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pier

white led

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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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hi AG

        Sorry I was a bit late . Could you send me a small schematic for the comparator . I tried and am not able to design it . Please help me .

Thanks
Pier Francis

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You asked me " can u get one "
U asked me wheather can i get LM10 at my place ?
Or can i get the circuit ?

If it is the circuit u should help me ? I cant design perfectly.
I request u to please send me a schematic of the sensing .

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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,
        How do i do that ? do you have any circuit for that  ? and till what voltage can we regulate ? . Wont that be tough AG to regulate such high voltage!!!!
Thanks
Pier .

       

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Hello AG
              I tried , there are only 80 to 100 volts available (darlington) .I found a bu808 on the net but i dont get it here. Can we do it with a 13005 ? .

Thanks
Pier

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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 Pier,
This circuit regulates the current for the LEDs. The high power resistor in series with the LEDs is no longer needed because the ST13005 power transistor becomes an automatically adjusted power resistor. Use a medium size heatsink for it so it can dissipate up to 7W.

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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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