Overview and introduction of the electronic tube of high frequency high frequency high frequency plastic heat sealing machine
1. Reverse non-repetitive peak voltage VRSM: under the condition of open pole control, the reverse peak voltage determined by the sharp bending point of the reverse volt-ampere characteristic curve;
2. Forward turning voltage VBO: The forward turning voltage VBO of the thyristor refers to adding a sine between its anode (A) and cathode (K) under the condition that the rated junction temperature is 100°C and the gate (G) is open. The peak voltage corresponding to the half-wave forward voltage when it is turned from the off state to the on state.
3. Off-state repetitive peak voltage VDRM: Off-state repetitive peak voltage VDRM refers to the maximum peak voltage allowed between the poles of A, K (or T1, T2) when the thyristor is blocked in the forward direction. This voltage is approximately the value of the forward turning voltage minus 100V.
4. On-state average current IT: On-state average current IT refers to the average value of the allowed current between A, K (or T1, T2) poles during normal operation of the thyristor under the specified ambient temperature and standard heat dissipation conditions.
5. Reverse breakdown voltage VBR: Reverse breakdown voltage refers to the sinusoidal half-wave reverse voltage applied between the anode and cathode of the thyristor at the rated junction temperature. When the reverse leakage current increases sharply, the corresponding peak voltage .
6. Reverse Repetitive Peak Voltage VRRM: Reverse Repetitive Peak Voltage VRRM refers to the maximum reverse peak voltage allowed between the A and K poles when the thyristor is open at the gate G. This voltage is about the peak voltage after reverse breakdown voltage minus 100V.
7. Forward average voltage drop VF: Forward average voltage drop VF is also called on-state average voltage or on-state voltage drop VT. It refers to the rated current when the current through the thyristor is under the specified ambient temperature and standard heat dissipation conditions. The average voltage drop between anode A and cathode K is usually 0.4~1.2V.
8. Gate trigger voltage VGT: Gate trigger VGT refers to the need to change the thyristor from the blocking state to the conducting state under the specified ambient temperature and a certain forward voltage between the anode and cathode of the thyristor The minimum gate DC voltage is generally about 1.5V.
9. Gate trigger current IGT: The gate trigger current IGT refers to the minimum required to change the thyristor from the blocking state to the conducting state under the specified ambient temperature and a certain voltage between the anode and cathode of the thyristor Gate DC current.
10. Gate reverse voltage: The gate reverse voltage refers to the rated voltage applied to the gate of the thyristor, which generally does not exceed 10V.
11. Off-state repetitive peak current IDR: off-state repetitive peak current IDR refers to the forward maximum average leakage current value of the thyristor in the off state, generally less than 100μA
12. Repetitive Repetitive Peak Current IRRM: Repetitive Repetitive Peak Current IRRM refers to the reverse maximum leakage current value of the thyristor in the off state, generally less than 100μA.
14. Application Examples of Unidirectional SCR
The thyristor has the most circuit patterns in practical applications is its gate trigger circuit. In summary, there are DC trigger circuit, AC trigger circuit, phase trigger circuit and so on.
1. DC trigger circuit: The following figure is a common overvoltage protection circuit for TVs. When the E+ voltage is too high, the voltage at point A also becomes higher. When it is higher than the voltage regulation value of the voltage regulator tube DZ, DZ can pass. The thyristor D is triggered and Datong short-circuits E+, which causes the fuse RJ to blow, thereby acting as an overvoltage protection.
2. Phase trigger circuit: The phase trigger circuit is actually a kind of AC trigger circuit. As shown in the figure below, the method of this circuit is to use the RC loop to control the phase of the trigger signal. When the R value is less, the RC time constant is less, and the phase shift A1 of the trigger signal is less, so the load obtains a larger electric power; when the R value is larger, the RC time constant is larger, the phase shift A2 of the trigger signal is more Large, so the load gets less electric power. This typical electric power stepless adjustment circuit is used in many electrical products in daily life.
15. Selection experience of thyristors
1. Choose the type of thyristor There are many types of thyristors, which should be selected reasonably according to the specific requirements of the application circuit.
If it is used for AC and DC voltage control, controllable rectification, AC voltage regulation, inverter power supply, switching power supply protection circuit, etc., ordinary thyristors can be used.
If used in AC switches, AC voltage regulation, AC motor linear speed regulation, lamp linear dimming, solid state relays, solid state contactors and other circuits, bidirectional thyristors should be used.
If it is used for AC motor frequency conversion speed regulation, chopper, inverter power supply and various electronic switching circuits, etc., the gate can be used to turn off the thyristor.
If it is used for sawtooth wave generator, long time delay, overvoltage protector and high power transistor trigger circuit, etc., BTG thyristor can be used.
If it is used in electromagnetic stoves, electronic ballasts, ultrasonic circuits, superconducting magnetic energy storage systems and switching power supplies, reverse conduction thyristors can be used.
If it is used in the operation monitoring circuit of photoelectric coupler, photodetector, photoalarm, photocounter, photoelectric logic circuit and automatic production line, optical control thyristor can be used.
2. Select the main parameters of the thyristor The main parameters of the thyristor should be determined according to the specific requirements of the application circuit.
The selected thyristor should have a certain power margin, and its rated peak voltage and rated current (on-state average current) should be higher than the maximum operating voltage and maximum operating current of the controlled circuit by 1.5~2 times.
The parameters such as the forward voltage drop of the thyristor, the gate trigger current and the trigger voltage should meet the requirements of the application circuit (referring to the control circuit of the gate), and cannot be too high or low, otherwise it will affect the normal operation of the thyristor.
16. Substitution experience of thyristors
After the thyristor is damaged, if there is no replacement of the thyristor of the same model, you can choose another type of thyristor with similar performance parameters to replace it.
When designing an application circuit, generally there is a large margin. When replacing the thyristor, just pay attention to its rated peak voltage (repeated peak voltage), rated current (on-state average current), gate trigger voltage and gate trigger current, especially the two indicators of rated peak voltage and rated current .
The replacement of the thyristor should be consistent with the switching speed of the damaged thyristor. For example, after a high-speed thyristor used in a pulse circuit or a high-speed inverter circuit is damaged, only a fast thyristor of the same type can be used instead of an ordinary thyristor.
When choosing to replace the thyristor, no matter what parameters, there is no need to leave an excessive margin. It should be as close as possible to the parameters of the replaced thyristor. Excessive margin is not only a waste, but also sometimes has side effects. , There is no trigger or insensitive trigger and other phenomena.
In addition, pay attention to the same shape of the two thyristors, otherwise it will bring disadvantages to the installation work.
17. Introduction of different thyristor detection methods
(1) Detection of unidirectional thyristors
1. Judging each electrode According to the structure of an ordinary thyristor, it is known that the gate G and the cathode K are a PN junction with unidirectional conductivity, and there are two PN junctions connected in series in reverse polarity between the anode A and the gate. Therefore, by measuring the resistance between the pins of the ordinary thyristor with a multimeter R×100A or R×1k, three electrodes can be determined.
The specific method is: connect the black meter pen of the multimeter to a certain pole of the thyristor, and the red meter pen to touch the other two electrodes in turn. If the measurement result has a resistance of several thousand ohms (kΩ) once, and another resistance of a few hundred ohms (Ω), it can be determined that the gate electrode G is connected to the black meter pen. In the measurement with a resistance of a few hundred ohms, the red test lead is connected to the cathode K, and in the measurement with a resistance of a few thousand ohms, the red test lead is connected to the anode A, if the resistance measured twice Very large, it means that the black table pen is not connected to the gate electrode G, and the same method is used to modify other electrodes until three electrodes are found.
You can also measure the forward and reverse resistance between any two pins. If the forward and reverse resistances are close to infinity, the two poles are the anode A and the cathode K, and the other leg is the gate G.
Ordinary thyristors can also judge each electrode according to its packaging form. E.g:
The bolt end of the bolt-shaped ordinary thyristor is the anode A, the thinner lead end is the gate electrode G, and the thicker lead end is the cathode K.
The leading end of the flat-shaped ordinary thyristor is the gate electrode G, the planar end is the anode A, and the other end is the cathode K.
A metal encapsulated (TO-3) common thyristor, the outer shell of which is anode A.
The middle pin of the plastic encapsulated (TO-220) ordinary thyristor is anode A, and it is mostly connected to its own heat sink. The figure below shows the pin arrangement of several common thyristors.
2. To judge whether it is good or bad, use a multimeter R×1k to measure the forward and reverse resistance between the anode A and cathode K of the ordinary transistor. Normally, they should be infinite (∞). If the forward and reverse resistance between A and K is measured If the value is zero or the resistance value is small, it indicates that the internal breakdown of the thyristor is short circuit or leakage.
Measure the forward and reverse resistance values between the gate G and the cathode K. Normally, there should be forward and reverse resistance values similar to a diode (the actual measurement result is smaller than the forward and reverse resistance values of ordinary diodes), that is, positive The forward resistance value is small (less than 2 kΩ), and the reverse resistance value is large (more than 80 kΩ). If the two measured resistance values are both very large or very small, it means that the G and K poles of the thyristor are open or short-circuited. If the positive and negative resistance values are equal or close to each other, it means that the thyristor has failed, and the PN junction between its G and K poles has lost its unidirectional conduction effect.
Measure the forward and reverse resistances between anode A and gate G. Normally, both resistances should be several hundred kilo-ohms (kΩ) or infinity. If the forward and reverse resistances are different (there are similar diodes) Unidirectional conduction), one of the two PN junctions connected in series between the G and A poles has broken down and shorted.
3. Trigger capability detection For ordinary thyristors of low power (operating current is below 5A), multimeter R×1 can be used for measurement. During the measurement, the black test lead is connected to the anode A, and the red test lead is connected to the cathode K. At this time, the hand is not moved, and the display resistance value is infinite (∞). Use tweezers or wires to short-circuit the anode A of the thyristor with the gate (see the figure below), which is equivalent to adding a positive trigger voltage to the G pole. At this time, if the resistance value is a few ohms to tens of ohms (the specific resistance value depends on the thyristor Different models will vary), it means that the thyristor is conducting due to the positive trigger. Then disconnect the connection between the A pole and the G pole (the test leads on the A and K poles do not move, only the trigger voltage of the G pole is cut off), if the indication of the needle remains at a position of a few ohms to tens of ohms, It means that the trigger performance of this thyristor is good.
For medium- and high-power ordinary thyristors with currents above 5A, due to their on-state voltage drop VT, sustain current IH and gate trigger voltage VG are relatively large, the current provided by the multimeter R×1 file is low, and the thyristor cannot be completely Conduction, so a 200Ω adjustable resistor and 1~3 1.5V dry batteries can be connected in series at the black test pen end (depending on the capacity of the tested thyristor, if the working current is greater than 100A, 3 1.5V dry batteries should be used) ),As shown below.
You can also use the test circuit in the figure below to test the triggering capability of a common thyristor. In the circuit, VT is the tested thyristor, HL is the 6.3V indicator light (small electric bead in the flashlight), GB is the 6V power supply (4 1.5V dry batteries or 6V regulated power supply can be used), S is the button, R is the current limit resistance.
When the button S is not turned on, the thyristor VT is in a blocking state, and the indicator light HL is off (if HL is on at this time, it is due to VT breakdown or leakage damage). After pressing the button S once (make S turn on once to provide the trigger voltage for the gate G of the thyristor VT), if the indicator light HL keeps on, it means that the triggering ability of the thyristor is good. If the brightness of the indicator light is low, it indicates that the performance of the thyristor is poor and the conduction voltage drop is large (normally the conduction voltage drop should be about 1V). If the indicator light is on when the button S is turned on, and the indicator light is off when the button is off, it means that the thyristor is damaged and the trigger performance is poor.
1. Use the multimeter R×1 or R×10 of each electrode to measure the positive and reverse resistance values between the three pins of the bidirectional thyristor. If a certain pin is not connected to the other two pins, then this pin is the main Electrode T2.
After finding the T2 pole, the remaining two feet are the main electrode T1 and the gate G3. Measuring the forward and reverse resistance values between these two pins will measure the two smaller resistance values. In a measurement with a small resistance value (about tens of ohms), the main electrode T1 is connected to the black test lead, and the gate electrode G is connected to the red test lead.
The bolt end of the bolt-shaped bidirectional thyristor is the main electrode T2, the thinner lead end is the gate electrode G, and the thicker lead end is the main electrode T1.
The shell of the metal encapsulated (TO-3) bidirectional thyristor is the main electrode T2.
The middle pin of the plastic package (TO-220) bidirectional crystal tube is the main electrode T2, which is usually connected to its own small heat sink.
The figure below is the pin arrangement of several bidirectional thyristors.
2. To determine whether it is good or bad, use multimeter R×1 or R×10 to measure the positive and reverse resistance values between the main electrode T1 and the main electrode T2, and between the main electrode T2 and the gate electrode G of the bidirectional thyristor. gigantic. If the measured resistance values are very small, it indicates that the thyristor electrodes have broken down or leakage short circuit.
Measure the positive and negative resistance values between the main electrode T1 and the gate electrode G. Normally, they should be between tens of ohms (Ω) and one hundred ohms (Ω) (black test lead connected to T1 pole, red test lead connected to G pole ), the measured forward resistance value is slightly smaller than the reverse resistance value). If the measured positive and negative resistance values between the T1 pole and the G pole are both infinite, it means that the thyristor has been opened and damaged.
3. Trigger capability detection For low power bidirectional thyristors with operating current below 8A, it can be directly measured with multimeter R×1. When measuring, first connect the black test lead to the main electrode T2, and the red test lead to the main electrode T1, then use tweezers to short-circuit the T2 pole with the gate G, and add a positive trigger signal to the G pole. If the measured resistance value at this time is infinite If it becomes more than ten ohms (Ω), it means that the thyristor has been triggered to conduct, and the conducting direction is T2→T1.
Then connect the black test lead to the main electrode T1, the red test lead to the main electrode T2, use tweezers to short-circuit between the T2 pole and the gate electrode G, when adding a negative trigger signal to the G pole, the measured resistance value should change from infinity to A dozen ohms, it means that the thyristor has been triggered to conduct, the direction of conduction is T1 → T2.
If the G pole is turned off after the thyristor is triggered and turned on, the low-resistance conduction state cannot be maintained between the T2 and T1 poles and the resistance value becomes infinite, which means that the bidirectional thyristor has poor performance or has been damaged. If the positive (or negative) polarity trigger signal is added to the G pole, the thyristor is still not conducting (the positive and reverse resistance values between T1 and T2 are still infinite), it means that the thyristor is damaged and there is no triggering conduction ability.
For medium and high power bidirectional thyristors with an operating current of 8A or more, when measuring their triggering capabilities, you can first connect 1~3 1.5V dry batteries in series with a multimeter pen, and then use the R×1 file as described above measuring.
For bidirectional thyristors with a withstand voltage above 400V, 220V AC voltage can also be used to test their triggering capability and performance.
The following figure is the test circuit of the bidirectional thyristor. In the circuit, EL is a 60W/220V incandescent bulb, VT is a bidirectional thyristor under test, R is a 100Ω current limiting resistor, and S is a button.
After the power plug is connected to the commercial power, the bidirectional thyristor is in the cut-off state, and the light bulb is not bright (if the light bulb is normally lit at this time, it means that the T1 and T2 poles of the tested thyristor have broken through the short circuit; if the light bulb is bright, it means The leakage of the thyristor under test is damaged). Press the button S once to provide the trigger voltage signal for the gate electrode G of the thyristor. Normally, the thyristor should be triggered and turned on immediately, and the light bulb normally emits light. If the light bulb cannot emit light, the open circuit inside the thyristor under test is damaged. If the light bulb lights when the button S is pressed, and the light bulb goes out after releasing the hand, it indicates that the triggering performance of the tested thyristor is poor. (In doubt, the thyristor whose polarity changes when the AC crosses zero should not work, and the trigger voltage should be added again.)
(3) Detection of the gate turn-off thyristor
1. The method for distinguishing the three electrodes of the thyristor from the gate of each electrode is the same as that of the ordinary thyristor, that is, using the R×100 file of a multimeter to find the two electrodes with diode characteristics, one of which is low resistance (hundreds of ohms), Another time is the larger resistance. In the measurement with a small resistance, the red test lead was connected to the cathode K, the black test lead was connected to the gate G, and the remaining pin was the anode A.
2. Detection of triggering capability and turn-off capability The detection method of the triggering capability of the turn-off thyristor is the same as that of ordinary thyristors. When detecting the turn-off capability of the gate turn-off thyristor, you can first make the thyristor in the conducting state according to the method of detecting the triggering capability, that is, use a multimeter R×1, the black test lead is connected to the anode A, and the red test lead is connected to the cathode K, and the resistance is measured The value is infinity. Then short-circuit the A pole with the gate electrode G. When a positive trigger signal is applied to the G pole, the thyristor is triggered and turned on, and the resistance between the A and K poles changes from infinity to a low resistance state. After the short-circuit point of the A pole and the G pole is disconnected, the thyristor maintains a low-resistance conduction state, indicating that its triggering capability is normal. Then add a reverse trigger signal between the gate G of the thyristor and the anode A. If the resistance value between the A and K poles changes from low resistance to infinity at this time, it means that the thyristor's shutdown capability is normal. The following figure is Schematic diagram of detection of shutdown capability.
You can also use the circuit shown in the figure below to detect the triggering ability and turn-off ability of the gate turn-off thyristor. In the circuit, EL is the 6.3V indicator light (small electric bead), S is the transfer switch, and VT is the thyristor under test. When the switch S is turned off, the thyristor is not turned on, and the indicator light is off. When the K1 contact of the switch S is connected, a positive trigger signal is added to the G pole, and the indicator light is on, indicating that the thyristor has been triggered and turned on. If the switch S is turned off and the indicator light remains on, it means that the triggering capability of the thyristor is normal. If the K2 contact of the switch S is turned on, a reverse trigger signal is added to the G pole, and the indicator light goes out, it means that the thyristor's turning off capability is normal.
(4) Detection of temperature-controlled thyristors
1. Distinguish each electrode The internal structure of the temperature-controlled thyristor is similar to the ordinary thyristor, so you can also use the method of distinguishing the electrode of the ordinary thyristor to find the electrode of the temperature-controlled thyristor.
2. Performance testing The quality of the temperature controlled thyristor can also be roughly measured with a multimeter. For the specific method, please refer to the testing method of ordinary thyristors.
The figure below is the test circuit of the temperature controlled thyristor. In the circuit, R is a shunt resistor, which is used to set the switching temperature of the thyristor VT. The smaller the resistance, the higher the setting value of the switching temperature. C is anti-interference capacitor, which can prevent false triggering of thyristor VT. HL is 6.3V indicator light (small electric bead), S is the power switch.
After the power switch S is turned on, the thyristor VT is not turned on, and the indicator light HL is off. Heat the thyristor VT with a hot air blower. When its temperature reaches the set temperature, the indicator light is on, indicating that the thyristor VT has been triggered to conduct. If you use the "cold air" stall of the hair dryer to cool the thyristor VT (or wait for it to cool naturally) to a certain temperature value, the indicator light can be extinguished, indicating that the thyristor has good performance. If the indicator light is on after the power switch is turned on, or the indicator light does not turn on after the thyristor is heated, or the indicator light does not go off after the thyristor is cooled, the thyristor under test is damaged or has poor performance.
(5) Detection of light-controlled thyristors
When using a multimeter to detect the low-power light-controlled thyristor, the multimeter can be placed in the R×1 file, and 1 to 3 1.5V dry batteries are connected in series to the black test pen to measure the positive and reverse resistance values between the two pins. Normally All should be infinity. Then use a small flashlight or laser pointer to illuminate the light-receiving window of the light-controlled thyristor. At this time, a small forward resistance value should be measured, but the reverse resistance value is still infinite. In a measurement of a smaller resistance value, the black pen is connected to the anode A, and the red meter is connected to the cathode K.
The following circuit can also be used to measure the light-controlled thyristor. Press the power switch S, illuminate the light receiving window of the thyristor VT with a flashlight, and add a trigger light source to it (high-power light-controlled thyristor comes with a light source, as long as the light-emitting diode or semiconductor laser in its optical cable is added to the working voltage, no need After adding the light source), the indicator light EL should light up, and the indicator light EL should keep glowing after evacuating the light source.
If the power switch S is turned on (the light source has not been added), the indicator EL lights up, indicating that the thyristor under test has broken down and short-circuited. If the power switch is turned on, and the trigger light source is added, the indicator light EL still does not light. If the electrode of the thyristor under test is connected correctly, the internal of the thyristor is damaged. If the indicator light is on after the trigger light source is added, but the indicator light goes off after the light source is cancelled, it means that the trigger performance of the thyristor is poor.
(6) Inspection of BTG thyristor
1. According to the internal structure of the BTG thyristor, it can be seen that each electrode includes a plurality of PN junctions connected in series between the positive pole A and the cathode K and between the gate G and the cathode K, and the anode A and the gate G There is only one PN junction. Therefore, as long as the A pole and G pole are measured with a multimeter.
Put the multimeter in the R×1k file, and connect the two test leads to any two pins of the thyristor under test (measure the positive and reverse resistance values). If a pair of pins is tested for low resistance, the black test lead is connected. Anode A, and the red lead is connected to the gate electrode G, and the other pin is the cathode K.
2. Judge whether it is good or bad Use multimeter R × 1k file to measure the positive and negative resistance values between the BTG thyristor electrodes. Normally, the forward and reverse resistances between anode A and cathode K are infinite; the forward resistance between anode A and gate G (referring to when the black test lead is connected to pole A) is several hundred ohms to several thousand ohms , The reverse resistance value is infinite. If the measured positive and negative resistance values between two poles are very small, it means that the thyristor has been short-circuited and damaged.
3. Trigger capability detection Put the multimeter in R×1 position, connect the black test lead to anode A, and the red test lead to cathode K. The measured resistance value should be infinite. Then touch the gate electrode G with your finger to add a human body induction signal. If the resistance value between A and K changes from infinity to a low resistance value (a few ohms) at this time, it means that the triggering ability of the thyristor is good. Otherwise, the performance of this thyristor is poor.
(7) Detection of reverse conduction thyristor
1. According to the internal structure of the reverse conduction thyristor, it can be seen that a diode is connected between the anode A and the cathode K (the anode is connected to the K pole), and there is a PN junction between the gate G and the cathode K, and the anode A is connected to the gate There are multiple PN junctions connected in series in reverse.
When measuring the forward and reverse resistance values between the electrodes with a multimeter R×100, you will find that there is a low resistance value between the one electrode and the other two electrodes in the forward and reverse measurement. This electrode is the cathode K . Connect the black test lead to the cathode K, and the red test lead touches the other two electrodes in turn, which is shown as low resistance. In one measurement, the red test lead is connected to the anode A. Then connect the red test lead to the cathode K, and the black test lead touches the other two electrodes in turn. In a measurement showing low resistance, the black test lead is connected to the gate electrode G.
2. To measure its quality, use the multimeter R×100 or R×1k to measure the positive and reverse resistance values between the anode A and cathode K of the reverse conducting thyristor. Normally, the forward resistance value (the black meter pen is connected to the A pole) is Infinity, the reverse resistance value is several hundred ohms to several thousand ohms (measured with R×1k file is about 7kΩ, with R×100 file is about 900Ω). If the forward and reverse resistance values are both infinite, it means that the diode connected in parallel inside the thyristor has been damaged. If the forward and reverse resistance values are very small, the thyristor is short-circuit damaged.
Normally, the positive and reverse resistance values between the anode A and the gate G of the reverse conducting thyristor are infinite. If the measured positive and negative resistance values between the A and G poles are very small, it means that the A and G poles of the thyristor are short-circuited.
Normally, the forward resistance value between the gate electrode G and the cathode K of the reverse conducting thyristor (the black test lead is connected to the G pole) is several hundred ohms to several thousand ohms, and the reverse resistance value is infinite. If the measured positive and negative resistance values are infinite or very small, it means that the G and K poles of the thyristor have been opened or shorted.
3. Trigger capability detection The detection method of the trigger capability of the reverse conducting thyristor is the same as that of the ordinary thyristor. Use a multimeter R×1, connect the black test lead to the anode A, and the red test lead to the cathode K (the high-power thyristor should connect 1 to 3 1.5V dry batteries in series on the black test lead or red test lead) to short-circuit the A and G poles instantly. The thyristor can be triggered and turned on, and the reading on the multimeter will change from infinity to low resistance. If it cannot be changed from infinity to a low resistance value, it means that the tested thyristor has poor triggering ability.
(8) Detection of four-terminal thyristors
1. Identify each electrode The four-terminal thyristors are mostly encapsulated in a metal shell. The following figure is a bottom view of the pin arrangement. Starting from the tube key (the protrusion on the shell), the clockwise direction is cathode K, cathode gate GK, anode gate GA, and anode A.
2. To judge whether it is good or bad, use a multimeter R×1k file to measure the positive and negative resistance values between the electrodes of the four-terminal thyristor. Normally, the forward resistance value between the anode A and the anode gate GA (the black lead is connected to the A pole) is infinite, and the reverse resistance value is 4~12kΩ; the forward direction between the anode gate GA and the cathode gate GK The resistance value (black test lead to GA) is infinite, the reverse resistance value is 2~10 kΩ; the forward resistance value between the cathode K and the cathode control electrode GK (black test lead to K) is infinite, and the reverse resistance value is 4 ~12 kΩ.
If the measured positive and negative resistance values between two poles are both small or infinity, it means that the thyristor is short-circuited or open.
3. Trigger ability detection Use multimeter R×1k, black test lead connects to anode A, and red test lead connects to cathode K, then the resistance value is infinite. If the K pole and the anode gate GA are momentarily short-circuited and the negative trigger pulse voltage is applied to the GA pole, the resistance value between the A and K poles rapidly changes from infinity to a low resistance value, indicating that the triggering capability of the GA pole of the thyristor is good.
After disconnecting the black test lead, connect it to the anode A again, the red test lead is still connected to the cathode K, and the multimeter shows that the resistance value is infinite. If the A pole and the GK pole are short-circuited instantaneously and the forward trigger voltage is applied to the GK pole, the resistance value between the A and K poles of the thyristor changes from infinity to a low resistance value, it can be determined that the GK pole of the thyristor has good triggering ability .
If the K, GA pole or A, GA pole is short-circuited, the resistance value between the A and K poles is still infinite, which means that the internal open circuit of the thyristor is damaged or the performance is poor.
4. Turn-off performance detection When the four-terminal thyristor is triggered to be in the on state, if the anode A and the anode gate GA or the cathode K and the cathode gate GK are momentarily short-circuited, the resistance between the A and K poles changes from a low resistance to Infinity indicates that the measured thyristor has good turn-off performance.
5. Reverse conduction performance test After short-circuiting anode A and anode gate GA, cathode K and cathode gate of thyristor respectively, use multimeter R×1k, black test lead to A pole, red test lead to K pole, normal resistance It should be infinite; measure the two strokes again, and the normal resistance between the K and A poles should be a low resistance (thousands of ohms).