Basic characteristics and main parameters of giant transistors

Basic characteristics and main parameters of giant transistors

Basic characteristics of GTR

(1) Static characteristics

In the static characteristics of GTR, the main analysis of collector output characteristics, that is, collector volt-ampere characteristics UCE = f (IC), the output characteristic curve of the common emitter circuit is shown in Figure 1.

Basic characteristics and main parameters of giant transistors
Figure 1 – Output characteristic curve of GTR common emitter circuit

The output characteristics are divided into 4 areas:

Cut-off area: UCE≤0, UBC<0, both the launch junction and the collector junction are reverse biased. At this time, the GTR is subjected to high voltage and has very little leakage current.

Amplified area: UCE>0, UBC<0, the transmitting junction is forward biased, and the collector junction is reverse biased. In this area, the collector current has a linear relationship with the base current.

Critical saturation zone: UCE>0, UBC<0. In this zone, the collector current and the base current have a nonlinear relationship.

Saturation zone: UCE>0, UBC≥0, the launch junction and the collector junction are forward biased. At this time, the base current IB changes, IC no longer changes, and the on-state voltage is the smallest. At this time, the voltage between the collector-emitter and the emitter is called the saturation voltage drop, which is expressed by UCES, and its size determines the power consumption when the device is switched.

In power electronic circuits, GTR works in the on-off state, that is, it works in the cut-off zone or the saturation zone.

(2) Dynamic characteristics

Figure 2 shows the relationship between the base current and the collector current waveform during GTR turn-on and turn-off.

Basic characteristics and main parameters of giant transistors
Figure 2 – GTR dynamic characteristic curve

The time required for the GTR to transition from the off state to the on state is called the turn-on time ton, and the delay time td and the rise time tr are required to pass when it is turned on;

The storage time ts and the fall time tf are required to elapse during shutdown, and the sum of the two is the shutdown time toff.

The delay time td is mainly caused by the charging of the junction capacitance. Increasing the base drive current iB and increasing diB/dt can shorten the delay time, but also shorten the rise time, thereby speeding up the opening process. The storage time ts is used to remove excess carriers in the base region and is the main part of the turn-off time. Reducing the saturation depth during turn-on can reduce the storage speed. Of course, reducing the saturation depth during turn-on will increase the saturation turn-on voltage UCES between the collector and the emitter, thereby increasing the on-state consumption. The fall time tf is the discharge time of the junction capacitance.

The turn-on time ton of GTR is generally 0.5~3μs, and the turn-off time toff is longer than ton. The storage time is 3-8μs and tf is about 1μs. The larger the capacity of the GTR, the longer the switching time. But much shorter than thyristor and GTO.

The main parameters of GTR

In addition to the aforementioned current amplification factor β, DC current gain h, leakage current ICES between collector and emitter, saturation voltage drop UCES between collector and emitter, turn-on time ton and turn-off time toff, the main parameters of CTR also include:

(1) Maximum working voltage

When the voltage applied to the GTR exceeds the specified value, breakdown occurs. The maximum operating voltage refers to the breakdown voltage. The breakdown voltage is not only related to the characteristics of the device itself, but also related to the connection of the external circuit. Figure 3 shows the different wiring methods of transistors, and the corresponding breakdown voltages are represented as BUCBO, BUCEO, BUCER, BUCES, and BUCEX. The relationship between these breakdown voltages is:

                            BUCBO﹥BUCEX﹥BUCES﹥BUCER﹥BUCEO                 (1-1)

Basic characteristics and main parameters of giant transistors
Figure 3 – Different wiring methods of transistors

When actually using GTR, in order to ensure safety, the highest working voltage UM should be lower than BUCEO. Generally take:

Basic characteristics and main parameters of giant transistors
(1-2)

(2) Collector maximum allowable current ICM

The large current effect of GTR will make the electrical performance of GTR worse. Usually, it is stipulated that the DC current amplification factor hFE is reduced to 1/2~1/3 of the specified value, and the corresponding IC is the maximum allowable current of the collector. In actual use, a margin must be left. Usually, the IC can only use about half of the ICM.

(3) The maximum power consumption of the collector PCM

Maximum power consumption PCM refers to the allowable power consumption at the highest operating temperature.