[time-nuts] One sure way to kill your FE-5680A or FE-5650A

jimlux jimlux at earthlink.net
Wed Jun 8 11:20:45 EDT 2016


On 6/8/16 6:19 AM, paul swed wrote:
> The units were never intended for a slow ramp
> I assume it runs into a meta stable condition
> Neither on or off and then corruption
> Glad you're can repair them
>
> On Tuesday, June 7, 2016, Bob Camp <kb8tq at n1k.org> wrote:
>
>>

Interesting, we just had a similar issue on a circuit here at work.. 
someone slowly brought the supply voltage up on a bunch of DC/DC 
converters, and some didn't start. This was in initial checkout of a new 
board.

Switch it on with a bang, and it works just fine.

So for some of these things there's apparently a minimum dv/dt.

I've seen this before with DC/DC converters.. if the voltage drops too 
low, they draw too much current - because they're basically constant 
power devices- and the overcurrent trip shuts them down.  There's a 
delicate interplay between the overcurrent and undervoltage trips,both 
of which have some sort of time constant, and I suspect that for a lot 
of circuits, the "slow ramp up of input voltage" isn't something they 
are designed for.  Once it's up and running, when the supply sags, the 
UV trip works just fine, tripping before the OC trip goes.


Linear regulators.. they may be not the most efficient thing in the 
world, but they have a lot less "weird" behavior.  (although I've had 
linear regulators go into thermally driven oscillation)







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