How to detect the cathode and anode and trigger level of thyristors?

Introduction of different thyristor detection methods

Detection of (I) unidirectional thyristor
1. Distinguish each electrode According to the structure of ordinary thyristor, there is a pn junction between gate G and cathode K, which has unidirectional conduction characteristics, while there are two pn junctions connected in series with opposite polarity between anode A and gate. Therefore, by measuring the resistance value between the pins of the common thyristor with a multimeter r× 100a or r× 1k, the three electrodes can be determined.

The specific method is to connect the black stylus of the multimeter to one pole of the thyristor, and the red stylus to touch the other two electrodes in turn. If the measurement result has a resistance value of several thousand ohms (kω) and another resistance value of several hundred ohms (ω), it can be determined that the black stylus is connected to the gate G. In the measurement with a resistance of several hundred ohms, the red stylus is connected to the cathode k, while in the measurement with a resistance of several thousand ohms, the red stylus is connected to the anode a. if the resistance values measured twice are large, it means that the black stylus is not connected to the gate g, and the other electrodes are measured by the same method until the three electrodes are found.

You can also measure the positive and reverse resistance between any two legs. If the positive and reverse resistance are close to infinity, the two poles are anode A and cathode K, and the other leg is gate G.

Ordinary thyristors can also determine each electrode according to its packaging form. For example:

The bolt end of the bolt-shaped ordinary thyristor is anode a, the thinner lead end is gate g, and the thicker lead end is cathode k.

The lead-out end of the flat-shaped ordinary thyristor is the gate g, the plane end is the anode a, and the other end is the cathode k.

Metal shell package (to-3) ordinary thyristor, the shell is anode a.

The middle pin of the common thyristor of the plastic package (to-220) is anode a and is mostly connected with its own heat sink. Figure 8-15 shows the pin arrangement of several common thyristors.

 

2. Judge whether it is good or bad. Use multimeter r× 1k to measure the positive and negative resistances between anode A and cathode K of ordinary transistors. Normally, they should be infinite (∞). If the positive and negative resistance values between A and K are measured to be zero or the resistance value is small, then the internal breakdown of thyristor is short-circuited or leakage is indicated.

Measure the positive and reverse resistance values between gate G and cathode K. Normally, there should be positive and reverse resistance values similar to diodes (the actual measurement results are smaller than those of ordinary diodes), I .e. the forward resistance value is smaller (less than 2 kω) and the reverse resistance value is larger (greater than 80 kω). If the resistance value of the two measurements is very large or very small, it indicates that the thyristor is open or short-circuited between the g and k poles. If the positive and negative resistance values are equal or close, it means that the thyristor has failed, and the pn junction between its g and k electrodes has lost the unidirectional conduction effect.

Measure the positive and reverse resistance between anode A and gate G. Normally, the two resistance values should be several hundred kiloohms (kω) or infinity. If the positive and reverse resistance values are different (there is unidirectional conduction similar to diodes), one of the two pn junctions connected in reverse series between G and A poles has broken down and short circuit.

3. Trigger capability detection For ordinary thyristors with low power (working current below 5a), a multimeter can be used to measure r× 1. During measurement, the black probe is connected to anode A and the red probe is connected to cathode K. At this time, the probe does not move and the display resistance is infinite (∞). Use tweezers or wires to short-circuit the anode A of the thyristor with the gate (see Figure 8-16), which is equivalent to adding a forward trigger voltage to the G pole. At this time, if the resistance value is several ohms to tens of ohms (the specific resistance value varies according to the type of thyristor), it indicates that the thyristor is turned on due to forward triggering. Then disconnect the connection between the pole and the G pole (the probe on the and K poles does not move, only the trigger voltage of the G pole is cut off). If the indicator value of the probe remains at a position of several ohms to tens of ohms, the trigger performance of the thyristor is good.

 

 

For medium-and high-power ordinary thyristors whose current is above 5a, the on-state voltage drop vt, holding current ih and gate trigger voltage vg are relatively large, and the current provided by the multimeter r× 1 gear is low, so the thyristor cannot be completely turned on, therefore, a 200ω adjustable resistor and 1~3 1.5v dry batteries can be connected in series at the pen end of the black watch during detection (depending on the capacity of the thyristor under test, if the working current is greater than 100a, 3 1.5v dry batteries shall be used), as shown in fig. 8-17.

The test circuit in Figure 8-18 can also be used to test the triggering capability of ordinary thyristors. In the circuit, vt is the thyristor to be tested, hl is 6.3v indicator light (small electric bead in flashlight),gb is 6v power supply (4 1.5v dry batteries or 6v stabilized power supply can be used),s is the button, and r is the current limiting resistor.

When the button s is not turned on, the thyristor vt is in a blocking state, and the indicator light hl is not on (if hl is on at this time, it is vt breakdown or leakage damage). After pressing the button s (make s turn on to provide trigger voltage for the gate g of thyristor vt), if the indicator hl is always on, it indicates that the thyristor has good trigger capability. If the brightness of the indicator light is low, it indicates that the thyristor has poor performance and large conduction voltage drop (normally, the conduction voltage drop should be about 1v). If the indicator light is on when the button s is 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.

Detection of (II) bidirectional thyristor

1. Distinguish each electrode. Use multimeter r× 1 or r× 10 to measure the positive and negative resistance values between the three pins of bidirectional thyristor respectively. If one pin is measured to be disconnected from the other two pins, this pin is the main electrode t2.

After finding the t2 pole, the remaining two legs are the main electrode t1 and the gate g3. Measuring the positive and negative resistance values between the two legs will measure the two smaller resistance values. In a measurement with a small resistance value (about tens of ohms), the black stylus is connected to the main electrode t1 and the red stylus is connected to the gate G.

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 housing of the metal-encapsulated (to-3) bidirectional thyristor is the main electrode t2.

The middle pin of the plastic-sealed (to-220) bidirectional crystal tube is the main electrode t2, which is usually connected with its own small heat sink.

Figure 8-19 shows the pin arrangement of several bidirectional thyristors.

 

 

2. To judge whether it is good or bad, use multimeter r× 1 or r× 10 to measure the positive and negative resistance values between main electrode t1 and main electrode t2 of bidirectional thyristor and between main electrode t2 and gate G. Under normal conditions, they should be close to infinity. If the measured resistance value is very small, it indicates that the thyristor electrode has been broken down or leakage short circuit.

Measure the positive and reverse resistance values between the main electrode t1 and the gate G, which should be between tens of ohms (ω) and 100 ohms (ω) under normal conditions (when the black stylus is connected to the t1 pole and the red stylus is connected to the G pole, the measured positive 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 infinite, it means that the thyristor has been damaged by open circuit.

3. Trigger capability detection For low-power bidirectional thyristors with working current below 8a, a multimeter can be used to directly measure r× 1 gear. During measurement, the black stylus is connected to the main electrode t2 and the red stylus is connected to the main electrode t1, then the t2 pole is short-circuited with the gate g with tweezers, and a positive trigger signal is added to the g pole. if the measured resistance value changes from infinity to more than ten ohms (ω), then the thyristor has been triggered to conduct, and the conduction direction is t2 → t1.

Then connect the black stylus to the main electrode t1 and the red stylus to the main electrode t2. Use tweezers to short-circuit the t2 pole and the gate G. When a negative trigger signal is added to the G pole, the measured resistance value should change from infinity to more than ten ohms, which indicates that the thyristor has been triggered to conduct, and the conduction direction is t1 → t2.

If the G pole is turned off after the thyristor is triggered and turned on, the low resistance on state cannot be maintained between t2 and t1 poles and the resistance value becomes infinite, then the bidirectional thyristor has poor performance or has been damaged. If the thyristor is still not conducting after adding a positive (or negative) polarity trigger signal to the G pole (the positive and reverse resistance values between t1 and t2 are still infinite), it means that the thyristor is damaged and has no trigger conduction capability.

For medium and high power bidirectional thyristors with working current above 8a, when measuring their triggering capability, 1~3 1.5v dry batteries can be connected in series on a meter pen of the multimeter, and then r× 1 gear can be used to measure according to the above method.

For the withstand voltage of more than 400v bidirectional thyristor, can also use 220v AC voltage to test its trigger ability and performance is good or bad.

Figure 8-20 is a test circuit for a 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 mains, the bidirectional thyristor is in the off state and the bulb is not bright (if the bulb emits light normally at this time, it means that the t1 and t2 poles of the tested thyristor have broken down and short circuit; If the bulb is slightly bright, it means that the tested thyristor is damaged by leakage). Press the button s to provide a trigger voltage signal for the gate g of the thyristor. normally, the thyristor should be triggered to turn on immediately and the bulb should emit light normally. If the bulb does not emit light, it means that the internal open circuit of the tested thyristor is damaged. If the bulb lights up when the button s is pressed, and the bulb goes out after the button is let go, it indicates that the trigger performance of the tested thyristor is poor.

Detection of (III) gate turn-off thyristor

1. The method for judging the three electrodes of each electrode gate turn-off thyristor is the same as that of ordinary thyristor, that is, using the r× 100 gear of multimeter to find out the two electrodes with diode characteristics, one of which is of low resistance (several hundred ohms) and the other is of larger resistance. In the measurement with small resistance, the red pen is connected to cathode k, the black pen is connected to gate g, and the remaining pin is anode a.

2. Detection of trigger capability and turn-off capability The detection method of the trigger capability of the turn-off thyristor is the same as that of the ordinary thyristor. When detecting the turn-off capability of the gate turn-off thyristor, the thyristor can be turned on according to the method of detecting the trigger capability, I .e. using multimeter r× 1 gear, the black probe is connected to anode a, the red probe is connected to cathode k, and the measured resistance value is infinite. When pole a is short-circuited with gate g and a positive trigger signal is added to pole g, the thyristor is triggered to turn on, and the resistance value between poles a and k changes from infinity to low resistance state. After disconnecting the short-circuit point between the pole and the g pole, the thyristor maintains a low resistance conduction state, indicating that its triggering ability is normal. Then add a reverse trigger signal between the gate g and anode a of the thyristor. if the resistance value between the pole and the k pole changes from a low resistance value to infinity, it indicates that the turn-off capability of the thyristor is normal. fig. 8-21 is a schematic diagram of the detection of the turn-off capability.

 

 

The circuit shown in FIGS. 8-22 can also be used to detect the triggering capability and turn-off capability of the gate turn-off thyristor. In the circuit, el is 6.3v indicator light (small electric bead),s is the transfer switch, and vt is the tested thyristor. When the switch s is turned off, the thyristor is not conducting and the indicator light is not on. When the k1 contact of the switch S is turned on, a positive trigger signal is added to the G pole, and the indicator light is on, indicating that the thyristor has been triggered to turn on. If the switch s is turned off and the indicator light remains illuminated, the triggering capability of the thyristor is normal. If the k2 contact of the switch s is turned on, the reverse trigger signal is added to the g pole, and the indicator light goes out, then the turn-off capability of the thyristor is normal.

Detection of (IV) temperature controlled thyristor

1. Distinguish the internal structure of each electrode temperature-controlled thyristor is similar to that of ordinary thyristor, so the electrode of temperature-controlled thyristor can also be found by distinguishing the electrode of ordinary thyristor.

2. Performance detection The quality of the temperature-controlled thyristor can also be roughly measured with a multimeter. The specific method can refer to the detection method of the ordinary thyristor.

Figure 8-23 is a test circuit for a 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 value, the higher the switching temperature setting value. C is an anti-interference capacitor, which can prevent the false triggering of the thyristor vt. Hl is 6.3v indicator light (small electric bead) and s is power switch.

After the power switch s is turned on, the thyristor vt is not turned on, and the indicator hl is not on. Use the hair dryer "hot air gear" to heat the thyristor vt. When the temperature reaches the set temperature value, the indicator light is on, indicating that the thyristor vt has been triggered to turn on. If the "cold air" gear of the hair dryer is used to cool the thyristor vt (or to be cooled 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 is not on after the thyristor is heated, or the indicator light is not off after the thyristor is cooled, the tested thyristor is broken down or has poor performance.

Detection of (V) optically controlled thyristor

When using a multimeter to detect low-power light-controlled thyristors, the multimeter can be placed in r× 1 gear, and 1~3 1.5v dry batteries are connected in series on the black pen to measure the positive and negative resistance values between the two pins. Normally, it should be infinite. Then use a small flashlight or laser pointer to irradiate 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 anode a is connected to the pen and the cathode k is connected to the red pen.

The circuit in Figure 8-24 can also be used to measure the optically controlled thyristor. Press the power switch s, use a flashlight to illuminate the light receiving window of the thyristor vt, and add a trigger light source to it (the high-power light-controlled thyristor has its own light source, as long as the light-emitting diode or semiconductor laser in its optical cable is applied with working voltage, no external light source is required), the indicator light el should be lit, and the indicator light el should keep emitting after the light source is withdrawn.

If the indicator light el is lit after the power switch s is turned on (no light source has been added), it means that the tested thyristor has been broken down and short-circuited. If the power switch is turned on and the trigger light source is added, the indicator light el is still not on. If the electrode of the tested thyristor is connected correctly, the internal damage of the thyristor is caused. If the trigger light source is added, the indicator light will emit light, but the indicator light will go out after the light source is canceled, then the trigger performance of the thyristor is poor.

detection of (VI) btg thyristor

1. Distinguish each electrode According to the internal structure of btg thyristor, it can be seen that there are multiple pn junctions connected in series between the resistor A and cathode K and between the gate G and cathode K, while there is only one pn junction between the anode A and gate G. Therefore, only a pole and g pole can be measured with a multimeter.

Place the multimeter in r× 1k gear, and the two pens are connected to one of the two pins of the thyristor under test (measuring its positive and negative resistance values). If a pair of pins is measured to have a low resistance value, the black pen is connected to anode A, while the red pen is connected to gate G, and the other pin is cathode K.

2. To judge its quality, use multimeter r× 1k to measure the positive and negative resistance values between the electrodes of btg thyristor. Normally, the positive and negative resistances between anode A and cathode K are infinite. The forward resistance value between anode A and gate G (when the black stylus is connected to pole A) is several hundred ohms to several thousand ohms, and the reverse resistance value is infinite. If the measured positive and reverse resistance between the two poles are very small, then the thyristor has been short-circuited damage.

3. Trigger capability test Put the multimeter in r× 1 gear, the black pen is connected to anode A, the red pen is connected to cathode K, and the measured resistance value should be infinite. Then touch the gate G with your finger and add a human induction signal to it. If the resistance value between A and K changes from infinity to low resistance value (several ohms), then the triggering ability of the thyristor is good. Otherwise, the performance of this thyristor is poor.

Detection of (VII) reverse conducting thyristor

1. Judging each electrode According to the internal structure of reverse conducting thyristor, a diode (positive electrode is connected to K electrode) is connected in parallel between anode A and cathode K, while a pn junction is connected between gate G and cathode K, and a plurality of pn junctions are connected in reverse series between anode A and gate.

When measuring the forward and reverse resistance values between each electrode with a multimeter r× 100, it will be found that there will be a low resistance value between one electrode and the other two electrodes during forward and reverse measurement, and this electrode is cathode k. The black pen is connected to cathode k, and the red pen touches the other two electrodes in turn. in a measurement with low resistance, the red pen is connected to anode a. Then connect the red pen to cathode k, and the black pen touches the other two electrodes in turn. in a measurement showing a low resistance value, the black pen is connected to gate g.

2. Measure its quality. Use multimeter r× 100 or r× 1k to measure the positive and reverse resistance values between anode A and cathode K of reverse conduction thyristor. Under normal conditions, the positive resistance value (black stylus connected to A pole) is infinite, and the reverse resistance value is several hundred ohms to several thousand ohms (measured by r× 1k gear is about 7kω, measured by r× 100 gear is about 900ω). If the positive and reverse resistance values are infinite, it means that the diode connected in parallel inside the thyristor is damaged by open circuit. If the forward and reverse resistance value is very small, it is the thyristor short circuit damage.

Normal reverse conduction thyristor anode a and gate g between the positive and reverse resistance are infinite. If the positive and reverse resistance values between the measured a and g poles are very small, it indicates that the and g poles of the thyristor are short-circuited.

Normally, the forward resistance value between the gate g and the cathode k of the reverse conduction thyristor (the black pen 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 reverse resistance values are infinite or very small, it means that the thyristor g, k electrode has been open circuit or short circuit damage.

3. Trigger Capability Detection The method for detecting the trigger capability of a reverse conducting thyristor is the same as that of an ordinary thyristor. With multimeter r× 1 gear, the black stylus is connected to anode A, and the red stylus is connected to cathode K (high-power thyristor shall be connected in series with 1~3 1.5v dry batteries on the black stylus or red stylus), the thyristor can be triggered to conduct, and the reading on the multimeter will change from infinity to low resistance. If it cannot be changed from infinity to low resistance, it indicates that the triggering ability of the tested thyristor is poor.

Detection of (VIII) four-terminal thyristor

1. It is judged that the four-terminal thyristor of each electrode is mostly encapsulated by metal shell. Figure 8-25 is the bottom view of its pin arrangement. From the tube key (the protrusion on the tube shell), the clockwise direction is the cathode k, the cathode gate gk, the anode gate ga, and the anode a.

2. To judge its quality, use a multimeter r× 1k to measure the positive and negative resistance values between the electrodes of the four-terminal thyristor respectively. under normal conditions, the positive resistance value between anode a and anode gate ga (black pen connected to pole a) is infinite, and the reverse resistance value is 4~12 kω; the positive resistance value between anode gate ga and cathode gate gk (black pen connected to pole ga) is infinite, and the reverse resistance value is 2~10 kω; the positive resistance value between the cathode k and the cathode control pole gk (the black stylus is connected to k) is infinite, and the reverse resistance value is 4~12 kω.

If the measured positive and reverse resistance values between the two poles are small or infinite, then the internal short circuit or open circuit of the thyristor.

3. Multimeter r× 1k is used for triggering capability detection. The black stylus is connected to pole A anytime and anywhere, and the red stylus is connected to cathode K. At this time, the resistance value is infinite. If the k pole and the anode gate ga are short-circuited instantaneously and a negative trigger pulse voltage is applied to the ga pole, the resistance value between a and k poles changes rapidly from infinity to low resistance value, then the trigger ability of the thyristor ga pole is good.

After disconnecting the black probe, connect it with anode a. the red probe is still connected to cathode k, and the multimeter shows that the resistance value is infinite. If the pole and the gk pole are short-circuited instantaneously, and the positive trigger voltage is applied to the gk pole, the resistance value between the pole and the K pole of the thyristor changes from infinity to a low resistance value, it can be determined that the trigger ability of the GK pole of the thyristor is good.

If the k, ga pole or a, ga pole short circuit, the resistance value pole between a and k pole is still infinite, then 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 instantaneously short-circuited, and the resistance value between the and K poles changes from low resistance to infinity, then the turn-off performance of the tested thyristor is good.

5. Reverse conduction performance test After short-circuiting the anode A and anode gate ga, cathode K and cathode gate of thyristor respectively, use multimeter r× 1k, black pen to connect A pole and red pen to connect K pole. Normally, the resistance value should be infinite. After two adjustments are made, the normal resistance value between K and A poles should be low resistance (several thousand ohms).