| Magura |
Wouldnt it be possible to use a monster mosfet in a to-264 package rated 300W as an adjustable bias resistor that has to dissipate 200W??
Magura |
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| peranders |
| Sure, as long as the transistor chip not gets too hot... but this is not an easy task. |
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| Steven |
Why use transistors with all their temperature problems when you can use resistors? Resistors are allowed to get a lot hotter. I think of using these new planar resistors. They do not use an additional heatsink, are small enough, can dissipate 100W at 25*C and are allowed to go to 350*C. Still you can mount them on a PCB.
Example below is from Nicrom-electronic, but such devices are also manufactured by Ohmite, BI technologies, and RCD components. Now I only have to find a distributor that sells them in small quantities. Anyone?
Steven |
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| Christer |
Magura,
with that signature, why do you even ask? ;)
Adding to Stevens comment. Caddock also makes a few types
of rather small film-based resistors. Can't remember the
model numbers now, but check ut Elfa, they carry them. |
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| Magura |
| quote: | Originally posted by peranders
Sure, as long as the transistor chip not gets too hot... but this is not an easy task. |
How exactly would that be done...it sounds like you have an idea???
Cheers
Magura |
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| joensd |
| quote: | | can dissipate 100W at 25*C and are allowed to go to 350*C. Still you can mount them on a PCB. |
If you mount a big fan directly over them, they even might not desolder themself and stay on the PCB. ;) |
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| Magura |
| quote: | Originally posted by joensd
If you mount a big fan directly over them, they even might not desolder themself and stay on the PCB. ;) |
I too found it hard to implement them in something for my living room....i sure like the option to keep them sub 175C :)
Magura |
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| Nelson Pass |
I don't want you to think that I regard light bulbs as the
solution to all problems, but they make great power resistors,
and you can vary the values by paralleling several and
unscrewing the ones you don't want. I use this to put the
Zen Lite into low power mode, unscrewing 2 or 4 of the 6
light bulbs. |
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| Steven |
| quote: | Originally posted by Magura
I too found it hard to implement them in something for my living room....i sure like the option to keep them sub 175C :)
Magura |
When it comes to heating your room, I think it makes no difference whether you dissipate 100W in a huge heatsink mounted monster mosfet with the heatsink at 100*C, or in a relatively small resistor that can be 350*C, or even in a small halogen bulb that can be 2500*C. :hot: :hot: It's just 100W.
If you care about the accuracy of the resistor over the temperature range I'm sure these thick film ruthenium oxide resistors win. They change less than 5% over the complete temperature range from 25*C to 350*C. Power derating is linear from 100% at 25*C ambient to 0% at 350*C.
Inductance is also extremely low at <50nH.
I'm not 100% sure, but I have the impression that you can use them at full power without auto-desoldering from the PCB. The stands are designed with low heat conducting properties. Maybe you need a few square cm of copper area on the PCB for each stand.
Steven |
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| Magura |
What i meant was that its a lot nicer to have something like a heatsink at 65C than a resistor at 300C in your living room. I would like a sealed box, in order to avoid dust and whatever else that usually resides in an old amp ;)
A sealed box prevents me from using anything i cant mount on a heatsink or outside the box :(
Cheers
Magura |
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| Panelhead |
These arte now my resistor of choice. The 5 watt model is only available up to 0.3 ohms now. But I have some 0.536 ohm that must be discontinued. These are perfect for some applications.
These are 1%, non-magnetic metal strip power resistors. Seem to have very little sonic signature.
George |
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| Magura |
| quote: | Originally posted by Panelhead
These arte now my resistor of choice. The 5 watt model is only available up to 0.3 ohms
George |
Hmmm....i guess 5 W is a little short :)
100 W is more like what im looking to get around, hence the idea about the TO-264 mosfets. They could even be adjustable ;)
Cheers
Magura |
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| Steven |
Hi Magura,
Since you don't like hot resistors, you can just take a type that can be heatsink mounted. The temperature of the heatsink will not be higher than with a transistor mounted on the same heatsink, dissipating the same power. But this solution is more stable and can handle bigger peak loads. An example from Vishay is shown below. This one can handle 500W at 70*C, but you need a large heatsink to keep it that temperature while dissipating 500W.
Steven |
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| joensd |
Magura, you could try to contact Peter.
Have a look here.
I ordered a whole buch of 4Ohm power resistors (50W) from him, they were nice priced, sent off quickly, he´s a nice contact and he´s living in denmark as well.
Maybe he´s got some left.
Also think about putting multiple resistors in series to get your value and much nicer heat distribution.
Cheers
Jens |
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