hey.. i wanted to use the ldr on high power circuit (i.e. 150 watt bulb running at 220volt ac supply) but i was unable to do so. (reason for using ldr is that i want to control the illumination of a room i.e. higher the light already present in the room, the lower will be the ilumination of bulb connected to it. making total illumination in the room constant)
i tried many different components but didnt find suitable component that would do the trick for me.
somebody suggested me to use phototransistor with an SCR, but i dont know if it will work the same way or it will just switch ON and OFF the output (which i dont want).

 

You need a dimmer circuit that uses a TRIAC.
http://www.electronics-project-design.com/Light-Dimmer-Circuit.html
A TRIAC is related to an SCR; a TRIAC is essentially two SCR's put together back-to-back.

In the circuit I linked to, you'd use a suitable LDR to replace R3. It should have a range of near 0 Ohms to ~136k. Of course, you will need to shield the LDR from any direct light from the bulb. This will only work for incandescent bulbs.

[eta]
After thinking about it, you may need exactly opposite of what that will do. I don't have time to simulate it at the moment. Maybe later.

 

i tried to simulate the whole circuit in multisim 11 but all i got was a simulation error, i tried to change the values of capacitors, some of them worked but not for long, after a few secs, i would see the same error again and again

(the diac and triac+ arent as described in the list, they are close matches of those components)
i used a triac (2n6071) and a diac (ecg6412)

 

Well, the ecg6412 has a far higher breakdown voltage than the HT32. If you have an ECG6408, give that a try - and you'll need to use 5 or more of them in parallel due to their lower current carrying ability than the HT-32.

I'm still out and away from my place; I'll look at it later this evening.

 

Interesting article on creating SPICE models for DIACS and Schockley diodes.
http://www.beigebag.com/case_shockley.htm

 

Maybe use an ldr to control a led's brightness coupled to a second ldr to control the dimmer intensity?

Kind of like this. However tweaking it to correspond exactly to the sensed light would be kind of hard.

 

i tried with the circuit diagram again, but the output was same as before but this time there were no errors..
but, when i varied the potentiometer, there was no change on the illumination of the bulb
kindly check this circuit that i am attaching with this post..,
thanks in advance

 

there was another circuit that i got from the internet
i designed the circuit on multisim and got the desired output and it varied the output with the change in potentiometer resistance BUT with one problem. there was this distortion in the output wave that at times..
i dont know if i need a filter here or what, to remove the distortion. kindly tell me the way to solve it
(i am attaching the pic of circuit and the output distortion seen with it )

 

i need that... can u please help me with that

 

I haven't forgotten about you.

I've been de-bugging DIAC models. I have to take one thing at a time, and lots of other people need help too.