white led

[audioguru2]

You shouldn't operate the LEDs at more than their max current of 30mA each. 500mA/20= 25mA.

I don't know how high your mains voltage surges. I don't know why because mine never does. So I don't know what will prevent it.

 

[jgeidl]

I have been following this thread to see the outcome.  One thing, based on th elast drawing, that should be noted is that you are not working with 20 LED/resistor combinations in series, you are working with 20 LED/resistor combinations in parallel so you might want to rework the numbers a little.

I am also really happy to see the transformer get into play.  Runnig this circuit without a transformer is just asking for someone to get hurt real bad, as AG has pointed out earlier and repeatedly.

As to cost, I can't help but wonder if a 12VDC wall-wort transformer and, maybe,  a 7805 wouldn't be a quick, easy and cheaper solution to building the power supply cicuit.  Even better would be 6VDC wall-wort.

Just some thoughts...

Jim

 

[audioguru2]

Hi Jgeidl,
In his country a wall-wart is too expensive, the mains has high voltage surges and the LEDs don't have a forward voltage rating. It will be a miracle if he can make something that works.

 

[pier1]

Hi AG
        The project is fine now, working and having enough brightness, but for the resistor i put 10k 20watt , it is running cooler now . Thanks for the help . I am making the housing for it now . 


Thanks
Pier .

 

[pier1]

hi AG

The brightness varies about twice or thrice in some time .

 

[audioguru2]

The brightness varies about twice or thrice in some time.

Does your mains voltage change that much?

 

[pier1]

yes , but none of the led's have failed yet .

 

[pier1]

Hi AG

        Hows this arrangement for the led's to switch when the voltage rise above 250 volts AC . Please tell me if this needs correction ?

Pier

View attachment 40367

 

[pier1]

i'm sorry i made a mistake , it is for the led's to switch off when the voltage rises above 250 volts ac .

Pier

 

[audioguru2]

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.

 

[pier1]

Hi AG ,
          Thanks a lot for the suggestion , could You sugest me which transistor would be good to use .

Thanks
Pier .

 

[audioguru2]

I don't know which high voltage transistors are available in your country.

 

[pier1]

st13005 (to220) is available in my country . how about this ?

 

[audioguru2]

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.

 

[pier1]

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

 

[audioguru2]

Making a comparator detect that the mains voltage is too high is simple, but giving it a reference voltage is difficult.
An LM10 is a voltage reference with an opamp and can be used. Can you get one?

 

[pier1]

Yes AG I can get them .

   

 

[pier1]

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 .

 

[audioguru2]

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.

View attachment 40379

 

[pier1]

Hi AG

        The circuit looks complicated but it is of interest to me . I dint understand what is that reference (200mV) you mentioned .