Power Supply with "Dying Gasp" feature - Page 1
Forum section: electronics / projects

author: wholder
author_rank: Regular Contributor
timestamp: May 23, 2020, 11:55:55 pm
content: My daughter recently got ATT, 1 GB fiber installed and, while reading though the brochure for the interface unit (an ALCATEL LUCENT G-010G-A) I noticed it listed a feature I'd not heard of before. Is said "Power supply withdying gasp functionality". I the found aWikipedia article on thiswhich said "A DSL interface with dying gasp must derive power for a brief period from another source so that the message can be sent without external power."I'm curious if anyone else ha designed a power supply with this kind of functionality and what it requires to implement it? Is this just as simple as having a big enough capacitor on the output side to supply the needed current, or are other techniques needed to make this this reliable?Wayne

author: bob91343
author_rank: Super Contributor
timestamp: May 24, 2020, 12:44:26 am
content: It depends on the current drain and the time required. Just a matter of energy and arithmetic.A capacitor may be enough or a backup battery.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 24, 2020, 08:58:39 pm
content: Just marketing speak for a supercap or two and an input monitoring circuit.Here's an open hardware version:https://github.com/prusa3d/MK3_Power_Panic

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 26, 2020, 05:16:50 pm
content: This "dying gasp" seems to be a standard term in some games, but also in networkingterms.Code:Dying Gasp resides on a hardware component on the High-performanceWAN Interface Card (HWIC) and supports the Fast Ethernet and Gigabit Ethernet interfaces.The networking devices rely on a temporary back-up power supply on a capacitor,that allows for a graceful shutdown and the generation of the dying-gasp message.This temporary power supply is designed to last from 10 to 20 milliseconds to performthese tasks. Dying-Gasp packets are created when you configure the host by using thedying-gasp configuration command. The show dying-gasp packets command displaysthe detailed information about the created packets.The SNMP server for the SNMP Dying Gasp message is specified through the snmp-serverhostconfiguration command. The syslog server sending the syslog Dying Gasp messageis specified through the logging host hostname-or-ipaddress transport udp command.The Ethernet-OAM Dying Gasp packets are created for interfaces where Ethernet-OAMis enabled.Source:https://www.cisco.com/c/en/us/td/docs/switches/connectedgrid/cgs2520/software/release/15_0_2_ed/configuration/guide/cgs_15_0_2ed/cgs_dying_gasp.pdf20ms is not much. It's just one period of the AC Mains.Mains powered SMPS circuits usually start by rectifying the mains voltage and charging a 400Vdc Electrolytic capacitor, which holds a significant charge. Just take any Power adapter with a Led in it, and watch how long it takes before the LED goes out after you pull the plug out of the wall.The only extra thing required would then be some detection that AC voltage input is lost, and communicate it in a timely fashion to the electronics.

author: Ice-Tea
author_rank: Super Contributor
timestamp: May 26, 2020, 05:29:39 pm
content: It used to be just some caps on the DC input. As far as I know, this is not normally implemented on the power supply itself but on the "main" board. Otherwise you'd have to run a signal from the power supply to the main board to signal power's going away (so the "dying gasp message" can be sent.)More recent, dedicated converters have been in use so that the energy is stored at a higher voltage (needs less cap) and lower voltaged DC/DC bricks can be used (example ->https://www.monolithicpower.com/en/mp111.html)

author: TimNJ
author_rank: Super Contributor
timestamp: May 26, 2020, 06:17:36 pm
content: I think they are talking about a feed-foward "power good" or "power fail" circuit? This signal tells the powered device that it's about to lose power so wrap up what you're doing and don't corrupt anything.

author: TimNJ
author_rank: Super Contributor
timestamp: May 26, 2020, 06:20:25 pm
content: https://www.sunpower-uk.com/glossary/what-is-power-fail/

author: DaJMasta
author_rank: Super Contributor
timestamp: May 26, 2020, 06:21:58 pm
content: Very similar to a 3d printer's "power panic" or similar feature. In their case, they monitor the mains voltage before the SMPS, so they have some tens of ms worth of reaction time with its capacitors and such - not a large addition of extra ones. That's enough time to store the current place in the gcode (instructions for printing the object) stop the movement of the print head, and store the head location. If you've stopped, there can still be potential slackening when powered off or external forces moving things, but it's a heck of a lot better than being in the middle of a move where you don't know how far you've progressed.