Serially produced dinistors in terms of electrical parameters do not always meet the creative interests of radio amateur designers. There are no, for example, dinistors with switching voltages of 5...10 and 200...400 V. All dinistors have a significant spread in the value of this classification parameter, which also depends on the ambient temperature. In addition, they are designed for a relatively low switching current (less than 0.2 A), and therefore low switching power. Smooth regulation of the switching voltage is excluded, which limits the scope of application of dinistors. All this forces radio amateurs to resort to creating analogues of dinistors with the desired parameters.
I have been searching for such an analogue of a dinistor for a long time. The original version was an analogue one, composed of a D814D zener diode and a KU202N trinistor (Fig. 1). As long as the voltage on the analog is less than the stabilization voltage of the zener diode, the analog is closed and no current flows through it. When the stabilization voltage of the zener diode is reached, it opens itself, opens the thyristor and the analogue as a whole. As a result, a current appears in the circuit in which the analogue is connected. The value of this current is determined by the properties of the thyristor and the load resistance. Using SCRs of the KU202 series with the letter indices B, V, N and the same zener diode D814D, 32 measurements of the current and switching voltage of the dnnistor analogue were made. The analysis shows that the average value of the analog switch-on current is approximately 7 mA, and the switch-on voltage is 14.5 ± 1 V. The variation in the switch-on voltage is explained by the difference in the resistance of the control pn junctions of the thyristors used.
The switch-on voltage Uon of such an analogue can be calculated using the simplified formula: Uon=Ust+Uy.e., where Ust is the stabilization voltage of the zener diode, Uy.e. - voltage drop across the control junction of the thyristor.
When the temperature of the thyristor changes, the voltage drop across its control junction also changes, but only slightly. This leads to some change in the analogue switch-on voltage. For example, for the KU202N thyristor, when the temperature of its case changed from 0 to 50 °C, the turn-on voltage changed within 0.3...0.4% relative to the value of this parameter at a temperature of 25 °C.
Next, an adjustable analogue of the dinistor with a variable resistor R1 in the control electrode circuit of the thyristor was investigated (Fig. 2). The family of current-voltage characteristics of this analogue version is shown in Fig. 3, their starting area is in Fig. 4, and the dependence of the switching voltage on the resistor resistance is shown in Fig. 5. As analysis has shown, the turn-on voltage of such an analogue is directly proportional to the resistance of the resistor. This voltage can be calculated by the formula Uon.p=Uct+Uy.e.+Ion.y.e*R1, where Uon.p is the switching voltage of the regulated analogue, Ion.y.e is the switching current of the regulated analogue of the dinistor along the control electrode.
rice. 3
rice. 4
rice. 5
This analogue is free from almost all the disadvantages of dinistors, except for temperature instability. As is known, as the temperature of the thyristor increases, its switching current decreases. In a regulated analogue, this leads to a decrease in the turn-on voltage, and the greater the resistance of the resistor, the more significant it is. Therefore, one should not strive for a large increase in the switching voltage with a variable resistor, so as not to worsen the temperature stability of the analogue.
Experiments have shown that this instability is small. Thus, for an analogue with a KU202N thyristor, when the temperature of its case changed within 20±10 °C, the switching voltage changed: with a 1 kOhm resistor - by ±1.8%. at 2 kOhm - by ±2.6%, at 3 kOhm - by ±3%, at 4 kOhm - by ±3.8%. An increase in resistance by 1 kOhm led to an increase in the switching threshold voltage of the adjustable analogue by an average of 20% compared to the switching voltage of the original dinistor analogue. Consequently, the average accuracy of the switching voltage of the regulated analogue is better than 5%.
The temperature instability of the analogue with the KU101G thyristor is less, which is explained by the relatively low turn-on current (0.8...1.5 mA). For example, with the same temperature change and a resistor with a resistance of 10, 20, 30 and 40 kOhm, the temperature instability was ±0.6%, respectively. ±0.7%, ±0.8%. ±1%. Increasing the resistance of the resistor for every 10 kOhm increased the turn-on voltage level of the analog by 24% compared to the voltage of the analog without a resistor. Thus, the analogue with the KU101G thyristor has a high turn-on voltage accuracy - its temperature instability is less than 1%, and with the KU202N thyristor it has a slightly worse turn-on voltage accuracy (in this case, the resistance of the resistor Rt should be 4.7 kOhm).
By ensuring thermal contact between the thyristor and the zener diode, the temperature instability of the analogue can be even less, since for zener diodes with a stabilization voltage greater than 8 V, the temperature coefficient of the stabilization voltage is positive, and the temperature coefficient of the opening voltage of the thyristors is negative.
The thermal stability of an adjustable analogue of a dinistor with a powerful thyristor can be increased by including a variable resistor in the anode circuit of a low-power thyristor (Fig. 6). Resistor R1 limits the current of the control electrode of the thyristor VS1 and increases its turn-on voltage by 1...2%. And the variable resistor R2 allows you to adjust the turn-on voltage of the thyristor VS2.
rice. 6
The improvement in temperature stability of this version of the analogue is explained by the fact that with an increase in the resistance of resistor R2, the switching current of the analogue at the control electrode decreases and its switching current at the anode increases. And since with a change in temperature in this case, the control electrode current decreases less and that the total switching current of the analogue increases, then for an equivalent increase in the switching voltage of the analogue, a lower resistance of resistor R2 is needed - this creates favorable conditions for increasing the temperature stability of the analogue.
To realize the thermal stability of such an analogue, the opening current of the thyristor VS2 must be 2...3 mA - greater than the opening current of the thyristor VS1, so that its temperature changes do not affect the operation of the analogue. The experiment showed that the switch-on voltage of the thermostable analogue practically did not change when the temperature of its elements changed from 20 to 70 °C.
The disadvantage of this version of the dinistor analogue is the relatively narrow limits for adjusting the switching voltage with variable resistor R2. They are narrower, the greater the switching current of the thyristor VS2. Therefore, in order not to worsen the thermal stability of the analogue, it is necessary to use trinisgores with the lowest possible switching current. The range of adjustment of the analog switch-on voltage can be expanded by using zener diodes with different stabilization voltages.
Adjustable analogues of the dinistor will find application in automation and telemechanics, and relaxation generators. electronic regulators, threshold and many other radio devices.
A dinistor is a type of semiconductor diodes belonging to the class of thyristors. The dinistor consists of four regions of different conductivity and has three p-n junctions. In electronics, it has found rather limited use; however, it can be found in the designs of energy-saving lamps with E14 and E27 sockets, where it is used in starting circuits. In addition, it is found in the ballasts of fluorescent lamps.
The conventional graphic designation of a dinistor in the diagram is a bit like a semiconductor diode, with one difference. It has a perpendicular line, which symbolizes the base area, and gives the dinistor its extraordinary parameters and characteristics.
But strange as it may seem, the image of the dinistor on a number of circuits can be different. Let's say the image of a symmetrical dinistor can be like this:
This variation in graphical notations is due to the fact that there is a huge class of thyristor semiconductors. These include dinistor, triac, and triac. In the diagrams they are all similar in the form of a combination of two diodes and additional lines. In foreign sources, this subclass of semiconductor is called trigger diode, diac. On circuit diagrams it can be designated by the Latin symbols VD, VS, V and D.
Working principle of trigger diode |
The basic principle of operation of a dinistor is based on the fact that when connected directly, it will not pass electric current until the voltage at its terminals reaches a specified value.
A conventional diode also has such a parameter as the opening voltage, but for it it is only a couple of hundred millivolts. When connected directly, a conventional diode opens as soon as a small voltage level is applied to its terminals.
To clearly understand the principle of operation, you need to look at the current-voltage characteristic; it allows you to clearly see how this semiconductor device works.
Let's consider the current-voltage characteristic of the most common symmetrical dinistor type DB3. It can be mounted in any circuit without observing the pinout. It will work accurately, but the turn-on (breakdown) voltage may differ slightly, by about three volts
As we can see the wallpaper branches characteristics are absolutely the same. (indicates that it is symmetrical) Therefore, the operation of DB3 does not depend on the polarity of the voltage at its terminals.
The current-voltage characteristic has three regions showing the operating mode of a DB-3 type semiconductor under certain factors.
The blue area shows the initial closed state. No current flows through it. In this case, the voltage level applied to the terminals is lower than the turn-on voltage level V BO – Breakover voltage.
The yellow section is the moment the dinistor opens when the voltage at its contacts reaches the turn-on voltage level ( VBO or U on.). In this case, the semiconductor begins to open and electric current passes through it. Then the process stabilizes and it moves to the next state.
The purple section of the current-voltage characteristic shows the open state. In this case, the current flowing through the device is limited only by the maximum current Imax, which can be found in the reference book. The voltage drop across the open trigger diode is small and amounts to about 1 - 2 volts.
Thus, the graph clearly shows that the dinistor in its operation is similar to a diode with one big “BUT”. If its breakdown voltage of a conventional diode is (150 - 500 mV), then to open the trigger diode it is necessary to apply a voltage of a couple of tens of volts to its terminals. So for the DB3 device the switching voltage is 32 volts.
To completely close the dinistor, it is necessary to reduce the current level to a value below the holding current. In the case of an asymmetrical version, when turned back on, it does not pass current until the reverse voltage reaches a critical level and it burns out. In amateur radio homemade products, the dinistor can be used in stroboscopes, switches and power regulators and many other devices.
The basis of the design is the relaxation generator on VS1. The input voltage is rectified by diode VD1 and supplied through resistance R1 to trimmer R2. From its engine, part of the voltage flows to capacitance C1, thereby charging it. If the input voltage is not higher than normal, the capacitor charging voltage is not enough for breakdown, and VS1 is closed. If the mains voltage level increases, the charge on the capacitor also increases and breaks through VS1. C1 is discharged through the VS1 headphone BF1 and the LED, thereby signaling a dangerous level of mains voltage. After this, VS1 closes and the container begins to accumulate charge again. In the second version of the circuit, the tuning resistance R2 must have a power of at least 1 W, and the resistor R6 must have a power of at least 0.25 W. The adjustment of this circuit consists of setting the lower and upper limits of the deviation of the mains voltage level with tuning resistances R2 and R6.
The widely used bidirectional symmetrical dinistor DB3 is used here. If FU1 is intact, then the dinistor is short-circuited by diodes VD1 and VD2 during the positive half-cycle of the 220V mains voltage. LED VD4 and resistance R1 bypass capacitance C1. The LED is on. The current through it is determined by the nominal resistance R2.
As we have already found out, a thyristor is a semiconductor device that has the properties of an electric valve. Thyristor with two terminals (A - anode, K - cathode), this is a dinistor. Thyristor with three terminals (A – anode, K – cathode, Ue – control electrode), this is a thyristor, or in everyday life it is simply called a thyristor.
Using the control electrode (under certain conditions), you can change the electrical state of the thyristor, that is, transfer it from the “off” state to the “on” state.
The thyristor opens if the applied voltage between the anode and cathode exceeds the value U = Upr, that is, the magnitude of the breakdown voltage of the thyristor;
The thyristor can also be opened at a voltage less than Upr between the anode and cathode (U< Uпр), если подать импульс
напряжения положительной полярности между управляющим
электродом и катодом.
The thyristor can remain in the open state for any length of time as long as the supply voltage is applied to it.
The thyristor can be closed:
- if you reduce the voltage between the anode and cathode to U = 0;
- if you reduce the anode current of the thyristor to a value less than the holding current Isp.
- by applying a blocking voltage to the control electrode (only for turn-off thyristors).
The thyristor can also remain in the closed state for any length of time until the triggering pulse arrives.
Thyristors and dinistors operate in both direct and alternating current circuits.
Operation of dinistor and thyristor in DC circuits.
Let's look at some practical examples.
The first example of using a dinistor is a relaxation generator of sound signals. 
We use KN102A-B as a dinistor.
The generator works as follows.
When you press the Kn button, capacitor C is gradually charged through resistors R1 and R2 (+ batteries - closed contacts of the Kn button - resistors - capacitor C - minus batteries). A chain of a telephone capsule and a dinistor is connected in parallel to the capacitor. No current flows through the telephone capsule and the dinistor, since the dinistor is still “locked”.
When the capacitor reaches the voltage at which the dinistor breaks through, a pulse of capacitor discharge current passes through the telephone capsule coil (C - telephone coil - dinistor - C). A click is heard from the phone, the capacitor is discharged. Next, capacitor C charges again and the process repeats.
The frequency of repetition of clicks depends on the capacitance of the capacitor and the resistance value of resistors R1 and R2.
With the voltage, resistor and capacitor ratings indicated in the diagram, the frequency of the sound signal using resistor R2 can be changed within the range of 500 - 5000 hertz. The telephone capsule must be used with a low-impedance coil of 50 - 100 Ohms, no more, for example, the TK-67-N telephone capsule.
The telephone capsule must be connected with correct polarity, otherwise it will not work. On the capsule there is a designation + (plus) and – (minus).
This scheme (Figure 1) has one drawback. Due to the large spread in the parameters of the KN102 dinistor (higher breakdown voltage), in some cases, it will be necessary to increase the power supply voltage to 35 - 45 volts, which is not always possible or convenient.
A control device assembled on a thyristor for turning on and off the load using one button is shown in Fig. 2.
The device works as follows.
In the initial state, the thyristor is closed and the light does not light. Press the Kn button for 1 - 2 seconds. The button contacts open, the thyristor cathode circuit is broken. At this moment, capacitor C is charged from the power source through resistor R1. The voltage across the capacitor reaches the value U of the power source.
Release the Book button. At this moment, the capacitor is discharged through the circuit: resistor R2 - control electrode of the thyristor - cathode - closed contacts of the Kn button - capacitor.
Current will flow in the control electrode circuit and the thyristor will “open”.
The light bulb lights up along the circuit: battery plus - load in the form of a light bulb - thyristor - closed contacts of the button - battery minus.
The circuit will remain in this state for as long as desired.
In this state, the capacitor is discharged: resistor R2, transition control electrode - thyristor cathode, contacts of the button Kn.
To turn off the light bulb, briefly press the button. In this case, the main power supply circuit of the light bulb is interrupted. The thyristor “closes.” When the contacts of the button are closed, the thyristor will remain in the closed state, since Uynp = 0 at the control electrode of the thyristor (the capacitor is discharged).
I have tested and worked reliably in this circuit various thyristors: KU101, T122, KU201, KU202, KU208.
As already mentioned, dinistor and thyristor have their own transistor counterpart.
The thyristor analogue circuit consists of two transistors and is shown in Fig. 3.
Transistor Tr 1 has p-n-p conductivity, transistor Tr 2 has n-p-n conductivity. Transistors can be either germanium or silicon.
The thyristor analogue has two control inputs. First input: A – Ue1 (emitter - base of transistor Tr1). Second input: K – Ue2 (emitter – base of transistor Tr2).
The analogue has: A - anode, K - cathode, Ue1 - the first control electrode, Ue2 - the second control electrode.
If control electrodes are not used, then it will be a dinistor, with electrodes A - anode and K - cathode.
A pair of transistors, for an analogue of a thyristor, must be selected of the same power with a current and voltage higher than that required for the operation of the device. The parameters of the thyristor analog (breakdown voltage Unp, holding current Iyd) will depend on the properties of the transistors used.
For more stable operation of the analogue, resistors R1 and R2 are added to the circuit. And with the help of resistor R3, you can regulate the breakdown voltage Upr and holding current Iyd of the dinistor analogue - a thyristor. The diagram of such an analogue is shown in Fig. 4.
If in the audio frequency generator circuit (Figure 1), instead of the KN102 dinistor, you include an analogue of the dinistor, you will get a device with different properties (Figure 5).
The supply voltage of such a circuit will be from 5 to 15 volts. By changing the values of resistors R3 and R5, you can change the tone of the sound and the operating voltage of the generator. Variable resistor R3 selects the breakdown voltage of the analogue for the used supply voltage. Then you can replace it with a constant resistor.
Transistors Tr1 and Tr2: KT502 and KT503; KT814 and KT815 or any others.
An interesting circuit is a voltage stabilizer with protection against short circuits in the load. If the load current exceeds 1 ampere, the protection will operate.
The stabilizer consists of:
- control element – zener diode KS510, which determines the output voltage;
- an executive element – transistors KT817A, KT808A, acting as a voltage regulator;
- resistor R4 is used as an overload sensor;
- the actuator protection mechanism uses an analogue of a dinistor, on transistors KT502 and KT503.
At the input of the stabilizer, capacitor C1 is installed as a filter. Resistor R1 sets the stabilization current of the KS510 zener diode, with a value of 5 - 10 mA. The voltage across the zener diode should be 10 volts. Resistor R4, 1.0 Ohm, is connected in series to the load circuit. Resistor R5 sets the initial mode for stabilizing the output voltage.
The greater the load current, the more voltage proportional to the current is released across it. In the initial state, when the load at the output of the stabilizer is small or turned off, the thyristor analogue is closed. The voltage of 10 volts applied to it (from the zener diode) is not enough for breakdown. At this moment, the voltage drop across resistor R4 is almost zero.
If you gradually increase the load current, the voltage drop across resistor R4 will increase. At a certain voltage on R4, the thyristor analogue breaks through and a voltage is established between point Tchk1 and the common wire equal to 1.5 - 2.0 volts. This is the anode-cathode transition voltage of an open thyristor. At the same time, LED D1 lights up, signaling an emergency. The voltage at the output of the stabilizer, at this moment, will be equal to 1.5 - 2.0 volts.
To restore normal operation of the stabilizer, you need to turn off the load and press the Kn button, resetting the protection lock. The output of the stabilizer will again be 9 volts, and the LED will go out.
By adjusting resistor R3, you can select the protection operation current from 1 ampere or more. Transistors T1 and T2 can be placed on one radiator without insulation. The radiator itself should be isolated from the housing.
Thyristors belong to semiconductor devices of the p-n-p-n structure, and belong, in fact, to a special class of four-layer, three (or more) transition devices with alternating conductivity.
The design of a thyristor allows it to operate like a diode, that is, it allows current to pass in only one direction.
And just like a field-effect transistor, it has a control electrode. Moreover, as a diode, a thyristor has a peculiarity - without the injection of minority working charge carriers through the control electrode, it will not go into a conducting state, that is, it will not open.
A simplified model of a thyristor allows us to understand that the control electrode here is similar to the base of a bipolar transistor, however, there is a limitation, which is that you can unlock the thyristor using this base, but you cannot lock it.
A thyristor, like a powerful field-effect transistor, can, of course, switch significant currents. And unlike field-effect transistors, the power switched by thyristors can amount to megawatts at high operating voltages. But thyristors have one serious drawback - a significant turn-off time.
In order to lock a thyristor, it is necessary to interrupt or greatly reduce its forward current for a sufficiently long time, during which the nonequilibrium main working charge carriers, electron-hole pairs, would have time to recombine or dissolve. As long as the current is not interrupted, the thyristor will remain in a conducting state, that is, it will continue to behave as .
Switching circuits for alternating sinusoidal current provide the thyristors with a suitable operating mode - the sinusoidal voltage biases the junction in the opposite direction, and the thyristor is automatically turned off. But to maintain the operation of the device, an unlocking control pulse must be supplied to the control electrode in each half-cycle.
In DC-powered circuits, additional auxiliary circuits are used, the function of which is to forcibly reduce the anode current of the thyristor and return it to the off state. And since charge carriers recombine when turned off, the switching speed of the thyristor is much lower than that of a powerful field-effect transistor.
If we compare the time of complete closing of a thyristor with the time of complete closing of a field-effect transistor, the difference reaches thousands of times: a field-effect transistor needs several nanoseconds (10-100 ns) to close, and a thyristor requires several microseconds (10-100 μs). Feel the difference.
Of course, there are areas of application of thyristors where field-effect transistors cannot compete with them. For thyristors, there are practically no restrictions on the maximum permissible switching power - this is their advantage.
Thyristors control megawatts of power in large power plants, they switch hundreds of amperes in industrial welding machines, and they traditionally control megawatt induction furnaces in steel mills. Field-effect transistors are not applicable here. In medium-power pulse converters, field-effect transistors win.
The long turn-off of a thyristor, as mentioned above, is explained by the fact that, once turned on, it requires removal of the collector voltage to turn off, and like a bipolar transistor, a thyristor takes a finite time to recombine or remove minority carriers.
The problems that thyristors cause due to this feature are primarily related to the inability to switch at high speeds, as field-effect transistors can do. And even before applying collector voltage to the thyristor, the thyristor must be closed, otherwise switching power losses are inevitable, and the semiconductor will heat up excessively.
In other words, the maximum dU/dt limits the performance. A graph of power dissipation versus current and on-time illustrates this problem. High temperature inside the thyristor crystal can not only cause false triggering, but also prevent switching.
In resonant inverters based on thyristors, the problem of blocking is solved by itself; there, a surge of voltage of reverse polarity leads to blocking of the thyristor, provided that the effect is long enough.
This reveals the main advantage of field-effect transistors over thyristors. Field-effect transistors are capable of operating at frequencies of hundreds of kilohertz, and control is not a problem today.
Thyristors will operate reliably at frequencies up to 40 kilohertz, closer to 20 kilohertz. This means that if thyristors were used in modern inverters, then devices with a sufficiently high power, say, 5 kilowatts, would turn out to be very cumbersome.
In this sense, field-effect transistors make inverters more compact due to the smaller size and weight of power transformer cores and chokes.
The higher the frequency, the smaller transformers and chokes are required to convert the same power, anyone who is familiar with the circuitry of modern pulse converters knows this.
Of course, in some applications thyristors turn out to be very useful, for example, those operating at a mains frequency of 50 Hz; in any case, it is more profitable to manufacture them using thyristors; they are cheaper than if field-effect transistors were used there.
And in, for example, it is more profitable to use field-effect transistors, precisely because of the simplicity of switching control and the high speed of this switching. By the way, when switching from a thyristor circuit to a transistor one, despite the high cost of the latter, unnecessary expensive components are eliminated from the devices.
Andrey Povny
A dinistor is a two-electrode device, a type of thyristor and, as I already said, an incompletely controlled switch that can be turned off only by reducing the current passing through it. It consists of four alternating regions of different conductivity types and has three np junctions. Let's assemble a hypothetical circuit similar to the one we used to study the diode, but add a variable resistor to it, and replace the diode with a dinistor:
So, the resistor resistance is maximum, the device shows “0”. We begin to reduce the resistance of the resistor. The voltage across the dynistor increases, but no current flow is observed. With a further decrease in resistance, at a certain point in time there will be a voltage on the dinistor that is able to open it ( U open). The dinistor immediately opens and the current value will depend only on the resistance of the circuit and the open dinistor itself - the “key” has worked.
How to close the key? We begin to reduce the voltage - the current decreases, but only due to an increase in the resistance of the variable resistor, the state of the dinistor remains the same. At a certain point in time, the current through the dinistor decreases to a certain value, which is usually called the holding current ( I beat). The dinistor will instantly close, the current will drop to “0” - the key is closed.
Thus, the dinistor opens if the voltage on its electrodes reaches U open and closes if the current through it is less than I beat. For each type of dinistor, of course, these values are different, but the operating principle remains the same. What happens if the dinistor is turned on “the other way around”? We assemble another circuit by changing the polarity of the battery.
The resistor resistance is maximum, there is no current. We increase the voltage - there is still no current and there will not be until the voltage on the dinistor exceeds the maximum permissible. As soon as it increases, the dinistor will simply burn out. Let's try to depict what we were talking about on the coordinate plane, on which we plot the voltage across the dynistor along the X axis, and the current through it along the Y axis:
Thus, in one direction the dinistor behaves like an ordinary diode in reverse connection (simply locked, closed), in the other it opens like an avalanche, but only at a certain voltage across it, or also closes as soon as the current through the open device drops below the specified rating value.
Thus, the main parameters of the dinistor can be reduced to several values:
— Opening voltage;
— Minimum holding current;
— Maximum permissible forward current;
— Maximum permissible reverse voltage;
— Voltage drop across an open dinistor.
