Circuit diagram to analyze that looks wrong to me

In summary, the conversation discusses a circuit diagram that appears to be incorrect. The diagram shows a power source connected to a photocell, but also connected to an NPN transistor in a way that suggests the intention to use the photodiode to switch the transistor and a light. The question is raised whether an NPN transistor can function with this type of bias, and the two classes of bi-polar transistors (NPN and PNP) are mentioned. The project in question is using an NPN transistor. The conversation also mentions that the circuit diagram may have misprints or omissions.
  • #1
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I have a circuit diagram to analyze that looks wrong to me. It is fairly straight forward and I will attempt to describe it. It is an unlabelled power source with the neg terminal feeding a photocell, that part I understand. Here is the problem, that same neg branch of the circuit also feeds into the collector terminal of an NPN transistor with the base terminal of the NPN transistor receiving the switched neg fom the photodiode. It appears the intention of the design was to use the photodiode to switch the transistor which switches a light. Kind of like how the steet lights come on at dark. My question is, can an NPN transistor function with this bias, neg to collector, switched neg to base and pos side of light bulb connected to emmitter?
 
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  • #2
What are the two classes of bi-polar transistor?
 
  • #3
NPN and PNP
 
  • #4
Ok, which one is your project using?
 
  • #5
npn by the symbol
 
  • #6
From your description this doesn't sound correct.
Perhaps you should post the schematic.
 
  • #7
circuit diagram
 

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  • #8
Circuit looks wrong, or it's a trick question (like the answer is "never").

The load should be directly connected to the collector, and the voltage source should have + on top of the load, and - down on the emitter. The cathode of the photodiode should also connect above the load to the + supply.
 
  • #9
In this case it looks like the battery symbol is backwards.
The same issue applies to the photodiode as well as the transistor.

Edit: You beat me to it B, I considered the "never" answer as well :smile:
 
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  • #10
Thanks to all that took the time to have a look at this thing. My text is full of misprints and omissions.
 

1. What is a circuit diagram?

A circuit diagram is a graphical representation of an electrical circuit. It uses symbols to show the components of the circuit and how they are connected.

2. How do I read a circuit diagram?

To read a circuit diagram, you need to understand the symbols used and how they are connected. The direction of the current flow is shown by arrows, and the components are connected by lines. You can also refer to a key or legend to understand the symbols used in the diagram.

3. What are the common mistakes in a circuit diagram?

Some common mistakes in a circuit diagram include incorrect symbol placement, incorrect component connections, and missing components. These mistakes can lead to a circuit not functioning properly or even causing damage to the components.

4. What should I do if a circuit diagram looks wrong to me?

If a circuit diagram looks wrong to you, double check the connections and symbols used. You can also consult with a more experienced person or use a multimeter to test the circuit. It's important to fix any mistakes before building the circuit to ensure it functions correctly.

5. Can I make changes to a circuit diagram?

Yes, you can make changes to a circuit diagram as long as you understand the circuit and how the changes will affect it. It's important to document any changes you make and ensure they are accurate before building the circuit.

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