Power supply failure after a few months??????

[Jester]

Below you will see a variable 0-48Vdc supply. This circuit is used to test an 8 channel analog input module and works as intended except that the PS1/PS2 power supply has now failed twice within a year.

PS1,2 are rated for 42ma, but do not have short circuit protection.
U1 is rated for 50ma
U4 is rated for 5ma

U1 and U4 did not fail and continue to work after replacing PS1,2 so I don't think the failure is related to over-current (perhaps due to a short on the other side of the Mux), or if it is somehow the Mux and OPA454 survive.

I'm speculating that the failure is somehow related to the way I have stacked the two power supplies to get 48V???

Can anyone point out why PS1,2 are failing after a few months of operation?

 

[D.A.(Tony)Stewart]

Pls try posting image, link or attach. again

 

[Jester]

Pls try posting image, link or attach. again

I'm not sure what happened to the picture?, Here goes again.

 

[tantalos]

The type of DC/DC converters you use don't have over-current protection and are very likely to fail if output is shorted even if the short occurs for very short period.

 

[Little_Master]

One of the reason can be capacitors in supply line, C2 and C5. As these are normal ceramic capacitors, due to mechanical stress on PCB time to time, these capacitors breaks and get shorted and short current flows which damage DC-DC but rest circuit remains unaffected like your case.

Solution: First of all, Please check rating of these capacitors, mostly it will be ok. Use OPEN MODE CAPACITORS, these are special capacitors used in battery line, so that if it breaks then supply line did not get shorted.

 

[wade_hassler]

Putting the two power supplies in series across 48V is a potential problem.
The two supplies will need to be very evenly loaded to avoid the voltage across one of them exceeding the specified +/-10% limit