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 long-term 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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The device presented here is a zener diode meter for testing the voltage value of an unknown zener diode. is a radio-electronic component that maintains a constant voltage at its contacts, and the source voltage Vs must be greater than the zener diode's own voltage Vz, and the current is limited by resistance Rs, so that its current value is always less than its maximum power.
Radio amateurs and all those who are good friends with electronics know that the task of finding a zener diode with the required characteristics (operating voltage) is boring and painstaking. It happens that you need to go through a lot of different instances until you find the desired Vz value. Checking the status of the zener diode is usually done using a regular multimeter diode scale, this test gives us an accurate idea of the condition of the component, but does not allow us to determine the Vz value. In general, a zener diode tester is a really convenient device when we want to quickly find out the value of the voltage Vz.
Device parameters
- Power supply 220 V.
- Digital indication Vz
- Measures zener diodes for voltages from 1 V to 50 V
- Two current modes - 5 mA and 15 mA
Diagram of a device for testing zener diodes
As you can see, the scheme is simple. The voltage from the transformer with two 24V secondary windings is rectified and filtered to obtain a constant voltage of about 80V, then goes to a voltage stabilizer formed by the elements (R1, R2, D1, D2 and Q1), which reduces the voltage to 52V to avoid exceeding the maximum operating voltage limit of the microcircuit LM317AHV .
Pay attention to the letter index of the microcircuit. U LM317AHV input voltage, unlike LM317T , can reach a maximum of 57V.
On LM317AHV A DC generator is assembled, where a switch (S2) is added together with a resistor (R4) to select two test modes (5 mA and 15 mA) as a current source for the zener diode under test.
Like most measuring instruments, multimeters (testers) are divided into analog and digital. Their main difference is that information about the measurement results of the first type is transmitted using a certain scale and arrows on it, while in the second case this data is displayed digitally on a liquid crystal screen.
Analog devices appeared earlier; their main advantage is their low price, and their disadvantage is measurement inaccuracy. Therefore, if the mark needs to be as accurate as possible, it is recommended to purchase a digital multimeter.
All tester options have at least two outputs - red and black.
- The first is used directly for measurements, also sometimes called potential,
- The second one is general. Modern models usually also have a switch, thanks to which it is possible to set the maximum limit values.
How to check a diode with a multimeter?
A diode is an element that conducts electricity in one direction. If we turn this direction, the diode will be closed. T Only if this condition is met is the element considered operational. Most tester models already have such a function as checking a diode with a tester.
Before starting the test, it is recommended to connect two multimeter probes together to make sure it is working, and then select the “diode test mode”. If the tester is analog, this operation is performed using the ohmmeter mode.
Checking diodes with a multimeter does not require additional skills. To ensure that the element is functioning, it is necessary to perform a direct connection, therefore, connect the anode to the positive value (red probe) and the cathode to the negative value (black). The value of the diode breakdown voltage should appear on the screen or scale of the device; this figure is on average ranges from 100 to 800 mV. If you turn it back on (swap the electrodes), the value will not be more than one. From this we can conclude that the resistance of the device is enormous and it does not conduct electricity. If everything happens exactly as described above, the electronic element is operational and functional.
There are situations when, when connecting probes, the diode passes current in both directions, or does not pass it at all (the values for direct and reverse connections are equal to one). In the first case, this means that the diode is broken, and in the second, it is burned out or has an open circuit. Such electronic elements are faulty and can be easily checked with a tester.
How to check the LED?
If we are talking about an LED, the check algorithm is similar, but the task will be further facilitated by the fact that when connected directly this the type of diode will light up. Of course, this will make it possible to finally make sure that he is okay.
But it happens that it is necessary to check the zener diodes. A zener diode is a type of diode; its main purpose is to maintain a stable output voltage regardless of changes in current level.
Unfortunately, there is not yet a dedicated function for checking this type of electronic elements. implemented in multimeters. Nevertheless, you can often ring them using the same principle as with diodes. But many experienced radio amateurs say that checking the zener diode using a digital tester is very problematic. The reason for this is the fact that the voltage of the zener diode must be lower than the voltage at the outputs of the multimeter. This is due to the fact that due to low voltage, it is possible to consider a faulty model to be working, and the accuracy of the readings decreases.
If when checking a diode it is necessary to pay attention to the value of the breakdown voltage, in the case of zener diodes the resistance will be indicative. This figure should be from 300 to 500 Ohm. And similar to the algorithm for dealing with diodes:
- If current is passed in both directions it is called breakdown,
- If the resistance is too high it is a break.
It is also important to remember that the digital value when ringing a zener diode will be higher than the value of conventional diodes. If you need to distinguish one element from another, such a check will help.
How to check zener diode
Zener diodes, the testing of which did not bring the desired results, are often tested by inventors using additional devices, sometimes designing them yourself. One of the simplest ways is to use a power supply with the ability to switch voltage to test. You must first connect a resistor with a resistance value that is optimal for the zener diode to the anode, and then connect the power supply. Then the voltage on the diode is measured and raised in parallel on the block. Upon reaching the stabilization voltage level, this figure should stop growing. In this case, the zener diode is normal; if there is any difference from the above circuit, it is faulty.
A zener diode (Zener diode) resembles a diode in appearance. However, its functions differ from the diode in terms of the current-voltage characteristic (VAC). A Zener diode has a high resistance, but when a certain voltage is applied to it, a breakdown occurs. Because of this, the current flowing through it increases. In breakdown mode, the voltage on the zener diode with a wide range of currents is maintained with the specified accuracy.
Checking the zener diode with a multimeter
In order to check the zener diode with a multimeter, you must have certain knowledge.
Measuring with a multimeter is similar to testing a diode. The operating state of a zener diode can be characterized by its ability to pass current in only one direction.
On the measuring device it may look like this:
- If measurements are carried out with a digital device, with a positive probe connected to the cathode terminal, indicated by a strip, and a negative probe to the anode terminal, then the readings should be reflected on the device in the form of numbers (for example, checking a 5.1 V zener diode is displayed on the multimeter display reading 688 Om). If you swap the probes, the device will display infinite resistance, which typically indicates a working radio element. When, when connecting, the multimeter shows infinite resistance in both directions, this indicates a break in the element. If the resistance in both directions is zero, then such an element is broken.
- Similarly, the measurement can be carried out with a pointer device, where in one direction, instead of numbers, the arrow indicates resistance, and in the other, infinite resistance.
In semiconductor technology, double-sided zener diodes (KS175A), as well as precision ones (D818), can be used. They cannot be tested by the method described above, since their resistance is infinite in both directions. To check these elements, you can use the method given below.
This method allows you to measure the parameters of radioelements by including them in the circuit and the applied voltage of the power source. Depending on the stabilization voltage of the component being tested, it is necessary to have a divider consisting of one or more resistors. The power source is connected directly to a pre-assembled electrical circuit connected with a common minus or a common plus. This circuit is a parametric voltage regulator:
Using an example, consider a Zener diode with 12 V stabilization. To do this, it is necessary to apply voltage so that at terminal 1 of the divider it is about 11 V, with the resistance of the divider selected to be approximately 100 Ohms. Voltmeter at pin 2 of resistor (no load). The voltage before and after the divider remains unchanged, depending on the selected resistance. If 12 V or higher is applied to pin 1 of the divider, then at the output of the pin divider the second voltage should not exceed 12 V, which indicates its serviceability.
Divider R is selected in such a way that the source current at pin 2 does not exceed the maximum current of the zener diode, which can lead to failure of the latter.
If the element under study is broken or incorrectly connected to the circuit, then the voltage on the voltmeter will be zero, and the divider will also heat up. If the element is broken, then the applied value at the input of the divider will be higher than 12 V, then the element under test can be considered faulty.
Precision and double-sided devices
Precision zener diodes are tested in a similar way. Double-sided zener diodes are connected to the terminals of the power source without observing polarity.
To check the stabilizer, you need to switch the multimeter to DC measurement mode, observing the polarity. Initially, the amount of power supply to the stabilizer is checked.
If the voltage is normal, then the multimeter is directly connected to the output of the stabilizer, measuring the voltage value at the output.
Many current buyers require stabilized power supplies. The core part of circuits that produce a stable output voltage is a semiconductor zener diode. This element provides an identical output voltage, independent of the amount of current consumed by the load. There are several methods to check the serviceability and typical operation of this part.
You will need
- Laboratory autotransformer (LATR), 10 kOhm resistor, 120 Volt rectifier, multimeter.
Instructions
1. Turn the multimeter into diode test mode. To do this, turn the handle of the device to the location shown in the figure. Touch the results of the zener diode with the multimeter probes. After this, swap the probes and touch them again to the zener diode results. In one of the locations, the multimeter should show a zener diode resistance of 300 - 600 Ohms; in another location, the display should show the number 1 in the leftmost case (which means that the measured resistance of the device is immeasurably huge for the given measurement range of the multimeter). In this case, the zener diode is working.
2. The zener diode is faulty if the multimeter in both measurement cases shows unlimited resistance (internal break), very low resistance (breakdown) or a resistance of the order of 30 - 500 Ohms (half-breakdown).
3. To check the functionality of the zener diode, assemble the following circuit: connect the 120-volt rectifier mains plug to a laboratory autotransformer. Place the laboratory autotransformer regulator in a location that corresponds to the minimum voltage at its output. Connect a zener diode to the output contacts of the rectifier in steps with a 10 kOhm resistor (cathode to the correct result of the rectifier), parallel to the zener diode, connect a multimeter turned on in the mode for measuring continuous voltage in the range of 200 Volts.
4. Turn on the laboratory autotransformer. By turning the autotransformer output voltage adjustment knob, gradually increase the voltage on the zener diode. At the same time, monitor the voltage readings on the multimeter display. The voltage should reach a certain value and stop increasing. This value will be the stabilization voltage of the zener diode. If it is less than 20 volts, switch the multimeter to the position of measuring continuous voltage in the 20 volt range. Read more accurate readings of the stabilization voltage of this zener diode from the multimeter display.