How much do you know about thyristors?

The bidirectional trigger diode has become a two-terminal AC device or a bidirectional diode, which came out at the same time as the bidirectional thyristor. Because the bidirectional trigger diode has a simple structure and low price, it is often used to trigger a bidirectional thyristor and can also constitute an overvoltage protection circuit.

How much do you know about thyristors?

Bidirectional thyristors are generally used together with bidirectional trigger diodes. Next, let’s talk about bidirectional trigger diodes first.

The bidirectional trigger diode has become a two-terminal AC device or a bidirectional diode, which came out at the same time as the bidirectional thyristor. Because the bidirectional trigger diode has a simple structure and low price, it is often used to trigger a bidirectional thyristor and can also constitute an overvoltage protection circuit.

The difference between the bidirectional trigger diode and the varistor is that the resistance of the sub-sensitive Resistor changes very slowly, while the bidirectional trigger diode changes very sharply, and the resistance is either infinite or close to zero.

In general, the two-way trigger diode is in a high-impedance cut-off state. The two-way trigger diode is only available when an external voltage (regardless of forward or reverse) is applied to the two-way trigger diode and the applied Voltage is higher than the breakdown voltage of the two-way trigger diode. Breakdown and conduction.

The breakdown voltage of a general two-way trigger diode is tens of volts.

The forward and reverse volt-ampere characteristics of the bidirectional trigger diode are almost completely symmetrical. When the voltage U applied across the device is lower than the forward turning voltage Ubo, the diode presents a high resistance state. When U is greater than Ubo, the diode breaks down and enters the negative resistance zone, and the forward current increases rapidly. When U is greater than the reverse turning voltage Ubr, the diode also enters the negative resistance zone.

How much do you know about thyristors?

The following is a table lamp dimming circuit composed of components such as bidirectional trigger diodes and bidirectional thyristors. In the circuit, VD1 is a bidirectional trigger diode, VS1 is a bidirectional thyristor, HL1 is a lamp, and RP1 is a variable Resistor for dimming. Triggering a bidirectional thyristor with a bidirectional trigger diode is a typical and commonly used trigger circuit.

How much do you know about thyristors?

The working principle of the circuit is: after the AC power is turned ON, in the positive half cycle of the AC voltage, 220v AC will charge the Capacitor C1 through RP1 and R2. When the charging voltage on C1 rises above the breakdown voltage of the bidirectional trigger diode, the capacitor C1 will be Discharge to the control electrode of the thyristor through the current limiting resistor R1 and the bidirectional trigger diode VD1, triggering the bidirectional thyristor to conduct, forming the current loop of the lamp HL1, and the lamp is on.

In the negative half cycle of alternating current, since the bidirectional trigger diode can work under both positive and reverse voltages, it can also trigger the bidirectional thyristor to turn on during the negative half cycle, and HL1 is on. The characteristic of the bidirectional trigger diode is in the positive and negative half cycles of the alternating current. Can work inside, and the work characteristics are the same.

When changing the resistance value of the resistor RP1, the charging time constant of the capacitor C1 is changed, so that the rising speed of the charging voltage on C1 can be changed, and the conduction time of the bidirectional thyristor (changing the conduction angle of the bidirectional thyristor) can be changed to achieve The purpose of adjusting the average value of current flowing through the lamp in an alternating current cycle, thereby adjusting the brightness of the lamp.

Trigger characteristics of bidirectional thyristor

The bidirectional thyristor, like the unidirectional thyristor, also has trigger control characteristics. However, its trigger control characteristics are different from unidirectional thyristors, that is, no matter what polarity voltage is connected between anode and cathode, as long as a trigger pulse (whether positive or negative pulse) is added to its control pole, it can make bidirectional The thyristor is turned on.

Four quadrant trigger modes of bidirectional thyristor:

How much do you know about thyristors?

1. Trigger mode The first anode T1 is positive, the second anode T2 is negative, the gate voltage G is positive, T2 is negative, and the characteristic curve is in the first quadrant, which is a positive trigger.

2. Trigger mode The first anode T1 is positive, the second anode T2 is negative, the gate voltage G is negative, T2 is positive, and the characteristic curve is in the second quadrant, which is a negative trigger.

3. Trigger mode The first anode T1 is negative, the second anode T2 is positive, the gate voltage G is negative, T2 is positive, and the characteristic curve is in the third quadrant, which is a negative trigger.

4. Trigger mode The first anode T1 is negative, the second anode T2 is positive, the gate voltage G is positive, T2 is negative, and the characteristic curve is in the fourth quadrant, which is a positive trigger.

After the bidirectional thyristor is turned on, the G pole voltage is removed, and it will continue to be in the on state. In this case, the following methods can be used to make the bidirectional thyristor turn on and turn off.

1. Reduce the current flowing through the main electrodes T1 and T2 to below the sustaining current.

2. Make the voltage between the main electrodes T1 and T2 0 or change the polarity of the voltage between the two electrodes.

Bidirectional thyristor application circuit

The following is a typical bidirectional thyristor application circuit, which is an AC voltage regulating circuit. VS1 in the circuit is a bidirectional thyristor, VD1 is a bidirectional trigger diode, and RL is a load resistance.Using bidirectional trigger diode VD1 to trigger bidirectional thyristor VS1 is a typical and commonly used trigger circuit

How much do you know about thyristors?

In the circuit, RP1, R1, R2, C1 and VD1 constitute VS1 which is a trigger circuit, and RP1 is a voltage adjustment variable resistor. The positive half-cycle voltage of 220V alternating current charges C1 through RL, RP1 and R1. When the charging voltage on C1 rises to a certain level, the voltage on C1 is added to the bidirectional trigger diode VD1 through R2 to turn on VD1 and turn on VD1. Then the voltage is applied to the control pole of VS1 to trigger VS1 to be turned on. After VS1 is turned on, the current loop RL of the load RL is formed to work.

The negative half-cycle voltage of 220v AC also charges C1 through RL, RP1 and R1. Because VD1 is a bidirectional trigger diode, VD1 can also be turned on. The negative voltage after it is turned on is added to the VS1 control pole to trigger VS1 to turn on, because VS1 is a bidirectional thyristor, and the negative trigger voltage can also turn it on. It can be seen that after adopting the bidirectional trigger diode and the bidirectional thyristor, this circuit can work in the positive and negative half cycles of the alternating current, and the bridge rectifier circuit in the ordinary thyristor voltage regulating circuit is omitted, making the circuit simple and reliable.

How much do you know about thyristors?

Bidirectional thyristors are generally used together with bidirectional trigger diodes. Next, let’s talk about bidirectional trigger diodes first.

The bidirectional trigger diode has become a two-terminal AC device or a bidirectional diode, which came out at the same time as the bidirectional thyristor. Because the bidirectional trigger diode has a simple structure and low price, it is often used to trigger a bidirectional thyristor and can also constitute an overvoltage protection circuit.

The difference between the bidirectional trigger diode and the varistor is that the resistance of the sub-sensitive resistor changes very slowly, while the bidirectional trigger diode changes very sharply, and the resistance is either infinite or close to zero.

In general, the two-way trigger diode is in a high-impedance cut-off state. The two-way trigger diode is only available when an external voltage (regardless of forward or reverse) is applied to the two-way trigger diode and the applied voltage is higher than the breakdown voltage of the two-way trigger diode. Breakdown and conduction.

The breakdown voltage of a general two-way trigger diode is tens of volts.

The forward and reverse volt-ampere characteristics of the bidirectional trigger diode are almost completely symmetrical. When the voltage U applied across the device is lower than the forward turning voltage Ubo, the diode presents a high resistance state. When U is greater than Ubo, the diode breaks down and enters the negative resistance zone, and the forward current increases rapidly. When U is greater than the reverse turning voltage Ubr, the diode also enters the negative resistance zone.

How much do you know about thyristors?

The following is a table lamp dimming circuit composed of components such as bidirectional trigger diodes and bidirectional thyristors. In the circuit, VD1 is a bidirectional trigger diode, VS1 is a bidirectional thyristor, HL1 is a lamp, and RP1 is a variable resistor for dimming. Triggering a bidirectional thyristor with a bidirectional trigger diode is a typical and commonly used trigger circuit.

How much do you know about thyristors?

The working principle of the circuit is: after the AC power is turned on, in the positive half cycle of the AC voltage, 220v AC will charge the capacitor C1 through RP1 and R2. When the charging voltage on C1 rises above the breakdown voltage of the bidirectional trigger diode, the capacitor C1 will be Discharge to the control electrode of the thyristor through the current limiting resistor R1 and the bidirectional trigger diode VD1, triggering the bidirectional thyristor to conduct, forming the current loop of the lamp HL1, and the lamp is on.

In the negative half cycle of alternating current, since the bidirectional trigger diode can work under both positive and reverse voltages, it can also trigger the bidirectional thyristor to turn on during the negative half cycle, and HL1 is on. The characteristic of the bidirectional trigger diode is in the positive and negative half cycles of the alternating current. Can work inside, and the work characteristics are the same.

When changing the resistance value of the resistor RP1, the charging time constant of the capacitor C1 is changed, so that the rising speed of the charging voltage on C1 can be changed, and the conduction time of the bidirectional thyristor (changing the conduction angle of the bidirectional thyristor) can be changed to achieve The purpose of adjusting the average value of current flowing through the lamp in an alternating current cycle, thereby adjusting the brightness of the lamp.

Trigger characteristics of bidirectional thyristor

The bidirectional thyristor, like the unidirectional thyristor, also has trigger control characteristics. However, its trigger control characteristics are different from unidirectional thyristors, that is, no matter what polarity voltage is connected between anode and cathode, as long as a trigger pulse (whether positive or negative pulse) is added to its control pole, it can make bidirectional The thyristor is turned on.

Four quadrant trigger modes of bidirectional thyristor:

How much do you know about thyristors?

1. Trigger mode The first anode T1 is positive, the second anode T2 is negative, the gate voltage G is positive, T2 is negative, and the characteristic curve is in the first quadrant, which is a positive trigger.

2. Trigger mode The first anode T1 is positive, the second anode T2 is negative, the gate voltage G is negative, T2 is positive, and the characteristic curve is in the second quadrant, which is a negative trigger.

3. Trigger mode The first anode T1 is negative, the second anode T2 is positive, the gate voltage G is negative, T2 is positive, and the characteristic curve is in the third quadrant, which is a negative trigger.

4. Trigger mode The first anode T1 is negative, the second anode T2 is positive, the gate voltage G is positive, T2 is negative, and the characteristic curve is in the fourth quadrant, which is a positive trigger.

After the bidirectional thyristor is turned on, the G pole voltage is removed, and it will continue to be in the on state. In this case, the following methods can be used to make the bidirectional thyristor turn on and turn off.

1. Reduce the current flowing through the main electrodes T1 and T2 to below the sustaining current.

2. Make the voltage between the main electrodes T1 and T2 0 or change the polarity of the voltage between the two electrodes.

Bidirectional thyristor application circuit

The following is a typical bidirectional thyristor application circuit, which is an AC voltage regulating circuit. VS1 in the circuit is a bidirectional thyristor, VD1 is a bidirectional trigger diode, and RL is a load resistance.Using bidirectional trigger diode VD1 to trigger bidirectional thyristor VS1 is a typical and commonly used trigger circuit

How much do you know about thyristors?

In the circuit, RP1, R1, R2, C1 and VD1 constitute VS1 which is a trigger circuit, and RP1 is a voltage adjustment variable resistor. The positive half-cycle voltage of 220V alternating current charges C1 through RL, RP1 and R1. When the charging voltage on C1 rises to a certain level, the voltage on C1 is added to the bidirectional trigger diode VD1 through R2 to turn on VD1 and turn on VD1. Then the voltage is applied to the control pole of VS1 to trigger VS1 to be turned on. After VS1 is turned on, the current loop RL of the load RL is formed to work.

The negative half-cycle voltage of 220v AC also charges C1 through RL, RP1 and R1. Because VD1 is a bidirectional trigger diode, VD1 can also be turned on. The negative voltage after it is turned on is added to the VS1 control pole to trigger VS1 to turn on, because VS1 is a bidirectional thyristor, and the negative trigger voltage can also turn it on. It can be seen that after adopting the bidirectional trigger diode and the bidirectional thyristor, this circuit can work in the positive and negative half cycles of the alternating current, and the bridge rectifier circuit in the ordinary thyristor voltage regulating circuit is omitted, making the circuit simple and reliable.

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