This is a classic comparison in the world of audio electronics. The fundamental difference lies in how they amplify the signal: Class AB uses linear amplification, while Class D uses switching amplification.
Here’s a clear, engineer-friendly compare—plus real parts you can buy.
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Big picture
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Class AB (linear): Output devices conduct as analog valves with a small bias so both halves overlap → low crossover distortion. Power is burned as heat when output transistors drop voltage while passing current.
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Class D (switching): Output devices are on/off switches driving a PWM (or similar) waveform → LC filter (and the speaker’s inductance) recovers audio. Very little time spent in the lossy linear region → high efficiency.
How they differ (at a glance)
| Aspect | Class AB | Class D |
|---|---|---|
| Output stage | Linear emitter/source followers with bias (push-pull) | Half/Full-bridge MOSFETs switching (PWM/ΔΣ) |
| Efficiency (real-world) | ~35–65% at medium power (peaks ~70% near full power) | ~85–95% across a wide range |
| Heat & size | Runs hot → big heatsinks, bulky PSU | Runs cool → small heatsinks, lighter PSU |
| Distortion “gotchas” | Crossover if bias is off | Dead-time & switching residue if loop/filter not tuned |
| Noise/EMI | Low RF noise | Needs good layout, LC filter, and EMI control |
| Idle power | Moderate (bias current) | Very low |
| Load interaction | Mostly resistive model; stable on tricky loads | Output filter interacts with Z_load at HF; design matters |
| Complexity | Simple, forgiving, easy to prototype | More complex: gate drive, dead-time, LC, feedback compensation |
| Latency | Essentially none | Small (µs-level), usually irrelevant for audio |
| Typical uses | Headphone amps, studio/hi-fi classics, guitar amps | Portable/battery, automotive, PA/pro audio, smart speakers |
Note: Class D isn’t “digital.” It’s an analog switching amplifier that often uses PWM or noise-shaped modulation.
When to choose which
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Pick Class AB if you want super-simple, low-EMI designs, or you’re building a low-power, ultra-low-noise pre/headphone amp and can handle the heat.
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Pick Class D for anything power/size constrained (battery, automotive, PA). You’ll get far less heat and cheaper magnetics/PSU for the same output power.
Concrete examples
Class AB ICs & modules
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TI LM3886 — ~68 W into 4 Ω, classic hi-fi AB power op-amp (through-hole friendly).
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ST TDA7293 / TDA7294 — 80–100 W AB audio power amps, widely used in DIY/pro amps.
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Onsemi NJM4556A (JRC4556) / TI OPA1622 — headphone-class AB drivers with very low THD+N.
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Discrete AB designs — e.g., many Yamaha/Marantz integrated amps (traditional hi-fi) use Class AB push-pull stages.
Class D ICs, controllers & modules
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TI TPA3116D2 — 2×50 W @ 4 Ω, super popular board-level Class D (great for DIY).
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TI TAS5630 / TAS5614 — 2×300 W-class, higher-power Class D stages.
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Infineon MERUS MA12070 — efficient multilevel Class D, great for compact hi-fi.
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Infineon IRS2092S — Class D controller that drives external MOSFETs for >500 W amps.
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Hypex UcD / Ncore modules, ICEpower (B&O) — audiophile/pro modules used in many modern amplifiers.
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Portable/IoT: MAX98357A (I²S in, Class D out) for small speakers.
Design tips (quick hits)
Class AB
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Set and thermally track bias to avoid crossover distortion but keep idle heat reasonable.
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Use adequate heatsinking and SOA margins; consider a dual-supply linear PSU for low noise.
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Star-grounding and short feedback loops keep hum and oscillation down.
Class D
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Keep the loop area of the switching half-bridge tiny; use tight gate-drive and proper dead-time.
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Output LC filter: pick L/C for your load and switching freq; watch damping (speaker impedance varies with frequency).
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Add common-mode chokes, RC snubbers, and solid ground planes for EMI; pass CISPR/FCC with enclosure filtering.
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Close the feedback after the LC (post-filter feedback) if you need better load-invariant response (many modern parts do this internally).
Rule-of-thumb math
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Heat (AB): Pdiss≈Vdrop⋅Iout — worst near mid-power; plan big heatsinks.
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Efficiency (D): dominated by switching + conduction losses; efficiency stays high over a broad power range, so battery life and thermal headroom are much better.
