FAQ
TL;DR: Gate drivers often source 1–4 A to charge MOSFET gates; “most have an inherent ‘body diode’.” This FAQ curates book-style resources, key behaviors, and safe-use tips for MOSFET projects without video rabbit holes. [Elektroda, Anonymous, post #21680779]
Why it matters: If you’re hunting for Babani-style, project-first guidance on MOSFETs, this gives you vetted starting points and practical answers.
Quick Facts
- MOSFET vs BJT pins: Emitter=Source, Base=Gate, Collector=Drain; plan layouts accordingly. [Elektroda, Anonymous, post #21680777]
- An “on” MOSFET conducts both ways, but the intrinsic body diode enforces reverse-direction behavior. [Elektroda, Anonymous, post #21680779]
- Step-by-step primers: MOSFET as a switch and as an amplifier (text tutorials, not videos). [Elektroda, Anonymous, post #21680776]
- Book-style depth: The Art of Electronics, 3rd ed., §3.5 covers power MOSFET gotchas and datasheet reading. [Elektroda, Anonymous, post #21680788]
- RF-oriented fundamentals: ARRL Handbook sections explain devices and practical circuits clearly. [Elektroda, Anonymous, post #21680784]
What books or resources mirror “110 Thyristor Projects,” but for MOSFETs?
Combine vendor app notes with modern handbooks. Siliconix and International Rectifier data books include application sections with buildable circuits. Pair these with The Art of Electronics for design insight. Expect sectioned examples, cautions, and parts lists similar to classic project books. [Elektroda, Anonymous, post #21680786]
How is a MOSFET different from a bipolar transistor in practice?
BJTs are current-controlled; MOSFETs are voltage-controlled. Map pins as Emitter→Source, Base→Gate, Collector→Drain. N‑channel enhancement MOSFETs often replace NPN roles, but they need the right gate voltage and careful gate driving. This mindset shift simplifies switching designs and reduces base/gate drive losses. [Elektroda, Anonymous, post #21680777]
Will a MOSFET conduct in both directions when it’s on?
Yes. With the channel enhanced, current flows either way through the channel. However, the intrinsic body diode conducts in the reverse direction regardless of gate state. Designers add series diodes or arrange devices to control reverse paths. “Most have an inherent ‘body diode’.” [Elektroda, Anonymous, post #21680779]
Why do gate drivers claim 1–4 A if MOSFET gates draw almost no DC current?
Because the gate is a capacitor. Driving it fast needs high peak current to charge and discharge gate capacitance. That’s why gate driver ICs list ampere-level source/sink ratings, even though steady-state gate current is near zero. Fast edges reduce switching losses and heating. [Elektroda, Anonymous, post #21680779]
Is there a simple IC example of bidirectional analog switching with MOSFETs?
Yes. The CD4053 integrates logic with three MOSFET analog switches (a “triple” mux/demux). It’s a small‑signal, bidirectional example useful for signal routing, audio, and sensor selection. Check it to see how control logic steers bilateral MOSFET channels safely. [Elektroda, Anonymous, post #21680782]
Where can I learn MOSFET switching and amplifier basics without YouTube?
Use text tutorials covering MOSFETs as switches and as amplifiers. They walk through symbols, biasing, load lines, and example schematics. You can prototype from these pages and progress into datasheets once fundamentals click. It’s the closest feel to classic “project books.” [Elektroda, Anonymous, post #21680776]
Any tips for reading MOSFET datasheets—what’s often “not said”?
Start with AoE §3.5 guidance on power MOSFETs. Watch typical vs. max ratings, conditions for RDS(on), pulsed vs. continuous current, and thermal limits. Cross‑check SOA plots and gate charge when selecting drivers. “What to watch out for in data sheets” matters. [Elektroda, Anonymous, post #21680788]
How do RF and high‑speed designers think about BJTs vs MOSFETs?
In 50‑ohm and wideband work, many treat BJTs as voltage‑controlled with base current as a nuisance. FET users admire BJT transconductance at equal current. Perspective shifts with impedance and bandwidth, influencing device choice and matching networks. [Elektroda, Anonymous, post #21680783]
What is a body diode, and when does it cause trouble?
It’s the intrinsic PN diode between body and drain/source in power MOSFETs. It conducts when reverse‑biased relative to channel direction. It can backfeed supplies or defeat blocking in H‑bridges. Add series elements or use back‑to‑back MOSFETs to block. [Elektroda, Anonymous, post #21680779]
Quick how‑to: use an N‑channel MOSFET as a low‑side switch?
- Put the load between +V and drain; source to ground.
- Drive gate to a valid logic/high level relative to source; add a gate resistor.
- Add a flyback diode across inductive loads; verify RDS(on) and thermal limits. [Elektroda, Anonymous, post #21680776]
What is a gate driver in this context?
A gate driver sources and sinks high peak current to charge and discharge the MOSFET’s gate capacitance quickly. Faster transitions cut switching losses and heat. Many drivers advertise 1–4 A capabilities for robust, clean edges in power stages. [Elektroda, Anonymous, post #21680779]
Are there book lists that bridge hobby and pro power electronics?
Yes: The Art of Electronics for design intuition, plus vendor application handbooks from Siliconix and International Rectifier for proven circuits and notes. Expect example schematics and parts selection advice akin to classic hobby texts. [Elektroda, Anonymous, post #21680786]
What is the CD4053 used for in MOSFET learning?
It’s a triple analog multiplexer/demultiplexer IC. Each channel is a bilateral MOSFET switch steered by logic. Studying it shows how to manage on‑resistance, control signals, and bidirectional conduction in small‑signal paths. [Elektroda, Anonymous, post #21680782]
Which handbook offers approachable RF‑centric device explanations?
The ARRL Handbook. Its device chapters provide clear basics, measurements, and practical RF circuits that sharpen understanding of transistors and FETs beyond pure theory. It’s a solid complement to project‑driven learning. [Elektroda, Anonymous, post #21680784]
Edge case: will the MOSFET block reverse current if the gate is off?
Not necessarily. The body diode can still conduct and bypass your intended block. That’s a common cause of backfeed failures. Use back‑to‑back MOSFETs or add diodes when true reverse blocking is required. [Elektroda, Anonymous, post #21680779]
