Hero999
Banned
That'll probably work but I'd recommend a Darlington pair.
The frequency has nothing to do with the regulation.
LM431 and opto1 does the regulation.
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?
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.
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