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TLV314: TLV314 VS NJU77550F

kevin.huang_FJXM
Expert 2925 points
Part Number: TLV314
Other Parts Discussed in Thread: TLV7011

Regarding the rail to rail operational amplifier TLV314, I would like to ask you the following questions:

Background: Our company will build a comparator with a window on TLV314 to control the AD value of photosensitivity, thereby controlling the brightness of night lights. The specific principle is shown in the following figure:

Question 1- As shown in the schematic diagram, the working voltage of the entire module is 5V. The input voltage of the operational amplifier on pin 4 (-) varies between 0 and 4.4V depending on the resistance value of the photoresist. Does this input voltage meet the requirements?

Problem 2- Our circuit's operational amplifier used NJU77550F (JRC) to build a window comparator, but due to its lack of material, when using the TLV314 operational amplifier, we found that its window voltage needs to be adjusted. Why is this? What parameters are causing it?

 

PCN

Window voltage corresponding to 2LUX photosensitivity value

Window voltage corresponding to 6.5LUX photosensitivity value

Resistance value corresponding to R4

 

NJU77550F

0.245V

0.965V

9.1K

TLV314

0.323V

1.273V

13K

Note: When using TLV314, the window voltage should be raised slightly overall to obtain the corresponding photosensitive lumen value
  • 0
    Guru 298860 points

    To insert a figure, you must use "Insert"/"Image" in the menu below the edit field.

  • 0 in reply to Clemens Ladisch
    TI__Mastermind 25360 points

    Hi Kevin,

    I don't see the schematic for the circuits described. Can you please include so we can better diagnose what is happening here?

    Thank you,

    Robert Clifton 

  • 0 in reply to kevin.huang_FJXM
    TI__Mastermind 25360 points

    Hi Kevin,

    Thank you for sharing this schematic. Can you please explain why you also changed R4 when using TLV314? The voltage numbers you are getting for hysteresis makes sense to me based on the value of the external components. 

    Best Regards,

    Robert Clifton 

  • 0 in reply to Robert Clifton56
    Expert 2925 points

    (1) Adjusting R4 is to achieve the same photosensitive lumen value as the existing mass-produced material (NJU77550F). Under the same specification parameters, TLV314 needs to raise the comparison window voltage, which parameter is related to the TLV314 operational amplifier?

    (2) According to the application of the schematic diagram, the input voltage will vary between 0-4.4V. Does this input voltage meet the requirements?

  • 0 in reply to kevin.huang_FJXM
    Guru 298860 points

    Both the NJU77550F and the TLV314 have very low input bias currents (1 pF); I have no explanation for the difference. If I had to guess, I would suspect that the phototransistor outputs a different current. Can you measure the voltages at pins 3 and 4 in both versions under the same circumstances?

    You are using the opamp as a comparator. It might be a better idea to use an actual comparator like the TLV7011 (same pinout, lower power, built-in hysteresis).

  • 0 in reply to Clemens Ladisch
    TI__Mastermind 25360 points

    Hi Kevin,

    It's been several weeks since we heard back. I'm going to assume that this issue has been resolved and close the thread.

    Best Regards, 

    Robert Clifton