Is this power supply selection circuit the best solution? - Page 1
Forum section: electronics / projects

author: daisizhou
author_rank: Super Contributor
timestamp: September 04, 2024, 02:51:26 am
content: Hallo everyoneI have some old appliances that have no battery backup and are usually powered by AC converted to DC power.I plan to use lithium batteries as power sources for them,The simple description is that when there is AC power supply, the internal AC power supply will continue to be converted to DC power supply,Use lithium battery as power supply when there is no AC power supply.The remaining space inside the host for the lithium battery to be placed.I drew the automatic switching circuit, but I don't know if it is the best choice.U1 (LM74610), U2 (IRF7478), and C1 form an "ideal diode",Because ordinary diodes have a voltage loss of 0.4V, I chose this solution.U2 I referred to the recommended model in the manual, but I don't know if it is the best choiceIf you have better suggestions, please tell me, thanks

author: inse
author_rank: Super Contributor
timestamp: September 04, 2024, 07:56:17 am
content: The negative side of the battery needs to be connected to GND, not 12Vin.If the device also works from two lithium cells (8.4V max) then why would you place the ideal diode circuit in the 12V supply?A loss of 0.3..0.4V should be acceptable- maybe feed the device from a lab supply and reduce voltage until it stops working properly to check out.Is the battery supposed to be charged by the AC supply, did you figure out a charging circuit already?

author: daisizhou
author_rank: Super Contributor
timestamp: September 04, 2024, 09:00:15 am
content: Quote from: inse on September 04, 2024, 07:56:17 amSorry, I drew the wrong battery mark.The battery is not just 2 18650 cells, this is a battery mark.Because I consider that if the current is 2A, then the energy loss in the diode will be 0.6-0.8 watts,So I put in an ideal diode, hoping to further reduce the circuit loss.

author: PGPG
author_rank: Frequent Contributor
timestamp: September 04, 2024, 11:19:46 am
content: Your battery is permanently connected with +12V Input. So no matter if AC power is connected or not there is always voltage. How your circuit is intended to discover if AC supply is or not?

author: daisizhou
author_rank: Super Contributor
timestamp: September 04, 2024, 11:26:13 am
content: Quote from: PGPG on September 04, 2024, 11:19:46 amMy initial plan was to input 220V AC voltage and generate+12V through an AC/DC power adapter,If the 220V input is normal, use a 12V power supply as the main power source,And charge the battery.If the 220V power supply disappears, use battery power supply

author: inse
author_rank: Super Contributor
timestamp: September 04, 2024, 11:42:17 am
content: Most simple solution: use a relay to switch between battery and mains power.The coil is powered via a separate diode on the low voltage AC side, no matter whether SMPS or transformer power supply.

author: ledtester
author_rank: Super Contributor
timestamp: September 04, 2024, 11:53:38 am
content: Lithium Ion batteries need special charging circuitry to control the charging process.It is also advisable to have over-current and over-discharge protection to protect the batteries.If you search for "diy mini ups" or "diy router ups" you'll find a lot of related projects.Some main design themes are:- relay + TP5100/TP4056 charging module + boost converter:https://drive.google.com/file/d/1IPLvyO6OsC7upF-XPZFyau-PHZSDgrgD/view- BMS module + boost converter:https://youtu.be/IlEnEn7ptmchttps://www.instructables.com/DIY-Mini-UPS-for-WiFi-Router-V20/- relay + power bank + boost converter:https://www.instructables.com/DIY-UPS-for-WiFi-Router-V40/