What determines the current in the circuit with Ideal operation amplifier realizing the voltage-controlled current source?

  • \$\begingroup\$ Not sure I understand your question. A VCCS has a current determined by the sense voltage, obviously. If it's ideal there would not be any other consumption. \$\endgroup\$ Dec 9, 2020 at 16:27
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    \$\begingroup\$ There is no generic schematic for what you appear to allude to hence, you need to post a specific schematic. \$\endgroup\$
    – Andy aka
    Dec 9, 2020 at 16:27
  • \$\begingroup\$ The operational amplifier output pin? Ideal op amps are usually modeled with VCVS's on the 'inside'\ \$\endgroup\$
    – Voltage Spike
    Dec 10, 2020 at 23:45

2 Answers 2


Maybe you can look into a 'Current Mirror' circuit. Here, you would typically use the current through a resistor (which is dependent on the voltage across the resistor) to supply an equally large current to other circuitry, buffered by a transistor. Thus, you would have a voltage-controlled current source - which is also utilized in Opamps


A typical example of a voltage-controlled current source (VCCS) is a common-emitter stage with emitter resistor R. Usually, it is connected in the negative feedback loop of an op-amp follower. The current is determined by the input voltage Vin and the emitter resistance Re (I = Vin/Re).

Another example, in addition to the current mirror VCCS: Do you know what an op-amp inverting amplifier is? If so, the input voltage Vin and the input resistor R1 determine the current I = Vin/R1 that flows through the output resistor R2 (the load). The disadvantage of this circuit solution is that the load is not connected to the real ground; but still it is connected to the virtual ground (the op-amp inverting input).

The Howland current source (pump) does not have this disadvantage. There both the input voltage source and load are real grounded.

And finally, if the load has (almost) zero resistance, you can make the simplest VCCS consisting of... only a resistor R in series to the input voltage source. The current is (approximately) determined by the input voltage Vin and the resistance R according to Ohm's law ( I = Vin/R).

See also How do we create current sources?


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