Hi Fahrulloh Muftarikka Yusuf ,

in a boost converter employing just an inductor, in each cycle a certain amount of energy (depending on the on-time) is transferred into the inductor, and from there to the capacitor at the output. With constant frequency and constant duty cycle, this results in a constant average power flow into the capacitor.

With a load R, the power P dissipated in the load has to be equal to the power delivered by the booster, in the stationary case.

P = V2 / R V = sqrt(P * R)

So, with increasing R the voltage V increases, too.

Under ideal conditions (infinite resonance frequency of the inductor, zero rise time of the MOSFET, infinite VDSmax), the voltage would rise without limit in the absence of a load.

If your goal is to have a nearly constant output voltage, independent of the load, there are at least two options:

a) Add a feedback path: The duty cycle has to depend on the output voltage.

b) Use a transformer instead of a simple inductor, and change the circuit in such a way that the voltage at the primary coil of the transformer never exceeds the input voltage.

I suspect you might be experiencing inductor saturation. Note you likely operate in continuous mode https://en.wikipedia.org/wiki/Boost_converter

Dear Fahrulloh Muftarikka Yusuf,

Any DC/DC converter has to be loaded; basically because one of the principle is that the current do not evolve instantaneously in the inductor ... so, if no load sinking the current, the output capacitor is never discharged, and then continuously charge : increasing progressively the output voltage.

At the opposite, if the load is too low, the inductor discharge so fast that you operates in non-continuous condition (the current in the inductor drop to 0) leading to a reduced output voltage ... to solve this isue, you can increase the frequency