MJE13007

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5

SPECIFICATION INFORMATION FOR SWITCHMODE APPLICATIONS

INTRODUCTION

The primary considerations when selecting a power

transistor for SWITCHMODE applications are voltage and

current ratings, switching speed, and energy handling

capability. In this section, these specifications will be

discussed and related to the circuit examples illustrated in

Table 2. (Note 1)

VOLTAGE REQUIREMENTS

Both blocking voltage and sustaining voltage are

important in SWITCHMODE applications.

Circuits B and C in Table 2 illustrate applications that

require high blocking voltage capability. In both circuits the

switching transistor is subjected to voltages substantially

≈ 0 in Table 2). The blocking

capability at this point depends on the base to emitter

conditions and the device junction temperature. Since the

highest device capability occurs when the base to emitter

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 improvement 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 6) are the

proper design limits.

For inductive loads, high voltage and 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 a Reverse Bias Safe Operating Area

(Figure 7) 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.

NOTE: 1. For detailed information on specific switching applications,

see ON Semiconductor Application Note AN719, AN873,

AN875, AN951.