Diodes Current–voltage characteristic

In summary: If the diodes were in parallel I knew how to solve it or even if they were Zener's. But with them connected in series I'm not making any sense of this.
  • #1
du.art
3
0

Homework Statement


http://img39.imageshack.us/img39/7496/59187398.th.jpg [Broken]
VDON=0,7
First it is asked to calculate V0 for Vin=-1V and Vin=-5V.
Secondly it is asked to draw V0(Vin) for -10<Vin<10

Homework Equations



08d7bd7060be987d4da37b7fc263a740.png


The Attempt at a Solution



Using Kirchhoff Volt Law I've established that for Vin=-1V D1 is ON and D2 is OFF and for Vin=-5V D1 is ON and D2 is ON an I believe I got it right.
I have also determined that D1 conducts for a Vin< -0.7V and that D2 needs Vin<-1.4V. Right now I'm stuck at linking their current–voltage characteristic and determining the slope value, which depends somehow of the resistance values, so that I can build the V0(Vin) graph
 
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  • #2
du.art said:

Homework Statement


http://img39.imageshack.us/img39/7496/59187398.th.jpg [Broken]
VDON=0,7
First it is asked to calculate V0 for Vin=-1V and Vin=-5V.
Secondly it is asked to draw V0(Vin) for -10<Vin<10

Homework Equations



08d7bd7060be987d4da37b7fc263a740.png


The Attempt at a Solution



Using Kirchhoff Volt Law I've established that for Vin=-1V D1 is ON and D2 is OFF and for Vin=-5V D1 is ON and D2 is ON an I believe I got it right.
I agree.

I have also determined that D1 conducts for a Vin< -0.7V...
Yes.
... and that D2 needs Vin<-1.4V.
Not quite. Think of it this way:
With D2 right at the "on/off" threshold, it has 0.7V and 0 current. That means the current through the 1kΩ is ____?
And therefore the current through the 4kΩ is _____?
So the voltage across the 4 kΩ is ______?
And Vin would equal _____?

Right now I'm stuck at linking their current–voltage characteristic and determining the slope value, which depends somehow of the resistance values, so that I can build the V0(Vin) graph
You can replace each diode with either an open circuit, or a 0.7V source, depending on whether it is off or on, respectively.
 
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  • #3
Redbelly98 said:
Not quite. Think of it this way:
With D2 right at the "on/off" threshold, it has 0.7V and 0 current. That means the current through the 1kΩ is ____?
And therefore the current through the 4kΩ is _____?
So the voltage across the 4 kΩ is ______?
And Vin would equal _____?

With D2 right at the "on/off" threshold, it has 0.7V and 0 current. That means the current through the 1kΩ is 0.7mA
And therefore the current through the 4kΩ is 0.7mA
So the voltage across the 4 kΩ is 2.8V
And Vin would equal 2.8V

Am I right?

Redbelly98 said:
You can replace each diode with either an open circuit, or a 0.7V source, depending on whether it is off or on, respectively.

I can do 1 graph for each diode. My problem is when I try to put them together in order to represent the whole circuit nothing that I do makes enough meaning for me to call it an answer to the problem
If the diodes were in parallel I knew how to solve it or even if they were Zener's. But with them connected in series I'm not making any sense of this.

From what I can tell I'm getting a positive diode clipper similar to this one http://www.circuitstoday.com/wp-content/uploads/2009/10/Output-Waveform-Positive-Clipper-and-Negative-Clipper-300x123.jpg" [Broken] (graph on the left) but with its max Vout at -0,7V? Is that it? But wouldn't I get the same with D1 only?
 
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  • #4
du.art said:
With D2 right at the "on/off" threshold, it has 0.7V and 0 current. That means the current through the 1kΩ is 0.7mA
And therefore the current through the 4kΩ is 0.7mA
So the voltage across the 4 kΩ is 2.8V
So far so good. :smile:
And Vin would equal 2.8V

Am I right?
There are two problems with this last step.
1. Vin is not equal to the voltage across the 4kΩ resistor. Rather, it is the sum of the voltages across the 4kΩ, D2, and D1.
2. Keep in mind the polarity: which end of D2 has a higher potential at the on/off threshhold, and therefore in what direction is current flowing through the resistors?
 

1. What is a diode's current-voltage characteristic?

A diode's current-voltage characteristic refers to the relationship between the voltage applied across a diode and the resulting current that flows through it. It is represented by a graph that shows how the current changes as the voltage is increased or decreased.

2. What does the current-voltage characteristic graph of a diode look like?

The current-voltage characteristic graph of a diode is a curve that starts at zero current when the voltage is below a certain threshold, known as the forward voltage. As the voltage increases beyond the forward voltage, the current also increases rapidly until it reaches a saturation point and the curve levels off.

3. How does the current-voltage characteristic of a diode differ from other electronic components?

The current-voltage characteristic of a diode is unique compared to other electronic components because it only allows current to flow in one direction. This means that the current-voltage graph for a diode will look different when the voltage is reversed, with very little current flowing until it reaches a much higher reverse voltage threshold.

4. What factors affect the shape of a diode's current-voltage characteristic graph?

Several factors can affect the shape of a diode's current-voltage characteristic graph, including the type of diode, the materials it is made of, and the temperature. The physical structure of the diode, such as its doping levels and junction capacitance, also play a role in determining the shape of the graph.

5. Why is the current-voltage characteristic graph of a diode important in circuit design?

The current-voltage characteristic graph of a diode is important in circuit design because it helps determine how the diode will behave in a given circuit. By understanding the voltage and current relationship of a diode, engineers can design circuits that utilize diodes in the most efficient and effective way for a specific application.

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