Voltage Regulator (Linear) Resistor/Output Calculator

Inspectable records

Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Area

Electrical & Electronics Engineering — Circuits, Power Systems, Electronics Lab

Tranche

tranche-4

Evidence ID

t4-268

Ledger rows

1

No ledger note is attached.

Review findings

The core nominal LM317-style voltage formula is correct, but the specification is incomplete and ambiguous because Iadj is undeclared, the inverse calculations are unspecified, and the promised minimum-load-current check has no defined threshold or method. The honest label is empty; it should state that this is an ideal nominal calculator and not a complete regulator design or compliance check.

Formula and scope findings

• The stated formula is standard for an ideal LM317-style adjustable regulator: Vout = Vref(1 + R2/R1) + Iadj·R2, assuming R1 is from OUT to ADJ and R2 is from ADJ to ground.
• The specification claims a min load current check, but provides no minimum-load-current threshold, regulator model, or formula for that check; its result cannot be defined unambiguously.
• Iadj appears in the formula but is missing from the declared inputs. The calculator must define whether Iadj is required, optional with a default, or assumed to be zero.
• The inverse formulas for calculating a missing resistor are not stated. For R2: R2 = (Vout - Vref)/(Vref/R1 + Iadj). For R1: R1 = Vref·R2/(Vout - Vref - Iadj·R2).
• The formula is an ideal nominal calculation and does not account for Vref tolerance, Iadj tolerance, resistor tolerance, dropout voltage, thermal limits, current limits, or regulator-specific behavior.

Unit assumptions

• Vref and Vout are in volts (V).
• R1 and R2 are in ohms (Ω), and both resistors must use the same resistance unit before arithmetic.
• Iadj is in amperes (A); for example, 50 µA must be entered as 0.000050 A.
• The resistor orientation is R1 from regulator output to adjust/reference node and R2 from that node to ground, as used by the LM317 convention.
• The formula computes nominal output voltage only; regulator input voltage must exceed Vout by the device's required dropout margin, but that condition is not represented by the formula.

Boundary hardening

Recorded hazards

• Division by zero occurs when calculating R2 if Vref/R1 + Iadj = 0; this can occur with invalid R1, zero Vref, or negative/unphysical Iadj.
• Division by zero occurs when calculating R1 if Vout - Vref - Iadj·R2 = 0.
• Calculated resistor values can be zero or negative; the calculator must reject nonpositive resistor values for a physical design, except that R2 = 0 is mathematically valid as a boundary test case.
• R1 = 0 is invalid because the forward formula contains R2/R1.
• Inputs must reject negative resistance, negative Vref where inappropriate, and inconsistent target values that require a negative resistor.
• The result may violate the regulator's minimum-load-current requirement, maximum output-current rating, power dissipation, or dropout-voltage requirement.
• Using milliamps or microamps as though they were amperes causes a factor-of-1000 or factor-of-1000000 error in the Iadj term.
• A fixed minimum-load threshold cannot be reported honestly without specifying the regulator part number or an explicit threshold.

Errata and corrections

No applied erratum is attached to this unique-name record.

Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

{
  "inputs": {
    "Vref_V": 1.25,
    "R1_ohm": 240,
    "R2_ohm": 720,
    "Iadj_A": 0.00005
  },
  "expected_outputs": {
    "Vout_V": 5.036
  },
  "working": "R2/R1 = 720/240 = 3. 1 + R2/R1 = 4. Vref·(1 + R2/R1) = 1.25·4 = 5.000 V. Iadj·R2 = 0.00005·720 = 0.036 V. Vout = 5.000 + 0.036 = 5.036 V."
}

Related workflows

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json · VERIFIED_CLEAN
• evidence-tranche4/tranche4-results.json