some advice on designing for limited space

[kubuni]

I'm designing a Smart LED Bulb, which seems to be a pretty simple project so far. I have a nice IC buck LED Driver that accepts Input 40V. It has a pwm pin to change the brightness that I'm driving with a bluetooth chip. The bluetooth chip can be powered by 3.3V; the real range is like 0 to 3.6 then goes through some internal LDO or optionally a DC/DC. Since Space is critical, Would it be possible to get a small transformer with 2 secondary coils then use some resistor -zener divider to supply power to the bluetooth module?

I got the idea from this PDF to use the resistor-zener.
http://www.newark.com/pdfs/techarticles/microchip/3_3vto5vAnalogTipsnTricksBrchr.pdf

[Kleinstein]

Normal 50/60 Hz transformers don't work well in small size. Everything below about 1 VA is usually pretty bad (e.g. higher no load loss of around 1 W) so they hardly get smaller even if just 0.1 VA. In theory one can get a little better with expensive custom ones. For low power a capacitive dropper (especially at 110 V) might be more interesting. Switched mode supplies also work reasonable well at low power, especially when starting from 40 V DC.

[Rerouter]

You left out wattage and voltage on the LED string, knowing these 2 could help,

as its a "LED bulb" I am going to guess it will be in the ballpark of 7-15W electrical power used,

Are you sure you cannot get by with a mains buck converter, rather than a 40V limited one?

In the past i may have just gated a thyristor on the tail end of the waveform to keep the rectified voltage low, but this looks a bit ugly on emissions tests.