I blew the switching FET with about 50 ma of current (12 volts) from a
DownEast Microwave transverter. Elecraft says it should have handled it, but
anyway, FWIW.
The FET has been replaced, and an intermediate switching transistor
installed in the switchbox for the several transverters. Now
A very simple device I use for amp switching is a reed relay from Radio
Shack (part # 275-233) that I power with a 9 volt battery. I have been
using this device for years on may rigs and it works fine.
Of course there are no solid state devices used on a well designed
circuit board, nor a
Jim,
The FET shouldn't have had any problem with 50 mA. It's a 2N7002 and is
rated for 115 mA continuous and 800 mA pulsed, with 60V max voltage when
off. One possibility is that the load being switched was inductive
(like a relay), and the FET's voltage rating was exceeded when the relay
The 2N7002 has an internal diode for any inductive collapse.
Sent from my iPad
Chuck, KE9UW
(Jack for BMW motorcycles)
On Mar 12, 2013, at 6:58 PM, Rich Heineck ric...@frontier.com wrote:
Jim,
The FET shouldn't have had any problem with 50 mA. It's a 2N7002 and is
rated for 115 mA
Isn't the 2N7002's internal diode arranged to conduct if the drain is
negative with respect to the source, but the inductive spike from low
side switching will be positive with respect to the drain?
What you really want for this situation where the relay is presumably
inaccessible and hence
There's a drain-source diode, but it doesn't protect the 2N7002 in this
configuration. Typical sink-to-ground relay driver circuits put a diode
across the coil so it keeps the switched side of the relay from going
way above the supply voltage when the relay is turned off.
Rich AC7MA
On
The DEM transverters also have the diode snubber.
So things remain a mystery, hopefully never to repeat.
73 - Jim K8MR
In a message dated 3/12/2013 8:02:08 P.M. Eastern Daylight Time,
c-haw...@illinois.edu writes:
The 2N7002 has an internal diode for any inductive collapse.
In my case the FET failed somewhat gradually. I made several QSOs by
momentarily turning off the transverter power. When I turned it back on, it
came
up in receive mode. Then I'd transmit, power cycle the transverter to
return to receive, and repeat.
After several such QSOs power cycling
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