[time-nuts] SMPS or conventional?

[Bruce Griffiths]

Original source about TEC lifetime reduction when the TEC ripple cureent is high:
https://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1991-02.pdf
Page 74
I suspect that someone there may have been bitten by the short TEC life experienced without the LC filter. 
Although they used relatively small TECs the size of the individual Peltier element is the determining factor for the ripple current frequency dependence of TEC life. HP used a 40kHz PWM frequency.

There should be a relatively uniform temperature gradient along the length of each Peltier element.

TEC module datasheets are generally silent on the effect of ripple current on TEC lifetime.

CUI merely indicate that keeping the TEC ripple current below 5% ensures that TEC performance is maximised.

Peltier element solder junctions to the ceramic endplates usually fail after 3000 cycles or therabouts.
CUI use a compliant thermally conductive adhesive to achieve a longer cycle life.
Bruce
> On 22 December 2020 at 12:43 Hal Murray <hmurray at megapathdsl.net> wrote:
> 
> 
> [Old mail, context is TECs]
> 
> bruce.griffiths at xtra.co.nz said:
> > If the drive current ripple is too high fatigue failure from cyclic
> > thermomechanical stress can be significant. 
> 
> Do good data sheets say anything about that?
> 
> Is there a frequency term in there?  Can I use PWM, which is as much ripple as 
> you can get, as long as the frequency is high enough?  If yes, ballpark of how 
> high?
> 
> Physically, where is the heat/cold generated?  Is it mostly at the junction?
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
> 
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