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3–680
Motorola Bipolar Power Transistor Device Data
t1
REVERSE BIAS SAFE OPERATING AREA AND INDUCTIVE SWITCHING
RESISTIVE
SWITCHING
OUTPUT WAVEFORMS
T
C
V
T
NOTE
PW and VCC Adjusted for Desired IC
RB Adjusted for Desired IB1
5 V
PW
DUTY CYCLE
≤
10%
tr, tf
≤
10 ns
68
1 k
0.001
μ
F
0.02
μ
F
1N4933
270
+5 V
1 k
2N2905
47
1/2 W
100
–VBE(off)
MJE200
D.U.T.
IB
RB
1N4933
1N4933
33
33
2N2222
1 k
MJE210
VCC
+5 V
L
IC
MR826*
Vclamp
*SELECTED FOR
≥
1 kV
VCE
5.1 k
51
+125 V
RC
SCOPE
–4.0 V
D1
RB
TUT
t1 ADJUSTED TO
OBTAIN IC
Lcoil (ICM)
t1
≈
VCC
t2
≈
Lcoil (ICM)
Vclamp
+10 V
25
μ
s
0
–8 V
Coil Data:
Ferroxcube Core #6656
Full Bobbin (~16 Turns) #16
GAP for 200
μ
H/20 A
Lcoil = 200
μ
H
VCC = 20 V
Vclamp = 300 Vdc
VCC = 125 V
RC = 15
D1 = 1N5820 or Equiv.
RB =
Test Equipment
Scope–Tektronics
475 or Equivalent
tr, tf < 10 ns
Duty Cycle = 1.0%
RB and RC adjusted
for desired IB and IC
IC
VCE
TIME
ICM
VCEM
t2
t
tf
tf CLAMPED
tf UNCLAMPED
≈
t2
Vclamp
Table 1. Test Conditions for Dynamic Performance
APPLICATIONS INFORMATION FOR SWITCHMODE SPECIFICATIONS
INTRODUCTION
The primary considerations when selecting a power tran-
sistor for SWITCHMODE applications are voltage and cur-
rent ratings, switching speed, and energy handling capability.
In this section, these specifications will be discussed and re-
lated to the circuit examples illustrated in Table 2.(1)
VOLTAGE REQUIREMENTS
Both blocking voltage and sustaining voltage are important
in SWITCHMODE applications.
Circuits B and C in Table 2 illustrate applications that re-
quire high blocking voltage capability. In both circuits the
switching transistor is subjected to voltages substantially
higher than VCC after the device is completely off (see load
line diagrams at IC = Ileakage
≈
0 in Table 2). The blocking ca-
pability at this point depends on the base to emitter condi-
tions and the device junction temperature. Since the highest
device capability occurs when the base to emitter junction is
reverse biased (VCEV), this is the recommended and speci-
fied use condition. Maximum ICEV at rated VCEV is specified
at a relatively low reverse bias (1.5 Volts) both at 25
°
C and
100 C. Increasing the reverse bias will give some improve-
ment in device blocking capability.
The sustaining or active region voltage requirements in
switching applications occur during turn–on and turn–off. If
the load contains a significant capacitive component, high
current and voltage can exist simultaneously during turn–on
and the pulsed forward bias SOA curves (Figure 1) are the
proper design limits.
For inductive loads, high voltage and current must be sus-
tained simultaneously during turn–off, in most cases, with the
base to emitter junction reverse biased. Under these condi-
tions the collector voltage must be held to a safe level at or
below a specific value of collector current. This can be ac-
complished by several means such as active clamping, RC
snubbing, load line shaping, etc. The safe level for these de-
vices is specified as a Reverse Bias Safe Operating Area
(Figure 2) which represents voltage–current conditions that
can be sustained during reverse biased turn–off. This rating
is verified under clamped conditions so that the device is
never subjected to an avalanche mode.
(1) For detailed information on specific switching applications, see
Motorola Application Notes AN–719, AN–767.