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Do-it-yourself radio engineering, electronics and circuits. Tester for checking optocouplers

Do-it-yourself radio engineering, electronics and circuits. Tester for checking optocouplers

Recently I had to tinker with various electronic ballasts and, in their composition, with a DB3 dinistor, optocouplers and zener diodes from other devices. Therefore, to quickly test these components, a specialized tester had to be developed and manufactured. Additionally, in addition to dinistors and optocouplers, in order not to create more testers for similar components, the tester can test zener diodes, LEDs, diodes, and transistor junctions. It uses light and sound indication and an additional digital voltage meter to assess the level of operation of dinistors and the voltage drop at the junction of the tested zener diodes, diodes, LEDs, and transistors.

Note: All rights to the diagram and design belong to me, Anatoly Belyaev.

2017-03-04

Description of the scheme

The tester circuit is shown below in Pic 1.

Note: to view the picture in detail, click on it.

Pic 1. Circuit diagram of the DB3 tester (dinistors), optocouplers, zener diodes, diodes, LEDs and transistor junctions

The tester is based on a high-voltage pulse generator, which is assembled on transistor VT1 according to the principle of a DC-DC converter, that is, high-voltage self-induction pulses enter the storage capacitor C1 through the high-frequency diode VD2. The generator transformer is wound on a ferrite ring taken from an electronic ballast (any suitable one can be used). The number of turns is about 30 per winding (not critical and winding can be done simultaneously with two wires at once). Resistor R1 achieves the maximum voltage on capacitor C1. I got about +73.2 V. The output voltage is supplied through R2, BF1, HL1 to the contacts of the XS1 socket, into which the components being tested are inserted.

A digital voltmeter PV1 is connected to pins 15, 16 of the XS1 socket. Bought on Aliexpress for 60 RUR. When checking dinistors, the voltmeter shows the opening voltage of the dinistor. If you connect LEDs, diodes, zener diodes, and transistor junctions to these XS1 contacts, then the PV1 voltmeter shows the voltage at their junction.

When checking dinistors, the indicator LED HL1 and sound emitter BF1 operate in pulse mode - indicating the serviceability of the dinistor. If the dinistor is broken, then the LED will glow constantly and the voltage on the voltmeter will be about 0 V. If the dinistor is broken, then the voltage on the voltmeter will be about 70 V, and the HL1 LED will not light up. Optocouplers are checked in the same way, only the indicator LED for them is HL2. To ensure that the LED operates pulsed, a working DB3 dinistor (KN102) is inserted into the XS1 contacts. When the optocoupler is working properly, the indicator LED glows pulsed. The optocouplers are available in DIP4, DIP6 housings and must be installed in the corresponding contacts of the XS1 socket. For DIP4 it is XS1, and for DIP6 it is XS1.

If you check zener diodes, then connect them to XS1. The voltmeter will show either the stabilization voltage if the zener diode cathode is connected to pin 16, or the voltage at the zener diode junction in the forward direction if the anode is connected to pin 16.

The voltage from capacitor C1 is directly output to the XS1 contacts. Sometimes there is a need to illuminate a powerful LED or use the full output voltage of a high-voltage generator.

Power is supplied to the tester only during component testing, when the SB1 button is pressed. Button SB2 is designed to control the tester supply voltage. When you simultaneously press the SB1 and SB2 buttons, the voltmeter PV1 shows the voltage on the batteries. I did this so that I could change the batteries in a timely manner when they run out, although I think that this will not happen soon, since the tester’s operation is short-term and the loss of battery energy is more likely due to their self-discharge than due to the operation of the tester itself when checking components. The tester is powered by two AAA batteries.

To operate the digital voltmeter, I used a purchased DC-DC converter. At its output I set +4.5 V - the voltage supplied to both the power supply of the voltmeter and the HL2 LED circuit - monitoring the operation of the output stage of the optocouplers.

The tester used a 1GW planar transistor, but you can use any suitable one, not just planar, which will provide a voltage on capacitor C1 greater than 40 V. You can even try using the domestic KT315 or the imported 2N2222.

Photo review of tester manufacturing

Pic 2. Printed circuit board of the tester. View from the side of the panel.

On this side of the board a socket, a sound emitter, a transformer, indicator LEDs and control buttons are installed.

Pic 3. Printed circuit board of the tester. View from the side of the printed conductors.

On this side of the board, planar components and larger parts are installed - capacitors C1 and C2, trimming resistor R1. The printed circuit board was made using a simplified method - cutting grooves between the conductors, although etching can also be done. The PCB layout file can be downloaded at the bottom of the page.

Pic 4. Internal contents of the tester.

The tester body consists of two parts: upper and lower. A voltmeter and a tester board are installed in the upper part. A DC-DC converter for powering the voltmeter and a container for batteries are installed in the lower part. Both parts of the body are connected by latches. Traditionally, the case is made of 2.5 mm thick ABS plastic. Tester dimensions 80 x 56.5 x 33 mm (excluding legs).

Pic 5. Main parts of the tester.

Before installing the converter in its place in the housing, the output voltage was adjusted to +4.5 V.

Pic 6. Before assembly.

In the top cover there are holes cut for a voltmeter indicator, for a contact socket, for indicator LEDs and for buttons. The voltmeter indicator hole is covered with a piece of red plexiglass (any suitable one can be used, for example, I have a shade of purple or violet). The holes for the buttons are countersunk so that you can press the button, which does not have a pusher.

Pic 7. Assembly and connection of tester parts.

The voltmeter and tester board are attached with self-tapping screws. The board is attached so that the indicator LEDs, socket and buttons fit into the corresponding holes in the top cover.

Pic 8. Before checking the operation of the assembled tester.

The PC111 optocoupler is installed in the socket. A known-good DB3 dinistor is inserted into contacts 15 and 2 of the socket. It will be used as a pulse generator supplied to the input circuit to check the correct operation of the output part of the optocoupler. If you use a simple LED glow through the output circuit, then this would be wrong, since if the output transistor of the optocoupler were broken, then the LED would also glow. And this is an ambiguous situation. When using the pulsed operation of an optocoupler, we clearly see the operability of the optocoupler as a whole: both its input and output parts.

Pic 9. Checking the functionality of the optocoupler.

When you press the component test button, we see a pulsed glow of the first indicator LED (HL1), indicating the serviceability of the dinistor, which works as a generator, and at the same time we see the glow of the second indicator LED (HL2), which pulsed operation indicates the serviceability of the optocoupler as a whole.

The voltmeter displays the operating voltage of the generator dinistor; it can be from 28 to 35 V, depending on the individual characteristics of the dinistor.

An optocoupler with four legs is checked in the same way, only it is installed in the corresponding contacts of the socket: 12, 13, 4, 5.

The socket contacts are numbered in a circle counterclockwise, starting from the bottom left and then to the right.

Pic 10. Before checking an optocoupler with four legs.

Pic 11. Checking the DB3 dinistor.

The dinistor being tested is inserted into contacts 16 and 1 of the socket and the test button is pressed. The voltmeter displays the response voltage of the dinistor, and the first indicator LED pulses to indicate the serviceability of the dinistor being tested.

Pic 12. Checking the zener diode.

The Zener diode being tested is installed in the contacts where the dinistors are also checked, only the glow of the first indicator LED will not be pulsed, but constant. The performance of the zener diode is assessed using a voltmeter, where the stabilization voltage of the zener diode is displayed. If the zener diode is inserted into the socket with the contacts in the opposite direction, then when checking on a voltmeter, the voltage drop across the zener diode junction in the forward direction will be displayed.

Pic 13. Checking another zener diode.

The accuracy of the stabilization voltage readings can be somewhat conditional, since a certain current through the zener diode is not set. So, in this case, the zener diode was tested at 4.7 V, and the reading on the voltmeter was 4.9 V. This may also be influenced by the individual characteristics of a particular component, since Zener diodes for a certain stabilization voltage have some spread among themselves. The tester shows the stabilization voltage of a specific zener diode, and not the value of its type.

Pic 14. Checking the bright LED.

To check the LEDs, you can use either contacts 16 and 1, where the dinistors and zener diodes are checked, then the voltage drop across the operating LED will be displayed, or you can use contacts 14 and 3, to which the voltage from the storage capacitor C1 is directly output. This method is convenient for checking the glow of more powerful LEDs.

Pic 15. Voltage control on capacitor C1.

If you do not connect any components for testing, the voltmeter will show the voltage on the storage capacitor C1. For me it reaches 73.2 V, which makes it possible to test dinistors and zener diodes in a wide range of operating voltages.

Pic 16. Checking the tester supply voltage.

A nice feature of the tester is monitoring the voltage on the batteries. When you press two buttons simultaneously, the voltmeter indicator shows the voltage of the batteries and at the same time the first indicator LED (HL1) lights up.

Pic 17. Different angles of the tester body.

In the side view you can see that the control buttons do not protrude beyond the top side of the cover; I made it so that there would be no accidental pressing of the buttons if the tester was put in a pocket.

Pic 18. Different angles of the tester body.

The case at the bottom has small legs for a stable position on the surface and so as not to rub or scratch the bottom cover.

Pic 19. Finished look.

The photo shows the finished view of the tester. Its dimensions can be represented by a standard box of matches placed next to it. In millimeters, the dimensions of the tester are 80 x 56.5 x 33 mm (excluding legs), as indicated above.

Pic 20. Digital voltmeter.

The tester uses a purchased digital voltmeter. I used a meter from 0 to 200 V, but it is also possible from 0 to 100 V. It is inexpensive, in the range of 60...120 P.

So I’m already ready for the next one. What prompted me to do this was reading questions on the forum from forum users who were determined to repair any electronic device themselves. The essence of the questions is the same and can be formulated as follows: “Which electronic component in the device is faulty?” At first glance, this is a completely modest desire, however, this is not so. Because knowing in advance the cause of a malfunction is like “knowing the purchase,” which, as you know, is the main condition for living in Sochi. And since no one from the glorious seaside city has been spotted, novice repairmen are left with a total check of all electronic components of the failed device to detect a malfunction. This is the most prudent and correct action. The condition for its implementation is that the electronics enthusiast has the entire list of testing instruments.

Schematic diagram of an optocoupler tester

To check the serviceability of optocouplers (for example, the popular PC817), there are testing methods and testing circuits. I chose the circuit I liked and added a voltage drop measurement with a multimeter to the light indication of serviceability. I wanted information in numbers. Whether this is necessary or not will become clear over time during the operation of the console.

I started with the selection of installation elements and their placement. A pair of medium-sized LEDs of different glow colors, a DIP-14 microcircuit socket, the switch was chosen without locking, with a push action in three positions (middle neutral, right and left - connection of the optocouplers being tested). I drew and printed out the arrangement of the elements on the body, cut it out and pasted it onto the intended body. I drilled holes in it. Since they will be checked, there will only be six and four-legged optocouplers from the socket, removing unnecessary contacts. I put everything in place.

The installation of components from the inside is naturally carried out using a hinged method on the contacts of the installation elements. There are not many parts, but in order not to make mistakes when soldering, it is better to mark each completed section of the circuit with a felt-tip pen on its printed image. Upon closer examination, everything is simple and clear (what goes where). Next, the middle part of the case is installed in place, through the hole in which the power supply wires with a soldered tulip-type connector are passed. The lower part of the case is equipped with pins for connecting to the multimeter sockets. This time (for testing), they were M4 screws (well, a very convenient option, provided that you treat the measuring device as a “workhorse” and not an object of worship). Finally, the wires are soldered to the connection pins and the housing is assembled into a single whole.

Now check the functionality of the assembled set-top box. After installing it in the multimeter sockets, selecting the “20V” DC voltage measurement limit and turning it on, 12 volts are supplied to the set-top box from the laboratory power supply. The display shows a slightly lower voltage, the red LED lights up, indicating the presence of the required supply voltage to the tester. The chip being tested is installed in the panel. The switch lever is moved to the right position (direction of the installation location of the optocoupler being tested) - the red LED goes out and the green LED lights up, a voltage drop is observed on the display - both indicate the serviceability of the component.

The attachment to the multimeter - optocoupler tester turned out to be functional and usable. Finally, the top panel of the case is decorated with a reminder - a sticker. I checked two PC817 optocouplers that were at hand, both were working, but they showed different voltage drops when connected. On one it dropped to 3.2 volts, and on the other to 2.5 volts. Food for thought; if there was no connection with the m/meter, it would not exist.

Video of the tester working

And the video clearly shows that it will be much faster to check an electronic component than to ask a question about whether it could have failed or not, and besides, with a high degree of probability, you simply will not get an answer to it. Author of the project Babay iz Barnaula.

Discuss the article ATTACHMENT TO THE MULTIMETER - OPTOCOUPLE TESTER

A simple way to test optocouplers was needed. I don’t often “communicate” with them, but there are times when I need to determine whether the optocoupler is to blame?.. For these purposes I made a very simple probe. "Construction of the Weekend Hour."

Probe appearance:

The circuit diagram of this probe is very simple:

Theory:
Optocouplers (optocouplers) are installed in almost every switching power supply for galvanic isolation of the feedback circuit. The optocoupler contains a conventional LED and a phototransistor. To put it simply, this is a kind of low-power electronic relay with short-circuit contacts.

The principle of operation of the optocoupler: When an electric current passes through the built-in LED, the LED (in the optocoupler) begins to glow, the light hits the built-in phototransistor and opens it.

Optocouplers are often available in Dip package
The first leg of the microcircuit, according to the standard, is designated by a key, a dot on the body of the microcircuit, which is also the anode of the LED, then the numbers of the legs go along the circumference, counterclockwise.

The essence of the test: Phototransistor, when light from the internal LED hits it,
goes into an open state, and its resistance will decrease sharply (from a very high resistance, to about 30-50 Ohms).

Practice:
The only disadvantage of this probe is that to test it is necessary to unsolder the optocoupler and install it in the holder according to the key (for me, the role of a reminder is the test button - it is shifted to the side, and the optocoupler key must face the button).
Next, when you press the button (if the optocoupler is intact), both LEDs will light up: The right one will signal that the optocoupler LED is working (the circuit is not broken), and the left one will signal that the phototransistor is working (the circuit is not broken).

(I only had a DIP-6 holder and had to fill the unused contacts with hot glue.)

For final testing, it is necessary to turn the optocoupler “off key” and check it in this form - both LEDs should not light up. If both or one of them are on, then this tells us about a short circuit in the optocoupler.

I recommend this probe as a first one for beginning radio amateurs who need to check optocouplers every six months or a year)
There are also more modern circuits with logic and signaling of “out of parameters,” but these are needed for a very narrow circle of people.

I advise you to look in your “bins”, it will be cheaper, and you won’t waste time waiting for delivery. Can be removed from boards.

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To quickly check the functionality of optocouplers, radio amateurs make various tester circuits that immediately show whether a given optocoupler is working or not, today I will propose to solder the simplest tester device for testing optocouplers. This probe can test optocouplers in both four-lead and six-lead packages, and using it is as easy as shelling pears, insert the optocoupler and immediately see the result!

Required parts for optocoupler tester:

Capacitor 220 uF x 10V;
Socket for microcircuit;
Resistor from 3 kOhm to 5.6 kOhm;
Resistor from 1 kOhm;
Light-emitting diode;
5V power supply.

How to make a device for testing optocouplers, instructions:

The optocoupler tester operates from 5 volts; if less, not all types of optocouplers can work correctly; any charger for a mobile phone can serve as a power supply. When the working optocoupler is correctly inserted into the tester panel, the LED will flash, which means that everything is in order with it; the frequency of flashes depends on the capacity of the electrolytic capacitor. If the optocoupler is burnt out or inserted on the wrong side, the LED will not light up, or if there is a breakdown of the transistor inside the optocoupler, the LED will simply glow but not blink.

The socket for testing optocouplers is made of a socket for a microcircuit and 4 pins are left at one end, for testing optocouplers in a 4-pin package, and at the other end of the socket there are 5 pins for a 6-pin package. I soldered the remaining parts of the device for testing optocouplers by hinged mounting on the contacts of the socket, but if desired, you can etch the board.

All that remains is to choose a suitable housing and a simple optocoupler tester is ready!

Instructions

If an optocoupler, the serviceability of which is specified under, is soldered into the board, it is necessary to disconnect it, discharge the electrolytic capacitors on it, and then unsolder the optocoupler, remembering how it was soldered.

Optocouplers have different emitters (incandescent lamps, neon lamps, LEDs, light-emitting capacitors) and different radiation receivers (photoresistors, photodiodes, phototransistors, photothyristors, phototriacs). They are also pinned. Therefore, it is necessary to find information about the type and pinout of the optocoupler either in a reference book or datasheet, or in the circuit diagram of the device where it was installed. Often, the pinout of the optocoupler is printed directly on the board of this device. If the device is modern, you can almost certainly be sure that the emitter in it is an LED.

If the radiation receiver is a photodiode, connect an optocoupler element to it and connect it, observing the polarity, in a chain consisting of a constant voltage source of several volts, a resistor designed so that the current through the radiation receiver does not exceed the permissible value, and a multimeter operating in measurement mode current at the appropriate limit.

Now put the optocoupler emitter into operating mode. To turn on the LED, pass through it in direct polarity a direct current equal to the rated one. Apply the rated voltage to the incandescent lamp. Using caution, connect the neon lamp or light-emitting capacitor to the network through a resistor with a resistance of 500 kOhm to 1 MOhm and a power of at least 0.5 W.

The photodetector must react to the inclusion of the emitter with a sharp change in mode. Now try turning the emitter off and on several times. The photothyristor and photoresistor will remain open even after the control action is removed until their power is turned off. Other types of photodetectors will react to every change in the control signal. If the optocoupler has an open optical channel, make sure that the reaction of the radiation receiver changes when this channel is blocked.

Having made a conclusion about the state of the optocoupler, de-energize the experimental setup and disassemble it. After this, solder the optocoupler back into the board or replace it with another one. Continue repairing the device that includes an optocoupler.

An optocoupler or optocoupler consists of an emitter and a photodetector separated from each other by a layer of air or a transparent insulating substance. They are not electrically connected to each other, which allows the device to be used for galvanic isolation of circuits.

Instructions

Connect the measuring circuit to the photodetector of the optocoupler in accordance with its type. If the receiver is a photoresistor, use a regular ohmmeter, and the polarity is not important. When using a photodiode as a receiver, connect the microammeter without a power source (positive to the anode). If the signal is received by a phototransistor of the n-p-n structure, connect a circuit of a 2 kilo-ohm resistor, a 3-volt battery and a milliammeter, and connect the battery with the positive side to the collector of the transistor. If the phototransistor has a p-n-p structure, reverse the polarity of the battery connection. To check the photodinistor, make a circuit of a 3 V battery and a 6 V, 20 mA light bulb, connecting it with the positive side to the anode of the dinistor.

In most optocouplers, the emitter is an LED or an incandescent light bulb. Apply the rated voltage to an incandescent light bulb in either polarity. You can also apply alternating voltage, the effective value of which is equal to the operating voltage of the lamp. If the emitter is an LED, apply a voltage of 3 V to it through a 1 kOhm resistor (positive to the anode).