Understanding the output waveform and using LTSpice

  • #1
182
15

Homework Statement:

Find the output waveform for the given circuit.

Relevant Equations:

Not sure about which equations to use here (if any)
Screenshot 2020-07-21 at 12.33.48 PM.png


For the following circuit I need to find the output waveform.

A. Conceptually I am at sea here but I will have a stab at it. My though process is as follows :
  1. At a given instant, the AC voltage is at a fixed value and this value drops (##V_drop##) across the resistor ##R##.
  2. The voltage (##V_drop##) across the diode and battery as well as the voltage across ##R_L## is constant for a given instant.
  3. Current flow would be affected across the diode when the voltage across it is less than the cut-in voltage of the diode (0.7 V), however this information seems irrelevant in finding the output voltage.
  4. At a given instant the AC source is the same as a DC source which is parallel to the voltage source ##V##. Two cases emerge here, one when the instantaneous voltage of the AC source is greater than ##V## and the other when the instantaneous voltage of the AC source is lesser than ##V##. In the former, V acts as a short (?) while in the latter the AC source can be neglected (?!).
  5. Can't quite put a finger on how V affects the output waveform.
How do I arrive at the output waveform?!

B. I tried to use LTSpice to analyse the circuit, could you please tell me if I have replicated the circuit correctly?

Screenshot 2020-07-21 at 12.33.17 PM.png


Thank you for your time!
 

Attachments

Answers and Replies

  • #2
DaveE
Gold Member
789
596
Try to re-run your simulation with a larger magnitude sine wave input, let's say 50V. This will give you more insight. If Vout is less than about 10.7V then the diode will always be off.

You can assume that at any moment in time the diode will either be conducting, or not. So, you can start by analyzing the circuit in each of these two modes (i.e. one with a short circuit, one with an open circuit in place of the diode). Then think about when the circuit will switch between these two states.
 
  • Like
Likes berkeman

Related Threads on Understanding the output waveform and using LTSpice

Replies
21
Views
826
  • Last Post
Replies
13
Views
5K
Replies
23
Views
5K
Replies
11
Views
2K
Replies
1
Views
1K
Replies
24
Views
2K
Replies
7
Views
1K
Replies
0
Views
7K
Replies
7
Views
1K
Top