Patent Application
20050162870
This disclosure is related to power converters, such as AC to DC converters, for example.
Power conversion usually results in some amount of power loss as a result of the conversion process. One example is conversion from alternating current (AC) to direct current (DC) power. Thus, new methods and/or techniques to accomplish power conversion, which result in improved efficiency, continues to be desirable.
Subject matter is particularly pointed out and distinctly claimed in the concluding portion of the specification. The claimed subject matter, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference of the following detailed description when read with the accompanying drawings in which:
Embodiments of systems, apparatuses, devices and/or methods for time slotting power switching are described. In the following description, numerous specific details are set forth. However, it is understood that the described embodiments may be practiced without these specific details. In other instances, well-known circuits, structures and/or techniques have not been shown in detail so as not to unnecessarily obscure the provided description.
Reference throughout this specification to “one embodiment” and/or “an embodiment” means that a particular feature, structure, and/or characteristic described may be included in at least one embodiment. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification typically do not refer to one particular embodiment or the same embodiment. Furthermore, various features, structures, and/or characteristics described through out this specification may be combined in any suitable manner in one or more embodiments.
Power conversion usually results in some amount of power loss as a result of the conversion process. One example is conversion from alternating current (AC) to direct current (DC) power. Thus, new methods and/or techniques to accomplish power conversion, which result in improved efficiency, continues to be desirable.
P=½ C V2f [1]
where P is power; C is a constant, which for an embodiment employing a charge pump, for example, may be related to capacitance, as explained in more detail hereinafter; V is root-mean-square (RMS) voltage of the AC power source applied; and f is the switching frequency. Thus, for this embodiment, power varies substantially linearly with the switching frequency.
Feedback may be accomplished by employing VCO 430 in conjunction with a reference voltage level 410 and an error amplifier 420, although, this is just one example, and many different schemes for feedback are included within the scope of the appended claims. Thus, in this particular embodiment, the voltage output signal, VOUT, produced by converter 470 is compared with a voltage reference signal level, Vref 410, and the error or difference is applied to VCO 430. As a result, VCO 430 may adjust the switching frequency which may affect the power and, likewise, the voltage output signal.
Referring now to
This embodiment also comprises here two transistor totem-pole configurations, 120 and 130; configuration 120 is coupled here to an AC Line 140 and configuration 130 is coupled to an AC Neutral 150. Likewise, a port or terminal of pump capacitance device 160 couples between configurations 120 and 130 at location 125 to drive or apply voltage to coil 290 of transformer 110 via the other port or terminal of capacitance device 160. It is noted, however, that alternatively, the pump capacitance device may be coupled between coil 290 and configuration 130, as shown. Thus, either location may be employed, depending on desirability. However, if the alternate location were not employed, for this embodiment, coil 290 would be coupled to configuration 130 through a short circuit connection. It is noted that, for this particular embodiment, the transistors comprise N-type metal oxide semiconductor field effect transistors, here MOSFETS, although, of course, the claimed subject matter is not limited to MOS devices, FET devices, N-type or P-type devices, or even to employing transistors. However, in this embodiment, configuration 120 comprises MOSFETs 122 and 124 and configuration 130 comprises MOSFETS 132 and 134. Likewise, it is noted that the diodes depicted in
Drive circuitry 170 drives the MOSFETs for this particular embodiment, as further illustrated in
Embodiment 100 includes other components illustrated in
In some embodiments, the capacitance of 220 may be generally 10 times as large as the capacitance of 245 or more. The values of inductance 230 and capacitance 220 may be selected such that their resonant frequency is in the order of ⅕ of the lower end of the desired drive frequency of the switches in the power converter for this embodiment. In addition, for this embodiment, the values of inductance 230 and capacitance 220 may be further selected such that their resonant frequency is approximately ten times the frequency of the input AC power supplied at input terminals 140 and 150. For example, capacitor 220 may have a value of approximately 4 uF and capacitor 245 may have a value of approximately 0.44 uF. Likewise, inductor 230 may have a value of approximately 100 uH. Of course, these are just example values. Thus, depending on the particular embodiment, a variety of factors may play into the selection of components, such as filtering the 50 to 60 Hz AC input current to reduce the AC ripple current component, filtering conducted emissions to reduce any potential injection into the AC power source. In general, for this particular embodiment, it is desirable to choose component values that are substantially in accordance with the following relationship:
1/(2π((L1C1){circumflex over ( )}1/2))<f<1/(2π((LTCP){circumflex over ( )}1/2)) [2 ]
where LT refers to the inductance of transformer 110 and the other values are defined in
In cases where the power transfer may be limited by the switch frequency becoming nearly equal to the resonant frequency of Cp and LT, the value of Cp may likewise be adjusted to increase the energy transferred on a switch transition. For example, increasing Cp by a factor of 2 may double the energy transferred with a switch transition, although this occurs at the cost of decreasing the allowable switch frequency by a factor of 1/(square root of 2). After applying relationship [1], however, the end result is an increase by a factor of the square root of two (or approximately 1.414) in the power that the converter can transfer.
Referring again to
In this particular embodiment, an optical-electronic-isolation system is employed to provide a feedback signal, although, of course, many other mechanisms may be employed to provide feedback and remain within the scope of the claimed subject matter, such as, for example, as described in connection with
Embodiment 100 of
Assuming that drive circuitry 170 applies a drive signal to gate drive transformer 180, transistors 122 and 124, here MOSFETs, turn on and conduct current while transistors 132 and 134 are turned off and are in a nonconductive state. As a result, charge pump capacitor 160 charges with an assumed positive charge at junction 125. Capacitor 160 and the inductance of transformer 110 form a resonant system such that the current flowing through 160 and primary winding 290 smoothly resonates in a sinusoidal fashion until capacitor 160 is fully charged. Current flows through primary winding and the magnetic circuit of transformer 110 results in current flowing in secondary winding 295.
Drive circuitry 170 is designed so that after the drive signal to gate drive transformer 180 is no longer applied, a delay of approximately 100 nanoseconds (ns) is applied before a drive signal is applied to drive transistors 132 and 134 of configuration 130. This delay is commonly referred to as a “blanking interval.” The delay reduces the risk of energizing configuration 130 before current has stopped flowing in configuration 120. Another blanking interval is applied after turning off configuration 130 and before turning on configuration 120. It is noted that there are many different mechanisms to create the blanking interval or a time delay, and the claimed subject matter is not limited to any particular approach. For example, an RC circuit may be employed or, alternatively, a digital delay might be employed, to provide only a few examples.
Once configuration 130 is energized a resonant current starts reverse flow through capacitor 160 and primary winding 290. Capacitor 160 and the inductance of transformer 110 are again a resonant system such that the current flowing through 160 and primary winding 290 smoothly resonates in a sinusoidal fashion until capacitor 160 is fully discharged. Reverse current flow through primary winding 290 of the magnetic circuit of transformer 110 results in a reverse current flowing in secondary winding 295. In this case, a current is flowing out of dot 291 which induces a current to flow into dots 292 and 293. Diode 301 now inhibits a current flow into dot 292 while diode 303 allows a current flow into dot 293, thus, transferring energy to the bulk storage capacitor 240.
The previously described embodiment provides a variety of advantages, although the claimed subject matter is not necessarily limited in scope to embodiments that have these advantages. This particular embodiment, for example, allows direct AC to DC power conversion without rectification on the AC primary side of the system and yields a power transfer that is at least substantially a linear function of drive frequency. This embodiment also allows the transistors to be turned on and off at substantially zero current, thus reducing the switch losses and improving power converter efficiency. Furthermore, the topology of the design reduces AC current harmonics by selecting f substantially in accordance with relationship [2] and provides a near unity power factor for reasonable loads without the cost, circuit complexity, and/or power loss of additional power factor correction circuitry. Likewise, the elimination of primary rectification and the use of substantially zero-current transistor switching rather than hard switching reduce radiated emissions and conducted emissions, which may be the subject of regulatory limits in some situations.
As implied by relationship [2] above, it may be desirable to select the switching frequency to be lower than that of the resonant frequency of the charge pump capacitor and the inductance of the isolation transformer, although the claimed subject matter is not limited in scope in this respect. Damping in this particular embodiment is relatively high which allows the converter switching frequency to range from a relatively low frequency, such as 10 kHz up to near the resonant frequency. For this embodiment, power transfer is substantially a linear function of frequency given by relationship [1], previously provided and repeated below:
P=½ C V2 f [1]
where, here, P is power, C is now the value of charge pump capacitance 160, V is the RMS voltage of the power source applied to terminals 140 and 150 of the power converter and f is the switching frequency of the power converter.
For example, an embodiment of an AC-DC converter, such as previously described, as one example, may be employed as demonstrated in
In the preceding description, various aspects of the claimed subject matter have been described. For purposes of explanation, specific numbers, systems and/or configurations were set forth to provide a thorough understanding of the claimed subject matter. However, it should be apparent to one skilled in the art having the benefit of this disclosure that the claimed subject matter may be practiced without the specific details. In other instances, well-known features were omitted and/or simplified so as not to obscure the claimed subject matter. While certain features have been illustrated and/or described herein, many modifications, substitutions, changes and/or equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and/or changes as fall within the true spirit of the claimed subject matter.
