All about LED voltage, and how to find out how many volts it is designed for

07.06.2019
LED is a semiconductor device that converts direct electric current into light radiation. The English name LED stands for light emitting diode. If earlier LEDs were of interest only to a narrow circle of scientists, now they are actively used by designers to decorate rooms and develop lighting design concepts. Unlike incandescent lamps, LEDs convert current into light radiation with minimal losses, that is, LED lamps practically do not heat up if there is a good heat sink.

If in the middle of the last century scientists were able to obtain a meager efficiency of only 2%, now LEDs on average produce an efficiency of 35-45%, although there are also real record holders whose efficiency reaches a fantastic 60%. LEDs can work for a long time. The devices are low-voltage, that is, safe for humans. The main aesthetic advantage of LEDs is that the light they emit is “clean”, as it lies in a narrow range of the spectrum. Devices have several basic characteristics: power, current consumption, color temperature and voltage. Let's talk about how to determine voltage further.

Concept of voltage drop (operating)

A light-emitting diode (aka LED) has one important characteristic - operating voltage or drop voltage. This value shows how many volts the voltage will decrease when passing through the LED in a series connection.

For understanding, it’s worth giving a small step-by-step example:

1. The diode has a drop of 3.4 V, and the supply voltage is 12 V.
2. After powering the first diode, 8.6 V will remain from 12 V (12-3.4 = 8.6).
3. On the second, another 3.4 V will be lost, and 5.2 V will remain (8.6-3.4 = 5.2).
4. After the third we get 1.8 V (5.2-3.4 = 1.8).

The final value is less than the voltage drop of the light-emitting diode, which means that it will not be possible to power more of them.

The operating voltage is influenced by the material from which the LED is made. According to operating voltage they are divided into:

1. LED with voltage from 3 V to 3.8 V: blue, white, blue-green.
2. LED with voltage from 1.8 V to 2.1 V: red, yellow, orange, green.

Correct LED activation

An LED is a diode that lights up when current flows through it. In English, an LED is called a light emitting diode, or LED.

The color of the LED glow depends on the additives added to the semiconductor. For example, impurities of aluminum, helium, indium, and phosphorus cause a glow from red to yellow. Indium, gallium, nitrogen makes the LED glow from blue to green. When a phosphor is added to a blue crystal, the LED will glow white. Currently, the industry produces LEDs of all colors of the rainbow, but the color does not depend on the color of the LED housing, but on the chemical additives in its crystal. An LED of any color can have a transparent body.

The first LED was manufactured in 1962 at the University of Illinois. In the early 1990s, bright LEDs appeared, and a little later, super bright ones. The advantages of LEDs over incandescent light bulbs are undeniable, namely:

* Low power consumption - 10 times more economical than light bulbs * Long service life - up to 11 years of continuous operation * High durability - not afraid of vibrations and shocks * Wide variety of colors * Ability to work at low voltages * Environmental and fire safety - no toxic substances in LEDs . LEDs do not heat up, which prevents fires.

LED markings

Rice. 1.

Design of 5 mm indicator LEDs

An LED crystal is placed in the reflector. This reflector sets the initial scattering angle. The light is then passed through an epoxy resin housing. It reaches the lens - and then it begins to scatter on the sides at an angle depending on the design of the lens, in practice - from 5 to 160 degrees.

Emitting LEDs can be divided into two large groups: visible LEDs and infrared (IR) LEDs. The former are used as indicators and illumination sources, the latter - in remote control devices, infrared transceivers, and sensors. Light-emitting diodes are marked with a color code (Table 1). First, you need to determine the type of LED by the design of its housing (Fig. 1), and then clarify it by color markings in the table.

Rice. 2.

Types of LED housings

LED colors

LEDs come in almost every color: red, orange, amber, amber, green, blue and white. Blue and white LED are a little more expensive than other colors. The color of LEDs is determined by the type of semiconductor material from which it is made, and not by the color of the plastic of its housing. LEDs of any color come in a colorless case, in which case the color can only be found out by turning it on...

Table 1.

LED markings

Multicolor LEDs

A multicolor LED is designed simply; as a rule, it is red and green combined into one housing with three legs. By changing the brightness or the number of pulses on each crystal, you can achieve different glow colors.

LEDs are connected to a current source, anode to positive, cathode to negative. The negative (cathode) of an LED is usually marked with a small cut of the body or a shorter lead, but there are exceptions, so it is better to clarify this fact in the technical characteristics of a particular LED.

In the absence of these marks, the polarity can be determined experimentally by briefly connecting the LED to the supply voltage through the appropriate resistor. However, this is not the best way to determine polarity. In addition, in order to avoid thermal breakdown of the LED or a sharp reduction in its service life, it is impossible to determine the polarity “at random” without a current-limiting resistor. For quick testing, a resistor with a nominal resistance of 1k ohms is suitable for most LEDs as long as the voltage is 12V or less.

When connecting an LED, the polarity must be observed, otherwise the device may be damaged. The breakdown voltage is specified by the manufacturer and is usually more than 5 V for a single LED. Why? As is clear from the name, an LED is not a rectifying diode, and although they share the property of passing current in one direction, there is a significant difference between them. In order for an LED to emit in the visible range, it has a significantly wider bandgap than a conventional diode. And the parasitic parameter of diodes, such as internal capacitance, directly depends on the band gap. When the direction of the current changes, this capacitance is discharged over a period of time, called the closing time, depending on the size of this capacitance. During a capacitance discharge, the LED crystal experiences significant peak loads for a much longer time than a conventional diode. With a subsequent change in the direction of the current to the “correct” one, the situation repeats. Since the turn-on/off time of conventional diodes is much shorter, it is necessary to use them in AC circuits, including in series with LEDs, to reduce the negative influence of alternating current on the LED chip. If the LED product does not have built-in reverse polarity protection, then a connection error will also lead to a decrease in service life. Some LEDs have a current-limiting resistor built into them “from the factory” and can immediately be connected to a 12 or 5 volt source, but such LEDs are quite rare and most often it is necessary to connect an external current-limiting resistor to the LED.

A word of warning: do not point the LED beam directly at your eye (or your friend’s eye) at close range, as this can damage your vision.

Supply voltage

The two main characteristics of LEDs are voltage drop and current. Typically, LEDs are designed for a current of 20 mA, but there are exceptions, for example, quad-chip LEDs are usually designed for 80 mA, since one LED housing contains four semiconductor crystals, each of which consumes 20 mA. For each LED, there are permissible values ​​of supply voltage Umax and Umaxrev (for direct and reverse switching, respectively). When voltages above these values ​​are applied, an electrical breakdown occurs, as a result of which the LED fails. There is also a minimum value of the supply voltage Umin at which the LED glows. The range of supply voltages between Umin and Umax is called the “working” zone, since this is where the LED operates.

Supply voltage - this parameter is not applicable for the LED. LEDs do not have this characteristic, so you cannot connect LEDs to a power source directly. The main thing is that the voltage from which the LED is powered (through a resistor) is higher than the direct voltage drop of the LED (the forward voltage drop is indicated in the characteristics instead of the supply voltage and for conventional indicator LEDs it ranges on average from 1.8 to 3.6 volts). The voltage indicated on the LED packaging is not the supply voltage. This is the amount of voltage drop across the LED. This value is necessary to calculate the remaining voltage that has not “dropped” on the LED, which takes part in the formula for calculating the resistance of the current-limiting resistor, since it is this that needs to be adjusted. A change in the supply voltage of just one tenth of a volt for a conventional LED (from 1.9 to 2 volts) will cause a fifty percent increase in the current flowing through the LED (from 20 to 30 milliamps).

For each LED of the same rating, the voltage suitable for it may be different. By switching on several LEDs of the same rating in parallel and connecting them to a voltage of, for example, 2 volts, we risk, due to the variation in characteristics, quickly burning some copies and under-illuminating others. Therefore, when connecting an LED, it is necessary to monitor not the voltage, but the current.

The current value for the LED is the main parameter, and is usually 10 or 20 milliamps. It doesn't matter what the tension is. The main thing is that the current flowing in the LED circuit corresponds to the nominal value for the LED. And the current is regulated by a resistor connected in series, the value of which is calculated by the formula:

R

— resistor resistance in ohms.
Upit
is the voltage of the power source in volts.
Upad
is the direct voltage drop across the LED in volts (indicated in the specifications and is usually around 2 volts).
When several LEDs are connected in series, the voltage drops add up. I
is the maximum forward current of the LED in amperes (indicated in the specifications and is usually either 10 or 20 milliamps, i.e. 0.01 or 0.02 amperes).
When several LEDs are connected in series, the forward current does not increase. 0.75
is the reliability coefficient for the LED.

We should also not forget about the power of the resistor. Power can be calculated using the formula:

P

— resistor power in watts.
Upit
is the effective (effective, root-mean-square) voltage of the power source in volts.
Upad
is the direct voltage drop across the LED in volts (indicated in the specifications and is usually around 2 volts).
When several LEDs are connected in series, the voltage drops add up. . R
is the resistance of the resistor in ohms.

Calculation of the current-limiting resistor and its power for one LED

Typical LED Characteristics

Typical parameters of a white indicator LED: current 20 mA, voltage 3.2 V. Thus, its power is 0.06 W.

Also classified as low-power are surface-mounted LEDs (SMD). They illuminate the buttons on your cell phone, the screen of your monitor if it is LED-backlit, they are used to make decorative LED strips on a self-adhesive base, and much more. There are two most common types: SMD 3528 and SMD 5050. The first contain the same crystal as indicator LEDs with leads, that is, its power is 0.06 W. But the second one has three such crystals, so it can no longer be called an LED - it’s an LED assembly. It is common to call SMD 5050 LEDs, but this is not entirely correct. These are assemblies. Their total power is, respectively, 0.2 W. The operating voltage of an LED depends on the semiconductor material from which it is made; accordingly, there is a relationship between the color of the LED and its operating voltage.

Table of LED voltage drop depending on color

By the magnitude of the voltage drop when testing LEDs with a multimeter, you can determine the approximate color of the LED glow according to the table.

Serial and parallel connection of LEDs

When connecting LEDs in series, the resistance of the limiting resistor is calculated in the same way as with one LED, simply the voltage drops of all LEDs are added together according to the formula:

When connecting LEDs in series, it is important to know that all LEDs used in the garland must be of the same brand. This statement should be taken not as a rule, but as a law.

To find out what is the maximum number of LEDs that can be used in a garland, you should use the formula

Where:

* Nmax – maximum permissible number of LEDs in a garland * Upit – Voltage of the power source, such as a battery or accumulator. In volts. * Upr - Direct voltage of the LED taken from its passport characteristics (usually ranges from 2 to 4 volts). In volts. * With changes in temperature and aging of the LED, Upr may increase. Coeff. 1.5 gives a margin for such a case.

With this calculation, “N” can have a fractional form, for example 5.8. Naturally, you cannot use 5.8 LEDs, so you should discard the fractional part of the number, leaving only the whole number, that is, 5.

The limiting resistor for sequential switching of LEDs is calculated in exactly the same way as for single switching. But in the formulas one more variable “N” is added - the number of LEDs in the garland. It is very important that the number of LEDs in the garland is less than or equal to “Nmax” - the maximum allowable number of LEDs. In general, the following condition must be met: N =

All other calculations are carried out in the same way as calculating a resistor when the LED is turned on individually.

If the power supply voltage is not enough even for two LEDs connected in series, then each LED must have its own limiting resistor.

Parallel connection of LEDs with a common resistor is a bad solution. As a rule, LEDs have a range of parameters, each requiring slightly different voltages, which makes such a connection practically unworkable. One of the diodes will glow brighter and take on more current until it fails. This connection greatly accelerates the natural degradation of the LED crystal. If LEDs are connected in parallel, each LED must have its own limiting resistor.

A series connection of LEDs is also preferable from the point of view of economical consumption of the power source: the entire serial chain consumes exactly as much current as one LED. And when they are connected in parallel, the current is as many times greater as the number of parallel LEDs we have.

Calculating the limiting resistor for series-connected LEDs is as simple as for a single one. We simply sum up the voltage of all the LEDs, subtract the resulting sum from the voltage of the power supply (this will be the voltage drop across the resistor) and divide by the current of the LEDs (usually 15 - 20 mA).

What if we have a lot of LEDs, several dozen, and the power supply does not allow connecting them all in series (there is not enough voltage)? Then we determine, based on the voltage of the power source, how many maximum LEDs we can connect in series. For example, for 12 volts, these are 5 two-volt LEDs. Why not 6? But something must also drop at the limiting resistor. Here we take the remaining 2 volts (12 - 5x2) for calculation. For a current of 15 mA, the resistance will be 2/0.015 = 133 Ohms. The closest standard is 150 Ohms. But we can now connect as many of these chains of five LEDs and a resistor each as we like. This method is called a parallel-series connection.

If there are LEDs of different brands, then we combine them in such a way that in each branch there are LEDs of only ONE type (or with the same operating current). In this case, it is not necessary to maintain the same voltages, because we calculate our own resistance for each branch.

Next, we will consider a stabilized circuit for switching on LEDs. Let's touch on the manufacture of a current stabilizer. There is a KR142EN12 microcircuit (a foreign analogue of LM317), which allows you to build a very simple current stabilizer. To connect an LED (see figure), the resistance value is calculated as R = 1.2 / I (1.2 is the voltage drop in the stabilizer) That is, at a current of 20 mA, R = 1.2 / 0.02 = 60 Ohms. The stabilizers are designed for a maximum voltage of 35 volts. It’s better not to overextend them and supply a maximum of 20 volts. With this switching on, for example, a white LED of 3.3 volts, it is possible to supply a voltage to the stabilizer from 4.5 to 20 volts, while the current on the LED will correspond to a constant value of 20 mA. With a voltage of 20V, we find that 5 white LEDs can be connected in series to such a stabilizer, without worrying about the voltage on each of them, the current in the circuit will flow 20mA (the excess voltage will be extinguished at the stabilizer).

Important! A device with a large number of LEDs carries a lot of current. It is strictly forbidden to connect such a device to an active power source. In this case, a spark occurs at the connection point, which leads to the appearance of a large current pulse in the circuit. This pulse disables LEDs (especially blue and white). If the LEDs operate in a dynamic mode (constantly turning on, off and blinking) and this mode is based on the use of a relay, then a spark should be prevented from occurring at the relay contacts.

Each chain should be assembled from LEDs of the same parameters and from the same manufacturer. Also important! Changing the ambient temperature affects the current flow through the crystal. Therefore, it is advisable to manufacture the device so that the current flowing through the LED is not 20 mA, but 17-18 mA. The loss of brightness will be insignificant, but a long service life will be ensured.

How to power an LED from a 220 V network.

It would seem that everything is simple: we put a resistor in series, and that’s it. But you need to remember one important characteristic of the LED: the maximum allowable reverse voltage. For most LEDs it is about 20 volts. And when you connect it to the network with reverse polarity (the current is alternating, half a cycle goes in one direction, and the second half in the opposite direction), the full amplitude voltage of the network will be applied to it - 315 volts! Where does this figure come from? 220 V is the effective voltage, but the amplitude is {root of 2} = 1.41 times greater. Therefore, in order to save the LED, you need to place a diode in series with it, which will not allow reverse voltage to pass through to it.

Another option for connecting an LED to a 220V power supply:

Or put two LEDs back-to-back.

The option of power supply from the mains with a quenching resistor is not the most optimal: significant power will be released through the resistor. Indeed, if we use a 24 kOhm resistor (maximum current 13 mA), then the power dissipated across it will be about 3 W. You can reduce it by half by connecting a diode in series (then heat will be released only during one half-cycle). The diode must have a reverse voltage of at least 400 V. When connecting two counter LEDs (there are even those with two crystals in one housing, usually of different colors, one crystal is red, the other is green), you can put two two-watt resistors, each with twice the resistance less. I’ll make a reservation that by using a high-resistance resistor (for example, 200 kOhm), you can turn on the LED without a protective diode. The reverse breakdown current will be too low to cause destruction of the crystal. Of course, the brightness is very low, but for example, to illuminate a switch in the bedroom in the dark, it will be quite enough. Due to the fact that the current in the network is alternating, you can avoid unnecessary waste of electricity on heating the air with a limiting resistor. Its role can be played by a capacitor that passes alternating current without heating up. Why this is so is a separate question, we will consider it later. Now we need to know that in order for a capacitor to pass alternating current, both half-cycles of the network must pass through it. But the LED only conducts current in one direction. This means that we place a regular diode (or a second LED) counter-parallel to the LED, and it will skip the second half-cycle.

But now we have disconnected our circuit from the network. There is some voltage left on the capacitor (up to the full amplitude, if we remember, equal to 315 V). To avoid accidental electric shock, we will provide a high-value discharge resistor parallel to the capacitor (so that during normal operation a small current flows through it without causing it to heat up), which, when disconnected from the network, will discharge the capacitor in a fraction of a second. And to protect against pulsed charging current, we will also install a low-resistance resistor. It will also play the role of a fuse, instantly burning out in the event of an accidental breakdown of the capacitor (nothing lasts forever, and this also happens).

The capacitor must be for a voltage of at least 400 volts, or special for alternating current circuits with a voltage of at least 250 volts. What if we want to make an LED light bulb from several LEDs? We turn them all on in series; one counter diode is enough for all of them.

The diode must be designed for a current no less than the current through the LEDs, and the reverse voltage must be no less than the sum of the voltage across the LEDs. Better yet, take an even number of LEDs and turn them on back-to-back.

In the figure, there are three LEDs in each chain; in fact, there may be more than a dozen of them. How to calculate a capacitor? From the amplitude voltage of the 315V network, we subtract the sum of the voltage drop across the LEDs (for example, for three white ones this is approximately 12 volts). We get the voltage drop across the capacitor Up=303 V. The capacity in microfarads will be equal to (4.45*I)/Up, where I is the required current through the LEDs in milliamps. In our case, for 20 mA the capacitance will be (4.45*20)/303 = 89/303 ~= 0.3 µF. You can place two 0.15 µF (150 nF) capacitors in parallel.

The most common mistakes when connecting LEDs

1. Connect the LED directly to the power source without a current limiter (resistor or special driver chip). Discussed above. The LED quickly fails due to poorly controlled current.

2. Connecting LEDs connected in parallel to a common resistor. Firstly, due to the possible scatter of parameters, the LEDs will light up with different brightness. Secondly, and more importantly, if one of the LEDs fails, the current of the second will double, and it may also burn out. If you use one resistor, it is more advisable to connect the LEDs in series. Then, when calculating the resistor, we leave the current the same (for example, 10 mA), and add up the forward voltage drop of the LEDs (for example, 1.8 V + 2.1 V = 3.9 V).

3. Switching on LEDs in series, designed for different currents. In this case, one of the LEDs will either wear out or glow dimly, depending on the current setting with the limiting resistor.

4. Installation of an insufficient resistance resistor. As a result, the current flowing through the LED is too high. Since part of the energy is converted into heat due to defects in the crystal lattice, it becomes too much at high currents. The crystal overheats, as a result of which its service life is significantly reduced. With an even greater increase in current due to heating of the pn junction region, the internal quantum output decreases, the brightness of the LED drops (this is especially noticeable for red LEDs) and the crystal begins to catastrophically collapse.

5. Connecting the LED to an alternating current network (eg 220 V) without taking measures to limit the reverse voltage. For most LEDs, the maximum permissible reverse voltage is about 2 volts, while the reverse half-cycle voltage when the LED is locked creates a voltage drop across it equal to the supply voltage. There are many different schemes that eliminate the destructive effects of reverse voltage. The simplest one is discussed above.

6. Installation of an insufficient power resistor. As a result, the resistor becomes very hot and begins to melt the insulation of the wires touching it. Then the paint burns on it, and eventually it collapses under the influence of high temperature. A resistor can safely dissipate no more than the power for which it is designed.

Flashing LEDs

A flashing LED (MSD) is an LED with a built-in integrated pulse generator with a flash frequency of 1.5 -3 Hz. Despite its compact size, the flashing LED includes a semiconductor generator chip and some additional elements. It is also worth noting that the flashing LED is quite universal - the supply voltage of such an LED can range from 3 to 14 volts for high-voltage ones, and from 1.8 to 5 volts for low-voltage units.

Distinctive qualities of flashing LEDs:

• Small dimensions • Compact light signaling device • Wide range of supply voltage (up to 14 volts) • Various emission colors.

Some versions of flashing LEDs may have several (usually 3) multi-colored LEDs built in with different flash frequencies. The use of flashing LEDs is justified in compact devices where high demands are placed on the dimensions of radio elements and power supply - flashing LEDs are very economical, since the electronic circuit of the MSD is made on MOS structures. A flashing LED can easily replace an entire functional unit.

The conventional graphic designation of a flashing LED on circuit diagrams is no different from the designation of a conventional LED, except that the arrow lines are dotted and symbolize the flashing properties of the LED.

If you look through the transparent body of the flashing LED, you will notice that it consists of two parts. A light-emitting diode crystal is placed on the base of the cathode (negative terminal). The generator chip is located on the base of the anode terminal. Three gold wire jumpers connect all parts of this combined device.

It is easy to distinguish an MSD from a regular LED by its appearance, looking at its body in the light. Inside the MSD there are two substrates of approximately the same size. On the first of them there is a crystalline cube of a light emitter made of a rare earth alloy. To increase the luminous flux, focus and shape the radiation pattern, a parabolic aluminum reflector (2) is used. In an MSD it is slightly smaller in diameter than in a conventional LED, since the second part of the housing is occupied by a substrate with an integrated circuit (3). Electrically, both substrates are connected to each other by two gold wire jumpers (4). The MSD housing (5) is made of matte light-diffusing plastic or transparent plastic. The emitter in the MSD is not located on the axis of symmetry of the housing, so to ensure uniform illumination, a monolithic colored diffuse light guide is most often used. A transparent body is found only in large-diameter MSDs with a narrow radiation pattern.

The generator chip consists of a high-frequency master oscillator - it operates constantly; its frequency, according to various estimates, fluctuates around 100 kHz. A logic gate divider works together with the RF generator, which divides the high frequency to a value of 1.5-3 Hz. The use of a high-frequency generator in conjunction with a frequency divider is due to the fact that the implementation of a low-frequency generator requires the use of a capacitor with a large capacity for the timing circuit.

To bring the high frequency to a value of 1-3 Hz, dividers are used on logic elements, which are easy to place on a small area of ​​the semiconductor chip. In addition to the master RF oscillator and divider, an electronic switch and a protective diode are made on the semiconductor substrate. Flashing LEDs, designed for a supply voltage of 3-12 volts, also have a built-in limiting resistor. Low-voltage MSDs do not have a limiting resistor. A protective diode is necessary to prevent failure of the microcircuit when the power supply is reversed.

For reliable and long-term operation of high-voltage MSDs, it is advisable to limit the supply voltage to 9 volts. As the voltage increases, the power dissipation of the MSD increases, and, consequently, the heating of the semiconductor crystal increases. Over time, excessive heat can cause the flashing LED to rapidly degrade.

You can safely check the serviceability of a flashing LED using a 4.5-volt battery and a 51-ohm resistor connected in series with the LED, with a power of at least 0.25 W.

The serviceability of the IR diode can be checked using a cell phone camera. We turn on the camera in shooting mode, catch the diode on the device (for example, a remote control) in the frame, press the buttons on the remote control, the working IR diode should flash in this case.

In conclusion, you should pay attention to such issues as soldering and mounting of LEDs. These are also very important issues that affect their viability. LEDs and microcircuits are afraid of static, incorrect connection and overheating; soldering of these parts should be as fast as possible. You should use a low-power soldering iron with a tip temperature of no more than 260 degrees and soldering should take no more than 3-5 seconds (manufacturer’s recommendations). It would be a good idea to use medical tweezers when soldering. The LED is taken with tweezers higher to the body, which provides additional heat removal from the crystal during soldering. The LED legs should be bent with a small radius (so that they do not break). As a result of the intricate bends, the legs at the base of the case must remain in the factory position and must be parallel and not stressed (otherwise the crystal will get tired and fall off the legs).

To protect your device from accidental short circuit or overload, you should install fuses.

Download:

1. Program for automatic selection of a resistor when connecting LEDs - Please Login or Register to access this content 2. Program for automatic calculation of a current-limiting resistor of an LED - Please Login or Register to access this content 3. Internet resource for automatic calculation and selection of LED resistors — Please Login or Register to access this content

How many volts are there?

The operating voltage of an LED can be determined not only by its appearance and characteristics, but also by the color glow of the LED. To do this, check out the table below.

How color affects brightness

To understand this aspect, you need to know what happens inside the diode and what affects the color type.

The internal structure of a semiconductor LED consists of two semiconductors designed for different levels of conductivity. An electric current passes through the first semiconductor due to a physical phenomenon that ensures the movement of free electrons. Current moves through the second conductor due to the movement of “holes”.

A “hole” is a place where an electron is missing.

At the junction of semiconductors, the stage of recombination of “holes” and electrons begins. An electron flies to the place of the “hole”, which makes the atom neutral - a photon is emitted, that is, color appears.

Color can change if it is influenced by the following factors:

• what type of semiconductor the LED was made from;
• what impurities were used at the points of contact between two semiconductors;
• width of the forbidden zone (recombination site);
• parameters and magnitude that influence the current strength in a section of the electrical circuit.

The color change occurs due to an increase or decrease in electrical current. When referring to Ohm's law, it must be remembered that the higher the voltage, the greater the current. This means that the photon's energy will also increase, thereby moving towards a cooler (blue) and brighter glow.

Method 1

A small fragment of PCB, literally a piece, but always with double-sided foil. A “spot” of solder must be applied to each so that in the future you can easily fix the wires and leads of the device for testing the LED. Probes from the multimeter, from which you should cut off (or unsolder, and then restore everything) the plug. The free ends need to be cleaned and tinned, that is, prepared for soldering. Paper clips – 2 pieces. They are given a shape that is clearly visible in the figure below. These will be the terminals of the device (analogous to plugs) that are connected to the multimeter. Although this is not the only option. Instead of paper clips, you can use flexible steel wire by cutting a couple of pieces of the required length.

LEDs.

The main thing is that these leads are slightly cushioned, then it will be much easier to connect them to the multimeter socket. Soldering acid. Using traditional pine flux is futile. The paper clips are made of steel, so the usual method for securely fixing them on PCB is of little use. Soldering iron. Power – at least 65 W. Trying to secure a paper clip to the board with a mounting tool (24, 36 W) is a waste of time. You will need to lay the melt in a relatively thick layer, and a low-power (miniature) soldering iron is useless in this case. Multimeter. These household appliances are available in several modifications. Their main difference is in functionality, that is, the ability to measure certain parameters of the circuit and parts.

It will be interesting How to make a power regulator on a triac with your own hands

You will need a multimeter that can test transistors. In principle, everything you need to make a simple device for checking an LED with a multimeter is always at hand. In the end it should look something like this. In order not to be confused with the polarity of connecting the probes to the LED, the terminals of the device should be slightly shifted from the center line. Then it’s easy to remember where the conditional “+” and “–” are. Checking the LED You need to insert the “contacts” of the device into the plug for testing Tr (anode terminal - to connector E, cathode - to C), put the multimeter switch in the “Transistor measurement” (hFE) position and attach the probes to the board at the points where they are soldered legs of the device (from the front or back, whichever is more convenient). If it is working properly and the polarity is correct (plus to the anode), it will begin to glow.

How to find out how many volts it is rated for

Using a power supply

One quick way to determine LED voltage is to use a regulated power supply. The power supply must be regulated from scratch and at the same time make it possible to control the current, or even better, limit it.

To measure, follow these steps:

1. Connect the LED to the source, observing the polarity.
2. Gradually increase the voltage to 3-3.5V.

At a certain moment, the diode will light up at full strength - this means that the voltage level corresponds to the operating current (it can be read using an ammeter). If the device does not have a built-in ammeter, the current must be monitored using an external device.

When the voltage rises, you cannot cross the 3.5 V line. If the LED does not light up at these levels, check the polarity of the device connection.

By appearance

The approximate strength of the operating voltage can be assessed by the appearance, markings and color of the LED. To determine by color spectrum, use the table that was written about earlier in the article.

There is no standard labeling; each manufacturer indicates its own parameters on it. Marking is usually indicated on packaging containers (boxes and bags). If you purchase LEDs that are wound into a reel, ask the seller for the packaging container to find out the LED markings.

Multimeter

To measure the operating voltage of an LED with a multimeter, follow these steps:

1. Turn on the multimeter and set the rotary switch to the “diode test” position.

2. The LED has two terminals and polarity: short (negative terminal), long (positive terminal). Connect the positive (red) probe of the multimeter to the positive terminal of the LED, and attach the negative (black) probe to the negative terminal.

3. If the LED is working properly, the light will light up.

Practical method

The most accurate data on the forward voltage drop across an LED can be obtained through practical measurements. To do this, you will need an adjustable DC power supply (PSU) with a voltage from 0 to 12 volts, a voltmeter or multimeter and a 510 Ohm resistor (more is possible). The laboratory circuit for testing is shown in the figure. Everything is simple here: a resistor limits the current, and a voltmeter monitors the forward voltage of the LED. Smoothly increasing the voltage from the power source, observe the increase in readings on the voltmeter. When the triggering threshold is reached, the LED will begin to emit light. At some point, the brightness will reach the nominal value, and the voltmeter readings will stop increasing sharply. This means that the pn junction is open, and a further increase in voltage from the output of the power supply will be applied only to the resistor.

How to determine current

Finding out what rated current an LED has without using special reference books is not so easy. By appearance, the current strength can be determined by the diode bulb: the larger it is, the greater the current. If during the test you cross the acceptable line, the color of the diode will change. For example, an initially yellow color may turn into a white or blue tint.

Most standard LEDs are rated at 20mA.

Modern technologies make it possible to supplement the device body with new components. The most commonly used are quenching resistors. In this way you can get an LED with a voltage of 5.12 or 220 V.

In addition, the rated current of the LED is determined by the same multimeter. When the light comes on, pay attention to the device screen; the voltage will be displayed on it; knowing it and Ohm’s law, you can easily calculate the LED current.

After watching the video, you can understand how to test different types of LEDs using a multimeter.

Types of diodes by junction size

Based on the size and nature of the pn junction, three types of devices are distinguished - planar, point and microalloy.

Planar parts

represent one semiconductor wafer in which there are two regions with different impurity conductivity. The most popular products are made of germanium and silicon. The advantages of such models are the ability to operate at significant direct currents and in conditions of high humidity. Due to their high barrier capacitance, they can only operate at low frequencies. Their main applications are AC rectifiers installed in power supplies. These models are called rectifiers.

Point diodes

have an extremely small pn junction area and are adapted to work with low currents. They are called high-frequency because they are used mainly to convert modulated oscillations of significant frequency.

Microalloy

models are obtained by fusing single crystals of p-type and n-type semiconductors. According to the principle of operation, such devices are planar, but their characteristics are similar to point devices.

LED lamp voltage

Modern LED lamps, manufactured for home use and industrial purposes, are designed for an alternating supply voltage of 110 - 220 V. This figure is achieved by combining several chips. In this case, the driver built into each lamp is responsible for lowering the voltage and obtaining a constant current.

The LEDs themselves in the lamp are designed for a lower DC voltage. Most lamps use SMD 5050 or SMD 2835 LEDs. Chinese Corn lamps use SMD 3014 LEDs. All these LEDs are designed for an operating voltage of 2-3.2 V (DC), the more accurate value depends on the emitted color, the voltage drop also Everyone is different, from 1.8 V to 3 V.

Power and Heat Dissipation

When the U drop across a resistance is important, you need to choose the right resistor that can dissipate the required power. A current consumption of 20 mA may seem low, but the calculated power suggests otherwise. So, for example, for a voltage drop of 30 V, the resistor must dissipate 1400 ohms. Power dissipation calculation P = (Ures x Ures) / R,

• P is the value of the power dissipated by the resistor, which limits the current in the LED, W;
• U is the voltage across the resistor (in volts);
• R—resistor value, Ohm.

P = (28 x 28) / 1400 = 0.56 W.

A 1 W LED supply voltage would not withstand overheating for a long time, and a 2 W LED would also fail too quickly. For this case, you need to connect two 2700 ohm / 0.5 W resistors in parallel (or two 690 ohm / 0.5 W resistors in a row) to distribute heat dissipation evenly.

LED strip voltage

LED strips use the same LEDs as lamps, so everything written above also applies to them, i.e. The operating voltage for the strip LED is 2-3.2 V.

To summarize, it is worth noting that each LED has its own individual characteristics, including voltage. In order to find out exactly how much a particular light-emitting diode is designed for, you need to read its manual, the so-called Datasheet.

Accurate power determination

You will need:

• Multimeter
• Power supply in which you can smoothly increase the voltage
• 500 ohm resistor

This technique is not applicable to laser LEDs! Connect the LED to the resistor and power supply. Observe polarity! It can also be determined using a multimeter. Smoothly increase the voltage on the power supply, comparing the readings on it and on the LED. It will be more convenient to use a power supply that shows the operating voltage, or use two voltmeters. What will happen? the initially identical voltage will gradually change on the block and the LED

It is important that the LED glows at normal brightness

What is a multimeter or tester

Let's first find out what can be measured using this miracle of a device and what indication is present on its front panel. So, you will be able to see the following symbols:

this position speaks for itself and means that the tester is in the off state.

This abbreviation tells us that the voltage change is measured here.

and here we are looking at constant voltage.

Here the direct current is measured.

and in this section the resistance is calculated.

For easier understanding, here is a visual image of a multimeter with explanatory notes

But if you need to measure current up to 10 A, then you need to move the red probe into the 10ACD connector. As a rule, on 830D series multimeter models, this connector is located above the rest and labeled accordingly. In other models it is also labeled, but may be located in another part of the device.

Details

Almost any LED can be used in the circuits shown here. Preferably super bright. Flashing LEDs connected in series circuits must be single-color.

A two- or three-color flashing LED does not blink, but switches its colors, and does not create significant impulses in the circuit, so non-blinking LEDs connected in series with it will not blink. At best, their glow will only flicker.

All new LEDs (not soldered from boards) have the anode marked with a longer lead. And the short one is the cathode. For soldered ones, the assignment of the terminals must be checked with a multimeter (since ordinary diodes ring).

Andreev S. RK-11-2018.

Knock sensor

Determines the shock wave during fuel combustion. The resistance indicators for each car are individual - look for information in different sources.

It's a little easier with tension. First remove the sensor. Connect the plus probe to the signal wire, the negative probe to ground, closer to the mounting bolt. Next comes the fun part - hit the sensor against a wall, chair or table. This is the only way the multimeter will record the voltage reading. The norm on most cars is from 30 to 40 millivolts.

Instead of an afterword

When buying a used car, it is useful to know how to find an electrical leak and understand its cause. Take a multimeter to inspect your car - you will save yourself from unpleasant surprises, such as a suddenly dead battery, power surges or burnt wiring.

For the same purpose, check the car's history. This can be done directly during a conversation with the seller. It is convenient to use the Autocode service - monitor information from 13 sources at once: traffic police, RSA, EAISTO, banks, tax and other services. The verification will take 5 minutes.

Afterwards you will find out the actual mileage, number of owners, history of fines, as well as information about theft, participation in an accident, restrictions on car registration and much more. Be carefull!

Having fully studied the online report, it is still worth taking a closer look at the technical nuances of the car when purchasing. And if you are not confident in your knowledge, or it is not possible to go for an inspection, order an on-site inspection service. The specialist will conduct a diagnosis for you and make a detailed conclusion from a professional point of view.

Source

Semi-automatic or automatic multimeter

It is much more convenient for professionals to work with it. After all, you don’t need to constantly switch measurement limits, but on a semi-automatic machine you still need to switch modes using the flip switch and the RANGE key. The latter already selects the required measurement modes. Also, semi-automatic and automatic multimeters have more functions than simpler ones. Measurement of inductance, capacitance, frequency. Analogue scale on the display, backlight, fastening to the belt, to the wall, magnetic for suspension. All the charms can be generalized from different models of multimeters, but they are all different. There are budget options, and there are also professional ones, with an increased accuracy class, device response speed and more discrete modes of operation and functionality of the devices.

As for old pointer instruments, some call them “grandfather’s”. You should not write off devices such as Tseshki, TL-4M and analogues. These testers have a higher accuracy class. The mirror scale on Tseshki reduces the parallax effect during measurements, i.e. allows you to see the mirror position of the arrow relative to the scale of the instrument head. Many high-level specialists still use good old Soviet-designed domestic devices in their practice today. They allow you to make the same measurements as multimeters. Their only drawback is a weak device protection system, and often its absence at all, but for professionals this is not a problem. One could also call their dimensions and amenities a minus, but this category of measuring equipment lives out its life very well, because Unlike most multimeters, pointers with a weak battery will not lie about their readings; they are considered to be the most accurate.

Oxygen sensor

Determines whether oxygen remains in the exhaust gases. Before taking measurements, also inspect it - it may be damaged and a multimeter will not be needed at all. Then the element just needs to be replaced.

If everything is in order, measure the voltage and resistance as with the ABS sensor. The algorithm is the same. Start the car and watch the device. After start-up, the numbers 0.1-02 volts will appear on the screen. When the car warms up, the device will show up to 0.9 volts. If you didn’t notice that the indicator has changed, the sensor is most likely faulty.

If the voltage test is successful, find out the resistance readings. The norm ranges from 10 to 40 ohms.

Schematic diagram

The figure below shows a diagram of such a divider. It consists of ten resistors with a resistance of 68 MOhm each, connected in series, and one resistor of 68 kOhm.

High-resistance resistors form one divider arm with a total resistance of 680 MOhm. And the second arm is formed by a 68 kOhm resistor. This results in a voltage divider of 10,000.

We connect the divider output to the “COM” and “VOmmA” sockets, and the input (X1 and X2) to the circuit being measured.

Rice. 1. Schematic diagram of a high voltage voltage divider for measuring high voltages using a multimeter.

The multimeter is set to the “2000mV” position, in which it will show voltages up to 20KV, and in the “20V” position, theoretically, up to 200KV. Although, it should be noted that in this way it is impossible to measure voltages of more than 50 KV, since the voltage divider attachment may break through.

Or you need to make a different attachment, taking a completely different approach to insulation, and with greater resistance. As for this attachment, all resistors must be large with a power of at least 2W, and installation must be done by arranging all resistors evenly in a line, so that the distance between terminals X1 and X2 is at least 200mm.

The insulation must withstand high voltage. The circuit can be assembled in a three-dimensional manner and placed inside a glass tube, the ends of which are closed with rubber stoppers (through which the wires can be released). You can make the installation on a sheet of organic glass on which to install the terminals.

In any case, the installation must prevent the occurrence of leakage currents, and the dielectric properties of the base must correspond to the magnitude of the measured voltage.