A voltage-follower buffer
Protect a divider from its load
An operational amplifier is a powered amplifier that compares two inputs. Negative feedback returns its output to the subtracting input. As a voltage follower, it holds output equal to input. High input impedance means it takes little input current.
EXPERIMENT BENCH
Change the circuit settings, predict the readings, then check a challenge. These are learning models, with the assumptions explained in each lesson.
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Why it works
Ideal follower draws zero input current and has unlimited output drive within this model. Real devices need power and have input, output, stability and current limits.
The buffer senses the unloaded divider and supplies the load itself. Direct connection places the load in parallel with the lower resistor, lowering the divider voltage.
Difficulty
Build · Build it
Power on with upper and lower resistors both 10 kΩ and the load disconnected. Read 2.50 V.
Need a hint?
R1 = R2 = 10 kΩ → 2.50 V
Explore · Change one thing
Connect a 10 kΩ load with both divider resistors at 10 kΩ. Compare buffered 2.50 V and direct 1.67 V.
Need a hint?
R1 = R2 = RL = 10 kΩ → 2.50 V / 1.67 V
Solve it · Solve the challenge
Connect a 1 kΩ load. Obtain buffered output 3.2–3.4 V while direct output is at most 1 V.
Need a hint?
R1 = 10 kΩ; R2 = 20 kΩ; RL = 1 kΩ → 3.33 V / 0.435 V
Extra reading and circuit recipes
Protect a divider from its load
A useful pattern
A buffer separates the signal-setting circuit from the current taken by a load.
Beyond this model
An actual amplifier cannot deliver unlimited current or always reach its supply rails.
A useful trap to avoid
The extra load energy comes from the amplifier’s power supply, not from an unpowered magic copy.
A load is added to the ideal follower. Its input current…
- equals load current
- remains zero
- becomes negative
Read more
The ideal model has zero input current; its powered output supplies the load.