Ohmforge DC Operating Point

SPICE netlist in, node voltages, branch currents, power and overload warnings out.

Try an example: Voltage divider (10 V, 1k/3k → 7.5 V) · Transistor switching an LED · Diode forward drop (Shockley)

How it works

Solves the DC operating point of a circuit with Ohmforge's SPICE-style engine (Modified Nodal Analysis, Newton–Raphson with junction limiting, damping, gmin and source stepping). Returns every node voltage, the current and power of every element, total supply power, parts beyond their ratings and plain-language convergence diagnostics.

The netlist is parsed (SPICE subset) and compiled into Modified Nodal Analysis unknowns: one voltage per node plus one current per voltage source, inductor and controlled-source output.
Nonlinear devices (Shockley diode with series resistance and breakdown, Ebers–Moll BJT with Early effect, Shichman–Hodges level-1 MOSFET) are linearised at each Newton–Raphson iteration; junction voltages are limited with the SPICE3 pnjlim rule.
If plain Newton–Raphson fails, the solver retries with damping (≤ 0.5 V per iteration), then gmin stepping (1e-2 S → 1e-12 S to ground on every node) and finally source stepping (all sources ramped 0 → 100 %). Every attempt is reported in plain words.
Topology checks run first: missing ground, loops of voltage sources/inductors (no unique solution) and nodes without a DC path to ground.
Element power is Σ(terminal current × node voltage); sources show negative power when delivering. Ratings (resistor watts, LED current, diode/transistor limits, capacitor voltage) are compared with the result.

Teaching-grade simulation: device models are simplified (Ebers–Moll BJT, level-1 MOSFET, behavioural op-amps and 555) and part ratings are typical values. Verify real designs on the bench and against manufacturer data before building anything connected to mains voltage.

Sources

SPICE: A Computer Program to Simulate Semiconductor Circuits (L. W. Nagel, UC Berkeley ERL-M520, 1975) (University of California, Berkeley)
The Modified Nodal Approach to Network Analysis (Ho, Ruehli, Brennan, IEEE Trans. Circuits and Systems, 1975) (IEEE)
ngspice User Manual (device models, convergence options, source syntax) (ngspice project)

For scripts and AI agents

JSON API: POST https://ohmforgedcoperatingpoint.usefulweb.site/api/v1/calculate (same calculation as this page)
Interface description: OpenAPI 3.1 · AI guide: llms.txt
MCP server (Streamable HTTP): https://ohmforgedcoperatingpoint.usefulweb.site/mcp · tool name ohmforge_dc_operating_point

Example request

curl -s -X POST https://ohmforgedcoperatingpoint.usefulweb.site/api/v1/calculate \
  -H 'content-type: application/json' \
  -d '{"netlist":"* Voltage divider\nV1 in 0 DC 10\nR1 in out 1k\nR2 out 0 3k\n.op\n.end"}'

Related tools

Ohmforge Transient Simulation – Simulate a circuit over time: waveforms, Vpp/RMS/frequency, CSV and a chart.
Ohmforge AC Sweep (Bode plot) – Frequency response of a circuit: Bode magnitude/phase, −3 dB corner and unity gain.
Ohmforge LED Resistor Calculator – Series resistor for LEDs, rounded to a standard value and checked with a real diode model.