Switch mode vs linear power supply: not only "how the textbook says it should be". In an industrial control cabinet, switch mode power supplies influence wasted heat, panel space, output noise, electromagnetic interference, availability of spare parts, and how quickly a maintenance team can replace a failed 24 VDC power source.
Short answer: switch-mode power supplies are usually the easier fit for PLC cabinets, HMIs, relay banks, and distributed I/O because they are smaller and more efficient. Linear power supplies still matter for low-ripple analog, RF-sensitive, and fast-response loads.
Quick Specs: Industrial 24 VDC SMPS Example
- Example unit: Omron S8VK-C06024 switch mode power supply
- Output: 24 VDC, 2.5 A, 60 W
- 100-240 VAC rated, 85-264 VAC permitted; 90-350 VDC permitted
- Efficiency: 88% at 230 VAC input
- Mounting: DIN rail, 32mm x 90mm x 110mm
- Operating range: -25 to 60 C
- Switch-Mode vs Linear Power Supplies at a Glance
- How Each Power Supply Converts Voltage
- Efficiency and Heat Dissipation
- Ripple, Noise, EMI, and Sensitive Loads
- Size, Weight, Input Range, and DIN Rail Fit
- The 24V Control Cabinet Selection Matrix
- FAQ
Switch-Mode vs Linear Power Supplies at a Glance
Both linear and switching power supplies take an input source and produce a controlled DC voltage. They change the process by regulation method: a linear design burns away excess voltage as heat. A switching design chops energy at high frequency, storing it temporarily in magnetic components, then filtering it back into a DC output voltage.
| Selection factor | Linear power supplies | Switching power supplies |
|---|---|---|
| Conversion method | Transformer, rectifier, filter, linear regulator | Rectification, high-frequency switching, transformer or inductor, output filter |
| Efficiency pattern | Lower when input-output voltage drop and load current are large | Higher efficiency is common because the transistor works mostly on or off |
| Heat | More heat dissipation in the pass element | Less heat for the same output power in many industrial loads |
| Ripple and noise | Usually cleaner output for sensitive analog circuits | Needs filtering and layout care for ripple, switching noise, and EMI |
| Panel space | Larger transformer and heat sink area | Compact DIN rail packages are common for 24 VDC cabinets |
| Best industrial fit | Low-noise bench, audio, RF, and precision analog work | PLC racks, HMIs, sensors, relay banks, and general control panels |
Which is better, switching or linear power supply?
In the typical industrial automation cabinet, a switching power supply is the more advantageous default because it is space- conserving, cool-running, and able to take a wide input voltage range. A linear power supply is an option when the load cannot tolerate ripple, switching spikes, or each conducted noise and the associated higher heat, size, and weight.
| Advantages | Limitations |
|---|---|
| SMPS: 24 VDC DIN rail models can fit a 60 W output into a 32 mm wide body. | SMPS: switching frequency creates ripple and EMI that must be filtered and grounded correctly. |
| Low-noise linear output can help analog measurement, RF, and audio circuits. | Regulator heat rises with voltage drop times current, so high-current linear loads become inefficient. |
How Each Power Supply Converts Voltage
Most linear supplies use an iron transformer to step down AC. The voltage is then rectified into pulsating DC, smoothed by a capacitor filter, and controlled with a linear regulator. In practice a linear regulator is simple, but the excess voltage has to go somewhere. It becomes heat.
Switch-mode power supplies, or SMPS units, work differently. They rectify or receive DC, then use a switching transistor and a control circuit to pulse energy at high frequency. Energy moves through an inductor or transformer and then gets filtered into DC. Because the switching element spends most of its time fully on or fully off, it wastes less power than a transistor sitting in a partly-on linear region.
This can be seen in the tradeoff. It is much easier to get quiet output with linear power supplies. This is because they avoid high-frequency switching. Switch mode power supplies are smaller because their magnetic components can run at much higher frequencies than a 50/60 Hz iron transformer.
Engineering Note: Heat generated in a linear regulator is tied to voltage drop times load current. If the regulator drops 12 V at 1 A, the pass transistor must handle around 12 W of heat before heat sink and enclosure cooling limits are considered.
Efficiency and Heat Dissipation
Efficiency is where the switch mode advantage becomes clearer. Michigan State University course material describes how SMPS efficiency can exceed 90% in some designs, while a linear regulator can be considerably less efficient when the output voltage is well below the input. Texas Instruments explains the same issue with the regulator loss relationship: the input-to-output voltage difference multiplied by load current becomes heat loss.
This is perceived by the cabinet buyers to be a real mounting concern. Heat reduces life, eating into the margin for the enclosure, and in some cases force changes to the spacing. itrustbot has listed a 60 W 24 VDC SMPS for an Omron S8VK-C06024 with 88% efficiency at 230 VAC input. At full rated output, under those circumstances, that indicates about 8 W of conversion loss, before considering derating and ambient temperature.
Perhaps this explains why 24 VDC switch mode power supply models are so popular in PLC cabinets. They run cooler inside the enclosure and usually require less physical clearance than a comparable transformer-based linear power supply.
Ripple, Noise, EMI, and Sensitive Loads
Noise is where the answer gets more specific. Compared with a typical SMPS module, a linear power supply often produces less high-frequency noise. Switching supplies produce ripple and electromagnetic interference from high-speed current and voltage transitions. Filtering, shielding, PCB layout, grounding, and load separation determine whether that noise is a real problem for the installation.
The Texas Instruments datasheet states that SMPS output voltage contains ripple at the transformer waveform frequency and that changes in the spectra of conducted and radiated emissions are likely to impact nearby electronics if not tuned out. Electromagnetic interference (EMI) training materials also detail the difference between differential mode noise and common mode noise. The ripple in the power supply's output voltage is an example of differential mode noise.
How can you tell if a power supply is linear or switching?
Start with the datasheet and product label. Switching supplies frequently reference SMPS, switch mode, PWM, switching frequency, wide input voltage, or DIN rail mounting. A linear supply of equal wattage is more likely to be larger and state its AC transformer. Whether measured by efficiency, output ripple, EMI class, or input range, visual appearance alone is not the best indicator.
| Load or system | Main risk | Usual direction | Check before buying |
|---|---|---|---|
| PLC CPU and digital I/O | Voltage sag during load changes | Industrial SMPS | Rated current, hold-up behavior, terminal type |
| Analog input cards | Ripple coupling into measurement | SMPS plus filtering, or linear for demanding signals | Ripple spec, grounding, sensor cable routing |
| RF, ham radio, audio bench | Audible or RF noise | Linear, or a proven low-noise SMPS | Real noise tests under load, not topology name alone |
| Relay and solenoid loads | Inrush and inductive transients | Industrial SMPS with protection margin | Peak current, surge rating, protection functions |
Important: Do not assume the linear supply is a low-noise solution just because somebody says "switching supplies are noisy." A poorly installed linear power supply can have configuration errors, and an industrial SMPS with good filtering can run cleanly enough for many control loads.
Size, Weight, Input Range, and DIN Rail Fit
Industrial panels tend to look for small dc power supplies with wide input voltage. The ability of switch-mode conversion to operate the transformer or inductor at a high frequency greatly reduces the size of its magnetic components and package. In many cases, spatial considerations are an issue when the package would also be used to house a PLC rack, safety relay banks, contactors, terminals, network switch, and even additional space for spare units and spares in the same enclosure.
itrustbot's listing of an Omron S8VK-C06024 is another good example: 60 W, 2.5 A, 24 VDC, DIN rail mount, 32 mm wide, 100-240 VAC input, and 90-350 VDC permissible direct current input. That wide DC input range would be hard to implement with a simple transformer-based linear supply, unless it involved tap changers or region-specific models.
If you are replacing an existing unit inside of a PLC enclosure, first compare the output voltage, rated current, derating curve, mounting width, terminal type, and approvals. Then compare whether EMI considerations and ripple are equivalent. Buyers who are used to supporting mixed brands of automation are more likely to wonder whether your DIN rail power supply will fit neatly in the same enclosure, than about the absolute theoretical type of its power circuit.
Cost, Spare Parts, and Lifecycle Risk
Cost is only one factor. Bigger risks include machine downtime, unavailable obsolete spares, heat build-up, and purchasing a supply that is electrically compatible but not mechanically compatible. Low-power linear supplies may be cheap and simple, but higher-current versions need larger transformers and more heatsinking. Switch mode designs are more complex internally, but they often run cooler in a cabinet and may be better stocked spares for industrial maintenance teams.
itrustbot positions itself as an independent supplier of off-the-shelf industrial automation parts with new, refurbished, and pre-owned stock. This is important when a plant is replacing failed power modules in an aging cabinet and cannot wait for a full redesign. In a critical job, check the exact model number, voltage, current, physical width, terminals, condition, and warranty before ordering.
- New PLC cabinet: take a DIN rail SMPS rated above the stabilized load plus startup margin.
- Obsolete machine: select the most similar original power supply footprint and wire terminations before changing topology.
- Analog or RF sensitive loads: measure ripple and noise at the load under real operating conditions, not just on an unloaded bench.
- Emergency change: request a replacement power supply quote with a photo of the label and terminal positions.
The 24V Control Cabinet Selection Matrix
Use the table below as the practical decision component absent from many articles comparing linear and switch mode power supplies. It effectively makes the choice between switch mode and linear power supplies a plant level decision.
| Application condition | Prefer | Reason | Check before release |
|---|---|---|---|
| 24 VDC PLC CPU, I/O, and HMI in one panel | SMPS | Compact DIN rail body and lower heat at cabinet load | Total current, derating, and spare capacity |
| Analog input card reading millivolt-level signals | SMPS with filtering or linear | Noise coupling can affect measurement quality | Ripple spec, shield termination, sensor grounding |
| Relay bank with several coils switching together | SMPS | Load steps and protection margin matter more than ultra-low ripple | Peak current and short-circuit protection |
| Bench audio or RF test setup | Linear or proven low-noise SMPS | The load may reveal switching noise that is irrelevant in a PLC cabinet | Measure noise at the receiver or amplifier, not only at the terminals |
| Machine exported across 100-240 VAC regions | SMPS | Wide input range avoids transformer taps and voltage selector mistakes | Input range, frequency, and local compliance marks |
| Legacy machine with fixed transformer wiring | Match original unless redesign is approved | Mechanical fit and grounding can be harder than voltage matching | Photos, wiring diagram, terminal pitch |
| Battery charger or variable source requirement | Depends on charger topology | Charging behavior is not decided by supply topology alone | Charge profile, current limit, and battery chemistry |
| High ambient cabinet near drives or heaters | SMPS with derating margin | Lower loss reduces enclosure heat load | Operating temperature curve and ventilation |
| Noise-sensitive load sharing a panel with VFDs | SMPS plus layout controls, or separate low-noise supply | Drive noise, grounding, and cable routing may dominate | Separation, filters, ferrites, and grounding path |
| Maintenance spare for common 24 VDC controls | SMPS | More common stocked form factor for modern industrial automation | Output current, dimensions, terminal type, warranty |
This approach also guards against a common mistake by reactive buying teams: changing a supply just based on its voltage. Voltage alone is not sufficient. Actual selection should consider current, range, ripple and noise budget, heat dissipation margin, mounting environment, and load start-up considerations.
When Linear Supplies Still Win
Although not redundant, linear power supplies remain the best choice when the system defines low noise and simple analog behavior over raw efficiencies, size and heat. They are still found in lab instruments, analog electronics, sound, radio work, and niche low noise applications.
What are the disadvantages of a linear supply?
Main disadvantages are heat, weight, size, and limited efficiency at higher current. As they convert excess electrical energy into heat, thermal design becomes compromised as load current increases. They cannot step voltage up in the same straightforward fashion as a switch mode topology.
Within the control enclosure, those disadvantages often dominate noise benefits. PLCs, HMIs and relay banks generally demand a stable 24VDC field more than scientific noise characteristics. Measurement chains may be different, especially if the signal is weak, unshielded or exists close to switching loads.
What Is Changing in Industrial Power Supply Sourcing
Search demand reveals the comparison topic remains stable, yet there is relatively high visitor interest around practical comparison terms such as DIN rail power supply. This pattern matches what maintenance teams want in practice: a compatible on shelf power supply which gets the machine running again without redesign.
During 2026 purchasing evaluations the practical step is to agree stock of spare power supplies, to be replaced by output voltage, output current class, mounting width, type of terminals, and design input range. Several facilities are known to stock many 24 VDC switch mode power supplies on hand, with documented exceptions for the couple of linear, low noise variants.
Related maintenance information can be found in itrustbot's guides to industrial automation control systems and PLC troubleshooting.
FAQ
Q: What is the main difference between linear and switch mode power supplies?
A linear supply regulates voltage by using a transformer, rectifier, filter, and linear regulator. Switch mode power supplies use high-frequency switching, magnetic storage, and filtering to regulate the output. Usually, the linear design is quieter but less efficient. In cabinet work, the switch mode design is usually smaller, cooler, and better suited to industrial space limits.
Q: Which is better, switching or linear power supply?
Switching is better for most industrial 24 VDC panels. Selected low-noise analog, RF, and bench applications are better candidates for linear power. Selection should come from the load's ripple tolerance, the enclosure heat limit, the available panel space, and the supply's actual datasheet.
Q: Which power supply has less noise?
Because they do not chop energy at a switching frequency, linear power supplies usually have less high-frequency switching noise. However, a quality SMPS with proper filtering, shielding, and grounding can be quiet enough for many control systems. Test the supply with the real load and cable layout when noise matters.
Q: Is a switch mode power supply good for PLC cabinets?
Yes. Switch mode power supplies are normally the default for PLC cabinets because they offer compact DIN rail mounting, lower heat for a given output, and wide input voltage support. Check output current, short-circuit protection, operating temperature, and derating. With analog modules, add filtering and grounding review rather than assuming the main supply alone decides signal quality.
Q: Can a linear regulator clean up SMPS noise?
It can help in some low-current circuits, especially when a local linear regulator follows a switching pre-regulator. This hybrid approach is common when the system needs the efficiency of SMPS conversion and the cleaner local rail of a linear regulator. Voltage headroom, thermal margin, and proper input/output capacitors still have to be checked.
Q: How do I choose a 24 VDC industrial power supply?
Start with the load current and add margin for startup and expansion. Then verify input voltage range, output ripple, protection functions, operating temperature, terminal type, mounting width, and compliance marks. If the machine is down, send the model number and label photo to a supplier before substituting a different supply.
Need a Replacement Power Supply?
If you are replacing a failed 24 VDC power supply or maintaining a replacement parts list, send itrustbot the model number, output voltage, rated current, terminal photo, and how urgent you need it. Request a power supply quote ->
About This Selection Guide
This article combines public power-supply references, itrustbot product-page data, and industrial automation sourcing context. It explains switch-mode vs linear power supplies for selection work, but final replacement decisions should still be checked against the machine schematic and the exact datasheet for the installed unit.
Related Articles
- Industrial Automation and Control Systems - panel-level context for control components
- Introduction to PLC Troubleshooting - practical checks before replacing hardware
- PLC Fundamentals and Technical Framework - how PLC hardware fits together
- What Is Fieldbus - signal and communication context inside automation systems
References & Sources
- Switch Mode Power Supplies - Michigan State University ECE 480 application note
- Design tips for linear and switched-mode power supplies - Texas Instruments Analog Design Journal
- The Causes and Impact of EMI in Power Systems - IEEE Life Members technical presentation
- 47 CFR Part 15 - Radio Frequency Devices - Electronic Code of Federal Regulations
- S8VK-C 60/120/240/480-W Models catalog - Omron Industrial Automation
- Omron S8VK-C06024 Switch Mode Power Supply - itrustbot product page
