DC-DC converter
View Patent ↗To present a DC-DC converter efficient in conversion and not requiring an external diode. The DC-DC converter includes a main NMOS transistor FET 1 as a main switching device, a driver DVH 1 for driving a gate terminal of the main NMOS transistor FET 1 , a capacitor C 2 connected between a source terminal of the main NMOS transistor FET 1 and a power source terminal of the driver DVH 1 , and an NMOS transistor FET 3 connected between a route leading to an input power source and the power source terminal of the driver DVH 1 . The NMOS transistor FET 3 does not conduct when the main NMOS transistor FET 1 conducts, and conducts when the main NMOS transistor FET 1 does not conduct.
1. A DC-DC converter comprising:
a main NMOS transistor constituting a main switching device;
a driver for driving a gate terminal of the main NMOS transistor;
a first capacitance connected between a source terminal of the main NMOS transistor and a power source terminal of the driver; and
a first switching device connected between a path to reach an input power source and the power source terminal of the driver;
wherein the first switching device is made non-conductive when the main NMOS transistor is conductive, and the first switching device is made conductive when the main NMOS transistor is non-conductive.
2. The DC-DC converter according to claim 1 wherein the first switching device is an NMOS transistor of which back gate terminal is connected to a terminal at side of the path to reach the input power source.
3. The DC-DC converter according to claim 2 further comprising a step-down regulator for stepping down input voltage supplied from the input power source, the step-down regulator being arranged between the input power source and the first switching device.
4. The DC-DC converter according to claim 3 , wherein a lower bound value of output voltage of the step-down regulator is threshold voltage of the main NMOS transistor.
5. The DC-DC converter according to claim 1 wherein the first switching device is a PMOS transistor of which back gate terminal is connected to a terminal at side of a power source terminal of the driver.
6. The DC-DC converter according to claim 5 further comprising a driving circuit for driving a gate terminal of the PMOS transistor, the driving circuit being constituted by connecting the power source terminal to the power source terminal of the driver.
7. The DC-DC converter according to claim 1 further comprising:
a second switching device arranged between the first switching device and a connection point of the power source terminal of the driver and the first capacitance;
a second capacitor connected between a connection point of the first switching device and the second switching device and a source terminal of the main NMOS transistor; and
a second switching device control part for making the second switching device conductive when conduction command of the main NMOS transistor is in an active state and between-terminal voltage of the first capacitance is predetermined voltage or lower.
8. The DC-DC converter according to claim 7 , wherein the first switching device is a first PMOS transistor of which a back gate terminal is connected to a terminal at side of the power source terminal of the driver.
9. The DC-DC converter according to claim 8 further comprising a first driving circuit for driving a gate terminal of the first PMOS transistor, the first driving circuit being constituted by connecting a power source terminal of the first driving circuit to a connection point of the first switching device and the second switching device.
10. The DC-DC converter according to claim 7 , wherein the first switching device is a first NMOS transistor of which a back gate terminal is connected to a terminal at side of the path to reach the input power source.
11. The DC-DC converter according to claim 7 , wherein the second switching device is a second PMOS transistor of which a back gate terminal is connected to a terminal at side of the power source terminal of the driver.
12. The DC-DC converter according to claim 11 further comprising a second driving circuit for driving a gate terminal of the second PMOS transistor, the second driving circuit being constituted by connecting a power source terminal of the second driving circuit to a connection point of the first switching device and the second switching device.
13. The DC-DC converter according to claim 7 , wherein the second switching device is a second NMOS transistor of which a back gate terminal is connected to a terminal at side of the path to reach the input power source.
14. The DC-DC converter according to claim 7 , wherein capacity of the first capacitor is larger than capacity of the second capacitor.