I just looked at the datasheet of IRFZ44 and couldn't see any "on-resistance vs drain current" or any other graph for Rds(on). I tried Vishay but failed. why? I need it to calculate the power dissipation. is there anyway to grab these informations?

Sounds like there is a graph for NXP IRFZ44.

 

Generally speaking for enhancement mode MOSFETs, Rdson is more a function of gate voltage and there probably is a chart for that. Rdson is relatively constant with respect to drain current.

ak

 

I need it to calculate the power dissipation. is there anyway to grab these informations?

those devices are meant to be used on full-on full-off situations so Rds(on) is what matters.

If you use them for linear applications, that's a different story.

 

Generally speaking for enhancement mode MOSFETs, Rdson is more a function of gate voltage and there probably is a chart for that. Rdson is relatively constant with respect to drain current.

ak

There is a chart[fig 3] for Vgs vs Id. then Rdson is 17.5mohm for this?

those devices are meant to be used on full-on full-off situations so Rds(on) is what matters.

If you use them for linear applications, that's a different story.

Not linear but sometimes you want to use it for a variety of applications. then you need to know Rds(on)

 

A question, I'm seeing SOA and looks like there isn't any line for DC(linear). Does it mean we cannot use it for linear applications?

 

Rds(on) is graphed in Fig 6 in the post #1 NXP link.

 

Rds(on) is graphed in Fig 6 in the post #1 NXP link.

Thanks Alec but I said it myself at OP.

 

To calculate the worst-case power dissipation you multiply the maximum ON operating current times the worst-case Rds(on) for the Vgs you applied (and Vgs should always equal or exceed the value used in the data sheet to characterise Rds(on).
Worst-case is what you should always use for design purposes.

 

A question, I'm seeing SOA and looks like there isn't any line for DC(linear). Does it mean we cannot use it for linear applications?

Enhancement MOSFETS are not designed for linear applications. Terrible for audio (class A or Class A-B amplifiers).

 

Enhancement MOSFETS are not designed for linear applications. Terrible for audio (class A or Class A-B amplifiers).

Don't know why you say that.
Enhancement MOSFETs are used in may audio amps with good results as long as they are properly biased..

 

Don't know why you say that.
Enhancement MOSFETs are used in may audio amps with good results as long as they are properly biased..

I haven't found an audio amplifier that sounds good (great) made with common "vertical" MOSFETS that use Class A or AB amplifier. There are some very good class D amps out there but I also don't understand the benefit of a vertical Mosfet in a non-class D amp . Some claim the "tube sound" but those are more associated with "Lateral MOSFETS" - an interesting and sweet sounding option for Class A or AB amps but not the type of MOSFET described by the OP.

You said properly biased but you also need proper thermal compensation. Thermal compensation is fairly easy with bipolar amps by mounting a bias bipolar transistor on the same heat sink as the power bjt. That doesn't work for power mosfet output stages.

That is my current opinion and experience but I would like to learn more.

I worked with some students to make a high powered audio amplifier some years ago and could not get decent sound in a PA system. We later discovered the appended notes on the Elliot Sound Products site that explained some of our difficulties.

(Scroll to last bold section for the autopsy of the Mitch Hodges design by Rod Elliot).
http://sound.whsites.net/articles/hexfet.htm