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new project using tlp741g (photo scr)


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Have you looked at thedata sheet for the tlp741g?  


It is a low-current (150ma), moderately high voltage (400v) SCR with a photo sensitive gate that can be triggered by light from the embedded LED with LED forward current up to 10 ma.

A resistor of 27K to 33K should be installed from gate to cathode of the SCR to suppress self-triggering due to leakage from anode to gate.

It can be applied like any SCR except that you trigger it with forward current though the LED rather than by a voltage applied to the gate.  The LED terminals are insulated from the SCR terminals for up to 4000 volts.  If you don't require isolation from LED to SCR then there's not much point in using an opto-isolated SCR.

The Photo SCR will block current in both directions until triggered by light from the embedded LED.   Once triggered it will conduct (conventional) current from anode to cathode until current drops below the holding current of 0.2 ma.  If forward current drops below 0.2 ma (and there is no current through the LED) the SCR will "commutate," that is, turn off.  Reverse voltage (i.e., SCR cathode more positive than SCR anode) will be blocked with or without LED current.

The photo triac operates like a conventional triac but can be triggered by current through the embedded LED.  It differs from the photo SCR in that it can conduct in the "reverse" direction if triggered by LED current.

Applications for either device are similar as those for conventional thyristors except that the photo-thyristors can be triggered by current through the LED.  I'm sure youcan find tons of applications for conventional SCRs and triacs on the 'net.


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