Can anyone explain me this circuit

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Discussion Overview

The discussion revolves around a circuit design intended for a laser security system, focusing on the functionality of components such as a thyristor and a light-dependent resistor (LDR). Participants seek clarification on how the circuit operates and its intended purpose.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants inquire whether the circuit is part of a homework exercise or a personal project.
  • One participant describes the circuit's operation, noting that the thyristor will activate the LED and speaker when the LDR is not illuminated, but its behavior changes when the LDR receives light.
  • Another participant requests further details about the circuit's operation and the components involved.
  • Information is provided about the thyristor's operational states, including reverse blocking, forward blocking, and forward conducting modes.
  • One participant specifies that the thyristor used is a BT-169 and mentions a potential issue with its suitability for DC operation.
  • Questions are raised about the speaker and the overall component acquisition for the project.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and seek clarification on the circuit's function, indicating that there is no consensus on the details of its operation or the implications of using the specified thyristor.

Contextual Notes

There are unresolved questions regarding the circuit's behavior under different conditions and the appropriateness of the components selected, particularly the thyristor's specifications for DC operation.

gaurav_dua
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http://prntscr.com/60xcwx

Thank you
circuit.jpg
 
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This is a homework exercise?

It should be in the homework subforum.
 
NascentOxygen said:
This is a homework exercise?

It should be in the homework subforum.
no, this is my project for school
 
What is the circuit supposed to do?
 
Seems a bit odd. If you connect the battery when there is no light on the LDR, the thyristor will turn on, the LED will start glowing and there will be a click in the speaker. When the LDR gets illuminated - it depends on the thyristor and the speaker (a thyristor will not turn off if the load current is large enough).
 
NascentOxygen said:
What is the circuit supposed to do?
this is the circuit of a laser security system
 
Svein said:
Seems a bit odd. If you connect the battery when there is no light on the LDR, the thyristor will turn on, the LED will start glowing and there will be a click in the speaker. When the LDR gets illuminated - it depends on the thyristor and the speaker (a thyristor will not turn off if the load current is large enough).
Can you explain in more detail?
Thanks
 
gaurav_dua said:
Can you explain in more detail?
Thanks

From http://en.wikipedia.org/wiki/Thyristor :
Thyristors have three states:

  1. Reverse blocking mode — Voltage is applied in the direction that would be blocked by a diode
  2. Forward blocking mode — Voltage is applied in the direction that would cause a diode to conduct, but the thyristor has not been triggered into conduction
  3. Forward conducting mode — The thyristor has been triggered into conduction and will remain conducting until the forward current drops below a threshold value known as the "holding current"
 
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Another thing I would like to add is the thyristor is BT-169
 
  • #10
What can you tell us about the Speaker?

Have you bought the components? How does the laser get used?
 
  • #11
gaurav_dua said:
Another thing I would like to add is the thyristor is BT-169

Look at http://www.nxp.com/documents/data_sheet/BT169_SER.pdf

A slight problem: BT-169 is not specified for DC operation.
 
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