Powering up MC34063 circuit with transformer
I am not a Multisim user, but the IC=??V specifications on the capacitors probably stand for "Initial Condition". Since the input filter capacitor starts with 30V, current flows backward from that capacitor to charge the 470uF capacitor. Another hint of that is Uin gets to be more than 24V. So, don't specify invalid initial conditions.
&amp; 3. You can connect the two converters directly to the transformer rectified output.


But, if the transformer has 30VAC output, you can easily get a rectified voltage that does not dipped below 30V. Why linear-regulate to 24V and boost it back to 27V? Regulate the rectified voltage directly to 27V.