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Design Project: Simple Component Curve-Tracer Circuit
5 questions By Tony R. Kuphaldt
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Question 1 of 5
What do each of the oscilloscope axes represent, in real-life terms (variables and units) when used in conjunction with this curve tracer circuit?
Reveal answerHorizontal axis: voltage applied across terminals of device under test (1 volt displayed = 1 volt).
Vertical axis: current through device under test (1 volt displayed = 1 mA)
Notes:The resistor’s specified value of 1 kΩ should make perfect sense when students see the voltage:current ratio for the vertical axis!
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Question 2 of 5
What mode does the oscilloscope have to be set in, in order to use with this curve tracer circuit?
Reveal answerThe oscilloscope needs to be set in the “X-Y” mode.
Notes:It is important for students to realize that the oscilloscope will not produce the desired display if configured for the normal “time-domain” display. For the circuit to be able to work, the curve tracer must provide the horizontal sweep, hence the dual inputs to the oscilloscope.
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Question 3 of 5
If quantitative accuracy is desired from this curve tracing circuit, the shunt resistor should be precisely 1 kΩ in size. Explain how a precise shunt resistance may be built without the use of precision components (i.e. a special 1 kΩ precision resistor).
Reveal answerHint: there’s a saying in the electronics world that goes something like this: “Don’t make it precise, make it adjustable!”
Notes:Though it may have been a while since you last discussed how to achieve precise (adjustable!) values of resistance from non-precision resistors, students should at least remember the general concept if not the exact implementation.
