DC-DC boost converter with a charge pump
View Patent ↗A DC-DC boost converter comprises a charge pump selectively operating in a voltage doubler or in a voltage tripler mode. A switching arrangement connects the charge pump to an input voltage terminal in a charge phase and to an output voltage terminal in a discharge phase. A controllable current source is connected in series with the charge pump in the discharge phase and an error amplifier has a first input connected to a reference voltage, a second input connected to the output voltage terminal and an output connected to a control input of the controllable current source. The converter further comprises a mode changeover circuit with a first comparator having a first input connected to the output of the error amplifier and a second input connected to a first threshold voltage source. A second comparator has a first input connected to the output of the error amplifier and a second input connected to a second threshold voltage source. A flip-flop has its set input connected to the output of the first comparator, its reset input connected to the output of the second comparator. The flip-flop has its output connected to the switch arrangement to switch the charge pump from doubler mode to tripler mode when the voltage at the output of the error amplifier exceeds the second threshold voltage and back to doubler mode when the output voltage at the error amplifier drops below the first threshold voltage.
1. A DC-DC boost converter, comprising:
a charge pump selectively operating in a voltage doubler mode or in a voltage tripler mode;
a switching arrangement connecting the charge pump to an input voltage terminal in a charge phase and to an output voltage terminal in a discharge phase;
a controllable current source connected in series with the charge pump in the discharge phase; and
an error amplifier having a first input connected to a reference voltage, a second input connected to the output voltage terminal, and an output connected to a control input of the controllable current source;
and further comprising a mode changeover circuit including:
a first comparator having a first input connected to the output of the error amplifier and a second input connected to a first threshold voltage source;
a second comparator having a first input connected to the output of the error amplifier and a second input connected to a second threshold voltage source; and
a flip-flop having a RESET input connected to the output of the first comparator, a SET input connected to the output of the second comparator, and an output connected to the switching arrangement to switch the charge pump from the voltage doubler mode to the voltage tripler mode when the voltage at the output of the error amplifier exceeds the second threshold voltage, and back to the voltage doubler mode when the output voltage at the error amplifier drops below the first threshold voltage.
2. The converter according to claim 1 , wherein the controllable current source is formed by a current mirror arrangement which includes a diode-connected MOS transistor in series with a current control MOS transistor between the input voltage terminal and ground; and a power MOS transistor that mirrors the current through the diode-connected MOS transistor, the gate of the current control MOS transistor being connected to the output of the error amplifier.
3. The converter according to claim 2 , wherein the switching arrangement is driven by a clock signal.
4. The converter according to claim 3 , wherein the switching arrangement driven by the clock signal disables the controllable current source in the charge phase.
5. The converter according to claim 4 , wherein the charge pump comprises:
a first pair of complementary MOS transistors connected between the input voltage terminal and ground;
a second pair of complementary MOS transistors connected in series between the input voltage terminal and ground;
a normally closed switch connected to the input voltage terminal;
a first charge accumulating capacitor having one electrode connected to the node between the first pair of MOS transistors and the other connected to the normally closed switch through a first diode;
a second charge accumulating capacitor having one electrode connected to the node between the second pair of MOS transistors and the other connected to the normally closed switch through a second diode; and
a third diode connecting the first and second charge accumulating capacitors in series.
6. The converter according to claim 5 , wherein the normally closed switch is a p-type MOS transistor.
7. The converter according to claim 6 , wherein the charge pump further comprises a fourth diode connecting the first charge accumulating capacitor to a load capacitor.
8. The converter according to claim 5 , wherein the charge pump further comprises a fourth diode connecting the first charge accumulating capacitor to a load capacitor.
9. The converter according to claim 3 , wherein the charge pump comprises:
a first pair of complementary MOS transistors connected between the input voltage terminal and ground;
a second pair of complementary MOS transistors connected in series between the input voltage terminal and ground;
a normally closed switch connected to the input voltage terminal;
a first charge accumulating capacitor having one electrode connected to the node between the first pair of MOS transistors and the other connected to the normally closed switch through a first diode;
a second charge accumulating capacitor having one electrode connected to the node between the second pair of MOS transistors and the other connected to the normally closed switch through a second diode; and
a third diode connecting the first and second charge accumulating capacitors in series.
10. The converter according to claim 2 , wherein the charge pump comprises:
a first pair of complementary MOS transistors connected between the input voltage terminal and ground;
a second pair of complementary MOS transistors connected in series between the input voltage terminal and ground;
a normally closed switch connected to the input voltage terminal;
a first charge accumulating capacitor having one electrode connected to the node between the first pair of MOS transistors and the other connected to the normally closed switch through a first diode;
a second charge accumulating capacitor having one electrode connected to the node between the second pair of MOS transistors and the other connected to the normally closed switch through a second diode; and
a third diode connecting the first and second charge accumulating capacitors in series.
11. The converter according to claim 10 , wherein the switching arrangement is driven by a clock signal.
12. The converter according to claim 1 , wherein the charge pump comprises:
a first pair of complementary MOS transistors connected between the input voltage terminal and ground;
a second pair of complementary MOS transistors connected in series between the input voltage terminal and ground;
a normally closed switch connected to the input voltage terminal;
a first charge accumulating capacitor having one electrode connected to the node between the first pair of MOS transistors and the other connected to the normally closed switch through a first diode;
a second charge accumulating capacitor having one electrode connected to the node between the second pair of MOS transistors and the other connected to the normally closed switch through a second diode; and
a third diode connecting the first and second charge accumulating capacitors in series.
13. The converter according to claim 12 , wherein the switching arrangement is driven by a clock signal.
14. The converter according to claim 1 , wherein the switching arrangement is driven by a clock signal.