SCR Ratings
Subscript
identification
First
subscript
F - Forward
bias
R - Reverse
bias
T - ON state
Second
subscript
T - Trigger
S- Surge or
Non-repetitive value
R-
Repetitive value
W- Working
value
Voltage
Ratings of SCR
1. Peak
Working Forward-blocking Voltage VDWM
Forward
blocking voltage across SCR in gate open condition. Beyond this value SCR will
switch on and device will damage
2. Peak
Repetitive Forward-blocking Voltage VDRM
It is the
maximum transient voltage that the SCR can block during it’s the forward
blocking state repeatedly or periodically.
3. Peak
Non-repetitive or Surge Forward-blocking Voltage VDSM
Maximum non
repetitive instantaneous voltage across SCR in forward blocking mode
4. Peak
Working Reverse Voltage VRWM
Maximum
Instantaneous value across SCR in reverse biased condition
5. Peak
Repetitive Reverse Voltage VRRM
Maximum
reverse transient voltage across SCR under reverse biased
6. Peak
Non-repetitive or Surge Reverse Voltage VRSM
Maximum non
repetitive instantaneous voltage across SCR in reverse blocking mode
7. ON-state
Voltage VT
Voltage drop
across the SCR at specific junction temperature
8. Gate
Triggering Voltage VGT
Minimum
voltgae required at gate for switching
9. Forward
dv/dt Rating
Maximum rate
of rise of anode voltage what will not turn ON the SCR
If dV/dt is
more than specific value more charge will induce in J2 (PN junction inside SCR)
and causes false trigger with our SCR.
Current
Ratings of SCR
1. Average
ON-state Current Rating ITAV
Maximum
value of average current that can flow through SCR given junction temperature
and rms current within limit
In case of
phase controlled rectifier for given average current, rms current increases
with decrease in conduction angle or increase in firing angle.
This lead to
increase in more voltage drop across SCR and power dissipation, which need to
be properly addressed for application.
2. RMS
ON-state Current ITRMS
Maximum
allowable SCR current given junction temperature within limit.
This
parameter need to be properly addressed for wide duty ratio application.
3. I2t Rating
Determines
thermal energy dissipation of device. Used majorly for selection of fuse
rating. I2t rating of fuse should be less than I2t rating of SCR
This
measures the thermal withstand capability of SCR before protective equipment
clears the fault
4. di/dt Rating
Maximum rate
of rise of current that is allowable within junction temperature. This directly
relate to rise time spread time for given gate current and voltage. Usually
exopress in A/uS
5. Latching
Current IL
Minimum ON
state anode current to keep the device ON even gate current is removed
6. Holding
Current IH
Minimum
value of anode current below which SCR OFF if gate current is removed
7. Gate Current IG
7. Gate Current IG
Maximum and
minimum value of gate current
Temperature
Rating of SCR
Forward and
reverse blocking state of SCR is determined by junction temperature Tj. This
can change the current rating of SCR
1. Power
Ratings of SCR
Product if
average anode current and voltage drop across the SCR
2. Gate
Power Dissipation PG
Product of
gate current and voltage. Should be with in limit mentioned in datasheet. For
high duty cycle application gate losses become significant
3. Turn ON
and Turn OFF Time Ratings
Time between
instant of gate signal applied to the rate of rise of anide current reached 90%
