Reading datasheets to pick a comparator

In summary, the conversation discusses the need for help in choosing a voltage comparator and interpreting datasheets. The datasheets for the LM393 and LM111 are mentioned, with the LM111 being capable of handling a dual supply of +&- 15 volts, making it suitable for the input voltage range of +&- 7.8 volts. The suggestion to upload the schematic for further assistance is also made.
  • #1
akaliuseheal
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8
Hello,
I've got a voltage comparator, well only on schematics, I need to chose one and I need some help interpreting datasheet. The datasheet I was looking at is of a lm393. My input voltage ranges from -7.8V to +7.8V. The datasheet says -0.3 to something. So it's not usable, right?
I was also looking at lm111 and here it is stated that input voltage can be from -15V to +15V which is great but I can't find information about output sink current.
 
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  • #2
akaliuseheal said:
The datasheet says -0.3 to something. So it's not usable, right?

You need to spend some time reading datasheets to learn the vocabulary.
The limitation is input voltage should lie between the power supply "rails"

That comparator can handle a dual supply of +&- 15 volts.
so you +&- 7.8 is well within that range.
You just have to give the comparatpr a +&- supply.
upload_2018-9-15_15-37-5.png
 

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  • #3
akaliuseheal said:
I've got a voltage comparator, well only on schematics, I need to chose one and I need some help interpreting datasheet.
Can you Upload the schematic? Use the Upload button in the Edit window to Upload a PDF or JPEG copy. That will help us a lot in suggesting things for you to look for as you pick the comparator IC to us. Thanks. :smile:
 

1. How do I determine the input voltage range for a comparator?

The input voltage range for a comparator can usually be found in the "Electrical Characteristics" section of the datasheet. Look for parameters such as "Input Voltage Range" or "Supply Voltage Range" to determine the acceptable voltage levels for the comparator.

2. What is the difference between input offset voltage and input bias current for a comparator?

Input offset voltage is the voltage difference between the two input terminals of a comparator when the inputs are at the same voltage. Input bias current, on the other hand, is the current that flows into or out of the input terminals when there is no input voltage. In simpler terms, input offset voltage affects the accuracy of the comparator's output, while input bias current affects the speed of the comparator.

3. How do I select the appropriate hysteresis value for a comparator?

Hysteresis is a built-in positive feedback mechanism in a comparator that helps to prevent output oscillations when the input signal is near the threshold. The appropriate hysteresis value depends on the application and the expected noise and signal levels. Usually, a hysteresis value of 5-10% of the input voltage range is recommended.

4. Can I use a comparator with a different power supply than the rest of my circuit?

In most cases, it is not recommended to use a comparator with a different power supply than the rest of the circuit. This can cause issues with signal levels and ground reference. However, some comparators have an option for a separate power supply pin, which allows for use with a different power supply.

5. How do I interpret the propagation delay time in a comparator datasheet?

The propagation delay time in a comparator datasheet refers to the time it takes for the comparator's output to change from one state to another in response to a change in the input signal. This parameter is important for applications where timing is critical, such as in pulse width modulation. The lower the propagation delay time, the faster the comparator will respond to changes in the input signal.

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