What must be checked before using the BJT load line relation?

Identify the region (cutoff, active, saturation) before using β or VCE(sat).

11. BJT transistors

BJT load line

Formula

V_{CE}=V_{CC}-I_CR_C

Detail

The load line joins (VCC,0) to (0,VCC/RC); the Q-point travels cutoff, active and saturation.

Explore the idea

Variables

$I_C,I_B,I_E$ A
$\alpha,\beta$ dimensionless
$V_{CE},V_{BE}$ V
$g_m$ S
$r_\pi$ Ω.

Conditions

Small-signal NPN unless stated; stay in the named region.

Intuitive explanation

For “BJT load line”: IB sets IC = β IB in the active region; the load line runs through cutoff, active and saturation.

Worked example

With

V_{CC}=10\,\mathrm V

and

R_C=1\,\mathrm{k\Omega}

, the load line joins

(I_C=0,V_{CE}=10\,\mathrm V)

and

(I_C=10\,\mathrm{mA},V_{CE}=0)

Common mistakes

using IC=β IB in saturation
forgetting VCE(sat)
swapping emitter and collector on the DCL

Frequently asked questions

What must be checked before using the BJT load line relation?: Identify the region (cutoff, active, saturation) before using β or VCE(sat).

Also known as

beta, load line, active region, saturation, Q point

Conventions

A, V, S or Ω

Last reviewed: 2026-09-19

Found an error? Contact us.

Related formulas

11. BJT transistors

BJT load line

In 11. BJT transistors

Formula

V_{CE}=V_{CC}-I_CR_C

Detail

The load line joins (VCC,0) to (0,VCC/RC); the Q-point travels cutoff, active and saturation.

Explore the idea

Variables

$I_C,I_B,I_E$ A
$\alpha,\beta$ dimensionless
$V_{CE},V_{BE}$ V
$g_m$ S
$r_\pi$ Ω.

Conditions

Small-signal NPN unless stated; stay in the named region.

Intuitive explanation

For “BJT load line”: IB sets IC = β IB in the active region; the load line runs through cutoff, active and saturation.

Worked example

With

V_{CC}=10\,\mathrm V

and

R_C=1\,\mathrm{k\Omega}

, the load line joins

(I_C=0,V_{CE}=10\,\mathrm V)

and

(I_C=10\,\mathrm{mA},V_{CE}=0)

Common mistakes

using IC=β IB in saturation
forgetting VCE(sat)
swapping emitter and collector on the DCL

Frequently asked questions

What must be checked before using the BJT load line relation?: Identify the region (cutoff, active, saturation) before using β or VCE(sat).

Also known as

beta, load line, active region, saturation, Q point

Conventions

A, V, S or Ω

Last reviewed: 2026-09-19

Found an error? Contact us.

BJT load line

Tags

Detail

Explore the idea

Variables

Conditions

Intuitive explanation

Worked example

Common mistakes

Frequently asked questions

Also known as

Conventions

Related formulas

BJT load line

Tags

Detail

Explore the idea

Variables

Conditions

Intuitive explanation

Worked example

Common mistakes

Frequently asked questions

Also known as

Conventions

Related formulas