Regulating capacitors, vibration

[David Harper]

Are there any advantages different types of capacitors have over other
types for regulating voltage? In my specific application, I have 2
ADCs, an accelerometer, and a pressure sensor (all of which use +5 as
reference).

As a follow up, does vibration affect capacitor's ability to regulate
voltage? (i.e. does microstrain in the cap cause voltage
fluxuations?) Are some more immune to vibration than others?

Thanks in advance for any insight!
Dave

 

[John Popelish]

Are there any advantages different types of capacitors have over other
types for regulating voltage? In my specific application, I have 2
ADCs, an accelerometer, and a pressure sensor (all of which use +5 as
reference).

As a follow up, does vibration affect capacitor's ability to regulate
voltage? (i.e. does microstrain in the cap cause voltage
fluxuations?) Are some more immune to vibration than others?

Thanks in advance for any insight!
Dave

High-K ceramics (Z5U, Y5V) definitely exhibit microphonic properties.

 

[Tim Wescott]

High-K ceramics (Z5U, Y5V) definitely exhibit microphonic properties.

-- and Tantalums, if you can use them, don't. I've been present when a
problem was discovered in a pixel clock PLL that turned out to be
microphonic caps -- the solution was back-to-back tantalums.

Unless your application is very sensitive to power supply noise (which
your accelerometer may be, if it's a strain-gauge type), you can
probably decouple the power supply with such caps. Its really your call.

 

[David Harper]

-- and Tantalums, if you can use them, don't. I've been present when a
problem was discovered in a pixel clock PLL that turned out to be
microphonic caps -- the solution was back-to-back tantalums.

Unless your application is very sensitive to power supply noise (which
your accelerometer may be, if it's a strain-gauge type), you can
probably decouple the power supply with such caps. Its really your call.

What about standard aluminum electrolytic caps? I'm just worried that
vibration during flight may cause the accelerometer (and ADC's) to
give inaccurate readings due to reference voltage fluxuations.

Thanks again,
Dave

 

[Tim Wescott]

What about standard aluminum electrolytic caps? I'm just worried that
vibration during flight may cause the accelerometer (and ADC's) to
give inaccurate readings due to reference voltage fluxuations.

Thanks again,
Dave

I don't know, but I suspect they'd be OK. We used tantalums because of
the allure of the solid sintered slug, and because aluminums dry out
over 50000 feet. But aluminums have the same basic structure (really
thin oxide dielectric formed by electrolytic action) so the ought to
work -- try it, and use at your own risk.

 

[Rich Grise]

What about standard aluminum electrolytic caps? I'm just worried that
vibration during flight may cause the accelerometer (and ADC's) to
give inaccurate readings due to reference voltage fluxuations.

Just put "mil spec" or variations in your search string. Mil spec
parts, while being ten times as expensive a normal parts, are, in
fact, characterized to operate over an astonishingly large range
of hostile conditions, microphonics being one of them. A good, solid
mechanical mounting is your best insurance against microphonics.

And, notwithstanding I've been kind of out of the loop, and so
haven't kept up with advances in technology, the term "silvered
mica" keeps popping up in my alleged mind. Something about being
paragons of stability, or maybe it was low HF ESR.

(and, BTW, capacitors don't actually "regulate" voltage - a closer
description would be "smooth out" the voltage, since they're sort
of a charge storage reservoir. One instructor in tech school said,
"A capacitor opposes a change in voltage; an inductor opposes a
change in current.")

Hope This Helps!
Rich

 

[John Fields]

On Thu, 11 Nov 2004 17:06:40 -0800, David Harper wrote: