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MJH16006 Datasheet PDF : 12 Pages
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MJH16006A
SAFE OPERATING AREA INFORMATION
FORWARD BIAS
There are two limitations on the power handling ability of
a transistor: average junction temperature and second
breakdown. Safe operating area curves indicate IC – VCE
limits of the transistor that must be observed for reliable
operation; i.e., the transistor must not be subjected to greater
dissipation than the curves indicate.
The data of Figures 14a and 14b is based on TC = 25_C;
TJ(pk) is variable depending on power level. Second
breakdown pulse limits are valid for duty cycles to 10% but
must be derated when TC ≥ 25_C. Second breakdown
limitations do not derate the same as thermal limitations.
Allowable current at the voltages shown on Figures 14a and
14b may be found at any case temperature by using the
appropriate curve on Figure 16.
TJ(pk) may be calculated from the data in Figure 18. At
high case temperatures, thermal limitations will reduce the
power that can be handled to values less than the limitations
imposed by second breakdown.
REVERSE BIAS
For inductive loads, high voltage and high current must be
sustained simultaneously during turn–off, in most cases,
with the base–to–emitter junction reverse biased. Under
these conditions the collector voltage must be held to a safe
level at or below a specific value of collector current. This
can be accomplished by several means such as active
clamping, RC snubbing, load line shaping, etc. The safe
level for these devices is specified as Reverse Biased Safe
Operating Area and represents the voltage current condition
allowable during reverse biased turnoff. This rating is
verified under clamped conditions so that the device is never
subjected to an avalanche mode. Figure 15 gives the
RBSOA characteristics.
SWITCHMODE III DESIGN CONSIDERATIONS
1. FBSOA —
Allowable dc power dissipation in bipolar power
transistors decreases dramatically with increasing collector
emitter voltage. A transistor which safely dissipates 100
watts at 10 volts will typically dissipate less than 10 watts at
its rated VCEO(sus). From a power handling point of view,
current and voltage are not interchangeable (see Application
Note AN875).
2. TURN–ON —
Safe turn–on load line excursions are bounded by pulsed
FBSOA curves. The 10 µs curve applies for resistive loads,
most capacitive loads, and inductive loads that are clamped
by standard or fast recovery rectifiers. Similarly, the 100 ns
curve applies to inductive loads which are clamped by
ultra–fast recovery rectifiers, and are valid for turn–on
crossover times less than 100 ns (see Application Note
AN952).
At voltages above 75% of VCEO(sus), it is essential to
provide the transistor with an adequate amount of base drive
VERY RAPIDLY at turn–on. More specifically, safe
operation according to the curves is dependent upon base
current rise time being less than collector current rise time.
As a general rule, a base drive compliance voltage in excess
of 10 volts is required to meet this condition (see Application
Note AN875).
3. TURN–OFF —
A bipolar transistor’s ability to withstand turn–off stress
is dependent upon its forward base drive. Gross overdrive
violates the RBSOA curve and risks transistor failure. For
this reason, circuits which use fixed base drive are often
more likely to fail at light loads due to heavy overdrive (see
Application Note AN875).
4. OPERATION ABOVE VCEO(sus) —
When bipolars are operated above collector–emitter
breakdown, base drive is crucial. A rapid application of
adequate forward base current is needed for safe turn–on, as
is a stiff negative bias needed for safe turn–off. Any hiccup
in the base–drive circuitry that even momentarily violates
either of these conditions will likely cause the transistor to
fail. Therefore, it is important to design the driver so that its
output is negative in the absence of anything but a clean crisp
input signal (see Application Note AN952).
SWITCHMODE DESIGN CONSIDERATIONS (Cont.)
5. RBSOA —
Reverse Biased Safe Operating Area has a first order
dependency on circuit configuration and drive parameters.
The RBSOA curves in this data sheet are valid only for the
conditions specified. For a comparison of RBSOA results in
several types of circuits (see Application Note AN951).
6. DESIGN SAMPLES —
Transistor parameters tend to vary much more from wafer
lot to wafer lot, over long periods of time, than from one
device to the next in the same wafer lot. For design
evaluation it is advisable to use transistors from several
different date codes.
7. BAKER CLAMPS —
Many unanticipated pitfalls can be avoided by using
Baker Clamps. MUR105 and MUR1100 diodes are
recommended for base drives less than 1 amp. Similarly,
MUR405 and MUR4100 types are well–suited for higher
drive requirements (see Article Reprint AR131).
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