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MOSFET question

 
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clcheung



Joined: 14 Apr 2008
Posts: 27

PostPosted: Mon Apr 14, 2008 9:26 am    Post subject: MOSFET question Reply with quote

Hi,

I have tried to use openservo on MG995. At this stage I just use IRF9450 and IRF540 to test it out instead of the IRF7307 or IRF7309. My knowledge on MOSFET is quite limited.

So far I am able to get it up and running well. However, I find that the temperature of the MOSFET goes up quickly to 100 degree C, even those the motor loading is not that high. I am wondering if it is a wrong pick of MOSFET or it is a normal behavior ? If using the small footprint IRF730x, will the temperature be lowered ?

It seems the temperature rising is caused by the PWM switching, i.e., even my motor do not move much, but whenever the PWM output is not zero, the MOSFET start to burn.

FYI, I am using the V2 schematic.

Many thanks.
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clcheung



Joined: 14 Apr 2008
Posts: 27

PostPosted: Tue Apr 15, 2008 3:22 am    Post subject: Reply with quote

problem fixed. Sorry to bother you guys.
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TCPIP_v6



Joined: 31 Aug 2008
Posts: 3

PostPosted: Fri Sep 05, 2008 7:22 pm    Post subject: Reply with quote

Hi clcheung,

What did you do to fix the problem?
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clcheung



Joined: 14 Apr 2008
Posts: 27

PostPosted: Sat Sep 06, 2008 1:20 am    Post subject: Reply with quote

Hi

I made a silly mistake in the schematic so everything works fine after fixing that.

I believe any MOSFET will work fine on the openservo schematic except that you may need to tune up on the delay time during direction switching.
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guru



Joined: 03 Jan 2006
Posts: 128
Location: St Pete Beach, FL

PostPosted: Mon Sep 15, 2008 8:50 pm    Post subject: Reply with quote

This problem can occur from floating mosfet inputs, thus the hbridge can be slightly active in both directions. (I experienced this designing hbridges.) Also, of course, a mistake in the software can make it happen too, but usually this makes them smoke, not just get very hot.


clcheung wrote:
Hi

I made a silly mistake in the schematic so everything works fine after fixing that.

I believe any MOSFET will work fine on the openservo schematic except that you may need to tune up on the delay time during direction switching.
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angelrita123



Joined: 23 Sep 2009
Posts: 1

PostPosted: Wed Sep 30, 2009 1:53 pm    Post subject: need to know Reply with quote

Ok... I've been playing with some hardware the past few months and I'm shocked at how much I forgot just by doing firmware over the years.

I need to run a 3.3V logic line to a P-Channel MOSFET. Its running to the gate and I have 5V at the Source. I will be drawing .08mA when active... I'm not switching this on at any fast rate.

I am running this model is switchercad and noticing different MOSFET's giving different results... mainly when trying to turn the fet off with 3.3V some can some wont and I cant seem to find what is the determining factor.

I would then like to get some MOSFET's from digikey.

Example: I run my simulation with...
Fairchild: FQB11P06,FDC5614P works! FDS9933A,FDS4953 doesnt

I am not sure if it has to deal with the Rds(on), Qgate ????
Well... thanks for your input in advance. Confused
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jharvey
co-admin


Joined: 15 Mar 2009
Posts: 359
Location: Maine USA

PostPosted: Thu Oct 01, 2009 10:24 am    Post subject: Reply with quote

I haven't done much modeling via spice or others. Some things you should keep in mind. The driving pin will drive hard at first to compensate for the capacitive components. So I might recommend driving it via resistor to help prevent spikes. Also a drain resistors is often good, something between gate and drain for low side driving. I see you mention P channel, that implies high side driving. Where's the load you are trying to drive?

Here's a good refresher about MOSFET's

http://en.wikipedia.org/wiki/Mosfet

For MOSFET's I typically recommend the PIP3104 as a general purpose. I like it because of it's over voltage protection scheme.
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jonnblaze



Joined: 02 Aug 2013
Posts: 2
Location: France

PostPosted: Fri Aug 02, 2013 5:52 am    Post subject: Reply with quote

I am running this model is switchercad and noticing different MOSFET's giving different results... mainly when trying to turn the fet off with 3.3V some can some wont and I cant seem to find what is the determining factor.
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Nevezyucharew



Joined: 14 Aug 2014
Posts: 13

PostPosted: Thu Aug 14, 2014 2:14 pm    Post subject: Reply with quote

A great exchange of information.
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