Using a FET as a rectifier?

[k4kyv]

Has anyone ever tried using a FET as a rectifier in place of a simple diode?  I know that the grid can be strapped to the plate of a triode and the tube will function as a diode.  This has an advantage over a silicon or germanium diode because the forward bias required for conduction is extremely low, while with a solid state diode it is a large fraction of a volt.  This makes the diode tube a sensitive detector because it will rectify extremely low voltages.

Since FETs can be used in many of the same ways as tubes, I was wondering if a FET would behave similarly to a triode tube, if the gate and drain are tied together, and it is used as a diode.  I was thinking that this might make a better substitute for the galena crystal in a crystal set than a diode like a 1N34.  Generally, commercial diodes work poorly in xtal sets because of the high forward bias required for the diode to conduct, while the galena requires very little forward bias.

[WBear2GCR]

A JFET will act as a constant current source... they sell them that way with different ratings based upon their IDSS (where they bias up to off the chip).

Not sure what a MOSFET will do, but suspect it won't do that much since it needs a positive bias to turn on... but might work above the threshold... wait... yep they do just that with what are called HEXFREDs, IR makes 'em, soft recovery power diodes.

                     _-_-bear

[WA1GFZ]

Don,
Try a 1N5711 or better yet a 1N5712. Same voltage drop as a 1n34 but about 100 times better leakage and much faster
FETs are used as sync rectifiers in power supplies and you would be surprised to know they are connected backwards so the internal diode conducts until the gate is switched on for an even lower resistance. That won't work in a crystal radio unless you build a sync detector into the radio to drive the FETs.