A Power Curve Tracer At Surplus Prices
by Dennis L. Feucht
Innovatia Laboratories
Curve tracers draw a graph of current versus voltage of electronic devices. They are usually used to plot the characteristic curves of transistors, but can also display diode curves, and the v-i characteristics of other two and three-terminal devices. A family of curves is drawn, each curve differing from the next by a change in a controlling quantity (or parameter), such as base current or gate voltage. A curve tracer not only can do pass/fail tests but the mode of failure can also often be determined.
The problem in equipping cost-sensitive electronics labs with a curve
tracer is simple: They cost too much! A Tektronix CT, such as the 576, can
run into thousands of dollars, even as used equipment. But there is one
vacuum-tube era CT, the Tek 575, on the surplus market for under $300. (For
instance, see www.electronicsurplus.com
in Cleveland, where the author found two good 575s languishing on the warehouse
shelf.) The 575 has a full-scale voltage of 200 V at up to 1 A and a 20
V range that can supply up to 20 A. That's 400 W of power -- well-suited
for testing power Darlingtons, diodes, MOSFETs, and IGBTs.
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