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I have a DC/DC converter that gives 3.3 V output.In our system it is the most important part.So we need a redundancy for this.So that if one of the converter fails the other should automatically get switched on. What kind of circuitry do we need to get this kind of logic.

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    \$\begingroup\$ What is the rating of your 3.3V power supply (in amps?) What duration of power outage can you tolerate? 1 msec? 10 msec? 100 msec? How do you define 'failure of a 3.3V supply'? \$\endgroup\$ – Li-aung Yip May 14 '15 at 10:15
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    \$\begingroup\$ 1.) What does the 3.3V load look like? 2.) if the main DC/DC converter fails, what will you use as the criterion for failure, and 3.) how much time can be allowed between the time failure is detected and the backup DC/DC converter kicks in? Also, can you post a link (good) to the DC/DC converter's data sheet or (better) post it directly? \$\endgroup\$ – EM Fields May 14 '15 at 10:28
  • \$\begingroup\$ The converter will be powering a micro controller.The output current is around 40mAmps.By saying failure,I mean the case where the converter's ic may fail resulting in deviations from 3.3 V.As soon as one converter fails,the other must be kicked on. \$\endgroup\$ – Naveen May 15 '15 at 5:13
  • \$\begingroup\$ the data sheet for the i.c used for converter is available in the below link linear.com/product/LTC3621 \$\endgroup\$ – Naveen May 15 '15 at 5:28
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Redundant systems would typically employ an ORing-FET as shown below (source):

The idea is that redundant DC-DC converters supply the required voltage in a current sharing configuration so that both converters supply equal current and therefore have (pretty much) equal thermal stress.

In a fault situation the ORing FET isolates the problematic converter and the other one takes over.

enter image description here

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How about this? I have made some presumptions:

  • The load is a general digital circuitry that doesn't draw insane amount of Amps
  • The converter always fails Open-Circuit - blow-thru causing input voltage to appear at the load is not detected
  • The load would be happy with 3.3V - Vf of D1

You will need to provide some additional info, otherwise we can only guess.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ 3.3 volts into a Schottky won't get you 3.3 volts out. \$\endgroup\$ – EM Fields May 14 '15 at 10:31
  • \$\begingroup\$ @EMFields No it won't, but depending on the load, it still may be good enough. \$\endgroup\$ – Dzarda May 14 '15 at 10:32

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