If the transformer is 12VAC at 15VA then it will work. But the output isn't regulated, the voltage will change if the mains voltage changes and it will change when the load current changes. The output will also have about 1V of 120Hz ripple. This circuit could feed a 7809 voltage regulator IC to give a regulated 9VDC output.

Originally Posted by hardcore misery

we were not required to use an IC to our project...

so is ti possible to step down a 220VAC into 15VDC? then by using a voltage multiplier, 15VDC can be 60VDC? that is my design... and it should be regulated...

In theory, but it's not generally a practical solution - forget about voltage multipliers, they are a waste of time!.

You use the correct voltage transformer, then (if it needs to be regulated) you add a discrete component regulator on the output - the transformer will need to be a different voltage for regulated or not!.

For the 15V rail either use a seperate winding or a seperate transformer, it's really too big a drop for a linear regulator.

Originally Posted by hardcore misery

sir, what do you mean by correct voltage transformer? so it is impossible to step down a 220VAC into a 60VDC or 15DC? the DC output should be regulated...

A mains transformer outputs AC, for an unregulated DC you would require a transformer a little over 40V AC to give roughly 60V DC after rectification and smoothing. For a regulated supply you need more than 60V to feed the regulator - so you would need a higher voltage transformer. The actual voltage depends on the design of the regulator, and on the specifications it needs to meet.

Yes, of course you can (and should), 220V is the PRIMARY of the transformer, it's the secondary that gives the output voltage.

If your knowledge is so limited I suggest you go and talk to your teacher, either you haven't been paying attention in class, or you've been ill and missed all the lessons!.

I've already shown you where to see a schematic for a discrete voltage.

But here's the Googles I've used to get the results.

http://www.google.com/search?num=100...ic&btnG=Search
http://www.google.com/search?client=...utf-8&oe=utf-8

Your 1k resistor has 27.5mA in it without a load. So if the load draws 27.5mA then the zener diode doesn't regulate and if the load draws more than 27.5mA then the output voltage drops.

A zener diode is a lousy voltage regulator because it wastes power when the supply doen't have a load.
Change the 1k resistor to 27 ohms. Then the current in it and in the zener diode is 1.02A without a load. The power in the 56V zener diode is a whopping 27.9W! But you can load it with 1A and it will still have 56V regulated.

A zener diode is a shunt regulator. Use a transistor as a series regulator (instead of the 1k resistor) then it won't waste much power when there isn't a load. A zener diode can be from its base to ground and the transistor is an emitter-follower. The zener diode and the base of the transistor will need a small amount of current from the 83V unregulated to function that is supplied by a suitable resistor.

This is getting frustrating. . .

You need to read up on this before you ask any more questions.

http://www.ee.washington.edu/faculty...332LE5rev3.pdf
http://en.wikipedia.org/wiki/Linear_regulator
http://www.du.edu/~etuttle/electron/elect9.htm
http://hyperphysics.phy-astr.gsu.edu...c/emitfol.html
http://www.ee.washington.edu/circuit...32/theory.html
http://ludens.cl/Electron/Ps20/Ps20.html
http://www.williamson-labs.com/480_xtor.htm
http://www.allaboutcircuits.com/vol_6/chpt_5/12.html
http://en.wikipedia.org/wiki/Bandgap_voltage_reference