They have gate zeners, so a bit of d-s leakage won't blow them up. I don't think that will affect my application, either.
Not sure what you mean by that. Only one opto can be on at a time. There is a 1G resistor load to ground, so the upper fet always conducts a bit.
I guess I could add a big resistor or a zener to clamp the source voltage, but it probably doesn't need it. Some mosfets are surprisingly leaky, so a zener option might be prudent.
Ok i missed the fig. ASO on page p.4/7
Since it is a one shot overload, it's ok. Apologies.
Habib
Oh, don't apologize, we all keep learning stuff.
I just did this, to better understand the mosfet.
They don't guardband that 1500 volt rating much!
It looks downright readable with a simple inversion!
Whoever encoded it in a JPEG, I can't help that much though. Can't quite tell if the image was antialiased to begin with, or the JPEG was just that s***ty. The fine print is almost Panteltje level readability.
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website:
My layout guy likes those colors. I don't.
Yep. I inverted it with Paint Shop Pro... came out much better than yours ;-)
Sno-o-o-ort >:-}
...Jim Thompson
A peculiar thing to say as I use PSP7 ;-)
Tim
PSP8 ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at
Forgot to say... I converted black background to white and all other colors to black.
Since the bottom of that output totem-pole is tied to ground I'd not use a photocoupler there, thus giving me a nice handle for a controlled shutdown. ...Jim Thompson
That was just a screen capture. It's readable enough to show the idea.
nts.JPG
John,
You measure VGss = +-42V ! OnSemi gives absolute VGss = +-20V
Strange ! Habib.
They built a gate protection zener into the chip, and it zeners at 42 volts. They don't want you to apply a low-impedance voltage source to that zener, or you'll fry it. The 20 volt limit is very conservative.
Most mosfets have 20 volt abs max gate voltages, even unprotected ones.
I've tested a few non-protected mosfets, and the gates typically blow out around 70 volts. The test destroys the fets.
This is a pulsed power-dissipation situation, and thermal mass is your friend. You want to look at the Effective Transient Thermal Impedance plots, which show the extra power you can safely dissipate for a short time. But oops, Sanyo's datasheet doesn't have one for this part. :-(
We do have an SOE (safe operating-area) plot, called ASO. Looking at the 1ms line, this says we can do 100V and 8A for 1ms. That's 800W, so the MOSFET shouldn't blow.
Actually, the capacitor voltage is dropping as we go, so we'd be safe for 2x that rating, or 3x your 500W example.
Avalanche, no doubt.
Oops, I was looking at the 2sk4117LS datasheet. That's a 400V part, with a different plot, weird. It's likely the same die, with the same transient thermal properties. The 2sk4117 ASO plot says 800V and 1A for 1ms, or also 800W.
Yep. Solved a thermal dissipation problem on the TOW missile (~1972 when I ran the Dickson Electronics hybrid facility) by switching a hybrid (three-legged regulator) from a Aluminum TO-3 package to a steel TO-3... thermal mass keeps the temperature rise under control until target is reached >:-} ...Jim Thompson
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As you say we all learn something new every day ...
Best regards, Habib.
That's not so bad, 5% is what we usually get for MOSFETs. It's more than we get for electrolytic capacitors. With a MOSFET we're not in too dangerous territory using it all the way up to its rating, but with electrolytic caps we'd better keep a 10% safety margin below the official rating.
BTW, in any design where the MOSFET's junction temp rises, we get as much as an extra 10% in the avalanche voltage.
I haven't measured that much, but we did recently blow up some 100 volt fets with inductive kicks of 110 or so. These parts have no avalanche energy specs. We were making 100 volt pulses, through a transmission-line transformer, into 50 ohms in under 1 ns.
On the other hand, mesfets and phemts seem to be OK at over-voltages like 2x to 3x specified max. I think the RF boys automatically cut the real abs max in half, assuming that X volts of power supply makes 2x volts of swing into a resonant tank. Or something. The specs on RF part data sheets are usually miserable.
It's fun to blow up parts and measure things.
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