SMPS design ?

[Hero999]

(1) I have started gathering components for practical design - the transistor I'm going to use is an MJE13003 with a Ptot of 40W, a ferrite core from a salvaged CFL of 36W. But I am in great doubt about your following comment:

That'll probably work but I'd recommend a Darlington pair.

If frequency and load is inversely related then how the Vout regulation can be acheaved? I think frequency and voltage is directly proportional. May be I have misunderstood you - please clarify.

The frequency has nothing to do with the regulation.

LM431 and opto1 does the regulation.

(2)My question was about the relation between frequency, voltage and turns.
According to you if I try with 5 turns as secondary to get an output of 12V, that means 200 turns at driver or primary have 480V. Is there really so high voltage ?! Please try to put some light on this.

As I said, it's a flyback, so the maximum output voltage will be higher than the turns ratio might suggest.

Notice the dots on the transformer? Each dot represents the start of the winding. Notice how the dot on the secondary is opposite to the primary?

Also please detail your schematic - it contains almost no component value. How should I proceed to construct?
I have really understood what Nigel has said because once I have experienced a severe shock from a detouched plug that was connected to a similar SMPSU

I wouldn't recommend building my schematic as I haven't tested it, you can if you like but it's your funeral.

For educational purposes, I'll go through the components and explain what each one does but I'm not going to specify their exact values, you'll have to do that yourself.

R6 limits the inrush current and provides a bit of protection by acting as a fuse.

C1 is the mains filter capacitor.

R1 biases Tr1 on, its value will depend on Tr1's gain.

C2 might not be needed but is present in most blocking oscillator circuits I've seen and helps kick start the oscillation.

R4 and C5 form a snubber network which protects Tr1 from the back EMF generated when the current in T1 is interrupted. If T1 had perfect coupling then all the inductive energy should be transferred to the output, in practise it isn't so it can zap Tr1 if it's left unchecked. The value of C5 and R4 depend on the inductance of Tr1 and its coupling co-efficient.

D2 is a programmable zener which turns on when the voltage on R5 equals 2.5V. When the LED in opto1 turns on the transistor in opto1 turns which shorts the bast of Tr1 so it stops oscillating. To calculate the values of R3 and R5 look at the LM431 datasheet.

R2 is a current limiter resistor for opto1's LED.

D1 prevents C4 from discharging through T1's secondary.

L1 is an EMI filter.

C4 is a DC smoothing capacitor.

I've missed some components off: it might be agood idea to add another capacitor before L1 and an X rated capacitor across the mains inlet.

EDIT:
For more information on how the oscillator works, Google for blocking oscillator.

 

[p55xp]

Though slowly, but definitely I am having increasingly better insight.

For educational purposes, I'll go through the components and explain what each one does but I'm not going to specify their exact values, you'll have to do that yourself.

It's a good idea!

Now please explain with example :

R4 and C5 form a snubber network which protects Tr1 from the back EMF generated when the current in T1 is interrupted. If T1 had perfect coupling then all the inductive energy should be transferred to the output, in practise it isn't so it can zap Tr1 if it's left unchecked. The value of C5 and R4 depend on the inductance of Tr1 and its coupling co-efficient.

 

[Hero999]

You're better off Googleing it.

Hint: a good way of looking at it is an LRC network, that's critically damped.

snubber network - Google Search

 

[p55xp]

Thanks a lot for a real real advice

 

[p55xp]

No one to shed some knowhow any more?
I am waiting for some more clarity?

 

[dougy83]

You could have a look at an off-line SMPS IC, e.g. FSQ0165 or FSQ0265.

The datasheet (which is quite descriptive) may be found at: https://www.electro-tech-online.com/custompdfs/2009/08/79161.pdf

 

[indulis]

Here ya go....

 

[p55xp]

I have now decided to make the SMPS on VIPer22A chip. It is available in Calcutta. Thanks for all suggestions. Please comment if you have any idea or experience about using this chip.