SCR Triggering / SCR Turn On Methods Full explanation.
SCR Triggering / SCR Turn On Method
SCR is a unidirectional, reverse-blocking semiconductor device. Today we are going to learn SCR Triggering Methods or you can say SCR Turn On Methods. Because we already know that SCR cannot conduct current in forward condition until we manually turn it on.
What is SCR Triggering?
The process of switching the SCR from the OFF state to the ON state is called SCR Triggering. That means the Turn ON of SCR is also known as SCR Triggering.In other words, we can say the process of switching the SCR from a forward blocking state to a forward conduction state is called SCR Triggering.
Basically, the SCR acts as a switch that allows or blocks the flow of electrical current in a circuit. By triggering the SCR, the switch can be turned on, enabling current to flow from the anode to the cathode. This switching function is essential for applications where precise timing and control of current flow are required. For example, SCR is used as a power control device in various applications, including motor control, lighting control, heating systems, and voltage regulation. By triggering the SCR, the conduction of current can be initiated and controlled. This allows for precise control over those devices.
Methods of SCR Triggering:
There are many methods of SCR turning on or triggering. The methods of SCR triggering are,- Thermal or Temperature Triggering
- Radiation or Light Triggering
- Voltage Triggering or Breakover Voltage Turn On
- dv/dt triggering
- Gate Triggering
What is the Thermal or Temperature Triggering of SCR?
We already know that when the anode of the SCR is positive with respect to the cathode the junctions J1 and J2 will be the forward bias and J2 will be the reverse bias. So a small amount of reverse leakage current will flow across junction J2.
As the leakage current depends on the temperature of the junction, in fact, it is directly proportional to the junction temperature. So when the reverse leakage current flow through the junction the temperature will increase which further increases the flow of current. So when the value of the current increases greater than the Latching Current the SCR will be Turn ON.
As the leakage current depends on the temperature of the junction, in fact, it is directly proportional to the junction temperature. So when the reverse leakage current flow through the junction the temperature will increase which further increases the flow of current. So when the value of the current increases greater than the Latching Current the SCR will be Turn ON.
Thermal triggering is commonly used in applications such as motor protection, where the SCR is used in motor control circuits. If the motor or the SCR experiences excessive temperature rise, the thermal triggering mechanism can shut off the SCR, protecting the motor from damage. It is also used in some high-power applications where thermal protection is crucial, such as in power electronics systems or industrial heating systems.
What is the Radiation or Light Triggering of SCR?
If a beam of light is applied to the junction of the SCR it can produce sufficient energy to break the electron-hole pairs in the semiconductor and the SCR will get Turn ON.
Light triggering enables fast switching of SCRs. By using a light source with a short duration and high intensity, the SCR can be triggered quickly, allowing for high-speed switching applications. So when the intensity of the applied light is increased more than a nominal value the SCR starts conducting. It is not an easy process which is why it is used rarely. This triggering is mainly used in HVDC Transmission Lines, pulse power systems, pulsed lasers, or high-frequency inverters.
In forward condition, the junction J1 and J3 are forward biased and the junction J2 is reverse biased. So if we add an additional voltage greater than the normal rated forward voltage across the SCR the Junction J2 will go to avalanche breakdown.
So the current will start flowing through junction J2. And also the current will flow through the whole SCR. This additional applied voltage is known as Breakover Voltage. Remember that in this case, the anode current would be limited by only the external load impedance.
In this situation, if we increase the rate of change in forward anode-cathode voltage a transient gate current will produce(even if the gate terminal is open) which can turn on the SCR.
As in this method, we create a change in the voltage with respect to the time it is called dv/dt triggering.
If we apply a positive voltage to the gate with respect to the cathode a current will flow through the gate terminal and if the gate current is large enough the SCR will switch ON.
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Thank you for visiting the website. keep visiting for more updates.Light triggering enables fast switching of SCRs. By using a light source with a short duration and high intensity, the SCR can be triggered quickly, allowing for high-speed switching applications. So when the intensity of the applied light is increased more than a nominal value the SCR starts conducting. It is not an easy process which is why it is used rarely. This triggering is mainly used in HVDC Transmission Lines, pulse power systems, pulsed lasers, or high-frequency inverters.
What is the Voltage Triggering or Breakover Voltage Turn On of SCR?
In forward condition, the junction J1 and J3 are forward biased and the junction J2 is reverse biased. So if we add an additional voltage greater than the normal rated forward voltage across the SCR the Junction J2 will go to avalanche breakdown.
So the current will start flowing through junction J2. And also the current will flow through the whole SCR. This additional applied voltage is known as Breakover Voltage. Remember that in this case, the anode current would be limited by only the external load impedance.
What is the dv/dt triggering of SCR?
We know that in forward condition the junction J1 and J3 are forward biased and the junction J2 is reverse biased. So we can assume that there is a capacitance will produce in the SCR whose junction J2 act as a dielectric medium and the upper portion of the junction J2 is connected to the positive voltage and the lower portion to the negative voltage.In this situation, if we increase the rate of change in forward anode-cathode voltage a transient gate current will produce(even if the gate terminal is open) which can turn on the SCR.
As in this method, we create a change in the voltage with respect to the time it is called dv/dt triggering.
What is the Gate triggering of SCR?
The process of addition of minority carriers into the gate region through the gate electrode to switch on the SCR is known as Gate Triggering.If we apply a positive voltage to the gate with respect to the cathode a current will flow through the gate terminal and if the gate current is large enough the SCR will switch ON.
Various methods of Gate triggering of SCR:
- Triggering by a DC Gate Signal
- Triggering by an AC Gate Signal
- Triggering by a Pulsed Gate Signal
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SCR Triggering / SCR Turn On Methods Full explanation.
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December 22, 2018
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Reviewed by Author
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December 22, 2018
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