Can anyone explain me this circuit

AI Thread Summary
The discussion centers around a circuit designed for a laser security system, which utilizes a thyristor (BT-169) to control an LED and speaker based on light detected by a light-dependent resistor (LDR). When the battery is connected without light on the LDR, the thyristor activates, causing the LED to glow and the speaker to click. However, when the LDR is illuminated, the thyristor's behavior depends on the load current, as it may not turn off if the current remains high. Participants express concerns about the suitability of the BT-169 for DC operation and seek clarification on the circuit's functionality and component specifics. Overall, the circuit's operation and component compatibility are key points of discussion.
gaurav_dua
Messages
5
Reaction score
0
http://prntscr.com/60xcwx

Thank you
circuit.jpg
 
Physics news on Phys.org
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"
 
  • Like
Likes zoki85
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.
 
Last edited by a moderator:

Similar threads

What is the operation principle of the LDR?
Replies
14
Views
2K
LDR circuit electricity question
Replies
3
Views
2K
Current Flow Through Lamps in Circuits
Replies
9
Views
2K
B Where Do Electrons Go When a Battery Loses Charge?
Replies
22
Views
6K
LDR Circuit Projects - Ideas for Science Fair
Replies
1
Views
16K
Name of software for drawing electric circuits
Replies
7
Views
2K
I Is the Poynting Vector Field the Only Factor in Energy Flow in Circuits?
Replies
16
Views
3K
Circuit Components-Potential differencd across LDR (photoresistor)
Replies
2
Views
2K
I Trying to understand the inner workings of a solar cell
Replies
2
Views
2K
Transistor Logic Gate : NOT Gate Explanation?
Replies
9
Views
3K

Hot Threads

Recent Insights

Back
Top