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CNC Power Supply Unit – MITSUBISHI PD21B
The PD21B is a power supply module (“Power Supply Unit”) manufactured by Mitsubishi Electric, used in CNC control units of the MELDAS series. The module receives AC mains voltage and converts it into regulated and filtered DC voltages required to power the control boards, processors, and interface modules of the CNC system. It is not a drive or CPU board: it is a dedicated power conversion module for the entire control electronics.
The power supply is the fundamental element of the CNC electrical system: it provides the regulated voltages (typically +5 V, ±15 V, +24 V DC) essential for the operation of all control boards, axis modules, and I/O interfaces. A failure of this module causes an immediate shutdown of the entire CNC unit, rendering the machine completely inoperative until the component is replaced or repaired.
Mitsubishi Electric is one of the leading Japanese manufacturers of industrial electronics, CNC systems, inverters, servo systems, and factory automation. The CNC division — historically known under the MELDAS brand — has been producing controllers for machine tools since the 1970s. Products in the PD series are legacy / discontinued: available exclusively as used, surplus, or through specialist repair services.
Main Technical Specifications
| Type | CNC power supply module (Power Supply Unit) |
| Part number | PD21B |
| Brand | Mitsubishi Electric |
| Known application | Mitsubishi CNC systems, MELDAS series |
| Function | Regulated DC power supply for CNC control boards and modules |
| Input | AC 200–240 V, 50/60 Hz (typical) |
| Main outputs | +5 V DC, ±15 V DC, +24 V DC (typical) |
| Interfaces | Edge connectors / internal bus (Mitsubishi CNC rack backplane) |
| Mounting | Plug-in module for Mitsubishi CNC rack |
| Weight | ~0.8–2.0 kg |
| Dimensions | ~150–250 mm |
| Production status | Legacy / discontinued — used/surplus/repair only |