Reverse recovery time of Schottky diodes

You dope it till it goes metallic (i.e. the bandgap disappears). There are also some metals that form a Schottky junction with a negative barrier, i.e. the Fermi level is above the bottom of the conduction band, and they're used sometimes too.

Sputtering generally gives you better films (especially better edge coverage), but both are used.

Cheers

Phil Hobbs

Schottky photodiodes are made by putting an interdigitated metal pattern on silicon, which forms two Schottky junctions, i.e. effectively two diodes in series-opposing, with a potential well in the middle.

In order to get any photocurrent, you have to bias it to reachthrough, where the applied E field overcomes the slope of the well on one side, allowing the diode to conduct.

Cheers

Phil Hobbs

All it takes is a majorly different capacitance and ... PHUT ... *BAM* .... hisssss ... followed by a nasty stench.

No, has to be strictly catalog parts on the board level for this project.

All it takes is a mixed batch with significantly different capacitances. I've had that happen in an RF rectifier and there was immediate evidence of a breakdown, in the form of a puff of smoke wafting off and comments like "Well, that must have been George!".

It's not that bad. Even if leakage adds a couple hundred milliwatts that's peanuts in my case. The diode will have to be heatsinked anyhow.

Actually, they are more honest these days than, quote "This is why Trr numbers are published at very low forward current conditions (like 10 mA on a >1 A diode)". It's usually published at an amp or more. Still peak current in a bost converter with a 5:1 to 10:1 step-up ratio is several times the rated average current and things could get ugly up there. Don't want to find that out after the design because on many of them I realistically get only one shot.

How about multiple diodes in parallel, with balancing resistors?

That doesn't help with the trr problem because it seems all 200V+ diodes have it. All you'd be doing is scale down the effect and then, by paralleling, scale it back up again.

I don't want to hear your complaining. I have to design a boost converter that makes 5000 volts.

All of the HV diodes that I can find have huge Trr times, 50 to 500 ns.

Den onsdag den 30. juli 2014 23.35.52 UTC+2 skrev Joerg:

nothing here?

-Lasse

I did mine about 20 years ago, for defibrillator discharge compatibility testing. The client engineers called it "the death machine" because of all the warnings and skull & bones on it. Later, the agency compliance guy walks in to witness the tests. I turn on the unit ... *TUNGGGG* ... oooouuuuiiiieeee .... guy rolls his chair all the way to the other end of the room. I had placed a big easel in the central hallway, urging everyone to back-up frequently because of electrical stress tests that day. After xx runs the PBX phone system quit working, shortly afterwards someone hollered "HEY, my computer just froze up!"

Yeah, except for SiC. Which I might have to use. Grrrrr.

That's one way to pass tests: scare the inspectors away.

Microsemi? Cree?

Not really. They call some of them ultrafast but still state a trr of

There are some intersting ones but in the farily non-standard TO-277 package which, in 200V and higher, is only popular with Vishay and with Comchip (rather poor datasheets). If it doesn't work I'd be screwed. I'll try to stay with SMC, DPAK or D2PAK as these are more mainstream.

I asked him if he'd do the honors and press that big mushroom button. "Umm, ahm, well, you better do that".

Yep, looking at this one:

Unfortunately it has tons of capacitance so I'll look for a slightly smaller one because I only need around 12A repetitive peak surge.

The alternative is designing a transformer-based converter but that requires custom magnetics. Which would be a pain in this case.

Here, hold this wire for me.

Last words of a redneck: "Hold my beer and watch me now".

I meet EEs, usually younger ones, who are afraid to touch a powered-up board that they know (or should know) has a max 5 volt supply.

Systems I work on have over 300, 200 volt diodes in series to form a single rectifier..

Each one has a small cap and R around it and it operates in the

Jamie

A few years ago I designed a board for optical switches that need a couple hundred volts or so. The system had only 12V available and thus people may not realize that the converter on this board could really zing. So I figured I better place a big fat warning on there, "DANGER! High Voltage! - PELIGRO! Alta Voltaje!"

Guess who got bitten first ...