Patent Application
20140153290
1. Field
The disclosed concept pertains generally to direct current to direct current (DC/DC) converters and, more particularly, to DC/DC converters with variable output ranges.
2. Background Information
A DC/DC converter is configured to receive an input direct current (DC) voltage and convert it into one or more output DC voltages. In many applications, such as electric vehicle chargers, a DC/DC converter must be able to provide a relatively wide output voltage range. For example, the electric vehicle charging voltage range required by the US SAE is 200-450 VDC.
One type of DC/DC converter is an LLC resonant converter. LLC resonant converters provide high efficiency, low levels of EMI emissions, high power density, and low cost. However, in prior LLC resonant converter designs, increasing the output voltage range detrimentally affects the efficiency of the LLC resonant converter by causing a larger shunt current in the primary side, thus increasing conduction loss.
Some prior LLC resonant converter designs have obtained a wider output range. In one prior configuration, a buck stage is added after the LLC stage, thus allowing a wider output voltage range. However, adding a buck stage increases the cost of the LLC resonant converter.
Another prior LLC resonant converter configuration is shown in
The secondary winding of the transformer 30 includes a common tap 31, two primary taps 32,32′ electrically connected to a primary rectifier circuit 40, and two secondary taps 33,33′ electrically connected to a secondary rectifier circuit 41. The LLC resonant converter also includes a switch 50 which is electrically connected to the secondary rectifier circuit 41. Closing the switch 50 allows current to flow through the secondary rectifier circuit 41, thus increasing the output voltage VOUT of the LLC resonant converter. The LLC resonant converter also includes a filtering capacitor 60 electrically connected across its output terminals.
While the secondary rectifier circuit 41 and switch 50 provide an extended output voltage range to the LLC resonant converter configuration of
Another prior LLC resonant converter configuration is shown in
The secondary winding of the transformer 130 includes a primary tap 131 and a secondary tap 132. A switch 150 is configured to electrically connect a rectifier circuit 140 to either the primary tap 131 or the secondary tap 132 of the secondary winding of the transformer 130, thereby changing the turns ratio of the transformer 130 and the output voltage VOUT. The LLC resonant converter also includes a filtering capacitor 160 electrically connected across its output terminals.
While the secondary tap 132 and switch 150 extend the output voltage range of the LLC resonant converter configuration of
There is room for improvement in DC/DC converters.
These needs and others are met by embodiments of the disclosed concept in which a DC/DC converter includes a switch which is generally operable to electrically connect and disconnect a tap of a transformer and a rectifier circuit.
In accordance with aspects of the disclosed concept, a DC/DC converter configured to receive an input voltage and to output an output voltage comprises: a bridge circuit configured to receive the input voltage and including at least one pair of power switches; a resonant network driven by the bridge circuit; a transformer having a primary winding electrically connected to the resonant network and a secondary winding having a plurality of taps including a common tap, a first tap, and a second tap; a plurality of rectifier circuits configured to output the output voltage, the rectifier circuits including a first rectifier circuit electrically connected to the common tap, a second rectifier circuit electrically connected to the first tap, and a third rectifier circuit electrically connectable to the second tap; a switch electrically connected between the second tap and the third rectifier circuit, wherein the switch is operable to electrically connect and disconnect the third rectifier circuit from the second tap; and a control unit configured to control switching of the at least one pair of power switches.
Also in accordance with aspects of the disclosed concept, a DC/DC converter configured to receive an input voltage and to output an output voltage comprises: a bridge circuit configured to receive the input voltage and including at least one pair of power switches; a resonant network driven by the bridge circuit; a transformer having a primary winding electrically connected to the resonant network and a secondary winding having a plurality of taps including a common tap, a first tap, and a number of additional taps; a plurality of rectifier circuits configured to output the output voltage, the rectifier circuits including a first rectifier circuit electrically connected to the common tap, a second rectifier circuit electrically connected to the first tap, and a number of additional rectifier circuits electrically connectable to the number of additional taps, respectively; a number of switches electrically connected between the number of additional taps and the number of additional rectifier circuits, respectively, wherein the number of switches are operable to selectively electrically connect and disconnect the number of additional rectifier circuits from the number of additional taps; and a control unit configured to control switching of the at least one pair of power switches.
A full understanding of the disclosed concept can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
Directional phrases used herein, such as, for example, left, right, front, back, top, bottom and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein.
As employed herein, the statement that two or more parts are “coupled” together shall mean that the parts are joined together either directly or joined through one or more intermediate parts.
As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality).
As employed herein, the statement that a component is on the “primary side of the DC/DC converter” and similar statements shall mean that the component is electrically connected, either directly or indirectly, to the primary winding of a transformer included in the DC/DC converter.
As employed herein, the statement that a component is on the “secondary side of the DC/DC converter” and similar statements shall mean that the component is electrically connected, either directly or indirectly, to the secondary winding of a transformer included in the DC/DC converter.
As employed herein, the term “switch” means any switch suitable for use in an electrical circuit. The term includes both mechanical type switches (e.g., without limitation, switches which physically separate contacts of the switch) and solid-state type switches (e.g., without limitation, transistors).
Referring to
Transformer 230 has primary and secondary windings. The primary winding of the transformer 230 is electrically connected to the resonant network 220. The transformer 230 has a magnetic inductance component. The magnetic inductance component may be caused by, for example and without limitation, a ferromagnetic core (not shown) of the transformer 230. The transformer 230 isolates the primary and secondary sides of the DC/DC converter 1 from each other.
The secondary winding of the transformer 230 includes three taps. The common tap 231 is electrically connected to a first rectifier circuit 240 and the first tap 232 is electrically connected to a second rectifier circuit 241. The second tap 233 is electrically connected to a first side of a switch 250. A second side of the switch 250 is electrically connected to a third rectifier circuit 242. The output voltage VOUT of the DC/DC converter 1 is provided on the secondary side of the DC/DC converter 1. Additionally, a filtering capacitor 260 is electrically connected between the output terminals of the DC/DC converter to smooth the output voltage VOUT.
The first rectifier circuit 240 includes first and second diodes 243,244. The first diode 243 is electrically connected between the common tap 231 of the transformer 230 and the positive output terminal of the DC/DC converter 1. The second diode 244 is electrically connected between the negative output terminal of the DC/DC converter 1 and the common tap 231 of the transformer 230.
The second rectifier circuit 241 includes first and second diodes 245,246. The first diode 245 is electrically connected between the first tap 232 of the transformer 230 and the positive output terminal of the DC/DC converter 1. The second diode 246 is electrically connected between the negative output terminal of the DC/DC converter 1 and the first tap 232 of the transformer 230.
The third rectifier circuit 242 includes first and second diodes 247,248. The first diode 247 is electrically connected between the second tap 233 of the transformer 230 and the positive output terminal of the DC/DC converter 1 when the switch 250 is closed. The second diode 248 is electrically connected between the negative output terminal of the DC/DC converter 1 and the second tap 233 of the transformer 230 when the switch 250 is closed.
The control unit 280 senses the output voltage VOUT of the DC/DC converter 1 and controls the switching of the power switches 211,212,213,214 in the full-bridge circuit 210. Changing the frequency at which the power switches 211,212,213,214 are switched adjusts the output voltage VOUT. However, adjusting the frequency at which the power switches 211,212,213,214 are switched also affects the efficiency of the DC/DC converter 1. As such, it is desirable to switch the power switches 211,212,213,214 at an optimally efficient frequency as much as possible.
The control unit 280 can also control a transition of the switch 250. Generally, the control unit 280 controls the frequency at which the power switches 211,212,213,214 are switched based on feedback from the output voltage VOUT. However, the transition of the switch 250 can cause a spike in the output voltage VOUT faster than the control unit 280 can sense the change in the output voltage VOUT and responsively adjust the frequency at which the switches 211,212,213,214 are switched. To prevent the voltage spike and provide a smoother output voltage during transitions of the switch 250, the control unit 280 can simultaneously control the transition of the switch 250 and adjust the frequency at which the power switches 211,212,213,214 are switched to account for the transition of the switch 250.
Referring to
In both the DC/DC converters 1,1′ shown in
Referring now to
Referring to
In
In
In
Referring to
The DC/DC converters 1,1′,2 of
Additionally, it is contemplated that the primary sides of the DC/DC converters 1,1′,2 can be structured as series resonant converters (e.g., without limitation, the resonant network 220 includes an inductor in series with a capacitor), parallel resonant converters (e.g., without limitation, the resonant network 220 includes an inductor and capacitor in parallel with the primary winding of the transformer 230), or series parallel resonant converters (e.g., without limitation, the resonant network 220 includes an inductor in series with a capacitor and a capacitor in parallel with the primary winding of the transformer 230) without departing from the scope of the disclosed concept.
While specific embodiments of the disclosed concept have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof.
