Continue to Site

Welcome to

Welcome to our site! is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

240 V AC to 48 V DC conversion without a transformer

Not open for further replies.


Newbie level 1
Oct 4, 2007
Reaction score
Trophy points
Activity points
ac to dc conversion without transformer

I have disassembled a mains (240V 50Hz) outlet controller, it has a digital timer which controls a 48V relay to turn the AC socket power off and on. The digital controller and relay are powered by a low voltage DC circuit derived from the 240V AC mains power. A four-diode bridge rectifier converts the AC voltage to DC. The AC power to the bridge rectifier is connected as follows. From the AC neutral the circuit is a 1M ohm resister in parallel with a .33uF capacitor. From the AC active side the circuit is a 150 ohm resistor. I measure about 50V AC at the input diodes to the bridge and about 48V DC at the bridge outputs. I understand the bridge rectification and how the 48V DC is generated. My question is how is the 240V AC mains converted to 50V AC at the bridge rectifier?
conversions of a.c to d.c without transformer

how is the 240V AC mains converted to 50V AC at the bridge rectifier?

The cap at the input side must be of high voltage rating with 10KuF range...

digital timer's frequecny must be less then 20Hz...

then only u can acheive a 48V o/p...

but with this controller there must be some restriction like minimium load, a voltage controlled diode at the output

capacities acts a voltage reducer in serial connection at ac voltage 'couse they have capacitive reactans features thats reply resistance at cross frequency.

voltage reduction in C:


f=mains frequency (50 or 60Hz in some countries)
C:capacite ( as Farad)
I: current (as amper)
dV: voltage (as volt)
Pi: 3,1415.... mathematical constant number


    Points: 2
    Helpful Answer Positive Rating
Not open for further replies.

Part and Inventory Search

Welcome to