Capacitor discharge

Question

So I came across this article on CircuitDigest where they explained the functionality of a voltage doubler designed with capacitors. The circuit shown is the following:

At first capacitor C3 is charged to 5v (source voltage) when Q (the output of the 555 timer in astable mode) is low. Afterwards, when Q is set to high the diode D1 avoids C3 from being discharged (since the plates now have a direct path to connect to each other) and instead it gets discharged via ground passing through capacitor C4 thus adding the charge to C4 and therefore doubling the voltage (on C4) at that instance.

What seems odd to me is how come the capacitor C3 was able to discharge? Don’t the plates of the capacitor need to be directly connected to each other? In this case it looks like C3 is being discharged through ground and not through the other plate of the capacitor. How is this possible?

If anyone cloud clear this out for me I’ll greatly appreciate it.

Answer 1

C3 discharges via the power supply. When the output of the 555 is high, you have basically the following circuit:

^{simulate this circuit – Schematic created using CircuitLab}

Q28 is conducting, so current can flow clockwise around this loop. The voltage on C3 is in series with the power supply, so the combined voltage is enough to forward bias D2 and push charge onto C4.

C3 discharges by virtue of the fact that current flows out of its positive terminal, through D2, C4, the power supply and Q28, back to its negative terminal. Note that the same current is flowing in to the positive terminal of C4, charging it.

Internals of the 555 are from the datasheet.