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Hi Pier,
An ordinary Triac or SCR is not turned off with its gate. The gate is used to turn it on and disconnecting its power source (like with each cycle of AC) or disconnecting its load current turns it off. Use a high voltage transistor instead.

I think high voltage zener diodes are very temperature sensitive and will begin conducting at a much lower voltage.

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The high voltage power transistor is fine. With an LED current of 25mA then the base current is about 1ma. You will need a high voltage resistor or some ordinary ones in series to turn on the transistor.

High voltage zener diodes have a problem with temperature and leakage current. Use resistors to make a voltage divider then a comparator to activate which turns off the high voltage darlington.

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An LM10 has a voltage reference and an opamp in a 8-pins IC.
The opamp is set to turn off when its inverting input is higher than the reference voltage, then it turns off the transistor.
Resistors are in series to double their voltage rating.
A voltage divider is used to reduce the DC sense voltage to be the same as the reference voltage.

More series resistors and a zener diode power the LM10.
I didn't calculate the resistor values yet because I wanted you to see how complicated this circuit will be.

post-1706-14279143378677_thumb.png

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Hi AG

        I am sorry for asking that question . I looked into the datasheet only after posting my question, But I would still like to know the element Which is used as a reference . I am interested to build it and test it AG if you give me the values . I dont mind if it takes some time even .

Thanks
Pier .

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The 200mV reference is a low current voltage regulator with an output voltage of 200mv and it is connected to the input of the reference opamp. Two resistors can allow the opamp to have voltage gain then the amplified voltage can be any regulated voltage within the supply voltage of the IC.

Instead of using the LM10 to turn off the LEDs when your mains voltage is too high, maybe it would be better and easier to use the high voltage transistor to regulate the current in the LEDs, then they won't need to be turned off.

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Hi AG
        Thanks a lot for the circuit . I will build the circuit today itself and test it, but one doubt (must be a dumb one, dont feel bad : i am weak in electronics) as u said before should i connect a high watt resistor as per previous calculations for the led's in series ?!!!

Thanks
Pier

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Hi AG

Thanks a million :D.The circuit works!!!!!!!. The 13005 is warm with a heatsink . I tried till only 280volts dc . I have to look for a high voltage transistor of to92  package (400volts as you said) for testing till the higher end of voltage . Mean while if you find some part numbers please let me know AG . I will look for it, if it is available here .

Thanks :)
Pier.   

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