# Diode and c.r.o. question

1. Nov 7, 2005

### 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?

2. Nov 7, 2005

### Ouabache

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)

3. Nov 8, 2005

### QueenFisher

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.

4. Nov 8, 2005

### Integral

Staff Emeritus
What is a c.r.o. ?

5. Nov 8, 2005

### andrevdh

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: Nov 29, 2006
6. Nov 8, 2005

### Ouabache

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: Nov 9, 2005
7. Nov 9, 2005

### andrevdh

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.

8. Nov 9, 2005

### Ouabache

Why is it a negative DC bias? What are some example magnitudes for turn-on voltage of a diode (Ge, Si, PIN) ?

9. Nov 14, 2005

### andrevdh

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. Nov 14, 2005

### lando45

yeah it depends really