How to test BTB16-700BW: using a circuit and a tester to diagnose a triac

Thyristors are used to control power. They are used in dimmers or to control the speed of engines. During the repair process, it is not difficult to identify the malfunction of such a radio component using a multimeter. All thyristors are tested in the same way. Knowing how to check BTB16-700BW, it will be possible to determine the operability of other elements of the thyristor family.

Purpose and device

A thyristor is an electronic device built on a semiconductor single crystal with several pn junctions. Such a device is characterized by two stable modes of operation: closed, when there is no conductivity, and open - the device is in a state of high conductivity. A thyristor can be thought of as an electronic key. Depending on its state, the electrical signal can either go further to the circuit or not.

The thyristor family includes several types of devices that differ in the type of conductivity, for example, triac, dinistor, trinistor. A triac is used to operate in an alternating current circuit, since it can conduct current in any direction. Such a device has three outputs in its design, therefore in the English literature it is called TRIAC (triode for alternating current), which translates as an alternating current triode.

Two connection points are called slave points and one is called master points. Triac has no anode and cathode. In electrical circuits, the electronic key is connected in series with the load. For its transition from a closed state to an open one, a signal of a certain amplitude must be sent to the control terminal of the device, while the current can flow freely in both directions.

A feature of the triac is that it does not require a constant the presence of voltage at the switching electrode, and to change the conductivity, only a short pulse. But at the same time, there is a condition that a current of a certain magnitude, called the holding current, must flow through the controlled outputs.

On the diagrams and in the technical literature, the triac is signed with the letters VS with a digit indicating its serial number. It is depicted in the form of triangles parallel to each other with oppositely directed vertices. From the base of one of the geometric shapes, a platform is displayed, denoted by the Latin letter G (shutter). The other two pins are labeled T1 and T2, denoting power pins. In some circuits, the controllable electrodes may be designated with the letter A.

An interesting fact is that this semiconductor device was invented at the Mordovian Scientific Research Electrotechnical Institute in 1963.

Principle of operation

Although the element is a fairly reliable device, it happens that it fails. But in order to correctly check the triac, it is necessary to be able not only to use measuring requisitions, but also to understand the essence of its work.

A semiconductor element can be represented by two thyristors, which are connected in antiparallel relative to each other. Like a diode, a triac has p-n junctions, but it has more of them. The structure of the device consists of five alternating layers. Depending on the applied voltage to the control terminal, the processes of recombination and motion of the majority charge carriers begin in the barrier transitions, or, conversely, the expansion of the forbidden gaps.

The triac goes into a state where charges can freely pass through it, when two conditions are met:

• its control output is supplied with a current of the required amplitude (unlocking);
• the potential difference between the controlled electrodes corresponds to a certain value determined by the parameters of the device.

In other cases, the semiconductor switch will be locked. When using the device in circuits with an alternating signal, the polarity of the voltage will constantly change at the terminals, therefore the operating mode of the device is divided into four quadrants. Each quadrant has its own conditions for unlocking or locking.

If the potential difference between the power terminals is equal to V A1-A2> 0, and relative to the gate electrode at input A1 there is negative voltage, then the triac corresponds to the second quadrant with its certain values ​​of unlocking (Igt) and holding (In) currents.

Due to its peculiarity of operation, this type of thyristor was originally used as a control element on production machines, allowing them to smoothly supply current. These were fairly large devices that required massive cooling. But the evolution of the device has led to a decrease in size and improving the technical manufacturing process. This made it possible to use triacs in conjunction with compressor equipment, electric heating systems, power tools and charging units.

Instrument characteristics

Like any electronic semiconductor device, a triac is characterized by a number of technical parameters. They make it possible to use it in a particular equipment. The correct operation of the device is determined by the compliance of the declared characteristics with the real ones, and the essence of the measurements is reduced to obtaining the values ​​of these parameters.

For a comprehensive measurement of characteristics, specialized devices are required that are not available for household applications, therefore, to test the triac, radio amateurs most often use a tester and special schemes. For example, The popular BTB16-700BW triac is characterized by the following technical parameters:

1. Maximum voltage Vrpm - 700 V. Indicates the boundary potential difference, the excess of which leads to damage to the structure of the element.
2. Cyclic impulse voltage Vdrm - 700 V. Even if the electronic key is closed, and the signal level applied to the element exceeds 700 volts, its transitions will fail.
3. The highest value of the average on-state current Irms - 16 A. It characterizes the current strength of a sinusoidal form, capable of passing through the triac for a long time without failure.
4. Itsm peak impulse current is 168 A. This parameter is necessarily indicated with a time during which the device will not be damaged. So, for BTB16-700BW it is 16.7 ms.
5. Gate current Ig - 10-50 mA. Depends on the polarity of the voltage applied to the terminals of the device and the parameters of the input signal. Specified as an interval.
6. The rate of rise of the current dI / dT is 14 A / ms. Defined for an open state. If it is exceeded, then the element will fail.
7. Turn-on time t - 2μs. Shows the time elapsed until the gate current reaches 10% of its highest value, when the voltage between the power electrodes has decreased by the same percentage.
8. The voltage rise rate dV / dT is 1000 V / μs. If this value is greater than the specified value, then the device will not be able to work correctly, that is, false openings and closings will occur.

In addition to these parameters, minor characteristics are often indicated, for example, the operating temperature range (from –40 ° C to +125 ° C), the type of package (TO-220 AB).

Testing an item

There are several ways to test a triac for operability. For the simplest, you only need a multimeter, and for more complex measurements, an autonomous power source or a test circuit.

With the help of a tester, verification is carried out using knowledge based on the principle of operation of a triac. Diagnostics with a multimeter will not be able to determine all the characteristics of the element, but it will be quite sufficient for the initial testing of performance.

A simple check can be done using a light bulb and a battery. To do this, one terminal of the battery is connected to the control and operating terminals of the triac, and the second to the base of the light bulb. The element lead is connected to the central contact of the illuminator. In this case, the transition must be open, then the light will light up.

If, even before the voltage was applied to the control output, the lighting device caught fire, then this indicates that the triac is faulty, and its transitions are broken. Such an element may not be checked further, since it is faulty.

Tester check

For carrying out tests, a device of any type of action is suitable, but at the same time it is necessary that the value of the current produced by it is sufficient to switch the element. Therefore, it would be preferable to use an analog device. For example, to check with the BTB12-800CW tester, you need to provide a current of about 30 mA, and for the BTB16-700BW, this figure should be 15 mA.

You will also need to pay attention to the condition of the battery in the tester. In a digital device, the battery replacement icon should not be displayed on the screen, and in an analog device, when the probes are short-circuited, the arrow should point to zero.

The essence of the measurement comes down to checking the device transitions. To do this, the tester switches to the resistance dialing mode for the smallest range. It is best to check in the following sequence:

1. The test leads are connected to the power leads of the triac T1 and T2. If the radio element is working properly, then the multimeter should show infinitely high resistance.
2. The polarity of the applied signal at the working terminals is reversed. For this, the measuring probes are rearranged. The resistance must also be great.
3. The working terminal T1 or T2 and the gate G are connected briefly.
4. The resistance of the junction between T1 and T2 is measured again. In one direction, it must change. So, for BTB12-800CW it will be about 50 ohms.
5. The polarity is reversed. In this case, the junction impedance must be large, which corresponds to the absence of reverse breakdown.

This behavior of the triac when checked by the tester indicates a high probability of its serviceability. It is also worth noting that during such a check it is not necessary to completely desolder the radioelement from the circuit, but it is enough just to disconnect its control contact.

Using the schema

There are many different circuits used by radio amateurs to test the performance of a triac. But it is better to use a universal circuit capable of testing any element of the thyristor family, for example, BTB16-700BW. It does not need any configuration and works right after assembly. In order to collect it, you will need the following elements:

1. Resistors R1 — R4 470 Ohm, R4 — R5 1 kOhm.
2. Capacitors C1 and C2 - 100 μF x 6.5 V.
3. Diodes VD1, VD2, VD5 and VD6 - 2N4148; VD2 and VD3 - AL307.

A KRONA battery can be used as a power source.

The essence of the measurements is reduced to the following actions: switch S3 is moved to the upper position, as a result, the device is supplied with power. After that, by briefly pressing the S2 button, current is applied to the control output of the element.

If the BTB16-700BW is working, then its transition should open, which will be signaled by the VD3 LED. Then the switch is set to the middle position, the LED should go out. In the next step, S3 is switched to the lower position and the button S2 is pressed. The result of these actions will light up the VD4 LED. This behavior of the triac will make it possible to declare its performance with absolute certainty.

Testing a triac is not so difficult, especially if you use a tester, although it is better to assemble a special circuit. But it should be noted that due to the high sensitivity of the triacs to the switching current, it is better to use dial gauges as multimeters.