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Vintage threads from the first ten years
| previous: Rob W. Hello :-) |
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Re: Silicon? Glass Passivated? ?
 10/4/1999 4:12 PM |
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| kg | Re: Silicon? Glass Passivated? ?
Glass passivated diodes have the junctions encased in glass. This protects them better from the environment, particularly humidity. Most diodes should be glass passivated. Fast action diodes are optimized to have a smaller junction capacitance, and a smaller amount of reverse current flow when the diode turns off. This makes the tiny back-surge of electrons SMALLER, which means that the diode isn't contributing so much noise. For example, a 30 nS Trr (reverse recovery) is damned good for a diode. Schottkys, due to their different mechanism, generally are around the 1 nS mark. They are very quiet diodes that do not produce much HF hash as they turn on and off. Other diodes, like the ubiquitous 1n400x, have MUCH larger Trr's, and as a result are much noisier. I don't recall the exact Trr, but it's something around a couple of microseconds. Orders of magnitude bigger, in any event. Generally you can quency these tranients with good snubber networks around the diodes. The smaller the transients are, obviously, the less work you have to do to quench them, or the quieter you can ultimately make them. 'Tis always better to make no noise to begin with, than to try to quiet it down after the fact. For the small extra cost it takes, I always go with the fastest diodes I can find that can take the current. The Trr's are not always listed, however. Even one step better than an ultra-fast recovery is a SOFT recovery as well. This is a more gentle turn off characteristic that creates even less upper harmonic energy as the diode ceases conduction. Ken | |
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| Rob W. Thank You Very Much KG!!! |