FETs and MOSFETs: basics
Analog electronics · Physics
DC circuit
Interactive 3DElectrons drift around the loop — raise the voltage and watch the current obey Ohm's law.
Controls
Drag the sliders or type a value — the simulation updates live.
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1V12V
Study notes
Worked example - JFET bias point. An n-channel JFET has IDSS = 10 mA and pinch-off Vp = -4 V. Find the drain current at VGS = -2 V. Step 1: use ID = IDSS(1 - VGS/Vp)^2. Step 2: VGS/Vp = (-2)/(-4) = 0.5. Step 3: ID = 10 x (1 - 0.5)^2 = 10 x 0.25 = 2.5 mA. Check the extremes: at VGS = 0, ID = IDSS = 10 mA (fully on); at VGS = -4 V = Vp, ID = 0 (pinched off). This square-law curve is why JFETs make naturally low-distortion audio stages when biased mid-range.
Related topics
- Diode circuits: rectifiers (half/full wave, bridge)
- Filters and voltage regulators
- BJT biasing and amplifiers (CE amplifier analysis)
- Operational amplifiers: ideal characteristics
- Op-amp applications: adder, subtractor, integrator, differentiator, comparator
- Oscillators: RC, LC and crystal (introductory)