Non-Isolated, Capacitor Fed, Voltage Step-Down

[rdpzycho]

madalas tayo maka-encounter nito pero konti ang literature on computations...eto yung yung AC padadaanin mo sa High Voltage cap bago i-rectify...

paper po on analysis nito at computation...

http://www.hamill.co.uk/pdfs/acfvsdsp.pdf

[Born2BeWired]

Thanks for this good reference. First time I saw a detailed analysis of this type of circuit.

I used capacitor voltage step down in quite a number of my designs. They are  cheap compared to a transformer step down, but I only use it with very low budget designs for reasons stated in that publication- this circuit is virtually defenseless to fast transients. I am happy it went along with one improvement that Ive been doing : add a series resistor in the circuit to provide some level of protection against potentially harmful transients.

Also worthwhile noting is the recommended use of Class X capacitors (Capacitors rated with AC working voltage). I have seen designs and actual products using the wrong type DC rated capacitors (e.g. 600VDC). This perhaps explains the short service life these products usually offers.

[rdpzycho]

pretty useful when doing auxilliary supplies that doesn't need isolation...this comes in handy for a quick power supply for 12Vdc fans...

marami nga pong gumagamit ng normal caps for this application, and most of the commercial products I saw (mostly chargers), the caps fails first...

when there are no X caps available around, I would normally use an MOV across the cap, but the X caps are still much better than them...

[marcelino]

sis, balikan natin ang nakaraan.

di ko pa binabasa ng maigi yung journal, pero matanong ko lang.

pareho pa din ba ang calculation ng power?

kunyari, 220V - 10mA (2.2W) sa input, sa output na 12V - 183.33mA (still 2.2W).

plano ko kasing gamitin sa power on delay (yung the typical 555 timer + relay). 183mA ay sobra-sobra na. typical 12V relay consumes less than 100mA.