1. Field of the Invention
The present invention relates to the field of electric power converters, and more particularly high frequency switching DC-DC converters.
2. Prior Art
Switch-mode topologies are widely used to convert power supply voltages from one value to another (DC-DC conversion). This function is mostly desirable when high efficiencies are required for lower power consumption or lower heat generation, such as, by way of example, in battery operated systems. Also battery operated and other modern systems tend to automatically shut down system facilities when not being used, both to conserve power and to reduce heat generation. Consequently such systems are often operating at substantially less than maximum capability, giving rise to another more recent requirement of such power supplies, namely good efficiency at load currents substantially lower than the rated current of the DC-DC converter.
When the load current is low, the efficiency of a switching converter is determined by losses due to the switching as well as power used by the control circuitry. In general, the power used by the control circuitry is derived from the input source.
FIG. 1 shows a very common DC-DC converter topology known as the step-down, or buck, topology. In this case, a high input voltage VIN, say 20 V, is converted to a low input voltage VOUT, say 5 V. In most cases the controller is powered from a linear regulator output voltage VR that is derived from the input power source voltage. Almost all controllers draw a relatively constant current. Therefore the power dissipation of the controller is given as: EQU Pd=VIN*Ic
where:
Pd=power dissipation PA1 VIN=the voltage of the input power source, and PA1 Ic=the controller current
The purpose of the present invention is to reduce the controller power consumption, thereby increasing the regulator efficiency, particularly at low loads. Furthermore, the invention reduces power dissipation in the controller for less heat generation.