AN1889

ESBT driving circuit

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base current during all the on state. It is evident that the real advantage of the proposed

It is worth noticing that the proposed circuit provides also an energy recovery function,

which minimizes the power needed to supply the base. The smaller capacitor stores all

charges coming from the base during the storage time, and gives them back to the base

during the next turn-on.

Figure 6, is practically constant and fixed according to the gain of the transistor used at

maximum current. This sort of "fixed voltage driven" method may cause some problems at

low load conditions and in general all the times the device works at low current level, in fact

in this case the storage time will be longer (over saturation effect), with consequent worse

turn-off performance.

It is clear that a proportional base biasing could positively impact the device performance at

lower current too. In the driving circuit reported in Figure 7 a current transformer associated

with the base of the ESBT implements a proportional base biasing and provides two further

advantages: firstly designer does not need to get a constant voltage anymore, secondly, the

Figure 7.

ESBT proportional driving circuit