Using Ideal and Constant Voltage Drop Models

In summary, the conversation revolves around analyzing a diode circuit using an ideal diode model and a constant voltage drop model. The initial circuit is redrawn to simplify the analysis. There is a discussion about the assumption of a 0V voltage drop for the ideal diode and the resulting short circuit in one of the resistors. The conversation concludes with the acknowledgement that this assumption makes the solution easier to obtain, but in practice the Vf versus If curve in the diode datasheet should be used for more accurate results.
  • #1
NBaumbick

Homework Statement


I am practicing diode circuit analysis for an ideal diode model and constant voltage drop model.I have an initial circuit shown here:
20170930_194140.jpg

Which I then redraw to look like this:
20170930_194155.jpg

I want to make sure my process in redrawing this was correct. When I attempt to get current through the two resistors, if I assume the diode is on in the ideal instance, I obtain a value for I1 but wouldn't that end up short circuiting the path to the second resistor giving a result of 0Amps for I2?
 
Physics news on Phys.org
  • #2
NBaumbick said:

Homework Statement


I am practicing diode circuit analysis for an ideal diode model and constant voltage drop model.I have an initial circuit shown here:
View attachment 212044
Which I then redraw to look like this:
View attachment 212045
I want to make sure my process in redrawing this was correct. When I attempt to get current through the two resistors, if I assume the diode is on in the ideal instance, I obtain a value for I1 but wouldn't that end up short circuiting the path to the second resistor giving a result of 0Amps for I2?
Welcome to the pf.

I didn't follow your re-draw part, but basically the diode will clamp/limit the voltage cross its parallel resistor to whatever you are given for Vf of the diode (0.6V? 0.7V?)...
 
  • #3
berkeman said:
Welcome to the pf.

I didn't follow your re-draw part, but basically the diode will clamp/limit the voltage cross its parallel resistor to whatever you are given for Vf of the diode (0.6V? 0.7V?)...
I'll use 0.7V for the constant voltage drop method but I have to be able to analyze a circuit like this using the ideal diode model as well which is where I am having trouble.
 
  • #4
You have chosen 0.7V for your initial ideal diode equations. Vf of a diode depends on If for a real diode.

I guess the super-ideal diode situation assumes 0V=Vf. Can you show your work for that assumption?
 
  • #5
I can try but it is basically still the picture representation. If I assume the diode to be on it is replaced with a short circuit and considering both paths are going to ground, doesn't this basically make a jumper wire effect?
 

Attachments

  • 20170930_210452.jpg
    20170930_210452.jpg
    25.2 KB · Views: 511
  • #6
I can try but it is basically still the picture representation. If I assume the diode to be on it is replaced with a short circuit and considering both paths are going to ground, doesn't this basically make a jumper wire effect?
20170930_210452.jpg
 
  • #7
Yes, if the diode Vf is 0V, then the one resistor is shrted and you are left with only one resistor.
 
  • #8
Ok, it seemed suspicious that a practice problem should want the current when the resistor is shorted. Thank you for affirming.
 
  • Like
Likes berkeman
  • #9
Welcome. And in the more practical circuit analysis problem, you would use the Vf versus If curve published in the diode datasheet to write the equation to figure out the currents and voltages. Using the Vf=0V ideal diode assumption just makes that solution easier to get to. :smile:
 
  • Like
Likes NBaumbick

1. What is the Ideal Voltage Drop Model?

The Ideal Voltage Drop Model is a theoretical model that assumes all components in an electrical circuit have zero resistance. This means that the voltage drop across each component is also zero, resulting in a constant supply voltage throughout the circuit.

2. What is the Constant Voltage Drop Model?

The Constant Voltage Drop Model is a simplified version of the Ideal Voltage Drop Model that takes into account the small resistance of components. In this model, the voltage drop across each component is considered to be constant, resulting in a slightly lower supply voltage throughout the circuit.

3. When should I use the Ideal Voltage Drop Model?

The Ideal Voltage Drop Model is best used in theoretical or ideal scenarios, such as in academic studies or simulations. It is not practical for real-world applications as it does not accurately reflect the behavior of components with non-zero resistance.

4. When should I use the Constant Voltage Drop Model?

The Constant Voltage Drop Model is suitable for real-world applications where the components have small resistance and the voltage drop is negligible. This model is often used in circuit design and analysis to simplify calculations and provide a close approximation of actual circuit behavior.

5. How accurate are the Ideal and Constant Voltage Drop Models?

Both models are simplified versions of the actual behavior of electrical circuits and therefore, may not accurately reflect real-world scenarios. The Ideal model is more idealistic and less accurate, while the Constant model provides a closer approximation but may still have some discrepancies. It is always recommended to use actual measurements and testing for accurate results in practical applications.

Similar threads

Engineering Calculating Voltage Drop Across Non-Ideal Diodes
    • Engineering and Comp Sci Homework Help
Replies
20
Views
3K
Engineering What is the output voltage of this ideal diode circuit?
    • Engineering and Comp Sci Homework Help
Replies
19
Views
4K
Engineering Understanding the output waveform and using LTSpice
    • Engineering and Comp Sci Homework Help
Replies
1
Views
1K
Can't handle finding currents on the diodes
    • Engineering and Comp Sci Homework Help
Replies
1
Views
995
Engineering Simplifying a series / parallel circuit and calculating unknown values
    • Engineering and Comp Sci Homework Help
Replies
3
Views
1K
How Does an Ideal Diode Affect Voltage in a Circuit?
    • Engineering and Comp Sci Homework Help
Replies
22
Views
15K
How to determine drain-source voltage for this MOSFET amplifier.
    • Engineering and Comp Sci Homework Help
Replies
0
Views
522
Engineering Why Is Nodal Analysis Confusing in This Circuit Example?
    • Engineering and Comp Sci Homework Help
Replies
7
Views
911
Engineering Why are the voltages calculated in this way? (CE BJT Amp circuit)
    • Engineering and Comp Sci Homework Help
Replies
8
Views
1K
I Physics domain analysis of Voltage drop in series resistor
    • Electromagnetism
Replies
7
Views
1K

Hot Threads

Recent Insights

Back
Top