DC-DC Buck Converter Questions - Page 1
Forum section: electronics / beginners

author: Ultron81
author_rank: Contributor
timestamp: August 30, 2019, 01:00:08 am
content: I'm replacing the linear power supply in a game console to save space and get rid of the large heat sink. The supply is a 7805, and I would say normal conditions draw 800mA, maybe max current draw is 1A. The input to the console is ~17VDC unregulated, coming from a wallwart. I plan on redesigning the power board, since it has a RF modulator on it that I don't plan on using in my new design.I've never really dealt with the design of a buck converter before. I did do a lot of reading online, but I'm still a little confused.I see there are non-synchronous and synchronous converters. What would be the best to use in my case? I've been looking in the 5V/1.5A-2A range.The part that really throws me for a loop is the switching frequency. I see some switchers at 150kHz, but then also a lot at 1.4MHz. What would be a good all-around frequency to use?I was looking at this part, but couldn't find much information on anyone's experience with it -http://www.ti.com/product/TPS5405I also saw this, looks like a direct 7805 replacement, though expensive -https://www.digikey.com/product-detail/en/murata-power-solutions-inc/OKI-78SR-5-1.5-W36-C/811-2196-5-ND/2259781Thanks in advance!

author: noname4me
author_rank: Regular Contributor
timestamp: August 30, 2019, 06:54:36 am
content: https://uk.farnell.com/wurth-elektronik/173010578/dc-dc-conv-buck-5v-300khz-sip/dp/2577479?st=Magi3c%205vEven simpler?It's a pin for pin compatible replacement for the 7805...Sent from my SM-N960F using Tapatalk

author: Ultron81
author_rank: Contributor
timestamp: September 02, 2019, 08:33:59 pm
content: Thanks, I'll check these out

author: Buriedcode
author_rank: Super Contributor
timestamp: September 02, 2019, 08:45:59 pm
content: Quote from: blueskull on August 30, 2019, 01:07:38 amI would be wary of those modules. I have no doubt the IC does what it claims, but the IO caps tend to be grossly insufficient. I would at least test the device with your average input and output voltage, and maximum current to see what the ripple and regulation are like. The few of those I have tried were good up to about 600mA but lost regulation beyond it.

author: wraper
author_rank: Unknown
timestamp: September 02, 2019, 08:48:19 pm
content: As you don't know much about them, better stay with lower frequencies. High frequency DC/DC converters are finicky and very sensitive to board layout.

author: wraper
author_rank: Unknown
timestamp: September 02, 2019, 08:53:41 pm
content: Quote from: Buriedcode on September 02, 2019, 08:45:59 pmCaps of such size should be sufficient because of 1.5 MHz switching frequency. Actual capacitance may be lower than needed though. I would suggest converter with non regulated output voltage. 3-12V range is questionable and should be sub-optimal in most of range.

author: yashrk
author_rank: Frequent Contributor
timestamp: September 04, 2019, 06:45:24 am
content: Quote from: wraper on September 02, 2019, 08:53:41 pmHe is replacing an existing linear regulator so it must have external capacitors already available onboard which he can replace to get the requisite capacitance.