Every radio amateur knows how sometimes it is important to know whether this or that radio component is working or not. Last but not least, this applies to zener diodes. A multimeter serves as a tester for checking electrical components for the presence of stabilization voltage.

Zener diode and its properties

For work electronic circuits the output needs stabilized voltage indicators. They are obtained by including semiconductor zener diodes in the circuit, which give the same output voltage, which does not depend on the magnitude of the transmitted electric current. Without these elements, many low-current systems do not work. So, for example, almost every radio amateur at least once in his life soldered the voltage regulator l7805cv or its analogues.

Zener diodes have non-linear current-voltage characteristics, in terms of properties, as well as in terms of appearance(in glass or metal) they resemble an ordinary diode, however, their tasks are somewhat different. Zener diodes are connected to the circuit in parallel with the consumer, and if the voltage rises sharply, the current flows through the zener diode, and the voltage in the network equalizes. If a strong current is applied for a long time, a thermal breakdown occurs.

Checking procedure

In order to determine whether a given zener diode is good or out of order, the multimeter must be switched to the mode that checks the diodes (or to the ohmmeter mode) - checking the zener diodes by ringing is carried out in a similar way.

The multimeter probes are connected to the terminals of the zener diode and the indicator readings are observed. Checking should be carried out in two directions:

  • the positive probe of the device touches the cathode of the part - the indicator shows infinite resistance;
  • the multimeter is connected to the anode of the zener diode - the resistance will be displayed on the screen in units or tens of ohms (voltage drop).

Such indicators appear because the working zener diode (like a conventional diode) is capable of conducting only unidirectional electricity, and the check should not cause a short circuit in the network.

If, when ringing in both directions, the multimeter shows infinite resistance, the zener diode is defective, since the electron-hole junction is broken, and current does not pass through the electrical component.

Note! Sometimes it happens that when measuring a zener diode with a multimeter, a resistance of several tens or hundreds of ohms is given in both directions. In the case of conventional diodes, this position means that the part is broken. However, this is not true for a zener diode, because it has a breakdown voltage: when the multimeter probe touches the ends of the zener diode, the internal voltage of the power supply affects measuring device. If his tension is more tension breakdown, then indicators of multi-ohm resistance will appear on the indicator.

So, with a multimeter battery voltage of 9 volts, a breakdown will be indicated for zener diodes with a voltage below this value. Therefore, experts do not recommend checking zener diodes with a low stabilization voltage using digital multimeters. For these purposes, the good old tester is better - an analogue.

How to check the zener diode on the board

If the zener diode is soldered to the board, then the procedure for checking it does not differ from that used for free electronic device of this type.

Important! When measuring and repairing the board, be sure to observe safety measures to protect against electric shock. When ringing a soldered zener diode, all other elements, except for the one being checked, can produce greatly changed indicators, this must also be taken into account.

If, when checking on the board, dubious results of the suitability of the zener diode were obtained, then it is worth unsoldering it and checking only this element with a multimeter, isolating it from the influence of the rest of the circuit details. Also, sometimes you can use an attachment to the multimeter, which you can solder with your own hands from available parts.

It is desirable for every radio amateur to know how to check a zener diode with a multimeter - this will help to assemble working circuits and save radio components by identifying non-working ones. However, with such a check, it is impossible to obtain a 100% reliable result. A guarantee of the suitability of a zener diode can only be given by its inclusion in the electrical circuit: if the device works, then the stabilizing element is functioning.

Video


For many homemade amateur radio stabilized power supplies are required. Their main element is a zener diode, which is able to provide a constant output voltage. There are several ways to check the performance and functioning of this radio element.


It is impossible to check it completely and with 100% certainty that this zener diode is serviceable with a digital multimeter. Of course, it can be checked, but you can mistakenly consider the working zener diode to be damaged. Is this possible?

Let's conduct a small practical experiment, take any zener diode with a small stabilization voltage, for example 2.4 volts. And connect to a digital multimeter, and it rings in both directions. And the whole trick is that there is about 5 volts on the probes of a digital multimeter, and therefore it simply breaks through in the opposite direction. Therefore, you should not check zener diodes with low stabilization voltage with digital multimeters, it is better to use an old analog tester, and if it is not there, you can assemble a small circuit below.

The main node of the circuit is a converter that converts 9 volts to 45, made on the MC34063 chip. This chip is specially applied in step-up, step-down and inverting converters with a minimum of elements. The output voltage of the MC34063, obtained by the boost converter, is set by resistors R2 and R4. Resistor R5 limits the output current to three milliamps so as not to damage the zener diode under test. The voltmeter is designed to measure the stabilization voltage.

The whole circuit is mounted on a printed circuit board. To connect to the multimeter, I adapted the plug from the old charger. I powered the circuit from a "Krona" type battery, which I placed in the box and fixed on the board. I wound the inductance on a plastic coil with dimensions: outer diameter - 15mm, inner - 5mm, distance between the cheeks - 15mm. The wire used PEL, PEV with a diameter of 0.2 mm, we wind it up to fill.

The proposed prefix to the multimeter will allow you to check the main parameter of any zener diode - stabilization voltage. The basis of the circuit is a voltage converter block from the Electronics MK-24 calculator, which you are unlikely to want to use for its intended purpose. The block has three conclusions: "+", "-" and "VBbo", on the body there is an inscription KF-29. If 1.5 V is applied to its input, the output will have a voltage of about 15 V. Resistor R1, together with the zener diode under test, constitute a parametric voltage regulator.

To connectors XS1 and XS2 connect a digital multimeter such as M-830 in voltage measurement mode. While the zener diode is not connected, the multimeter shows the output voltage of the converter. As soon as we connect the tested zener diode, the multimeter will show the stabilization voltage. If you connect it as a diode, then you will see 0.7 V on the display. If it shows almost zero with both connections, then the zener diode is broken. Please note that zener diodes with a stabilization voltage above 15 volts cannot be checked.

If you can’t find a block converter from a calculator, you can use this scheme:


The basis of the circuit is the transistor VT1 and the transformer T1 on which the blocking generator is assembled. The pulses from the output of the transistor VT1 are rectified by the diode VD1, through the resistor R1 they are fed to the connectors XS1 and XS2. .

Transformer T1 assembled on ferrite ringК10*6хЗ mm with magnetic permeability 1000-2000. Primary winding consists of 20 turns, and the secondary - 10 turns of PEV-2 wire 0.31

Diode 1N5817 can be replaced by 1N5818, 1N5819.

The scheme of the device is quite simple. The voltage coming from the secondary windings of the 24 volt transformer is rectified and a constant voltage of 80 V is obtained at the filter output, which is supplied to the voltage regulator assembled on the elements (R1, R2, D1, D2 and Q1), a constant voltage of 52 Volts is obtained from its output so as not to exceed the maximum threshold voltage on the LM317AHV chip.



A generator is built on the LM317AHV chip direct current, where switch S2 with resistor R4 is introduced to generate two test modes (5mA and 15mA) as current sources for the zener diode under test.

The circuit of this device for checking the zener diode is easy to repeat using standard and cheap radio elements. Ready impulse block power can be borrowed from an unnecessary DVD, and one of the cheap Chinese multimeters, such as the D-830, can be used as a voltmeter.

The proposed circuit serves to simply determine the voltage rating of the stabilization of the zener diode using a voltmeter, as well as to determine its serviceability.

Now the industry produces an incredible number of different electronic components and often when assembling a radio-electronic product, there are many difficulties in determining the value of the component. Especially in this regard, the domestic industry “distinguished itself” - in particular, zener diodes in a glass case have, at times, very similar markings, which are not possible to distinguish. Good example these are the KS211 and KS175 zener diodes - sometimes there are marking options in which both look like a small output glass diode with black stripe. They can also be confused, for example, with the D814 zener diode. Anyway, remember color coding zener diodes are not the best idea considering how easy they are to test.

To determine the stabilization voltage, you need a simple circuit:


Typically, the operating current range of low-power zener diodes is in the range of 1-10 mA, so the resistor value is 2.2 kOhm. This is optimal for testing low power zener diodes. To check powerful zener diodes, the resistance may have to be reduced - for this, a jumper is provided in the circuit. To test low-power zener diodes, the jumper must be placed in the upper position, to test powerful ones, in the lower position.

The optimal supply voltage is 25V.

If the zener diode is connected correctly - anode to X1, cathode to X2, then the voltmeter will show its stabilization voltage, and if wrong - some very small voltage near zero. If, with one connection, the multimeter shows a minimum voltage, and with another - the maximum, equal to the voltage of the power source, then the radio element under test is either a simple diode or a zener diode with a stabilization voltage higher than the voltage of the power source. If you are sure that this is a zener diode, you need to increase the source voltage to the expected value and check again.

If the voltmeter shows the minimum voltage, or the supply voltage for any connection, then this zener diode or diode is faulty.

If the stabilization voltage is shown with any connection, then this is a two-way zener diode.

In a similar way, you can check the health of diodes and LEDs, only the polarity will be opposite. The method is good because it allows you to find out the voltage drop, which is very important. When checking the LEDs, it must be remembered that some LEDs are very sensitive to an overestimated reverse voltage, so it is advisable to set the source voltage when checking them no higher than 9V.


Modern digital multimeters allow a radio amateur to measure the resistance of a resistor, the capacitance of a capacitor, the value of the inductance, the frequency of the signal, the temperature of the object, and so that the stabilization voltage of the zener diode - I have not seen such. And at the disposal of the radio amateur of them, zener diodes, there are many and different ones. 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 body of the zener diode has the inscription BZX79 5V6, then 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, it is necessary to have an attachment to the multimeter on hand, which will help determine the stabilization voltage and distinguish the diode from the zener diode.
How does a zener diode work? A zener diode is such a diode, which, unlike a conventional rectifier diode, when a certain value of the reversely applied voltage (stabilization voltage) is reached, passes the current in the opposite direction, and with its further increase, reducing its internal resistance, tends to keep 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 (CVC) of the zener diode, the voltage stabilization mode is shown in the negative region of the applied voltage and current. As the reverse voltage increases, the zener diode first "resists" and the current flowing through it is minimal. At a certain voltage, the current of the zener diode begins to increase. Such a point is reached (point 1 on the I–V characteristic), after which a further increase in the voltage across the resistor-zener diode divider does not cause an increase in the voltage across p-n junction zener diode. In this section of the I–V characteristic, the voltage increases only across the resistor (Fig. 1a). The current passing through the resistor and zener diode continues to rise. 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 CVC). After point 2, the zener diode starts to heat up and may fail. The section between points 1 and 2 is the working section of stabilization, on which the zener diode acts as a regulator. Manufacturers of zener diodes always indicate the stabilization voltage at a certain current (5 ... 15mA). The proposed attachment uses the same current value when measuring the stabilization voltage.
A radio amateur with an adjustable power supply can use a simple probe to determine the stabilization voltage. The scheme is shown in Fig.2. A current stabilizer is made on the LM317 microcircuit stabilizer. The current can be set to 5 or 15mA. If you use LM317AHV (input voltage 52V maximum), then you can measure the stabilization voltage up to 48V, and with LM317 - up to 35V.

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

To assemble the circuit, we 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 the DIL 8 package. It is installed on the socket.
Chip - LM334Z in the TO-92 package (current stabilizer).

PCB, 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 was used, suitably modified for this purpose. Power supply - 3 AAA elements connected in series, total 4.5V. The batteries are placed in a box fixed on the board. The power is turned on by a small button. The inductance is wound on a plastic coil with dimensions: outer diameter - 15mm, inner - 5mm, distance between cheeks - 15mm. Wire PEL, PEV with a diameter of 0.2 mm, wind up to fill. I measured the value of the inductance turned out to be 2000 μG. If there is no LM334Z chip, then you can exclude 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 was installed on the board, the installation was checked, you can begin to check the performance of the set-top box. I must 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, of course, by connecting the power source. At pin 6 there should be a supply voltage, at pins 7,8,1 - a little less. Turn off the power and, if everything is fine, install the chip in place. We 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 console. To do this, insert the plug with the board into the sockets of the multimeter, as in photo 4.

On the multimeter, set the limit to 200V DC voltage, press the S1 button and read the voltmeter readings. At a power supply voltage of 4.5V, the output DC voltage was 33.8 V. The current in the measuring circuit was 10mA. 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, the resistor R2 was replaced with a variable one in order 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 up to 34V at 9V Upit. When adjusting with resistor R4, only a voltage change from 40 to 44V was observed. As a result, with the help of this attachment, we can measure the stabilization voltage of zener diodes up to 40V.
Let's move on to measurements:
- connect the prefix 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 button S1;
- connect the zener diode to the clamps, as in photo 5, press S1 and read the readings;

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

Naturally, I wanted to make sure that the prefix accurately measures. The same zener diode was tested in a radio workshop on an industrial tester L2-54. It turned out that the readings of the device and the attachment are almost the same (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;
- connection of the DB3 dinistor with any polarity showed a breakdown voltage of 29.5V;
- the diode with one polarity showed the minimum voltage, with the reverse - the output voltage of the set-top box - 44V;
- the transistor in the role of a zener diode gave the following results: KT315B, E - 7.3V; S9014 - 9V.
Before installing the radio element in the attachment for measurements, check it for an open or short circuit inside the case in order to avoid unnecessary questions.
High-voltage zener diodes cannot be checked with this device; more high voltage. Over time, we will consider such a device.
If the set-top box is placed in a suitable case, then you can take it with you to the radio market in order to protect yourself from dishonest sellers by buying zener diodes.

Download scheme: (downloads: 966)
Download printed circuit board: (downloads: 933)

Information for beginner radio amateurs:
there is no function for checking zener diodes in multimeters.

And do not look for a multimeter with a zener meter. But it is clear that it is necessary to check. Moreover, it is necessary to test even a serviceable component for the parameter of the actual stabilization voltage. The truth is written. Here's just how, so as not to assemble a separate device and not use one of the existing methods, which take, albeit not very, but a relatively long time, not only in terms of the time of the test, but also in preparation for it. But one well-known humorist turned out to be right, arguing that in the entire post-Soviet space, the people have no problems with the “reason”.

I decided to assemble the device as an attachment to the multimeter, and compact. Enclosure from safety blades packaging Schick". Terminal socket telephone cable Came up in size and color, and it was possible to attach a power button to it. Considering some originality of the case, the assembly had to be done, so to speak, in a “step by step” way.

Step one

step two- cleaning all of the above into the niche of the case and installing the pins in place (forming an impromptu plug for connecting the probe to the multimeter) by using a threaded connection on them and two M4 nuts for each. The distance between the centers of the pins is 18.5 mm.

Step Three- installation of LEDs and limiting resistors.

I hid the contents “out of sight” and screwed suitable contacts on top for connecting the tested zener diodes. Contacts can be rotated around its axis and thus change the distance between them depending on the length of the component being tested. I'm trying it out:

imported zener diode BZX85C18- a bit did not reach the declared parameter.

But domestic KS515A did not let us down, as they say "in the bull's-eye." And now I have in my arsenal Schick arch tester of zener diodes.))

Video

Of course, the multimeter itself can be replaced by any, even a pointer, voltmeter - this will be useful if you often have to check such details in the course of work in the workshop. I wish you success, Babay. Russia, Barnaul.