A voltage regulator power supply is typically used to ensure that the electrical power supplied to an electronic device is maintained at a relatively constant voltage while providing the (variable) current needed for the proper functioning of the electronic device. There are several types, or topologies, of voltage regulators, each with different advantages and disadvantages. Design considerations for selecting the type of voltage regulator to use in a given situation often involve tradeoffs between parameters such as conversion efficiency and output voltage noise. The efficiency generally refers to the amount of power that can be provided by the regulator with a given input power. The noise generally refers to any fluctuation, including “ripple”, exhibited by the output voltage, usually during steady state operating conditions, but also when changes occur in either the available input line voltage or the output load current draw.
A linear regulator is a type of voltage regulator that provides an output voltage with relatively low noise. A low-dropout (LDO) linear regulator, for instance, may be capable of as little as a 500 microvolt ripple in a 5-Volt output, i.e. about 0.01% noise. The efficiency of such regulators, however, is typically relatively low, since they ineffectively convert input power to output power, the wasted energy being dissipated as heat. For instance, a linear regulator with a high input voltage (e.g. Vin about 12 Volts) and a low output voltage (e.g. Vout about 5 Volts) is typically less than 50% efficient.
A switching power supply (e.g. a buck converter, a step-down DC to DC converter, a switched-mode power supply, etc.), on the other hand, is typically very efficient, usually 90-95% (or higher) efficient. The noise, however, can be quite significant. A switching power supply that produces 5 Volts, for example, may exhibit a total peak-to-peak ripple of anywhere from 5 to 200 millivolts, i.e. 0.1 to 4% noise.
FIG. 1 shows a simple example of a prior art switching power supply (buck converter 100) that converts a given input voltage Vin to an appropriate output voltage Vout for an output load 101. The buck converter 100 generally includes a switch 102, a diode 103, an inductor 104 and a capacitor 105 configured as shown. An appropriate control component (not shown) typically controls the switch 102, based on feedback of the output voltage Vout. When the switch 102 is closed, the input power (at voltage Vin) provides current to the inductor 104, so the current in the inductor 104 increases. When the switch 102 is open, the current to the inductor 104 (provided through the diode 103) decreases. A graph 106 illustrating this increasing and decreasing (ripple) of the current in the inductor 104 is shown in FIG. 2. In this example, the current in the inductor 104 fluctuates about 200 milliamps around 1.5 Amps. As a consequence of the current ripple in the inductor 104, the output voltage Vout ripples accordingly, as shown in a graph 107 in FIG. 3. The output voltage Vout fluctuates about 8 millivolts around about 3.29 Volts, which calculates to about 0.24% noise.
A more complicated intermediary solution to improve both efficiency and noise reduction involves a combination of a switching power supply and an LDO regulator. The switching power supply generally takes an input voltage down to a lower intermediate voltage with a relatively high efficiency, but with an undesirably high noise level. The LDO regulator then takes the lower intermediate voltage and produces the desired low noise output voltage. Since the LDO regulator starts with a lower voltage, the loss in the LDO regulator is smaller than in solutions that use only the LDO regulator. Thus, the end result of this combination has a greater efficiency (about 75% or less) than an LDO regulator alone and a lower noise level than a switching power supply alone. A disadvantage is, however, that a device manufacturer often must use two components (the switching power supply and the LDO regulator) instead of one, thus increasing the size, complexity and cost of the resulting device.
A continuing trend in the electronics industry is the need for ever greater conversion efficiency combined with ever lower operating voltage noise levels in addition to ever smaller device/component sizes and costs. Current technology is reaching the limits of the efficiency and noise capabilities of the available power supply topologies. A new topology is needed.
It is with respect to these and other background considerations that the present invention has evolved.