How to choose a 5 V on-board AC/DC power module
Four questions that decide which 5 V AC/DC module fits your board — and how the MORNSUN LS and LHE parts we stock differ from each other.
Who this is for: Hardware engineers specifying a 5 V auxiliary rail on a mains-powered board, and buyers checking a specified part.
An on-board AC/DC module puts the whole mains-to-5 V stage on your PCB: one component, an isolated output, no separate power supply and no mains wiring inside the enclosure. Picking the right one usually comes down to four questions.
1. How much current does the 5 V rail really need?
Add up the worst case, not the typical case — the MCU at full clock, the radio transmitting, the relay coils pulled in, the backlight at full brightness — and then decide whether those peaks happen at the same time. Modules are rated on continuous output; a 3 W part delivering 600 mA at 5 V has no headroom for a 1 A burst.
Then look at the derating curve in the datasheet. Every one of these modules delivers its full rating only up to a certain ambient temperature, and sealed enclosures get hot. If your board sits in a closed box at 55 °C, size on the derated figure, not the headline one.
2. What is the real input range?
“Universal input” is not one thing. A standard 85-305 VAC part covers ordinary single-phase mains worldwide. But if the product can end up across a phase-to-phase connection, on an industrial network with a floating neutral, or somewhere the line can swing hard, you want the wide-input version.
That is the difference between LS10-13B05R3 (85-305 VAC) and LS10-26B05R3 (85-528 VAC). Same 10 W, same 5 V / 2 A output — the 26B part simply survives a much higher line voltage, and it is a little larger and has 4000 VAC isolation instead of 3600 VAC.
3. How much isolation do you need?
Isolation voltage is a safety and creepage question, not a performance one. Check what your product standard requires between mains and the accessible secondary side, then check the module's input-to-output rating and the isolation class stated in the datasheet. The parts below range from 3000 VAC to 4000 VAC.
4. How much board space is there?
This is often what actually decides it. A 3 W SIP module is 26.4 × 12.58 × 11 mm. A 60 W part is 109 × 58.5 × 30 mm and weighs 300 g — it needs mechanical support, not just solder pads.
The 5 V parts we publish, side by side
| Part | Output | Input | Isolation | Size (mm) | Good when |
|---|---|---|---|---|---|
| LS03-13B05R3 | 3 W · 5 V / 600 mA | 85-305 VAC · 70-430 VDC | 3000 VAC | 26.4 × 12.58 × 11 | A small controller or sensor board where space is the binding constraint and EMC demands are moderate |
| LS10-13B05R3 | 10 W · 5 V / 2 A | 85-305 VAC · 100-430 VDC | 3600 VAC | 32 × 17.2 × 15.05 | The general-purpose choice: enough current for an MCU plus a radio or a couple of relays |
| LS10-26B05R3 | 10 W · 5 V / 2 A | 85-528 VAC · 100-745 VDC | 4000 VAC | 38 × 20 × 15.25 | Same job as above but on a high or unstable line — phase-to-phase, industrial networks |
| LHE60-20B05 | 50 W · 5 V / 10 A | 85-264 VAC · 100-370 VDC | 4000 VAC | 109 × 58.5 × 30 | A 5 V rail that has to drive real loads; also available with chassis (A5) or DIN-rail (A6) mounting |
Figures from the current MORNSUN datasheets; each product page shows the revision and the date we checked it.
A note on EMC
The compact LS parts are, in MORNSUN's own words, aimed at applications that do not have high EMC requirements; for harsh environments the datasheet's Design Reference application circuit with the recommended input filtering is not optional. The LHE60 family meets EMI Class B and ±2 kV / ±4 kV surge without additional circuitry. If you have to pass EN 55032 Class B at the product level, factor that difference in before you compare prices.
Still unsure?
Tell us the input range, the 5 V current including peaks, the ambient temperature and the space you have, and we will suggest parts with the datasheets attached — including MORNSUN parts that are not published on this site.
Written by Raitop. Product parameters are taken from MORNSUN official datasheets; see each product page for the source, the datasheet revision and the date it was checked.
