Mosfet heating Up in DC DC converter

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Hello,
I have a problem in power supply which i have designed. I have
designed a dual supply of 3.3V and 5.4V from 30 V using semtech
SC2442H DC DC converter and Infineon BS0604NS2 Mosfet.
The problem is that mosfet is getting heated up a lot, it goes to
about 100 C.
I have calculated the power, it turn to be 0.72 W and the Mosfet can
handle upto 2 W. Can some one point why is the mosfet getting
heated???Because of this the inductor and capacitor near it is also
getting heated up.
DC DC converter operating frequency is 250 KHz.

Thanks and regards
Praveen


Re: Mosfet heating Up in DC DC converter

> Hello,
> I have a problem in power supply which i have designed. I have
> designed a dual supply of 3.3V and 5.4V from 30 V using semtech
> SC2442H DC DC converter and Infineon BS0604NS2 Mosfet.
> The problem is that mosfet is getting heated up a lot, it goes to
> about 100 C.
> I have calculated the power, it turn to be 0.72 W and the Mosfet can
> handle upto 2 W. Can some one point why is the mosfet getting
> heated???Because of this the inductor and capacitor near it is also
> getting heated up.
> DC DC converter operating frequency is 250 KHz.
>
> Thanks and regards
> Praveen

And the connection with Satellite's and GPS is ?




Re: Mosfet heating Up in DC DC converter
>> I have calculated the power, it turn to be 0.72 W and the Mosfet can
>> handle upto 2 W. Can some one point why is the mosfet getting
>> heated???
>
> And the connection with Satellite's and GPS is ?

To the original idiot crossposter:

Get a 13.2V power source such as a car battery. Get a 240 ohm, 1 watt
resistor. Connect the resistor across the power source (0.72 W) and
hold the resistor in your hand for one hour. Come back and report
your findings.

--
The state religion of the USA is atheism, as established by the courts.


Re: Mosfet heating Up in DC DC converter

>
> > Hello,
> > I have a problem in power supply which i have designed. I have
> > designed a dual supply of 3.3V and 5.4V from 30 V using semtech
> > SC2442H DC DC converter and Infineon BS0604NS2 Mosfet.
> > The problem is that mosfet is getting heated up a lot, it goes to
> > about 100 C.
> > I have calculated the power, it turn to be 0.72 W and the Mosfet can
> > handle upto 2 W. Can some one point why is the mosfet getting
> > heated???Because of this the inductor and capacitor near it is also
> > getting heated up.
> > DC DC converter operating frequency is 250 KHz.
> >
> > Thanks and regards
> > Praveen
>
> And the connection with Satellite's and GPS is ?
>
>
It may have escaped your attention that sometime things are crossposted, for
example I am reading your post in the NG 'sci.electronics.design', which
would seem to be appropriate ??

--
Regards ..... Rheilly Phoull




Re: Mosfet heating Up in DC DC converter

>
> >
> > > Hello,
> > > I have a problem in power supply which i have designed. I have
> > > designed a dual supply of 3.3V and 5.4V from 30 V using semtech
> > > SC2442H DC DC converter and Infineon BS0604NS2 Mosfet.
> > > The problem is that mosfet is getting heated up a lot, it goes to
> > > about 100 C.
> > > I have calculated the power, it turn to be 0.72 W and the Mosfet can
> > > handle upto 2 W. Can some one point why is the mosfet getting
> > > heated???Because of this the inductor and capacitor near it is also
> > > getting heated up.
> > > DC DC converter operating frequency is 250 KHz.
> > >
> > > Thanks and regards
> > > Praveen
> >
> > And the connection with Satellite's and GPS is ?
> >
> >
> It may have escaped your attention that sometime things are crossposted,
for
> example I am reading your post in the NG 'sci.electronics.design', which
> would seem to be appropriate ??
>
> --
> Regards ..... Rheilly Phoull
>
>

Yes I agree with you, but I still ask the question, what is the relevance to
Satellite's and GPS.?
All the replies are also coming to sci.geo.satellite-nav group, just because
the original person could not be bothered to check what groups he (she) was
sending to, and all the people replying just reply without checking where
their replies are going to.







Re: Mosfet heating Up in DC DC converter

>
> >
> > >
> > > > Hello,
> > > > I have a problem in power supply which i have designed. I have
> > > > designed a dual supply of 3.3V and 5.4V from 30 V using semtech
> > > > SC2442H DC DC converter and Infineon BS0604NS2 Mosfet.
> > > > The problem is that mosfet is getting heated up a lot, it goes to
> > > > about 100 C.
> > > > I have calculated the power, it turn to be 0.72 W and the Mosfet can
> > > > handle upto 2 W. Can some one point why is the mosfet getting
> > > > heated???Because of this the inductor and capacitor near it is also
> > > > getting heated up.
> > > > DC DC converter operating frequency is 250 KHz.
> > > >
> > > > Thanks and regards
> > > > Praveen
> > >
> > > And the connection with Satellite's and GPS is ?
> > >
> > >
> > It may have escaped your attention that sometime things are crossposted,
> for
> > example I am reading your post in the NG 'sci.electronics.design', which
> > would seem to be appropriate ??
> >
> > --
> > Regards ..... Rheilly Phoull
> >
> >
>
> Yes I agree with you, but I still ask the question, what is the relevance
to
> Satellite's and GPS.?
> All the replies are also coming to sci.geo.satellite-nav group, just
because
> the original person could not be bothered to check what groups he (she)
was
> sending to, and all the people replying just reply without checking where
> their replies are going to.
>
 Ahh, such is human nature. Better to 'bend with the flow' you are never
going to change this sort of thing (worst luck), theres always the old
killfile thingy :-)

Cheers.... R.P




Re: Mosfet heating Up in DC DC converter
> Hello,
> I have a problem in power supply which i have designed. I have
> designed a dual supply of 3.3V and 5.4V from 30 V using semtech
> SC2442H DC DC converter and Infineon BS0604NS2 Mosfet.
> The problem is that mosfet is getting heated up a lot, it goes to
> about 100 C.
> I have calculated the power, it turn to be 0.72 W and the Mosfet can
> handle upto 2 W.

This is a nice misunderstanding. The fact that your mosfet can handle 2 W
does not mean that it does not heat up at 0,7W. Check the thermal resistance
from the datasheet, multiply that with your power (0,72W) and this gives you
the temperature rise above ambient. If that gives you 100C, the circuit is
ok and you just need to cool the mosfet. If the calculated rise is lower,
you either do not have sufficient drive voltage to the gate (mosfet not
completely on) or you have an unwanted oscillation at a high frequence which
can also produce a lot of dissipation.

Meindert




Re: Mosfet heating Up in DC DC converter

> I have a problem in power supply which i have designed. I have
> designed a dual supply of 3.3V and 5.4V from 30 V using semtech
> SC2442H DC DC converter and Infineon BS0604NS2 Mosfet. The
> problem is that mosfet is getting heated up a lot, it goes to
> about 100 C. I have calculated the power, it turn to be 0.72 W
> and the Mosfet can handle upto 2 W. Can some one point why is the
> mosfet getting heated???Because of this the inductor and
> capacitor near it is also getting heated up. DC DC converter
> operating frequency is 250 KHz.

 Did your calculations allow for the switching losses?

 I've just been simulating a simple 1300 Hz PWM switch
 where the simulation shows that the MOSFETs dissipate
 about 2.5W each.  But only 1.5W of that is the "dc"
 loss, another 1W comes from the switching losses. In
 fact the simulation shows a peak of 160 V*I during
 each on/off edge.

--
Tony Williams.


Re: Mosfet heating Up in DC DC converter

> Hello,
> I have a problem in power supply which i have designed. I have
> designed a dual supply of 3.3V and 5.4V from 30 V using semtech
> SC2442H DC DC converter and Infineon BS0604NS2 Mosfet.
> The problem is that mosfet is getting heated up a lot, it goes to
> about 100 C.
> I have calculated the power, it turn to be 0.72 W and the Mosfet can
> handle upto 2 W. Can some one point why is the mosfet getting
> heated???Because of this the inductor and capacitor near it is also
> getting heated up.
> DC DC converter operating frequency is 250 KHz.

Multiposted to far too many groups. Reply the SED only.

The new SO8 FETS are indeed specified for 2W.
It is your problem to get rid of the heat though.
To give you an idea, a double layer copper on a pcb
of 1 inch in square  gets pretty hot with 1 W.

Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net


Re: Mosfet heating Up in DC DC converter
On 22 Dec 2004 00:33:59 -0800, snipped-for-privacy@rediffmail.com

>Hello,
>I have a problem in power supply which i have designed. I have
>designed a dual supply of 3.3V and 5.4V from 30 V using semtech
>SC2442H DC DC converter and Infineon BS0604NS2 Mosfet.
>The problem is that mosfet is getting heated up a lot, it goes to
>about 100 C.
>I have calculated the power, it turn to be 0.72 W and the Mosfet can
>handle upto 2 W. Can some one point why is the mosfet getting
>heated???Because of this the inductor and capacitor near it is also
>getting heated up.
>DC DC converter operating frequency is 250 KHz.
>
>Thanks and regards
>Praveen

Sounds like inadequate heat sinking. This is an SO-8 dual MOSFET, and
it doesn't have real good thermal properties to begin with. See
Infineon's application note on thermal considerations with their SO-8
devices:
http://www.infineon.com/cmc_upload/documents/086/819/ThermalPackageConsideration-DPAK-SO-8.pdf

If you are using the device without any provision for heat sinking,
you're going to see it run something close to 80K over ambient at 0.72
W. You need a low-thermal-resistance path to several square
centimeters of copper just to get the thermal resistance down to 60K/W
or so. If this isn't feasible, you need something in a different
package for which you can more readily arrange a proper heat sink.

--
Chris Green



Re: Mosfet heating Up in DC DC converter
Another one that will cause it to overheat is if the driver
circuit for the MOSFET either has too slow a rise/fall time
or does not drive it completely on or off.  Too much time
in the linear region causes lots of heat problems too.

mikey

> On 22 Dec 2004 00:33:59 -0800, snipped-for-privacy@rediffmail.com
> (praveen) wrote:
>
> >Hello,
> >I have a problem in power supply which i have designed. I have
> >designed a dual supply of 3.3V and 5.4V from 30 V using semtech
> >SC2442H DC DC converter and Infineon BS0604NS2 Mosfet.
> >The problem is that mosfet is getting heated up a lot, it goes to
> >about 100 C.
> >I have calculated the power, it turn to be 0.72 W and the Mosfet can
> >handle upto 2 W. Can some one point why is the mosfet getting
> >heated???Because of this the inductor and capacitor near it is also
> >getting heated up.
> >DC DC converter operating frequency is 250 KHz.
> >
> >Thanks and regards
> >Praveen
>
> Sounds like inadequate heat sinking. This is an SO-8 dual MOSFET, and
> it doesn't have real good thermal properties to begin with. See
> Infineon's application note on thermal considerations with their SO-8
> devices:
>
http://www.infineon.com/cmc_upload/documents/086/819/ThermalPackageConsideration-DPAK-SO-8.pdf
>
> If you are using the device without any provision for heat sinking,
> you're going to see it run something close to 80K over ambient at 0.72
> W. You need a low-thermal-resistance path to several square
> centimeters of copper just to get the thermal resistance down to 60K/W
> or so. If this isn't feasible, you need something in a different
> package for which you can more readily arrange a proper heat sink.
>
> --
> Chris Green
>




Re: Mosfet heating Up in DC DC converter
Quite so. Just that it is not strictly necessary to explain his
situation. His 100C temperature is consistent with his calculated 0.72W
dissipation and something around 100K/W thermal resistance. An SO-8
with no heat sink will do that without any further design flaws.
--
Chris Green



Mosfet heating Up in DC DC converter
Hello Mr. Meindert,

Thanks for the reply.

About maximum temperature rise:
Thermal resistance 15%0 K/w (50+100)
So temperature rise= 114 K so it means 50 C increase in temperature.
So junction temperature is around 80 c which very much below the
juction temperature (150 c). About the drive voltage higher FET has
around 35-40 V and lower 8-10 V.

Please correct me if i am wrong.
Is there some thing which i am missing???
Is have not provided any heat sink. My boss is not agreeing with any
PCB changes. If it is very much require i have to convince him.
It need your feedback from you people.


Thanks and regards
Praveen


Re: Mosfet heating Up in DC DC converter

> Hello Mr. Meindert,
>
> Thanks for the reply.
>
> About maximum temperature rise:
> Thermal resistance 15%0 K/w (50+100)
> So temperature rise= 114 K so it means 50 C increase in temperature.
> So junction temperature is around 80 c which very much below the
> juction temperature (150 c). About the drive voltage higher FET has
> around 35-40 V and lower 8-10 V.
>
> Please correct me if i am wrong.
> Is there some thing which i am missing???
> Is have not provided any heat sink. My boss is not agreeing with any
> PCB changes. If it is very much require i have to convince him.
> It need your feedback from you people.
>
Either get a new boss or go into biz with him.
--
Best Regards,
Mike


Mosfet heating Up in DC DC converter
Hello Mr. Tony,

Thanks for the reply.

Yes i did. 0.72 W include the total power losses.

Total conduction loss:0.27W
switching loss:
Upper FET: 0.45W
Lower FET: 0.03 W
Gate loss: 0.03 W(upper)+.0075 W(lower)
Switching frequency 250 kHz.
Average current 2A%
rise time/fall time30% nsec
 
Thanks and regards
Praveen


Re: Mosfet heating Up in DC DC converter

> Yes i did. 0.72 W include the total power losses.

> Total conduction loss:0.27W
> Average current 2A%.

 I think it should be RMS current for the
 I-squared*R power dissipation calculation.

 Any chance that your lack of heat sink puts the
 device into the dRds(on)/dT thermal runaway ambush?

 ie, The increase in Tj increases Rds(on), which
 increases the power dissipation, and if the heatsink
 is inadequate the resultant increase in Tj increases
 Rds(on) further, increasing Pdiss..... and so on.

 This phenomenon is nicely explained in International
 Rectifier App Note No. 942.

--
Tony Williams.


Mosfet heating Up in DC DC converter
Hello Chris,
Thanks for the reply.

I donot have any heat sink, but 80K over ambient temperature looks ok.
AS the junction temperature is around 150 C.

If i am wrong please correct me.

Thanks and regards
Praveen


Re: Mosfet heating Up in DC DC converter
> Hello Chris,
> Thanks for the reply.
>
> I donot have any heat sink, but 80K over ambient temperature looks ok.
> AS the junction temperature is around 150 C.
>
> If i am wrong please correct me.
>
> Thanks and regards
> Praveen

What you can do to improve the thermal resistance is to glue a heat-sink
onto the package. There are special glues for that so they do not get loose
with the high temperatures. This is of course only a bad substitute for a
better layout with large free copper areas as recommended in the
manufacturers data sheets.
--
ciao Ban
Bordighera, Italy




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