High step up DC-DC converter switch mode power supply
Where did you get that circuit? It is unusual and the extra portion at right compared to "normal" (transformer D2 D3 C1) is probably not necessary and it is not at all obvious that this circuit has been "designed". 

Lm D1 M1 form a classic boost converter.
Xfmr then attempts to take boost voltage across Lm and "pedestal it" on boost output at D1 cathode, adding N:1 x boost voltage via C1 at D2 Cathode. BUT eg Xfmr primary  becomes part of Lm functionally and must be designed as part of Lm. In fact Lm is not needed with Xfmr present.

Recommendation:  Try removing Xfmr D2 D3 C1 and connect D! cathode to C3 and see how it goes. 20:1 is doable but care needs to be taken with eg stray capacitances which store energy during the flyback  period and reduce voltage rise 

After having tried the above, ask for more information if required.