# Inductance for MCU / DC Electronics — Resources ## Knowledge ### Primary sources (manufacturer application notes) - [Allegro MicroSystems — AN296235, "Driving Inductive Loads"](https://www.allegromicro.com/-/media/files/application-notes/an296235-driving-inductive-loads.pdf?sc_lang=en) Short, dense, and exactly on-mission. States `V = L(dI/dt)` as Equation 1 and the central rule: current in an inductor cannot be stopped instantaneously, so a decay path must be provided. Covers diode rectification vs synchronous rectification. **Use for:** the core equation, recirculation paths, half-bridge/MOSFET driving. - [Texas Instruments — SLVAE59, "Using Motor Drivers to Drive Solenoids"](https://www.ti.com/lit/pdf/slvae59) Categorises solenoid types, driver configurations, and freewheeling vs clamping strategies. **Use for:** solenoid-specific design, choosing a driver topology. - [ON Semiconductor — AND90158, "Understanding Power MOSFET Avalanche"](https://www.onsemi.com/download/application-notes/pdf/and90158-d.pdf) What actually happens inside the MOSFET when an unclamped inductive load is switched off. **Use for:** why an unprotected transistor dies, and repetitive avalanche ratings. - [Infineon — Power MOSFET Avalanche Design Guidelines](https://www.infineon.com/dgdl/Infineon-Power_MOSFET_avalanche_design_guidelines-ApplicationNotes-v01_01-EN.pdf?fileId=8ac78c8c882315570188295e1c6a22f7) **Use for:** designing deliberately *with* avalanche (fast solenoid turn-off). - [STMicroelectronics — AN4402, "Driving inductive loads"](https://www.st.com/resource/en/application_note/an4402-multichannel-drivers-driving-inductive-loads--with-l99mc6-and-l9733-stmicroelectronics.pdf) **Use for:** integrated active-clamp behaviour in real driver ICs. ### Motors and microcontroller limits - [ESP32 Series datasheet — Espressif](https://documentation.espressif.com/esp32_datasheet_en.html) Table 5-1 (Absolute Maximum Ratings) and Table 5-3 (DC Characteristics) carry the numbers that decide whether anything can hang off a pin: 40 mA per-pin source, 28 mA sink, 1200 mA cumulative, 3.6 V absolute max on a pin. Note the footnote that per-pin source current degrades toward ~29 mA when several pins in a domain source at once. **Use for:** any "can the pin drive this?" question. The authoritative source — there is a lot of folklore online (the 12 mA figure is from the ESP8266). - [Pololu — Micro Metal Gearmotors](https://www.pololu.com/category/60/micro-metal-gearmotors) Publishes honest free-run *and* stall current for every variant (6 V: LP 50/360 mA, MP 80/670 mA, HP 120/1600 mA). **Use for:** realistic motor numbers when the motor on the bench has no datasheet. - [EDN — "Getting a handle on brushed DC motor current"](https://www.edn.com/getting-a-handle-on-brushed-dc-motor-current/) Why stall current is the design number: a spinning motor's back-EMF is what limits its current, and at zero speed there is none. **Use for:** the current-vs-speed relationship, inrush, and driver sizing. ### Datasheets used as worked examples - [Omron G5V-2 relay datasheet](https://omronfs.omron.com/en_US/ecb/products/pdf/en-g5v2.pdf) One of the few small relays that publishes **coil inductance** (armature ON and OFF). **Use for:** any worked example needing real L, R and I numbers. - [Omron G5V-1 relay datasheet](https://omronfs.omron.com/en_US/ecb/products/pdf/en-g5v_1.pdf) Coil ratings and 5 ms operate/release timing. **Use for:** release-delay trade-offs. ### Textbook / theory - [Physics LibreTexts — Inductance (GSU)](https://phys.libretexts.org/Courses/Georgia_State_University/GSU-TM-Introductory_Physics_II_(1112)/08:_Electromagnetic_Induction_AC_Circuits_and_Electrical_Technologies/8.13:_Inductance) Derivation of `E = ½LI²` and self-inductance from first principles. **Use for:** where the equations come from, when intuition needs backing. - [All About Circuits — Inductors and Calculus](https://www.allaboutcircuits.com/textbook/direct-current/chpt-15/inductors-and-calculus/) Free textbook chapter on the `v = L(di/dt)` relationship. **Use for:** a second explanation when the first one doesn't land. - [Spinning Numbers — Inductor i-v equation in action](https://spinningnumbers.org/a/inductor-iv-equation-in-action.html) Both derivative and integral forms, worked visually. **Use for:** building intuition for the integral form (current as accumulated volt-seconds). - _The Art of Electronics_, Horowitz & Hill, 3rd ed. — §1.6 (inductors) and the power-switching material. The reference standard; worth owning. **Use for:** the authoritative answer when sources disagree. ### Tools - [Falstad CircuitJS](https://www.falstad.com/circuit/) — free in-browser circuit simulator. Substitutes for the oscilloscope this bench doesn't have. **Use for:** watching any transient before building it. ## Wisdom (Communities) - [EEVblog Electronics Community Forum](https://www.eevblog.com/forum/index.php) One of the largest active electronics forums; strong professional presence. **Use for:** design review of a circuit before you build it, part-selection sanity checks. - [r/AskElectronics](https://reddit.com/r/AskElectronics) Well-moderated Q&A subreddit (~180k). Rules require a schematic, which is itself good discipline. **Use for:** "why did this die?" post-mortems, quick component questions. - [EDAboard](https://www.edaboard.com/) Organised by topic with a "Best Answers" section. **Use for:** deeper or more obscure driver/clamping questions. _No community preference recorded yet — ask Charlie whether they want to post to any of these, and record the answer here._ ## Gaps - No verified source yet on **RC snubber sizing** for DC inductive loads — needed before the lesson on snubbers vs diodes. - No verified source yet on **contact arcing and relay contact life** as a function of clamp choice (the reason fast clamping matters beyond just speed). - No verified source yet on **brushed-motor commutation noise** — the transients a motor produces continuously while running, distinct from the turn-off transient. Needed before advising on motor decoupling capacitors. - No verified primary source yet on **logic-level MOSFET gate drive at 3.3 V**. The claim that "logic level" parts spec R_DS(on) at 4.5–5 V rather than 3.3 V appears only in blogs and forums so far — must be confirmed against actual datasheets before Lesson 03 teaches it. Check a specific part (e.g. IRLZ44N vs AO3400) rather than a general claim. - No verified source yet on **freewheeling diode reverse-recovery** requirements under PWM. Only becomes relevant if the project adds speed control — currently out of scope.