Parameters of the Test:
This is a rough bench test to determine the pros and cons of using the Recom R78 Series switching converters in place of the standard 78## linear Regulators in simple circuits.
Input voltage used for this test was 15 volts regulated.
All load resistors are assumed accurate at marked resistances
All meters are assumed accurate within reasonable expectations for the scope of this test.
All current measurements are listed in milliamps.
All Voltages are listed in volts.
Load Resistance is in Ohms
Subjects of the test:
Pictures taken from Recom Data Sheet
Bench Testing the Recom R-78E5.0-0.5 & R-785.0-1.0 Converters
Against the LM7805 Linear Regulator
R-785.0-1.0 R-78E5.0-0.5 7805 Linear
---------------- ----------------- ----------------
LOAD Iin Vout Efficiency Iin Vout Efficiency Iin Vout Efficiency
No Load 4.8 5.05 - 0.5 5.1 - 5.0 5.05 -
1000 6.8 5.04 24% 4.4 5.05 37% 10.0 5.05 16%
470 8.9 5.04 37% 7.0 5.04 48% 15.9 5.05 21%
100 21.1 4.99 79% 18.4 4.99 90% 50.5 5.04 33%
10 156 4.43 82% 153 4.63 92% 481 4.91 33%
5 255 4.3 96% 265 4.4 97% 770 4.84 30%
(Load above Max Specs)
Pros and Cons:
Cost from Newark:
R-785.0-1.0 Newark Part # 62X9542 Cost $7.49
R-78E5.0-0.5 Newark Part # 62X9499 Cost $2.49
LM7805 Newark Part # 34C1092 Cost $0.68
Efficiency :
The Recom Series is consistently more efficient than the LM7805. This is of course a design factor as the LM7805 is using linear resistive means to regulate to the 5.0 volts and the R78 series is using switching technology.
Heat:
The Recom R78 runs cool enough so that it does not need a heat sink, while the LM7805 must have a heat sink for lower resistive loads.
Size:
Both the R-78 and the 7805 are comparable in size. See picture above. The 7805 does require more room in the event that it must be attached to a heat sink.
Deviation from Nominal Voltage:
Up to 50mA the Recom R-78 series was fairly true to the nominal 5.0 volts. After this point the output voltage dropped until at the 5 Ohm load level and nearly 900 mA the output had dropped approximately 0.5 volts to 4.5 volts.
The LM 7805 on the other hand held to the Nominal 5.0 volt level until the load dropped to 10 Ohms and nearly 500 mA. At the 5 Ohm load level the LM7805 still had only dropped 0.16 Volts to 4.84 volts.
The Linear regulator holds nominal output voltage levels better than the R-78
Output Ripple:
Assuming a ripple free input voltage the LM 7805 delivers a very pure DC output while the R-78 has 20mV to 30mV ripple at the operating frequency which can vary between 280kHz and 430kHz depending on load. This ripple can be handled with a suitable decoupling capacitor. Both manufacturers have recommended decoupling capacitors in their data sheets.
Warranty:
R-78XX Series: 3 Years
LM78## Series: Not Listed
Data Sheets:
http://www.farnell.com/datasheets/1833222.pdf
http://www.farnell.com/datasheets/1833229.pdf
http://www.farnell.com/datasheets/1855686.pdf
Summary:
In routine applications a standard LM7805 would trump the R-78XX series because of the lower cost, more stable output regulation over a greater load range, and lower ripple. This advantage can however be easily off set by the increased efficiency of the R-78 series. In situations where power resources are critical the move from 30% efficiency to over 90% can be a real game changer. This can be especially true for battery operated applications. The small size of the Recom R-78XX and the fact that it does not need a heat sink is also a point in its favor. The R-78E, I assume that means economy, only costs $1.81 more than the LM7805, which makes me think that for applications with less than 500 mA current demand and tolerance of a potential 10% output voltage drop at the higher loads, the R-78E would definitely be my choice.
I realize that The Recom R-78 Series is not a new product and that there is an even newer more accurate Recom R-78C device that has been available since 2011. However last week there was a posting on the Forum about an excellent book, “DC/DC Book of Knowledge” by Steve Roberts M.Sc. B.Sc. that was being offered free for PDF download or available in paperback cover for $2.25. After I received the book I learned about the Recom R-78 Series of Switching converters. I also thought of how many times I had seen the LM7805 recommended on the forum for applications where the R-78 would have definitely been a better suited recommendation. For this reason I decided to do a blog on the Recom R-78 series just to call its attention to others like myself who have missed knowing about it.
Here is the link to the Recom Book announcement.
John
