Voltage Regulators

The voltage regulator parts model linear (series-pass) regulators that turn a higher input voltage into a lower regulated output. de:volt ships fixed-output regulators (7805, AMS1117-3.3, AMS1117-5.0) and one adjustable regulator (LM317). All four drop voltage across an internal pass element, so load current can produce substantial package heat.

Fixed regulators

These hold a preset output as long as the input has enough headroom above it.

The 7805 is a conventional linear regulator; the AMS1117 parts are LDOs that regulate with less input headroom. That does not make an AMS1117 intrinsically cooler: at the same input voltage, output voltage, and load current, both dissipate approximately (Vin − Vout) × Iout.

Fixed pinout

All three fixed regulators share the same three-pin model.

The canvas labels are authoritative. The AMS1117 entries represent labeled breakout/module terminals, not the spatial lead order of a bare SOT-223 IC. A bare fixed-output AMS1117 has pin 1 = GND, pin 2 and the tab = OUT, and pin 3 = IN. On a standard 7805 TO-220, the flat face forward gives IN / GND / OUT left to right and the tab is GND. Always verify the exact package datasheet before wiring hardware.

Adjustable regulator (LM317)

The LM317 has no fixed output. Instead it holds a constant 1.25 V reference between its OUT and ADJ pins, and you set the output with two external resistors:

Vout = 1.25 * (1 + R2 / R1)

R1 connects OUT to ADJ; R2 connects ADJ to GND. A common starting point is R1 = 240 Ω with R2 to ground. For example, R1 = 240 Ω and R2 = 720 Ω give Vout = 1.25 * (1 + 720/240) = 5.0 V. The output is adjustable from ~1.25 V (R2 = 0) up to ~37 V.

LM317 pinout

The canvas LM317 is also a labeled three-terminal breakout/module abstraction; connect IN, ADJ, and OUT by label. A common bare LM317T TO-220 has ADJ / OUT / IN left to right when viewed from the front, and the metal tab is OUT (not GND). The simplified simulator omits a real LM317’s adjustment-pin-current term and minimum-load requirement. In hardware, follow the selected datasheet’s full equation and recommended resistor values (240 Ω from OUT to ADJ is a common starting point).

How the simulation behaves

The engine models electrical regulation together with package heat for exact catalog identities. The active electrical regime depends on input headroom, load, and thermal-shutdown state.

• Constant-voltage (CV). With enough input headroom and a load under the current limit, the output sits at its target (or the divider value for the LM317). This is normal regulation.
• Dropout. If the input falls below Vout + dropout, the regulator can no longer hold the target and the output falls with the input. It approaches 0 V when the input is removed; it does not become negative merely because the supply is off. For the 7805 the input must stay above ~7 V; for the AMS1117 parts above Vout + ~1.1 V; for the LM317 above Vout + ~2 V.
• Current limit. If the load tries to pull more than the limit (1.0 A for the 7805, 0.8 A for the AMS1117, 1.5 A for the LM317), the regulator caps the current and the output sags.
• Off. With insufficient input, or while thermal shutdown is active, the pass branch is high impedance. It does not clamp the output to ground and does not backfeed an externally driven output into IN in this model.

Because a linear regulator dissipates approximately P = (Vin − Vout) × Iout plus its own supply loss, a large input-to-output gap at high current means a lot of heat. The exact catalog models route input/output power and quiescent current, then feed solved package dissipation into a persistent one-pole junction-temperature model. They also report an ambient-adjusted continuous-power allowance.

These are compact package/board assumptions, not universal hardware constants. Copper area, airflow, mounting, and heatsinking can move the real result substantially. The 7805 and LM317 restart points are assumed; both LM317 thresholds are compact-model assumptions. The AMS1117 model’s 165 °C protection point is above its 150 °C absolute-junction rating, so shutdown is not a safe operating target. Crossing the trip point turns the simulated pass output off; regulation resumes only after cooling below the restart point.

The electrical current limit is not evidence that an unheatsinked part can deliver that current continuously. The model omits loop stability, output noise, startup transients, detailed current-limit/foldback curves, reverse-current protection paths, and temperature feedback into every electrical parameter.

Input and output capacitors

Real linear regulators need the datasheet-recommended input and output capacitors for transient response and stability. Place those capacitors explicitly if you want their electrical impedance in the simulated circuit. The regulator macro-model itself does not model control-loop stability, so a simulated run cannot prove that a hardware capacitor choice is stable.

• 7805: 0.1 µF ceramic close to IN and OUT.
• AMS1117: these LDOs need bulk capacitance: about 10 µF on both input and output.
• LM317: 0.1 µF on IN and ~1 µF on OUT.

Example circuit

A 9 V battery regulated down to a 5 V logic rail with a 7805:

9V Battery + ─── IN ──[ 7805 ]── OUT ─── +5V rail
                       │
0.1µF ┤              GND ┤ 0.1µF
                       │
9V Battery − ──────────┴────────────────── GND

Adjustable 5 V rail from the LM317 (R1 = 240 Ω, R2 = 720 Ω):

Vin ─── IN ──[ LM317 ]── OUT ──┬─── Vout (5.0 V)
                          │    │
                          │   R1 240 Ω
                          │    │
                          └── ADJ
                               │
                              R2 720 Ω
                               │
                              GND

Tune R2 (or swap it for a potentiometer) to dial Vout from 1.25 V upward.

Model identity and readouts

The package-specific thermal and quiescent-current defaults require the exact persisted catalog ID. A legacy, custom, or mismatched component uses labelled fallback behaviour rather than silently borrowing a package. Select the regulator to see its model identity, electrical regime, current direction, input/output power flow, temperature, thermal-shutdown state, and Included / Not included disclosure. Missing telemetry is shown as unavailable, not as a false zero.