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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Re: Be careful as the cathode may be connected to the tab... posted by ABliss on December 31, 2006 at 16:24:21:
The easiest is with a multimeter that has a diode function. These read out a voltage that comes from applying about three volts through a resistor to the device attached to the test leads. The diode will read the open-circuit voltage in the reverse direction, and some value between 0.5 and 1.2 volts in the forward direction. HexFREDs will read a little higher than conventional silicon rectifier diodes in the forward direction. Compare the diodes to a known-polarity rectifier to be sure of the meter polarity.If you lack such a multimeter, but have a simple one, you can gin up your own test circuit with a couple of dry cells and a resistor of about 1000 ohms or higher. Test for the voltage across the diode as above.
If you know the manufacturer of your diodes, you can likely find a web page similar to the IR page I referenced. It is likely your diodes have the same pinout as the IR diodes, since they are sold into the same market.
HexFREDs and similar rectifiers have a good reputation because they reduce a common problem in linear power supplies. Conventional (p-n junction silicon) recifier diodes store some electrical charge as part of the process of forward conduction. When the applied voltage reverses, this charge is swept out of the diode as a reverse-current pulse with a very steep trailing edge. The trailing edge steepness contains a lot of RF energy that stimulates the transformer and remainder of the AC supply circuit to ring. The ringing is a resonant phenomenon that induces noise in nearby audio circuits.
HexFREDs were designed to minimize the stored charge because this is a significant power loss mechanism in switching power supplies. These types of diodes are good for audio, but the DIY audio market is far too small to have supported their design and production. More and more switching power supplies are being used, so I'm sure the demand for these diodes is growing.
There are now some high-voltage Schottky rectifiers made of silicon carbide. The Schottky diode does not store charge in the same way as silicon p-n junction diodes. The down-side of these is that silicon carbide is a refractory material and very difficult to make in single-crystal form. CREE makes silicon carbide Schottky rectifiers, but I've heard of reliability problems with the early versions.
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Follow Ups
- A couple of ways to identify polarity... - Al Sekela 11:09:00 01/01/07 (3)
- Re: A couple of ways to identify polarity... - ABliss 14:27:56 01/01/07 (2)
- He's wrong. - Al Sekela 14:45:51 01/02/07 (1)
- But aren't we all? ...at times - pmkap 13:05:00 01/05/07 (0)
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