2 · Diode I–V curve

Status: ✅ Runs today

Goal: sweep a source and watch a nonlinear part respond.

Build

02-diode-iv.circuit.tsx

import { analog } from "tscircuit"

export default () => (
  <board routingDisabled>
    <voltagesource name="V1" voltage="0V" />
    <resistor name="R1" resistance="100" footprint="0402" />
    <diode name="D1" footprint="sod123" />
    <trace from=".V1 > .pin1" to=".R1 > .pin1" />
    <trace from=".R1 > .pin2" to=".D1 > .anode" />
    <trace from=".D1 > .cathode" to=".V1 > .pin2" />
    <voltageprobe name="VD" connectsTo=".D1 > .anode" referenceTo=".D1 > .cathode" />
    <analog.dcsweepsimulation name="DIODE_IV" spiceEngine="ngspice"
      sweepSource=".V1" sweepStart="0V" sweepStop="2V" sweepStep="0.1V" />
  </board>
)

analog.dcsweepsimulation steps V1 from 0 V to 2 V and solves the DC circuit at each step, the same as .dc in SPICE.

Run

bunx tsci simulate 02-diode-iv.circuit.tsx

What you see

One row per step. v(n2) is the diode voltage, and the last column is the current (shown negative, as it flows out of the source):

V1	Diode V	Current
0.5 V	0.4998 V	2.5 µA
0.6 V	0.5915 V	85 µA
0.7 V	0.6413 V	0.59 mA
1.0 V	0.6851 V	3.15 mA
2.0 V	0.7210 V	12.8 mA

Check by hand

• Below about 0.5 V, almost no current flows and the whole voltage sits across the diode.
• Above the knee, the diode holds about 0.65–0.72 V, and R1 takes the rest: (2 − 0.721) / 100 Ω = 12.8 mA ✓
• The diode voltage rises about 36 mV between 3.15 mA and 12.8 mA, roughly a factor of 4. That fits about 60 mV per decade of current.

Try this

Sweep to 5 V and work out the current at the end from R1 alone.