Electronics > Projects, Designs, and Technical Stuff

Power Supply with "Dying Gasp" feature

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wholder:
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 with dying gasp functionality".  I the found a Wikipedia article on this which 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

bob91343:
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.

NiHaoMike:
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

Doctorandus_P:
This "dying gasp" seems to be a standard term in some games, but also in networking
terms.


--- Code: ---Dying Gasp resides on a hardware component on the High-performance
WAN 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 perform
these tasks. Dying-Gasp packets are created when you configure the host by using the
dying-gasp configuration command. The show dying-gasp packets command displays
the detailed information about the created packets.

The SNMP server for the SNMP Dying Gasp message is specified through the snmp-server
hostconfiguration command. The syslog server sending the syslog Dying Gasp message
is specified through the logging host hostname-or-ipaddress transport udp command.
The Ethernet-OAM Dying Gasp packets are created for interfaces where Ethernet-OAM
is enabled.
--- End code ---

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.pdf

20ms 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.

Ice-Tea:
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)

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