Switching power supply: what it is in plain terms
A switching power supply (SMPS), also called an impulse power supply, is a DC source that first rectifies the mains and then converts it at high frequency (typically 20–100 kHz) through a small high-frequency transformer. It is this high frequency that lets the transformer be dozens of times smaller and lighter than in a classic "linear" supply running at 50 Hz. Hence the main benefit: for the same power rating, a switching supply weighs less, runs cooler and reaches a higher efficiency.
Practically every industrial power supply today is a switching type: the Mean Well, Delta and Schneider power supplies in our catalog are SMPS units with a universal 85–264 V input and 76–92.5% efficiency. Linear (transformer) supplies remain mostly in audio gear and lab reference sources, where ultra-clean voltage with no high-frequency ripple is essential.
How a switching power supply works
A switching supply works in four sequential stages:
- Input rectification and filtering. The AC mains (220 V, 50 Hz) is rectified by a diode bridge and smoothed by a capacitor into roughly 310 V DC.
- High-frequency conversion. A transistor switch (MOSFET) "chops" this DC into pulses at 20–100 kHz. This is the heart of the unit — and the reason it is called a switching (impulse) supply.
- Galvanic isolation via an HF transformer. The high-frequency pulses pass through a small ferrite transformer that both steps the voltage down to the target level (for example 24 V) and isolates the output from the mains for safety.
- Output rectification and regulation. The output pulses are rectified and filtered again, while a feedback loop (PWM controller) constantly adjusts pulse width to keep the output voltage stable regardless of load or mains fluctuations.
Thanks to this feedback, a switching supply holds, say, exactly 24 V whether the mains drops to 180 V or rises to 250 V. That is the very regulation for which a power supply — rather than a plain transformer — is fitted into a control cabinet.
Switching vs transformer power supply: comparison
To avoid confusing the two technologies, here are the key differences across parameters that matter in practice:
| Parameter | Switching (SMPS) | Transformer (linear) |
|---|---|---|
| Efficiency | 80–93% (lower losses, less heat) | ~50–60% (much heat on the ballast) |
| Weight and size | Small: HF transformer is far smaller | Large and heavy: massive 50 Hz transformer |
| Input range | Wide, 85–264 V (works during sags) | Narrow, tied to the winding rating |
| Ripple / noise | HF ripple present (filtered; non-critical for most tasks) | Very low HF ripple, "clean" voltage |
| Price per watt | Lower at medium and high power | Higher above a few tens of watts |
| Heating | Moderate (heat scales with losses) | High (excess voltage is "burned" as heat) |
For a control cabinet, where space on the DIN rail, energy efficiency and a wide input matter, a switching supply is effectively the only sensible choice.
Advantages and limitations of switching supplies
Advantages
- High efficiency of 80–93% — less wasted energy and less cabinet heating.
- Compact and lightweight — frees up DIN-rail space and eases mounting.
- Wide 85–264 V input — stable operation even during the mains sags typical of industry.
- Built-in protections — against overload, short circuit, overvoltage and overheating.
- Redundancy and parallel connection options for fault-tolerant systems.
Limitations
- High-frequency ripple at the output — sensitive analog/measurement circuits sometimes need an extra filter.
- More complex circuit — repair is less obvious than with a plain transformer (offset by the reliability of industrial series).
- Power headroom required — pick the unit with a 20–30% margin, otherwise running constantly "at the edge" shortens its life (see derating).
Where it is used in industry
A 24 V switching power supply is effectively the standard "nervous system" of modern automation. It is fitted to power:
- controllers (24V power supplies for PLCs), operator panels (HMI), sensors and output relays;
- CCTV systems (12 V cameras), access control, gate and barrier automation;
- servo amplifiers, stepper drivers, variable-frequency drives (auxiliary-circuit power);
- LED lighting and any industrial DC load.
For cabinet mounting, DIN-rail models are convenient, such as the Mean Well NDR-240-24 (240 W, 10 A, with active PFC). For open panel mounting, enclosed units like the LRS-100-24 (108 W, 4.5 A, 90% efficiency, from UAH 640) are the usual pick.
Efficiency and PFC in brief
Efficiency shows how much of the energy drawn from the mains reaches the load and how much turns into heat. In modern industrial SMPS it reaches 90–92.5% — for instance, the Mean Well NDR-480-24 is around 92.5%. The higher the efficiency, the less the unit heats and the longer it lasts.
PFC (Power Factor Correction) shapes the input current. Without PFC, a switching supply draws current in short "spikes" that stress the grid and generate harmonics. PFC makes the drawn current nearly sinusoidal, lifting the power factor to 0.9–0.99. For higher-power units (typically from ~150–200 W), PFC is often mandatory under grid rules — which is why series like the Mean Well NDR and RSP include active PFC.
How to choose a power supply
In short: pick the voltage (usually 24 V), add up the total current of all loads, add a 20–30% margin, choose the form factor (DIN rail or enclosed), and check for PFC and the protections you need. For a step-by-step walkthrough with calculation examples, see our pillar guide on how to choose a power supply for a control cabinet, or jump straight to the industrial power supplies catalog. For a typical automation task you usually do not need a transformer supply at all — a compact 24 V switching unit such as the LRS-100-24 (108 W, 4.5 A) from UAH 640 is enough.
Not sure which unit fits your circuit — message us and we will size it from your load list and a power-headroom margin. Genuine Mean Well, Delta and Schneider products with warranty, shipped from stock.
