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BUS98-D Datasheet PDF : 8 Pages
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BUS98 BUS98A
SWITCHING TIMES NOTE
In resistive switching circuits, rise, fall, and storage times
have been defined and apply to both current and voltage
waveforms since they are in phase. However, for inductive
loads which are common to SWITCHMODE power
supplies and hammer drivers, current and voltage
waveforms are not in phase. Therefore, separate
measurements must be made on each waveform to
determine the total switching time. For this reason, the
following new terms have been defined.
tsv = Voltage Storage Time, 90% IB1 to 10% Vclamp
trv = Voltage Rise Time, 10–90% Vclamp
tfi = Current Fall Time, 90–10% IC
tti = Current Tail, 10–2% IC
tc = Crossover Time, 10% Vclamp to 10% IC
An enlarged portion of the inductive switching
waveforms is shown in Figure 7 to aid in the visual identity
4
3
2
TC = 100°C
1
0.7
TC = 25°C
0.5
βf = 5
2
4 6 8 10
20 30
IC, COLLECTOR CURRENT (AMPS)
Figure 9. Storage Time, tsv
of these terms.
For the designer, there is minimal switching loss during
storage time and the predominant switching power losses
occur during the crossover interval and can be obtained
using the standard equation from AN–222:
PSWT = 1/2 VCCIC(tc) f
In general, trv + tfi ] tc. However, at lower test currents this
relationship may not be valid.
As is common with most switching transistors, resistive
switching is specified at 25_C and has become a benchmark
for designers. However, for designers of high frequency
converter circuits, the user oriented specifications which
make this a “SWITCHMODE” transistor are the inductive
switching speeds (tc and tsv) which are guaranteed at
100_C.INDUCTIVE SWITCHING
0.8
0.6
TC = 100°C
0.4
0.2
TC = 100°C
0.1
TC = 25°C
tc
tfi
βf = 5
TC = 25°C
2
4 6 8 10
20 30
IC, COLLECTOR CURRENT (AMPS)
Figure 10. Crossover and Fall Times
3
2
tsv
1
TC = 25°C
IC = 20 A
VBE(off) = 5 V
0.5
0.3
tc
0.2
0.1
tfi
0.05
0.03
2
4
6
8
10
βf, FORCED GAIN
Figure 11. Turn–Off Times versus Forced Gain
3
2
tsv
1
TC = 25°C
IC = 20 A
βf = 5
0.5
0.3
0.2
tc
0.1
tfi
0.05
0.03
1
2
3
4
5
Ib2/Ib1
Figure 12. Turn–Off TM Times versus Ib2/Ib1
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5
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