Well let me say I share everyone's frustration. I myself do not want to use this part, but it works faithfully at 185 degrees Celsius which is a requirement of this application (nevermind what datasheet about temp., i assure you it works). With this temp restriction, I only have limited choices.
...

Eeks!

Lead tin solder starts to melt around 180'C. And every cap, resistor and inductor will be rated for 85'C max apart from some specialty 105'C parts and maybe some MILspec parts at 120'C. Never mind the "zener diodes" you just asked about.

Is this another troll fest?

...re 185'C ...(nevermind what datasheet about temp., i assure you it works)...

Yep, ignore the datasheet max temps and ask random internet strangers to improve your circuit and make it work. That's the way to design a product.

 

I'm not frustrated. I'm only suggesting that you're not bound to that particular configuration.

The op mentions a temperature if 185C - that's more than the melting point of 60/40 solder, but I don't remember off hand what it is for lead-free.

Either way, its sailing close to the wind as far as reliability is concerned.

Having said that, once I was called out to an allegedly portable TV (it had a handle on top) which was capable of 12V operation but more likely to be used on mains. When I took the back off, there was a TO5 transistor laying in the bottom of the case - it had run hot enough to melt the solder and the owner (a little old lady) dislodged it by thumping the set when the picture went all wavy.

The original cause was a flaked out reservoir electrolytic - the TO5 transistor checked out OK, so once I'd replaced the electrolytic I put the transistor back where it fell out of.

 

Hmm. I guess if I were going to run outside the spec. I'd try to get a FET with a high temperature rating and oversize it for the current. Maybe like this one?
http://www.mouser.com/ds/2/149/FDD5614P-93137.pdf

Same with the Schottky diode.

 

I knew that was the response I would get, that's why I never mention the environmental conditions and restrictions. I am using a high melting point solder for use at 220C, my pcb will be spec'd out to work at 200c, I am also using components that are known to work at these temperatures, regardless of what datasheet says. They are proven and reliable. From performing search after search I found that Texas Instruments has a software called SwitcherPro, which I absolutely highly recommend!! i simply input min input voltage, low input voltage, output voltage and output current and voila. Out came an optimized schematic for optimal efficiency, with a BOM, Analysis report, Stress Test, Efficiencies accross diff load conditions, even suggestion on layout.

Thanks for your help on this. Cant wait to pop this baby in the oven while baking a chicken.

 

I knew that was the response I would get, that's why I never mention the environmental conditions and restrictions. I am using a high melting point solder for use at 220C, my pcb will be spec'd out to work at 200c, I am also using components that are known to work at these temperatures, regardless of what datasheet says. They are proven and reliable. From performing search after search I found that Texas Instruments has a software called SwitcherPro, which I absolutely highly recommend!! i simply input min input voltage, low input voltage, output voltage and output current and voila. Out came an optimized schematic for optimal efficiency, with a BOM, Analysis report, Stress Test, Efficiencies accross diff load conditions, even suggestion on layout.

Thanks for your help on this. Cant wait to pop this baby in the oven while baking a chicken.

Sure that's not a turkey?

 

Maybe it's F & not C??

 

Maybe it's F & not C??

The OP seems clear enough that its "degrees celcius".

 

I will perform testing at 185c in other words 365f. ok, turkey sounds more like it, except that the test target goal is 250 hours. Turkey will b long gone by then!

 

Take a look at life curves for electrolytic capacitors vs temperature. Maybe 250 hours.
What current do you plan on for this

 

http://www.avx.com/docs/catalogs/thj.pdf

 

250ma tops

 

http://www.avx.com/docs/techinfo/tantcapt.pdf

$20 Cool. They have a 200C one for $75

 

I hadnt seen these before thanks. I wouldnt be surprised if they are exactly the same part except that they are pre-screened to meet certain criteria.

 

Take a look at life curves for electrolytic capacitors vs temperature. Maybe 250 hours.
...

And the reduced life of the semiconductors. I'm not sure what "tests" the OP did to prove the parts can handle running at that temperature but I am sure their operating life will be shortened by a huge amount.

We have to be careful in SMD reflow to only keep the parts at a high temperature for seconds, or the failure rate of the parts and product go through the roof.

 

Where does this go that it needs to run at 200C?

 

Here is a pretty good diode.
http://www.diodes.com/datasheets/apd/SBR20150.pdf


I've seen designs like this where someone comes across a combination that works even though the specs don't look like it, but usually it is something like an op amp that has better noise or offset - or something like that.

 

And a nice inductor for $130.

http://www.mouser.com/catalog/specsheets/04x04_in_High-Current.pdf

 

I have a $1 inductor I just ordered that does wonders. http://www.epmag.com/item/New-downhole-components-meet-for-extreme-high-temperatures_121596

 

Ahh, so money is no object.
I understand now why your boss insists on this chip. Someone probably worked long and hard to find one that would work so far out of spec..
Better by a bunch before TI cost reduces it.