MORNSUN® B0505S-1W Review

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Mornsun B0505S-1WRecently when I was developing a digital light controller project, I wanted to have the interface isolated from the common ground to avoid spurious noise and other issues. Since I didn’t have a quick solution to proceed with something from my parts bin, I ended up buying a batch of MORNSUN® B0505S-1W isolated dc-dc converter modules from InkOcean ( The minuscule power supply module can provide a magnetically isolated 5V/1W dc output which proved to be good enough for my project. Here’s a short introduction to MORNSUN® B0505S-1W!

MORNSUN® B0505S-1W Module

Quick Intro: The module is designed for application where isolated output is required from a distributed power system. It’s a fixed input, isolated and unregulated single output dc-dc converter capable of delivering a maximum of 200mA current at 5V dc output. Notably, no external component required for this popular 4-pin module available in a SIP package.

B0505S-Mornsun Outline Clip

Input & Output: As clearly indicated in the datasheet, you can use the module well if you have a >300mA input dc supply in 4.5-5.5V range but the maximum output load current never exceeds the 200mA at 5VDC limit.

Morsun Datasheet Clip

Ripple & Noise: Since the module’s ripple and noise is ≤100 & 100 mV respectively, it’s good only for certain projects where a low ripple noise is not an absolute necessity. Further, the isolated 5VDC output from the module is not regulated, and it calls for 31mA of input current at no load. Typical efficiency at full load (100%) is 70% while it’s 40% at light load (10%). Refer typical efficiency curves of the module shown below.

MORNSUN B0505S-Efficiency Curve

External Parts: This particular S0505S-1W isolated dc-dc converter module hardly requires external components for a proper run. However you can attach a small EMI recommended component – one 1uF/50V ceramic capacitor – across its input leads.

Inside Circuitry: Although I didn’t get a worthy chance to break apart the B0505S-1W module, it came to my notice that its inside electronics is mainly based on the “Royer Oscillator” ( circuit. As far as I know, the traditional Royer oscillator circuit only provides basic functions but once the circuit is abnormal, the  module may be damaged and even cause serious consequences. At present, the module is available without a continuous short circuit protection (SCP) feature!

MORNSUN B0505S-Short Circuit Module

Cheerful Design Revisions

R1 to R3: First in the series of fixed input voltage dc-dc converters by MORNSUN® is ofcourse the above explicated version R1(B0505S-1W). The following fixed input voltage series R2 (B0505S-1WR2) further improve system reliability to a great extent, and now the third one R3 series is on the road (B0505S-1WR3). The R3 series gets an independent oscillator circuit based on chip technology thus features effective continuous short circuit protection (SCP) by a modified push-pull circuit. R3 series not only achieve a great improvement in short circuit protection and start-up, but also gently improve the capacitive load ensuring a normal start-up in CC mode where large capacitive load exists.

MORNSUN B0505S-R3 Module

Further, B0505S-1WR3’s stand-by power consumption is 25mW and no-load current is 5mA. R3 series with 5VDC output not only provide an efficiency to over 82% at full load (100%) but also over 75% at light load (10%), which reduces temperature rise of the device at light load. Following is a brief comparison table of B0505’s key performance for your quick reference.

MORNSUN B0505S-Brief Comparison

Role of Input/Output Capacitors

Adding a capacitor at the input terminal can absorb the voltage spikes, and keep the voltage stable. Similarly, an output capacitor can greatly reduce the output ripple. For R3, recommended value of the input capacitor is 4.7uF and the value of output capacitor is 10uF. Below you can see the schematic drawing of the initial version of my “Universal B0505S-1W Breakout Board”.

Mornsun Breakout v1

Note down that it’s commonly recommended (particularly for version R1) to use conventional ceramic capacitors, not tantalum capacitors because the ESR of a tantalum capacitor is very low thus it appears as a dummy output short during start-up. This results in the input current impacts and damages the converter!

Finally, a candid shot of my basic experiments with B0505S-1W (R2) dc-dc converter module(s). There’s also a quick test report table prepared after the initial evaluation.


Input Voltage: 5.03VDC (500mA)Input Current (No Load): 20mA
Output Voltage: 5.12VDCOutput Load (No Load, Only DVM)

Next up, I’ve to build a few do-it-yourself projects for my readers. Assist ardent electronics hobbyists in making projects similar to the ones I build and to teach them about working with electronics is always a cheerful experience. So, simply stay tuned!

Courtesy Note

This article is prepared with inputs from articles/datasheets published mainly by MORNSUN ® . A couple of retouched snips from that resources are also used here for the sake of clarity. Source:  and


  1. if you had a 1s BMS and want to run a singular 18650 battery and a 5v BT chip and 3-5v class d amp, is this the right isolator for me? i understand the input would be 3.7v max being one battery.

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