Operating Frequency Information
Operating frequency information for a typical device
(Figure 3) is presented as a guide for estimating device
performance for a specific application. Other typical
frequency vs collector current (ICE) plots are possible using
the information shown for a typical unit in Figures 5, 6, 7, 8, 9
and 11. The operating frequency plot (Figure 3) of a typical
device shows fMAX1 or fMAX2; whichever is smaller at each
point. The information is based on measurements of a
typical device and is bounded by the maximum rated
junction temperature.
fMAX1 is defined by fMAX1 = 0.05/(td(OFF)I+ td(ON)I).
Deadtime (the denominator) has been arbitrarily held to 10%
of the on-state time for a 50% duty factor. Other definitions
are possible. td(OFF)I and td(ON)I are defined in Figure 21.
Device turn-off delay can establish an additional frequency
limiting condition for an application other than TJM. td(OFF)I
is important when controlling output ripple under a lightly
loaded condition.
fMAX2 is defined by fMAX2 = (PD - PC)/(EOFF + EON). The
allowable dissipation (PD) is defined by PD = (TJM - TC)/RJC.
The sum of device switching and conduction losses must not
exceed PD. A 50% duty factor was used (Figure 3) and the
conduction losses (PC) are approximated by
PC = (VCE x ICE)/2.
EON and EOFF are defined in the switching waveforms
shown in Figure 21. EON is the integral of the instantaneous
power loss (ICE x VCE) during turn-on and EOFF is the
integral of the instantaneous power loss (ICE x VCE) during
turn-off. All tail losses are included in the calculation for
EOFF; i.e., the collector current equals zero (ICE = 0).