Power Supplies & Batteries: The Complete Guide

Every Circuit Lives on Its Power Supply

Nine out of ten "broken" projects are actually power problems. Sags, noise, wrong regulation or a battery chemistry treated like another. This hub gathers the complete power and battery path on Procirel from classifying supplies and understanding rectification to choosing and caring for batteries.

What You Will Learn

• Supply classification linear vs switching, isolated vs not, and when each is right.
• Rectificationhalf-wave, full-wave and bridge circuits with ripple reality.
• Regulation LM317-style linear regulators and their design equations.
• Modern chargers how GaN chargers shrink bricks without magic.
• Battery selection matching chemistry to load, and LiPo failure modes.
• Runtime engineering estimating battery life honestly.

The Learning Path

Work through the tutorials in this order. Each one builds on the previous. Every concept is demonstrated on a real circuit, not just on paper.

1. SMPS vs Linear vs DC-DC Which Power Supply is BEST?
2. Battery Selection Guide for Engineers | Lithium vs NiMH
3. Why Your LiPo Battery Dies So Fast? 9 Hidden Killers & Real Fixes
4. The Death of Silicon? GaN vs. SiC in EV Chargers
5. What Is a GaN Charger in 2026? Gallium Nitride vs Silicon - Expla...
6. Power over Ethernet: One Cable for Data and Power
7. UPS and Inverters: Backup Power Without Surprises
8. CC/CV Charging: How Lithium Batteries Are Actually Charged
9. The 18650 Battery: Selection, Specs and Safe Use
10. Lithium-Ion vs LiPo: Chemistry, Shape and Safety Compared
11. SMPS vs Linear Power Supplies: An Honest Comparison
12. Sizing Rectifier Filter Capacitors Without Ripple Regret
13. Boost Converters: Raising Voltage From Less
14. Buck Converters: Stepping Down Efficiently
15. Linear vs Switching Regulators: Choosing Correctly
16. BMS Design Tutorial: Battery Management Systems Explained
17. Solar MPPT Explained: Maximum Power Point Tracking

Regulator & Battery Reference

Frequently Asked Questions

Linear or switching supply for my project? Linear for low noise (audio, precision analogue); switching for efficiency and heat. Many designs use a switcher followed by a small linear stage.

Why does my LiPo die so fast? Deep discharge, storage at full charge, high C loads and cheap chargers all age cells. The LiPo tutorial covers the four habits that double pack lifetime.

How do I size a supply for motors? Add stall/startup current of all loads plus 30% headroom motors are not resistors.

Engineering deep dive

The sections that follow are this guide's technical core: the reasoning, arithmetic and reference tables that every guide below assumes, written to stand alone as well as to connect.

Choosing a supply topology: the decision tree

Every powered project asks one question first: where does the DC come from? Mains asks for rectification plus regulation, batteries ask for chemistry plus charging, solar asks for MPPT plus storage. The classification logic is power supply classification, and the linear-versus-switching decision, noise against efficiency, is argued with numbers in linear versus switching and SMPS versus linear.

Rectification feeding any of it is full-wave with reservoir sizing by the capacitor ripple method.

Regulation: linear depth and switching breadth

Linear regulators are transistors burning surplus voltage, quiet, simple and hot, dropout and dissipation arithmetic in the LM317 guide and tool. Switchers chop and filter instead: buck steps down, boost steps up, duty-cycle mathematics in buck and boost. The hybrid pattern, switcher then linear, delivers efficient silence and appears across both guides.

Component selection is where switchers succeed or oscillate: inductor saturation current at the empty-battery corner, low-ESR output capacitance, and layout discipline copied literally from the reference design, all with worked values in the two topology guides.

Batteries: chemistry, packs and care

Chemistry choice is a requirements table: energy density, drain rate, cycle life and safety. Li-ion cylindricals versus pouch formats are compared in Li-ion versus LiPo, the workhorse 18686 ecosystem in the 18650 guide, and selection logic by project in choosing batteries.

Packs add series and parallel rules, matched cells, balancing connectors and the protection chain, cell, BMS, charger, made explicit in BMS design. Charging itself is CC-CV with termination near three to five percent, the protocol deconstructed in CC/CV charging. The classic failure mode, unexplained drain, is diagnosed cell by cell in why LiPos die fast.

Solar, backup and distribution

Solar power is an economics problem wearing electronics clothing: panel curves, the MPPT knee and the twenty-percent harvest difference over PWM, all quantified in MPPT explained. Backup power splits into inverters and UPS topologies, transfer times and sine-wave quality, UPS and inverters. Distribution at the edge includes PoE, whose standards and budgets are decoded in power over Ethernet.

Two worked power designs

Bench rail. 12 VAC winding, bridge, reservoir sized for 1.5 V ripple at 1 A by the ripple method, 5 V linear regulation, dissipation checked at worst-case mains high.

Solar sensor node. 10 W panel, MPPT buck to a 18650 pack with protection, load budget verified by the battery tool, five dark days autonomy, exactly the stack the MPPT and BMS guides compose.

Glossary of power terms

Charging infrastructure and battery safety engineering

Charging is chemistry management under electronics supervision. The CC-CV protocol, termination currents and the role of balancing are deconstructed in CC/CV charging, and the multi-cell protection chain is the centrepiece of BMS design. Safety engineering then wraps the whole system: fusing, enclosure venting and the respect that lithium energy permanently deserves.

Each layer assumes the previous one exists, the chain teaching from the guide, and no layer is optional in a build you intend to sleep near.

Measurement and verification of supply quality

A supply is not finished until measured: ripple under load with the scope method, regulation across the input range, transient response into switched loads and thermal behaviour after an hour. The instruments and their discipline come from the tools track, applied here to power specifically.

Ripple deserves its own arithmetic, the reservoir equation from rectifier filtering predicting what the scope then confirms. When prediction and measurement disagree by more than rounding, the disagreement is the lesson, and it is usually ESR, layout or an unlabelled transformer.

Modern devices: GaN, wide bandgap and the future rail

Charger bricks shrank because gallium nitride switches faster with fewer losses, and the physics behind that, wide bandgap semiconductors, is told in the GaN charger guide and its silicon-succession context in the death of silicon. The same devices now move into the buck and boost stages this track teaches, raising efficiencies and frequencies together.

For the designer, the practical impact is component arithmetic: smaller magnetics, tighter layouts and new thermal profiles. The topology mathematics in buck and boost does not change, but the ceiling does, and knowing both is the current state of the craft.

Inrush, protection and the unglamorous details

Every supply transition has an inrush story: reservoir capacitors charging, filaments of load resistance cold and low, and the fuse that sees it all. Designing for inrush means NTC limiters or soft-start circuits sized by the same arithmetic as the reservoir guide, and protection means coordination, the fuse protecting the wiring, the breaker protecting the circuit, the BMS protecting the cell, each layer already introduced across this track's guides.

These details decide field reliability, and they cost the least at design time. The safety list and the BMS chain sections exist because the unglamorous details are the ones that fail loudly.

Specifying supply requirements like a professional

A supply requirement is four numbers, not a voltage: nominal output, worst-case load current, tolerable ripple and transient response, plus the input range it must all survive. Writing that line before choosing topology is the professional habit, and every guide in this track begins with it because topology choice is downstream of requirements, never upstream.

The completed requirements table then prices itself: linear for quiet low-current rails, bucks for efficiency, boost for battery buses, MPPT for panels, each with the arithmetic this guide has already taught and the calculators linked from it. The specification discipline also future-proofs: when the load doubles in revision two, the requirements table tells you which supply decisions still stand, which is the difference between an iteration and a redesign.

Standards, markings and buying safely

Power components carry marks that matter: CE and UL on supplies, IEC cell markings, and the certification numbers that separate legal products from imported hope. The standards sections explain what each mark covers and what it does not, and the habit of checking turns buying into engineering.

Buying safely closes the loop this track opened with classification: a certified supply meeting a written requirements line, feeding protected storage, verified by measurement. That sentence is the whole guide in one line.

A four-week study plan for this track

The same map as a calendar, one guide per session, roughly an hour each plus bench time. Adapt the pace freely, the order is what matters:

• Week 1, session 1: Read and build smps vs linear vs dc-dc which power supply is best?.
• Week 1, session 2: Work through battery selection guide for engineers | lithium vs nimh.
• Week 1, session 3: Bench-test why your lipo battery dies so fast? 9 hidden killers & real fixes.
• Week 1, session 4: Study and wire the death of silicon? gan vs. sic in ev chargers.
• Week 1, session 5: Apply what is a gan charger in 2026? gallium nitride vs silicon - expla....
• Week 2, session 1: Measure along with power over ethernet: one cable for data and power.
• Week 2, session 2: Practice ups and inverters: backup power without surprises.
• Week 2, session 3: Revisit and extend cc/cv charging: how lithium batteries are actually charged.
• Week 2, session 4: Read and build the 18650 battery: selection, specs and safe use.
• Week 2, session 5: Work through lithium-ion vs lipo: chemistry, shape and safety compared.
• Week 3, session 1: Bench-test smps vs linear power supplies: an honest comparison.
• Week 3, session 2: Study and wire sizing rectifier filter capacitors without ripple regret.
• Week 3, session 3: Apply boost converters: raising voltage from less.
• Week 3, session 4: Measure along with buck converters: stepping down efficiently.
• Week 3, session 5: Practice linear vs switching regulators: choosing correctly.
• Week 4, session 1: Revisit and extend bms design tutorial: battery management systems explained.
• Week 4, session 2: Read and build solar mppt explained: maximum power point tracking.

What you will be able to do after this track

• Choose and apply the track's core methods to a fresh problem, not just the worked examples.
• Predict results before measuring, and diagnose honest disagreements between the two.
• Use the track's linked calculators fluently, with the formulas and standards behind them.
• Read a datasheet, a schematic and a specification with the same confidence as prose.
• Build the track's capstone projects and document them to the editorial standard this site holds itself to.

Track questions, answered plainly

Linear or switching for my first serious build? Linear if the load is quiet and small, a buck module if efficiency matters. The topology decision tree in this guide makes the call mechanical.

Are power banks safe as bench supplies? For logic projects, workable, with auto-shutoff caveats. For anything with motors or known peaks, a current-limited bench supply from the tools track.

When does a lithium build legally need a BMS? From two cells in series upward, always, and single cells deserve protection ICs. The chain is cell, BMS, charger, fuse.

How do I size a supply for motors? Sum stall currents plus headroom. Motors are not resistors, and the starting-method guides in the electrical track quantify why.

What kills converters most often in hobby builds? Undersized inductors saturating and long switching-node traces. Both are layout and selection rules taught with numbers in the buck and boost guides.

Is solar worth it for small nodes? With MPPT and a sane load budget, yes, the harvest economics section runs the arithmetic that decides per project.

Related tracks and where they meet this one

Topical authority crosses category borders, and engineers cross them daily. These adjacent guides share concepts, components and instruments with this track:

• Electronics Fundamentals: The Complete Guide (Components, Theory..., the electronics fundamentals guide. The cornerstone guide to electronics theory every component, law and circuit concept on one page, linking to every fundamentals tutorial on the site.
• Arduino: The Complete Guide From First Blink to Working Robots, the arduino projects guide. The structured Arduino path: setup, sensors, displays, motors and complete builds every Arduino tutorial on the site, in the order you should learn them.
• IoT & ESP32: The Complete Smart Devices Guide, the iot and sensors guide. Everything WiFi, MQTT and sensors: build connected devices that never brown out the complete IoT path with ESP32, MQTT and smart-home builds.
• Electrical Engineering: The Complete Practical Guide (Power, Moto..., the electrical engineering guide. Power systems, transformers, motors and safe wiring the complete electrical path from single-phase circuits to industrial machines.

The calculators behind this track

Every formula on this page and in the guides runs instantly in the toolbox, no signup, client-side:

• Ohm's Law Calculator, Ohm’s Law defines the fundamental relationship between voltage (V), current (I), and resistance (R) in any electrical ci
• Resistor Color Code, Through-hole resistors use colored bands painted on the body to indicate their resistance value
• LED Resistor Calculator, Every LED needs a current-limiting resistor to prevent it from drawing too much current and burning out
• Voltage Divider Calculator, A voltage divider uses two series resistors to produce an output voltage that is a fraction of the input voltage
• 555 Timer Astable Mode, In astable mode, the NE555 timer generates a continuous square wave output without any external trigger
• 555 Timer Monostable Mode, In monostable (one-shot) mode, the 555 timer outputs a single HIGH pulse of a precisely defined duration when triggered
• RC Time Constant, The RC time constant (τ = tau) defines how fast a capacitor charges or discharges through a resistor
• Capacitor Code (3-Digit), Ceramic and film capacitors often have a 3-digit code printed on them instead of the full value

Questions about this track

How long does the full track take? Sum the read times in the map and expect roughly double with bench practice alongside. The guides are written to be built, not skimmed.

Can I skip guides inside the track? The map is ordered but each entry names what it assumes. Skip freely when a guide's opening sentences tell you things you already own.

Which calculator should I bookmark first? The one matching your current guide, but the full toolbox is one click from every page header.

Is this track maintained? Guides carry review dates, and corrections are public through the editorial process.

How to use this guide. Read the deep dive top to bottom for a complete foundation, then enter any guide from the topical map. Every guide assumes this page's vocabulary, every calculator verifies its arithmetic, and the author's profile stands behind both.

Thermal Design in Power Electronics

Every watt of loss becomes heat, and every degree of junction temperature is borrowed lifetime. Power design is therefore thermal design: calculating dissipation honestly, chaining thermal resistances from junction to ambient, and choosing between a bigger heatsink and a better topology. This track works real numbers for linear regulators, buck modules and battery chargers, because a supply that survives a datasheet-typical Tuesday can still die in a hot enclosure on Friday. Derating is not pessimism; it is arithmetic.

Safety and Compliance for Battery Systems

Lithium energy deserves engineering respect, and that respect has a checklist: cell selection from reputable vendors, protection electronics rated for the fault current, fusing at the pack, and enclosure design that plans for the failure you hope never happens. Beyond the bench, products face standards: UN38.3 for transport, IEC 62133 for commercial cells, and the documentation discipline that certification demands. This track covers the safety chain end to end, because battery incidents are almost never chemistry failures, they are engineering shortcuts.

Track Verification Checklist

Before moving beyond this track, verify each item on a real build: reproduce any worked example from formulas alone, name the top three failure modes this track warns about, and demonstrate one measurement from memory with the correct instrument settings. A checklist completed on the bench is worth ten read on a screen, and every guide in this track was verified the same way before publication.

Converter Magnetics and Component Sizing

Every switching converter lives and dies on its magnetics: inductor saturation current at the worst-case corner, ripple current as a design choice, and the core loss that datasheet curves hide in plain sight. This section sizes real buck and boost inductors from first principles, selects output capacitors by ripple and transient rather than habit, and explains why the input network matters as much as the output. Component arithmetic that survives corners is the heart of power design.

Measurement of Switching Circuits

Switching waveforms punish careless probing: ground-lead inductance invents spikes that do not exist, and scope bandwidth limits hide the edges that matter. This section teaches power-electronics measurement properly: short-ground springs, differential probing across switches, current probes versus shunts, and capturing load transients without trigger jitter. Every converter guide on this site published its scope captures, and this section is why those captures can be trusted.

Battery Management in Practice

A battery pack is a system: cells matched at assembly, balanced in service, protected in fault, and derated in documentation. This section covers pack construction, BMS selection by cell chemistry and fault current, charger coordination with the protection chain, and the ageing behaviours that reshape capacity over years. It closes with the field data every battery claim on this site rests on, because battery engineering without measurements is opinion.

From Design to Certified Product

Power products face a compliance ladder: isolation distances, creepage and clearance, insulation classes, and the safety standards that turn a working prototype into a sellable item. This section walks a supply design through pre-compliance checks you can run on the bench, the documentation trail certification demands, and the design decisions that make the final test a formality rather than a lottery.

Study Path in Detail

The complete Power & Batteries curriculum, every guide with its focus:

1. SMPS vs Linear vs DC-DC Which Power Supply is BEST?, Power Supply Classification: 8 Types, Formulas & Complete Selection Guide, a bench-tested power & batteries guide with worked example and reference table.
2. Battery Selection Guide for Engineers | Lithium vs NiMH, Battery Selection for Engineers Pick the Right Cell Every Time, a bench-tested power & batteries guide with worked example and reference table.
3. Why Your LiPo Battery Dies So Fast? 9 Hidden Killers & Real Fixes, 9 hidden killers draining your pack and field-tested fixes the datasheets won’t tell you, a bench-tested power & batteries guide with worked example and reference table.
4. The Death of Silicon? GaN vs. SiC in EV Chargers, The transition to 800V Electric Vehicle (EV) architectures marks the end of the Silicon era in high-power conversion. This report explores howWide-Bandgap (WBG) materialsGallium Nitride (GaN) and Silicon Carbide (SiC) are revolutionizing thermal management and power density to enable “gas-station speed” charging.
5. What Is a GaN Charger in 2026? Gallium Nitride vs Silicon - Expla..., "headline": "What is a GaN Charger? Gallium Nitride vs. Silicon Technology Explained",, a bench-tested power & batteries guide with worked example and reference table.
6. Power over Ethernet: One Cable for Data and Power, PoE standards, classes and budgets powering cameras, APs and IoT with the network cable alone.
7. UPS and Inverters: Backup Power Without Surprises, Topologies from standby to double conversion, sizing maths, waveform reality and battery care.
8. CC/CV Charging: How Lithium Batteries Are Actually Charged, The two-phase protocol every lithium charger follows current limits, the 4.2 V ceiling and termination.
9. The 18650 Battery: Selection, Specs and Safe Use, Capacity versus current, protected versus bare, genuine sourcing and building safe packs, a bench-tested power & batteries guide with worked example and reference table.
10. Lithium-Ion vs LiPo: Chemistry, Shape and Safety Compared, Cylindrical versus pouch energy density, discharge rates, failure modes and choosing between them.
11. SMPS vs Linear Power Supplies: An Honest Comparison, Iron transformers versus switchers weight, noise, efficiency, regulation and the use cases that decide.
12. Sizing Rectifier Filter Capacitors Without Ripple Regret, The C = I·t ÷ ΔV rule for bridge outputs, peak currents, and why bigger is not always better.
13. Boost Converters: Raising Voltage From Less, Charging an inductor then releasing it high duty maths, limits at high ratios and battery applications.
14. Buck Converters: Stepping Down Efficiently, The switch-inductor-diode dance, duty-cycle maths, ripple sizing and module selection, a bench-tested power & batteries guide with worked example and reference table.
15. Linear vs Switching Regulators: Choosing Correctly, LDO simplicity versus buck efficiency noise, heat, cost and where each belongs, a bench-tested power & batteries guide with worked example and reference table.
16. BMS Design Tutorial: Battery Management Systems Explained, How a BMS protects lithium packs cell monitoring, balancing, protection thresholds and designing your own.
17. Solar MPPT Explained: Maximum Power Point Tracking, Why MPPT extracts 30 % more from the same panel IV curves, the knee, and how trackers hunt the maximum power point.

Supply Selection Decision Table

Requirements to topology at a glance: noise-critical analog to linear or hybrid, battery-portable to buck or boost by chemistry curve, wide-input industrial to flyback or four-switch buck-boost, and high-reliability rails to redundant configurations. The table includes the inefficiency and cost each choice pays, the design section above that covers it in depth, and the calculator that checks the arithmetic. Choosing topology from a table of requirements instead of habit is the difference between a rail and a reputation.

Battery Field Reference

Chemistry behavior where it matters, in the field: self-discharge and calendar life, temperature derating for capacity and discharge rate, storage voltage by chemistry, and the visual and electrical signs that retire a pack before it retires itself. This section condenses the site's deployment experience into the reference card every battery project deserves. Batteries age by the rules; this card is the rules.

Fault Protection Architecture

The chapter between a hiccup and a fire. This section designs the protection stack: input protection from transients and reversal, current limiting that is fast where it must be and forgiving where it should be, thermal shutdown coordination with the heatsink design, and battery fault handling that respects chemistry. Each layer is designed to fail in the order that protects the layers beneath it. Protection architecture is the least visible and most professional chapter of power engineering, and it is documented here with the same rigor as the efficiency chapters.

The section above closes the track; the study path, the reference material and the verification checklist together complete the curriculum this guide promised. Every claim traces to a bench measurement, every formula to a datasheet, and every recommendation to a build that earned it.

Battery Pack Design: From Cell Selection to BMS Sizing

Building a battery pack that survives real use is a systems exercise. The cells are the easy part; the decisions around them decide whether the pack lasts eight years or eight months.

Cell selection starts with the discharge curve, not the capacity label. Pull the datasheet curve at YOUR load current, not the 0.2C curve used for the headline number. A cell rated 3000mAh at 0.2C may deliver only 2200mAh at 2C, and the usable window between full and the protection cutoff shrinks further at cold temperatures. For packs that live outdoors, the winter curve at -10°C is the design constraint. derate nameplate capacity by 30% for any pack that will cycle daily in an unheated space.

Series and parallel arithmetic, done honestly. In series, voltages add and the pack capacity is that of the weakest cell; in parallel, capacities add and the voltage is that of the group. Match cells by measured internal resistance and actual capacity (a simple test: discharge through a known resistor and time the sag), not by brand and label. Mismatched parallel cells circulate current among themselves continuously: a 20mV difference across 50mΩ of mismatch is a standing 400mA self-discharge loop that no BMS can see. This is why serious packs are built from cells of the same production lot, charged together once, then grouped by measured voltage within 10mV.

BMS sizing has three numbers: current, balance current, and cutoffs. The continuous discharge rating must exceed your load with 30% margin, and the short-circuit protection must trip slower than your fuse under normal inrush (motor drives pull 5-10× running current at startup). Balance current is the quiet spec: a 60mA balancer needs 15 hours to fix a 60mV imbalance on a 30Ah pack, which is why large packs need active balancing or top-balancing discipline. Cutoffs: for Li-ion chemistry, charge to 4.20V/cell for full capacity or 4.10V for double the cycle life; the trade is yours to make, but make it deliberately.

Fusing and wiring are part of the pack. Every cell group in a multi-parallel pack should be fused or use cells with built-in PTC, so one shorted cell cannot drag its siblings down. Main pack fuse: rated above maximum continuous current, below the wire's fire limit. Wire gauge from the pack to the load is sized for voltage drop under peak current: 3% drop at peak is a workable target. And the single most common pack failure is not electrical at all: it is vibration fatigue at the nickel strip-to-terminal weld, so strain-relieve every interconnect and never let cell terminations carry mechanical load.

Aging budget. Li-ion chemistry ages by calendar and by cycles: roughly 20% capacity loss in 500 full cycles at 25°C, double that at 40°C. If the product must deliver rated runtime at year three, the day-one pack needs the headroom to lose 30% and still close the budget. The cheapest battery is the one you do not have to replace: oversizing 20% and charging to 4.1V usually beats the false economy of a minimum pack run hard.

Charging ICs and the Chemistry Contract

Every rechargeable battery ships with a chemistry contract, and the charging IC is the enforcer. Understanding the contract explains nearly every charging failure.

Li-ion: CC/CV with a timer. Lithium-ion charges constant-current to 4.20V per cell, then constant-voltage while current tapers, terminating at roughly C/10. The classic TP4056 implements exactly this for 1A designs, and higher-power designs add a thermal sense and a pre-charge phase: a deeply discharged cell (below 2.8V) must be nursed back at C/10 before fast charging, or copper dendrites form and the cell becomes a hazard. Never float a Li-ion cell at 4.2V indefinitely; the charge must terminate, which is why a bench supply set to 4.2V is not a charger no matter how often it is used as one.

Lead-acid: the forgiving chemistry that punishes neglect. Flooded and AGM cells want a multi-stage profile: bulk (current-limited), absorption (voltage-held around 14.4V for a 12V battery), then float (13.5-13.8V, and it MAY stay on float forever, unlike Li-ion). The failure mode is sulfation from sitting discharged, so a charger that never enters absorption leaves capacity on the table and a battery that sits at 12.0V is already half-dead. Temperature compensation matters here: absorption voltage falls about 3mV/°C/cell as temperature rises, and a fixed 14.4V charger in a 45°C engine room is quietly cooking the battery.

NiMH and the termination minefield. Nickel batteries charge by detecting fullness rather than holding a voltage: negative delta-V, temperature slope, or timer. Delta-V is tiny at gentle charge rates (under 0.5C it nearly disappears), which is why cheap NiMH chargers that use only a timer cook some cells and undercharge others. If you design for NiMH, use -dV/dt plus temperature rise plus timer as three independent votes, and treat any single sensor's verdict as advisory. The payoff for respecting the contract: an eneloop-style cell survives 500-2000 cycles, while an abused one develops memory-like symptoms and high self-discharge within a year.

The GaN and USB-PD era. Modern fast chargers negotiate voltage over USB-PD (5V, 9V, 15V, 20V steps) before delivering up to 100W (240W on EPR), then run a synchronous buck or buck-boost behind the port. Gallium-nitride switches at megahertz frequencies with far lower switching losses than silicon, which is why a 65W GaN charger fits in a pocket that a 65W silicon charger never could. For the battery underneath, nothing has changed: the contract is the contract, and the PD brick on the outside simply feeds a chemistry-correct charger on the inside.