Op-amp current source
Op-amp current source with circuit equations and operating-limit checks.
Development preview. Check the assumptions below before relying on a result. Calculations run in your browser.
How it calculates
Current regulation: Isense = Vcontrol/Rsense (loop mode: 4 mA + command * 16 mA)
Compliance: Vload,max = Vsupply - Isense Rsense - Vheadroom
BJT collector current: IC = Isense beta/(beta+1)
Assumptions
- Sink topology: supply -> load -> transistor -> sense resistor -> ground. Op-amp holds the sense node at the control voltage. BJT mode reports collector current including base-current loss. Set current is not clipped when compliance fails.
Worked example
These are the calculator's default inputs. Change any input above to recalculate.
Inputs
- Circuit
- sink
- Control voltage
- 1 V
- Sense resistor R13
- 100 Ω
- Positive supply
- 12 V
- Load resistance
- 500 Ω
- Output/pass-device headroom
- 1 V
- BJT current gain (0 means MOSFET)
- 0
- 4-20 mA command
- 50 %
- Howland R11 mismatch
- 0.1 %
- Howland nominal R11 = R14 = R15
- 10000 Ω
Results
- Load current
- 0.01 A
- Load voltage
- 5 V
- Maximum load voltage
- 10 V
- Maximum load resistance
- 1000 Ω
- Pass-device dissipation
- 0.06 W
- Signed Howland output resistance
- Not modelled Ω
- Howland amplifier output
- Depends on pass device gate/base voltage V