SCR RATING
The semiconductor product (device) have infinity levels to their capacity and transcend (exceeding) even for small time get outcome (result) in failure, losing control , importable deterioration. All semiconductor device uses in their own limits and should contain extreme conditions as may exist during circuit damages, get hold of account load, power system, temperature and surrounding variations. The highest condition are not exactly predict to can’t be valued, the suitable operating region (margin) to chose and allow the unknown factors. The secure operating regions detected experiment appearances. The operation considered the different type of rating included
- Voltage Rating
- Current Rating
Voltage Rating
The necessary potential capacity of a SCR is not excess during working even for very short period of time.
So the thyristor is manufactured with different voltage levels, whatever are the maximum voltages at which the thyristor duty normally interconnections are without breakdown. The above mentioned hunk states of thyristor can withstand against voltage transients. The different voltage classified of an SCR.
OPERATION PEAK – OFF STATE FORWARD VOLTAGE (VDWM)
This is the maximum instant value of the Forward OFF state voltage that occurs around the SCR excluding all repetitive and non – repetitive transient voltages.
REPETITIOUS HIGH – OFF STATE FORWARD VOLTAGE (VDrm)
The VDrm peak temporally voltage that a thyristor in the OFF state can block continually in the forward direction. The categorization is identify at maximum accredited junction temperature with gate circuit open otherwise with a particular operating condition resistance in the middle of the gate and cathode terminals.
NON – REPETITIVE PEAK – OFF STATE FORWARD VOTLAGE (VDSM)
The highest instantaneous range of any non-repetitive transient OFF state voltage that induced across a thyristor.
WORKING PEAK REVERSE VOLTAGE (VRWM)
The highest instantaneous range of the reverse voltage that induced across the device excluding all repetitive and non- repetitive induced voltages.
REPETITIOUS PEAK REVERSE VOLTAGE (vRRM)
The high reverse temporary (transient) range appear continuously in the reverse direction at the permit maximum junction temperature. The value raised thryristor get damage in junction temperature.
NON-REPETITIVE PEAK REVERSE VOLTAGE (VRSM)
This is highest temporary reverse potential that can be safety blocked by the thyristor. The temporary reverse potential rating can be enlarge by put a diode of same current value in series with the thryistor.
ON STATE VOLTAGE (VT)
ON state voltage fall between anode and cathode with identify forward ON state current and junction temperature. The on state range of order 1 to 1.5 v.
GATE TRIGGER VOLTAGE (VT)
This is minimum gate potential necessary to produce the gate trigger current.
VOLTAGE SAFETY FACTOR (VF)
To prevent damage to a thyristor due to unknown situation, normal operating range voltage is hold on under the VRSM range of the device. The working range VRSM value are related by the voltage safety factor Vf that explained as
Vf = (VRSM (Peak inverse voltage)) / (√2 * RMS Value of input voltage)
FORWARD dv/dt VALUE ( VALUE of Arise of OFF state voltage)
The dv/dt value of thyristor specifies the higher ratio of anode voltage that will not trigger the device without any gate signal. If the range of increase of forward potential is maximum than the identify maximum range , it may cause change to ON – OFF state. The instrument for this caution can be described in terms of internal capacitance that the SCR demonstrated. Although potential through device is larger, charges flow through way similar to the charging current of capacitor ( i = C ). The larger the estimate of rise of given voltage, the larger will flow of charges. As the rate of enlarge, necessary charges will sometime flow to act in the same way as the charge give when the gate energized with a positive voltage as to cathode, and the thyristor will turn-on.
The dv/dt evaluate also corresponds on the junction temperature. Larger the junction temperature , smallest the dv/dt of the device. Hence the dv/dt activate random turn – on of a thyristor, it is not possible in practice. The circle designer may often limit the maximum dv/dt applied to thyristor by means added suppressors on other word “snubber” circuit locate across a device terminals.