Add .5 degrees C per watt to accommodate the package to sink interface. That puts the junction 42 degrees above the sink.
I would try for junction at 130 to 140 C, or sink at 90C to be safe.
John
Determin8ng if something definitely can have an audible effect is very difficult and can only be certain for the cases where the result is "yes", and even then can be very tricky. Lots of things Ive done seem to have audible effect for me, but it would be foolish to neglect that it might be only becaus it was me who DID those things. So how can you expect an answer to question#1?
For question#2, because it MIGHT be audible, and we're technogeeks and might not want to worry whether something is hurting the sound experience. And because its a hobby.
If one wants to examine the internal metal workings of a plastic enclosed device, I recommend DMSO as a solvent, it will strip off the plastic without mechanical intervention.
Handle appropriately, it will go thru anything except glass and some plastics, smells kinda awful, is readily available at the feed and seed store as people use it on animals.
Other solvents?
Cheers
Alan
Handle appropriately, it will go thru anything except glass and some plastics, smells kinda awful, is readily available at the feed and seed store as people use it on animals.
Other solvents?
Cheers
Alan
Permanent solution for some problematic ambient.
Not necessary for measurement at that accuracy.
The ON Semi devices have a metal back, but I'm using Fairchild devices that are completely encased. I'm sure it's very thin on the back of the device. With the metal back you need to put an insulator between the back and the heatsink so don't think a little bit of plastic is going to be much worse than a mica or silicone pad. Just grease up the back and cinch it down. Easy peasy.
se
DMSO is a nice solvent (read: nasty) for certain plastics, but Scott is right here that these are quite chemically resistant epoxies. Fuming nitric is certainly one way to get there, although I would worry what that would do to the bondwires. Of course, my natural solution to any organic problem tends to be piranha (3:1 concentrated H2SO4 to 30% H2O2, generally heated to boot). 😀
Edit: just read up, dilute nitric dissolves aluminum, but concentrated nitric passivates the aluminum surface. Learn something new!
Likewise, not sure how much thermal paint is (and how small of quantities are available), but given the application, might that work?
SE,
I understand your trepidation with ruining one of only two prototype boards but what are the chances that you would actually damage the boards even if you over-temp a device? As far as someone leaving the unit on in a room and locking up the house and seeing anything like 50 degrees C is rather slim chance I would think. 50C is 122F, that is damned hot for a closed house, I don't think I have ever experienced that in a house, now a closed truck or car yes, but a room in a house! Just glue on the therm o-couple and slowly increase the temperature while monitoring the case temp. if you get close to the limit you know you have a problem, if not your safe in 99.9% of all cases. Production units are going to be a different story, you can't control for every variable, if someone lives in the Mojave desert and leaves the unit on when the ambient temp goes to 120F and the windows are all closed the unit may just be toast but who's going to do that? In that case a fan that switches in at a high set point would be the only solution.
Me think you over thinkin this!
I understand your trepidation with ruining one of only two prototype boards but what are the chances that you would actually damage the boards even if you over-temp a device? As far as someone leaving the unit on in a room and locking up the house and seeing anything like 50 degrees C is rather slim chance I would think. 50C is 122F, that is damned hot for a closed house, I don't think I have ever experienced that in a house, now a closed truck or car yes, but a room in a house! Just glue on the therm o-couple and slowly increase the temperature while monitoring the case temp. if you get close to the limit you know you have a problem, if not your safe in 99.9% of all cases. Production units are going to be a different story, you can't control for every variable, if someone lives in the Mojave desert and leaves the unit on when the ambient temp goes to 120F and the windows are all closed the unit may just be toast but who's going to do that? In that case a fan that switches in at a high set point would be the only solution.
Me think you over thinkin this!
Last time we bought thermo-chromic liquid crystal paint it was very expensive. There's cheap arts and crafts stuff set up for around body temperature which probably does not help.
A solution in search of a problem.
(and that's assuming that the pair really are 75 Ohm)
Yes, I know it's a rather slim chance. I'd just like to know if it would survive it or not. And it may not destroy a board if one of the output devices pops, but I can't be sure.
I think I've finally decided to just not worry about it right now. The pre-production units will be going to select people. I'll wait until we have production boards and I'll just build one up, put it in the oven and see what happens.
se
I've done it on potted cubes, when it was done even the transistor cases were gone.
I'd rather not use fuming nitric acid 🙂
I'm sure the acid is faster, took a couple days of soaking.
Cheers
Alan
I would be very careful with DMSO. I had some spilled on my pants, and it carried the green dye into my system. I got quite ill.
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