# Working with peak current of mosfet

In the datasheet, the transistor has two max current values, in the case of the IRF510

Continuous Drain Current = 5.6A
Pulsed Drain Current a IDM = 20A


with a pulse width of 20uS

Which is the assumed duty cycle for this values? Ts = 40uS and D = 50%?

Which current value should I consider if I want to work with a different duty cycle? 80% for example.

• Note that those 'max current values' are absolute maxium ratings, not normal operating currents. The data sheet says: 'CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied.' May 25 '16 at 16:19
• @BruceAbbott In this particular case the absolute maximum ratings are the same as the peak operating ratings (at least the parameters in the OP). May 25 '16 at 16:31
• @user57709 No, they are stress ratings, not operating ratings. Operating an IRF510 at 20A peak or 5.6A continuous will seriously impact its reliability. May 25 '16 at 17:09
• @BruceAbbott The datasheet has the same values (for these two parameters) under "Absolute Maximum Ratings" and under "Specifications". There is usually a difference in these values, but not for this device. May 25 '16 at 17:16
• If its not explicit in the datasheet, then you should limit your duty cycle such that the average of the 'pulsed' current doesn't exceed the 'continuous' rating. May 25 '16 at 17:20

From the notes underneath that part of the datasheet:

Notes a. Repetitive rating; pulse width limited by maximum junction temperature (see fig. 11).

Fig. 11:

From this, you can see that for 80% duty cycle (Duty factor, D = 0.8) we are beyond the scope of the graph (it only covers D <= 0.5). For that reason, you will need to work within the continuous rated current of the device.

For duty cycles <= 50%, you can read off the transient thermal impedance reduction for short pulses & low duty cycle, add in the impact of the case-to-ambient conditions and then ensure that the junction temperature stays below the absolute maximum rating for your power dissipation.

That said, I would just work well within the continuous current rating of the device and in fact overrate it by a significant margin to ensure that the circuit you design is robust in a wide variety of conditions.

• There is a curve on this figure for different values of duty cycle. There isn't a curve for a value of 0.8, so one can't be assumed. This value would appear to be outside the scope of a repetitive pulse (in this context) and so the continuous ratings should be used (as you point out). May 25 '16 at 16:34
• You're quite right - I misread to 0-0.50 curve label. Will update the answer appropriately. May 25 '16 at 16:35
• In addition 5.6A is the ideal value with Case temperature = 25C. Depending on the cooling conditions you need to further derate http://www.vishay.com/docs/91015/sihf510.pdf Fig 9 May 25 '16 at 20:21