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

Bernd Neubig BNeubig at t-online.de
Wed Jun 8 12:35:58 EDT 2016

The same problem may appear on some poorly designed crystal oscillators.
Some circuits depend on the spectral component of a fast power-on and will not start reliably if the supply voltage is ramped slowly - as can happen if the oscillator stage is fed by a voltage regulator with high value capacitor blocking at its output.
That is why oscillator testing standards like IEC 60679-1 define the test for reliable start-up to consist of a slowly ramping up supply voltage.
Another way to identify potential start-up problems is to cool down the unpowered oscillator to the minimum operating temperature (or upper operating temperature) and then to apply a slow supply voltage ramp

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Von: time-nuts [mailto:time-nuts-bounces at febo.com] Im Auftrag von jimlux
Gesendet: Mittwoch, 8. Juni 2016 17:21
An: time-nuts at febo.com
Betreff: Re: [time-nuts] One sure way to kill your FE-5680A or FE-5650A

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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