Attached simulation of op-amp .

enter image description here Q1) In Op-amp ckt 1 has power supply of 20V and In Op-amp ckt 2 has power supply of 15V (rest everything is same). How current consumption is more in 20V rather than 15V supply ( see image opamp ckt 1 and opamp ckt 2 , current consumption is 1.33mA and 1mA respectfully). If everything is same then current consumed should be low or high.

Q2) How to Calculate total power consumption in opamp ckt 3. ( as per simulation result, see image opamp ckt 3)

Q3) In opamp ckt 3 , Input power consumption is 15 V*1m A=15 mW , and output power given is 9.59 V*9.59 mA= 91.9 mW, how output can divilerd more power than input consumed.

  • 3
    \$\begingroup\$ You're assuming that the model for the opamp is a realistic model. Obviously it is not ! This model obviously does not take the current supplied from the output into account. Maybe you should try a more realistic model for the opamp, perhaps a transistor level model. \$\endgroup\$ May 12, 2016 at 9:23
  • \$\begingroup\$ Read this for a really good explanation of opamp models: linear.com/docs/4139 \$\endgroup\$ May 12, 2016 at 11:40

1 Answer 1


Q1: There is some internal circuitry within opamps (bias, ...) whose current consumption depend on the provided voltage. So, even if it does not change anything to the opamp output, changing its supply voltage can change the current it internally draws (called the quiescent current).

Q2: You can't, with this model (see below)

Q3: It is indeed inconsistent. If the opamp sources 9mA to its output, the positive supply current should be at least 9mA (plus the internal quiescent current). And if it sinks XmA, the negative supply current should be -XmA. In real life, that's how it is. Now, in simulation models, most often, this is not taken into account. Most manufacturers publish opamp models that are inaccurate regarding supply current, because it simplifies their models a lot, and supply current is not usually checked during simulations.

In short: to check the opamp consumption, you, most often, have to do it manually: compute the power used to sink/source the required output current, and add the power used from the quiescent current given in the datasheet (which is always provided).


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