Transformerless Power Suppply

[T.Jackson]

20-30mA?, lets see...

XC = 1/ 2Pie(FC)
= 1 / 6.283185307 x (50Hz x 0.00000047F)
= 1 / 6.283185301 x 0.0000235
= 6772Ω

Now, there's a 470K bleed resistor in parallel with the cap.

XC = 1 / (1/ 6772) + (1 / 470K)
= 1 / ( 0.000147666 + 0.000002127)
= 6675Ω

As you can see the 470K only knocks about 100Ω off the total reactance.
For those who don't know, reactance in an AC circuit is like resistance.

Rectified high voltage rail from RMS value (full wave rectification)

= 240VAC x 1.414
= 339.36VDC 'Peak value, has same heating effect as 240 RMS

(half wave rectification)...

= 0.637 x 339.36VDC
= 216.17VDC Average

Absolute max current (short circuit)

= 216.17VDC / 6675Ω
= 32.38mA

There's a 5V rail being produced from a LM78L05. It's input VCC must always be at least 2.5V greater than the output in order for it to maintain adequate regulation.

Absolute max current @ 5V

= (216.17VDC - 7.5VDC) / 6675Ω
= 208.67VDC / 6675Ω
= 31.26mA

Absolute max power @ 5V

= 31.26mA x 5
= 156mW

Spot on. In the perfect World, Melanie's supply should be good for about 30mA.
Component tolerances often compromise the accuracy of calculated events. Such is life.

Trent Jackson