BUH515D datasheet(4/7 Pages) STMICROELECTRONICS

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Switching Time Resistive Load

In order to saturate the power switch and reduce

conduction losses, adequate direct base current

IB1 has to be provided for the lowest gain hFE 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 IB2 which

minimizes

power

losses,

fall

time

and,

consequently, Tj. A new set of curves have been

defined to give total power losses, ts and tf as a

function of IB2 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:

(IC)2 =

(VCEfly)2

ω= 2 πf =

√

L C

Where IC= operating collector current, VCEfly=

flyback voltage, f= frequency of oscillation during

retrace.

BASE DRIVE INFORMATION

BUH515D

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