Why is a bridge rectifier necessary in this circuit?

  • Context: Engineering 
  • Thread starter Thread starter Femme_physics
  • Start date Start date
  • Tags Tags
    Bridge Diode
Click For Summary

Discussion Overview

The discussion revolves around the necessity of a bridge rectifier in a specific circuit configuration. Participants explore the implications of short-circuiting certain diodes and the resulting current flow, focusing on both positive and negative cycles of operation.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that short-circuiting D1 and D2 leads to a complete short circuit of the entire circuit, limiting current flow.
  • Another participant interprets "short-circuit D1 and D2" as replacing them with wires, indicating a different understanding of the circuit modification.
  • A participant notes that disconnecting D3 means that current cannot flow through the location where D3 was connected.
  • Current flow is modeled only during the positive cycle, as illustrated by one participant.
  • There is a question about the role of a block on the right side of the circuit, including whether it draws current and the conditions under which an SCR is conductive.
  • One participant asserts that there is no negative cycle because the SCR blocks it, leading to all voltage dropping across the SCR instead of the load.
  • A later reply asks for an explanation of why a bridge rectifier is necessary, indicating a lack of clarity on its function in the circuit.

Areas of Agreement / Disagreement

Participants express differing views on the behavior of the circuit when certain diodes are short-circuited, particularly regarding the presence of a negative cycle and the role of the SCR. The discussion remains unresolved regarding the necessity of the bridge rectifier.

Contextual Notes

There are limitations in the assumptions made about the circuit's behavior, particularly concerning the modeling of current flow during different cycles and the specific roles of components like the SCR and the bridge rectifier.

Femme_physics
Gold Member
Messages
2,548
Reaction score
1
I am told that in this circuit (above pic) we shortcircuit D1 and D2, and disconnect D3 and D4... then we are to calculate Vrl(average)

But the way I see it, if we shortcircuit D1 and D2 the entire circuit is shortcircuit and current only flows like this (below pic)

http://img195.imageshack.us/img195/8396/d1d2d3.jpg
 
Last edited by a moderator:
Physics news on Phys.org
When the question asks "shortcircuit D1 and D2", I think it means: "replace D1 with a wire and replace D2 with a wire"
 
Yep.
And disconnecting D3 means taking D3 out.
So there cannot go current anymore through the place where D3 used to be...
 
Yep. The current would flow like that. :)

What about that block on the right? What does it do?
Does it draw any current?
And is the SCR always conductive?
Doesn't that depend on the voltage at its gate?
 
So current only flows at the positive cycle

Yes and no. You have only modeled the positive cycle.

To model the negative cycle put the diodes back and pretend the other two are shorted/conducting.
 
The block to the right is a circuit to control firing angle (At 30 degrees).

CWatter - There is no negative cycle. The SCR blocks it! All the voltage falls on the SCR and nothing on the load.
 
Okay.
Then I guess you are set to calculate the average Vrl.
 
Femme_physics said:
CWatter - There is no negative cycle. The SCR blocks it! All the voltage falls on the SCR and nothing on the load.

Perhaps you can explain why a bridge rectifier is needed then :-)
 

Similar threads

  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 8 ·
Replies
8
Views
3K
  • · Replies 9 ·
Replies
9
Views
6K
Replies
1
Views
7K
  • · Replies 6 ·
Replies
6
Views
5K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 11 ·
Replies
11
Views
6K