Can turn off the principle of thyristor

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A three-terminal thyristor that applies a gate signal of the appropriate polarity to switch from an on state to an off state or from an off state to an on state. Generally expressed in GTO, it can also be expressed as GCS.

The GTO symbol and forward steady-state volt-ampere characteristics are shown in Figure 1GTO symbol (a) and forward steady-state volt-ampere characteristics (b).

GTO is an ideal DC switching component. When it is used as a switch, it has the most outstanding advantages compared with ordinary thyristors (thyristors): it can be self-shutdown, does not require complicated commutation loops; and has a high operating frequency. The disadvantage is that the current is large under the same working conditions. The holding current refers to the minimum anode current required to maintain the on-state just after going from the off state to the on state and cutting off the gate current. The turn-off pulse requires a high rate of rise in power and negative gate current.

Compared with power transistors, GTO has the advantages of high voltage and high current; it can withstand surge current; only transient pulse power is required for switching. The disadvantage is that the gated loop is more complicated.

Structure and working principle GTO has three extraction electrodes (Fig. 2 GTO unit structure), which are represented by anode (A), cathode (K) and gate (G), respectively. In the forward direction, a positive pressure is applied between the anode and the cathode. If the gate has no voltage, the GTO anode voltage is not turned on when the anode voltage is lower than the corner voltage; if the gate is positively pressurized, the GTO is gated when the anode voltage is less than the turning voltage. The pole triggers conduction (Fig. 1b GTO symbol (a) and forward steady state volt-ampere characteristics (b)).

The GTO is turned off by adding a certain negative voltage to the gate, so that the negative current is drawn, so that the cathode conduction region shrinks from the edge close to the gate to the central region of the cathode, and can always shrink to the order of the carrier diffusion length. Because the width of the cathode strip of the GTO is small, the lateral voltage drop caused by the lateral resistance of the P region is smaller than the reverse breakdown voltage of the gate and cathode when pumping. At this time, since the GTO cannot maintain the positive feedback of the internal current, the on-state current begins to decrease. After a certain period of time, the GTO is turned off.

GTO is widely used in induction heating regulators, static inverters, electrical equipment for electric locomotives, etc. Its development direction is high frequency, high voltage and high current.

The gate assisted shutdown thyristor adds a negative voltage to the gate at some point after the anode current crosses zero, causing the device to resume the blocked GTO. Gate-assisted turn-off thyristors usually use amplifying gate and cathode short-circuit structures, and the gate and cathode patterns are highly interdigitated. The advantages of this device are short, the turn-off time is good, the turn-on characteristics are good, and the allowable on-state current rise rate and on-state voltage rise rate are high. It can be used to form circuits with high operating frequencies such as choppers and inverters.