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TL082: the output PIN output was low(normal Io voltage to ground is 0.55V, low Io = 0.51V)

user5707026
Genius 3145 points
Part Number: TL082
Other Parts Discussed in Thread: TL052A, LM358B, LM358BA

Hi Engineer,

When the test found that the input was unchanged,

a new batch of TL082CDR was used, and the output PIN output was low (normal Io voltage to ground is 0.55V, low Io = 0.51V), and replaced with TL082CDR one year ago , Out PIN increased to normal, the entire product test can pass.

As long as it is this batch of materials, there will be problems as soon as it is powered on;

The following is the circuit schematic, please help review.

Thank you

Best Regards

Elsa Duan

  • 0
    TI__Guru*** 140106 points

    Hello Elsa,

    During this test, what is the voltage at U1 pins 6 and 7? Also needed is the supply voltages for TL082, VCC+, VCC-.

      

  • 0 in reply to Ron Michallick
    Genius 3145 points

    Hi Ronald

    During this test, the voltage at U1 pins 6 and the supply voltages for TL082, VCC+, VCC- are as below:

    From the data in the table, it seems that Vcc- of TL082 is a little lower.
    Is there a problem with TL082, and then the voltage is lowered?
    How much power supply voltage is required and how high is the accuracy requirement? Is the specification not within ± 18V?

    Please speed up the analysis of TL082, it has affected our production.

    Thanks a lot

    Best Regards

    Elsa Duan

  • 0 in reply to user5707026
    Guru 140200 points

    Hi Elsa,

    the deviation is the result of manufacturing tolerances of HCPL-7840 (and circuitry at its input), input offset voltage of TL082 and resistors R8...R11.

    Let's have some error analysis.

    Nearly perfect parts would yield:

    Worst case resistor tolerances (+/-1%) can result in:

    Worst case input offset voltage of TL082 can yield:

    Both together can result in:

    So, two different TL082 circuits can produce an output offset voltage deviation of 2 x 177mV = 354mV. Such a high deviation is very very improbable, of course, but possible. But what you see is a deviation of only 0.55V - 0.51V = 40mV which is way less than the absolute worst case deviation discussed above.

    Don't forget that the HCPL-7840 itself also produces an error. Here the deviation is only -15mV:

    A good cure is to use an OPAmp with a much lower input offset voltage. We take in a simlar application the TL052A, by the way. And it might be a good idea to use +/-0.1% resistors.

    elsa_tl082.TSC

    Kai

  • 0 in reply to kai klaas69
    TI__Guru*** 140106 points

    Elsa,

    Kai's advice is good. The gain of the circuit is 5 so the offset error will be amplified by 6. Some version of TL082 are allowed to have an offset voltage up to +/-15mV.  That creates the +/-90mV output swing (variance). 

    Lowest cost replacement would be LM358B or LM358BA. TL052A is also a good choice.