BJT Bias Point Calculator (Voltage Divider Bias) mechanism

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

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