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tlc071

Other Parts Discussed in Thread: TLC071

1. I am presently using op-amp tlc071.the problem with this op-amp is this that when it is being biased by +/- 5V power supply it is getting heated. As this is a single power supply op-amp but  by using dual power supply tolal voltage across it is 10V (not violating the maximum voltage 16V). So what could be the reason of heating?

2. If I am using op-amp in single supply mode so the formula of amplification will remain same as in case of dual power supply OR it will be different?

3. Why  dual power supply is used for op-amp(particularly for analog electronics)?

  • Akhilesh,

    Please see my comments added to your questions:

    1. I am presently using op-amp tlc071.the problem with this op-amp is this that when it is being biased by +/- 5V power supply it is getting heated. As this is a single power supply op-amp but  by using dual power supply tolal voltage across it is 10V (not violating the maximum voltage 16V). So what could be the reason of heating?

    If you are not driving a load the quiescent TLC071 quiescent current will be about 2 to 3 mA. The quiescent power will be on the order of 20 to 30 mW which would result in a small rise in package temperature that would be barely detectable. If you are driving a load the TLC071 can deliver more than 100mW output power and the internal power dissipation increases, increasing the package temperature by a few tens of degrees at most. That is detectable and normal.

    You didn't mention the package your TLC071 device uses. Most often when a user is having a thermal problem with a TLC07x device they are using product in one of the PowerPad packages. They either fail to mechanically attach (solder) the PowerPad to an appropriate copper pad on the PC board, or they do solder it as required but have the wrong electrical potential on that copper pad. The PowerPad must be placed at the same electrical potential as the TLC071 GND pin. If you use dual supplies and the GND pin is at -5V, then the PowerPad has to be at -5V as well. If the Power Pad is placed at 0V while GND is -5V, then junctions internal to the TLC071 die become forward biased and draw much current. The device gets extremely hot in that instance.

    2. If I am using op-amp in single supply mode so the formula of amplification will remain same as in case of dual power supply OR it will be different?

    Indeed the gain relationships described by the formulas hold for dual supply applications.

    3. Why  dual power supply is used for op-amp(particularly for analog electronics)?

    Quite often the signals to be amplified are centered about a zero volts. Therefore, the operational amplifier used to amplify the signal must be able to operate in a linear region centered about zero. The internal stages of the amplifier must then be biased from supply levels above (+V) and below (-V) zero volts. If the input signal has a dc level that falls within the common-mode and output swing ranges of the operational amplifier it may be possible to use a single supply consisting of +V and 0V.

    Regards, Thomas

    PA - Linear Applications Engineering

     

  • 1. Does dual power supply  in op-amp is also responsible for noise reduction as compared to single power supply ?

  • I am using DIP package of TLC071.It is working satisfactorily while biased with single power supply but getting heated if biased using dual power supply. what could be the reason ?

  • Akhilesh,

    No, the noise performance of the operational amplifier should be nearly identical for single or dual supply operation when operated with equivalent node voltages between pins. There is a small increase in noise in the 1/f region with increased supply voltage as seen in TLC071 data-sheet, Figure 13. I suspect this is due to the small increase in supply current with increased supply voltage. But it is not related to single vs. dual supply operation.

    If you are speaking of common-mode noise reduction of the amplifier, operating the TLC071 with equivalent node voltages between pins should result in equivalent common-mode rejection of that noise for single and dual supply operation.

    Regards, Thomas

    PA - Linear Applications Engineering

  • Akhilesh,

    The point is the TLC071 should not be getting any hotter in dual-supply operation vs. single-supply operation providing the voltages between pins are equivalent and the input and output conditions are equivalent. The internal currents should be the same for both supply configurations and excessive heat in the dual-supply case would indicate that the operating conditions are not equivalent to the single-supply case. Have you checked the pin voltages for both the single and dual supply conditions? Have you confirmed that the two circuits are equivalent with regard to the voltages between pins?

    Another thing that can result in high operating power is circuit instability. If the amplifier becomes unstable and oscillates when you power it from the dual supplies the operating current can rise resulting in excessive heat being generated. I suggest you place a 10x O-scope probe on the TLC071 output and connect it to a wideband oscilloscope. If you see an ac waveform at the output with no input applied the amplifier is oscillating. I would expect it to be unstable for both single and dual supply scenarios, but sometimes things aren't exactly equivalent when we think they should be.

    You could provide your application circuit for both the single-supply and dual supply conditions. Having the schematic for both cases might reveal the problem.

    Regards, Thomas

    PA - Linear Applications Engineering