How to determine the polarity of an LED strip. All methods for determining the polarity of LEDs

LED is a semiconductor optical device that transmits electric current in the forward direction. When connected inversely, there will be no current in the circuit, and, naturally, no glow will occur. To prevent this from happening, you need to maintain the polarity of the LED.

The LED in the diagram is indicated by a triangle in a circle with a crossbar - this is the cathode, which has a “-” (minus) sign. On the opposite side there is an anode with a “+” (plus) sign.

Wiring diagrams must include a pinout (or pinout) to identify all connection contacts.

How to determine the polarity of a diode while holding a tiny light bulb in your hands? After all, for correct connection you need to know where it is minus and where it is plus. If the pinout is mixed up, the circuit will not work.

Visual method for determining polarity

The first method of determination is visual. The diode has two terminals. The short leg will be the cathode; the anode of the LED is always longer. It’s easy to remember, since the initial letter “k” is present in both words.

When both pins are bent or the device is removed from another board, their length can be difficult to determine. Then you can try to see a small crystal in the case, which is made of transparent material. It is located on a small stand. This pin corresponds to the cathode.

Also, the LED cathode can be identified by a small notch. New models of LED strips and lamps use surface-mount semiconductors. The existing bevel key indicates that this is a negative electrode (cathode).

Sometimes LEDs are marked “+” and “-”. Some manufacturers mark the cathode with a dot, sometimes a green line. If there is no mark or it is difficult to see because the LED was removed from another circuit, you need to test.

Testing with a multimeter or battery

It's good if you have a multimeter at hand. Then the polarity of the LED will be determined in one minute. Having selected the ohmmeter mode (resistance measurement), it is easy to perform the following action. By applying the probes to the legs of the LED, the resistance is measured. The red wire should be connected to the positive, and the black wire to the negative.

When turned on correctly, the device will produce a value approximately equal to 1.7 kOhm, and a glow will be observed. When turned back on, the multimeter display will display an infinitely large value. If the test shows that the diode shows low resistance in both directions, then it is broken and should be discarded.

Some devices have a special mode. It is designed to check the polarity of the diode. Direct switching will be signaled by a backlit diode. This method is suitable for red and green semiconductors.

Blue and white LEDs only provide an indication at voltages greater than 3 volts, so the desired result cannot be achieved. To test them, you can use multimeters like DT830 or 831, which have a mode for determining the characteristics of transistors.

Using the PNP part, one lead of the LED is inserted into the collector socket, the second into the emitter hole. In case of direct connection, an indication will appear; inverse connection will not give a similar effect.

How to determine the polarity of an LED if you don’t have a multimeter at hand? You can resort to a regular battery or accumulator. For this you will need any other resistor. This is necessary to protect the LED from breakdown and failure. A series-connected resistor, the value of which should be approximately 600 Ohms, will limit the current in the circuit.

And a few more tips:

• If the polarity of the LED is known, it is no longer possible to apply reverse voltage to it. Otherwise, there is a risk of breakdown and failure. At correct operation The LED will serve well, as it is durable, and its body is well protected from moisture and dust;
• Some types of LEDs are sensitive to static electricity (blue, violet, white, emerald). Therefore, they need to be protected from the influence of “statics”;
• When testing an LED with a multimeter, it is advisable to perform this action quickly; touching the terminals should be short-term in order to avoid breakdown of the diode and its failure.

It is known that an LED in operating condition passes current only in one direction. If you connect it inversely, then D.C. will not pass through the circuit, and the device will not light up. This happens because, in essence, the device is a diode, but not every diode is capable of glowing. It turns out that there is a polarity of the LED, that is, it senses the direction of current flow and works only in a certain direction.
Determining the polarity of the device according to the diagram is not difficult. The LED is indicated by a triangle in a circle. The triangle always rests on the cathode (sign “−”, crossbar, minus), the positive anode is on the opposite side.
But how to determine the polarity if you are holding the device itself in your hands? Here in front of you is a small light bulb with two wire leads. To which wiring should the plus of the source be connected, and to which to the minus, for the circuit to work? How to correctly set the resistance where is the plus?

Determine visually

The first way is visual. Let's say you need to determine the polarity of a brand new LED with two leads. Look at its legs, that is, its conclusions. One of them will be shorter than the other. This is the cathode. You can remember that this is a cathode by the word “short”, since both words begin with the letters “k”. The plus will correspond to the pin that is longer. Sometimes, however, it is difficult to determine the polarity by eye, especially when the legs are bent or have changed their sizes as a result of the previous installation.

Looking into the transparent case, you can see the crystal itself. It is located as if in a small cup on a stand. The output of this stand will be the cathode. On the cathode side you can also see a small notch, like a cut.

But these features are not always noticeable in LEDs, since some manufacturers deviate from the standards. In addition, there are many models made according to a different principle. Today, on complex structures, the manufacturer puts “+” and “−” signs, marking the cathode with a dot or a green line, so that everything is extremely clear. But if there are no such marks for some reason, then electrical testing comes to the rescue.

Using a power source

A more efficient way to determine polarity is to connect the LED to a power source. Attention! You must select a source whose voltage does not exceed the permissible voltage of the LED. You can build a homemade tester using regular battery and a resistor. This requirement is due to the fact that if the connection is reversed, the LED may burn out or deteriorate its light characteristics.

Some say that they connected the LED this way and that, and it did not deteriorate. But the whole point is in the limiting value of the reverse voltage. In addition, the light bulb may not go out immediately, but its operating life will be reduced, and then your LED will not work for 30-50 thousand hours, as indicated in its characteristics, but several times less.

If the power of the battery for the LED is not enough, and the device does not light up no matter how you connect it, then you can connect several elements into a battery. We remind you that one hundred elements are connected in series plus to minus, and minus to plus.

Application of a multimeter

There is a device called a multimeter. It can be successfully used to find out where to connect the plus and where the minus. This takes exactly one minute. In the multimeter, select the resistance measurement mode and touch the probes to the LED contacts. The red wire indicates connection to the positive, and the black wire to the negative. It is advisable that the touch be short-lived. When turned back on, the device will not show anything, and when direct connection(plus to plus, and minus to minus), the device will show a value in the region of 1.7 kOhm.

You can also turn on the multimeter in diode test mode. In this case, when turned on directly, the LED light will glow.

This method is most effective for light bulbs that emit red and green light. An LED that produces blue or white light is designed for a voltage greater than 3 volts, so it will not always glow when connected to a multimeter even with the correct polarity. You can easily get out of this situation if you use the mode for determining the characteristics of transistors. On modern models, such as the DT830 or 831, it is present.

The diode is inserted into the grooves of a special block for transistors, which is usually located at the bottom of the device. The PNP part is used (as for transistors of the corresponding structure). One leg of the LED is inserted into connector C, which corresponds to the collector, the second leg is inserted into connector E, corresponding to the emitter. The light bulb will light up if the cathode (minus) is connected to the collector. Thus the polarity is determined.

Capable of passing electric current in a certain direction. If the connection is made inversely, the electric current does not pass through the circuit, and the desired electrical appliance will not turn on. This is explained by the fact that the devices are based on diodes, and not all have the ability to glow. This indicates that the LED has polarity and operates in a certain direction of current. In this regard, for connection it is important to correctly determine where the minus and plus of the LEDs are. Let's look at several ways.

Visually

If you have an LED in your hands where the plus and where the minus are, you don’t know, try to do it visually. How to visually determine LED polarity? Simple enough.
The new LED has two leads, one should be shorter. The short lead is the cathode. It’s easy to remember: “short” - “cathode”, both words start with “k”. The plus is where the long lead is. If we are dealing with a used LED whose legs are bent, the task becomes more complicated.
Then we peer into the body, where the most important element is located - the crystal. It lies on a tiny stand, a cup. The output from the stand is the cathode, on its side there is a cut or notch.
BUT this method not always applicable. Many manufacturers today do not comply with production standards, and the range of models is amazingly diverse. Some manufacturers mark the cathodes with a green dot or line, or use “-” and “+” signs. If there are no external identifying signs, you need to conduct electrical testing.

Power supply to help

The second way to determine the LED polarity is to connect it to. The main thing is to choose the right power source with voltage so that it does not exceed the maximum voltage level of the LED, otherwise it will burn out or deteriorate. The elements are connected like this: “-” is connected to “+”, “+” is connected to “-”.

Multimeter

If the above methods do not work, use a multimeter. Using a multimeter to determine the polarity of the LED will take a maximum of a minute. First you need to select the resistance level measurement mode on the equipment, and then touch the LED contacts with special pliers. The black wire goes to "-" and the red wire to "+". You don't need to touch for too long, 20-30 seconds is enough. If the switching was performed directly (“+” to “+”, and “-” to “-”), the multimeter displays an indicator in the region of 1.7 kilo Ohms. If the activation is reversed, the measurements are not displayed on the device.
It is somewhat easier to measure in diode mode: when connected directly, the light will light up. This mode is suitable for green and red light bulbs, but white and blue light bulbs are designed for current with a voltage of more than 3 V. For this reason, when blue and white light bulbs are connected, they can light up even with the correct polarity.
In this case, the mode for measuring transistor characteristics is used. The LED is inserted into the grooves of the block, at the bottom of the multimeter. The PNP part is used: one leg of the diode is inserted into connector “E” - the emitter, and the second into “C” - the collector. The light bulb lights up when the cathode is connected to the collector.
Thus, determining polarity is not particularly difficult.

All diodes must have positive and negative terminals. These findings received special names: positive is called anode, and negative - cathode. The diode cathode is easily identified by a red or black stripe located at this terminal on the case.

In Fig. 4.8 just shows a diode with a similar polarity marking. The strip thus corresponds to the vertical line of the circuit symbol of this element. It is important that when "reading" schematic diagram any device, you correctly interpreted the location of the diode in it and the direction of the flowing current

Rice. 4.8. When using diodes, always remember their polarity. A stripe at one end of the diode body indicates its

Attention
As mentioned at the very beginning of this section, diodes allow current to flow through them in the forward direction and block current flowing in the reverse direction. Thus, if you insert a diode into the circuit incorrectly, the circuit will either not work, or some elements are at risk of failure. Always carefully check the polarity of the diodes in the circuit - it is better to double-check than to eliminate the consequences once!

These semiconductor radio components are used in various electronic circuits as indication elements. As a rule, there are no problems with their installation on the board. To solder 2 legs inserted into the corresponding holes on the “tracks”, you do not need to be a major specialist in this field. But with polarity, which must be taken into account when working with all semiconductor devices, and not just LEDs, people without experience have difficulties. How to determine the correct polarity?

The easiest way is if the LED is new and never used. His conclusions are not the same - one is a little longer. It's easy to remember this analogy. The words “cathode” and “short” begin with the same letter – “K”.

Therefore, the other leg, the longer one, is the anode of the LED. Knowing this, it is difficult to confuse. Although some manufacturers have something different - they may be the same. Worth considering.

According to internal filling

If the flask is clearly visible, then finding the “cup” (and this is the cathode) is not at all difficult.

Finding out the polarity of the LED is not everything. It must be installed correctly on the board. A circuit diagram of this semiconductor is shown in the figure. The top of the device symbol (triangle) points to the cathode (negative terminal).

By body

This way, you can’t check the polarity of all LEDs, as it depends on the manufacturer. But some have a small mark (notch) on the “rim” opposite the cathode. If you look closely, it's easy to spot. As an option - a small point, a slice.

Using a battery

Also a simple technique, but here it is necessary to take into account that LEDs different types differ in breakdown voltage. To prevent the semiconductor from being damaged (partially or completely), a limiting resistance must be connected in series to the circuit. A nominal value of 0.1 - 0.5 kOhm is quite sufficient.

Multimeter

By the way, it is quite possible to use and, which is already equipped with everything necessary - a power supply and probes. This is even better.

Polarity determination method 1 is based on the property of an LED to “light up” when current passes through it. Consequently, its anode will be where the “plus” of the multimeter battery is (the socket for the “+” probe), and the cathode, accordingly, will be where the minus is. To check for “glow”, the device switch is set to the “diode measurement” position.

Polarity determination method 2 - here the resistance of the p-n junction is measured. Multimeter switch – to the “resistance measurement” position, the limit, depending on the modification of the tester, to a position of more than 2 kOhm. For example, at 10.

Touching the LED terminals with the probes is only momentary, so as not to damage the radio component. If the polarities of the P/P and the power source match, then the resistance will be small (from hundreds of Ohms to several kOhms). In this case, the red probe (usually inserted into the “+” socket of the device) points to the anode leg, and the black (“–”), respectively, to the cathode.

If the multimeter shows a high resistance, it means that when the probes touched the leads, the polarity was broken. The measurement should be repeated, changing it to ensure there is no internal break. Only in this case can we talk not only about the polarity of the LED, but also about its serviceability and readiness for intended use.

On various thematic forums there are opinions that nothing terrible will happen; you can connect the power source in any polarity, and this will not affect the LED. But this is not entirely true.

• Firstly, it all depends on the magnitude of the breakdown voltage, that is, the characteristics of a particular semiconductor.
• Secondly, it may work in the future, but partially lose its properties. Simply put, shine, but not as much as it should.
• Thirdly, such experiments negatively affect the service life of the LED. If its manufacturer-guaranteed MTBF is about 45,000 hours (on average), then after such polarity checks it will last much less. Confirmed by practice!