Source: https://guthlabs.ai/docs/instruments/bjt-bias-point-calculator-voltage-divider-bias/mechanism/

instrument mechanism / verified-with-binding-errata

# BJT Bias Point Calculator (Voltage Divider Bias) mechanism

The inspectable method record for BJT Bias Point Calculator (Voltage Divider Bias), kept separate from implementation and qualification.

Status: **VERIFIED_WITH_ERRATA**Lifecycle: **verified-with-binding-errata**

## Model scope

The core equations are acceptable as a simplified large-signal NPN bias estimate, but the instrument is not fully specified because β is listed yet ignored and the claimed saturation/cutoff check has no definition. Vector 4 was evaluated from the supplied numerical inputs; its correct raw result is VB=2 V, IE=IC=1.3 mA, and VCE=0.45 V, so it demonstrates a near-saturation case rather than a negative-VCE case.

- The formulas are valid only as a simplified NPN forward-active approximation with a fixed VBE of 0.7 V and IE≈IC.

- The optional β input is unused. If β is exposed, the specification must state that it is intentionally ignored or provide a β-dependent base-current/divider-loading model, such as IB=(VTH−VBE)/(RTH+(β+1)RE), IC=βIB, and IE=(β+1)IB.

- The exact collector-emitter voltage is VCE=VCC−IC·RC−IE·RE; VCC−IC·(RC+RE) is only consistent with the stated IE≈IC approximation.

- No formula or threshold is specified for the saturation/cutoff check. A negative computed VE or IC should not be reported as a physically valid negative current; cutoff handling and saturation clamping are required.

- The fixed 0.7 V base-emitter drop is not valid across temperature, current, or transistor type and should be explicitly labeled as an assumed silicon NPN approximation.

## Units and conventions

- Vcc, VB, VE, and VCE are in volts.

- R1, R2, RC, and RE must all use the same resistance unit; if resistance is entered in ohms, currents are in amperes, while using kilohms with volts produces currents in milliamperes.

- The examples use NPN polarity with positive VCC, a common-emitter resistor RE, and a collector resistor RC.

- β is dimensionless and is ignored by the supplied formulas.

- The 0.7 term assumes VBE=0.7 V exactly.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "Vcc_V": 12,
    "R1_ohm": 47000,
    "R2_ohm": 10000,
    "RC_ohm": 2200,
    "RE_ohm": 1000,
    "beta": 100
  },
  "expected_outputs": {
    "VB_V": 2.105263158,
    "IE_A": 0.001405263158,
    "IC_A": 0.001405263158,
    "VCE_V": 7.503157895,
    "saturation_cutoff_check": "active under the simplified model"
  },
  "working": "VB=12·10000/(47000+10000)=120000/57000=2.105263158 V. VE=2.105263158−0.7=1.405263158 V. IE=VE/RE=1.405263158/1000=0.001405263158 A. IC≈IE=0.001405263158 A; β=100 is ignored by the supplied formula. VCE=12−0.001405263158·(2200+1000)=12−0.001405263158·3200=12−4.496842105=7.503157895 V."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

The specification has an undefined divider case when R1+R2=0, and its supplied active-region formula produces negative VCE values after the saturation boundary without defining a separate saturation model or clamp. Resistor-position conventions also materially change the result if R1 and R2 are mislabeled.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/bjt-bias-point-calculator-voltage-divider-bias/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/bjt-bias-point-calculator-voltage-divider-bias/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/bjt-bias-point-calculator-voltage-divider-bias/qualification/>)

## Sources and evidence

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

- `VERIFIED_LEDGER.json`

- `evidence-tranche5/tranche5-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`