"Upgrade?" 7805 Linear Regulator vs OKI-78SR-5 Switching Regulator - Page 1
Forum section: electronics / beginners

author: CkRtech
author_rank: Regular Contributor
timestamp: June 20, 2015, 10:11:26 pm
content: Greetings,I have recently started to look into the perks of upgrading 7805s in old game consoles (Nintendo, Sega, NEC, etc) to an OKI-78SR-5. I have done it in one console (Super Nintendo) so far, and I did it as a drop-in replacement (no other components added).(TL;DR - is a reduction in heat output the only advantage I am going to see with this swap?)Most of these consoles use an external AC/DC brick that spits out 9V/10V and gets fed to the 7805. They were all mass-produced circa late 80s and early 90s.It seems like a win-win situation to replace the 7805 with an OKI-78SR-5. It doesn't cost much and immediately allows me to toss the oftentimes large heatsink in the system - therefore creating more space for audio/video modifications.Questions:1: Should I have any concerns about doing a drop-in replacement provided the 1.5amps is enough (generally they all use 1 amp or less, but I will double check before doing a switch)2: Any comments regarding noise/ripple on something like the OKI vs. a 7805?3: Somewhat tied to #2 above, would replacing the regulator potentially benefit (cleaner power/noise reduction) the various audio mixing and amplification circuits in the system?All feedback on this is appreciated. Thanks!

author: LabSpokane
author_rank: Super Contributor
timestamp: June 21, 2015, 06:21:21 am
content: I'll check the ripple tomorrow, but the OKI is a solid regulator. The spec sheet on it is very conservative. I found that the quiescent current is only 200uA which makes it great for a battery-powered application.If you want to get fancy, spin your own board using the switcher IC. It's good for 2.5A and supposedly can go down to 100uA quiescent. Those specs may sound poor but the Vin range is 7 to 36V at 90% efficiency. It's just a great drop in solution. Not cheap though.

author: schwarzrmsu
author_rank: Contributor
timestamp: June 21, 2015, 02:56:55 pm
content: This is an interesting mod. I would switch the regulators out one at a time and test performance in-between. I would be slightly worried about added noise to the system which may affect some potentially sensitive portions of your gaming system. Especially since you have no control of your ground plane. Adding a significant amount of switching noise to a ground plane that is not designed for it may cause issues.

author: LabSpokane
author_rank: Super Contributor
timestamp: June 21, 2015, 07:12:40 pm
content: Quote from: CkRtech on June 20, 2015, 10:11:26 pmMy regulator is soldered to my PCB, so this measurement is with a couple caps, RTC on board, etc., but powered off 12VDC, the ripple is <10mV, which is as low as my scope will go. I used a 20MHz BW limit. With the noise in my lab, the ripple coming off the switcher after my caps is indistinguishable from a battery. I'd swap out the 7805 with confidence.

author: schwarzrmsu
author_rank: Contributor
timestamp: June 21, 2015, 09:13:59 pm
content: Good stuff. These OKI-78SR's are pretty neat!

author: CkRtech
author_rank: Regular Contributor
timestamp: June 24, 2015, 12:51:38 am
content: Thank you both for sharing your thoughts. I will most likely look to integrate more of these into some of these systems in the future and check the results. I just wanted to make sure that treating it as a "drop-in replacement for a 7805" didn't come with a little asterisk next to it.