diode with a reverse voltage of 100 volts or more;
- low-power soldering iron so as not to overheat the LED.
Since the number of parts is minimal, the board is not used in installation. The indicator is connected in parallel to the electrical appliance.
For those who do not want to run around looking for a diode, manufacturers have come up with a ready-made two-color indicator in the form of two LEDs of different colors built into one housing. Usually these colors are red and green. In this case, the number of circuit parts is further reduced.
There are other connection schemes in which the resistor is replaced with a capacitor or diode bridges, transistors, etc. are used. But no matter what design features are introduced, the main task is to rectify the current and reduce it to a safe value.
Light indication is an integral part of electronics, with the help of which a person can easily understand the current state of the device. In household electronic devices, the role of indication is performed by an LED installed in the secondary power circuit, at the output of the transformer or stabilizer. However, in everyday life there are also many simple electronic designs that do not have a converter, in which an indicator would be a useful addition. For example, an LED built into a wall switch key would be an excellent reference for the location of the switch at night. And the LED in the body of the extension cord with sockets will signal that it is connected to a 220 V power supply.
Below are several simple diagrams with which even a person with minimal knowledge of electrical engineering can connect an LED to an AC network.
Connection diagrams
An LED is a type of semiconductor diode with a supply voltage and current much lower than in a household electrical network. If connected directly to a 220 volt network, it will instantly fail. Therefore, the light-emitting diode must be connected only through a current-limiting element. The cheapest and easiest to assemble are circuits with a step-down element in the form of a resistor or capacitor.
An important point that you need to pay attention to when connecting an LED to an AC network is the reverse voltage limitation. This task can easily be accomplished by any silicon diode designed for a current no less than that flowing in the circuit. The diode is connected in series after the resistor or with reverse polarity in parallel with the LED.
There is an opinion that it is possible to do without limiting the reverse voltage, since electrical breakdown does not cause damage to the light-emitting diode. However, reverse current can cause overheating of the pn junction, resulting in thermal breakdown and destruction of the LED crystal.
Instead of a silicon diode, you can use a second light-emitting diode with a similar forward current, which is connected in reverse polarity in parallel with the first LED.
The downside to current-limiting resistor circuits is that they require a lot of power to dissipate. This problem becomes especially relevant when connecting a load with high current consumption. This problem is solved by replacing the resistor with a non-polar capacitor, which in such circuits is called ballast or quenching.
A non-polar capacitor connected to an AC network behaves like a resistance, but does not dissipate the power consumed in the form of heat.
In these circuits, when the power is turned off, the capacitor remains undischarged, which creates a risk of electric shock. 
This problem is easily solved by connecting a 0.5-watt shunt resistor with a resistance of at least 240 kOhm to the capacitor.
Calculation of a resistor for an LED
In all of the above circuits with a current-limiting resistor, the resistance is calculated according to Ohm's law: R = U/I, where U is the supply voltage, I is the operating current of the LED. The power dissipated by the resistor is P = U * I. This data can be calculated using.
Important. If you plan to use the circuit in a low-convection package, it is recommended to increase the maximum power dissipation value of the resistor by 30%.
Calculation of the capacity of the quenching capacitor (in μF) is carried out using the following formula: C = 3200*I/U, where I is the load current, U is the supply voltage. This formula is simplified, but its accuracy is sufficient for connecting 1-5 low-current LEDs in series.
Important. To protect the circuit from voltage surges and impulse noise, a quenching capacitor must be selected with an operating voltage of at least 400 V.
It is better to use a ceramic capacitor of the K73–17 type with an operating voltage of more than 400 V or its imported equivalent. Electrolytic (polar) capacitors must not be used.
You need to know this
The main thing is to remember safety precautions. The presented circuits are powered by 220 V AC, and therefore require special attention during assembly.
Connecting the LED to the network must be carried out in strict accordance with the circuit diagram. Deviation from the diagram or negligence can lead to a short circuit or failure of individual parts.
You should carefully assemble transformerless power supplies and remember that they do not have galvanic isolation from the network. The finished circuit must be reliably isolated from adjacent metal parts and protected from accidental contact. It can only be dismantled with the power supply switched off.
A little experiment
To lighten up the boring diagrams a little, we suggest that you familiarize yourself with a small experiment that will be of interest to both novice radio amateurs and experienced professionals.
Read also
To power the LEDs, a constant current source is required. In addition, this current must be stabilized. The household voltage is 220V, which is significantly more than what is needed to power conventional LEDs. Plus, this voltage is variable. How to combine the incompatible and connect the LED to a 220V network? Nothing is impossible, but first let’s try to figure out why this connection might be needed at all.
First of all, we can talk about connecting powerful light sources. In this case, very simple methods cannot be used; specialized drivers or similar devices will be required that will be capable of delivering a stabilized high-power current. Let's leave this option for last.
It is also often necessary to connect a low-power indicator LED to 220V - to, in fact, indicate that voltage is currently present. Or you may need low-power emergency lighting, for which you don’t want to fuss with complex electronics. In these cases, if the required LED currents do not exceed 20-25mA, you can get by with a minimum number of additional parts. Let's take a closer look at these connections.
The easiest way to limit current is to use a resistor. This option is also suitable for an alternating current network with a voltage of 220V. You just need to take into account one important nuance: 220V is the ACTUAL voltage. In fact, the voltage in the household network varies within a wider range - from -310V to +310V. This is the so-called AMPLITUDE voltage. Read more about why this is so on Wikipedia. For us, it is important that to calculate the values of the current-limiting resistor, it is necessary to use not the effective value, but the amplitude value of the alternating current network, i.e. 310V.
The resistance of the resistor is calculated according to the usual Ohm's law:
R = (U a - U L) / I, where U a is the amplitude voltage value (310V), U L is the voltage drop across the LEDs, I is the required current.
The current limiting resistor must be very powerful because it will dissipate a large amount of heat, which will depend on the operating current and the resistance of the resistor:
P = I 2 * R
The resistor will heat up and, if it turns out that it is not designed to dissipate the amount of heat that is generated on it, it will burn out quite effectively. Therefore, you should never forget about the permissible power of the resistor, and for real use, select it with a reserve. If you don't want to do your own resistor calculations, you can use the LED Calculator.
Simple circuits for connecting an LED to a 220V network with a current-limiting resistor
LEDs can only withstand small reverse voltages (up to 5-6V) and require protection to operate on AC power. In the simplest case, a diode can be used for this, which is connected in series with the LED. Requirements for the diode - it must be designed for a reverse voltage of at least 310V and for the forward current that we need. For example, a 1N4007 diode is suitable - reverse voltage 1000V, forward current 1A.
The second option is to connect the diode in parallel with the LED, but in the opposite direction. In this case, any low-power diode, for example, KD521 or similar, will do. Moreover, you can connect a second LED instead of a diode (as shown in the right diagram). In this case, they will protect each other and glow at the same time.
To limit the current in an alternating network, you can also use a so-called ballast capacitor. This is a non-polar ceramic capacitor that is connected in series. Its permissible voltage must be at least one and a half times greater than the mains voltage - at least 400V. The current limitation will depend on the capacitance of the capacitor, which can be calculated using the following empirical formula:
C = (4.45 * I) / (U a - U L), where I is the required current in milliamps. The capacitance value will be in microfarads.
Using a ballast capacitor to connect an LED to a 220V network
In the above circuit, resistor R1 is needed to discharge the capacitor after power is turned off. Without its use, capacitor C1 will retain its charge and will give a very painful blow if you then touch it with its output. Resistor R2 serves to limit the initial charging current of capacitor C1. Its use is very desirable because it extends the life of other parts, in addition, if the capacitor breaks down, it will serve as a fuse and will burn out first, protecting the rest of the circuit.
The remaining parts - LED D1 and protective diode D2 are already familiar to us from previous circuits.
Why not use capacitors instead of a current limiting resistor all the time? The fact is that high-voltage capacitors are quite large in size and even when using them, resistors are still needed - the finished circuit will ultimately take up more space. Their advantage is that they practically do not heat up.
The given diagrams for connecting LEDs to a 220V network are often used in practice. Indicator LEDs can be found in backlit switches.
Diagram of a conventional backlit switch
As you can see, there is not even a protection diode used here! The fact is that the resistance of the resistor is very high, the resulting current is very small - about 1mA. The LED glows not brightly at all, but this glow is enough to illuminate a switch in a dark room.
Ballast capacitor circuits are used in simple LED lamps.
LED lamp circuit with power up to 5W
Here the current is rectified by a diode bridge. Resistors R2 and R3 serve to protect the bridge and LEDs, respectively. To reduce the flicker of light, capacitor C2 is used.
