BUH515D Datasheet, PDF (4/7 Pages) STMicroelectronics – HIGH VOLTAGE FAST-SWITCHING NPN POWER TRANSISTOR

BUH515D
Switching Time Resistive Load
BASE DRIVE INFORMATION
In order to saturate the power switch and reduce
conduction losses, adequate direct base current
I_B1 has to be provided for the lowest gain h_FE at
100 ^oC (line scan phase). On the other hand,
negative base current IB2 must be provided to
turn off the power transistor (retrace phase). Most
of the dissipation, especially in the deflection
application, occurs at switch-off. Therefore it is
essential to determine the value of I_B2 which
minimizes power losses, fall time tf and,
consequently, Tj. A new set of curves have been
defined to give total power losses, ts and tf as a
function of I_B2 at 16 KHz frequencies for
choosing the optimum negative drive. The test
circuit is illustrated in fig. 1.
Inductance L₁ serves to control the slope of the
negative base current IB2 to recombine the
excess carrier in the collector when base current
is still present, this avoid any tailing phenomenon
in the collector current.
The values of L and C are calculated from the
following equations:
1
2
L
(I_C)²
=
1
2
C
(V_CEfly)²
ω
=
2
πf
=
1
√LC
Where IC= operating collector current, VCEfly=
flyback voltage, f= frequency of oscillation during
retrace.
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