Charging a big capacitor

[lilmantis]

        Hello, what is generally the best idea for a CC capacitor charger implementation?

my Case: 12-24V input and 35V output on the capacitor. Capacitor is half drained periodically to power some LEDs so it will vary between 17-35V.
I tried SEPIC and ZETA topologies but I get very high currents.

I am thinking about a constant current converter but this is complex and expensive. Any suggestions?