Joerg said:
Rene said:
Joerg wrote:
Hey guys, [snip]
I have to do a 100Hz PWM at a couple of amps and with this sort or
"performance" SSR relays don't cut it, plus would probably go phut
... *BANG*.
Another reason that wasn't mention was the price.
They are too expensive anyway. ...
Usually but not always. This is a very low qty app where having a
block with four screw terminals and a big mounting bolt in the middle
would have been much better that assembling a circuit board. Even if
it cost $50-$100.
... As relay replacement
their advantage is the infinite number of on-off
cycles. And most are made as zero crossing switch
anyway.
When we're talking about power, don't forget the
rather hefty voltage across them, in the order of
1.5V at least. There is nothing like 10mOhm or so.
Not for the MOSFET versions. They have only their Rdson.
Yes, it is only the resistive part, but the mosfets
are not of the most advanced sort. A standard SO8
cased 40V NFet is available with about 10mOhms.
A 40V Photomos Relay in DIL8 is having in the order
of 600mOhms. While the Fet is specified at above 10A,
the relay is for 500mA. Similar the voltage drop at the
rated current, the fet drops 100mV, the relay drops
300mV. This tells me, the FET technology within the
relays is at least 5 year back.
If it wasn't for the, related to the case, astonishing
isolation voltage, the two spare pins on the LED side
could have been used to supply some electronics on the
secondary side.
My comment about the 1.5V across were for a 25A part
where we measured somewhat above 1V at rated current.
A line unit in a beefy case.