1. i want to built a switch (on/off) circuit .
to controll with DC. voltage of 5v (from microcontroller).
controlled curent 4-10 A / 220-240 V ac.

i assume with triac and moc
but don't know how?

2. if i will use a simple relay can i simply connect the relay to the
microcontroller or do i need a buffer or something ??

 

If the micro-controller can source or sink the current needed by the relay, then no driver will be needed. The probability is you will need a MOSFET or Darlington to drive the relay.

 

i have got a 8051 microcontroller.

should i connect the relay directly to the output port?
or maybe to the dac ?

i'm afraid of current leakage form the relay or something that will
burn the micro...

 

8051 is a generic series. What is a specific part no, so that we would know the sourse/sink capacity of pin. But as thingmaker3 said, you probably will need a transistor to drive the relay. Don't forget to put a free wheeling diode across relay (to protect transitor and probably a microcontroller).

P.S. : You also need to be sure about the state of µc pin after resetting to avoide chattering of relay during power-up.

All the best.

 

can i use a moc (photo)"moc3041" and a triac (BTA12)??