On State Voltage: The voltage which appears across the SCR during its ON state is known as its ON state Voltage. The
maximum value of voltage which can appear across the SCR during its conducting state is called its
maximum on state voltage. Usually it will be 1V to 4V.
Finger Voltage: The minimum voltage, which is required between the anode and cathode of an SCR to trigger it to
conduction mode, is called its finger voltage.
Rate of Rise of Voltage (dV/dt) The rate at which the voltage across the device rises ( for forward condition) without triggering the
device, is known as its rate of rise of voltage.
Voltage Safety Factor: The normal operating voltage of the SCR is kept well below its peak inverse voltage(V
PIV
) to avoid
puncture of SCR due to uncertain conditions. The operating voltage and peak inverse voltage are related
by voltage safety factor V
f
V
f
= Peak inverse voltage / ( 2 x RMS value of input voltage)
Normaly V
f
value lies between 2 and 2.5
Current Ratings: The current carrying capacity of the device is known as its current rating.
It can be of two types.
1. Continuous
2. Intermittent.
Maximum average ON state current ( I mac ): This is the average value of maximum continuous sinusoidal ON state current with conduction angle
180deg, at frequency 40 to 60Hz, which should not be exceeded even with intensive cooling.
51 |
P a g e
Maximum rms ON-state current: (I mrc ) It is the rms value of the maximum continuous sinusoidal ON state current at the frequency 40 to 60 Hz
and conduction angle 180deg, which should not be exceeded even with intensive cooling.
