Checking zener diodes for high voltage. Methods for checking a zener diode with a multimeter and tester Diodes are different

Hello dear radio amateurs, today we will look at the necessary lesson on testing a semiconductor device, a zener diode. Its presence in a number of circuits is simply necessary; a faulty element prevents the normal functioning of the electronic device, and sometimes its switching on. We will fight this, read the page carefully, how to test a zener diode with a multimeter.

Why do you need a zener diode?

It is somewhat similar to a diode, visually, in glass and metal design, and it belongs to semiconductor devices. The terminals of this device are called similarly, anode and cathode, although its task is somewhat different.

Let's remember a little about the purpose of the zener diode; it stabilizes the voltage in electronic circuits. The Zener diode, which is its original name, operates in breakdown mode. Signed on the circuit diagram as VD, switching is done with the cathode to the plus.

Checking the zener diode with a multimeter

Checking a zener diode with a multimeter is absolutely identical to checking a diode. In operating condition, it should not pass current in both directions, and there should also be no short circuit when checking it.

We set the device to the mode for measuring resistance or checking diodes, apply the positive probe to the cathode, which with a strip should show infinite resistance. We swapped the probes, the display shows some resistance (voltage drop).

We check the zener diode 1N49471A with a multimeter

Let me remind you that this zener diode has a nominal voltage of 24 volts; if you apply a voltage from 22.8 to 25.2 volts to it, it will still output 24. We perform the actions described above. When the zener diode is connected directly, this is when there is a plus to the anode, there is some resistance. We change the probes, there is no reading, the resistance is huge, the zener diode is most likely working.

It is impossible to give a one hundred percent guarantee with this verification method. How to check it for sure and find out what its stabilization voltage is if the rating is not indicated? I'll tell you in the next lesson.

Hello dear visitors. Over forty years of passion for radio engineering, a whole bunch of zener diodes, both domestic and imported, both with and without markings, have accumulated, in connection with this there was a need to manufacture an attachment for a multimeter to determine the integrity and parameters of zener diodes. At least voltage stabilization. It took a couple of hours to make the console, including etching the board. I took as a basis the current stabilizer circuit (see Fig. 1) from the documentation for the LM431 microcircuit, analogue of 142EN19.

The diagram of the resulting set-top box is shown in Figure 2. A current stabilizer is assembled on the transistor VT1 and the DA1 142EN19 microcircuit; with the resistor values ​​indicated in the diagram, the stabilization current is approximately seventeen milliamps. An LED is included as an indicator of current flow when measuring with the circuit. You can use any LED with a forward current of at least 20mA. To make a set-top box, you will need a power plug from some unnecessary Chinese crap (see photos 1, 2).



Or rather, a spare part from it, shown in photo 2. The attachment is assembled on a small printed circuit board made of fiberglass. The appearance of the board is shown in photos 3 and 4. I hope the design of the console is also clear. So that the contact pins of the former power plug fit freely into the sockets of the device, solder them to the scarf while inserted into them.

The diagram shows the maximum possible input voltage for these elements - 35V. But if you check, for example, the KS107A stabistor at this voltage, then the voltage on it will drop 0.7V, and 34.3V - I Ur2 will drop on the transistor VT1. Where I Ur2 is the voltage drop across the resistor R2 = 0.017A 200 = 3.4V. 34.3 – 3.4 = 30.9V – is this the voltage that will drop across transistor VT1, hence the transistor collector power will be U I = 30.9V 0.017A? 0.525W. The collector power of the KT503 transistor is 0.35 W. So, the measurement must be done very quickly, either replace the transistor with a more powerful one, or reduce the supply voltage of the set-top box, which will reduce the number of brands of zener diodes being tested. Well, I think you can decide for yourself. Download the PCB drawing.

Yes, the stabilization current depends on the value of the resistor R2, R2 = 2.5/Ist, where Ist is the value of the stabilization current. Goodbye. K.V.Yu.

Today, electronics have become a part of life and are included in any device or gadget. But, sadly, it was also the devices and gadgets that break down and become unusable. The most common reason why many devices break down is the breakdown of one of the elements of the electrical network, for example a diode.

It is possible to check the breakdown or malfunction of this element yourself. In the article we will analyze in detail how to check a diode with a multimeter, as well as what this device is and how to use it.

Diodes are different

A simple diode is an element of an electrical network and plays the role of a semiconductor, that is, a p-n junction. It is designed in such a way that it can easily pass current through the circuit, but only in one direction. And this is carried out from the anode to the cathode. To do this, be sure to connect a “plus” to the anode and a “minus” to the cathode.

It’s definitely worth considering and remembering! The current in the diode cannot move in the opposite direction. Because of this distinctive point, the product can be checked for malfunction using a tester or multimeter. Let's look at what types of diodes there are and how they differ from each other.

Diode types:

1. Simple diode.
2. Zener diode, as the name implies, prevents the voltage from increasing, that is, it stabilizes it.
3. A varicap, a diode with a capacitance, is often found in VHF receivers.
4. A thyristor, a diode with a control electrode, when a signal is applied to the control electrode, you can control the state of the thyristor, that is, open or close it. This element is often found in power electronics.
5. A triac is approximately the same as a thyristor only for alternating voltage. Diagnostics of this diode will be discussed in another article.
6. LED, a diode that emits light when current passes through it.
7. Schottky diode, a diode with increased speed and low voltage drop.

There are also photodiodes, infrared diodes, etc.

Despite the fact that the diodes differ in purpose and transition, their testing is performed in the same way. The operating principle of diodes is similar.

What is a multimeter?

A multimeter is a device that has a number of functions:

• Measurement of voltage, current;
• Resistance measurement;
• Continuity test, in this mode the multimeter shows the voltage drop in mV.
• There may also be functions for measuring capacitance, temperature, frequency, etc.

How to check a diode with a multimeter?

Once you have decided on the type of diodes, their differences and features, as well as the purpose of this device, you can consider the procedure for working with it. The test consists of checking the current flow through them. If this rule is followed, then we can safely say that the circuit element is working properly and has no flaws.

Conventional diodes can be checked with this device without much effort. To diagnose these elements, simply perform the following steps:

Checking the performance of a diode, LED, zener diode.

• We set the device to the dialing mode, if there is no such mode, then to the 1 kOhm resistance measurement mode;
• We make sure that the probes of the device are connected to the required sockets of the multimeter;
• The red wire is connected to the anode, and the black wire is connected to the cathode;

• We make a measurement. In continuity mode, when a diode is connected, the device shows a voltage drop from 200 to 400 mV for germanium diodes, from 500 to 700 mV for silicon ones. When measuring resistance, the device will show the resistance of the diode. For example, for germanium elements the resistance ranges from 100 kilo-ohms to 1 mega-ohm, for elements made of silicon this figure is 1000 mega-ohms. If the rectifier semiconductor is tested, then the value is even higher. This must be taken into account in order to avoid mistakes when determining the results;
• Swap the red and black probes of the device;
• We make a measurement. If the diode is connected in the opposite direction, the device will display the unit “1”, that is, the value of resistance or leakage voltage is infinitely large;

• You need to remember that there may not be a breakdown at all, but a leak. This option is possible in two cases, if the device has been in use for a long time or its assembly was not done well. If there is a short circuit or leakage, the meter will show low resistance. Moreover, when determining the result, you need to take into account the type of semiconductor.

• We draw conclusions about the performance of the element.

If all indicators are met, then we can safely say that it is working correctly and in good working order. But if at least one parameter is incorrect, then this indicates that the element needs to be replaced.

Signs of a faulty diode

• If the diode is faulty, then in the continuity mode the device will beep, and in the resistance measurement mode it will show a value close to 0, which indicates that the diode is short-circuited, that is, broken.
• If in both measurements the device shows 1, that is, an infinitely large value, this means that the diode is open.

Diode bridge

It happens that there is a need to diagnose a diode bridge. It is an assembly that consists of 4 semiconductors. Moreover, they are connected in such a way that the alternating voltage is converted into direct voltage. The verification principle is almost the same. An important distinguishing feature is that you need to determine how the diodes in the diode bridge are connected and check each diode in the forward and reverse directions.

Conclusion

It is not difficult to diagnose the performance of semiconductors in a device yourself. It is important to follow the procedure for using the multimeter and strictly follow the instructions. But at the same time, when starting the test, you must pay attention to the type of element, have an idea of ​​​​what the operating resistance and voltage should be for a working diode of this type, and only then carry out diagnostics and draw conclusions.

When using a device to check the health of a diode or for any other purposes, you must adhere to safety precautions when using it. All probes must be in good condition, the insulation of the wires must be intact. If there are any defects, it is advisable to eliminate them immediately so as not to injure yourself during measurement. It is also important to remember that each device has its own error; in cheap models it is very large. And this is important to take into account when conducting an audit. The result of the test and its accuracy will depend on how correctly all diagnostic steps are performed. Therefore, you need to pay due attention to this.

Modern digital multimeters allow a radio amateur to measure the resistance of a resistor, the capacitance of a capacitor, the value of inductance, the frequency of a signal, the temperature of an object, and the stabilization voltage of a zener diode - I have never seen anything like it. And at the disposal of a radio amateur there are many different ones, zener diodes. In metal, glass, plastic cases, sometimes with unreadable inscriptions. How to distinguish a zener diode from a diode, especially in a glass case? (Photo1).

It is especially important to know the stabilization voltage of the zener diode Ust. In many cases, the breakdown voltage of a silicon zener diode can be found in the technical documentation or simply determined from its name. For example, if the inscription BZX79 5V6 on the zener diode body, this means that it has a stabilization voltage of 5.6 V and belongs to the BZX family. But on the other hand, when the name of the zener diode is unknown (the inscriptions have been erased) or it is necessary to check its performance - what to do? In this case, you need to have a multimeter attachment on hand, which will help determine the stabilization voltage and distinguish a diode from a zener diode.
How does a zener diode work? A zener diode is a diode that, unlike a conventional rectifier diode, upon reaching a certain value of the reversely applied voltage (stabilization voltage), passes current in the opposite direction, and with its further increase, reducing its internal resistance, strives to maintain this voltage at a certain level. Let's look at its current-voltage characteristic (Fig. 1b).

Fig.1a               Fig.1b

On the current-voltage characteristic (volt-ampere characteristic) of a zener diode, the voltage stabilization mode is depicted in the negative region of the applied voltage and current. As the reverse voltage increases, the zener diode initially "resists" and the current flowing through it is minimal. At a certain voltage, the zener diode current begins to increase. A point is reached (point 1 on the current-voltage characteristic), after which a further increase in the voltage at the resistor-zener diode divider does not cause an increase in the voltage at the p-n junction of the zener diode. In this section of the current-voltage characteristic, the voltage increases only across the resistor (Fig. 1a). The current passing through the resistor and zener diode continues to increase. From point 1, corresponding to the minimum stabilization current, to a certain point 2 of the current-voltage characteristic, corresponding to the maximum stabilization current, the zener diode operates in the required stabilization mode (green section of the current-voltage characteristic). After point 2, the zener diode begins to heat up and may fail. The section between points 1 and 2 is the stabilization working section, in which the zener diode acts as a regulator. Manufacturers of stabilitrons always indicate the stabilization voltage at a certain current (5...15mA). The proposed set-top box uses the same current value when measuring stabilization voltage.
A radio amateur who has an adjustable power supply can use a simple probe to determine the stabilization voltage. The diagram is shown in Fig. 2. The LM317 microcircuit stabilizer is a current stabilizer. The current can be set to 5 or 15mA. If you use LM317AHV (input voltage 52V maximum), then you can measure stabilization voltage up to 48V, and with LM317 - up to 35V.

The diagram of a mobile set-top box for measuring stabilization voltage is shown in Fig. 3.

The basis of the circuit is a specialized microcircuit MC34063, which is a control circuit for a DC/DC converter. This chip is specially designed for use in boost, buck and inverting converters with a minimum number of elements. The output voltage produced by the boost converter is determined by two resistors R2 and R4. The calculation of resistor values ​​can be performed using an online calculator posted on the Radioactive website.

To assemble the circuit we will need:
Resistors: R1 - 180 Ohm; R2 - 56k; R3 - 9.1 Ohm; R4 - 1k6; R5 - 22 Ohm.
Capacitors: C1 - 330p; C2 - 470mk*16V; C3 - 10mk*100V.
Inductance - 1900 µH. Schottky diodes - 1N5819, 2 pcs.
The microcircuit is MC34063 in a DIL 8 package. Installed on a socket.
The microcircuit is LM334Z in a TO-92 package (current stabilizer).

Printed circuit board, Fig. 4

The appearance of the assembled device can be seen in photos 2, 3.

Everything is mounted on a printed circuit board. To connect to the multimeter, a plug from the charger is used, suitably modified for this purpose. Power source - 3 AAA elements connected in series, total 4.5V. The batteries are placed in a box mounted on the board. Power is turned on using a small button. The inductance is wound on a plastic coil with dimensions: outer diameter - 15mm, inner diameter - 5mm, distance between the cheeks - 15mm. We wind PEL, PEV wire with a diameter of 0.2 mm until it is filled. My measured inductance value turned out to be 2000 μH. If there is no LM334Z chip, then you can eliminate it and instead insert a 15k resistor between the VD2 cathode and the VDC pin, then the 22 Ohm resistor is also not needed.
When everything has been installed on the board and the installation has been checked, you can begin to check the functionality of the set-top box. I’ll say right away that the scheme worked for me the first time. But first things first. Without inserting the microcircuit into the socket, we check the voltage in the sockets of the socket, naturally by connecting the power source. There should be a supply voltage on pin 6, a little less on pins 7,8,1. Turn off the power and, if everything is fine, install the chip in place. Turn on the power and measure the current consumption without load. At a voltage of 9.4V, the current was 10.6 mA, and at 4.9V - 26.5 mA. Now you can check the voltage at the output of the set-top box. To do this, insert the plug with the board into the sockets of the multimeter, like in photo 4.

On the multimeter we set the limit to 200V DC voltage, press the S1 button and read the voltmeter readings. With a power supply voltage of 4.5 V, the output DC voltage was 33.8 V. The current in the measuring circuit was 10 mA. At 9V, the output voltage decreased to 21.8V, i.e. it is necessary to recalculate the values ​​of resistors R2 and R4 in order to increase the output voltage. In order to increase the output voltage, resistor R2 was replaced with a variable one to see how the voltage would change when it was adjusted. With a resistance of 120k, the voltage increased to 44V (Upit -4.5V), and to 34V at 9V Upit. When adjusted with resistor R4, only a voltage change from 40 to 44V was observed. As a result, using this attachment we can measure the stabilization voltage of zener diodes up to 40V.
Let's move on to taking measurements:
- connect the attachment to the multimeter, select the measurement limit of 200V (constant);
- check the presence of voltage at the output of the set-top box by briefly pressing the S1 button;
- connect the zener diode to the terminals, as in photo 5, press S1 and read the readings;

When an asymmetrical zener diode is connected with the anode to “+” and the cathode to “-”, the multimeter will show the minimum voltage (0.3...0.6V). When you change the polarity of the connection - with the cathode to “+” and the anode to “-”, the multimeter will show the stabilization voltage if it is below 44V. In our case, 0.7V and 14.6V, respectively. The stabilization voltage of the tested zener diode is 14.6V (photo 6);

Naturally, I wanted to make sure whether the prefix measures accurately. The same zener diode was tested in a radio workshop using an industrial tester L2-54. It turned out that the readings of the device and the set-top box almost coincide (0.5V and 14.7V on the device). Quite satisfactory for a homemade device.
- when connecting a symmetrical zener diode (KS162A), the stabilization voltage was 6.2V with any polarity;
- connecting the DB3 dinistor with any polarity showed a breakdown voltage of 29.5V;
- the diode with one polarity showed a minimum voltage, with the opposite polarity the output voltage of the set-top box was 44V;
- the transistor acting as a zener diode gave the following results: KT315B,E - 7.3V; S9014 - 9V.
   Before installing the radio element into the attachment for measurements, check it for breaks or short circuits inside the housing to avoid unnecessary questions.
   High-voltage zener diodes cannot be tested with this device; a higher voltage is required. Over time, we will consider such a device.
   If the set-top box is packaged in a suitable case, then you can take it with you to the radio market in order to protect yourself from unscrupulous sellers when buying zener diodes.

Download the diagram: (downloads: 965)
Download PCB: (downloads: 933)

In the process of repairing household appliances or other electronic devices: monitor, printer, microwave, computer power supply or car generator (for example, Valeo, BOSCH or BPV), etc. there is a need to check the integrity of the elements. We'll tell you in detail about testing diodes.

Given the diversity of these radioelements, there is no uniform method for testing their performance. Accordingly, each class has its own testing method. Let's look at how to test a Schottky diode, photodiode, high frequency, bidirectional, etc.

As for testing devices, we will not consider exotic testing methods (for example, a battery and a light bulb), but will use a multimeter (even such a simple model as DT-830b will do) or a tester. Radio amateurs almost always have these devices at home. In some cases, you will need to assemble a simple circuit for testing. Let's start with classification.

Classification

Diodes are simple semiconductor radioelements based on a p-n junction. The figure shows a graphical representation of the most common types of these devices. The anode is marked “+”, the cathode – “-” (shown for clarity; in the diagrams, a graphical designation is sufficient to determine the polarity).

Accepted notations

Types of diodes shown in the figure:

• A – rectifying;
• B – zener diode;
• C – varicap;
• D – microwave diode (high voltage);
• E – reversed diode;
• F – tunnel;
• G – LED;
• H – photodiode.

Now let's look at the verification methods for each of the listed types.

Checking the rectifier diode and zener diode

The protective diode, as well as the rectifier diode (including the power diode) or Schottky diode, can be checked using a multimeter (or use an ohmmeter); to do this, we switch the device to the continuity mode as shown in the photo.

We connect the probes of the measuring device to the terminals of the radio element. By connecting the red wire (“+”) to the anode and the black (“-”) wire to the cathode, the multimeter (or ohmmeter) display will display the threshold voltage value of the diode being tested. After we change the polarity, the device should show infinitely high resistance. In this case, we can state that the element is in good condition.

If, when connecting back, the multimeter registers a leak, it means that the radio element has “burned out” and needs to be replaced.

Note that this testing technique can be used to test diodes on a car generator.

Zener diode testing is carried out according to a similar principle, however, such a test does not allow one to determine whether the voltage is stabilized at a given level. Therefore, we need to assemble a simple circuit.

Designations:

• PSU – adjustable power supply (displaying load current and voltage);
• R – current-limiting resistance;
• VT – Zener diode or avalanche diode under test.

The verification principle is as follows:

• we assemble the circuit;
• set the multimeter mode, which allows you to measure DC voltage up to 200 V;

• turn on the power supply and begin to gradually increase the voltage until the ammeter on the power supply shows that current is flowing through the circuit;
• connect the multimeter as shown in the figure and measure the stabilization voltage.

Varicap testing

Unlike conventional diodes, varicaps have a p-n junction with a variable capacitance, the value of which is proportional to the reverse voltage. Checking for open or short circuits for these elements is carried out in the same way as for conventional diodes. To check the capacity, you will need a multimeter that has a similar function.

To test, you will need to set the multimeter to the appropriate mode, as shown in photo (A) and insert the part into the connector for capacitors.

As one of the commentators on this article correctly noted, it is indeed impossible to determine the capacitance of a varicap without using the rated voltage. Therefore, if there is a problem with identification by appearance, you will need to assemble a simple attachment for a multimeter (I repeat for critics, a digital multimeter with the function of measuring the capacitance of capacitors, for example UT151B).

Designations:

The device requires configuration. It is quite simple, the assembled device is connected to a measuring device (a multimeter with a capacitance measurement function). Power must be supplied from a stabilized power source (important) with a voltage of 9 volts (for example, a Krona battery). By changing the capacitance of the substring capacitor (C2), we achieve a reading on the indicator of 100 pF. We will subtract this value from the device reading.

This option is not ideal, the need for its practical use is questionable, but the circuit clearly demonstrates the dependence of the varicap capacity on the rated voltage.

Checking the suppressor (TVS diode)

Protective diode, also known as limiting zener diode, suppressor and TVS diode. These elements come in two types: symmetrical and asymmetrical. The former are used in alternating current circuits, the latter - in direct current. If we briefly explain the principle of operation of such a diode, it is as follows:

An increase in input voltage causes a decrease in internal resistance. As a result, the current in the circuit increases, which causes the fuse to trip. The advantage of the device is its fast response, which allows it to absorb excess voltage and protect the device. Response speed is the main advantage of a protective (TVS) diode.

Now about the verification. It is no different from a regular diode. True, there is an exception - Zener diodes, which can also be attributed to the TVS family, but in essence they are a fast zener diode operating according to the “mechanism” of avalanche breakdown (Zener effect). But the performance check reverts to a regular dialing test. Creating triggering conditions leads to failure of the element. In other words, there is no way to check the protective functions of a TVS diode; it’s like checking a match (whether it’s good or not) by trying to light it.

High Voltage Diode Testing

It will not be possible to check the high-voltage diode of a microwave oven in the same way as a regular one, due to its features. To test this element, you will need to assemble a circuit (shown in the figure below) connected to a 40-45 volt power supply.

A voltage of 40-45 volts will be enough to test most elements of this type; the testing methodology is the same as for conventional diodes. The resistance value R should be in the range from 2 kOhm to 3.6 kOhm.

Tunnel and reverse diodes

Considering that the current flowing through a diode depends on the voltage applied to it, testing consists of analyzing this dependence. To do this, you will need to assemble a circuit, for example, such as shown in the figure.

List of elements:

• VD – tunnel type diode under test;
• Up – any galvanic power source with a discharge current of about 50 mA;
• Resistances: R1 – 12Ω, R2 – 22Ω, R3 – 600Ω.

The measurement range set on the multimeter should not be less than the maximum current of the diode; this parameter is indicated in the datasheet of the radio element.

Video: Example of checking a diode with a multimeter

Testing algorithm:

• the maximum value is set on variable resistor R3;
• the element under test is connected, observing the polarity indicated on the diagram;
• By decreasing the value of R3, we observe the readings of the measuring device.

If the element is in good condition, during the measurement process the device will show an increase in current up to I max of the diode, followed by a sharp decrease in this value. With a further increase in voltage, the current will decrease to I min, after which it will begin to increase again.

LED testing

Testing LEDs is practically no different from testing rectifier diodes. How to do this was described above. We check the LED strip (more precisely, its SMD elements), infrared LED, and also laser LED using the same method.

Unfortunately, a powerful radio element of this group, which has a higher operating voltage, cannot be tested using the indicated method. In this case, you will additionally need a stabilized power source. The testing algorithm is as follows:

• We assemble the circuit as shown in the figure. The power supplies are set to the operating voltage of the LED (indicated in the datasheet). The measuring range on the multimeter should be up to 10 A. Note that you can use the charger as a power supply, but then you need to add a current-limiting resistor;

• measure the rated current and turn off the power supply;
• set the multimeter mode, which allows you to measure DC voltage up to 20 V, and connect the device in parallel to the element under test;
• turn on the power supply and remove the operating voltage parameters;
• We compare the data obtained with those indicated in the datasheet, and based on this analysis we determine the performance of the LED.

Checking the photodiode

In a simple test, the reverse and forward resistance of a radio element placed under a light source is measured, after which it is darkened and the procedure is repeated. For more accurate testing, you will need to take the current-voltage characteristic; this can be done using a simple circuit.

To illuminate the photodiode during testing, you can use an incandescent lamp with a power of 60 W or more as a light source or bring the radio component to a chandelier.

Photodiodes sometimes have a characteristic defect, which manifests itself in the form of a chaotic change in current. To detect such a malfunction, it is necessary to connect the element under test as shown in the figure and measure the reverse current for a couple of minutes.

If during testing the current level remains unchanged, then the photodiode can be considered working.

Testing without desoldering.

As practice shows, it is not always possible to test a diode without desoldering it when it is on the board, like other radio components (for example, a transistor, capacitor, thyristor, etc.). This is due to the fact that elements in the circuit may produce an error. Therefore, before checking the diode, it must be desoldered.