Main parameters of thyristor

1. Forward repetitive peak voltage (off state repetitive peak voltage) UDRM

When a forward voltage is applied between the anode and cathode of a thyristor and no voltage is applied to the control electrode, the thyristor is in a forward blocking state.

When the gate is disconnected or the thyristor is in a forward blocking state, and the junction temperature is at the rated value, it is allowed to repeatedly apply the forward peak voltage between the anode and cathode of the thyristor, which is called the forward repetitive peak voltage and is represented by the symbol UDRM.

2. Reverse repetitive peak voltage URRM

When the gate is disconnected and the junction temperature is at the rated value, it is allowed to repeatedly apply the reverse peak voltage between the anode and cathode of the thyristor, which is called the reverse repetitive peak voltage and is represented by the symbol URRM.

3. Rated voltage UT

Usually, the smaller of UDRM and URRM is taken as the rated voltage of the thyristor. In practical applications, due to the poor overvoltage and overcurrent capabilities of thyristors, the rated voltage value of thyristors is generally selected to be 2-3 times the maximum voltage during actual operation. For example, if the effective value in a single-phase AC circuit is 220V and the maximum value is 311V, the rated voltage of the thyristor should be selected as 600V, 700V, or 800V.

4. On state average voltage UT (AV)

Under the specified ambient temperature and standard heat dissipation conditions, when the component is subjected to a sine half wave rated current, the average voltage drop between the anode and cathode is called the on state average voltage, represented by the symbol UT (AV). UT (AV) has levels, from level A to level I, with level A being 0.4V,, Level I is 1.2V.

5. Rated current (rated on state average current) IT (AV)

The average sine half wave current allowed to pass between the anode and cathode of a thyristor under the specified cooling conditions at an ambient temperature of 40 ℃, when the junction temperature is stable and does not exceed the rated junction temperature, is called the rated current of the thyristor and is represented by the symbol IT (AV). In practice, due to the poor overcurrent capability of thyristors, a safety margin of 1.5 to 2 times should be considered when selecting the rated current.

6. Maintain current IH

The minimum anode current required to maintain the continuity of the thyristor under the specified ambient temperature and gate disconnection is called the holding current, represented by the symbol IH. When the anode current of the thyristor is less than the holding current, the thyristor turns off.