In my application, I am using a MAX6699 for monitoring the temperature of the PCB. The chip supports four channels, whereas I am using only 2 for monitoring the PCB temperature (through P-N diode). Now I have an additional requirement of monitoring the temperature of the metal enclosure of my system also. Since I have 2 spare channels in the above device, my first choice would be to use that to do the job.
However, the P-N diode which I used CMPT3906 is SMD and cannot be used on the chassis for monitoring. And I couldn't find any other component which is both chassis-mountable and can interface to my sensor through a cable or some discrete wires. Can anybody suggest me a solution?
Best Answer
Diodes are not as good as diode-connected transistors in this kind of multi-current \$\Delta V_{BE}\$ temperature measurement circuit. I note that the part number you specify is actually a BJT, not a diode.
Recall the ideality factor that is close to 1 for a diode-connected transistor and more like 2 for a diode.
The manufacturer also has detailed recommendations for the type of transistor to be used, and recommends that large power transistors not be used.
You could try a small power transistor such as a BD159STU (That one is in the convenient TO-126 through-hole package), or simply make a small PCB with the SMT part on one side and no tracks or vias on the other, and attach that to the panel (that's probably what I'd do- it could be connectorized, and made as a snap-off bit attached to some other board).