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Registered Member #1667
Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 374
You're right. I should have looked at the datasheet first. I thought IAmSmooth intended to put two separate diodes in parallel but the diode he plans to use can be used as a 2x 30A double diode or a single (paralleled) diode. I just hope that 100V will be enough in his application.
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
As Steve said co-packed Schottky diodes are fabricated on the same wafer at the same time so have excellent matching of intrinsic properties. The close proximity achieved by sharing one die and heat-spreader also means that if one device heats up, they both do. The device properties (particularly Vf) track each other and current sharing is maintained.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Although the 'ideal' V-I curve is exponential and very temperature dependant, real diodes have series resistance which dominates the V-I curve at high current, so any two similar diodes in parallel; will NOT share current at 'low' currents but WILL share when used as high current rectifiers.
Registered Member #2123
Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312
Where I work, we don't package dual die (not scribed apart) from the same wafer, although the die will often be from the same wafer, in our dual diodes (Schottkey and DQ ultrafast) unless by special customer order. Our apps. folks say matching in duals would be close but not exact. I'd still prefer to use one 60A diode than two 30A diodes in a dual package wired parallel.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Interesting... Where do you work, APT?
While we have a semiconductor expert on the line, I have a question. Hi-fi designer Douglas Self once used the MOSFET models in PSpice to "show" that MOSFETs had worse crossover distortion in audio amps than BJTs. Lately I'm starting to think, well, he showed that the models have terrible crossover distortion, but how well do they model the real devices down near threshold, as they're only just starting to turn on?
I have some N/P pairs of lateral MOSFETs made for audio, and I can't get anything out of them that looks like Self's results. In fact, I can't measure any crossover distortion from them at all! I wondered if the maker could do some sort of tweak to them to smooth out their behaviour at low currents, so they cross over smoothly, but Spice can't model it because it doesn't fit the model.
If this gets anywhere I can split it into another thread, otherwise please excuse the digression!
Registered Member #1667
Joined: Sat Aug 30 2008, 09:57PM
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"Why do hot dogs come in packages of ten, but hot dog buns only come in packages of just eight?"
well I think they are handy in combination with center-tapped secondary windings to get a full bridge-like combination of the half waves with only one p-n junction in the way.
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
That diode has two leads because one probibly can't handle the current in operation. The case connection is one of the connections (like bolting it directly to a heat synk) and then the center lead is cut and the two anode leads connect to the source of the fet
Registered Member #2123
Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312
I work at what used to be APT but is now Microsemi Power Products Group. I'm their wet etch/dry etch/ gold electroplate process engineer, not their semiconductor expert. I defer to our device engineers when I have a question.
But to get back to your query, linear N-ch mosfets we make use an assymetrical gate structure, two different thickness gate oxides under one gate finger (hundreds of such gate fingers in parallel), hence two different threshold voltages. I don't believe we make a P-ch linear device.
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Schottkys in parallel
