Step 2: Get an IRF730 from Mouser

Picture of get an IRF730 from Mouser
I adapted this method from info from Dmitri Grinberg’s post on Hackaday, “Lamp Fading and Remote Control for the Lazy”.
But I had been trying for a number of weeks to perfect this, as in, find the correct transistor that would not overheat or burn out (one that is rated for a high enough voltage since it’s using AC 120 V). I followed this circuit from Dmitri’s blog, except instead of the IRF 250 I used an IRF730.

You can purchase those particular transistors at the above link from Mouser for under $2. 

At first, I was using the IRF 520, with a 100 V drain source voltage and a 9 amp continuous drain current. It worked fine at first, and then it burnt out (there was connectivity between the gate-source and gate-drain). So I got an IRF540, with a 100 V drain source voltage and a 33 continuous drain current. This similarly worked at first, then burnt out.

Finally, I used the IRF730 which works pretty well so far! And doesn’t burn out – it is rated upto 400 V (which far surpasses the 120 V wall voltage in the US).
buteman3 years ago
Good to see your efforts and what I say below is in no way meant to discourage you but rather to help you and others.
We all make mistakes and it can be a way to learn. Better not to kill ourself in the process though. :-(
Just so you know for anything else you might build here is why you had problems with the IRF520 and IRF540. You are using the bridge rectifier to turn the 110volt A.C to D.C. When it is 110volt A.C that is what is called the R.M.S voltage which means the average value of the voltage. For 110volt A.C you will have a peak voltage of 1.414 x 110 volts = 154 volts. Rectifying it does not reduce that voltage by more than 1.2 volts ( approx - due to the diodes in the rectifier ) so you are subjecting the transistors to way more than their specification so it is no wonder they failed.
So they could have easily handled the current which for your 150 watt bulb ( less than 1 amp ) they could not handle the voltage.
I agree with other comments about the danger of plugging in the low voltage supply while it is connected to the mains.