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NPN models

NPN bipolar transistor Compare its models in the same order shown in the component inspector.

Symbol

NPN symbol
Default symbol for a new NPN component.

Model choice belongs to each placed NPN component. Changing one component does not change other instances or the default for future placements.

All datasheet fields use positive magnitudes. OhmSpice applies NPN polarity to voltages and currents.

1

Signal

Continuous transistor behavior set by current gain and base-emitter voltage, with a fixed Early-effect approximation and no capacitance.

Default
Qualified analyses
  • Operating point
  • DC sweep
  • AC sweep
  • Transient

Model definition

Signal fits the base-emitter exponential curve at the entered collector-current point and applies the selected forward current gain.

A fixed output slope provides qualitative Early-effect behavior without adding capacitance or stored charge.

Equations

IS=IC,refexp⁡(VBE,ref/VT),VT=25.852 mV at 27∘CI_S=\frac{I_{C,\mathrm{ref}}}{\exp(V_{BE,\mathrm{ref}}/V_T)},\qquad V_T=25.852\,\mathrm{mV}\ \text{at}\ 27^\circ\mathrm C
The entered base-emitter voltage and collector-current pair sets the transport saturation current.
IC≈ISexp⁡ ⁣(∣VBE∣VT) ⁣(1+∣VCE∣VA),VA=100 VI_C\approx I_S\exp\!\left(\frac{\lvert V_{BE}\rvert}{V_T}\right)\!\left(1+\frac{\lvert V_{CE}\rvert}{V_A}\right),\qquad V_A=100\,\mathrm V
The forward-active approximation includes the fixed 100 V Early-effect slope.
IB≈ICβFI_B\approx\frac{I_C}{\beta_F}
The entered forward current gain sets active-region base current.

Parameters

ParameterDefaultAccepted values
Current gainForward current gain (β / hFE).100Greater than 1
Base-emitter voltageBase-emitter voltage magnitude at the stated collector current; the polarity applies its sign.0.7 V at 1 mAGreater than 0; reference condition greater than 0

Limits

  • Junction capacitance, storage time, saturation fitting, breakdown, temperature, and noise are omitted.
  • The output slope is a fixed generic approximation.
2

Switching

Datasheet-calibrated gain, VBE, saturation, transition frequency, output capacitance, and stored charge.

Qualified analyses
  • Operating point
  • DC sweep
  • AC sweep
  • Transient

Model definition

Switching retains the Signal active-region fit and adds one forced-beta saturation point, transition frequency, collector-base capacitance, and storage time.

The saturation datum calibrates collector resistance. Frequency and charge data set the forward and reverse transit-time behavior.

Equations

IS=IC,refexp⁡(VBE,ref/VT),βR=1I_S=\frac{I_{C,\mathrm{ref}}}{\exp(V_{BE,\mathrm{ref}}/V_T)},\qquad \beta_R=1
The active-region reference point sets saturation current; reverse current gain is fixed at one.
IR=βFIB,sat−IC,sat1+(βF+1)/βR,IF=βFIB,sat−βFβRIRI_R=\frac{\beta_F I_{B,\mathrm{sat}}-I_{C,\mathrm{sat}}}{1+(\beta_F+1)/\beta_R},\qquad I_F=\beta_F I_{B,\mathrm{sat}}-\frac{\beta_F}{\beta_R}I_R
The paired saturation currents are decomposed into native forward and reverse junction currents.
VCE,int=VTln⁡ ⁣(IFIR),RC=VCE(sat)−VCE,intIC,satV_{CE,\mathrm{int}}=V_T\ln\!\left(\frac{I_F}{I_R}\right),\qquad R_C=\frac{V_{CE(sat)}-V_{CE,\mathrm{int}}}{I_{C,\mathrm{sat}}}
Collector resistance makes the native intrinsic saturation point match the entered terminal VCE(sat).
gm=IC,fTVT,τF=12πfT−Cobogm,τR=tstorageg_m=\frac{I_{C,f_T}}{V_T},\qquad \tau_F=\frac{1}{2\pi f_T}-\frac{C_{obo}}{g_m},\qquad \tau_R=t_{\mathrm{storage}}
Transition frequency, collector-base capacitance, and storage time set the native forward and reverse transit times.
CJC=Cobo,CJE=0,VA=100 VC_{JC}=C_{obo},\qquad C_{JE}=0,\qquad V_A=100\,\mathrm V
Output capacitance is constant; emitter capacitance is omitted and Early voltage is fixed.

Parameters

ParameterDefaultAccepted values
Current gainForward current gain (β / hFE).100Greater than 1
Base-emitter voltageBase-emitter voltage magnitude at the stated collector current.0.7 V; at IC 10 mAGreater than 0; reference condition greater than 0
VCE(sat)Collector-emitter saturation voltage magnitude at the stated collector current.0.2 V; at IC 1 AGreater than 0; reference condition greater than 0
Saturation base currentBase current used with the stated collector current for the VCE(sat) test.100 mAGreater than 0
Transition frequencyUnity current-gain frequency at the stated collector current.100 MHz; at IC 10 mAGreater than 0; reference condition greater than 0
Output capacitanceConstant effective collector-base output capacitance.20 pFGreater than 0
Storage timeReverse transit time controlling stored charge after saturation.200 nsGreater than 0

Limits

  • The model fits one active point and one forced-beta saturation point.
  • Quasi-saturation, nonlinear capacitance, breakdown, electrothermal behavior, and temperature are omitted.
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