3-level buck-boost converter with flying capacitor voltage balancing circuit
A 3-level buck-boost converter includes: an inductor connected in series between a switching node and a ground terminal; an output capacitor connected between an output terminal from which an output voltage is output and a ground terminal; a first switch connected between an input terminal to which an input voltage is input and a top plate node; a second switch connected between the top plate node and the switching node; a third switch connected between the switching node and a bottom plate node; a fourth switch connected between the bottom plate node and the output terminal; a flying capacitor connected between the top plate node and the bottom plate node; balancing switches connected between the switching node and the balancing node; a top balancing capacitor connected between the input terminal and the balancing node; and a bottom balancing capacitor connected between the balancing node and the output terminal.
1. A 3-level buck-boost converter with a flying capacitor voltage balancing circuit, comprising:
an inductor connected in series between a switching node and a ground terminal;
an output capacitor connected between an output terminal from which an output voltage is output and a ground terminal;
a first switch connected between an input terminal to which an input voltage is input and a top plate node;
a second switch connected between the top plate node and the switching node;
a third switch connected between the switching node and a bottom plate node;
a fourth switch connected between the bottom plate node and the output terminal;
a flying capacitor connected between the top plate node and the bottom plate node;
balancing switches connected between the switching node and the balancing node;
a top balancing capacitor connected between the input terminal and the balancing node; and
a bottom balancing capacitor connected between the balancing node and the output terminal.
2. The 3-level buck-boost converter of claim 1 , wherein
the flying capacitor is connected in parallel with the top balancing capacitor for at least a period of time during operation of the 3-level buck-boost converter, and is connected in parallel with the bottom balancing capacitor for another period of time during operation of the 3-level buck-boost converter.
3. The 3-level buck-boost converter of claim 2 , wherein
a voltage of the flying capacitor, a voltage of the top balancing capacitor, and a voltage of the bottom balancing capacitor have substantially same values.
4. The 3-level buck-boost converter of claim 3 , wherein
the voltage of the flying capacitor, the voltage of the top balancing capacitor, and the voltage of the bottom balancing capacitor maintain a value obtained by dividing a value obtained by subtracting the output voltage from the input voltage by 2.
5. The 3-level buck-boost converter of claim 1 , wherein
when a duty ratio D is less than approximately 0.5,
during a first time, the first switch, the third switch, and the balancing switches are turned on, and the second switch and the fourth switch are turned off; thus the flying capacitor and the top balancing capacitor are connected in parallel,
after the first time has elapsed, during a second time following the first time, the third switch and the fourth switch are turned on, and the first switch, the second switch, and the balancing switches are turned off,
after the second time has elapsed, during a third time equal to the first time, the second switch, the fourth switch, and the balancing switches are turned on, and the first switch and the third switch are turned off; thus the flying capacitor and the bottom balancing capacitor are connected in parallel, and
after the third time has elapsed, during a fourth time equal to the second time, the third switch and the fourth switch are turned on and the first switch, the second switch, and the balancing switches are turned off.
6. The 3-level buck-boost converter of claim 1 , wherein
when a duty ratio D is approximately 0.5,
during a fifth time, the first switch, the third switch, and the balancing switches may be turned on, and the second switch and the fourth switch are turned off; thus the flying capacitor and the top balancing capacitor are connected in parallel, and
after the fifth time has elapsed, during a sixth time equal to the fifth time, the second switch, the fourth switch, and the balancing switches are turned on, and the first switch and the third switch are turned off; thus the flying capacitor and the bottom balancing capacitor are connected in parallel.
7. The 3-level buck-boost converter of claim 1 , wherein
when a duty ratio D is greater than approximately 0.5,
during a seventh time, the first switch, the third switch, and the balancing switches are turned on, and the second switch and the fourth switch are turned off; thus the flying capacitor and the top balancing capacitor are connected in parallel,
after the seventh time has elapsed, during an eighth time following the seventh time, the first switch and the second switch are turned on, and the third switch, the fourth switch, and the balancing switches are turned off,
after the eighth time has elapsed, during a ninth time equal to the seventh time, the second switch, the fourth switch, and the balancing switches are turned on, and the first switch and the third switch are turned off; thus the flying capacitor and the bottom balancing capacitor are connected in parallel, and
after the ninth time has elapsed, during a tenth time equal to the eighth time, the first switch and the second switch are turned on, and the third switch, the fourth switch, and the balancing switches are turned off.