I-v curve measurement CVS or CCS ?

Thread Starter

Kih

Joined Nov 3, 2011
10
Hi All !
I am going to measure the iv curve of a thermoelectric material(small resistance) using a curve tracer.
However, I have no idea what are the cons%pros when using constant voltage source(or constant current source)......:confused:
Or how to evaluate both methods......
Hope you can share your experience~

Thanks in advance!:D
 

someonesdad

Joined Jul 7, 2009
1,583
As the current is always related to the voltage through the definition of resistance, take your pick. I don't have a curve tracer, but when I want the i-V characteristic of something, I hook it up to a DC power supply and run things in constant current mode and measure the voltage drop across the device. But this is just habit -- I could just as easily put a constant voltage across the device and measure the current. Probably one reason I use a constant current is I have a fairly-well developed engineering judgment that comes from letting the magic smoke out of things. This means I can usually spot when I'm running too much power through things before I damage it (OK, well, if you call me on it, the judgment comes more from those white burns on the whorls of my fingertips :p).
 

Ron H

Joined Apr 14, 2005
7,014
As the current is always related to the voltage through the definition of resistance, take your pick. I don't have a curve tracer, but when I want the i-V characteristic of something, I hook it up to a DC power supply and run things in constant current mode and measure the voltage drop across the device. But this is just habit -- I could just as easily put a constant voltage across the device and measure the current. Probably one reason I use a constant current is I have a fairly-well developed engineering judgment that comes from letting the magic smoke out of things. This means I can usually spot when I'm running too much power through things before I damage it (OK, well, if you call me on it, the judgment comes more from those white burns on the whorls of my fingertips :p).
You have probably had at least one white (or red) "D" on a fingertip from touching a TO92 package at the wrong time. I know I have. :eek:
 

DickCappels

Joined Aug 21, 2008
6,306
If the resistance of your thermoelectric material changes with temperature, you will probably want to sweep through the IV curve manually, going very slowly so that the thermal lag inherent in the device does not distort the curve. Of course going very slowly would mean that a scope with infinite persistence would be beneficial. You can also sweep through the IV curve more quickly and compare that with the slow curve to get an idea of the thermal lag inherent in the device.

The circuit at the URL below was intended for very small PTC thermistors and the occasional diode and is limited to about 50 ma and 2.5 volts. You might gain some inspiration for your own circuit from it.

http://cappels.org/dproj/CURVE_TRACER/CURVE_TRACER_MANUAL.html
 

Thread Starter

Kih

Joined Nov 3, 2011
10
agree . I can always take a look at the current so that i can know how much power is absorded by the device....
 
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