Measuring diodes with a multimeter. How to ring and check a diode and zener diode with a multimeter

In this article we will explain how to test a diode with a multimeter. A semiconductor diode, as a component of an electronic circuit, quite often fails for various reasons, for example, exceeding the maximum permissible forward current, reverse voltage, and the like. There are two types of diode malfunction - breakdown and short circuit.

The effect of a diode, as a semiconductor device with a p-n junction, is that it passes electric current only in one direction (from the anode to the cathode), while no current flows in the opposite direction (from the cathode to the anode).

Knowing this property of the diode, you can easily check it for malfunction using a regular one.

Conventional diodes, as well as zener diodes, can be checked using a multimeter. To test this semiconductor device using a digital multimeter, set the multimeter's switch to diode test mode, usually this mode has a diode icon:

It should be noted that when testing in this mode, the multimeter displays direct voltage, and not resistance, when the diode is simply rung in resistance mode.

Signs of a working diode:

When you connect the positive probe (red) of the multimeter to the anode of the diode, and the negative probe (black) to the cathode of the diode, a certain value of the forward voltage of this diode should be displayed on the multimeter screen. Different types of diodes have different forward voltages. So for germanium diodes it is approximately 0.3...0.7 volts, for silicon diodes 0.7...1.0 volts. Although some types of multimeters may show a lower forward voltage value in test mode.

And vice versa, when you connect the negative probe of the multimeter to the anode of the diode, and the positive probe to the cathode of the diode, the screen will show zero.

If the multimeter readings are different, it can be argued that the diode being tested is faulty.

An alternative way to check the health of the diode

If your multimeter is not equipped with a diode test mode, you can check the diode using the simple diagram shown below.

During this test, the multimeter must be switched to constant voltage measurement mode. If a working diode is connected as indicated in the diagram, the voltmeter will show the forward voltage on the diode. If the diode leads are now swapped, it will not conduct current, and the voltmeter will indicate the supply voltage (in this case, 5 volts).

You can also ring the diode and determine its general condition by measuring resistance, both in the forward and reverse directions.

To do this, you need to switch the multimeter to resistance measurement mode, range up to 2 kOhm. When connecting a diode in the forward direction (red to the anode, black to the cathode), the measuring device will show a resistance of several hundred Ohms; in the opposite direction, the device will show an open circuit symbol, which indicates a very high resistance.

How to check a diode bridge

Before moving on to the issue of checking the diode bridge, we will briefly describe it. A diode bridge is an assembly of four diodes connected in such a way that the alternating voltage (AC) supplied to two of the four terminals of the diode bridge turns into a direct voltage (DC) taken from its other two terminals.

Thus, the purpose of the diode bridge is to rectify alternating voltage in order to obtain a constant voltage.

A diode (rectifier) bridge consists of four rectifier diodes connected according to a specific circuit:

Since the diode bridge is designed to rectify alternating voltage (sinusoid), during the first half-wave of alternating voltage one pair of diodes is involved in the operation:

and at the next half-wave another pair of rectifier diodes operates:

Checking a diode bridge is no different from checking a regular diode. You just need to decide which terminals to connect the multimeter to. Conventionally, we number the rectifier terminals from 1 to 4:

It follows that to check the diode bridge we only need to ring 4 diodes:

1st: conclusions 1 – 2;
2nd: conclusions 2 – 3;
3rd: conclusions 1 – 4;
4th: conclusions 4 – 3;

When checking, you must rely on the readings of the multimeter, as when checking conventional diodes.

Today we can’t live without electronics. It is an integral part of any modern device or gadget. At the same time, all devices, sadly, cannot work forever and periodically break down. One of the fairly common causes of failure of a number of electrical appliances is the failure of an electrical element such as a diode.

You can check the serviceability of this component yourself at home. This article will tell you how to test a diode with a multimeter, as well as what these elements are and what the measuring device itself is.

Diode diode discord

A standard diode is a component of the electrical network and acts as a p-n junction semiconductor. Its structure allows current to pass through the circuit in only one direction - from the anode to the cathode (different ends of the part). To do this, you need to apply “+” to the anode and “-” to the cathode.

Note! Electric current in diodes cannot flow in the opposite direction, from the cathode to the anode.

Due to this feature of the product, if you suspect a breakdown, it can be checked with a tester or multimeter.
Today there are several types of diodes in radio electronics:

Types of diodes

Light-emitting diode. When an electric current passes through such an element, it begins to glow as a result of the transformation of energy into a visible glow;
protective or regular diode. Such elements in the electrical network act as a suppressor or voltage limiter. One of the varieties of this element is the Schottky diode. It is also called a Schottky barrier diode. Such an element, when connected directly, gives a low voltage drop. In Schottky, instead of a p-n junction, a metal-semiconductor junction is used.

If ordinary parts and LEDs are used in the vast majority of electrical appliances, then Schottky ones are used mainly in high-quality power supplies (for example, for devices such as computers).
It is worth noting that testing a conventional diode and a Schottky diode is practically no different, since it is carried out according to the same principle. Therefore, there is no need to worry about this issue, because the operating principle of both Schottky and conventional diodes is identical.
Note! Here it is only worth noting that Schottkis in most cases are found double, located in a common building. Moreover, they have a common cathode. In such a situation, you can not solder these parts, but check them “on the spot”.

Schottky diode

Being a component of an electronic circuit, such semiconductor elements often fail. The most common reasons for their failure are:

exceeding the maximum permissible direct current level;
excess reverse voltage;
poor quality part;
violation of the device operating rules established by the manufacturer.

Moreover, regardless of the cause of loss of performance, failure can be directly caused by either a “breakdown” or a short circuit.
In any case, if there is an assumption that the electrical network has failed in the semiconductor area, it is necessary to diagnose it using a special device - a multimeter. Only to carry out such manipulations you need to know how to check the diode using it correctly.

Multimeter

A multimeter is a universal device that performs a number of functions:

measures voltage;
determines resistance;
checks wires for breaks.

Multimeter

Using this device you can even determine the suitability of the battery.

How is the check carried out?

After we have figured out the semiconductors of the electrical circuit and the purpose of the device, we can answer the question “how to check the diode for serviceability?”
The whole point of checking diodes with a multimeter is their one-way electrical current carrying capacity. If this rule is observed, the electrical circuit element is considered to function correctly and without failures.
Conventional diodes and Schottky diodes can be easily tested using this device. To check this semiconductor element with a multimeter, you need to do the following manipulations:

Examination

you need to make sure that your multimeter has a diode test function;
If such a function is available, we connect the probes of the device to the side of the semiconductor from which the “ringing” will be carried out. If this function is missing, then use the switch to switch the device to 1 kOhm. You should also select the mode for measuring resistance;
the red wire of the measuring device must be connected to the anode end, and the black wire to the cathode end;
after this, you need to observe changes in the forward resistance of the semiconductor;
we draw conclusions about the presence or absence of voltage

The unit can then be switched to check for leaks or high circuits. To do this, you need to change the location of the diode output. In this state, it is also necessary to evaluate the obtained values of the device.

Diode bridge

Sometimes there is a situation when you need to check the functionality of a diode bridge. It looks like an assembly consisting of four semiconductors. They are connected in such a way that the alternating voltage supplied to two of the four soldered elements becomes direct. The latter is removed from the other two terminals. As a result, the alternating voltage is rectified and converted into constant voltage.

Essentially, the principle of verification in this situation remains the same as described above. The only feature here is the determination of which output the measuring device will be connected to. There are four connection options that you should call:

conclusions 1 – 2;
conclusions 2 – 3;
conclusions 1 – 4;
conclusions 4 – 3;

By checking each output, you will get four results. The obtained indicators should be evaluated according to the same principle as for an individual semiconductor.

Analyzing the results

When checking diodes (regular and Schottky) with a multimeter, you will get a certain result. Now we need to understand what it could mean. Signs that indicate the health of the semiconductor include the following:

when connecting a part of the electrical circuit to the device, the latter will output the value of the available direct voltage in this element;

Note! Different types of diodes have different voltage levels, which is why they differ. For example, for germanium products this parameter will be 0.3-0.7 volts

when connected in the opposite way (the probe of the device to the anode of the product), zero will be recorded.

Reverse check

If these two indicators are met, then the semiconductor is working adequately and the cause of the failure is not in it. But if at least one of the parameters does not correspond, then the element is considered unusable and must be replaced.
In addition, it should be borne in mind that it is not a breakdown, but a “leakage” that is possible. This unpleasant defect can appear during prolonged use of the device or poor-quality assembly.
If there is a short circuit or leakage, the resulting resistance will be quite low. Moreover, the conclusion must be made based on the type of semiconductor. For germanium elements, this indicator in this situation will range from 100 kilo-ohms to 1 mega-ohm, for silicon - thousands of mega-ohms. For rectifier semiconductors, this figure will be many times higher.
As you can see, it is not so difficult to assess the performance of semiconductors in any electrical device on your own. The above principle is suitable for testing diode elements of various types and types. The main thing in this situation is to correctly connect the measuring device to the semiconductor and analyze the results obtained.

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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 pn 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.

In accordance with the classification, the most important parameters and characteristics of diodes are presented:

maximum permissible indicators of reverse DC voltage level;
maximum permissible indicators of the reverse pulse voltage level;
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 of a direct type under rated 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 circuits that 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 a semiconductor element using a digital multimeter will require switching the device to diode test mode. An alternative option, if there is no switching to the “diode test” position, is testing 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 of 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” pin and the red probe to the “V ΩmA” pin, 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

The main, most common diode faults can be presented:
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 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 emits a characteristic sound signal. The reverse connection option with a closed p-n junction is indicated by one.

As the practice of independent testing shows, current flow, regardless of the connection polarity, most often accompanies a 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 circuit adjustment 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. By setting the switch to the “continuity check, open circuit check” 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 high-power LEDs with a metal substrate. 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, telephone, 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 the electrical circuit for several minutes and the change in current in the load is monitored. 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.

Types of diodes

So, diodes pass current in the forward direction and block it in the reverse direction. On electrical diagrams, diodes are indicated by black arrows bounded by a crossbar. The symbol shows the direction of the current in the physical sense - the directional movement of positive particles. To create a forward current, a negative potential is applied to the end of the arrow, and a positive potential is applied to the beginning. Otherwise, the diode will be in a “locked” state.

When electrons move due to the imperfection of the molecular lattice, heat is lost, which entails a voltage drop in the forward direction. Silicon diodes have a higher direct potential, germanium diodes have a lower one. Schottky diodes are characterized by a smaller potential drop due to the replacement of one semiconductor layer with a metal one, i.e. there is no p-n junction. The loss current increases, and the voltage drop across the open switch in the forward direction is record low.

The effect is not typical in all voltage ranges. Schottky diodes are most effective at voltages equal to tens of volts. They are used in output filters of switching power supplies. Remember: the voltage ratings of the system unit are 5, 12, 3 V. The method of constructing circuits using a Schottky diode is typical.

A popular type of diode is a zener diode. Its working area is the breakdown area. Where a conventional diode fails, a zener diode protects the equipment. The process is characterized by an increase in voltage to nominal and a sharp stabilization. Through zener diodes, sensitive and weak microcircuits of switching power supply controllers are powered from high-voltage lines so that they cut the voltage into pulses of large amplitude. Without zener diodes, powering microcircuits is solved using extremely complex methods.

When evaluating a Zener diode using a multimeter, take into account that the working area is the reverse branch. Technically, the breakdown voltage for testing is obtained from batteries connected in series, then the presence of stabilization is checked. Direct connection of a zener diode is used extremely rarely; ringing in the traditional way is a bad idea. Zener diodes also include an avalanche diode, where the impact ionization effect is used to stabilize the current.

It happens that the specifics of the device are not clear. The printed circuit boards are marked - each element has a strictly defined designation, and the powerful diodes of the rectifier bridge cannot be confused with a tiny glass zener diode. The worst option is a tangle of conductors with unknown elements: either a diode, or an unusual type of resistor, or an exotic capacitor.

When faced with a similar situation, they carefully take an enlarged photo, then search the Internet using the image. Although the markings of zener diodes are illegible, it is possible to find information on the Internet. This step greatly speeds up the process of identifying and assessing the performance of the device.

An infrared diode is checked with a multimeter in the same way: we remove the forward voltage, then make sure that there is no reverse current flowing. To check the glow, use the viewfinder of a night video camera. It directly registers the infrared radiation of objects. A working IR diode is visible in the viewfinder - like a star. They check the glow with thermal imagers and night vision devices, being careful: the radiation power of light and IR diodes is high, comparable to the power of laser radiation.

The inscription inside the printer about the presence of a laser cannot be considered a joke. And neglect her. Keep your retina away from the infrared diode.

How to check a diode using a tester

To test diodes, multimeters are equipped with a special scale marked with the corresponding icon - a schematic designation of a diode. When the mode is turned on, low resistances turn on the buzzer, high ones are characterized by the nominal value or the voltage dropping across it. Based on the readings, they judge the characteristics of the diode, for example, the resistance of direct connection.

To correctly interpret the readings, it is important to take into account the characteristics of the tester: constant voltage and low nominal voltage used for evaluation. Example: when measuring resistance, the tester passes current through it, applying a certain voltage to the probes. Any multimeter model is characterized by unique parameters. The voltage is recognized by the charge of the capacitor: turn the multimeter into the ringing or diode testing mode, after a short time a potential difference will form on the capacitor plates. Measured using the standard scale of the tester. The value ranges from hundreds of millivolts (fractions of a volt) to units of volts.

Knowing the voltage applied to the diode, the accuracy of the reading is verified using its current-voltage characteristic. Enter a search query on Yandex and get acquainted with the full technical documentation for the element being studied. Then they place an abscissa ruler at the right place on the scale to find the output current. Using Ohm's formula, the open state resistance is calculated: R = U/I, where U is the auxiliary voltage generated by the tester. Compare the value found from the graph with that indicated on the display.

This is one of many techniques. It is important to know how to find the right paths, analyze and compare data. The first step is to search for generalized information: what diodes are, their characteristics (primarily current-voltage), the intricacies of the operation of a particular device. Knowing the theoretical foundations, it is easy to operate with information and draw correct conclusions from research results.

Let's move on to a real-life example: let's examine a diode bridge from a car generator!

How to determine the performance of a diode bridge

A car needs electricity - for air conditioning systems (along with engine energy), wipers, exterior and interior lighting. Constantly loading the battery, which is done while parked, is not economical. The problem is solved by connecting a synchronous alternating current generator to the motor shaft. Previously we used a collector circuit. But the brushes do not tolerate shaking, and there was a need for frequent maintenance.

Three-phase generators are now being installed. Because the revolutions constantly fluctuate, the constancy of the output characteristics is maintained by changing the rotor feeding current. As a result, the strength of the alternating magnetic field of the stator monitors every change in the operation of the motor. The price to pay is instability of the output voltage. It is rectified and filtered using a Larionov diode bridge circuit.

Deep technical details are redundant, let’s limit ourselves to light knowledge:

For any method of connecting the generator windings, there are three output points. Each is connected to ground through a diode in the negative half-cycle, and to consumers of the car network - in the positive half-cycle.
In total, there are six diodes.
The bridge consists of two crescent-shaped planes isolated from each other, made of durable alloy. There are three diodes on each, electrical connections are made according to the diagram (see figure).

From the diagram you can see:

Three diodes are connected in pairs with zero resistance between the cathode (negative polarity) and the anode (positive polarity). The generator terminals go here.
Two triplets of diodes (lying in the same crescent-shaped plane) call each other as cathodes or anodes. Depending on which electrode produces a short circuit, the branch is determined - load or going to ground.

Having created the correct electrical connection layout, they begin checking each diode individually. The branch going to ground is tested from the generator side, the other from the load side. The direction is known from Larionov's scheme. We check the diode bridge with a multimeter, touching the base of the black arrow (see figure) of each element with a red probe, and the tip of the same element with a black probe. At the same time, check the insulation of contacts with crescent-shaped planes, incl. neighboring. Based on the data obtained, the need to continue troubleshooting is assessed.

Conclusion: the diode, without desoldering, is checked with a multimeter on a rough structure like a car generator bridge. Ringing an electronic board is more difficult. Any check is carried out with specially shaped probes. For rough designs, use crocodile grips, and check the motherboard with thin needle-shaped probes. In the latter case, there is a chance to test the diode with a multimeter on the board under voltage with the risk of burning the tester.

We hope that the reader now understands how to test a diode with a multimeter.