Voltage comparator in a photo sensing circuit

In summary, the conversation discussed the confusion around how a voltage comparator compares two inputs in a parallel circuit. The person questioned how the voltages across the two inputs can be different, but then realized that one branch may receive ambient lighting while the other receives both ambient and a wanted signal. They also mentioned that the photodiode's resistance varies with the intensity of light. The conversation ended with the person admitting their mistake and understanding the concept of voltage variation in the circuit.
  • #1
tachyon_man
50
0
Hello, I attached a picture below but I am confused as to how the voltage comparator is comparing the two inputs (I know how a comparator works). The test points are running down to the two inputs but wouldn't the voltage always be identical across them since voltage doesn't drop in a parallel circuit but instead if it's 12V source, there would be 12V across each 'section' in a parallel circuit. Would someone please be able to explain to me how the voltages across those can be different from each other which would then explain how the comparator is working. Thank you so much.
 

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  • #2
I would presume that one branch gets ambient lighting, while the other side gets ambient plus some wanted signal? Photodiode's resistance varies with the intensity of incident light.
 
  • #3
At 2:30 am this morning I realized how silly I was sounding and figured out how the voltages vary. I know exactly how this works; I don't know where I went wrong before. :D
 

1. What is a voltage comparator in a photo sensing circuit?

A voltage comparator is an electronic device that compares the voltage at two input terminals and outputs a digital signal indicating which input has the higher voltage. In a photo sensing circuit, the voltage comparator compares the voltage from a photosensor with a reference voltage to detect changes in light levels and trigger a response.

2. How does a voltage comparator work in a photo sensing circuit?

In a photo sensing circuit, the voltage comparator compares the voltage from a photosensor with a reference voltage. When the voltage from the photosensor exceeds the reference voltage, the comparator outputs a high signal. When the voltage from the photosensor is lower than the reference voltage, the comparator outputs a low signal. This allows the circuit to detect changes in light levels and trigger a response, such as turning on a light or activating an alarm.

3. What are the advantages of using a voltage comparator in a photo sensing circuit?

Using a voltage comparator in a photo sensing circuit allows for a more precise and reliable detection of changes in light levels. It also allows for a faster response time compared to other methods, such as using a microcontroller. Additionally, voltage comparators are relatively inexpensive and easy to implement in a circuit.

4. Can a voltage comparator be used in other types of circuits?

Yes, a voltage comparator can be used in a variety of different circuits. It is commonly used in applications that require precise voltage comparison, such as in audio amplifiers, power supplies, and motor control circuits.

5. How do I choose the right voltage comparator for my photo sensing circuit?

When choosing a voltage comparator for a photo sensing circuit, it is important to consider the required input voltage range, output voltage levels, response time, and power consumption. It is also important to choose a comparator with a high enough input impedance to minimize the loading effect on the photosensor. Consulting with a datasheet and conducting testing with different comparators can help determine the best fit for your specific circuit.

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