Product Review: OKI78SR-5/1.5 Switching Regulator from muRata Power Solutions

This non-isolated switching DC-DC regulator module by muRata power solution comes in a handy 10.4 x 16.5 mm package which is smaller than any linear regulator with same kind of specs. Drop-in replacement for 78xx series (TO-220 Pack) of Linear regulator, this module gives an efficiency of >85%. You cannot expect linear regulators to give an efficiency of more than 25%.

OKI-78SR comes in two output ratings 3V3 and 5V DC and can pump up to 1.5A current. It provides excellent Line regulation and Load regulation of +/- 0.25% at typical operating conditions. The best thing about this DC-DC module is, no external parts are required to make it work; it’s a drop in replacement to any TO-220 78xx linear regulators.  Though the OKI78SR gives a higher efficiency with smaller size and higher current output, it has a clear cost disadvantage in terms of common usage. This module costs around 8- 10 times to any linear regulator of same specifications.  This module can be used at places where higher power efficiency is desired and system cost can be sacrificed for efficiency.

OKI-78SR-5/1.5

OKI-78SR-5/1.5

Design – The circuitry is built around MP2467 step down switching regulator by Monolithic Power Solutions, it’s a 2.5A, 36V regulator, and it works at fixed switching frequency of 500 KHz which is a rather high frequency for a buck regulator. High switching frequency makes it possible to reduce the size of design, as; higher the switching frequency lower is the size of inductor required.  OKI78SR-5/1.5 uses a 10uH SMD inductor.

The circuit seems to look like the application circuit provided in the MP2467 Datasheet. The output rectifier diode supplies the current to the inductor when the high side switch is off, to reduce the losses due to the diode forward voltage and recovery times, a Schottky diode is required, OKI78SR uses B360A diode in DO-214AC package. Normally a diode with maximum reverse voltage greater than max input voltage is required, B360A has max reverse voltage of 60V which is far greater than maximum specified input voltage range for OKI78SR. B360A has forward current rating of 3A, which is greater than the specified load current.

MP2467 Based Switching regulator Circuit

MP2467 Based Switching regulator Circuit

Back side view of OKI-78SR-5/1.5

Back side view of OKI-78SR-5/1.5

Front side view of OKI-78SR

Front side view of OKI-78SR

OKI78SR 7805 Size Comparison

OKI78SR Vs 7805 Size Comparison

References -

MP2467 Product Page

MP2467DN Datasheet by Monolithic PS INC

OKI-78SR Datasheet by Murata Power Solutions 

B360A Datasheet by Diode Inc

Product Samples Sponsored by Farnell Electronics, UK