Hot standby (redundant) power supply circuit

[[email protected]]

Dear Experts,
I have an embedded application using VMEbus backplane with one CPU
and a few I/O boards. The vendor of the VME system provides one 80W
18-24 VDC input power supply which provides 3 outputs: +5V 8A(max),
+12V 3A(max), -12V 1A(max). Our end customer requires a dual power
supply to work in redundant/hot standby mode. He intends to power each
power supply from two different 24VDC sources. So if power fails on one
(or if one of the power supply fails), the other one takes over
immediately (without getting the CPU's to reset/restart - i.e. hot
standby).
We need to now merge the outputs of the two power supplies on to
another PCB which handles this switching and then power the VME
backplane with the output of this board. What is the best way to achive
this? Please note that designing a new redundant power supply is not an
option for us. We must achieve redundancy by combining the outputs of
the two power supplies in some way. Thanks.

Ganesh Okade
Sunlux Technologies Ltd.
http://www.sunlux-india.com

 

[budgie]

Dear Experts,
I have an embedded application using VMEbus backplane with one CPU
and a few I/O boards. The vendor of the VME system provides one 80W
18-24 VDC input power supply which provides 3 outputs: +5V 8A(max),
+12V 3A(max), -12V 1A(max). Our end customer requires a dual power
supply to work in redundant/hot standby mode. He intends to power each
power supply from two different 24VDC sources. So if power fails on one
(or if one of the power supply fails), the other one takes over
immediately (without getting the CPU's to reset/restart - i.e. hot
standby).
We need to now merge the outputs of the two power supplies on to
another PCB which handles this switching and then power the VME
backplane with the output of this board. What is the best way to achive
this? Please note that designing a new redundant power supply is not an
option for us. We must achieve redundancy by combining the outputs of
the two power supplies in some way. Thanks.

Unless I am missing something in the description, a pair of Schottky diodes for
each PSU output rail voltage. You need to increase each voltage by the diode
forward rop at load curent. That only leaves the PSU input side, where you
would need to ensure that a PSU fault wouldn't take down the 24V source
protection.

 

[[email protected]]

Dear budgie,
Thanks for the response. I do not have an option of increasing the
output voltage of the power supply rails itself as the power supplies
are from a different vendor and provide for a fixed voltage only.
Instead I can use a DC-DC converter at the output of each rail after
the newly added diodes (say a 5V-5V DC-DC converter at the +5V rail)
using which I can get a regulated output at the rated voltage. What do
you think of this scheme? I know that adding an active component AFTER
the redundancy point defeats to some extent the redundancy itself but I
can't think of any other way of doing this. Thanks.

Ganesh