Two-way thyristor schematic

November 16, 2020

ESD electrostatic protection tube 5V two-way 0201

Supply 1206 red and green two-color 1210 red and green two-color LED light-emitting diode

Two-way thyristor schematic - nicknamed "two-way thyristor"

Bidirectional thyristor is a P1N1P2N2 four-layer three-terminal device based on silicon single crystal. It is an AC switch device developed on the basis of ordinary thyristor. Its English name TRIAC is a three-terminal bidirectional AC switch. Intention, invented in 1957. The two-way thyristor is a unidirectional conductive switch that can replace two thyristors with reverse polarity in parallel, and only requires one trigger circuit. The thyristor has two states: on and off, and the main types of the thyristor are: a bolt shape, a flat plate shape, and a flat bottom shape.

Since the bidirectional thyristor is similar to a vacuum thyristor, it is commonly referred to as a silicon thyristor in the world, referred to as a thyristor T; and since the thyristor is initially used for controlled rectification, it is also called silicon controllable. The rectifying element is simply referred to as a thyristor SCR.

Figure 1 Two-way thyristor outline drawing

Two-way thyristor schematic - structural schematic

The two-way thyristor belongs to the NPNPN five-layer device, and the three electrodes are T1, T2, and G, respectively. Although the two-way thyristor can be seen as a combination of two common thyristors, it is actually a power integrated device composed of seven transistors and a plurality of resistors.

Since the device can be bi-directionally connected, the two electrodes except the gate G are collectively referred to as the main terminal, and T1 and T2 are used. Indicates that it is no longer divided into an anode or a cathode. It is characterized in that when the voltages of the G pole and the T2 pole are relative to T1, the voltage is positive, T2 is the anode, and T1 is the cathode. Conversely, when the voltages of the G and T2 poles are negative with respect to T1, T1 becomes the anode and T2 becomes the cathode. Since the two-way thyristor has symmetry in the forward and reverse characteristic curves, it can be turned on in either direction.

Compared with unidirectional thyristor, the biggest difference between the two-way thyristor is that it can be bi-directional, no longer has the anode and cathode, and is replaced by T1 and T2. The structure is shown in Figure 2(a). If you do not consider the difference of the G-class, divide it into the Figure 2 (b), it can be seen that the two unidirectional thyristors are connected in anti-parallel, as shown in Figure 2 (c).

Figure 2 Schematic diagram of the two-way thyristor structure

Two-way thyristor schematic - characteristics

TRIAC is a three-terminal component, the three ends of which are T1 (second terminal or second anode), T 2 (first terminal or first anode) and G (control electrode) are also a gate control switch, and SCR maximum The difference is that the TRIAC can be turned on regardless of the forward or reverse voltage, and its symbol structure and appearance are shown in Figure 3. Because it is a bidirectional component, regardless of the polarity of the voltages of T1 and T2, if the gate has a signal, T1 and T2 are in a conducting state; otherwise, if the gate triggering signal is applied, there is a pole between T1 and T2. High impedance.

(a) symbol (b) construction

Figure 3 TRIAC

Two-way thyristor schematic - triggering characteristics

Since the TRIAC is a controllable bidirectional thyristor, the four combinations of the polarity of the gate voltage VG and the voltage VT1T2 between the anodes are as follows:

(1). VT1T2 is positive and VG is positive.

(2). VT1T2 is positive and VG is negative.

(3). VT1T2 is negative and VG is positive.

(4). VT1T2 is negative and VG is negative.

It is generally best to use symmetrical conditions (1 and 4 or 2 and 3) to achieve symmetrical results for positive and negative half cycles. The most convenient control method is the control state of 1 and 4, because the gate signal is the same as VT1T2. polarity.

Figure 4 TRIAC VI characteristic curve

Figure 4 above shows the VI characteristic curve of TRIAC. Comparing this figure with the VI characteristic curve of SCR, it can be seen that the characteristic curve of TRIAC is similar to SCR, except that the positive and negative voltages of TRIAC can be turned on, so the curve of the third quadrant Similar to the curve of the first quadrant, the TRIAC can be regarded as the breakdown voltage of the T1-T2 of the two SCR anti-parallel TRIACs. It can also be seen that the voltage of the positive and negative half cycles can make the TRIAC turn on, generally making the TRIAC cut off. The method is the same as the SCR, that is, trying to reduce the current between the two anodes to the holding current below the TRIAC is cut off.

Two-way thyristor schematic - phase control

The phase control of TRIAC is similar to that of SCR. It can be triggered by DC signal, AC phase signal and pulse signal. The difference is that TRIAC can still be triggered when V T1-T2 is negative voltage. TRIAC can be double-conducted and can be triggered in both positive and negative half cycles. It can be used as full-wave power control. Therefore, TRIAC has the advantages of SCR and is more convenient for AC power control.

Figure 5 (a) is the TRIAC phase control circuit, which can change its excitation angle only by appropriately adjusting the RC time constant; Figure 5 (b), 5 (c) are the VT1-T2 and the load when the excitation angle is 30 degrees, respectively. The voltage waveform, generally TRIAC can control the load is much smaller than the SCR, in general, about 600V, 40A or less.

(a)

(b) Voltage waveform across the AC

Figure 5 TRIAC phase control circuit

Two-way thyristor schematic - detection method

The following describes the method of determining the bidirectional thyristor electrode using the multimeter RXl file, and also checks the triggering capability.

1. Determine the T2 pole

As can be seen from Fig. 6, the G pole is very close to T1 and is far from T2. Therefore, the positive and negative resistances between G and T1 are small. When measuring the resistance between any two legs with RXl file, only the low resistance exists between G-T1, the positive and negative resistances are only tens of ohms, and the positive and negative between T2-G and T2-T1. The resistance is infinite. This shows that if one foot and the other two feet are not connected, it is definitely the T2 pole. In addition, the T2-pole is usually connected to the small heat sink by using a bidirectional thyristor in the TO-220 package, and the T2 pole can also be determined accordingly.

2. Distinguish between G pole and T1 pole

(1) After finding the T2 pole, first assume that one of the remaining two legs is the T1 pole and the other leg is the G pole.

(2) Connect the black pen to the T1 pole, the red pen to the T2 pole, and the resistance to infinity. Then use the red tip to short-circuit T2 and G, and add a negative trigger signal to the G-pole. The resistance should be about ten ohms (see Figure 6(a)), which proves that the tube is turned on and the conduction direction is T1-T2. Then, the red tip is disconnected from the G pole (but still connected to T2). If the resistance value remains unchanged, it is proved that the tube can maintain the conduction state after the trigger (see Figure 6(b)).

Figure 6 Using a multimeter to determine the bidirectional thyristor electrode

Two-way thyristor schematic - working principle

The two-way thyristor is a P1N1P2N2 four-layer three-terminal structural component with three PN junctions. When analyzing the principle, it can be considered as consisting of a PNP tube and an NPN tube.

Figure 7 Bidirectional thyristor equivalent diagram

When anode A is applied with a forward voltage, both BG1 and BG2 tubes are in an amplified state. At this time, if a forward trigger signal is input from the gate G, the BG2 has a base stream ib2 flowing through it, and the collector current ic2=β2ib2 is amplified by the BG2. Since the collector of BG2 is directly connected to the base of BG1, ib1=ic.

At this time, the current ic2 is amplified by BG1, so that the collector current ic1 of BG1 = β1ib1 = β1β2ib2. This current flows back to the base of BG2, which is positive feedback, which increases the ib2. As a result of the forward feed loop, the current of the two tubes increases sharply, and the thyristor turns the saturation on.

Due to the positive feedback effect of BG1 and BG2, once the thyristor is turned on, even if the current of the gate G disappears, the thyristor can maintain the conduction state, since the trigger signal only acts as a trigger, and does not turn off. Function, so this thyristor is not switchable.

Since the thyristor has only two working states, on and off, it has a switching characteristic, which requires certain conditions to be converted, as follows:

Table 1 Conversion conditions for thyristor turn-on and turn-off states

Two-way thyristor schematic - naming rules

1, TRIAC:

Three ends: TRIode (take the first three letters);

AC semiconductor switch: ACsemiconductor switch (take the first two letters).

The above two groups of nouns are combined into "TRIAC", and the Chinese translation is "triac". It can be seen that "TRIAC" is a general term for two-way thyristors.

2, BCR:

Bidirectional: Bi-directional (take the first letter);

Control: Controlled (take the first letter);

Rectifier: Rectifier (take the first letter).

Then the first letter of these three groups of English nouns is combined: "BCR", Chinese translation "two-way thyristor". Typical manufacturers of two-way thyristors named "BCR" are Mitsubishi of Japan, such as BCR1AM-12, BCR8KM, BCR08AM and so on.

3, BT:

Bidirectional: Bi-directional (take the first letter);

Three-terminal: Triode (take the first letter).

The above two groups of words are combined into "BT", and the model of the two-way thyristor product can also be named. Typical manufacturers such as ST ST and Philips-Philips of the Netherlands all name the two-way thyristor. Representative models such as: PHILIPS BT131-600D, BT134-600E, BT136-600E, BT138-600E, BT139-600E, etc., these are four quadrant / non-insulated / two-way thyristor.

Figure 8 Two-way thyristors have different naming schemes