Simulate Circuits with a Prompt

Flux now has built-in circuit simulation, and your AI design assistant knows how to use it.

If you've ever designed a circuit board, you know the feeling. You finish your schematic, send it off for fabrication, wait for the boards to arrive, and then hold your breath. Will it work? Did you get the filter cutoff right? Is that decoupling cap actually sized correctly?

For most of hardware design history, the answer has been: build it and find out.

Simulation was always supposed to solve this. And technically, it can. SPICE has been around for decades. But in practice, simulation has been so cumbersome to set up that most engineers skip it entirely. Even some of the best-resourced hardware teams in the world have left simulation on the table because the overhead just isn't worth it for everyday design decisions.

That changes today.

Simulation that fits into how you actually work

We're introducing circuit simulation built directly into Flux. Describe what you want to simulate in plain language through the Flux AI chat, and Flux handles the rest: building the netlist, configuring the analysis, running the simulation, and returning charts with clear explanations.

No setup wizard. No exporting netlists. No switching tools.

Two ways to start:

From a prompt. Don't even have a schematic yet? Just describe the circuit and what you want to measure.

You: "Simulate a first-order RC low-pass filter with a 10 kΩ resistor and 10 nF capacitor. Generate the bode plot and find the -3 dB cutoff frequency."
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Flux: Runs an AC sweep, returns the bode plot, reports the -3 dB point at ~1.59 kHz, and confirms it matches the theoretical value of 1/(2πRC).

One sentence in, full analysis out.

From your schematic. Already have a design in progress? Even better. Flux pulls context from your parts, net connections, and datasheets to build the simulation automatically. You don't need to export anything or set up a separate project. Just ask.

You: "Simulate the voltage across C3. Show me the output ripple voltage in a plot.
Check the actual project.

Flux: Uses the components and connections already in your design, runs the analysis, and returns results without you specifying a single component value.

Your schematic is the test bench.

What you can simulate

The simulator handles the kinds of analyses engineers actually run day-to-day:

Filters and frequency response

Passive or active, from simple RC low-pass to second-order Sallen-Key and multiple-feedback topologies. Get bode plots, -3 dB points, phase response, rolloff slopes, and bandwidth in seconds.

Try it: "Simulate a second-order Sallen-Key low-pass filter using an ideal op-amp, with equal resistor values of 10 kΩ and equal capacitor values of 4.7 nF. Produce the bode plot, identify the corner frequency, and report the slope after cutoff."
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Transient analysis and timing

RC charge/discharge curves, step responses, debounce circuits, pulse timing. Verify time constants and measure voltage thresholds over time.

Try it: "Simulate an RC charging circuit with a 5 V step input, a 100 kΩ resistor, and a 1 µF capacitor. Plot the capacitor voltage over time and report the time to reach 63.2% and 90% of final voltage."
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Voltage and current ripple

Measure ripple across rectifier circuits, filter stages, and switching approximations. Compare ripple across different capacitor values without rebuilding the test bench every time.

Try it: "Simulate a full-wave bridge rectifier using 0.7V-per-diode bridge model, with a 15 V RMS 50 Hz AC source, a 1000 µF filter capacitor, and a 100 Ω load. Report the average DC voltage, ripple frequency, and peak-to-peak ripple voltage."
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Tips for getting great results

The simulator is powerful, and a little context on how it works helps you get more out of it.

It runs on industry-standard SPICE. Under the hood, Flux uses a proven SPICE engine with access to a verified component library of 340,000+ models. When you request a simulation, Flux interprets your request, constructs the netlist, configures sources and analysis parameters, executes the simulation, and returns results with clear explanations.

Component models matter. Flux draws from its verified model library automatically, but here's what happens at the edges:

• Want to know if a model exists for a part?Just ask. Flux will tell you.
• Need a model we don't have?You can upload your own SPICE model file directly.
• Not sure what model is being used?Ask Flux proactively — it can tell you whether it's using a full manufacturer model, a behavioral approximation, or an ideal stand-in. Knowing this upfront helps you gauge how much to trust the numbers.

It's conversational, not one-shot. Think of simulation in Flux as a back-and-forth. If the first result isn't quite right, adjust parameters, zoom in on a range, or ask for a different visualization. The iteration is the workflow, not a sign that something went wrong.

Start with what you know. If you have a rough idea of expected results (a ballpark cutoff frequency, a target ripple range) you'll be able to validate output quickly and course-correct.

Verification as a design loop

Here's where things come together. Because simulation lives inside the same AI assistant you're already using to design, results don't just sit in a chart. They feed back into your workflow.

Ask Flux to simulate a circuit, evaluate results against your spec, and adjust component values if the numbers don't work out. Instead of hand-calculating a filter cap value and hoping for the best, you can size it based on actual simulated performance.

This works for nearly any quick validation: filter cutoffs, ripple targets, timing thresholds. Describe what "good" looks like, and let Flux iterate toward it.

Getting started

• Be specific in your prompts.Include component values, node names, and what measurements you want. The more detail you give, the better the result.
• Start from your schematic when you can.Flux pulls context from your design automatically. Less for you to specify, fewer things to get wrong.
• Ask about models.Before trusting results for critical decisions, ask Flux what component models it's using. You can always upload your own if you need higher fidelity.
• Ask follow-up questions.After a simulation, ask Flux to zoom in, compare to theory, or re-run with different values.
• Start simple, build up.The simulator excels at focused, targeted analyses. Run one simulation at a time and layer complexity as you go.

The fastest way to verify a circuit is to just describe it.

Open Flux and try it today!