Patent Application
20160181932
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2014-255549, filed on Dec. 17, 2014, the entire contents of which are incorporated herein by reference.
The present disclosure relates to a DC/DC converter.
A variety of home appliances such as televisions and refrigerators are operated with commercial AC power supplied from the outside. Electronic devices such as laptop computers, mobile phone terminals and tablet terminals can be also operated with the commercial AC power, or their internal batteries can be charged with the commercial AC power. Such home appliances and electronic devices (hereinafter collectively referred to as electronic devices) contain a power supply device such as an AC/DC converter for converting a commercial AC (alternating current) voltage to a DC (direct current) voltage. Alternatively, in some cases, an AC/DC converter may be incorporated in external power supply adaptors (AC adaptors) of electronic devices.
A commercial AC voltage VAC is input to the filter 102 via a fuse and an input capacitor (not shown). The filter 102 removes a noise from the commercial AC voltage VAC. The rectification circuit 104 is a diode bridge circuit for full-wave rectifying the commercial AC voltage VAC. An output voltage of the rectification circuit 104 is converted to a DC voltage VIN by being smoothed by the smoothing capacitor 106.
The isolated DC/DC converter 200r receives the DC voltage VIN input at its input terminal P1 to drop the DC voltage VIN down, and supplies an output voltage VOUT, which is stabilized at a target value, to a load (not shown) connected to its output terminal P2.
The DC/DC converter 200r includes a primary side controller 202, a photo coupler 204, a shunt regulator 206, an output circuit 210 and other circuit components. The output circuit 210 includes a transformer T1, a diode D1, an output capacitor C1 and a switching transistor M1. The topology of the output circuit 210 is the same as that of a typical flyback converter and therefore will not be explained for the sake of brevity.
As the switching transistor M1 connected to the primary winding W1 of the transformer T1 is switched, the input voltage VIN is dropped down to generate the output voltage VOUT. The primary side controller 202 stabilizes the output voltage VOUT at a target value by adjusting a duty ratio of switching of the switching transistor M1.
The output voltage VOUT of the DC/DC converter 200r is divided by resistors R1 and R2. The shunt regulator 206 amplifies an error between the divided voltage (voltage detection signal) Vs and a predetermined reference voltage VREF (not shown), and pulls up an error current IERR corresponding to the error from a light emitting element (light emitting diode) at the input side of the photo coupler 204 (sink).
A feedback current IFB corresponding to the error current IERR at a secondary side is flown into a light receiving element (phototransistor) at the output side of the photo coupler 204. The feedback current IFB is smoothed by a resistor and a capacitor and is input to a feedback (FB) terminal of the primary side controller 202. The primary side controller 202 adjusts the duty cycle of the switching transistor M1 based on a voltage (feedback voltage) VFB of the FB terminal.
From a recent demand for energy saving, there is a desire to reduce the power consumption of the AC/DC converter 100r in light load or no-load conditions (also referred to as a waiting state or standby state) as much as possible. To meet this demand, the DC/DC converter 200r is operated in a so-called burst mode (also referred to as a PFM mode) during the standby period. In the burst mode, the primary side controller 202 switches the switching transistor M1 once or more, raises the output voltage VOUT up to the target level, and then stops the switching of the switching transistor M1 until the output voltage VOUT is reduced to a lower limit level determined in accordance with the target level. As such, the power required to switch the switching transistor M1 (for example, power required to charge/discharge the gate capacitance of the switching transistor M1) is reduced, and thereby the efficiency thereof is increased.
The present inventors have reviewed the AC/DC converter 100r of
Since the output voltage VOUT is maintained to be higher than the target level for most of the period during which the DC/DC converter 200r is operating in the burst mode, the error current IERR flowing through the input side of the photo coupler 204 is increased and the current IFB flowing through the output side of the photo coupler 204 is also increased accordingly. These currents IERR and IFB are a loss which decreases the efficiency of the AC/DC converter 100r.
One exemplary objective of the present disclosure is to provide some embodiments of a DC/DC converter which is capable of reducing power consumption during the standby period.
According to one embodiment of the present disclosure, there is provided an isolated DC/DC converter including: a transformer having a primary winding and a secondary winding; a switching transistor connected to the primary winding of the transformer; a rectification element connected to the secondary winding of the transformer; a photo coupler; a feedback amplifier connected to the input side of the photo coupler and configured to generate an error current which increases as an output voltage of the DC/DC converter decreases; a primary side controller having a feedback terminal and configured to switch the switching transistor with a larger duty ratio as a voltage of the feedback terminal becomes higher; and a non-inversion type feedback circuit connected to the output side of the photo coupler and the feedback terminal and configured to raise the voltage of the feedback terminal as a feedback current flowing through the output side of the photo coupler increases.
According to this embodiment, it is possible to reduce the currents respectively flowing through the input and output sides of the photo coupler in the standby state (light or no load conditions) operating in the burst mode, and thereby increase the efficiency.
The non-inversion type feedback circuit may include a resistor positioned between the feedback terminal and a ground. The photo coupler may be connected to the feedback terminal such that the photo coupler sources the feedback current.
The rectification element may include a synchronous rectification transistor. The DC/DC converter may further include a synchronous rectification controller which controls the synchronous rectification transistor.
The DC/DC converter may be of a flyback type or a forward type.
According to another embodiment of the present disclosure, there is provided a power supply (AC/DC converter) including: a filter configured to filter a commercial AC voltage; a diode rectification circuit configured to full-wave rectify an output voltage of the filter; a smoothing capacitor configured to generate a DC input voltage by smoothing an output voltage of the diode rectification circuit; and the above-described DC/DC converter configured to drop down the DC input voltage and supply the dropped-down voltage to a load.
According to another embodiment of the present disclosure, there is provided an electronic device including: a load; a filter configured to filter a commercial AC voltage; a diode rectification circuit configured to full-wave rectify an output voltage of the filter; a smoothing capacitor configured to generate a DC input voltage by smoothing an output voltage of the diode rectification circuit; and the above-described DC/DC converter configured to drop down the DC input voltage and supply the dropped-down voltage to the load.
According to another embodiment of the present disclosure, there is provided an AC adaptor including: a filter configured to filter a commercial AC voltage; a diode rectification circuit configured to full-wave rectify an output voltage of the filter; a smoothing capacitor configured to generate a DC input voltage by smoothing an output voltage of the diode rectification circuit; and the above-described DC/DC converter configured to drop down the DC input voltage to generate a DC output voltage.
According to another embodiment of the present disclosure, there is provided a feedback amplifier integrated circuit disposed at the secondary side of an isolated DC/DC converter. The isolated DC/DC converter includes: a transformer having a primary winding and a secondary winding; a switching transistor connected to the primary winding of the transformer; a rectification element connected to the secondary winding of the transformer; a photo coupler; a primary side controller which has a feedback terminal and switches the switching transistor with a duty ratio corresponding to a voltage of the feedback terminal; a non-inversion type feedback circuit which is connected to the feedback terminal and configured to raise the voltage of the feedback terminal as a feedback current flowing through the output side of the photo coupler increases; and the feedback amplifier integrated circuit. The feedback amplifier integrated circuit includes: an output terminal connected to the input side of the photo coupler; an input terminal which receives a detection signal corresponding to an output voltage of the DC/DC converter; a ground terminal; a reference voltage source which generates a reference voltage; a differential amplifier having a non-inverted input terminal to which the detection signal is input, and an inverted input terminal to which the reference voltage is input; and an output transistor having a control terminal connected to an output of the differential amplifier, a first terminal connected to the output terminal, and a second terminal connected to the ground terminal. The feedback amplifier integrated circuit is packaged into a single module.
Any combinations of the above-described elements or any modifications to the representations of the present disclosure between methods, apparatuses and systems are effective as embodiments of the present disclosure.
Preferred embodiments of the present invention will now be described in detail with reference to the drawings. Throughout the drawings, the same or similar elements, members and processes are denoted by the same reference numerals and explanation of which may not be repeated. The disclosed embodiments are provided for the purpose of illustration, not limitation, of the present disclosure and all features and combinations thereof described in the embodiments cannot be necessarily construed to describe the substance of the present disclosure.
In the specification, the phrase “connection of a member A and a member B” is intended to include direct physical connection of the member A and the member B as well as indirect connection thereof via other member as long as the other member has no substantial effect on the electrical connection of the member A and the member B. Similarly, the phrase “interposition of a member C between a member A and a member B” is intended to include direct connection of the member A and the member C or direct connection of the member B and the member C as well as indirect connection thereof via other member as long as the other member has no substantial effect on the electrical connection of the member A, the member B and the member C.
The isolated DC/DC converter 200 includes a primary side controller 202, a photo coupler 204, an output circuit 210, a non-inversion type feedback circuit 208, a synchronous rectification controller 300 and a feedback amplifier IC (Integrated Circuit) 400. The output circuit 210 has a flyback synchronous rectification type topology and includes transformer T1, a switching transistor M1, a synchronous rectification transistor M2 and an output capacitor C1. In this embodiment, the synchronous rectification transistor M2 is placed at a side with higher potential (output terminal P2 side) than a secondary winding W2 of the transformer T1.
A circuit consisting of an auxiliary winding W4 of the transformer T1, a diode D4 and a capacitor C4 generates an external power supply voltage VCC1 based on the source of the synchronous rectification transistor M2. The synchronous rectification controller 300 is placed at the secondary side of the DC/DC converter 200 and switches the synchronous rectification transistor M2. The external power supply voltage VCC1 is supplied to a power supply (VCC) terminal of the synchronous rectification controller 300. A ground (GND) terminal of the synchronous rectification controller 300 is connected with the source of the synchronous rectification transistor M2. A drain voltage VD of the synchronous rectification transistor M2 is input to a VD terminal of the synchronous rectification controller 300. The gate of the synchronous rectification transistor M2 is connected to an OUT terminal thereof. The synchronous rectification transistor M2 may be embedded in the synchronous rectification controller 300.
The control scheme of the synchronous rectification transistor M2 by the synchronous rectification controller 300 is not particularly limited. For example, the synchronous rectification controller 300 may generate a pulse signal at least based on a voltage across the synchronous rectification transistor M2, i.e., a voltage VDS between a drain and a source, and may switch the synchronous rectification transistor M2 based on the pulse signal.
More specifically, the synchronous rectification controller 300 can generate the pulse signal based on the voltage VDS between the drain and a source and two negative threshold voltages VTH1 and VTH2 (VTH1<VTH2<0V). For example, VTH1 may be −50 mV and VTH2 may be −10 mV. If the drain-source voltage VDS is lower than the first negative threshold voltage VTH1, the synchronous rectification controller 300 sets the pulse signal to a level that instructs to turn on the synchronous rectification transistor M2 (ON level, e.g., high level), and then sets the pulse signal to a level that instructs to turn off the synchronous rectification transistor M2 (OFF level, e.g., low level) if the drain-source voltage VDS is higher than the second negative threshold voltage VTH2. A drive circuit drives the synchronous rectification transistor M2 based on the pulse signal generated as discussed above.
The feedback amplifier IC (Integrated Circuit) 400 is placed at the secondary side of the DC/DC converter 200, generates an error current IERR in response to an output voltage VOUT, and supplies it to the primary side controller 202 via the photo coupler 204. The feedback amplifier IC 400 includes an error amplifier 410, a diode D2 and a reference voltage source 416, and is packaged into a single module.
A voltage detection signal VS corresponding to the output voltage VOUT is input to a VO terminal of the feedback amplifier IC 400. A GND terminal thereof is connected to a ground line at the secondary side of the transformer T1. A cathode of a light emitting element (light emitting diode) at the input side of the photo coupler 204 is connected to a photo coupler connection (PC) terminal.
The reference voltage source 416 generates a reference voltage VREF. The error amplifier 410 amplifies an error between the voltage detection signal VS corresponding to the output voltage VOUT of the DC/DC converter 200 and the target voltage VREF, and draws the error current IERR corresponding to the error from the photo coupler 204 via the PC terminal (sink).
In this embodiment, the feedback amplifier IC 400 increases the error current IERR as the output voltage VOUT of the DC/DC converter 200 decreases, i.e., as the voltage detection signal VS decreases. That is, it performs the operation opposite to the shunt regulator 206 of the AC/DC converter 100r shown in
The error amplifier 410 has an output stage of an open collector or open drain type, and includes an output transistor 412 and a differential amplifier 414. The differential amplifier 414 receives the voltage detection signal VS at its inverted input terminal (−) and the reference voltage VREF at its non-inverted input terminal (+). The collector (or drain) of the transistor 412 at the output stage is connected to the PC terminal, and the emitter (or source) thereof is connected to the GND terminal. A control terminal (base or gate) of the output transistor 412 is connected to an output of the differential amplifier 414. A base current or gate voltage of the transistor 412 is adjusted by the output of the differential amplifier 414 corresponding to the error between the voltage detection signal VS and the reference voltage VREF. With this configuration, the error current IERR flowing through the output transistor 412 decreases as the voltage detection signal VS becomes higher.
Although it is illustrated in this embodiment where the diode D2 is placed between the collector of the transistor 412 and the PC terminal for the purpose of circuit protection or voltage level shift, the diode D2 may be omitted in other embodiments.
The shunt regulator 206 shown in
The primary side controller 202 has a feedback (FB) terminal, and switches the switching transistor M1 with a larger duty ratio as a voltage VFB of the FB terminal becomes higher. The primary side controller 202 may be implemented with techniques commonly known in the art and the configuration thereof is not particularly limited.
The non-inversion type feedback circuit 208 is connected to the output side of the photo coupler 204 and the FB terminal of the primary side controller 202. The non-inversion type feedback circuit 208 raises the voltage VFB of the FB terminal as the feedback current IFB flowing through the output side of the photo coupler 204 increases.
When the feedback current IFB flowing through the output side of the photo coupler 204 increases, the capacitor C11 is charged, the voltage drop of the feedback resistor R11 increases and the feedback voltage VFB increases accordingly.
The primary side controller 202 includes a duty controller 220 and a driver 222. The duty controller 220 generates a pulse signal SPWM having a duty ratio corresponding to the feedback voltage VFB. The duty controller 220 may be constituted by, but is not limited to, a voltage mode or current mode modulator. The duty controller 220 is configured to be operated in a burst mode under no-load or light load conditions where a load current of the DC/DC converter 200 is substantially zero or very small. The driver 222 switches the switching transistor M1 based on the pulse signal SPWM. The primary side controller 202 may include a resistor R12 for discharging charges of the capacitor C11. Alternatively, the resistor R12 may be externally attached to the primary side controller 202 and may be a part of the non-inversion type feedback circuit 208.
The non-inversion type feedback circuit 208 shown in
It should be understood by those skilled in the art that any configurations of the non-inversion type feedback circuit 208 other than the circuit illustrated herein can be implemented to perform the same function.
The configuration of the DC/DC converter 200 has been described above. Subsequently, the operations thereof will be described.
When the voltage detection signal VS becomes higher than the reference voltage VREF, the current IERR drawn by the output transistor 412 decreases and the current IFB of the light receiving element (phototransistor) at the output side of the photo coupler 204 decreases accordingly. At this time, since the feedback voltage VFB is reduced by the non-inversion type feedback circuit 208, the duty ratio (ON time) of the switching transistor M1 is reduced and a feedback is applied in such a way that the voltage detection signal VS approaches (i.e., is reduced) to the reference voltage VREF.
Conversely, when the voltage detection signal VS becomes lower than the reference voltage VREF, the current IERR drawn by the output transistor 412 increases and the current IFB of the light receiving element increases accordingly. Since the feedback voltage VFB increases at this time, the duty ratio of the switching transistor M1 is increased and a feedback is applied in such a way that the voltage detection signal VS approaches (i.e., is increased) to the reference voltage VREF. In this way, the output voltage VOUT of the DC/DC converter 200 is stabilized at its target level.
As described above, when the DC/DC converter 200 is in the light load or no load conditions, the primary side controller 202 operates in the burst mode. In the burst mode, the switching transistor M1 is turned on once or more to increase the output voltage VOUT, and then, the output capacitor C1 is discharged by a small load current or a leak current and the switching is stopped until the output voltage VOUT is reduced to the target level.
In other words, in the standby period during which the DC/DC converter 200 operates in the burst mode, the output voltage VOUT is maintained to be relatively higher than that in the normal switching operation. In the DC/DC converter 200 shown in
Specifically, in cases where the DC/DC converter 200r shown in
Therefore, it is possible to significantly reduce the power consumption of the DC/DC converter 200 during the standby period as compared to that in
The DC/DC converter 200A will be described such that the descriptions mainly focus on its differences from the DC/DC converter 200 shown in
The isolated DC/DC converter 200A includes an inversion type primary side controller 202A, a photo coupler 204, an output circuit 210, a synchronous rectification controller 300 and a feedback amplifier IC 400.
The feedback amplifier IC 400 generates an error current IERR corresponding to an output voltage VOUT and supplies it to the primary side controller 202A via the photo coupler 204, in the same manner as shown in
The feedback current IFB flowing through a phototransistor of the photo coupler 204 is converted to a feedback voltage VFB by an inversion type feedback circuit 209. The inversion type feedback circuit 209 may have, for example, the same configuration as that in
A FB# terminal of the primary side controller 202A has the opposite polarity to the FB terminal of the primary side controller 202 shown in
The inversion type duty controller 221 generates a pulse signal SPWM# with a larger time ratio of low level as the feedback voltage VFB becomes higher. The driver 222 drives the switching transistor M1 based on the pulse signal SPWM#.
The inversion type duty controller 221 shown in
The inversion type duty controller 221 shown in
The primary side controller 202A shown in
It should be understood by those skilled in the art that any configurations of the inversion type primary side controller 202A other than the circuit illustrated herein can be implemented to perform the same function.
The configuration of the DC/DC converter 200A has been described as above. The DC/DC converter 200A as above, as in the first embodiment, may significantly reduce the power consumption of the DC/DC converter 200A during the standby period as compared to that of
Subsequently, the use of the DC/DC converter 200 described in the first or second embodiment will be described.
The present disclosure describes some embodiments as above. The disclosed embodiments are exemplary, and thus, it should be understood by those skilled in the art that various modifications to combinations of the elements or processes above may be made and such modifications will also fall within the scope of the present disclosure. Some exemplary modifications will be described below.
The synchronous rectification transistor M2 may be provided at the ground side rather than the secondary winding W2. In this case, the power supply voltage of the synchronous rectification controller 300 may be taken from the output voltage VOUT and the ground voltage thereof may be the ground voltage of the DC/DC converter 200. Further, in this case, the synchronous rectification transistor M2 may be incorporated in the synchronous rectification controller 300
Although the DC/DC converter 200 of the synchronous rectification type has been described in the above embodiments, the present disclosure is not limited thereto but may be applied to a diode rectification type DC/DC converter 200 as well.
The synchronous rectification controller 300 and the feedback amplifier IC 400 may be modularized into a single package.
Although the flyback converter has been described in the above embodiments, the present disclosure may be applied to a forward converter as well. In this case, a plurality of synchronous rectification transistors is disposed at the secondary side of the transformer T1. In the synchronous rectification controller, the drive circuit 302, which is configured to switch the plurality of synchronous rectification transistors, and the error amplifier 410 are modularized into a single package. Alternatively, a plurality of synchronous rectification controllers shown in
At least one of the switching transistor and the synchronous rectification transistor may be a bipolar transistor or an IGBT.
According to some embodiments of the present disclosure, it is possible to provide a DC/DC converter which is capable of reducing power consumption during a standby period.
While certain embodiments have been described using specific languages, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosures. Indeed, the novel methods and apparatuses described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the disclosures. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosures.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-255549 | Dec 2014 | JP | national |
