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.

One more addition. Using this attachment, you can detect Schottky barrier diodes, which are known to have a low forward voltage drop. The picture shows the test of 1N5819 - with a Schottky barrier. Upr. = 0.24V. Great!

I used this zener diode probe for a long time. It has only one single drawback - it requires a landline telephone line, because it is powered from it, from its 50 volts with a unique current of 20 milliamps. It is obvious that the line voltage covers the entire visible voltage range of zener diodes used in practice by radio amateurs. There are no words for how convenient it is.

But the phone was gone, but the need for measurements remained, a new probe had to be made, and the circuit underwent changes only in terms of the number of electronic components involved, and in the direction of reduction. The probe will be powered from a laboratory power supply with an adjustable output voltage of 0 - 30 volts.

The kit required for manufacturing includes:

  • 22 nF capacitor, 2.4 MΩ/0.5 W resistor, 10 kΩ/2 W resistor
  • two lids and a neck from any suitable plastic container
  • a pair of connecting contacts, a pair of network pins and nuts with M4 screws

Holes are pierced in the covers with an awl, in one at a distance of 19 mm from each other and pins are installed in them, in the other at an arbitrary distance for connecting contacts. Electronic components are connected to each other by soldering (look at the photo and diagram).

The component assembly is installed in place and secured with nuts. One of the caps is screwed onto the thread, the second is put on “tightly” on the opposite side of the neck (it turns out like a latch, you just need to trim the edges correctly to “catch” the required diameter). And don’t forget to organize a power supply.

We put information stickers on the top cover of the finished probe body and it can be used. The probe circuit and method have been tested over five years of operation. This is exactly the case when a product is characterized by the saying “both cheap and cheerful.” The time required for its production is no more than an hour.

How to use the sampler

The procedure for using the probe is as follows: the probe is inserted with pins into the corresponding sockets of the multimeter, the measurement limit is selected “20” or “200” volts DC depending on the expected stabilization voltage of the zener diode. Next comes the connection to a DC source, the best option is a power supply with adjustable output voltage from zero and current up to 1 ampere. We correctly place the tested zener diode on the contacts, slowly increase the output voltage and look at the multimeter display. There we will see the stabilization voltage of the zener diode we are interested in. But everything will work out, even if there is no regulated power supply, you can use ordinary batteries, connecting them in series until the required voltage is reached.

The device presented here is a zener diode meter for testing the voltage value of an unknown zener diode. - this 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.

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

And don't look for a multimeter with a Zener meter. But it is clear that it is necessary to check. Moreover, even a serviceable component must be tested for the actual stabilization voltage parameter. The truth is simple. Just how, so as not to assemble a separate device and not to use one of the existing methods, which take, albeit not very much, but a relatively long time, and 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, claiming that throughout the entire post-Soviet space people have no problems with “thinking”.

I decided to assemble the device as an attachment to a multimeter, and a compact one at that. Housing from packaging of safety blades " Schick" The socket for the end of the telephone cable matched both in size and color, and we managed to attach the power button to it. Given some of the uniqueness of the case, the assembly had to be done, so to speak, in a “step-by-step” manner.

Step one

Step two- removing all of the above into the housing niche and installing the pins in place (forming an improvised 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 on top suitable contacts for connecting the zener diodes being tested. The contacts can be rotated around their axis and thereby change the distance between them depending on the length of the component being tested. I'll try it out:

Imported zener diode BZX85C18- fell just short of the stated parameter.

But domestic KS515A didn’t disappoint, as they say, “right on the bull’s eye.” And now I have it in my arsenal Schick arny zener diode tester.))

Video

The multimeter itself, of course, can be replaced with any voltmeter, even a dial voltmeter - this will be useful if you often have to check such parts while working in the workshop. I wish you success, Babay. Russia, Barnaul.