ESBT driving circuit

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ESBT driving circuit

As already mentioned in the Chapter 1: ESBT: theory and evolution, a simple constant

voltage is enough to supply the base of the ESBT, nevertheless it could not be sufficient to

properly drive the device when very high voltage level and/or high switching frequencies are

handled. First problem is related to the dynamic saturation phenomenon always present in

all "bipolar devices" during turn-on operations. This phenomenon is related to the delay of

bipolar datasheet). It is evident that the higher is the working frequency, the worse this effect

will be. A common used method to moderate this effect consists in heavily injecting the base

with minority carriers in the fastest possible way, practically by providing a very high current

peak at turn-on. The consequent high base current acts in contrast with the need not to over

saturate the device since this will badly impact the turn-off loss: as a result, in fact, the

benefits got at the turn-on could become a weakness for the turn OFF performance. A

particular modulation of the base current that allow the optimization of both switching

phases can be achieved with the circuit in the figure below.

Figure 6.

ESBT driving circuit and relevant waveforms

the first part of the turn-on, accomplishing the current spike need. From this value, both the

maximum current value and duration of the initial spike can be adjusted: the lower is the

limited only by the zener voltage.

The zener diode allows a tight base current control, by setting the exact difference between

operation are those reported in Figure 6. The proposed circuit allow us to achieve an

optimization of base current behavior in the first zone described without jeopardizing the

turn-off behavior: the big pulse of base current during the first instants of turn-on (achieved

E

T

R

R

V

V

D

C

C

V

Fig. 6a

Fig. 6b