1. Field of the Invention
The present invention relates to a non-isolated power conversion circuit, and more specifically to a DC-DC converter including one having a step-up, step-down and combined capabilities, a driving method and a drive unit.
2. Description of the Related Art
Conventionally non-isolated power conversion circuits are known that include DC-DC converters in which a capacitor is charged via a coil by making or breaking a conduction path extending from a direct-current (DC) power supply to the coil, via a switching element, and causing a desired DC voltage to be output.
Moreover, as for non-isolated DC-DC converters, a step-down type that produces a DC voltage lower than a supply voltage of a DC power supply, a step-up type that produces a DC voltage higher than the supply voltage of the DC power supply, and a step-up-and-down type capable of producing a DC voltage higher than the supply voltage, from a DC voltage lower than the supply voltage of the DC power supply are representative. None of these types of non-isolated DC-DC converters however can produce a negative voltage lower than a ground voltage of 0V corresponding to the potential on a negative electrode side of the DC power supply.
Moreover, non-isolated DC-DC converter types such as a Ćuk converter, a Zeta converter, a single ended primary inductor converter (SEPIC), or any other type of converter that charges and discharges a capacitor are known. However, while such types of converters can output a voltage lower than the supply voltage or a voltage higher than the ground voltage, none can control an output voltage over a wide range from a negative voltage equal to or lower than the ground voltage to a positive voltage exceeding the supply voltage.
Multiple-output DC-DC converters including combinations of various types of DC-DC converters are also known, for example as described in JP-A-2003-164143, and have been developed in an attempt to address limitations of the above described converters.
For example, the multiple-output DC-DC converter described in JP-A-2003-164143 includes, as shown, for example, in FIG. 17 of the present application, a DC power supply 20, and a coil 23 having one terminal connected to a negative electrode side of the DC power supply 20, that is, a ground, via a switch 21 and having the other terminal connected to a positive electrode side of the DC power supply 20 Via a switch 22. The anode of a diode 24 is connected to a node between the coil 23 and switch 21. A capacitor 25 having one terminal grounded to the ground and a load 31 having one terminal grounded to the ground are connected to the cathode of the diode 24. The cathode of a diode 26 is connected to a node between the coil 23 and switch 22. A capacitor 27 having one terminal grounded to the ground and a load 32 having one terminal grounded to the ground are connected to the anode of the diode 26.
A control circuit 30 turns the switch 21 on or off while the switch 22 is held on causing a current to flow into the coil 23 while the switch 21 is held on. The control circuit 30 further controls the capacitor 25 via the diode 24 using a high voltage generated at the coil 23 while the switch 21 is held off so that the voltage at the capacitor 25 will have a voltage value larger than the supply voltage. In other words, the switch 22 being held on causes the coil 23, switch 21, and diode 24 to operate as a step-up DC-DC converter, and supplies a DC voltage Vo1, which is higher than the supply voltage of the DC power supply 20, to the load 31.
The control circuit 30 turns the switch 22 on or off while the switch 21 is held on causing a current to flow into the coil 23 while the switch 22 is on and causes a current to flow into the coil 23 via the diode 26 while the switch 22 is off. Thus, the control circuit 30 controls an output voltage fed from the capacitor 27 to the load 32 to be a negative voltage lower than the ground voltage. In other words, the control circuit 30 holds the switch 21 on allowing the coil 23, switch 22, and diode 26 to operate as an inverted-output step-up-and-down DC-DC converter.
While, according to the foregoing multiple-output DC-DC converter, both a positive voltage and a negative voltage can be outputted to an external load, disadvantages are present in that the multiple-output DC-DC converter outputs the positive voltage and negative voltage through different terminals thereof. Therefore, although the multiple-output DC-DC converter can output the positive voltage and negative voltage to loads connected to the respective terminals, the multiple-output DC-DC converter cannot change an output voltage directed to one load from the negative voltage to the positive voltage.
Moreover, even if circuitry that outputs a positive voltage and a negative voltage to one load via a switch or the like can be devised and a range of voltages that can be outputted falls into a voltage range higher than the supply voltage of the DC power supply 20 and a negative voltage range lower than the ground voltage disadvantages are still present. For example, since the DC-DC converter that produces the positive voltage is of a step-up type and the DC-DC converter that produces the negative voltage is of a step-up-and-down type, an inverted output provided. The inversion poses a disadvantage in that voltages in a range relative to the ground voltage of 0V to the supply voltage cannot be outputted.