Understanding Diode Display on a C.R.O.

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Homework Help Overview

The discussion revolves around understanding the cathode ray oscilloscope (C.R.O.) display for a diode, particularly in the context of AC input signals and their representation on the oscilloscope. Participants are exploring the characteristics of the voltage over time as it relates to diode behavior.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are attempting to clarify whether the C.R.O. display for a diode would resemble that of an AC input, with reflections of negative portions of the waveform. Questions about the nature of the input signal and the diode's characteristics, such as biasing and conduction thresholds, are also raised.

Discussion Status

The discussion is active, with participants providing insights into the behavior of diodes in circuits and the implications for oscilloscope readings. Some guidance on the expected waveform characteristics has been shared, though multiple interpretations of the setup and conditions are being explored.

Contextual Notes

There are mentions of specific diode types and their turn-on voltages, as well as the impact of circuit configuration on the observed waveform. The discussion also highlights the need for biasing in diode operation.

QueenFisher
i have to draw the c.r.o. display for a diode, is it just the same as for an a.c. input but with the parts that were below the x-axis, intead reflected in the x-axis?
 
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I don't quite follow you.. Are you supplying AC to a diode (and hopefully a load resistor) and looking at the time varying characteristics of voltage on a scope? Or are you interested in the voltage versus current charateristics of the diode which can be measured with a curve tracer? (See second to last row for diode examples)
 
i assume that i have a circuit with a diode in it, connected to a c.r.o., and i have to draw the voltage/time shape that it would produce. e.g. for mains ac you would get a sinusoidal wave form - that's the kind of setting I'm on.
 
What is a c.r.o. ?
 
The signal will be clipped on one side, this is actually when the diode is conducting - it's resistance is low. In the attachment the zero voltage level is the dotted line.
 
Last edited:
Integral said:
What is a c.r.o. ?
c.r.o. - cathode ray oscilloscope

andrevdh that's right, only one half of the cycle would be displayed, the other half is clipped. (though on yours, it appears, there was a negative dc bias applied as well).
QueenFisher, can you guess what a diode in this configuration, is also called?
 
Last edited:
What I am try to indicate is that the diode needs a bit of bias (depending on the type of diode) before it starts to conduct. It does not conduct straight away.
 
andrevdh said:
What I am try to indicate is that the diode needs a bit of bias (depending on the type of diode) before it starts to conduct. It does not conduct straight away.
Why is it a negative DC bias? What are some example magnitudes for turn-on voltage of a diode (Ge, Si, PIN) ?
 
It just depends on which way round you connect the diode or the oscilloscope in the circuit. I could just as well have drawn the mirror image of the diagram. The forward voltage drop is usually of the order of 1 volt (0.6 for silicon diodes).
 
  • #10
yeah it depends really
 

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