Neutron STEM Lab
Virtual engineering lab

Bench Power Supply Fundamentals

Practice setting voltage and current limits on a virtual DC bench supply and observe the physical transition between constant-voltage and constant-current regulation as load resistance changes.

Electrical Engineering / InstrumentationintroductoryValidated educational model
Learning mode

Guided laboratory

Use the checklist when you want a structured lab. Explore mode leaves the instruments unrestricted.

Virtual instrument

DC bench power supply

OUTPUT ONCV
Voltage12.000 V
Current0.50000 A
Constant voltage6.0000 W
+Positive
⏚Earth
−Negative
Load fixture

Adjustable resistive load

CV region
Unrestricted demand0.50000 A
Current limit1.0000 A
CV/CC transition12.000 Ω
Delivered power6.0000 W

At 24 Ω, the load requests 0.5 A, so the supply can maintain 12 V in CV mode.

Measurements

Instrument readings

Actual output voltage
—
Regulated terminal voltage after CV/CC limiting is applied.
Actual output current
—
Current delivered to the resistive load.
Load power
—
Electrical power delivered to the load.
Unrestricted current demand
—
Current that Vset/Rload would draw without current limiting.
CV/CC transition resistance
—
Load resistance at which current demand equals the configured current limit.
Result visualization

Regulation operating point

Compare unrestricted load current with the configured current limit. The supply remains in CV below the limit and enters CC above it, reducing terminal voltage until Iout = Ilimit.

Operating mode
Constant voltage
Unrestricted demand
—
Current limit
—
Transition resistance
—

Independent check: calculate Rtransition = Vset/Ilimit. Loads above that resistance operate in CV; loads below it require CC regulation in this ideal resistive model.

Theory

Equations and model

Constant-voltage regulation

When the connected load demands less current than the configured current limit, the supply maintains the requested output voltage. The current is then determined by the load resistance.

Iload=VsetRloadI_{\mathrm{load}} = \frac{V_{\mathrm{set}}}{R_{\mathrm{load}}}CV  when  VsetRload≤Ilimit\frac{\mathrm{CV}\; \text{when}\; V_{\mathrm{set}}}{R_{\mathrm{load}}} \le I_{\mathrm{limit}}

Constant-current regulation

If the load would demand more current than the configured limit, the supply reduces output voltage until the load current equals the current limit. Current limiting therefore changes the actual output voltage rather than allowing the requested voltage and excessive current simultaneously.

Iout=IlimitI_{\mathrm{out}} = I_{\mathrm{limit}}Vout=Ilimit⋅RloadV_{\mathrm{out}} = I_{\mathrm{limit}} \cdot R_{\mathrm{load}}CC when Vset / Rload > Ilimit

CV/CC transition load

The boundary occurs when the voltage-setpoint current demand exactly equals the current limit. This gives a useful threshold resistance for predicting the operating mode before changing the load.

Rtransition=VsetIlimitR_{\mathrm{transition}} = \frac{V_{\mathrm{set}}}{I_{\mathrm{limit}}}Pout=Vout⋅IoutP_{\mathrm{out}} = V_{\mathrm{out}} \cdot I_{\mathrm{out}}
Validation

Independent checks

Bench supply load-line checkNot run

Checks the regulated output against the independent piecewise CV/CC relationship derived from Ohm’s law.

Expected
—
Simulated
—
Error
—
Tolerance
0.001%

Run the experiment to perform this check.

Engineering interpretation

Run the experiment to generate an engineering interpretation.

Assumptions and limitations
Assumptions
  • The supply is an ideal regulated DC source within its 0–30 V and 0–5 A educational limits.
  • The connected load is purely resistive, linear, and time invariant.
  • CV/CC transition is instantaneous with no control-loop transient or overshoot.
  • Lead resistance, output impedance, ripple, noise, and thermal behavior are omitted until later non-ideality work.
Limitations
  • This Phase 1.5 model does not include supply ripple, transient response, remote sensing, series/parallel channels, tracking, OVP/OCP latching, foldback, or thermal derating.
  • Current limiting is modeled as an ideal CC regulator; real supplies have finite control bandwidth and minimum output resistance/voltage behavior.
  • The resistive load fixture is intended to teach regulation behavior rather than emulate an arbitrary electronic load.
Local experiment export

Save your measurements and setup

Exports are generated in your browser. No account or server upload is required.

Settings JSON
Current parameters and instrument controls, including waveform, output enable, scope coupling, timebase, trigger, and cursors when present. Data labs also include the dataset, mappings, exclusions, budget, or propagation setup.
Measurements CSV
Completed instrument readings with labels, units, and descriptions.
Plot PNG
The current canvas-based scope, transient, sweep, or statistics visualization when available.
Summary
Markdown report with objectives, setup, measurements, validation, interpretation, assumptions, and graded guided concept-check results.

Ready to export the current local experiment state.

Learning objectives

What this experiment should establish

  • Set an output-voltage limit and current limit independently.
  • Predict load current from Ohm’s law before energizing the output.
  • Recognize constant-voltage operation when load current demand is below the current limit.
  • Recognize constant-current operation when the load would otherwise exceed the current limit.
  • Calculate the load resistance at which the supply transitions between CV and CC behavior.
  • Relate output voltage, current, and power to the connected resistive load.
Check your understanding

Questions to answer from the experiment

  1. Why does the terminal voltage decrease when the supply enters constant-current mode?
  2. For a 5 V, 0.5 A limit, what load resistance marks the CV/CC transition?
  3. Why is setting an appropriate current limit useful before connecting an unknown or newly assembled circuit?
  4. What would an ideal current-limited supply do as load resistance approaches zero, and what real-world effects are still omitted here?
Continue learning
Digital Multimeter FundamentalsMeasure DC voltage and current independently using the virtual DMM.Introductory Circuits WorkbenchReview Ohm’s law and resistive load behavior used by the bench-supply model.Electrical Design WorkbenchApply supply, load, conductor, and protection concepts in broader electrical designs.

Sources and model review

Reviewed 2026-09-08. The educational model exposes its assumptions and validation; source references do not imply external certification.

  • DC bench-supply regulation fundamentals — Uses Ohm’s law and a piecewise ideal regulator model to distinguish constant-voltage and constant-current operation.