How this calculator works
Each bias mode reduces the base loop to a supply and resistance, with emitter feedback adding (beta+1)RE to the base-loop denominator. The divider mode uses its loaded Thevenin equivalent, so base current is not ignored. In collector feedback, collector resistance carries both base and collector current. VEE is a signed emitter supply and is zero for a single-supply emitter-feedback circuit. Design modes rearrange the same base-loop equations around a target collector current, or find RC from a target VCE. The constant-beta model only applies while the collector-base junction remains reverse biased.
Formula
Ib = (Vth - VEE - VBE)/(Rth + (beta+1)RE). Divider: Vth = VCC R2/(R1+R2), Rth = R1R2/(R1+R2). Collector feedback adds (beta+1)RC to the denominator. In fixed bias RB = beta(VCC-VBE)/Ic; RC = (VCC-VCE)/Ic. Ic = beta Ib; Ie = (beta+1)Ib.
Worked example
Fixed bias with VCC = 10 V, VBE = 0.7 V, RB = 93 kohm, RC = 1 kohm and beta = 50 gives Ib = 0.1 mA, Ic = 5 mA and Vc = 5 V. Collector feedback with RB = 42 kohm gives the same base current and Vc = 4.9 V.
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Frequently asked questions
Does this calculate a saturated switching transistor?
No. Saturation invalidates Ic = beta Ib. The tool rejects that operating region.
Is VBE always 0.7 V?
No. It varies with current, temperature and device. Enter an appropriate operating-point estimate.
Why include both divider currents?
They differ by base current. Showing both makes the loading of the bias divider explicit.