Patent Application
20080007236
For a more complete understanding of the present invention and for further features and advantages, reference is now made to the following description taken in conjunction with the accompanying drawings.
b are schematic diagrams in partial block form of exemplary implementations for a power converter with segmented power module, according to embodiments of the invention.
Embodiments of the present invention and their advantages are best understood by referring to
According to embodiments of the present invention, systems and methods are provided for a power converter which may operate efficiently at a variety of current levels or other operating conditions. In some embodiments, this can be accomplished by providing a power converter with a segmented power module in which different segments can be chosen or selected to optimize or increase the efficiency of operation of the power converter under the various conditions. Each segment may comprise a switch or transistor (e.g., metal-oxide-semiconductor field effect transistor (MOSFET)). In some embodiments, the selection of segments can be accomplished by using a look-up table which specifies certain segments to turn on in response to the power dissipation in the power converter during operation. Power dissipation in the converter can be measured or determined, for example, by measuring the voltage drop across the switch in a currently selected segment and deriving power dissipation using the on-resistance value across its source and drain (Rdson). In some embodiments, the power converter can be a buck (step-down) converter, boost (step-up) converter, buck-boost converter, flyback converter, or other converter which converts a direct current (DC) voltage at one magnitude into a direct current (DC) voltage at another magnitude (lower or higher).
Power converter 100 may also include or be coupled to an inductor 112 and a capacitor 114. As used herein, the terms “coupled” or “connected,” or any variant thereof, covers any coupling or connection, either direct or indirect, between two or more elements. Inductor 112 may carry an alternating current (AC) component and a DC component. The AC component of inductor 112 ramps up and down during operation of the power converter 100; the DC component is stable.
Segmented power module 102 of power converter 100 comprises a number of segments 108 (e.g., 108a, 108b, 108c, 108d, 108e, and 108f). Any suitable number n of segments 108 can be provided, where n can be, for example, 2, 3, 4, or 5. As shown, one group 110a of segments 108 may be provided for a “high-side” of the power converter 100, and another group 110b of segments 108 may be provided for a “low-side” of the power converter 100. The high-side group 110a of segments 108 is coupled between a voltage source Vp and the SW output node; the low-side group 110b of segments 108 is coupled between the SW output node and ground. Such an arrangement with high-side and low-side is known as a half-bridge or “totem pole” arrangement. In other embodiments, groups of segments 108 can be connected in other arrangements, such as, for example, arrangements for flyback converter, boost converter, buck-boost converters, or other DC-to-DC converters used in mobile and handheld devices.
Each segment 108 is implemented with a switch, such as, for example, a metal-oxide-semiconductor field effect transistor (MOSFET), an IGBT, a MOS-gated thyristor, or other suitable power device. The switches (in each group) are connected in parallel between two nodes (i.e., either Vp and the SW output node, or the SW output node and ground). Each switch has a gate to which driving voltage may be applied to turn the switch on or off. In one embodiment, the switches in the high-side group 110a can be high-performance switches (i.e., having relatively fast switching times, but also high Rdson), while the switches in the low-side group 110b may be more efficient switches (i.e., having low Rdson).
When one or more switches in the high-side group 110a of segmented power module 102 are turned on, the power converter 100 ramps up the inductor current of inductor 112 and charges up capacitor 114. When one or more switches in low-side group 110b are turned on, the power converter 100 ramps down the current of inductor 112 and discharges capacitor 114. The switches in the groups 110a, 110b can be driven to alternatingly conduct. That is, none of the switches in high-side group 110a are turned on simultaneously with any of the switches in low-side group 110b, and vice versa. Rather, when any switch is turned on and conducting in the high-side group 110a, every switch in the low-side group 110b is turned off; and when any switch in the low-side group 110b is turned on and conducting, every switch in the high-side group 110a is turned off.
The switches for the various segments 108 (in a group 110) can be implemented in different sizes. For example, the size of the switch for segment 108b can be twice that of switch for segment 108a, and the size of the switch for segment 108c can be four times that of switch for segment 108a. Different size switches have different characteristics. For example, a larger size switch has lower on-resistance across its source and drain (Rdson). Thus, larger size switches are advantageous to reduce conduction losses, which are directly proportional to Rdson. A smaller size switch has lower gate charge capacitance (Qg), which is the capacitance that must be overcome to turn a switch on and off. As such, smaller size switches are advantageous to reduce gate capacitance switching losses, which are directly proportional to Qg. It should be understood that any selection of sizes for the switches can be used consistent with the teachings described herein.
One or more segments 108 (in a group 110) can be selected—i.e., the respective switches turned on—depending on the operating conditions of power converter 100. In particular, different size switches may be turned on at different points of operation in order to minimize the power losses which may occur in the power converter 100, thereby optimizing or providing improved efficiency for power converter 100.
Driver logic 106 and drivers 104 are connected to the segments 108 of the segmented power module 102. Driver logic 106 outputs a number of control signals for selecting corresponding segments 108 in the segmented power module 102. In one embodiment, each control signal may cause a respective driver 104 to drive the switch corresponding to the respective segment.
Driver logic 106 can be implemented as a digital controller (e.g., programmable logic array), an analog controller, or combination thereof, for performing one or more of the functions described herein. In some embodiments, driver logic 106 may have one or more inputs for sensing or receiving information to derive or calculate one or more operating conditions of the power converter 100 (e.g., voltage drop across a group 110, load current, power dissipation, etc.), so that driver logic 106 may output control signals in response thereto. For example, as shown, driver logic 106 is connected to the Vp voltage, the SW output node, and ground, and as such, has input for the voltage drop across group 110a (i.e., the voltage difference between Vp and the SW output node) and for the voltage drop across group 110b (i.e., the voltage difference between the SW output node and ground). Driver logic 106 may also keep track of or know which segments 108 are turned on or selected at a given moment of operation.
In some embodiments, driver logic 106 may comprise a look-up table or other logic (not expressly shown) which can be used to adjust the control signals for selecting segments 108 in the segmented power module 102. The look-up table may comprise a number of entries that specify which segment(s) 108 should be selected based upon power dissipation in the power converter 100, such as, for example, the power dissipated in the switches of segmented power module 102. Such power dissipation can be directly proportional to the on-resistance (Rdson) of a switch. In one embodiment, for example, if the Rdson of the switch of each segment 108 is known, and the driver logic 106 knows which switch or switches are on at a particular moment, then the power dissipation in the converter 100 can be determined or calculated by taking a measurement of voltage across or current flowing through those switch(es). That is, P=V2/R=I2R, where P is power, V is the voltage across the switch, I is the current flowing through the switch, and R is the Rdson of the switch. The look-up table in driver logic 106 may map which segment 108 to turn on for a given power dissipation for converter 100 during various points of operation.
In one embodiment, driver circuitry is provided to drive the segments 108 with control signals having voltages which are variable, such as, for example, proportional to the load current or power dissipation. This can provide a further improvement in efficiency for power converter 100. Circuitry and methods for implementing such technique for variable gate driver voltage is described in pending U.S. application Ser. No. 11/006,345, entitled “Current Controlled Gate Driver for Power Switches,” filed on Dec. 7, 2004, which is incorporated by reference herein in its entirety.
In some embodiments, segmented power module 102, drivers 104, and driver logic 106 of power converter 100 can be implemented on a single or multiple semiconductor dies (commonly referred to as a “chip”) or discrete components. Each die is a monolithic structure formed from, for example, silicon or other suitable material. For implementations using multiple dies or components, the dies and components can be assembled on a printed circuit board (PCB) having various traces for conveying signals therebetween. In one multiple-die implementation, the segments 108 of the high-side group 110a are provided on a first die, the segments 108 of the low-side group 110b are provided on a second die, and the driver logic 106 and drivers 104 are provided on a third die.
By providing power converter 100 with a segmented power module 102 implemented with a plurality of switches of varying sizes, different switches can be selected at different points of operation to optimize the efficiency of the power converter 100. This is shown in
Referring now to
As described herein, the selection of segments 108 (switches) can be based on power dissipation. This may provide an advantage over previously developed systems in which segments (implemented with switches of varying sizes) are selected based on load current. In particular, when only load current is used as the basis of segment selection, then a circuit designer is constrained or restricted to using switches (e.g., MOSFETs) which are matched for particular current ranges. By using power dissipation as the basis of selecting segments, a circuit designer is given more freedom (i.e., less restricted) in choosing switches for implementing each segment.
Power converter implementations 200 and 300 may include or be connected to a pulse width modulation (PWM) controller 150 which supports or provides PWM control for the power converter. PWM controller 150 outputs signals for fault (OD), pulse width modulation (PWM), and signal ground (SGND) to logic unit 124. As shown, the PWM controller 150 may be implemented on a separate die or chip, but in other embodiments, the PWM controller 150 may be provided on the same chip as one or more of the other components of power converter implementations 200 and 300.
The segmented power module 102 in each of the implementations 200 and 300 includes a first group 110a of segments 108 for a high-side of the power converter implementation and a second group 110b of segments 108 for a low-side. The high-side group 110a of segments 108 is coupled between a voltage source Vp and a node SW; the low-side group 110b of segments 108 is coupled between the node SW and ground.
Each of the high-side and low-side groups 110a, 110b includes three segments 108. Each segment 108 is implemented with a respective switch (e.g., MOSFET). The switches in each group 110 can vary in size, from smallest to largest. Smaller size switches provide for lower gate capacitance switching losses. Larger size switches provide for lower conduction losses. The three switches in each group 110a, 110b can be turned on or off in any combination, thus providing seven alternatives for switching. The segments 108 in each group 110 may be selected (i.e., the respective switches turned on) in order to optimize or increase efficiency of the power converter implementation.
Drivers 104 provide drive signals to the gates of the switches in segmented power module 102. Logic unit 124, multiplexer (MUX) 122, and AND gates 120 implement logic for controlling the driving of the switches. These components output control signals to the drivers 104.
Logic unit 124 may receive the OD, PWM, and SGND signals from PWM controller 150. Logic unit 124 may also receive information which it can use to calculate the power dissipation in the power converter implementation, such as, for example, the power dissipated in the switches of the segmented power module 102 (which can be related to conduction losses which are proportional to the on-resistance (Rdson) of each switch). For this, logic unit 124 is connected to the SW node. In response to the received information, logic unit 124 outputs signals to multiplexer (MUX) 122 and AND gates 120 for selecting various segments 108 in each of the high-side and low-side groups 110a, 110b of segments 108. Logic unit 124 may keep track of or know which segments 108 are turned on or selected at a given moment of operation. In some embodiments, logic unit 124 may have a look-up table comprising a number of entries that specify which segment(s) 108 should be selected based upon power dissipation in the power converter implementation 200 or 300.
Multiplexer 122 receives control signals from logic unit 124. These control signals can be used to select individual segments 108 (switches) in the segmented power module 102. In operation, multiplexer 122 allows some of the selection signals to pass through the AND gates 120 and prevents other selection signals from being provided to the driver 104.
AND gates 120 receive control signals from each of logic unit 124 and multiplexer 122. Some of the AND gates 120 (e.g., half) are associated with or provided for the high-side, and the other AND gates 120 (e.g., the other half) are associated with or provided for the low-side. The AND gates 120 for the high-side may all receive the same signal from the logic unit 124, such signal for selecting the high-side. The AND gates 120 for the low-side may likewise receive the same signal from the logic unit 124, with this signal selecting the low-side. Each AND gate receives a separate signal from multiplexer 122, which can be used to select an individual segment in the segmented power module 102. Each AND gate 120 performs an AND operation on the signals it receives from logic unit 124 and multiplexer 122, and if these control signals have the appropriate values, then the AND gate 120 will output a signal to cause a respective driver 104 to drive an associated switch.
Referring to
As described herein, in one embodiment, driver circuitry may be provided to drive the segments 108 with control signals having voltages which are proportional to the load current, which can provide a further improvement in efficiency for a power converter.
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims. That is, the discussion included in this application is intended to serve as a basic description. It should be understood that the specific discussion may not explicitly describe all embodiments possible; many alternatives are implicit. It also may not fully explain the generic nature of the invention and may not explicitly show how each feature or element can actually be representative of a broader function or of a great variety of alternative or equivalent elements. Again, these are implicitly included in this disclosure. Where the invention is described in device-oriented terminology, each element of the device implicitly performs a function. Neither the description nor the terminology is intended to limit the scope of the claims.
