Transistor & Amplifier Calculator
Work through the transistor and amplifier math the Associate CET exam tests. Calculate BJT bias currents and voltages, current and voltage gain, and op-amp circuits — each with the formula shown and the answer worked out.
BJT Voltage-Divider Bias
The most common and stable way to bias a transistor. R1/R2 set the base voltage, and the calculator finds the resulting currents and the collector-emitter voltage (the Q-point). Assumes an NPN with VBE ≈ 0.7 V. Base current loading is included (Thevenin model); if the result would put VCE below about 0.2 V the calculator reports saturation instead.
BJT Current Gain
A bipolar transistor is current-controlled: a small base current produces a much larger collector current. Beta (β) is the ratio; alpha (α) relates collector to emitter current.
Common-Emitter Voltage Gain
An approximate voltage gain for a common-emitter stage. With the emitter resistor fully bypassed by a capacitor, gain is set by RC and the internal emitter resistance r′e. Unbypassed, RE adds to r′e, lowering the gain (but improving stability); −RC/RE is the shortcut when RE ≫ r′e. Gains are with no load: with a load RL, use RC∥RL in place of RC.
Op-Amp Gain
Operational amplifiers set their gain with two external resistors. Pick the configuration; the inverting amp flips signal polarity (negative gain), the non-inverting amp keeps it (gain is always at least 1).