Identifying Semiconductor Power Device Triggering

Semiconductor power devices are crucial components in power electronics, used for switching or controlling high currents and voltages. These devices need a signal to switch them ON or OFF. This process is called triggering or gating.

Triggering mechanisms can generally be classified based on whether a current signal or a voltage signal is used to initiate the switching.

Understanding Current Triggering Devices

A current triggering device requires a current pulse or a continuous current applied to a control terminal (like the gate) to initiate conduction (turn ON). The amount of current flowing into the control terminal determines if the device turns ON.

Analyzing the Given Semiconductor Power Devices

Let's examine each of the given options to determine their triggering mechanism:

• Thyristor (SCR - Silicon Controlled Rectifier): A standard thyristor is turned ON by applying a positive gate current pulse between the gate and cathode. Once triggered, it remains ON even after the gate signal is removed, as long as the anode current is above the holding current. It is a current-triggered device for turning ON.
• TRIAC (Triode for Alternating Current): A TRIAC can conduct current in both directions and is turned ON by a gate current pulse, regardless of the polarity of the main terminal voltage (within limits). Like a thyristor, it requires a gate current to initiate conduction. It is a current-triggered device.
• GTO (Gate Turn-Off Thyristor): A GTO is a type of thyristor that can be turned ON by a positive gate current pulse (similar to an SCR) and, significantly, can be turned OFF by applying a negative gate current pulse. While it has turn-off capability via the gate, its turn-on is typically initiated by a gate current. For the purpose of initial triggering, it is considered current-triggered.
• MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor): A power MOSFET is fundamentally a voltage-controlled device. The conduction between the drain and source terminals is controlled by the voltage applied between the gate and source ($V_{GS}$). Applying a sufficient positive voltage between the gate and source creates a channel for current flow. Removing this voltage turns the device OFF. It requires a gate-source voltage, not a gate current, for control. It is a voltage-triggered device.

Comparison of Triggering Mechanisms

We can summarize the triggering mechanisms in a table:

Based on this comparison, the Thyristor, TRIAC, and GTO are primarily triggered by a current signal applied to their gate terminal. The MOSFET, however, is controlled by the voltage applied to its gate terminal relative to its source terminal ($V_{GS}$).

Conclusion: Which Device is Not Current Triggered?

Out of the given options, the MOSFET is the only device that operates based on voltage control at its gate terminal rather than current control. Therefore, it is not a current triggering device.