Contents
What is voltage safety factor of SCR?
The value of voltage safety factor lies is in the range of 2.0 to 2.5.
What does the maximum surge current rating of an SCR specifies?
Detailed Solution. Surge current rating specifies the maximum non-repetitive or surge current that the SCR can withstand for a limited number of times during its life span. If the peak amplitude and the number of cycles of the surge current are exceeded, the SCR may get damaged.
What is DV dt and di dt rating of SCR?
• dv/dt: dv/dt rating of thyristor indicates maximum rate of rise of anode voltage that will not trigger the device without any gate signal. • di/dt: di/dt rating of thyristor indicates maximum rate of rise of anode to cathode current.
What is surge current in SCR?
(v) Surge Current. It is the maximum admissible peak value of a sinusoidal half cycle of 10 ms duration at a frequency of 50 Hz. The value is specified at a given junction temperature.
What is the working of SCR?
Working/Operation of SCR The basic working principle in the SCR is that as the triggering or the biasing is applied at the terminal gate then the conduction begins. As it is a unidirectional device the current will be in a single direction.
Why DV dt rating of SCR is important?
The value of capacitance of the junction is constant hence when dv/dt increases to a suitable value that leakage current occurs a avalanche breakdown across junction J2. This value of dv/dt in called forward dv/dt rating which can turn on the SCR without help of gate current.
When an SCR is reverse biased?
When a negative voltage is applied to the anode and a positive voltage to the cathode, the SCR is in reverse blocking mode, making J1 and J3 reverse biased and J2 forward biased. The device behaves as two diodes connected in series. A small leakage current flows. This is the reverse blocking mode.
What does surge current rating on SCR mean?
The surge current rating of an SCR ( IFM or ITSM) is the peak anode current that an SCR can handle for a brief duration. These durations must be isolated by SCR can handle for a brief duration. These durations must be isolated by enough time for the SCR junction to return to its rated operating temperature.
Why is the voltage rating of the SCR important?
The specific rating of voltage, current, power and maximum limit of temperature is given the SCR data sheet in order to protect SCR against over voltage, over current or any other malfunction. If the voltage and current rating of the SCR increases beyond its specific rating, the junction temperature increases and SCR may damages.
How is the size of a SCR chosen?
Selection of current rating decides the size of the SCR. Current rating chosen may be the normal operating current level or maximum expected overload current. In data books SCR are categorized according to their current ratings. Unlike voltage rating, the current rating for a chosen SCR is rarely utilized.
What’s the difference between SCR and RMS current rating?
The surge current rating may be five to twenty times as large as the repetitive RMS current rating (IT(RSM)). An SCR is designed to withstand a maximum of 100 surges during its operating life because it may be left with damage due to excessive exposure to high temperatures.