[Paid] Design help required. - Page 1
Forum section: electronics / projects

author: Dubbie
author_rank: Unknown
timestamp: December 05, 2021, 09:54:54 pm
content: Wondering if there is anyone about who is experienced in power switching involving ~15V @ ~6A who would be interested in giving me a little design help with variation of a power mux circuit.I am happy to pay for your time. I can do a lot of the work, but I just need a wiser, more experienced brain to give me some input.DM me if you have some experience here.

author: strawberry
author_rank: Super Contributor
timestamp: December 06, 2021, 01:42:13 am
content: for example for DChigh side BTS6133low side VNB10N07commonly used in automotive applicationsor discrete P MOSFET , N MOSFET , Bidirectional switch circuit configurationfor ACSSRif both sources are not in phase is fireworks

author: Dubbie
author_rank: Unknown
timestamp: December 06, 2021, 02:08:46 am
content: Sorry, to add to the info, I want to monitor two sources and switch between them seamlessly. Kind of like ORing, but I don't just want the highest voltage to win. I want to actively control the source.I'm talking about DC

author: strawberry
author_rank: Super Contributor
timestamp: December 06, 2021, 02:38:24 am
content: take two switches and tie outputs togetherand to prevent cross conduction failure add deadtime or switch blocking comparator on output voltage level so that output is equal source level during switching on

author: Dubbie
author_rank: Unknown
timestamp: December 06, 2021, 06:18:08 am
content: Yeah it’s stuff like avoiding reverse conduction and things which I am slightly fuzzy on also if I could protect against reverse polarity without a diode drop that would be a bonus.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: December 07, 2021, 04:14:16 am
content: Hi,There are parts designed to do this. Analog Devices calls them 'Prioritized PowerPath (TM) Controllers'.The LTC4421 is one of these parts.Link:https://www.analog.com/en/products/ltc4421.html#product-overviewThe application looks like this:There two back-to-back MOSFETs in each path. This prevents current flow through the body diodes.They also have a demo board:Link:https://www.analog.com/media/en/technical-documentation/user-guides/dc2866a.pdfThe demo board is 10A. It could be modified to 6A.Regards,Jay_Diddy_B

author: strawberry
author_rank: Super Contributor
timestamp: December 07, 2021, 05:02:34 am
content: clever, suppressors discharge output capacitor

author: Dubbie
author_rank: Unknown
timestamp: December 07, 2021, 06:10:41 pm
content: Thanks Jay Diddy! I had spent a long time looking but hadn’t come across that part. I will take a look at the datasheet. Thanks again.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: December 09, 2021, 04:31:33 am
content: More magic words are "high side switch"https://html.duckduckgo.com/html?q=high+side+switchThese are (usually) glorified MOSfet's with built in level conversion for the gate signal and extra protection circuitry against over current and over temperature.Another possibility are "photo mos" relays. These have an IR diode, some photovoltaic cells and power MOSfets. The photovolaic cells then provide the gate voltage for the FET's.If you put two N-channel MOSfets back to back such as in the circuit that strawberry posted, then you can also control them with a small isolated SMPS circuit.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: December 10, 2021, 04:36:52 am
content: Quote from: Doctorandus_P on December 09, 2021, 04:31:33 amIf you look at the datasheet for LTC4421 you will see it is a lot more complicated than two high side switches and two window comparators and some logic.For example, if you a switching from a high voltage supply to a low voltage supply, you have to wait till the load discharges the output capacitor before you close the low voltage switch. If you don't wait for the output to fall, you will back feed the high voltage to the low voltage input.If switching from a low voltage to a higher voltage you have to limit the inrush current.It is pretty hard to roll your own.Jay_Diddy_B

author: Dubbie
author_rank: Unknown
timestamp: December 11, 2021, 01:08:36 am
content: Yes, it seems like there are a ton of corner cases that could let the magic smoke out. Before I was alerted to the LTC4421, I realised I was way out of my depth in designing from scratch.