[TriEmbed] MOSFET or Relay

[Brian]

One important note on SSRs: If you're switching DC, make sure you get a 
DC-rated SSR.  Many AC-rated SSRs have zero-cross circuits to minimize 
switching noise; this means that once the drive signal is received, the 
relay waits until the voltage across its "contacts" crosses zero before 
it actually turns on.  Obviously with a DC supply, the voltage never 
crosses zero, so the relay would never turn on.

As a side note, zero-cross circuits also have the effect of making most 
AC SSRs useless for triac-style dimming.  The relay won't turn on until 
the next zero-cross, and the silicon won't turn off until another 
zero-cross.

On 12/7/2015 8:50 AM, Adam Haile via TriEmbed wrote:
> A FET is going to be WAY faster at switching than a relay. Multiple
> orders of magnitude faster. Relays will often carry far more current for
> less cost. Then there is the weird in between of the two... the Solid
> State Relay. Also, not that a mechanical relay is true on/off. Whereas a
> FET or SSR (which is usually just an opto isolated FET in a nice
> package) are /generally/ on/off, but there's fancy things you can do to
> actually have the output voltage vary... or if you supply way to much
> voltage in it will just allow it through and short out. I don't really
> understand that part... I just ensure I read the datasheet and stay
> within the specs.
>
> here's a good comparison of mechanical relays vs SSRs:
> http://electronicdesign.com/components/electromechanical-relays-versus-solid-state-each-has-its-place
>
> On Mon, Dec 7, 2015 at 8:41 AM, Grawburg via TriEmbed
> <triembed at triembed.org <mailto:triembed at triembed.org>> wrote:
>
>     Just for my future information. Presuming that current draw is not
>     an issue, given the choice between using a MOSFET or a suitably
>     opto-isolated relay to switch 12V, is there any significant
>     advantage of one over the other? The MOSFET seems more 'elegant',
>     but that hardly seems like a good answer.
>
>     BTW, there should be some kind of law against so many people helping
>     guys like me. :-)  Imagine if the Manhattan Project had a group like
>     TriEmbed.
>
>
>     Thanks,
>     Brian Grawburg
>
>
>
>
>
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