Plus and minus on the motherboard. How to determine the polarity of electrolytic capacitors, where is the plus and minus? Computer power supply connectors and voltages

Any lover of homemade products and electronics use diodes as indicators, or as lighting effects and lighting. In order for the LED device to glow, you need to connect it correctly. You already know that a diode conducts. Therefore, before soldering, you need to determine where the anode and cathode of the LED are.

You may see two LED designations on a circuit diagram.

The triangular half of the designation is the anode, and the vertical line is the cathode. The two arrows indicate that the diode is emitting light. So, the diagram indicates the anode and cathode of the diode, how to find it on a real element?

Pinout of 5mm diodes

To connect the diodes as in the diagram, you need to determine where the plus and minus of the LED are. First, let's look at the example of common low-power 5 mm diodes.

The figure above shows: A - anode, K - cathode and schematic symbol.

Pay attention to the flask. You can see two parts in it - this is a small metal anode, and a wide part that looks like a bowl is the cathode. The plus is connected to the anode, and the minus to the cathode.

If you are using new LED elements, it is even easier for you to determine their pinout. The length of the legs will help determine the polarity of the LED. Manufacturers make short and long legs. The plus is always longer than the minus!

If you are not soldering a new diode, then its plus and minus are the same length. In this case, a tester or a simple multimeter will help to determine the plus and minus.

How to determine the anode and cathode of diodes 1W or more

In floodlights, 5mm samples are used less and less; they have been replaced by powerful elements with a power of 1 watt or more or SMD. To understand where the plus and minus are powerful LED, you need to carefully look at the element from all sides.

The most common models in such a case have a power of 0.5 watts. The polarity mark is circled in red in the figure. IN in this case The plus sign marks the anode of a 1W LED.

How to find out the polarity of SMD?

SMDs are actively used in practically any technology:

Light bulbs;
LED strips;
flashlights;
indication of something.

You won’t be able to see their insides, so you need to either use testing devices or rely on the LED housing.

For example, on the SMD 5050 case there is a mark on the corner in the form of a cut. All pins located on the tag side are cathodes. Its body contains three crystals, this is necessary to achieve high brightness.

A similar designation for SMD 3528 also indicates the cathode, take a look at this photo of the LED strip.

The marking of the SMD 5630 pins is similar - the cut indicates the cathode. It can also be recognized by the fact that the heat sink on the bottom of the case is shifted towards the anode.

How to determine the plus on a small SMD?

In some cases (SMD 1206), you can find another way to indicate the polarity of LEDs: using a triangle, U-shaped or T-shaped pictogram on the surface of the diode.

The protrusion or side that the triangle points to is the direction of current flow, and the terminal located there is the cathode.

Determine polarity with a multimeter

When replacing diodes with new ones, you can determine the plus and minus of your device's power supply from the board.

LEDs in spotlights and lamps are usually soldered onto an aluminum plate, on top of which a dielectric and current-carrying tracks are applied. It usually has a white coating on top; it often contains information about the characteristics of the power source, and sometimes the pinout.

But how can you find out the polarity of an LED in a light bulb or matrix if there is no information on the board?

For example, on this board the poles of each LED are indicated and their name is 5630.

To check for serviceability and determine the plus and minus of the LED, use a multimeter. We connect the black probe to minus, com or a socket with a grounding sign. The designation may differ depending on the multimeter model.

Next, select the Ohmmeter mode or the diode test mode. Then we connect the multimeter probes one by one to the diode terminals, first in one order, and then vice versa. When at least some values appear on the screen, or the diode lights up, it means the polarity is correct. In diode testing mode, the values are 500-1200 mV.

In measuring mode the values will be similar topics what is in the picture. A unit in the leftmost digit indicates exceeding the limit, or infinity.

Other ways to determine polarity

The easiest option for determining where the LED is plus is batteries from the motherboard, size CR2032.

Its voltage is about 3 volts, which is quite enough to light the diode. Connect the LED, depending on its glow you will determine the location of its pins. This way you can test any diode. However, this is not very convenient.

You can assemble a simple probe for LEDs, and not only determine their polarity, but also the operating voltage.

Homemade probe circuit

When the LED is connected correctly, a current of about 5-6 milliamps will flow through it, which is safe for any LED. The voltmeter will show the voltage drop across the LED at this current. If the polarity of the LED and the probe match, it will light up and you will determine the pinout.

You need to know the operating voltage, since it differs depending on the type of LED and its color (red takes less than 2 volts).

And the last method is shown in the photo below.

Turn on the Hfe mode on the tester, insert the LED into the connector for testing transistors, into the area marked as PNP, into holes E and C, with the long leg in E. This way you can check the functionality of the LED and its pinout.

If the LED is made in a different form, for example, smd 5050, you can use this method simply - insert regular sewing needles into E and C, and touch them with the LED contacts.

Any lover of electronics, and even homemade products in general, needs to know how to determine the polarity of an LED and how to check them.

Be careful when choosing the elements of your circuit. IN best case scenario they will simply fail faster, and in the worst case, they will instantly burst into blue flame.

Electric current flowing through the LED in the forward direction causes optical radiation. Plugging it back into the electrical circuit will not have the same effect and may even damage the LED. To avoid troubles in operation, this electronic component must be tested, i.e., its polarity must be determined. The following methods for determining the minus and plus pins are most often used for low-power emitting diodes in packages with a diameter of 3.5, 5.0, 10.0 mm.

Visual difference between anode and cathode terminals

A new LED typically has two leads (legs), one of which is slightly longer than the other. The long lead is the anode. It is connected to the positive of the power source. The short lead is the cathode, which is connected to the negative or common wire. Sometimes the cathode terminal is marked with a dot or a small cut on the body. A soldered or used LED has shortened legs of the same length. In this case, you need to determine where the plus and where the minus are by carefully examining the crystal through a plastic lens. The anode (plus) is distinguished by a much smaller contact size inside the lens compared to the cathode. The cathode contact (minus), in turn, resembles a flag on which the crystal is placed.

When repairing electronic components, you may encounter light-emitting diodes with a non-standard pinout. The manufacturer can mark them on the side of the legs or thicken one of the terminals. Sometimes the pinout of such LEDs is not intuitive, and the special structure does not allow visual determination of the polarity. In such cases, you will have to resort to electrical measurement.

Power supply polarity detection

For quick testing, you will need a current source with a voltage of 3 to 6 volts (battery or accumulator), a resistor with a resistance of 300–470 Ohms of any power and, directly, an LED. Due to the low value of the reverse voltage, it is not recommended to test the LED from a source with a voltage greater than 6 V. The resistor must be soldered to one of the legs and then touch the contacts of the power source. By touching the anode to the plus and the cathode to the minus, a serviceable emitting diode will glow. Repair shop workers are often armed with dead three-volt batteries from a computer motherboard or wall electronic watch(CR2032). After making sure that the current of such a battery does not exceed 30 mA, it is briefly inserted between the terminals of the LED without a resistor. Plus and minus are determined by its glow.

Checking with a multimeter

A multimeter is a little assistant to a true master. It is also called a tester because it can diagnose most electronic components, identify short circuits, and measure basic electrical parameters. Testing an LED with a multimeter provides the following benefits and determines:

polarity (anode, cathode);
glow color;
suitability for use.

You can determine the polarity of the LED using one of the following: three ways. In the first case, to take measurements, you need to set the tester switch to the “resistance check - 2 kOhm” position and briefly touch the leads with the probes. When the red (plus) probe touches the anode, and the black (minus, connected to the COM connector of the multimeter) touches the cathode, a number in the range of 1600–1800 will blink on the screen. Such testing of a faulty semiconductor device will display only one on the screen. The disadvantage of this method is the lack of illumination of the crystal.

The second method involves setting the switch to the “continuity test, diode check” position. By touching the red probe to the anode and the black probe to the cathode, the LED will light up slightly. A number will be displayed on the screen, the value of which depends on the type and color of the emitting diode.
The third method allows you to do without probes. To do this, the tester must have a compartment for testing PNP and NPN transistors. Fortunately, most models are equipped with this feature. To determine the polarity, you will need two sockets marked E - emitter and C - collector. As you know, a negative bias is applied to the collector of a PNP transistor. Therefore, when testing an LED, it will light up if the cathode is inserted into the hole labeled “C” and the anode into the hole labeled “E” of the PNP compartment. By determining the polarity in the NPN compartment, a working LED will glow if the legs are swapped. This method– the fastest and most effective, and the glow reaches maximum brightness. You can also test other types of LEDs with multimeter probes. For example, in dialing mode you can highlight individual segments LED indicator. In addition to single-color LEDs, two-color and multi-color analogues are produced in a five-millimeter housing. Moreover, they can have 2, 3 or 4 outputs. Two-terminal two-color light-emitting diodes visually have complex shape crystal. When the tester checks the plus and minus, they conduct current in both directions, but glow different colors. Determining the polarity of a 3- or 4-pin LED involves looking for a common minus or plus, which depends on the manufacturer. To do this, use the probes of a multimeter to touch the leads and record the glow of the crystal.

How to determine the polarity of an unknown power source? Let's assume that you come across some kind of constant voltage power supply, battery or accumulator. But... it doesn’t indicate where the plus is and where the minus is. Yes, the matter is resolved quickly, but what if you don’t have it at hand? Calmly.There are three proven working methods.

I think this is the easiest way to determine polarity. First of all, pour some water into a container. Preferably Not metal. We remove two wires from a power source with unknown terminals, drop them into our water and look carefully at the contacts. Hydrogen bubbles will begin to form at the negative terminal. Electrolysis of water begins.

Using raw potatoes

Take a raw potato and cut it in half.

We plug our two wires from an unknown source into it direct current and wait 5-10 minutes.

A light green color appears on the potato near the positive terminal.

Using a PC fan

We take a fan from the computer. It has two terminals, and sometimes even three. The third may be the yellow wire - the speed sensor. But we still won’t use it. We only care about two wires - red and black. If there is a plus on the red wire and a minus on the black wire, then the fan will rotate

If you didn’t guess right, then the blades will stand still.

We use a fan if it is known that the power source voltage is from 3 to 20 Volts. Applying a voltage of more than 20 volts to the fan is fraught with death.

Conclusion

In conclusion, I would like to say that these chips cannot be rolled with alternating current. And as you know, single-phase alternating current consists of two wires - phase and zero. For those who don’t remember how they can be determined, please look here. I would also like to wish you never to confuse the polarity, because “foolproof protection” (reverse polarity protection) is not installed in all electronic devices.

Using raw potatoes

Take a raw potato and cut it in half.

We plug our two wires from an unknown DC source into it and wait 5-10 minutes.

A light green color appears on the potato near the positive terminal.

Using a PC fan

If you didn’t guess right, then the blades will stand still.

We use a fan if it is known that the power source voltage is from 3 to 20 Volts. Applying a voltage of more than 20 volts to the fan is fraught with death.

Conclusion

In conclusion, I would like to say that these chips cannot be rolled with alternating current. And as you know, single-phase alternating current consists of two wires - phase and zero, who does not remember how they can be determined, please take a look right here. I would also like to wish you never to confuse the polarity, because “foolproof protection” (reverse polarity protection) is not installed in all electronic devices.