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Here is the datasheet of a transistor: http://www.adafruit.com/datasheets/TIP120.pdf

In maximum ratings, there is a section called "Collector Current (Pulse)". What does that mean in practice?

Lets say this transistor is applied 30V constant DC to its ends. So the max. collector current should not exceed 5A. But if the applied 30V is in the shape of a pulse with lets say %99 duty cycle will the max. current be 8A? Thats what I understand but Im not sure.

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Here's a guide published by On Semiconductor on how to interpret their IGBT datasheets. It says that:

The pulsed collector current describes the peak collector current pulse above the rated collector current specification that can flow while remaining below the maximum junction temperature. The maximum allowable pulsed current in turn depends on the pulse width, duty cycle and thermal conditions of the device. (P. 2)

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It really only applies to the TIP122 part and not the TIP120. You need to look into the data sheet at figure 4 - safe operating area and you will see that the TIP122 can take certain durations of current for certain lengths of time. Plotted on that graph is collector current versus collector-emitter voltage: -

enter image description here

From this graph I infer that the TIP122 can take a maximum of 8A for a maximum duration of 5 milli seconds with a voltage across it of 30V. If the voltage across it were 45 volts (about) I would infer that the duration is about 1ms.

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  • \$\begingroup\$ The SOA limits apply to TIP120, 121 too, their graph is misleading (aka 'wrong')- those vertical lines should go all the way up to the 100us line. The only difference between the parts is breakdown voltage so they are trying to show that. \$\endgroup\$ Jul 25 '15 at 11:47
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    \$\begingroup\$ @SpehroPefhany yup you are correct. \$\endgroup\$
    – Andy aka
    Jul 25 '15 at 15:14

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