BUS98 BUS98A

5

Motorola Bipolar Power Transistor Device Data

SWITCHING TIMES NOTE

In resistive switching circuits, rise, fall, and storage times

have been defined and apply to both current and voltage wa-

veforms 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 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 us-

ing 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 con-

verter 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

4

Figure 9. Storage Time, tsv

IC, COLLECTOR CURRENT (AMPS)

2

4

6

8 10

20

30

2

1

0.7

Figure 10. Crossover and Fall Times

Ib2/Ib1

2

Figure 11a. Turn–Off Times versus Forced Gain

βf, FORCED GAIN

4

6

8

0.5

0.2

0.03

0.8

Figure 11b. Turn–Off TM Times versus Ib2/Ib1

IC, COLLECTOR CURRENT (AMPS)

0.6

0.4

0.2

0.1

3

3

0.5

βf = 5

TC = 100°C

TC = 25°C

2

4

6

8 10

20

30

βf = 5

tc

tfi

TC = 100°C

TC = 25°C

2

1

0.3

0.1

0.05

10

tsv

tc

tfi

TC = 25°C

IC = 20 A

VBE(off) = 5 V

1

2

3

4

0.5

0.2

0.03

3

2

1

0.3

0.1

0.05

5

TC = 25°C

IC = 20 A

βf = 5

TC = 25°C

TC = 100°C

tsv

tc

tfi