08-11-2012, 02:36 PM
(08-11-2012, 02:10 PM)Joe Wrote: Are solid state relays otherwise known as 'Opto-Isolators'? It'll certainly be something new to fiddle with.
No - SSRs are completely different - they are encapsulated smart electronic relays (typically at mains voltages) that are turned on by an isolated LED and they only switch when the voltage passes through 0V (aka "ZCS" - zero crossing switching) to minimise noise.
Optio-isolators just provide galvanic isolation for a given signal, typically at logic (0-5VDC) or other low voltges...
(08-11-2012, 02:10 PM)Joe Wrote: What I don't understand with this 741 is why the LED is lit with both inputs disconnected. I've tried a couple so it's not a faulty chip.
Probably because with the inputs floating and no feedback, the amp will be at maximum open loop gain and will pick up any old Electro-smog loitering in your workshop, amplify it hugely, and turn on the LED ! Try shorting the inputs together and connecting them to 0V.
(08-11-2012, 02:10 PM)Joe Wrote: As so often something that sounds simple is proving anything but.
Heh !
Linear Technology's App Note 105 at http://cds.linear.com/docs/Application%20Note/an105.pdf lists most of the common topologies. There are monolithic sense chips too - food for thought...
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