# How to charge a capacitor using repeatable damped sinusoid current signals?

I am trying to charge a capacitor using repeatable damped sinusoid current signals from a piezoelectric bender - Result of the free vibration of the piezo beam(Current source plus piezoelectric capacitance in parallel). The current from the piezo bender is rectified and used to charge a capacitor. I have simulated it Matlab/Simulink but it yields a weird behaviour when the input is a damped sinusoid current signals. The voltage across the capacitor never reaches the open circuit voltage but grows indefinitely.

This is the expected behaviour (From a sinusoidal no-damped current input): Graph1: Voltage Across Cp1(Piezo Bender) Graph2: Voltage Across Capacitor that is being charged.

However, this is what I get (The voltage across the capacitor never reaches the open circuit voltage but grows indefinitely): Graph1: Voltage Across Cp1(Piezo Bender) Graph2: Voltage Across Capacitor that is being charged.

Would you have any suggestion on how to fix this problem? Thank you very much for your help in advance. Best wishes, Lucas

I have simulated it Matlab/Simulink but it yields a weird behaviour when the input is a damped sinusoid $$\\color{red}{\text{current}}\$$ signal
You are using a $$\\color{red}{\text{current}}\$$ signal and that will inevitably keep putting charge into the storage capacitor. Just think about what a capacitor does when you apply a current source to it: -
$$I = C\dfrac{dv}{dt}\longrightarrow V = \dfrac{1}{C}\int i.dt$$