Side-by-side comparison
| Parameter | Linear | Switching Power Supply |
|---|---|---|
| Regulation Method | Series pass element (BJT or MOSFET) in linear region dissipates excess voltage | Switch operates at 50 kHz–2 MHz; energy stored in inductor/capacitor |
| Efficiency | η = Vout/Vin × 100% — 7805 at 9V→5V: ~56% | 75–95% typical; LM2596 at 12V→5V/3A: ~88% |
| Heat Dissipation | High — (Vin−Vout)×Iout as heat; needs large heatsink | Low — losses mainly in switching transitions and inductor DCR |
| Output Noise / Ripple | Very low — <100 µV ripple typical | 10 mV to 100 mV ripple at switching frequency |
| Size and Weight | Larger — requires heatsink; transformer-based at AC input | Compact — high-frequency transformer is small; e.g., 65 W GaN charger fits in palm |
| Input Voltage Range | Narrow — Vin must be higher than Vout by dropout voltage (~2–3 V) | Wide — buck/boost/flyback topologies handle wide Vin variation |
| Transient Response | Fast — no energy storage lag; responds in microseconds | Slower — feedback loop has bandwidth limitation; 100 µs typical |
| EMI / RFI Generation | None from regulator itself | Significant — requires input/output EMI filter, PCB layout discipline |
| Common ICs / Modules | LM7805, LM317, LM2940 (LDO), AMS1117 | LM2596, UC3842, LM3481, TPS54360, Mean Well modules |
| Cost for Low Power (<1 W) | Cheaper — 7805 costs ₹10; minimal BOM | More expensive — inductor + MOSFET + controller IC + EMI filter |
Key differences
A linear regulator acts as a variable resistor: efficiency is simply Vout/Vin, so a 5 V output from a 12 V input wastes 58% of input power as heat regardless of load. A switching regulator stores energy magnetically (inductor) or electrostatically (capacitor) and transfers it in controlled pulses, keeping efficiency above 85% over a wide load range. The noise penalty: every switching edge generates a current spike that couples into the output as ripple (typically 20–50 mV at the switching frequency — 50 kHz for LM2596). EMI filtering adds bulk and cost. For audio circuits, precision ADC references, and low-noise RF front-ends, linear regulators (especially LDOs like AMS1117) remain the right choice despite poor efficiency.
When to use Linear
Use a linear regulator (LM7805, AMS1117-3.3) when input-to-output voltage difference is small (<3 V), load current is low (<500 mA), and output noise must be minimal — ADC AVCC supplies, RF receiver power rails, and audio preamplifier supplies.
When to use Switching Power Supply
Use a switching regulator (LM2596, TPS54360, Mean Well module) when efficiency matters, input-output voltage difference is large, or power exceeds 1 W — telecom 48 V→5 V conversion, laptop chargers, LED driver bucks, and any battery-powered portable device.
Recommendation
Choose switching regulator for any application above 1 W or where Vin/Vout ratio exceeds 2:1 — the efficiency savings far outweigh the added complexity. Choose linear regulator only when noise is paramount and power is small. A hybrid approach (SMPS to near-target voltage, then LDO for final clean regulation) is common in precision analog systems.
Exam tip: Examiners ask you to calculate efficiency of a 7805 supplied from 12 V at 500 mA — apply η = Vout×Iout / Vin×Iin = (5×0.5)/(12×0.5) = 41.7% — then state what happens to the other 58.3% (heat in pass transistor).
Interview tip: Interviewers at power electronics and embedded companies ask the trade-off in one sentence — say "linear is low-noise but wastes (Vin−Vout)×Iout as heat; switcher is 85–90% efficient but injects switching ripple into the output rail."