Inverter MOSFET

Thread Starter

R!f@@

Joined Apr 2, 2009
9,918
As Sgt had explained the study of gate charge between the Z46 and 540 tells me that the Z46 requires more time to turn on at a given gate voltage as the capacitance is twice that of 540.
Which will result in higher power dissipation than the 540.
So I assume that if the I can get the DC voltage at the converter output the FET's are working at the slight heat is due to the FET turn on delay caused by increased by gate capacitance.
Other than that there is no other reason for the slight heat up as the Power handling are almost same.
I am going to seam heat sinking will handle the warm up.
Am I right Sgt?
 

SgtWookie

Joined Jul 17, 2007
22,230
If the existing heat sinking did not provide enough dissipation to keep the IRF540's cool, what makes you think that the IRFZ46's will be kept cool enough?

You have also decreased the Vdss rating without really improving anything else.

Are you using an O-scope to look at the Vgs, or just using a DMM? You need to look at the waveform to see what kind of rise/fall times you are getting vs the ON and OFF times. If you're measuring 5.6v DC on the gates, that's not good.
 

Thread Starter

R!f@@

Joined Apr 2, 2009
9,918
Sorry Sgt, I do not have a scope :(. I wish I had one. But it still is way out of my budget. But I hoping to get one soon.
The Inverter blew and got so much damage as a crew used a heater and the result blew the fuse, so as usual moron's here does, he jumped the fuse and
KAPOOOOOW! There goes the MOSFET's.
I have installed every thing and at a quiescent current of 400mA, the 500W inverter produces 230VAC. I ran it idle for a few minutes. Only the I noticed it the Iq slowly drops a few milli amperes. Casing is cool, no heat up whatsoever. I am going to load the sucker tonight and see how warm it gets.
 
Last edited:

SgtWookie

Joined Jul 17, 2007
22,230
If the quiescent current is dropping, it may be due to the MOSFETs heating up, causing their Rds(on) to increase.

Keep a sharp eye on their temp. If you melt them down, you'll have another mess on your hands.
 

Thread Starter

R!f@@

Joined Apr 2, 2009
9,918
Darn it...and I thought it was good think. :eek: I never thought of the Rds doing that. What the heck was I thinking.

But now it's a too late, tomorrow I'll know if I have a mess.
I powered a heater intermittently and the Iq Over shoot my meters range.
I did this a couple of times and still it is stable. then I ran my laptop with it. It works..no heat. Yaaaaaaaaaay!! :D

So I sent it to be brute tested.
Thanks Sgt. You are becoming to be my mentor :p
 

Thread Starter

R!f@@

Joined Apr 2, 2009
9,918
The Inverter is up an running.
Thanks for all the help Sgt
I got another to meddle with as now someone knows that these could be repaired in Male' :D
 
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