High voltage series switching power supply

After the article "CATV Series Switching Power Supply" was published in the 24th issue of "Electronic News" last year, a reader called and said that he hoped to provide a series switching power supply with input AC220V and output DC200V0.2A. After designing the experiment, the author obtained the circuit shown in the attached figure, whose output voltage is quite stable and the efficiency is over 85%. The working principle of this circuit is the same as above, so I will not repeat it here.

Component selection: IRF740 (400V 10A) for VT1, C2299 (400V 0.5A) or MPSA42 (300V 0.5A) for VT2, P2298T (400V 0.5A) or MPSA94 (300V 0.5A) for VT3. The inductance of inductor L can be between 100~200μH. If you want to make it yourself, you can use Φ0.31mm wire to wind 30 turns on the EI28 ferrite core, and there should be a gap in the core. The power of R not marked in the figure is 1/4W, and VT1 must add a heat sink. When the output voltage is 200V, it is replaced by a fixed resistor according to the actual data after RP adjustment. When the output voltage of this circuit is adjusted to 150V, the load current can reach 1A, and the output voltage is quite stable. If used in other occasions, the wire diameter of inductor L should be thickened, and the rest does not need to be changed.