Circuit diagram below is a high side n-channel mosfet with bootstrap(while C1 is discharging)
It says that after charging of bootstrap capacitor:
The upper optocoupler opt1 gets ON for 1s and lower optocoupler Opt2 remains OFF for 1s. The capacitor C1 now tries to maintain the 12V across it and this raises the source voltage to 12V. This makes the diode D1 reverse biased as its cathode voltage is now 24V for maintaining the 12V across the capacitor. The capacitor C1 now starts discharging through upper optocoupler Opt1 and the gate of the MOSFET Q1 develops 24V.
BUT I cannot understand how the 12 volts from the source is added to the 12 volts of the charged capacitor. I mean, at the time of discharging, the capacitor is not in series with the 12 volts source. (it seems to me that the capacitor and source is in parallel to gate of mosfet)
I think the current does added up but not the voltage. How so the source voltage is added to capacitor voltage to become 24V?