[time-nuts] Diodes as temperature sensors

Al Wolfe alw.k9si at gmail.com
Sun Jul 20 22:07:42 EDT 2014

Back in the 1970's I was tasked with coming up with a thermometer that could 
be read in the studio of an AM radio station. I bought a Heathkit 
indoor-outdoor unit. It worked great at night but was all over the place in 
the daytime when the AM transmitter was on the air. Turned out the sensor 
was just a silicon diode forward biased. A small ceramic capacitor across 
the diode sensor fixed the RF sensitivity.

Apparently, the forward biased silicon diode was temperature sensitive 
enough that a small D.C. amplifier could drive a meter to read-out with 
reasonable accuracy. Well, maybe not accurate by Time-nut standards but 
close enough for its intended purpose.

A lot of better audio amplifiers use a silicon diode as a temperature sensor 
in the output stages to sense the case temperature to control the biasing 
and prevent thermal run-away.

Seems like there are IC's that contain two diodes, one as a sensor and one 
as a heater. Part numbers escape me now.

Al, retired, mostly 

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