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
was released due to inductive kickback. The simplest solution to snub
the kickback spike is to put a reverse diode, like a 1N4002, across the
relay coil (cathode side to the relay's '+' supply).
It's also possible the FET was defective or damaged to begin with, which
led to an early failure.
73,
Rich AC7MA
On 03/12/2013 01:28 PM, [email protected] wrote:
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 switching 1 or 2
ma,
hope that holds!
73 - Jim K8MR
____________________________________
From: [email protected]
To: [email protected]
Sent: 3/12/2013 12:07:26 P.M. Eastern Daylight Time
Subj: [Elecraft] KX3 Relay Control For Desktop Amplifiers
Most common desktop amps have a relay circuit that requires a transceiver
to short 12 VDC at 100 ma to key the amplifier on.
In the KX3 specs, the maximum amp relay current is stated to be 100 ma.
Has anyone keyed a desktop amp directly with a KX3 or is it recommended to
use an intermediate external relay circuit?
Thanks,
W9DBR
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