Switching power supply and method for controlling switching power supply

A switching power supply and a method for controlling the switching power supply, the switching power supply includes: an input power supply, a front-stage circuit which includes a first inductor and at least two switch devices, and a post-stage isolated circuit which includes a primary-side switch circuit, a transformer and a secondary-side rectification circuit. One end of the first switch device is connected to a positive electrode of the input power supply, one end of the second switch device and an input-end of the first inductor are jointly connected to another end of the first switch device, another end of the second switch device is connected to a negative electrode of the input power supply, an output-end of the first inductor is connected to the primary-side switch circuit of post-stage isolated circuit, and another end of the primary-side switch circuit is connected to another end of the second switch device.

TECHNICAL FIELD

The present document relates to the field of electronic technique, and especially, to a switching power supply and a method for controlling the switching power supply.

BACKGROUND OF THE RELATED ART

In the power supply architecture of the existing communication systems, due to the consideration of security and efficiency, an isolated Intermediate Bus Architecture IBA is extensively applied. In the architecture, the input voltage of the system is firstly converted into an intermediate voltage through an isolated Intermediate Bus Converter IBC, and then the intermediate voltage is converted into a voltage required by a load circuit through multiple post-stage non-isolated power supplies.

In order to adapt to different systems, an intermediate bus power supply is always required to adapt to a wider input voltage, in the case of processing a certain power, a power device thereof is required to simultaneously meet a high voltage stress, and a large current stress during low voltage input, therefore it is difficult to optimize the device selection. With regard to a common input voltage range 36˜75V of the communication systems, the power device is required to select a margin at least twice the rated power. Meanwhile, the power device as the bus power supply is required to process all power demands of one system, thus efficiency is also a foremost index, but selecting a device with a larger power margin always leads to lower efficiency and enlarges a power supply volume, which affects a power density index.

In the related art as shown inFIG. 1, a traditional switching power supply structure with voltage transformation is implemented with the Pulse Width Modulation PWM technology. When the input voltage range is wider, the pulse width duty ratio is varied greatly, so that energy storage elements such as an inductance and so on are required to constantly store and release more energy in the voltage conversion process, which causing that both volume and loss of the energy storage elements increase. The wide input voltage range also makes the power device need to simultaneously tolerate the high voltage stress during high voltage input and the large current stress during low voltage input, therefore, it is required to select a power device with a power much greater than the actual output power, which results in that both volume and loss of the power device increase. Therefore, the traditional switching power supply structure will lead to a problem of efficiency reduction and power density decline in the wide input voltage range.

In order to solve the problem of stress margin increase of the power device brought by the wide range of input voltage, a common scheme dealing with that is a two-stage structure as shown inFIG. 2, a non-isolated voltage stabilizing front-stage circuit and a transformer isolated post-stage circuit are included, so that the post stage is only required to deal with the fixed input voltage by the front-stage voltage stabilizing circuit, which avoids the stress problem brought by the wide input voltage range. However, the scheme does not solve the problem of larger variation of the front-stage duty ratio brought by the wide input voltage range. With regard to the buck switching power supply, the efficiency and the volume of energy storage elements can be optimal when the duty ratio is maximum, which correspondingly in such structure when the input voltage is lowest such as 36V but not the rated operational voltage. Therefore, both efficiency and volume cannot be optimal when the system is at the rated operational voltage such as 48V.

In order to deal with the problem of larger variation of the duty ratio brought by the wide range of input voltage, in the non-isolated switching power supply, the output non-inverting Buck-Boost topology as shown inFIG. 3is usually adopted to effectively solve the problem, and it is widely applied to battery-powered terminal devices without isolation requirements. In the topology, the output voltage may be set as an intermediate value. When the input voltage is higher than a set value of the output value, the circuit works in a Buck mode. When the input voltage is lower than the set value of the output value, the circuit works in a Boost mode. Therefore, the duty ratio variation range may be halved.

The related art shown inFIG. 4is a schematic diagram of the Buck-Boost topology added with an isolation function, an isolation part thereof is implemented by a traditional buck bridge circuit or other resonance circuits such as Logical Link Control circuit and so on. The circuit may achieve the advantage of narrow duty ratio variation range of the non-isolated Buck-Boost mentioned above, and meanwhile, the post-stage isolated circuit is also not required to deal with the stress problem of the power device brought by the wide range of input voltage, which is an application with higher efficiency in the related art.

But the technology is substantially equivalent to a composition of Buck+Boost+bridge isolated three-stage circuits, and a main application thereof is an isolated post stage with multiple different transformation ratios to form the division-ratio power supply architecture with various voltage outputs, and it employs relatively more power devices, which causes that the volume increase is greater when the power devices are used as a single power supply, and the power density is not high.

Therefore, the post-stage bridge circuit only plays a role of isolation or buck in the related art, but brings the problem of wide duty ratio variation range and low efficiency or many power devices and lager volume.

SUMMARY

The embodiments of the present document provide a switching power supply and a method for controlling the switching power supply, to solve the problem of wide duty ratio variation range and low efficiency or many power devices and lager volume brought as the post-stage bridge circuit only plays a role of isolation or buck in the related art.

In order to solve the above technical problem, on the one hand, the embodiment of the present document provides a switching power supply, which includes: an input power supply, a front-stage circuit and a post-stage isolated circuit; herein, the front-stage circuit includes: a first inductor and at least two switch devices—a first switch device and a second switch device; and the post-stage isolated circuit includes: a primary-side switch circuit, a transformer and a secondary-side rectification circuit;

herein, one end of the first switch device is connected to a positive electrode of the input power supply, one end of the second switch device and an input end of the first inductor are jointly connected to another end of the first switch device, another end of the second switch device is connected to a negative electrode of the input power supply, an output end of the first inductor is connected to the primary-side switch circuit of the post-stage isolated circuit, and another end of the primary-side switch circuit is connected to another end of the second switch device.

Alternatively, the primary-side switch circuit includes: at least two switch devices, herein, switched-on of one switch device or switched-on of a combination switch containing the one switch device makes the first inductor connected to a charging state, switched-off of another switch device or switched-off of a combination switch containing another switch device makes energy in the first inductor transferred to the secondary-side rectification circuit via the transformer.

Alternatively, said switched-on of one switch device or switched-on of a combination switch containing the one switch device makes the first inductor connected to a charging state, in order to connect the output end of the first inductor to a negative end of the input power supply, or to connect the output end of the first inductor to the negative end of the input power supply through a primary-side winding.

Alternatively, in a case that a transformer primary side includes one winding, and the primary-side switch circuit includes four switch devices—a third switch device, a fourth switch device, a fifth switch device and a sixth switch device, one end of the third switch device is connected to the output end of the first inductor, another end of the third switch device is connected to the fourth switch device and a current inflow end of the transformer primary side, another end of the fourth switch device and one end of the fifth switch device and the negative electrode of the input power supply are connected jointly together, another end of the fifth switch device and one end of the sixth switch device and a current outflow end of the transformer primary side are connected jointly together, and another end of the sixth switch device is connected to the output end of the first inductor.

Alternatively, in a case that a transformer primary side includes one winding, and the primary-side switch circuit includes two switch devices—a third switch device and a fourth switch device, and a second inductor, one end of the third switch device is connected to the output end of the first inductor, another end of the third switch device is connected to the output end of the first inductor via the fourth switch device and the second inductor, a junction of the third switch device and the fourth switch device is connected to the negative electrode of the input power supply; the output end of the first inductor is connected to a current inflow end of the transformer primary side, and a current outflow end of the transformer primary side is connected to a junction of the second inductor and the fourth switch device.

Alternatively, in a case that a transformer primary side includes two windings, and the primary-side switch circuit includes two switch devices—a third switch device and a fourth switch device, one end of the third switch device is connected to a current inflow end of a first winding of the transformer primary side, one end of the fourth switch device is connected to a current outflow end of a second winding of the transformer primary side, a current outflow end of the first winding and a current inflow end of the second winding are jointly connected to the output end of the first inductor, and another end of the third switch device and another end of the fourth switch device are jointly connected to the negative end of the input power supply.

Alternatively, in a case that a transformer secondary side includes one winding, and the secondary-side rectification circuit includes four switch devices—a seventh switch device, an eighth switch device, a ninth switch device and a tenth switch device, a dotted end of the transformer secondary side corresponding to the current inflow end of the transformer primary side and one end of the seventh switch device and one end of the eighth switch device are connected jointly together, another end of the seventh switch device is connected to another end of the eighth switch device via the ninth switch device and the tenth switch device, a junction of the ninth switch device and the tenth switch device is jointly connected to another end of the dotted terminal of the transformer secondary side, and another end of the seventh switch device and another end of the eighth switch device serve as an output end of the secondary-side rectification circuit.

Alternatively, in a case that a transformer secondary side includes two windings, and the secondary-side rectification circuit includes two switch devices—a seventh switch device and an eighth switch device, one end of the seventh switch device is connected to a current inflow end of a first winding of the transformer secondary side, one end of the eighth switch device is connected to a current outflow end of a second winding of the transformer secondary side, a current outflow end of the first winding and a current inflow end of the second winding jointly serve as one output end of the secondary-side rectification circuit, another end of the seventh switch device and another end of the eighth switch device are connected and jointly serve as another output end of the secondary-side rectification circuit, so that the one output end of the secondary-side rectification circuit and the another output end form an output end of the secondary-side rectification circuit.

Alternatively, the switch devices at least include one of the following: a triode, an MOS transistor and a diode.

On the other hand, the embodiment of the present document further provides a method for controlling a switching power supply, which is used for controlling the switch circuit mentioned in any item above, and includes: in a case of supplying an input voltage, controlling switch devices of the primary-side switch circuit, so that switched-on of a combination of at least one switch device makes the first inductor connected to the charging state, and switched-off of a combination of at least one switch device makes energy in the first inductor transferred to the secondary-side rectification circuit via the transformer; and the secondary-side rectification circuit performing rectification on the energy transferred by the primary-side switch circuit to form output voltage of the switching power supply.

Alternatively, when the switch circuit works in a boost state, the front-stage circuit works in a shoot-through state to implement a boost function; and when the switch circuit works in a buck state, the post-stage isolated circuit works in the shoot-through state to implement a buck function.

The structure of the front-stage circuit of the embodiment of the present document is simple, both the buck-boost circuit and the isolated circuit are designed in the switching power supply, and the number of circuit stages of the switching power supply jointly formed with the post-stage isolated circuit is smaller, thus the volume is smaller, which solves the problem of wide duty ratio variation range and low efficiency or many power devices and lager volume brought as the post-stage bridge circuit only plays a role of isolation or buck in the related art.

PREFERRED EMBODIMENTS

In order to solve the problem of wide duty ratio variation range and low efficiency or many power devices and lager volume brought as the post-stage bridge circuit only plays a role of isolation or buck in the related art, the embodiments of the present document provide a switching power supply and a method for controlling the switching power supply. The embodiments of the present document will be described in detail in combination with the accompanying drawings below. The embodiments of the present document and the characteristics in the embodiments can be arbitrarily combined with each other in the case of no conflict.

The embodiment of the present document provides a switching power supply, and a structure of the switching power supply is as shown inFIG. 5, which includes:

an input power supply10, a front-stage circuit20and a post-stage isolated circuit30.

Herein, the front-stage circuit includes a first inductor101and at least two switch devices.

Herein, one end of the first switch device102is connected to a positive electrode of the input power supply, one end of the second switch device103and an input end of the first inductor are jointly connected to the other end of the first switch device, the other end of the second switch device is connected to a negative electrode of the input power supply, an output end of the first inductor is connected to the primary-side switch circuit of the post-stage isolated circuit, and the other end of the primary-side switch circuit is connected to the other end of the second switch device.

The structure of the front-stage circuit of the embodiment of the present document is simple, both the buck-boost circuit and the isolated circuit are designed in the switching power supply, and the number of circuit stages of the switching power supply jointly formed with the post-stage isolated circuit is smaller, thus the volume is smaller, which solves the problem of wide duty ratio variation range and low efficiency or many power devices and lager volume brought as the post-stage bridge circuit only plays a role of isolation or buck in the related art.

In the design, the primary-side switch circuit includes at least two switch devices. Herein, in the two switch devices, turn-on of one switch device or turn-on of a combination switch containing one switch device makes the first inductor connected to a charging state, turn-off of the other switch device or turn-off of a combination switch containing the other switch device makes energy in the first inductor transferred to the secondary-side rectification circuit via the transformer. The secondary-side rectification circuit includes at least two switch devices used for performing rectification on the energy transferred by the primary-side switch circuit to form an output voltage of the switching power supply. A person skilled in the art may employ the rectification circuit in the related art, and may also make a design based on the achieved effect above. In the design process, different circuits may be designed according to different switch devices, and the switch devices may be a triode, an MOS transistor and a diode and so on. In the implementation process of the circuit, the turn-on of one switch device or the turn-on of a combination switch containing one switch device making the first inductor connected to a charging state may include various on-off states. In order to make a connection state accurate, the turn-on of the above switch is required to be able to connect the output end of the first inductor to a negative terminal of the input power supply, or to connect the output end of the first inductor to the negative terminal of the input power supply through a primary-side winding.

During the specific implementation for the above design, it is required to perform circuit layout on the transformer, primary-side switch circuit and secondary-side rectification circuit according to the design requirements. According to different requirements, circuits in different conditions will be described respectively below.

Based on a difference of the number of windings of the transformer primary side and a difference of the number of switch devices of the primary-side switch circuit, various circuits may be set, but based on the consideration of duty ratio variation range, efficiency, power and volume and so on, the embodiment provides three preferred cases to make a description.

(1) In a case that the transformer primary side includes one winding, and the primary-side switch circuit includes four switch devices,

one end of the third switch device is connected to the output end of the first inductor, the other end of the third switch device is connected to the fourth switch device and a current inflow end of the transformer primary side, the other end of the fourth switch device and one end of the fifth switch device and the negative electrode of the input power supply are connected jointly together, the other end of the fifth switch device and one end of the sixth switch device and a current outflow end of the transformer primary side are connected jointly together, and the other end of the sixth switch device is connected to the output end of the first inductor.

(2) In a case that the transformer primary side includes one winding, and the primary-side switch circuit includes two switch devices and a second inductor,

one end of the third switch device is connected to the output end of the first inductor, the other end of the third switch device is connected to the output end of the first inductor via the fourth switch device and the second inductor, a junction of the third switch device and the fourth switch device is connected to the negative electrode of the input power supply; the output end of the first inductor is connected to a current inflow end of the transformer primary side, and a current outflow end of the transformer primary side is connected to a junction of the second inductor and the fourth switch device.

(3) In a case that the transformer primary side includes two windings, and the primary-side switch circuit includes two switch devices,

one end of the third switch device is connected to a current inflow end of a first winding of the transformer primary side, one end of the fourth switch device is connected to a current outflow end of a second winding of the transformer primary side, a current outflow end of the first winding and a current inflow end of the second winding are jointly connected to the output end of the first inductor, and the other end of the third switch device and the other end of the fourth switch device are jointly connected to the negative terminal of the input power supply.

Based on a difference of the number of windings of the transformer primary-secondary side and a difference of the number of switch devices of the secondary-side switch circuit, various circuits may be set, but also based on the consideration of duty ratio variation range, efficiency, power and volume and so on, the embodiment provides two preferred cases to make a description.

(1) In a case that the transformer secondary side includes one winding, and the secondary-side rectification circuit includes four switch devices,

a dotted terminal of the transformer secondary side corresponding to a current inflow end of the transformer primary side and one end of the seventh switch device and one end of the eighth switch device are connected jointly together, the other end of the seventh switch device is connected to the other end of the eighth switch device via the ninth switch device and the tenth switch device, a junction of the ninth switch device and the tenth switch device is jointly connected to the other end of the dotted terminal of the transformer secondary side, and the other end of the seventh switch device and the other end of the eighth switch device serve as an output end of the secondary-side rectification circuit.

(2) In a case that the transformer secondary side includes two windings, and the secondary-side rectification circuit includes two switch devices,

one end of the seventh switch device is connected to a current inflow end of a first winding of the transformer secondary side, one end of the eighth switch device is connected to a current outflow end of a second winding of the transformer secondary side, a current outflow end of the first winding and a current inflow end of the second winding jointly serve as one output end of the secondary-side rectification circuit, the other end of the seventh switch device and the other end of the eighth switch device are connected and jointly serve as the other output end of the secondary-side rectification circuit, so that one output end of the secondary-side rectification circuit and the other output end form an output terminal of the secondary-side rectification circuit.

Three kinds of circuits in different cases of the primary side and two kinds of circuits in different cases of the secondary side have been respectively introduced above. The above circuits corresponding to the primary side and the secondary side may be designed with each other in a combinational way according to the requirements.

The embodiment of the present document also provides a method for controlling a switching power supply, which is used for controlling any of the switching power supplies provided above. A flow of the method is as shown inFIG. 6, and step S601to step S602are included.

In step S601, in a case of supplying an input voltage, switch devices of a primary-side switch circuit are controlled, so that turn-on of a combination of at least one switch device makes a first inductor connected to a charging state, and turn-off of a combination of at least one switch device makes energy in the first inductor transferred to a secondary-side rectification circuit via a transformer.

In step S602, the secondary-side rectification circuit performs rectification on the energy transferred by the primary-side switch circuit to form an output voltage of the switching power supply.

When the circuit works, in a case that the switch circuit works in a boost state, a front-stage circuit works in a shoot-through state to implement a boost function; and in a case that the switch circuit works in a buck state, a post-stage isolated circuit works in a shoot-through state to implement a buck function.

PREFERRED EMBODIMENTS

As shown inFIG. 7, the circuit includes a front-stage non-isolated circuit with a buck function and a post-stage isolated circuit with a boost function, the front-stage circuit and the post-stage circuit may share one inductor, so that the whole circuit may achieve a buck-boost function to adapt to the wide range of input voltage. The implementation process thereof is to utilize a characteristic that the traditional buck isolated power supply may work bi-directionally when the synchronous rectification technology is used, reverse working may be understood as boost, and the output thereof is connected to the front-stage non-isolated BUCK circuit, thus a two-stage isolated circuit that can implement the buck-boost function may be constituted. Meanwhile, an output inductor of the BUCK circuit and an output inductor of the reversely connected bridge isolated circuit may be shared in time division. Compared with the single-stage traditional buck bridge isolated power supply scheme, it is only required to increase two Buck switch devices, and the original output inductor is transferred to the primary-side high voltage terminal, the processing current is smaller, which may greatly reduce the volume and improve the efficiency and power density while implementing the buck-boost function to adapt to the wide range of input.

The above scheme will be further described in combination with the related art and the accompanying drawings of the preferred embodiments of the present document.

FIG. 1is a typical structure of an isolated switching power supply in the related art. Through an alternate switched-on of the bridge circuit switch devices101/103and102/104, the input voltage is modulated to an alternating signal with certain pulse width, and the alternating signal is transferred to the secondary side via the transformer isolation, and then goes through a rectification circuit composed of107˜109and a lowpass filtering circuit composed of an output inductor110and a capacitor111, and the final direct-current output voltage is obtained. A transformation ratio of the output voltage and the input voltage is decided by a pulse width duty ratio of the bridge circuit and a primary-secondary side transformation ratio of the transformer. When the input voltage range is wider, variation of the pulse width duty ratio of the bridge circuit is also greater. When the bridge circuit is switched on, the input power supply transfers energy to the output via the transformer, the inductor110starts to store energy; and when the bridge circuit is switched off, the inductor110releases energy to supply power for the output. Therefore, when the input voltage is higher and the duty ratio is lower, that is, when the switched-off time of the bridge circuit is longer, the inductor110is required to store more energy, which causes that both volume and loss of the inductor are larger. Therefore, the efficiency of the circuit and the volume of the energy storage elements can be optimal when the duty ratio is maximum, and correspondingly when the input voltage is minimum. However, the minimum input voltage such as 36V is normally not the rated operational voltage of the system, which causes that both efficiency and volume cannot be optimal when the system works at the rated operational voltage such as 48V.

Meanwhile, when the input voltage is higher, the switch devices101˜104and106˜109are all required to select devices with higher withstand voltage, but also required to select switch devices with higher current during the low-voltage input, therefore, it is difficult to optimize the selection of the switch devices. With regard to a common input voltage range 36˜75V of the communication systems, the switch devices are required to select a margin at least twice the rated power, which also brings increased volume and loss.

FIG. 2is a two-stage structure of the circuit in the related art, the frequently used two-stage structure is to solve the problem of stress margin increase of the power device brought by the wide range of input voltage.FIG. 2adds one stage of non-isolated front-stage voltage stabilizing circuit201based on the related art shown inFIG. 1. The output voltage205of201is a stable voltage, so that the post-stage traditional bridge buck isolated circuit is not required to bear a wider input voltage range. But the switch duty ratio of the front-stage201of the circuit is not improved, thus the problem of larger stress of the switch devices202and203and higher stored energy of the output inductor204still exists.

FIG. 3is a non-isolated Buck-Boost circuit in the related art, which can implement a buck-boost function. In the circuit, the output voltage may be set as an intermediate value. When the input voltage Vinis higher than the output voltage Vout, the switches301and302perform pulse width modulation, the circuit works in a Buck mode. When the input voltage Vinis lower than the output voltage Vout, the switches303and304perform pulse width modulation, the circuit works in a Boost mode. Therefore, the duty ratio variation range may be halved, but the circuit does not have an isolation function.

FIG. 4is a Buck-Boost circuit added with an isolated circuit in the related art. A front-stage401thereof is the Buck-Boost circuit shown inFIG. 3, and an isolation part is the buck bridge isolated circuit as shown inFIG. 1. The circuit shown inFIG. 4may achieve the advantage of narrow duty ratio variation range during the wide range of input through the front-stage non-isolated Buck-Boost circuit401, and meanwhile, the post-stage isolated circuit is also not required to deal with the stress problem of the power device brought by the wide range of input voltage, which is an application with higher efficiency in the related art. But compared to the related art shown inFIG. 1, the circuit is required to increase, for example, four switch devices and one power inductor and one capacitor contained in401, which leads to a larger volume increase and affects the efficiency and power density.

The embodiment 1 of the present document is as shown inFIG. 7.FIG. 1is a schematic diagram of a structure of the power supply topology in the embodiment of the present document. Compared to the related art shown inFIG. 1, it is only required to increase two switches501and502to implement the buck-boost function and achieve the advantage of narrow duty ratio variation during the wide range of input, meanwhile, the post-stage circuit is also not required to deal with the wider input voltage range.

In order to further describe the structure and principle of the circuit diagram inFIG. 7, as shown inFIG. 8, it can be seen fromFIG. 8that the present document utilizes the synchronous rectification technology (that is, a characteristic that the output current thereof may flow bi-directionally when106˜109are switch devices replaced with the diodes) in the secondary-side rectification circuit by using the buck bridge isolated circuit in the related art inFIG. 1, the input and output thereof are reversed and then connected to the front-stage Buck circuit, that is, the output inductor110thereof is connected to the output inductor603of the front-stage Buck, and the input power supply end112is connected to the output capacitor111.

In the related art shown inFIG. 1, it is a buck structure from the end112to the end113, through the reverse connection, in the structural diagram shown inFIG. 8, a boost structure from the end113to the end112may be formed, and in combination with a Buck voltage reducing circuit constituted by601,602and603, a buck-boost structure is formed. In the structure, the voltage stress of the primary side and secondary side switch devices106˜109and101˜104of the post-stage circuit is decided by the output voltage Vout, and the output voltage Voutin most of applications is a stable value, thus the post-stage devices are also not required to deal with the problem of large stress brought by the wide range of input voltage. Moreover, the inductors603and110connected in series may be equivalently combined into one, thereby forming a simple invention structure as shown inFIG. 7.

In order to further describe the specific working implement of the present document, as shown inFIG. 9, when the structure of the embodiment of the present document shown inFIG. 7works in a buck state, the switch devices504˜507and509˜512of the post-stage bridge isolated circuit work according to a duty ratio approximate to 50%, the post-stage isolated circuit704is equivalent to one switch direct-current transformer, the output capacitor513may be equivalently converted to the primary side according to the value of C0/N2. Herein, N is a turns ratio of the primary side winding and secondary side winding of the transformer508, and C0is a capacitance value of the output capacitance513which is connected to an output end of the inductor503. An equivalent capacitor701and the switch devices501and502and the output inductor503of the front-stage just form a whole Buck voltage reducing circuit703. A value of the output voltage702thereof is Vin×D, herein, D is a duty ratio of the switch device501. Then702is turned into the output voltage Voutaccording to the transformation ratio N:1 via the above-mentioned equivalent switch direct-current transformer704, and thus the output voltage Vout=Vin×D/N, herein D<1. The buck function is implemented.

As shown inFIG. 10, when the structure of the embodiment of the present document shown inFIG. 7works in a boost state, the front-stage buck circuit works in a shoot-through state, that is, the switch502is switched off and the switch501is switched on, the inductor503is connected to the input power supply, and it is equivalent to the output inductor110of the buck bridge isolated circuit as shown inFIG. 1, and a reversely connected buck circuit is formed to implement a boost function. Specifically, the primary side switch devices504˜507works according to the working mode of the switch devices106˜109in the original synchronous rectification shown inFIG. 1, a duty ratio thereof is greater than 50%, that is, the504˜507have a simultaneous switched-on time, when the504˜507are simultaneously switched on, the inductor503charges through the input voltage Vin, at this point voltages of the primary side and secondary side windings of the transformer508are all 0, and the switch devices509˜512are simultaneously switched off. When the504˜507are diagonally and alternately switched on, that is,504and506are simultaneously switched on, or505and507are simultaneously switched on, the corresponding diagonal switch devices510and512of the secondary side are simultaneously switched on, or509and511are simultaneously switched on, the secondary-side winding of the transformer is connected to the output voltage Vout, and the primary-side winding voltage Vout×N is connected to the output end of the inductor503to discharge the inductor. When the inductor current achieves a dynamic balance, Vout=Vin/(2×(1−D))/N, and the boost function is implemented, herein, D is a duty ratio of the switch devices504˜507, D>0.5.

The preferred embodiment 2 of the present document is as shown inFIG. 11.FIG. 11is a structure diagram that the secondary side of the post-stage isolated circuit uses two switch devices and the secondary side of the transformer is two windings in the embodiment of the present document. The secondary side of the transformer901includes two windings902and903, which corresponds to a reversed connection mode of the push-pull isolated buck circuit using the full-bridge rectification. Specifically, when the504˜507are simultaneously switched on, the secondary-side switch devices904and905are switched off, and the inductor503charges through the input voltage Vin. When the504˜507are diagonally and alternately switched on, that is,504and506are simultaneously switched on or505and507are simultaneously switched on, the secondary-side switch device904or905is correspondingly switched on, so that the winding902or903is connected to the output voltage Vout, and the voltage induced to the winding of the primary side of the transformer discharges the inductor503.

The preferred embodiment 3 of the present document is as shown inFIG. 12.FIG. 12is a structure diagram that the primary-side switch circuit of the post-stage isolated circuit uses two switch devices1001and1002in the present document. The primary side of the transformer1005further includes two windings1003and1004, which corresponds to a reversed connection mode of the push-pull isolated buck circuit using the secondary-side duplex winding structure rectification. Specifically, when the primary-side switch devices1001and1002are simultaneously switched on, the secondary-side switch devices904and905are switched off, and the inductor503charges via the windings1003and1004and switch devices1001and1002through the input voltage Vin. When the1001and1002are alternately switched on, the secondary-side switch device904or905is correspondingly switched on, so that the winding902or903is connected to the output voltage Vout, and the voltage induced to the corresponding winding1003or1004of the primary side of the transformer discharges the inductor503.

The preferred embodiment 4 of the present document is as shown inFIG. 13.FIG. 13is a structure that the primary-side switch circuit of the post-stage isolated circuit uses two switch devices and two windings as mentioned inFIG. 12and the secondary side uses one winding and four switch devices as mentioned inFIG. 7, which corresponds to a reversed connection mode of the full-bridge isolated buck circuit using the secondary-side duplex winding structure rectification. Specifically, when the primary-side switch devices1001and1002are simultaneously switched on, the secondary-side switch devices509˜512are all switched off, and the inductor503charges via the windings1003and1004and switch devices1001and1002through the input voltage Vin. When the1001and1002are alternately switched on, the corresponding diagonal switch devices509and511of the secondary side are simultaneously switched on or510and512are simultaneously switched on, the winding of the secondary side of the transformer is connected to the output voltage Vout, and the voltage induced to the corresponding winding1003or1004of the primary side of the transformer discharges the inductor503.

The preferred embodiment 5 of the present document is as shown inFIG. 14.FIG. 14is a structure diagram that the primary side uses two primary-side inductors in the embodiment of the present document, which corresponds to a reversed connection mode of the full-bridge isolated buck circuit using the secondary-side current-double rectification. Specifically, when the primary-side switch devices1203and1204are simultaneously switched on, the secondary-side switch devices509˜512are all switched off, and the inductors1201and1202charges via the switch devices1203and1204through the input voltage Vin. When the switch1203is switched off and the1204continues to be switched on, the inductor1202continues to charge through the Vin, the secondary-side switch devices510and512are switched on, the output voltage Voutis connected to the winding of the secondary side of the transformer, and the voltage induced to the primary-side winding1206discharges the inductor1201. When the switch1204is switched off and the1203continues to be switched on, the inductor1201continues to charge through the Vin, the secondary-side switch devices509and511are switched on, the output voltage Voutis negatively connected to the winding of the secondary side of the transformer, and the voltage induced to the primary-side winding1206discharges the inductor1202.

It can be seen from the above embodiments of the present document that the switching power supply provided in the preferred embodiments of the present document charges the first inductor by controlling switch-on of the switch devices of the primary-side switch circuit, when the switch devices of the primary-side switch circuit are not simultaneously switched on, by controlling the switch devices of secondary-side rectification circuit, the output voltage is connected to the secondary-side winding of the transformer, and the voltage induced to the primary-side winding discharges the first inductor.

Though the preferred embodiments of the present document have been disclosed for the purpose of illustration, the people skilled in the art will recognize that various improvements, additions and replacements are also possible, therefore, the scope of the present document should not be limited to the above embodiments.

INDUSTRIAL APPLICABILITY

The structure of the front-stage circuit of the embodiment of the present document is simple, both the buck-boost circuit and the isolated circuit are designed in the switching power supply, and the number of circuit stages of the switching power supply jointly formed with the post-stage isolated circuit is smaller, thus the volume is smaller, which solves the problem of wide duty ratio variation range and low efficiency or many power devices and lager volume brought as the post-stage bridge circuit only plays a role of isolation or buck in the related art.