CALCULATORS / ANALOG CIRCUITS AND FILTERS

Current-sense resistor and amplifier calculator

Shunt and ideal amplifier current measurement.

analog-current-sense.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

This source describes an analytical model. Its quantities and checks are the view.

Scenario	shuntDropV	outputV	lossW
	0.05	1	0.25
	0.04	0.8	0.16

All calculated quantities are listed with the inputs. Switch to Source to inspect the equations.

SCENARIOS / CALCULATED VALUESSAME SOURCE

Change an input to see the consequences.

shunt power budget0.25 W✓ passes

BASELINE INPUTS

current5 Ashunt0.01 ohmgain20

CALCULATED

shuntDrop0.05 V

output1 V

loss0.25 W

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# Current-sense resistor and amplifier
# Scope: Shunt and ideal amplifier current measurement.
# Status: illustrative worked example; engineering review pending.
# Inputs are example values. Checks are editable example requirements, not standards.

current = 5 A
shunt = 0.01 ohm
gain = 20

shuntDrop := current*shunt [V]
output := shuntDrop*gain [V]
loss := current^2*shunt [W]

check shunt power budget: loss <= 0.5 W

scenario alternative: current = 4 A

Calculated from your source · not saved

Baseline · Baseline

shunt power budget0.25 W ✓ passes

alternative · alternative

shunt power budget0.16 W ✓ passes

Illustrative first-order example. Checks are editable requirements, not design standards. The broader topic may require additional equations, data, and validation.

Formula and units

This example uses the following equations. Input names and units match the editable source above.

shunt drop: shuntDrop = current*shunt [V]
output: output = shuntDrop*gain [V]
loss: loss = current^2*shunt [W]

Original worked example

These are the baseline values in the downloadable source. Edits above let you test your own values.

Given

current: 5 A
shunt: 0.01 ohm
gain: 20

Calculated

shunt drop: 0.05 V
output: 1 V
loss: 0.25 W

Assumptions and limits

Shunt and ideal amplifier current measurement.

The requirement checks use the limits written in this example. Passing a check does not establish that the model covers every load, material behavior, or operating condition in a real design.

Download this .napkin example ↓

Take it further with your agent

Napkin keeps the inputs, equations, checks and assumptions together in one study. Your agent sets it up; you change the numbers.

Try with Claude ↗

codex 'Use Napkin (https://napkin.engineering/mcp, or the local Napkin plugin) to build a study: Current-sense resistor and amplifier. Inputs: current bounds; shunt; gain; ADC range. Outputs: voltage range; losses; quantization. Model scope: Lumped small-signal models within device operating ranges. Read napkin_capabilities and the current snapshot. Ask me for the values that matter, label assumptions with units, author .napkin source, validate it and apply it with napkin_source using the current revision, then open the study. Add checks for the limits I supply. Keep unsupported analyses explicit.'

Claude needs the Napkin connector; Codex needs the Napkin plugin. Set up your agent ↗

The broader study

The topic brief below describes the broader scope. The worked example above states the particular calculation it implements.

Inputs: current bounds, shunt, gain, ADC range
Outputs: voltage range, losses, quantization
Modes: calculate, compare, sweep
Drawing: Schematic and Bode plot

EXECUTABLE WORKED EXAMPLE · FIRST-ORDER MODEL · CHECK THE SCOPE & ASSUMPTIONS