white led

[pier1]

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 .

 

[audioguru2]

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.

 

[pier1]

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 .

       

 

[audioguru2]

The LEDs don't need a voltage regulator, they need a current regulator.
if you can find a high voltage darlington power transistor then I will go to Google and get a schematic for you.

 

[pier1]

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

 

[audioguru2]

Hi Pier,
Try this regulated current circuit:

View attachment 40382

 

[pier1]

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

 

[audioguru2]

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.

 

[pier1]

Thankyou so much AG, I am using MPSA42 as the small high voltage transistor . No problem naa ?

Thanks
Pier .

 

[audioguru2]

the MPSA42 has a voltage rating of only 300V. If your mains has such wild voltage swings as you said then if it "hiccups" then the MPSA42 will be destroyed. A 400V transistor is more suitable.

 

[pier1]

Hi AG

Thanks a million .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.   

 

[audioguru2]

I don't use power supplies without a transformer.
My mains voltage is half the voltage of yours so I don't know high voltage parts.

 

[pier1]

Hi Ag

      I am still searching , I've asked a shop owner for the same and he said he will let me know in 2 days . By the way AG hows 13003 for the small one ?

 

[audioguru2]

I am in Canada. I use American parts. I have never seen parts from ST Micro.

The ST13003 is big but will work fine as the smaller high voltage transistor.

 

[pier1]

Hi AG

        The circuit works fine now, but no brightness . Before with high wattage resistor it was really bright . But now it is less . I forgot to tell you AG that I am using 49 white leds . What could be the reason ?

Thanks
Pier.

 

[audioguru2]

Post the DC voltages at various parts of the operating circuit without electrocuting yourself. The voltage across the 27 ohm resistor should be about 0.65V then the LED current is 0.65/27= 24ma which is a little less than their max allowed continuous current of 30mA.

Check which pin is which on the transistors from their pictures in their datasheets.

The circuit should work nearly the same with 1 LED or with up to about 87 white LEDs in series.

 

[pier1]

Hi AG
        I apologise for electrocuting myself :-X . I measured the voltages at different parts of the circuit :

across 27 ohms resistor : 0 volts (no voltage)
at the base of 13003 with respect to gnd : 14.25 volts
across the 10k resistor : 0.59 volts
at the collector of 13005 with respect to gnd : 152.22 volts

All this voltages was measured when the input voltage was 300 volts DC.
No components are heating up .

Thanks
pier

 

[audioguru2]

Hi Pier,
The base-emitter of the ST13003 is supposed to be a forward biased diode with a max voltage of 1V. You measure 13.7V so I think you connected its base and emitter pins reversed, causing the base-emitter to be reverse-biased and acting like a 13.7V zener diode.

View attachment 40397

 

[pier1]

Hi AG
        Ur great!!!!Thanks for pointing out my mistake . The collector and emitter was in reverse . Now it is very bright and i have a little doubt will it blow off !!! Where do u measure its current AG . I am in front of it now .

Thanks
Pier

 

[audioguru2]

Hi Pier,
Good, you fixed it!

The LED current flows through the 27 ohms resistor. Ohm's Law says that the current is the voltage across the resistor divided by its resistance value.

If the 27 ohm resistor has 0.65V across it then the current in the LEDs is 24mA.
The absolute max continuous current in most ordinary LEDs is 30mA.