Power supply module: enclosed and open-frame AC-DC switching supplies mounted on a chassis or inside equipment

01

Rated power falls at low output voltages inside the same 350 W enclosure

Mean Well's LRS-350 specification gives the same 215 × 115 × 30 mm enclosure eight output voltages, but its 3.3, 4.2 and 5 V models are limited to 60 A, so they deliver 198, 252 and 300 W, while the 12 to 48 V models deliver 348–350.4 W. Efficiency (typ.) rises from 79.5% at 3.3 V to 89% at 48 V, ripple and noise is 150 mVp-p up to 24 V and 200 mVp-p at 36 and 48 V, and voltage tolerance tightens from ±4.0% at 3.3 V to ±1.0% from 15 V upward. [1]

Editorial calculation: at full load the 3.3 V model dissipates about 198 × (1/0.795 − 1) ≈ 51 W inside the enclosure to deliver 198 W, and the 24 V model about 350.4 × (1/0.88 − 1) ≈ 48 W to deliver 350.4 W. [1]

Give the supplier the output voltage and continuous current, peak current and its duration, input voltage range, ambient temperature inside the equipment, mounting orientation and airflow, hold-up time needed through mains dips, and the safety and EMC standards for the end product.

02

Built-in fan or convection cooling, and the temperature at which output derates

The LRS-350 has a built-in fan switched by a thermistor, on at 50 °C or above and off at 40 °C or below, and is rated for −25 to +70 °C by its derating curve; the LRS-150 is rated −30 to +70 °C by its curve. [1] [2] TDK-Lambda's LS series of 25–150 W supplies is convection-cooled, rated −25 to +70 °C, with output derating linearly above +40 to +50 °C depending on model, and withstands 300 VAC input surges for 5 s. [3]

Editorial calculation: LS150-24 at 6.5 A delivers 156 W, the same as the LRS-150-24 at 6.5 A, yet the stated hold-up at 230 V is 28 ms against 40 ms. [3] [2]

03

Inrush, peak load and what the supply does on overload

Mean Well states an inrush of 60 A (typ.) for the LRS-350 at 115 or 230 VAC and overload protection at 110–140% of rated power: the 3.3–36 V models go into hiccup mode and recover once the fault is removed, while the 48 V model shuts down and latches off until power is cycled. The 12–48 V models carry a 150% peak load for up to 1 s and enter hiccup mode if the peak lasts longer. [1] TDK-Lambda states overcurrent protection above 110% for the LS series and cold-start inrush of 30–60 A at 230 VAC by model. [3]

Editorial note: a load that needs more than 150% for longer than 1 s, such as a motor or a capacitive bank, will put the LRS-350 into hiccup mode; ask the supplier for peak-load curves at your duration, and check whether latch-off or auto-recovery suits your machine.

04

Send the load, environment and protection requirements together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Output: [voltage; continuous current; peak and duration]
Input: [voltage range; 115/230 V switch; DC input]
Thermal: [ambient inside equipment; orientation; airflow]
Hold-up: [ms at your mains]
Protection: [hiccup or latch-off; overvoltage]
Compliance: [IEC/UL 62368-1; EMC class]

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