How to test a three-terminal diode with a multimeter. How a multimeter can help you check a diode for functionality. Why is a diode bridge better than a diode?

It is possible to check the performance of the LED using a device such as a multimeter. A digital multimeter or tester is a multifunctional measuring device. The performance of the LED is checked using the functionality of any multimeter. LED failure is a fairly common cause of failure of a number of electrical appliances.

You can check the serviceability of this component yourself, but you must have a multimeter available.

The process is not complicated, but, as practice shows, situations are different, especially when we are talking about beginners in such matters. Electronics engineer with experience appearance can determine the parameters of most LEDs, and in some cases their condition - serviceability or failure.

A diode is a component of an electrical network that acts as a conductor with p-n junction. Its design allows electricity to flow through the circuit in one direction - from the anode to the cathode. If it breaks, you can check it using a tester or multimeter.

In radio electronics, the following types of diodes are distinguished:

• LED - when an electric current passes through it, it begins to emit light as a result of the transformation of energy into a visible glow.
• A regular or protection diode is a voltage limiter or suppressor. A variation of such a diode is a Schottky diode, which, when connected directly, gives a slight decrease in voltage; it uses a metal-semiconductor junction.

The use of conventional parts and LEDs is used in most devices, and Schottky is mainly used for high-quality power supplies, such as computers. Testing both diodes is no different in principle, the only difference is that the Schottkys are found in double diodes, since they are placed in a common housing and also have a common cathode. This allows you to check these parts without soldering, on site.

Schottky diodes are components electronic circuits, and break down quite often. The main reasons for this are:

• Poor quality parts;
• Violation of the rules for operating the device;
• Exceeding the maximum direct current level allowed by the manufacturer;
• Excessive reverse voltage.

It is necessary to check their functionality using a multimeter, which will allow you to measure voltage, determine the resistance level, and also check the wiring for breaks. This method is considered the simplest and most convenient for all types of light-emitting diodes, regardless of their design and number of pins. The test is carried out by “ringing” the diode, connecting the red probe to the anode and the black probe to the cathode. As a result, a working LED should light up, and when the polarity of the probes is changed, the tester display should display one.

How to test a rectifier diode

The protective, rectifying or Schottky diode can be checked using a multimeter or using an ohmmeter. To do this, you need to switch the measuring device to the “dialing” mode, after which the tester probes are attached to the terminals of the radio element. To obtain the threshold voltage value of the diode being tested, it is necessary to connect the red wire to the anode and the black wire to the cathode, after which the display of the multimeter or ohmmeter should light up. After changing the polarity, the measuring device should show a very high resistance, which indicates that the diode is working properly. If the multimeter shows a leak, it means the radio element is faulty.

How to test an LED with a multimeter

To check the LED with a multimeter, you need to translate meter to Hfe mode to test transistors, then insert the LED into connector C of the PNP zone (plus), and the cathode, in turn, into connector E of the NPN zone (minus). If a glow appears, then the test has been carried out; if not, then there is an error in polarity or the diode does not work.

To check the LED with a tester, you need to switch the device to the appropriate “dialing” mode and connect the contacts to the multimeter probes. When connecting, do not forget about the polarity of the diode. The anode is connected to the red probe, and the cathode is connected to the black one. In the absence of information about the electrodes, which is which, it is possible to confuse the polarity, but this is not a big deal, and the multimeter will not show any results. Once connected correctly, the LED lights up.

Checking the infrared diode

Without a doubt, every home has LEDs; they have found a special use in TV remote control. The infrared diode, which is not visible to the human eye, can be easily seen through the phone's camera. The same diodes are used for video surveillance cameras.

You can check an infrared diode with a multimeter in the same way as a regular one. But you can use another method by soldering a red LED in parallel to it, which will be a clear indicator of the operation of the IR diode. When it flickers, signals are sent to the diode, which means the IR diode needs to be replaced. If there is no flickering, therefore no signal is being received, then the problem is with the remote control and not with the diode.

There is one more nuance in the control scheme of equipment from a remote control, namely the presence of a photocell, to check which you need to turn on the resistance mode with a multimeter. If light hits a photocell, the state of its conductivity changes, which means its resistance also changes downward.

To check an LED lamp with a multimeter, you need to remove the diffuser, which is often glued. After access to the board with LEDs is opened, you need to touch their terminals with the probes of the tester, which should then light up with a dim light. You can also check the serviceability using a “continuity test” from the Krona battery. This check should be carried out by briefly touching the poles of the diodes. If the polarity is determined correctly and the light does not light up, then the LED needs to be replaced.

How can you check a diode using a tester without desoldering?

The principle of verification remains the same, but the method of implementing this verification changes. A convenient and practical way is to check LEDs without soldering, using probes. Standard size probes will not fit the transistor connector, Hfe mode. But any thin conductors, such as sewing needles, a piece of wiring (twisted pair) or individual cores from a multi-core cable, are suitable for it. By soldering such a conductor to the probe and attaching it to probes without plugs, you get a kind of adapter. And then it will be possible to ring the LEDs with a tester without desoldering.

Diodes are popular and widely used electronic elements with varying levels of conductivity.

Before you check the diode with a multimeter (test the diode and zener diode with a tester), you need to know the features of such a testing device and the most important rules for its use.

Diodes are electrical converting and semiconductor devices that have one electrical junction and two p-n junction outputs.

The currently generally accepted classification of such devices is as follows:

• in accordance with their purpose, diodes are most often rectifier, high-frequency and ultra-high-frequency, pulse, tunnel, reverse, reference type devices, as well as varicaps;
• in accordance with the design and technological characteristics, diodes can be represented by planar and point elements;
• in accordance with the source material, diodes can be germanium, silicon, gallium arsenide and other types.

According to the classification, the most important parameters and characteristics of the diodes are presented:

• maximum permissible indicators of reverse DC voltage level;
• maximum permissible indicators of the reverse voltage level of the pulse type;
• maximum permissible indicators of direct current of direct type;
• maximum permissible indicators of direct current of pulse type;
• rated direct current direct current;
• direct current voltage constant type under nominal conditions, or the so-called “voltage drop”;
• direct current of reverse type, indicated under the conditions of the maximum permissible reverse voltage;
• spread of operating frequencies and capacitance indicators;
• breakdown voltage level;
• level of thermal housing resistance, depending on the type of installation;
• the maximum possible indicators of dissipative power.

Depending on the power level, semiconductor elements can be low-power, high-power or mid-power.

When choosing a diode, you need to remember that the symbol of such elements can be represented not only by standard markings, but also by UGO applied to electrical diagrams, which are of fundamental importance.

Checking the rectifier diode and zener diode

In terms of independent diode testing with a multimeter, the following is of particular interest:

• conventional diodes based on p-n junction;
• Schottky diode elements;
• Zener diodes that stabilize the potential.

Conventional testing, in this case, can only determine the integrity of the pn junction, and it is for this reason that in such devices the operating point must be shifted.

Diagram of the simplest method for checking zener diode voltage

It is enough to use a simple circuit that includes a conventional power supply and a resistor to limit the current. For non-standard testing, a multimeter is used to measure voltage under conditions of a smooth increase in the supply potential.

If, under conditions of increasing supply voltage, a constant potential difference is observed, as well as a potential difference equal to the declared values, then the diode device is considered to be working and cannot be replaced.

Circuit assembly

The standard scheme, carried out through wall-mounted installation, consists of several main elements, presented:

• 16-18 V power supply;
• 1.5-2 kOhm resistor;
• digital or pointer voltmeter;
• device being tested.

How to test a Schottky diode with a multimeter

A feature of some multimeters is the presence of a “diode test” function. Under such conditions, the instrument displays the actual diode forward voltage at current conduction.

A tester equipped with a special function registers a slightly underestimated level of forward voltage, which is due to the insignificant current value that is involved in the test.

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Setting up the multimeter

Testing semiconductor element using a digital multimeter will require switching the device to diode test mode. Alternative option, in the absence of switching to the “diode test” position, testing is carried out in resistance mode, with a range of no more than 2.0 kOhm.

In this case, a direct connection is made: the red wire is connected to the anode, and the black wire to the cathode. With this setting of the multimeter, measurements show a resistance equal to several hundred Ohms; in the opposite direction, an open circuit is detected.

Multimeter UNI-T

It should be noted that different types diode devices can differ significantly in terms of forward voltage.

For example, germanium devices are characterized by a voltage in the range of 0.3-0.7 V, and for silicon elements values ​​of 0.7-1.0 V are acceptable.

As practice shows, some types of testers, when testing diode elements, show lower values ​​of the forward voltage level.

Less common dual diodes are distinguished by the presence of three terminals and a common anode or cathode in one housing, but testing such elements is no different from testing a standard diode device.

Turning on the power supply

If checking the performance of diodes with a multimeter involves switching the tester to the “diode” icon position with connecting the black probe to the “COM” terminal and the red one to the “V ΩmA” terminal, then the presence of a power supply is to identify the following problems:

• connecting the unit is accompanied by a “jerking” of the fan power supply, stopping, lack of output voltage and blocking the power source;
• connecting the unit is accompanied by voltage ripple at the output and protection is triggered without blocking the power source.

AC current measurement

Quite often, a sign of a leak in Schottky diodes is the spontaneous shutdown of the power supply. It is also very important to consider that incorrect circuit design on power supplies can cause leakage of diode rectifiers and overload of the primary circuit.

Testing consists of setting the measurement limit to a value of 20 K, and measuring the reverse diode resistance. With this method, a working diode shows an infinitely high resistance level on the device.

Connecting a multimeter

• breakdown, accompanied by current conduction regardless of direction, as well as the actual absence of resistance;
• a break accompanied by a lack of current conduction;
• leakage accompanied by the presence of a slight reverse current.

The procedure for setting up the device for verification and sequential testing is very simple.

The connection of the anode and the multimeter probe to “+”, as well as the cathode and p-n junction to “-” must be open. In this case, the device produces a characteristic beep. The reverse connection option with a closed p-n junction is indicated by one.

As we show in the practice of independent testing, current flow, regardless of the connection polarity indicators, most often accompanies short circuit, and the absence of ringing in both directions is observed when there is a break in the circuit.

Video on the topic

Testing an LED with a multimeter is the easiest and most correct way to determine its performance. A digital multimeter (tester) is a multifunctional measuring instrument, the capabilities of which are reflected in the switch positions on the front panel. LEDs are checked for functionality using functions present in any tester. Let's look at the testing methods using the DT9208A digital multimeter as an example. But first, let’s touch a little on the topic of the reasons for the malfunction of new light-emitting diodes and the failure of old ones.

The main causes of malfunction and failure of LEDs

A feature of any emitting diode is its low reverse voltage limit, which is only a few volts higher than the drop across it in the open state. Any electrostatic discharge or incorrect connection during setup of the circuit can cause the LED (abbreviation for Light-emitting diode) to fail. Ultra-bright, low-current LEDs, used as power indicators for various devices, often burn out as a result of power surges. Their planar counterparts (SMD LEDs) are widely used in 12V and 220V lamps, strips and flashlights. You can also verify their serviceability using a tester.

It is worth noting that a small proportion of defective LEDs (about 2%) are supplied from the manufacturer. Therefore, additional checking of the LED with a tester before mounting it on a printed circuit board will not hurt.

Diagnostic methods

The simplest method, which is most often used by radio amateurs, is to check light-emitting diodes with a multimeter for performance using probes. The method is convenient for all types of light-emitting diodes, regardless of their design and number of pins. Having set the switch to the “continuity check, open circuit” position, touch the leads with the probes and observe the readings. By connecting the red probe to the anode and the black probe to the cathode, the working LED should light up. When changing the polarity of the probes, the number 1 should remain on the tester screen.

The glow of the emitting diode during testing will be small and on some LEDs in bright light it may not be noticeable.

To accurately test multi-color LEDs with multiple leads, you need to know their pinout. Otherwise, you will have to randomly sort through the terminals in search of a common anode or cathode. Don't be afraid to test powerful LEDs with metal backing. The multimeter is not capable of disabling them by measuring in dial mode.

Testing an LED with a multimeter can be done without probes, using sockets for testing transistors. Typically, these are eight holes located at the bottom of the device: four on the left for PNP transistors and four on the right for NPN transistors. The PNP transistor is opened by applying a positive potential to the emitter “E”. Therefore, the anode must be inserted into the socket labeled “E”, and the cathode into the socket labeled “C”. A working LED should light up. To test in the holes for NPN transistors, you need to change the polarity: anode - “C”, cathode - “E”. This method is convenient for testing LEDs with long and solder-free contacts. It does not matter in what position the tester switch is located.
Checking an infrared LED occurs in the same way, but has its own nuances due to invisible radiation. At the moment the probes touch the terminals of the working IR LED (anode - plus, cathode - minus), a number of about 1000 units should appear on the device screen. When changing polarity, there should be a unit on the screen.

To check the IR diode in the transistor testing sockets, you will additionally have to use a digital camera (smartphone, phone, etc.). The infrared diode is inserted into the corresponding holes of the multimeter and the camera is pointed at it from above. If it is in good condition, then IR radiation will be displayed on the gadget’s screen in the form of a glowing blurry spot.

Testing high-power SMD LEDs and LED matrices for functionality requires, in addition to a multimeter, a current driver. The multimeter is connected in series to electrical circuit for a few minutes and monitor the change in current in the load. If the LED is of poor quality (or partially faulty), then the current will gradually increase, increasing the temperature of the crystal. The tester is then connected in parallel with the load and the forward voltage drop is measured. By comparing the measured and passport data from the current-voltage characteristics, we can conclude that the LED is suitable for use.

Read also

To determine the health of the diode, you can use the following method for checking it with a digital multimeter.

But first, let's remember what a semiconductor diode is.

A semiconductor diode is an electronic device that has the property of unidirectional conductivity.

The diode has two terminals. One is called the cathode, which is negative. The other output is the anode. It is positive.

At the physical level, a diode is one p-n junction.

Let me remind you that semiconductor p-n devices There may be several transitions. For example, the dinistor has three of them! A semiconductor diode is essentially the simplest electronic device based on just one p-n junction.

Let us remember that the operating properties of the diode appear only when connected directly. What does direct connection mean? This means that a positive voltage is applied to the anode terminal ( + ), and to the cathode – negative, i.e. ( - ). In this case, the diode opens and through its p-n junction current begins to flow.

When turned back on, when a negative voltage is applied to the anode ( - ), and to the cathode is positive ( + ), then the diode is closed and does not pass current.

This will continue until the voltage on the reverse-connected diode reaches a critical value, after which damage to the semiconductor crystal occurs. This is the main property of the diode - one-way conductivity.

The vast majority of modern digital multimeters (testers) have the ability to test a diode in their functionality. This function can also be used to test bipolar transistors. It is designated as symbol diode next to the marking of the multimeter mode switch.

A little note! It is worth understanding that when checking diodes in direct connection, the display does not show the transition resistance, as many people think, but its threshold voltage! It is also called voltage drop across the p-n junction. This is the voltage above which the pn junction opens completely and begins to pass current. If we draw an analogy, this is the amount of effort aimed at opening the “door” for electrons. This voltage ranges from 100 to 1000 millivolts (mV). This is what the device display shows.

In reverse connection, when a negative one is connected to the anode ( - ) tester output, and to the cathode positive ( + ), then no values ​​should be shown on the display. This indicates that the junction is working properly and does not allow current to flow in the opposite direction.

In the documentation (datasheets) for imported diodes, the threshold voltage is referred to as Forward Voltage Drop(abbreviated V f), which literally translates as " voltage drop in direct connection".

The voltage drop across the pn junction itself is undesirable. If we multiply the current flowing through the diode (direct current) by the magnitude of the voltage drop, then we get nothing more than power dissipation - the power that is uselessly spent on heating the element.

You can find out more about the diode parameters.

Diode check.

To make it more clear, let’s check the 1N5819 rectifier diode. This is a Schottky diode. We will soon see this.

I draw your attention to the fact that during measurements you cannot hold the leads of the element being tested and the metal probes with both hands. This is a big mistake. In this case, we measure not only the parameters of the diode, but also the resistance of our body. This can significantly affect the result of the test.

You can hold the probes and terminals of the element with only one hand! In this case, only the measuring device itself and the element being tested are included in the measuring circuit. This recommendation is also valid when measuring the resistance of resistors, as well as when checking capacitors. Don't forget this important rule!

So, let's check the diode in direct connection. In this case, the positive probe ( red) connect the multimeter to the anode of the diode. Negative probe ( black) connect to the cathode. In the photo shown earlier, you can see that the cylindrical body of the diode has a white ring on one edge. It is on this side that it has a cathode terminal. This is how the cathode terminal of most imported diodes is marked.

As you can see, the threshold voltage value for 1N5819 appeared on the display of the digital multimeter. Since this is a Schottky diode, its value is small - only 207 millivolts (mV).

Now let's check the diode in reverse connection. We remind you that when switched in reverse, the diode does not allow current to pass through. Looking ahead, we note that in the reverse connection, a small current still flows through the pn junction. This is the so-called reverse current (I arr.). But it is so small that it is usually not taken into account.

Let's change the connection of the diode to the multimeter's test leads. Red connect the probe to the cathode, and black to the anode.

The display will show " 1 " in the high order of the display. This indicates that the diode does not pass current and its resistance is high. Thus, we checked the 1N5819 diode and it turned out to be fully operational.

Many people ask the question: “Is it possible to test a diode without desoldering it from the board?” Yes, you can. But in this case, it is necessary to remove at least one of its pins from the board. This must be done in order to exclude the influence of other parts that are connected to the diode being tested.

If this is not done, then the measuring current will flow through everything, including through the elements connected to it. As a result of testing, the multimeter readings will be incorrect!

In some cases, this rule can be neglected, for example, when it is clearly visible that printed circuit board there are no details that can affect the result of the test.

Diode faults.

The diode has two main faults. This breakdown transition and its break.

Breakdown. During a breakdown, the diode turns into an ordinary conductor and freely passes current, either in the forward direction or in the reverse direction. In this case, as a rule, the multimeter buzzer beeps, and the display shows the value of the junction resistance. This resistance is very small and amounts to several ohms, or even zero.

Break. When broken, the diode does not pass current either in forward or reverse connection. In any case, the device display shows " 1 ". With such a defect, the diode is an insulator. "Diagnosis" - a break can be accidentally made to a working diode. This is especially easy to do when the tester probes are quite worn out and damaged. Make sure that the measuring probes are in good working order; their wires are oh so “thin” and with frequent use they tear easily.

And now a few words about how the value of the threshold voltage (voltage drop at the junction - Forward Voltage Drop ( V f)) you can roughly judge the type of diode and the material from which it is made.

Here is a small selection made up of specific diodes and their corresponding values V f, which were obtained when testing them with a multimeter. All diodes were previously checked for serviceability.

A semiconductor type diode refers to those electronic devices that are characterized by conductivity in only one direction.

What is a semiconductor diode

Users are often faced with the question of how to test a diode. In order to check whether the diode is functioning normally, it is best to use the method of monitoring its condition using a digital multimeter. All diodes have two outputs. One of them - the anode - has a plus sign, and the other - the cathode - has a minus sign.

From a physical point of view, any diode- this is a transition device p-n type. You should know that devices with a semiconductor system can have several such transitions (the dinistor has 3 transitions). Meanwhile, a conventional semiconductor diode is the most basic electronic device in existence, based on one such junction. It should also be remembered that a diode with a semiconductor system can fully exhibit its physical properties only after it is turned on. full force.

Turning on at full strength implies the fact that the anode of a particular diode was connected to a voltage with a plus sign, and the cathode to a voltage with a minus sign. Only then does the diode fully open and its transition begins to conduct the electrical dock. If you do everything the other way around and connect a negative voltage to the anode of the diode, and a positive voltage to the cathode, then this diode will be considered closed and will not allow electric current to pass through it. This process will last until the voltage in the device reaches its maximum level, which will entail the destruction of the crystalline base of the semiconductor. Thus, the principle of operation of the diode - conductivity in one direction - is confirmed.

Answer to the question: “How to test a diode with a multimeter?”- very simple. In most cases, any modern digital tester (multimeter) that can now be found on sale is equipped with a function for checking the physical health of diodes. This property can be used in situations where you need to check the functionality of the transistor.

When checking the functionality of the device, it is not the value of the junction resistance that appears on the screen, but the so-called “breakdown” voltage in the diode. This means: if this threshold is exceeded, the junction will open and the diode will start working. As a rule, the value of this indicator is in the range from one hundred to eighty millivolts. They will be displayed on the device monitor. If you swap the multimeter leads (from negative to positive and vice versa), then the monitor should not show anything. This will be evidence that the diode does not pass current in the other direction, and therefore functions normally.

How to test a diode

In order to facilitate the verification process, it is advisable to have a breadboard with you. First of all, you should make sure that you do not touch the diode outputs and tester probes with both hands. You can’t do this, because then your body will also affect the measurement results - its resistance will be added. Therefore, everything must be held with only one hand - then only the elements necessary for this will be included in the measurement chain.

This feature should not be forgotten when measuring other devices, for example, capacitors or resistors. You should start by checking during a direct connection. To do this, the positive probe of the multimeter (it is red) must be connected to the anode of the diode, and the negative probe (it is black) must be connected to the cathode. The cathode output is located on the side of the device on which the ring is painted with white paint.

This is how the cathode output is noted in most modern diodes. If everything went well and the monitor displayed a normal voltage value, then you can check the diode by swapping the contacts. It is worth noting that diodes still pass electric current in the opposite direction, but in such small quantities that this indicator is never taken into account in calculations. So if you connect a black probe to the anode and a red probe to the cathode, the display should show the value “one”. This will indicate that the diode is functioning absolutely normally.

Possible faults

Semiconductor diodes, as a rule, are characterized by two types of faults: junction breakdown and junction breakage. The following is worth knowing about them:

• Breaking through the transition. In this case, the diode will become the most common conductor and will have the property of passing electric current both in one direction and in the other. The user can be told about this by the screeching buzzer of his tester, and the monitor will show a resistance value that is not typical for this diode. She will be unusually small
• Transition break. If a junction break occurs, the diode under study will not pass electric current in either direction. In such a situation, the multimeter monitor will always show the number “one”. If this happens, the diode under test will become an insulator. However, there are situations when an absolutely normally functioning diode is diagnosed with a “break”. This happens mainly when a tester with damaged or simply worn probes is used. This point needs to be controlled, because their wires are often subject to mechanical stress, which leads to breakage

What you should know about breakdown voltage

The breakdown voltage of most germanium diodes is in the range of three hundred to four hundred millivolts. For example, the often used diode model D9, which is also used as a detector in radio receivers, is characterized by this indicator in the amount of four hundred millivolts.

Here are the main types of diodes and the voltages that correspond to them:

• Silicon diodes. They have the highest breakdown voltage - from four hundred to eight hundred millivolts
• Diodes from germanium. Have an average breakdown voltage of three hundred to four hundred millivolts
• Schottky diodes. Their breakdown voltage ranges from one hundred to two hundred and fifty millivolts

Using this technique, you can not only check how well the diode functions, but also approximately find out what material served as the raw material for its manufacture. This can be determined by finding out the breakdown voltage.

Where can I order a diode test?

If you have concerns that you will not be able to independently check the health of the diode using a multimeter, it would be best to contact a specialist. Using the services of the Yudu platform, you can order the services of a specialist to check the diode with a multimeter in just ten minutes.

This can be done in the following ways:

On the Yudu platform, you will not be limited in choosing a specialist and will be able to use the services of the specialist whom you consider the most qualified. All Yudu performers passed a special check during registration on the site and can guarantee high quality of the work performed.