hello every one can anybody tell me what is the purpose of Vr1 and D5 in the circuit and why they are connected in this pattern and how it works in smps design for +12V, 5v with 1A output
and what is the purpose of TNY ic and what is the purpose of optocoupler to trigger the TNY ic

 

VR1 and D6 clamp flyback overshoot because of leakage inductance in the transformer and slow recovery time on the output rectifier 110V to protect the output MOSFET in the power supply chip.

D1, D2, D3, and D4 form a full wave bridge rectifier.

 

VR1 and D5 is a Zener Clamper circuit. During turn off, a high voltage spike due to the transformers leakage inductance appears on TNY IC.
This excessive voltage spike on the TNY IC may lead to breakdown and eventually failure of the IC. A clamping circuit placed across the primary winding helps to limit the voltage spike caused by this leakage inductance to a safe value.

And TNY 274 is a flyback controller + switching MOSFET. And the optocoupler provide a galvanic separation between input high voltage and low output voltage and provide a necessary feedback information to set Vout.

 

why we need L1 and L2 for filtering L1 is enough to filter the AC signal
and why they are connected 4.7K resistor between the -ve polarities across capacitor

 

In your case, L1 and L2 values are way to small to have any effect. And 4.7k resistor will damp inductance quality ( prevent parasitic resonance oscillations).

 

VR1 and D6 clamp flyback overshoot because of leakage inductance in the transformer and slow recovery time on the output rectifier 110V to protect the output MOSFET in the power supply chip.

D1, D2, D3, and D4 form a full wave bridge rectifier.

When I got started in electronics, I had a hard time understanding the use of the word "clamp" in most circuit explanations that I studied. It wasn't until I learned that those components where actually performing a "short circuit", or rather became almost fully conductive after a threshold voltage was reached that I realized they were meant to absorb a momentary spike in voltage and transform it into heat. It also allowed me to understand that there's a limit (or a duty cycle) to the amount of energy that they can dissipate over time.

I'm making this comment in the hope that the OP better understands the concept, since linguistics can be misleading. Especially if English is not one's native language.

 

what is the use of resistor R2,R3 and capacitor C3
according to datasheet they have mentioned C3 is use to pick the current limit, according to the designer.

 

what is the use of resistor R2,R3 and capacitor C3
according to datasheet they have mentioned C3 is use to pick the current limit, according to the designer.

R2,3 are high value resistors upto 4M to enable shutdown for under voltage in less than 0.5 second,

 

I want to know the purpose of that variable resistor across the AC. (Figuring somebody will ask that anyway

 

I want to know the purpose of that variable resistor across the AC. (Figuring somebody will ask that anyway

that is not variable resistor it is an mov 275 Vac

 

R2,3 are high value resistors upto 4M to enable shutdown for under voltage in less than 0.5 second,

what is the purpose of capacitor c3 and RF1 resistor

 

what is the purpose of capacitor c3 and RF1 resistor

RF1 prevents damage to the bridge diodes when the power is turned on at a peak of the input voltage: the filter caps would look like a short at that point.

The capacitor BPM is explained at lenghthon page 2 of the datasheet