Mean Well DRA-40-12 DIN Rail Power Supply

A 12 V DIN rail supply with an adjustable current limit

The Mean Well DRA-40-12 is a 40 W AC/DC DIN rail power supply with a 12 V DC output and 3.34 A rated current. What separates the DRA-40 from ordinary 40 W rail supplies is that the constant-current level can be changed from outside: Mean Well specifies adjustment through an external 1 to 10 Vdc signal, a PWM signal or a resistance, in addition to the internal voltage potentiometer.

The unit accepts 90 to 264 VAC, runs from -30 to +70 C under free-air convection and reaches 85% typical efficiency at 12 V. The datasheet gives a constant-current region of 3 to 12 V, and the 40 mm width keeps it compatible with TS-35/7.5 and TS-35/15 rails. Mean Well also states that the series passes the limited power source (LPS) requirement and carries a three-year warranty.

Technical specifications

Why an adjustable current limit matters

A fixed overload limit is fine for a logic rail, but it is awkward when the load is a battery, a heater element or a string of loads that must be capped. With a controllable current limit, the same supply can behave as a voltage source for normal operation and as a current source during charging or start-up, and the limit can be changed by a controller instead of by swapping the unit. Mean Well names machine vision inspection systems and plant cultivation systems as target applications for this model.

Selection and wiring checks

Match the current limit to the load: the datasheet overload threshold is 95 to 108% of rated output, so the supply starts limiting very close to nominal current. Decide whether the control input will be a 1 to 10 V analogue signal, a PWM signal or a fixed resistor, and consult the datasheet for the terminal connections. Verify the output voltage with the potentiometer under load and allow the clearances recommended on the rail. For a design that needs a conventional supply with a DC OK contact, the MDR-40 series is the usual alternative. Test the current-limit setting with a dummy load during commissioning, and document the control signal level so the setting can be reproduced after replacement.

Documents and quotation

The datasheet attached to this page belongs to the DRA-40 family and includes dimensions, derating information and the model table. To obtain a quotation for DRA-40-12, tell us the quantity, the voltage and frequency of the site supply, the real load profile, the cabinet temperature and the approvals that apply. Browse Power Modules for alternatives.