2026-07-15 “`html
When people ask about the components of a PLC, they are often talking about the visible parts: the CPU, power supply, input and output modules, and communication modules. Look inside those assemblies, however, and you find another layer of components doing the actual work: microcontrollers, memory ICs, optocouplers, interface transceivers, driver arrays, MOSFETs, rectifiers, converters, and protection devices.
This distinction matters when sourcing parts. Someone maintaining a factory may need a complete replacement PLC module. An OEM building an industrial controller, or a repair team working at PCB level, is more likely to need the individual electronic components inside that module. EASYIEE focuses on this second category: board-level component sourcing and BOM support for industrial control electronics rather than complete replacement PLC racks.
A PLC is an industrial computer, but its component choices are different
A PLC still reads inputs, executes stored logic and controls outputs, just as a computer receives data, processes it and produces a result. The difference is the environment. A controller mounted beside motors, contactors and power converters must continue operating despite electrical noise, temperature changes, vibration and years of continuous service.
That is why selecting industrial automation components is not simply a matter of matching voltage and package size. Temperature grade, isolation rating, surge tolerance, lifecycle status and traceability can be just as important as the headline specification.
The processor is the natural place to begin. It executes the control program and handles timers, counters, communication and diagnostics. Depending on the design, this function may be provided by an industrial microcontroller, microprocessor or system-on-chip. For compact embedded controllers, devices such as the ATMEGA644PA-AUR illustrate the kind of microcontroller features designers may evaluate: non-volatile program memory, GPIO, timers, serial interfaces and analog inputs.
It is not a universal substitute for a commercial PLC CPU, of course. The point is that controller selection starts with the real workload: number of I/O points, communication requirements, scan time, memory capacity and expected product lifetime. The official Microchip ATmega644PA documentation is a useful example of the information that should be verified before procurement.
Memory deserves more attention than it usually gets
Program code, configuration data, event records and firmware updates all need somewhere to live. Some controllers rely mainly on memory integrated into the processor, while more capable designs add external NOR Flash, EEPROM, SRAM or managed storage.
Memory problems are particularly awkward during a redesign. A replacement may offer the same nominal capacity but differ in voltage, command set, erase architecture, package, endurance or boot behaviour. That is why we recommend comparing the full ordering code rather than searching only for “128 Mbit Flash” or another broad description.
Our SPI NOR Flash Memory sourcing guide explains these checks in more detail. Product families such as IS25WP080D-JNLE and IS25LP128F-JBLE-TR also show why density alone is not enough to confirm compatibility.
The I/O section is where the industrial world meets the logic circuit
PLC inputs may receive signals from switches, proximity sensors, encoders, pressure transmitters or temperature sensors. Outputs may operate relays, valves, lamps and contactors. The voltage levels and electrical conditions on the field side are very different from those tolerated by a processor.
This is where isolation and interface components earn their place. Optocouplers can transfer digital control signals while maintaining galvanic separation between two circuit domains. High-speed optocouplers may be selected for faster signals, while gate-driver optocouplers are used when an isolated control signal must drive a power switching stage.
If you are comparing isolation parts, start with the required isolation voltage, data rate, output type, propagation delay and temperature range. The package and creepage distance also matter. Our optocoupler selection guide covers these trade-offs, while the optocoupler product category provides a route into available product pages.
Outputs often need another layer of current amplification. The MC1413PG, for example, is a seven-channel NPN Darlington driver array historically used to drive higher-current loads from logic signals. It is now an obsolete onsemi part, so sourcing it is not the same as ordering a current-production driver.
For an existing design, the first question is whether the original part is mandatory. If substitution is allowed, engineers need to compare pinout, input characteristics, output voltage, current capability, clamp-diode arrangement and package. The original onsemi MC1413 datasheet should remain the reference rather than a reseller description.
Power conversion and protection quietly determine reliability
Every PLC needs stable internal power rails. Depending on the architecture, the power section may contain controllers, MOSFETs, rectifiers, inductors, transformers, regulators, isolation components and protection devices. A failure here can make a perfectly healthy processor appear dead.
MOSFET selection involves more than choosing a voltage and current rating. Gate charge, on-resistance, switching behaviour, thermal limits and package all affect the result. The SI4362DY-T1-E3 is one example from the EASYIEE catalog, while our broader MOSFET sourcing guide explains how to review these parameters.
Rectifiers also appear in power conversion and protection circuits. Devices such as the MURS120T3G may be considered where the design calls for an ultrafast rectifier, subject to verification of voltage, current, recovery behaviour, package and thermal requirements. More application context is available in the power electronics components guide.
| PLC function | Typical board-level components | What procurement should verify |
|---|---|---|
| Processing and control | MCUs, MPUs, clocks, watchdogs | Exact ordering code, firmware compatibility, temperature grade and lifecycle |
| Program and data storage | NOR Flash, EEPROM, SRAM | Density, voltage, interface, command set, endurance and package |
| Input isolation | Optocouplers, digital isolators, signal conditioners | Isolation rating, speed, output type, creepage and temperature |
| Output driving | Driver arrays, MOSFETs, relays and gate drivers | Pinout, load current, clamp protection, switching loss and thermal limits |
| Power and protection | Regulators, rectifiers, TVS devices, inductors and converters | Transient rating, efficiency, thermal margin, package and qualification |
| Communication | RS-485, CAN and Ethernet transceivers | Protocol, isolation, ESD protection, data rate and industrial temperature range |
Where PLC component sourcing usually becomes difficult
The hardest BOM lines are not always the most expensive. A low-cost memory IC or driver can delay an entire production batch if its package is uncommon, the original manufacturer has issued an end-of-life notice, or the approved alternative has not been qualified.
Older industrial equipment creates another challenge. These systems are often kept in service for many years, long after some of their semiconductors have left normal distribution. The result is a mixture of active, legacy and obsolete parts within one BOM.
For an obsolete device such as MC1413PG, a useful RFQ should include the exact manufacturer part number, required quantity, acceptable date-code range, packaging requirement and whether substitutes may be proposed. Buyers dealing with this situation may also find our guide to obsolete electronic component sourcing useful.
The same principle applies to a new design. Sending only a shortened model number creates room for mistakes. Tape-and-reel suffixes, temperature grades and package codes often form part of the orderable MPN. Removing them can turn a precise request into a guessing exercise.
A better way to send a PLC control-board BOM
If the BOM is small, part number, manufacturer, quantity and target delivery date may be enough to begin. For a larger project, it helps to identify which lines are fixed and which allow alternatives. It is also worth marking safety-related, isolation and firmware-dependent parts, because these usually require stricter substitution rules.
We normally suggest keeping technical and commercial requirements in the same file. That means including package, temperature grade and approved manufacturer alongside annual usage, required delivery and packaging preference. It saves several rounds of questions later.
The OEM BOM sourcing guide goes deeper into this process. It is especially relevant when one project combines current-production components with hard-to-find or obsolete parts.
Need help sourcing electronic components for an industrial control BOM?
Send EASYIEE the manufacturer part numbers, quantities and required delivery schedule. If alternatives are acceptable, tell us which specifications cannot change. We can then review the request as a component-sourcing project rather than treating every line as an isolated search.
A few questions buyers often ask
Does EASYIEE supply complete PLC modules?
This article focuses on board-level electronic components used in PLCs and industrial control electronics. For an inquiry, provide the exact manufacturer part number so the required product type can be confirmed before quotation.
Can an obsolete PLC component be replaced with a newer part?
Sometimes, but not from the description alone. The replacement needs to be checked against the original datasheet, pinout, electrical limits, package, protection features and any firmware dependency. Similar function does not automatically mean drop-in compatibility.
What information should be included in an RFQ?
Include the complete MPN, manufacturer, quantity, packaging preference and required delivery date. For legacy parts, add date-code and traceability requirements. If alternatives are permitted, state the parameters and manufacturers already approved by engineering.
Choosing the right components of a PLC is ultimately a balance between electrical performance, industrial reliability and supply continuity. Accurate part-number data and a well-prepared BOM will usually do more for a project than a long list of loosely matched alternatives.
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