[SI-LIST] Re: Reset problem with power supply

> Cable inductance absolutely should not be an issue.  If it actually
> is, be grateful that you found a design flaw before you reached
> production! This might be related to the power risetime.  Your POR
> circuit needs to operate properly even if you slowly bring the voltage
> up manually.  Some circuits depend on fast power risetime to operate
> properly, and work OK... most of the time.  The worst ones capacitor
> couple the voltage bus into a transistor.  Not only do these fail to
> reset on a slow rise, if an aluminum electrolytic cap is used, the
> value will drop with age as it dries out and eventually the circuit
> won't work even for normal supply risetime.  A Schmitt trigger is a
> good basis for a bullet-proof approach, as are any number of
> supervisor ICs that also check for overvoltage, brown-out, and the
> like. 

How does a Schmitt trigger solve the problem?  I'd expect it to make things 
cleaner if the input signal has a slow rise time, but that's not going to 
solve the problem of reset going away before the power is stable.

Are electrolytics getting old really a serious problem with modern caps?  
I've seen lots of credible reports of very old gear being brought back to 
life by replacing all the old filter caps.  I hadn't thought much about the 
implications on gear I was designing.  How should I think about modern filter 
caps getting old?


-- 
These are my opinions, not necessarily my employer's.  I hate spam.



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