Walk through any panel and count the extra components: a 24V power supply bought becuase somebody defaulted to DC without thinking. The xLogic family ships in both 110-240VAC and 12-24VDC versions — SR-12AC, PR-12AC, PR-14AC, PR-18AC, SR-22AC, PR-24AC, PR-26AC and the EXM-8AC on one side; a matching DC range on the other. The choice is not a footnote. It is a cabinet-level decision.
Most engineers pick DC becuase that is what they know. That is a habit, not an analysis.
When AC Is the Smarter Buy
Retrofit scenario: an old machine running on 220V, a control cabinet with no 24V rail, and a budget that does not include a power supply, a filter, and the wiring to feed them. The AC version of the CPU drops straight onto the existing supply. No converter. No extra component to fail. One less thing on the spare-parts list.
The AC models also make sense for simple machines — a fan controller, a lighting panel — where adding a DC supply just to feed a 12-I/O CPU is pure overhead. The cost difference between AC and DC versions is usually smaller than the cost of the power supply you are skipping.
When DC Is Non-Negotiable
Sensors are the hidden driver. Photoelectric sensors, proximity switches, encoders — most of the modern ones run on 12/24VDC. If your input field devices are DC, feeding the CPU with AC only creates a second supply anyway, this time for the sensors. DC in, DC out, one rail, one source: that is the clean design.
Add battery-backed or solar sites to the DC column. A 12V battery bank running a pump controller is a solved problem with a DC CPU and basically a non-problem that nobody wants with AC.
Real Comparison: Two Panels, Two Choices
Panel one, a greenhouse ventilation unit: four fans, two shutters, a temperature sensor, existing 220V power. AC CPU, zero extra components, commissioned in an afternoon. Panel two, a packaging machine: twelve DC sensors, a labeler, a small HMI. DC CPU on a 24V rail with the sensors, one supply, clean grounding. Each panel used exactly one supply voltage, and each choice saved real money.
The mistake would have been forcing both onto the same answer.
Expansion Modules Follow the Same Rule
Digital expansion modules come in both 12/24VDC and 110/240VAC flavors, so the expansion chain can match the CPU's world. Analog expansion modules are 12/24VDC only — a fact worth remembering when you plan an analog-heavy panel on an AC CPU: you will need a small DC supply for the analog module anyway. Read that twice before finalizing the BOM.
Mixing voltages inside one cabinet is legal, common, and requires discipline. Label the rails. Keep 220V and 24V in separate ducts. The CPU does not care; the electrician who comes after you will care a great deal.
The Two-Question Test
Ask yourself: what voltage do my sensors need, and what is already in the cabinet? If the answers point the same way, you are done. If they disagree, add the supply you are missing and stop there — no third voltage, no creative grounding, no "we will just use a resistor."
The Supply Side Nobody Prices
Here is a purchasing detail that never appears in the datasheet comparison: the AC version removes an entire component from the supply chain. No 24V supply to source, no spare to stock, no second voltage to explain to the electrician. For a machine builder shipping a hundred units a year, that is a hundred fewer power supplies in the BOM, a hundred fewer wiring hours, and a hundred fewer points of failure.
The DC version has its own supply-chain logic: a 24V rail that already exists, sensors that already run on it, and a cabinet that is already wired for one voltage. The decision is not component cost — it is which side of the panel already has the infrastructure. Answer that question first, and the supply voltage chooses itself.
The OEM lens changes the math again. If the machine ships to a market where 220V is the norm and the customer's electrician is happiest with a straight line from the mains, the AC version is the lower-installation-risk option regardless of component prices. If the machine ships with a control cabinet full of 24V components anyway, DC wins. The market decides; the datasheet merely confirms.
Voltage Choice and the Expansion Chain
The rule that bites late is the expansion one: digital expansion modules come in both AC and DC versions, matching the CPU's world, but analog expansion modules are 12/24VDC only. An AC-powered CPU with an analog-heavy machine will need a small DC supply for the analog module regardless — and the panel designer who discovers that after the schematic is done pays a rework invoice.
Plan the whole cabinet at once: CPU voltage, expansion voltage, sensor voltage, HMI voltage. One sheet of paper listing every powered component and its rail — that sheet catches the mismatch before the cabinet exists. The pattern in this platform is consistent: read the small print, match the families, and the panel builds itself.
And keep the rails labeled. A mixed-voltage cabinet is a legitimate design; an unlabeled mixed-voltage cabinet is a future electrician's trap. Ten minutes of labels saves a service call at 2 AM.
The best power-supply decision is the one that makes the cabinet boring. Boring cabinets work for years. Exciting ones keep the service phone ringing.
