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Electronics => Beginners => Topic started by: alank2 on August 31, 2014, 02:00:36 am

Title: How can I calculate mosfet heat dissappation?
Post by: alank2 on August 31, 2014, 02:00:36 am

Hi Everyone,

I'm feeding it a 8kHz PWM signal and it is switching a 40mA load (which I realize is very little for a mosfet).

It is a IRLD024PBF-ND.

Thanks,

Alan

Title: Re: How can I calculate mosfet heat dissappation?
Post by: T3sl4co1l on August 31, 2014, 02:42:52 am

Circuit?

Title: Re: How can I calculate mosfet heat dissappation?
Post by: Pedram on August 31, 2014, 03:49:13 am

it depends on RDS(on) , gate voltage , frequency , driver's output impedance and gate capacitance

according to datasheet, RDS(on) is 0.1ohms on 5V DC Gate voltage.  at 50ma it dissipate less than 250uW

Title: Re: How can I calculate mosfet heat dissappation?
Post by: DanielS on August 31, 2014, 12:03:35 pm

The fundamental way of calculating dissipation in any component is: sum of integral of i(t)v(t) on all pins averaged over a number of complete operating cycles.

A simplified ballpark figure if the rise/fall curves are roughly linear: ((t_rise + t_fall)*I_{DSrise+fall average}*V_DSoff/2 + t_on * R_DSon * Ids^2) / period.

The exact rise/fall waveforms can vary considerably depending on circuit design and operating region. If the MOSFET drives an inductor operating in continuous mode at 10A average current and has a 500ns rise/fall time, 30V input voltage and 0.02 R_DSon, you lose about 15W from rise/fall and 1W from ON-time.