Source: https://mokxi.com/learn/path/analog-amplifiers Updated: 2026-11-11 All paths # Transistors and op-amps for real Intermediate, after Electronics basics: the diode curve, biasing a BJT, common-emitter gain, the MOSFET as switch and resistor, op-amp gain both ways, comparators with hysteresis and split supplies. Free 7 lessons 4 h 3 chapters 2,038 XP Electrical ยท Intermediate +150 XP 0 of 7 done Start the course free The diode curve Lesson plan for teachers What you will build ## 3 projects, built step by step 7 lessons in 3 chapters, about 4 hours on a simulated breadboard. Free, in your browser, every step checked by the simulator. Chapter 1 project ### MOSFET as a switch and as a resistor A 2N7000 with a knob on its gate: fully on with about 2 ohm left, fully off, and in between a resistor the gate voltage sets. Gate threshold, on resistance and why a MOSFET takes no gate current. Open it in the simulator Chapter 2 project ### Inverting and non-inverting amps An LM358 amplifier on one 5 V supply, read with AC meters: a gain of 3.2 from two resistors, a gain of 2, a DC offset that pushes it into its top clip, and the inverting amplifier on paper. Open it in the simulator Chapter 3 project ### Split supplies A TL072 inverting amplifier on +12 V and -12 V: a gain of -4.7 on a signal centered on ground, a DC output below zero, what happens without the negative rail, more gain, and where it clips. Open it in the simulator The map ## Chapter by chapter Each lesson opens when the one before it is done, and each chapter ends in a project. Chapter 1 ## Diodes and transistors The diode curve, a BJT biased by hand, and the MOSFET both ways. Open 169 XP ### The diode curve A red LED on a bench supply with a 10 ohm sense resistor: almost no current below the knee, then a flood. Why a diode is not a fixed 2 V drop, and why every LED gets a resistor. 0 of 5 steps Start What is in it Locked 218 XP ### Biasing a BJT A 2N2222 and an LED: hard on as a switch, then starved of base current until the collector current follows the base current a hundred and seventy times over. Picking a base resistor for the current you want. 0 of 6 steps Project Locked 436 XP ### MOSFET as a switch and as a resistor A 2N7000 with a knob on its gate: fully on with about 2 ohm left, fully off, and in between a resistor the gate voltage sets. Gate threshold, on resistance and why a MOSFET takes no gate current. 0 of 6 steps 5 questions, graded as you go. Chapter 2 ## Gain A transistor amplifier and an op-amp amplifier, each set by two resistors. Locked 218 XP ### Common-emitter gain A divider-biased 2N2222 amplifier on 9 V: read the operating point, measure a gain of about 4.5 with AC meters, halve it, clip it, and see what bad bias does. 0 of 6 steps Project Locked 374 XP ### Inverting and non-inverting amps An LM358 amplifier on one 5 V supply, read with AC meters: a gain of 3.2 from two resistors, a gain of 2, a DC offset that pushes it into its top clip, and the inverting amplifier on paper. 0 of 5 steps 5 questions, graded as you go. Chapter 3 ## Real-world analog Clean decisions with hysteresis, and room on both sides of ground. Locked 187 XP ### Comparators and hysteresis An LM393 comparing a knob with 2.5 V: an open-collector output, an LED that lights past the threshold, and one feedback resistor that gives it two thresholds so a noisy signal cannot make it chatter. 0 of 5 steps Project Locked 436 XP ### Split supplies A TL072 inverting amplifier on +12 V and -12 V: a gain of -4.7 on a signal centered on ground, a DC output below zero, what happens without the negative rail, more gain, and where it clips. 0 of 6 steps 5 questions, graded as you go. Syllabus ## Every lesson in the course All 7 lessons, in order, each with what it covers. Any of them opens in the editor right away. Chapter 1 ### Diodes and transistors - The diode curve A red LED on a bench supply with a 10 ohm sense resistor: almost no current below the knee, then a flood. Why a diode is not a fixed 2 V drop, and why every LED gets a resistor. - Biasing a BJT A 2N2222 and an LED: hard on as a switch, then starved of base current until the collector current follows the base current a hundred and seventy times over. Picking a base resistor for the current you want. - MOSFET as a switch and as a resistor A 2N7000 with a knob on its gate: fully on with about 2 ohm left, fully off, and in between a resistor the gate voltage sets. Gate threshold, on resistance and why a MOSFET takes no gate current. Chapter 2 ### Gain - Common-emitter gain A divider-biased 2N2222 amplifier on 9 V: read the operating point, measure a gain of about 4.5 with AC meters, halve it, clip it, and see what bad bias does. - Inverting and non-inverting amps An LM358 amplifier on one 5 V supply, read with AC meters: a gain of 3.2 from two resistors, a gain of 2, a DC offset that pushes it into its top clip, and the inverting amplifier on paper. Chapter 3 ### Real-world analog - Comparators and hysteresis An LM393 comparing a knob with 2.5 V: an open-collector output, an LED that lights past the threshold, and one feedback resistor that gives it two thresholds so a noisy signal cannot make it chatter. - Split supplies A TL072 inverting amplifier on +12 V and -12 V: a gain of -4.7 on a signal centered on ground, a DC output below zero, what happens without the negative rail, more gain, and where it clips. Keep going ## The next course on your track Transistors and op-amps for real is part of the electrical track, a ladder of courses from zero to expert. Next course ### Power and batteries Where the volts come from and how to keep them: Ohm's law on a real meter, cells in series and parallel, a regulator, a LiPo on a TP4056, a boost converter, a battery gauge, and a power bank you build yourself. Open the next course Track ### Electrical track Current and voltage you can see, then transistors, op-amps, filters, power and PCBs. Every circuit runs in a real circuit simulator in your browser. See every course on the track Kits ## Build it on your bench too Every lesson runs in the simulator with nothing to buy. When you want the real thing, these kits have the parts. Have a kit already? ### Find your kit Pick the starter kit you own and run every lesson in its manual with the same parts on the same pins. See every kit Questions ## About Transistors and op-amps for real Is Transistors and op-amps for real free? Yes. All 7 lessons of Transistors and op-amps for real are free and run in your browser, with nothing to install and no parts to buy before you start. Do I need any parts? No. Every circuit is built on a simulated breadboard, and the simulator checks each step as you go. When you want to build it for real, the same parts and wiring work on a real bench. How long does Transistors and op-amps for real take? About 4 hours: 7 lessons in 3 chapters, each one a few short steps. Your progress is kept, so you can stop after any lesson and pick up where you left off. What will I build? Each chapter ends in a project that puts it together: MOSFET as a switch and as a resistor, Inverting and non-inverting amps and Split supplies. Where do I start? With "The diode curve", and each lesson builds on the one before it. New to circuits? Electronics basics is the course that starts from zero.