MOSFET over heating at lower than expected load currents

[ReadyEdi]

Hello there,

I'm testing a new switch method for my battery cut off circuit and when testing the  FQP27P06https://www.sparkfun.com/datasheets/Components/General/FQP27P06.pdf  P channel mosfet at 12V at the source and 0V at the input it generates quite alot of heat without a heat sink at 5A and when measuring the Vds voltage and multi pling it by the current I get around 2.15Ohm which is way above what is being said in the datasheet.

Why is that?

Thanks for helping

[danadak]

At Vgs = 12 V you are getting somewhere around .07 Rdson,
so P = 5² x .07 = ~ 1.75 W, so part w/o a heat sink
would be quite hot, burn your pinkie.

Tj-c is ~ 62 C/W, so case would fry eggs.


Regards, Dana.

[ReadyEdi]

Hi thanks for the replay regarging that do you maybe know of any other better component to suit that need that doesn't require a heat sink for long continues operations?

[Freelander]

You can get lower RDSon devices but it is not too bad to start with. I presume this is fully on ? - not pwm'd etc ?, so not operating in the linear region at all. If the gate is at 0v and the source at 12v then you will have the device fully on.
You can put multiple devices in parallel, it is a method we have used in various devices many times.  Worth putting a low value gate resistor for each fet - 100r 'ish. that will work fine.