Brief Single Supply Op Amp Current Source LM358 Operational Amplifier

A current source limits current to a certain amount, regardless of what the load is. As long as the power supply can provide that much power.

Simple single supply op amp current source circuit schematic diagram by electronzap electronzapdotcom
Simple single supply op amp current source circuit schematic diagram by electronzap electronzapdotcom
  • Op amp negative feed back, which is when the output is electrically connected to the inverting input (-), sets the output voltage to where the voltage at the inverting input (-) will be the same voltage that is applied to the non inverting (+) input.
  • A load between the output and (-) input means that the output will have to provide the voltage that it needs to set at the (-) input PLUS whatever voltage is needed to get current through the load between them. The supply voltage must be high enough that it is able to do so. Vout = +Vin + load voltage.
  •   A resistor from (-) input to ground, will also have the voltage across it that is set at the (-) input.  They share the same node (part of the circuit where components connect directly).
  • The resistor will pass current (I) based on the voltage across it and it’s resistance. Ohms law formula I=V/R.
  • The current that flows through the resistor has to come from the op amp output because the inputs do not let current in or out. They only leak an insignificantly small amount of current.
  • Since the load is between the output and current setting resistor, it has that same amount of current passing through it as that which passes through the resistor. The output has to the provide the extra voltage needed to do so while holding the (+) input voltage at the (-) input and the current setting resistor.


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