What are the main parameters of thyristors and diodes and their meanings?

There are dozens of parameters used to characterize the performance and characteristics of thyristors and diodes in the IEC standard, but there are about ten items that users often use. This article briefly introduces the main parameters of thyristors and diodes.

• Forward average current IF(AV) (rectifier tube)
  

On-state average current IT(AV) (thyristor)

It refers to the average value of the maximum sine half-wave current that is allowed to flow through the device at the specified heat sink temperature THS or case temperature TC. At this point, the junction temperature of the device has reached its maximum allowable temperature Tjm. The radiator temperature THS or case temperature TC value corresponding to the corresponding on-state current is given in the product manual of Taiwan-based company. The user should select the appropriate type of device according to the actual on-state current and heat dissipation conditions.

• Forward root mean square current IF (RMS) (rectifier tube)
  

On-state rms current IT (RMS) (thyristor)

It refers to the maximum effective current value that is allowed to flow through the device at the specified heat sink temperature THS or case temperature TC. In use, the user must ensure that under any conditions, the effective value of the current flowing through the device does not exceed the RMS current value at the corresponding case temperature.

• Inrush current IFSM (rectifier), ITSM (thyristor)
  

Indicates the instantaneous maximum overload current value that the device can withstand under abnormal conditions. Expressed with a 10ms bottom width sine half-wave peak value, the inrush current value given by Taiji Company in the product manual is the test value under the condition that the device is at the highest allowable junction temperature and 80% VRRM is applied. The number of times the device can withstand surge current is limited in its lifetime, and users should try to avoid overloading during use.

• Off-state non-repetitive peak voltage VDSM
  

Reverse non-repetitive peak voltage VRSM

Refers to the maximum turning voltage that the thyristor or rectifier diode can withstand when it is in the blocking state. Generally, a single pulse test is used to prevent device damage. The user should not apply this voltage value to the device during testing or use, so as not to damage the device.

• Off-state repetitive peak voltage VDRM
  

Reverse repetitive peak voltage VRRM

Refers to the maximum repetitive peak voltage that the device can withstand in the off-state and reverse when the device is in the blocking state. Generally, 90% of the non-repetitive voltage of the device is marked (high-voltage devices are marked with the non-repetitive voltage minus 100V). The user must ensure that under no circumstances should the device be subjected to an actual voltage that exceeds its off-state and reverse repetitive peak voltages.

• Off-state repetitive peak (drain) current IDRM
  

Reverse repetitive peak (drain) current IRRM

It is the forward and reverse peak leakage current flowing through the element when the thyristor is in the blocking state and is subjected to the off-state repetitive peak voltage VDRM and the reverse repetitive peak voltage VRRM. This parameter is measured at the maximum junction temperature Tjm at which the device is allowed to operate.

• On-state peak voltage VTM (thyristor)
  

Forward peak voltage VFM (rectifier tube)

Refers to the peak voltage when the device passes the specified forward peak current IFM (rectifier) or on-state peak current ITM (thyristor), also known as the peak voltage drop. This parameter directly reflects the on-state loss characteristics of the device and affects the on-state current rating capability of the device.

The on-state (forward) peak voltage of the device at different current values can be approximated by the threshold voltage and slope resistance:

VTM=VTO+rT*ITM VFM=VFO+rF*IFM

Taiji Company provides the maximum on-state (forward) peak voltage, threshold voltage and slope resistance of each type of device in the product manual. When the user needs, the measured threshold voltage and slope resistance value of the device can be provided.

• Circuit commutation turn-off time tq (thyristor)
  

Under specified conditions, after the forward main current of the thyristor drops to zero-crossing, the minimum time interval from the zero-crossing point to the element that can withstand the specified re-applied voltage without turning on. The turn-off time value of the thyristor depends on the test conditions. Taiji Company provides the measured value of the turn-off time of each device for the fast and high-frequency thyristors manufactured by Taiji Company. Unless otherwise specified, the corresponding test conditions are as follows:

l     The on-state peak current ITM is equal to the device ITAV;

l     On-state current drop rate di/dt=-20A/μs;

l     Reapply voltage rise rate dv/dt=30A/μs;

l     Reverse voltage VR=50V;

l     Junction temperature Tj=115°C.

If the user needs a test value of the off-time under a specific application condition, they can make a request to us.

• On-state current critical rate of rise di/dt (thyristor)
  

It refers to the maximum value of the on-state current rise rate that the thyristor can withstand when the thyristor switches from the blocking state to the conducting state. The critical rise rate di/dt of the on-state current that the device can withstand is greatly affected by the gate triggering conditions, so we recommend that the user use a strong trigger method in the application, trigger pulse current amplitude: IG≥10IGT; pulse rise time: tr≤ 1μs.

10. Off-state voltage critical rise rate dv/dt

The maximum allowable rate of forward voltage rise under specified conditions that will not cause the thyristor to transition from the off-state to the on-state. The minimum dv/dt value of all types of thyristors is given in the product manual of Taiji Company. When users have special requirements for dv/dt, they can be put forward when ordering.

• Gate Trigger Voltage VGT
  

Gate trigger current IGT

Under specified conditions, the minimum gate voltage and gate current required to make the thyristor switch from the off state to the on state. The turn-on time and turn-on loss of a thyristor during turn-on are greatly affected by the strength of the trigger signal applied to its gate. If a more critical IGT is used to trigger the thyristor in the application, the thyristor will not be able to obtain good turn-on characteristics, and in some cases, the device may even fail or be damaged prematurely. Therefore, we recommend strong trigger mode in user application, trigger pulse current amplitude: IG≥10IGT; pulse rise time: tr≤1μs. To ensure reliable operation of the device, IG must be much larger than IGT.

• Junction to case thermal resistance Rjc
  

It refers to the temperature rise generated by the unit power consumption flowing from the junction to the case of the device under specified conditions. The junction-to-case thermal resistance reflects the heat dissipation capability of the device, and this parameter also directly affects the on-state rated performance of the device. In the product manual of Taiji Company, the steady-state thermal resistance value under double-sided cooling is given for flat-panel devices, and the thermal resistance value under single-sided cooling is given for semiconductor power modules. Users should pay attention that the junction-to-case thermal resistance of flat-panel devices is directly affected by the installation conditions. Only by installing according to the installation force recommended in the manual can the junction-to-case thermal resistance of the device meet the requirements.

For more thyristor and diode knowledge, please pay attention to the official website of Liujing Rectifier Co., Ltd.