Hi,
You don't need anything special to do 200V. Typically, for isolated converters, a TL431 is used on the secondary side. The TL431 is basically just an error amplifier with an integrated voltage reference. It's not a zener diode, though it is often drawn that way.
In the attached schematic, the resistors of interest are Ra, Rb, and Rc3.
The TL431 continually tries to maintain 2.5V on its REF pin by feeding an error signal back to primary-side controller. The primary side responds accordingly and the error is corrected on the secondary side.
To set up the output divider, we know that TL431's REF pin will be always be 2.5V, and that we'd like Vout to be 200V. Let's choose Rb, the bottom resistor, based on a reasonable amount of dissipation in the output divider, maybe 100K to start.
Now we know 3 out of 4 variables in our voltage divider equation. Just rearrange to solve for Ra.
2.5 = 200 * (100K)/(100K + Ra)
Ra = 7.9MegOhm
So if you want 200V on the output, you need a 7.9M + 100K resistor (or another combination of the same ratio).
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Rc3 sets up the bias current through the optocoupler's LED. Sometimes it's referred to as the "master gain" resistor. You need sufficient LED bias to ensure the control loop can respond to different events.
Rc3 = (Vout - VLED- V431)/ (Ibias), where VLED is around 1.0V and V431 is 2.5V max.
Typically, 1-10mA is needed through the LED. If you design around 5mA, then you'd need a 39K resistor for Rc3.
Hope this helps.