Electronics Basics #26 | Depletion MOSFET DC Analysis: Voltage-Divider Bias

Instructor: Dr. Süleyman Burak ÇELİK

Find the DC operating point of the original n-channel depletion MOSFET circuit, step by step. We start with the goal and the insulated-gate distinction, then solve the unloaded divider, derive both current roots, reject the nonphysical root and check saturation. Original values: VDD=18V, RD=1.8kΩ, RS=750Ω, upper divider110MΩ, lower10MΩ, IDSS=6mA, VP=−3V. Verified ideal results: ID≈3.117mA, VGS≈−0.838V, VDS≈10.052V. A depletion MOSFET is normally on and permits positive gate-source voltage within its ratings; do not carry over the JFET-only gate restriction. Ideal saturation model, negligible gate leakage, suitable real device ratings assumed. The very high-resistance divider is sensitive to leakage in real hardware. A complete worked problem is kept together; displayed rounding is distinguished from full-precision calculation. Chapters: 0:00 The goal: find the current before applying a signal 1:11 An insulated gate and a normally-on channel 2:27 Find the gate voltage, then the control voltage 4:19 One unknown links the circuit and the device 6:14 Two algebraic roots, one physical candidate 8:15 Calculate the voltages and test saturation 11:01 The checked operating point and a reusable method