These devices are advantageous where a reverse or

of reverse blocking. These devices are advantageous where a reverse or freewheel diode must
be used. Because the SCR and diode never conduct at the same time, they do not produce
heat simultaneously and can easily be integrated and cooled together. Reverse conducting
thyristors are often used in frequency changers and inverters.
Reference:
d) MOS-Controlled thyristor (MCT)

Physical Structure:
Most of the MCT characteristics can be understood easily by referring the equivalent circuit
of P-Channel MCT shown above. MCT closely approximates a bipolar thyristor with two
opposite polarity MOSFET transistors connected between its anode and the proper layers to
turn it on and off. As MCT is NPNP device output terminal or cathode must be negatively
biased. Driving the gate terminal negative with respect to the common terminal or anode
turns the P channel FET on, firing the bipolar SCR. Driving the gate terminal positive with
respect to the anode turns on the N channel FET on shunting the base drive to PNP bipolar
transistor making up part of the SCR, causing the SCR to turn off. When no gate to anode
voltage is applied to the gate terminal of the device, the input terminals of the bipolar SCR
are unterminated. Operation without gate bias is not recommended.
Operation Principle:

The following diagram shows the working principle of the MOS control thyristor. It is a
combination of current and voltage capabilities with the help of MOS gated. The MOS gated
is used for the switch ON/OFF of MCT. By using the negative voltage pulse the device is
turned in ON state with respect to the anode. The gate terminal is made negative with respect
to the anode with the help of the voltage pulse in between the anode and gate terminals.
Hence the MOS control thyristor is switched ON state. In the starting stage the MOS control
thyristor is a forward bias. If the negative voltage is applied to the negative voltage pulse,
then the ON mode FET is turned ON as well as the OFF FET mode is already existed as OFF
state.
The device is turned OFF with the help of the positive voltage pulse. It is applied to the gate
terminal with respect to the anode. Then the OFF FET switched ON mode and the ON FET
switched to the OFF state. If the OFF FET is switched ON then the p-n-p transistor is short
circuited by the emitter and base terminals. Thus, the anode current flows through the OFF
FET. Hence the base current of N-P-N transistor is decreased. Reverse voltage blocking
capability is the negative point of this device.
Voltage-Current Characteristic:
Reference: