The assignee for this patent, patent number 8633682, is
Reporters obtained the following quote from the background information supplied by the inventors: "This invention relates to switching power supply controllers.
"Switching power supply controllers are typically fabricated as an integrated circuit (IC), which is connected to external components such as an output inductor and capacitor to form a complete switching power supply. A switching power supply requires one or more switching elements, which can be on- or off-chip.
"A typical switching power supply configuration is shown in FIG. 1. The on-chip components include a switching transistor MP1 connected between an input voltage V.sub.in and a switching node 10, and a switching transistor MN1 connected between switching node 10 and an internal chip ground node 12. An error amplifier A1 receives a feedback signal V.sub.fbd which varies with the power supply's output voltage V.sub.out (typically via a resistive divider 14) and a reference voltage V.sub.ref at respective inputs, and produces an output which drives the controller's switch driving circuitry 16, typically using pulse width modulation (PWM). When so arranged, both V.sub.fbd and V.sub.ref are referred to internal chip ground node 12. External components such as output inductor L and output capacitor C are connected to the controller IC to complete the switching power supply. The controller operates to regulate output voltage V.sub.out by controlling a `switching cycle`, which includes a first portion during which MP1 is closed and MN1 is open, and a second portion during which MP1 is open and MN1 is closed.
"However, a problem can arise with a switching power supply controller IC having on-chip switches, such as that shown in FIG. 1. During the portion of the switching cycle when MN1 is turned on (and MP1 is off), all of the switch current i.sub.sw flows through chip ground node 12. However, chip ground node 12 must be connected an external ground node 20, to which the external components are referred. Ideally, there would be no resistance between chip ground node 12 and external ground node 20. However, in practice, a parasitic resistance R.sub.P is present between these nodes. When switch current i.sub.sw flows through R.sub.P, a voltage drop is developed across R.sub.P which can reduce the accuracy of feedback signal V.sub.fbd. This inaccuracy does not affect the feedback signal during the portion of the switching cycle when MP1 is turned on (and MN1 is off), because during this period, the switch current flows through switching node 10 and into inductor L, rather than through R.sub.P. Thus, there is an error in the feedback signal only during certain portions of the switching cycle. Moreover, the parasitic resistance between the external ground node and the chip ground node is generally beyond the direct control of the controller designer, and so the magnitude of the resulting voltage drop is unknown.
"One previous effort to address this problem involves the use of separate power and analog grounds to enable the controller to obtain an accurate measurement of the output voltage throughout the entire switching cycle. This approach, however, requires additional pins which are too costly for many applications. Another approach is to estimate the voltage drop caused by the switch current flowing through the parasitic resistance and to adjust the feedback accordingly. This approach, however, requires knowledge of the parasitic resistance value, which as mentioned above, is generally beyond the control of the designer."
In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventor's summary information for this patent: "A switching power supply controller is presented which employs selective feedback sampling and may also provide waveform approximation, enabling the controller to overcome the problems noted above.
"The present switching power supply controller is adapted to be connected to external components to produce a regulated output voltage at an output node. The controller requires at least one switching element, and is arranged to control a switching cycle during which the switching elements are switched on and off to regulate the output voltage. The controller has a feedback signal which represents the output voltage produced at the output node, and a circuit node--such as a chip ground node--which conducts a current that is higher during a second portion of the switching cycle than it is during a first portion of the switching cycle, such that the feedback signal varies with the current conducted by the circuit node.
"To overcome feedback signal inaccuracies, a sampling circuit is used to sample a signal which varies with the feedback signal only during the first portion of the switching cycle. The controller is then arranged to regulate the output voltage in response to the sampled signal.
"The sampling circuit can be a sample and hold (S/H) circuit, a track and hold (T/H) circuit, or a combination of both, and may be differential or single-ended. The sampling circuit may be further arranged to produce an output which approximates the portion of the feedback signal waveform which is not sampled.
"Further features and advantages of the invention will be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings."
For more information, see this patent: Richardson, Kenneth G.. Switching Power Supply Controller with Selective Feedback Sampling and Waveform Approximation. U.S. Patent Number 8633682, filed
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