Best way to create a redundant power supply
Posted by: MicroE
on
I need to design a 5V 10W converter which can easily be done with a TNY279 device. The problem is that this design needs to run from 2 different AC Sources. Is it best to do this with 2 separate supplies and combine the outputs using an IC such as an LT4351 or by combining the HV DC Bus voltage and using just 1 converter?
Thanks in advance for your responses.
Dave Willis
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Thanks for your comments and questions. The main goal is to keep the 5V output active if 1 of the AC supplies fails. The additional redundancy provided for by using 2 supplies would also be nice but does add to the product cost...
Some of my concerns were in regards to if a "Y" capacitor was used that this "connects" the 2 ac input supplies together in a questionable manner.
Failure modes of commoning the HV inputs assuming diode isolation after "bridge" rectification of the ac supply are also of some concern.
It depends on the goal and philosophy of the redundant system. What failures are you trying to protect against?
For example, the latter will provide protection against failure of one of the AC supplies but not failure of the PSU.
If you decide to use 2 PSU's and parallel the 2 outputs, you don't need to do anything special at all. It's just that the PSU with the higher regulation setpoint (due to tolerances), will provide all the output power, while the other will be delivering no output. If the first one fails, the other will immediately take up the load. An advantage of the TNYSwitch is that the response is very fast (especially with zener as opposed to TL431 regulation) and you will see no glitch on the output.