TWI489762B - High efficiency AC - DC voltage conversion circuit - Google Patents

Description

High efficiency AC-DC voltage conversion circuit

The present invention relates to the field of switching power supplies, and more particularly to a high efficiency AC-DC voltage conversion circuit.

At present, the two-stage structure commonly used in the AC-DC voltage conversion circuit includes a PFC circuit and a flyback converter. Referring to FIG. 1, a schematic block diagram of a two-stage AC-DC voltage conversion circuit composed of a PFC circuit and a flyback converter in the prior art. The former PFC circuit is used to improve the power factor, thereby improving the working efficiency of the power supply, and the flyback converter of the latter stage is used to transmit the output voltage of the front stage to the secondary side through the isolated topology. However, since the AC/DC circuit with PFC function usually adopts a step-up type circuit, its output voltage is higher than the input voltage. When it is used in a wide output voltage range with a high input voltage, the output voltage will be further increased. These circuit devices, such as diode D ₁ , transistor Q ₁ , transistor Q _{2 ,} and capacitor C ₁ , need to use high voltage resistant devices. In addition, the energy storage capacity of capacitor C ₁ will also increase, so the cost Higher; in addition, no matter how the load changes, its two-stage structure is always in working state, and the conversion efficiency of the circuit is difficult to improve.

In view of the above, an object of the present invention is to provide a high-efficiency AC-DC voltage conversion circuit that converts an input AC power source into a constant DC output using a two-stage structure, and in the first operating state, the AC power source The two-stage voltage conversion circuit sequentially generates an electrical signal to supply power to the load; in the second operating state, the output of the first-stage voltage conversion circuit is controlled to match the desired electrical signal to supply power to the load to improve the conversion efficiency of the circuit. Since the topology of the second-stage voltage conversion circuit is preferably a buck converter, the capacitance value of the output capacitor is low, and the requirement can be achieved without using an electrolytic capacitor, thereby reducing the cost; in addition, the AC-DC voltage conversion The flyback converter in the circuit preferably adopts the primary side control mode without using an optocoupler element or the like, thereby facilitating circuit integration. Thus, the AC-DC voltage conversion circuit according to the present invention has the advantages of high efficiency, easy integration, and low cost.

A high-efficiency AC-DC voltage conversion circuit according to an embodiment of the invention includes: a first-stage voltage conversion circuit and a second-stage voltage conversion circuit, wherein the first-stage voltage conversion circuit has a power factor correction function An isolated topology for converting the received AC power to a first output voltage; the second stage voltage conversion circuit is a non-isolated topology for converting the received first output voltage to a constant An electric signal; in the first working state, the alternating current power passes through the first stage voltage in sequence After the conversion circuit and the second-stage voltage conversion circuit, the constant electrical signal is generated to drive the subsequent load; in the second operating state, the second-stage voltage conversion circuit does not perform a voltage conversion operation, and the first-stage voltage conversion circuit is It is currently desired that the electrical signal voltage convert the alternating current source such that the output electrical signal of the first stage voltage conversion circuit matches the current desired electrical signal.

Further, the first stage voltage conversion circuit comprises a bridge rectifier, a flyback converter and a power factor correction control circuit; wherein the bridge rectifier is connected to the alternating current power source to convert the alternating current power source into a direct current a voltage; the flyback converter is respectively coupled to the bridge rectifier and the power factor correction control circuit to receive the DC voltage, and the power factor correction control circuit controls the input voltage and the input current of the flyback converter to be in phase .

Preferably, in the second operating state, the feedback voltage of the feedback circuit in the first-stage voltage conversion circuit or a reference value thereof is adjusted to make the output electrical signal of the first-stage voltage conversion circuit and the current desired power The signals match.

Preferably, in the first working state, the second-stage voltage conversion circuit operates in a PWM mode, and maintains a constant output electrical signal by controlling a duty cycle of the transistor; in the second operating state, the second-stage voltage conversion The branch between the input and output of the circuit remains in a through state, and the other branches remain in an off state to stop the voltage conversion operation.

Preferably, the topology of the second-stage voltage conversion circuit is non-isolated. The non-synchronous step-down circuit maintains its main power transistor in an on state in the second operating state.

Preferably, the topology of the second-stage voltage conversion circuit is a non-isolated synchronous buck circuit. In the second operating state, the main power transistor maintains an on state, and the synchronous power transistor maintains an off state.

Further, the AC-DC voltage conversion circuit further includes a selection circuit, a PWM control circuit, and a linear adjustment circuit. In the first working state, the selection circuit selects the PWM control circuit to control the transistor in the second-stage voltage conversion circuit. The switching action; in the second operating state, the selection circuit selects the linear adjustment circuit to control the switching action of the transistor in the second-stage voltage conversion circuit.

Further, the AC-DC voltage conversion circuit further includes: a PWM control circuit, a detection circuit, and a logic circuit; wherein the detection circuit outputs a valid signal in the second working state; the PWM control signal output by the PWM control circuit and the The effective signal outputted by the detection circuit controls the switching state of the transistor in the second-stage voltage conversion circuit through the logic circuit.

Preferably, the flyback converter adopts a primary side control mode to control the operating state of the flyback converter by sampling an output voltage of the auxiliary winding of the flyback converter.

Preferably, the flyback converter further includes a primary side transistor, the primary side of the flyback converter is coupled to the primary side transistor, and the power factor correction control circuit controls the primary resonance control mode. The switching action of the primary side transistor.

FIG. 1 is a schematic block diagram of a conventional two-stage AC-DC voltage conversion circuit.

2 is a circuit diagram of a first embodiment of an AC-DC voltage conversion circuit according to the present invention; and FIG. 3 is a circuit diagram of a second embodiment of an AC-DC voltage conversion circuit according to the present invention; A circuit diagram of a third embodiment of an AC-DC voltage conversion circuit in accordance with the present invention is shown.

Several preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the invention is not limited to these embodiments. The present invention encompasses any alternatives, modifications, equivalents and alternatives to the spirit and scope of the invention. The details of the invention are described in detail in the preferred embodiments of the present invention, and the invention may be fully understood by those skilled in the art.

Referring to Figure 2, there is shown a circuit diagram of a first embodiment of an AC-DC voltage conversion circuit in accordance with the present invention; including a first stage voltage conversion circuit and a second stage voltage conversion circuit.

Wherein, the first-stage voltage conversion circuit is an isolated topology having a power factor correction function, and specifically includes a bridge rectifier, a flyback converter and a power factor correction control circuit; wherein the bridge rectifier and the bridge rectifier An AC power connection to convert the AC power to a DC voltage; the flyback converter is respectively coupled to the bridge rectifier and the power factor correction control circuit to receive the DC voltage; a primary side transistor S ₁ is connected to the primary side of the flyback converters, the power factor correction control circuit controlling the lateral transistor S switching operation of the _first time, to reach the input voltage and input current of the flyback converter in phase, increasing the power The purpose of the factor. The secondary side output of the flyback converter passes through an output diode D ₁ and an output capacitor C _out1 to obtain a first output voltage V _out1 ; the second stage voltage conversion circuit is a non-isolated topology. The embodiment specifically includes a DC/DC converter for converting the received first output voltage V _out1 into a constant DC voltage V _out output.

In order to improve the conversion efficiency of the entire circuit, in the first working state, that is, when the AC-DC voltage conversion circuit operates normally, the AC power source sequentially passes through the first-stage voltage conversion circuit and the second-stage voltage conversion circuit to generate a constant The DC voltage is used to drive the subsequent load; in practical applications, the second stage voltage conversion circuit can operate in PWM mode.

In the second working state, that is, when the AC DC voltage conversion circuit operates in the standby state, the second-stage voltage conversion circuit keeps the branch between the input terminal and the output terminal through logic control or linear control, and other branches The circuit is turned off to stop the voltage conversion operation, and the first-stage voltage conversion circuit performs voltage conversion on the AC power supply according to the desired electrical signal of the current driving load, so that the output electrical signal matches the desired electrical signal to supply power to the load.

What needs to be explained here is the control of the primary side transistor S ₁ , the control mode is not limited, the peak current control mode, the constant conduction time control, the average current mode control, the single-cycle control, and the like are applicable. In the present invention. The topology of the second-stage voltage conversion circuit may also be a conventional non-isolated topology such as buck, boost, cuk, zeta or sepic, which is within the scope of the present invention.

In practical applications, the AC-DC voltage conversion circuit according to the present invention is applied to a 12V constant voltage power supply of a television set, and the second stage voltage conversion circuit is a buck converter, wherein the first stage voltage is taken as an example. The conversion circuit outputs a DC voltage greater than 12V, and the DC conversion through the second voltage conversion circuit can provide a stable 12V output voltage in accordance with the specification. The efficiency of the entire circuit using the two-stage structure shown in Fig. 1 is 82.7%, and when realized by the AC-DC voltage conversion circuit according to the present invention, the efficiency is improved to 88.4%, and the cost is reduced by 37%. It can be seen that the AC-DC voltage conversion circuit according to the present invention has the advantages of high efficiency and low cost.

Referring to FIG. 3, there is shown a circuit diagram of a second embodiment of an AC-DC voltage conversion circuit in accordance with the present invention; in this embodiment, further comprising a selection circuit, a PWM control circuit and a linear adjustment circuit; The topology of the conversion circuit is preferably a non-isolated non-synchronous step-down circuit composed of a main power transistor S ₂ , a diode D ₂ , an inductor L ₁ , and an output capacitor C _out2 , and the output is a DC voltage V _{out .} In the first working state, the control mode of the flyback converter in the first stage voltage conversion circuit is secondary side control, and the voltage dividing resistor R ₁₁ and the resistor R _{12 are} connected in series and receive the first output voltage V. _{OUT1 of,} a transistor S ₃ and a resistor R ₁₃ connected in series to ground and in parallel with the resistor R _12; in the first operating state, the transistor S ₃ is turned on, the first output voltage V _out1 via the resistor R ₁₁ and the resistor After R ₁₂ and R ₁₃ are connected in parallel with equivalent resistance, they are fed back to the control wafer 301 through the optical coupler to control the switching action of the primary side transistor S ₁ , and convert the received AC power into the first output voltage V. _out1; the Receiving information characterizing the selection circuit to select the load state of the PWM control circuit when controlling a first operation state of the main power switching transistor S _2, in order to ensure that the input stage of the second voltage conversion circuit for subsequent load.

In the second working state, the selection circuit selects the linear adjustment circuit to control the main power transistor S _{2 to} maintain a conducting state, and at this time, the non-synchronous step-down circuit suspends the voltage conversion operation, so as to ensure that the first-stage voltage conversion circuit can According to the expected supply voltage of the load, the voltage of the AC power supply is converted, and the feedback voltage of the first-stage voltage conversion circuit needs to be adjusted. In this embodiment, the linear adjustment circuit outputs an effective signal and is inverted. Controlling the transistor S _{3 to be} turned off. At this time, the first output voltage V _out1 is divided by the resistor R ₁₁ and the resistor R ₁₂ , and the feedback signal representing the first output voltage V _out1 is correspondingly changed due to the connection change of the voltage dividing resistor. When the control period of the primary side transistor S ₁ is controlled, the first output voltage V _out1 is decreased compared with the normal operation, and after filtering by the inductor L ₁ and the output capacitor C _out2 , The load is normally powered.

Since the output voltage of the buck circuit is lower than the input voltage, the capacitance of the output capacitor is lower, and the requirement is not required to use an electrolytic capacitor, thereby reducing the cost. In addition, the buck circuit has a wide bandwidth, which can effectively eliminate the harmonic output of the first voltage conversion circuit, thereby reducing the capacitance requirement of the output capacitor C _out1 , so that the capacitance of the output end of the first voltage conversion circuit does not need to be electrolyzed. The capacitor can meet the requirements.

It should be noted that, in the embodiment shown in FIG. 3, by adjusting the feedback voltage of the feedback circuit of the first-stage voltage conversion circuit to match the output electrical signal of the first-stage voltage conversion circuit with the desired electrical signal, In practical applications, the same technical effect can be achieved by adjusting the reference value corresponding to the feedback voltage, which is also within the protection scope of the present invention.

In addition, the second-stage voltage conversion circuit adopts a non-isolated topology, and the specific implementation is not limited to the non-synchronous buck circuit, and other suitable such as synchronous buck circuit, non-synchronous boost circuit, synchronous buck circuit, and the like. Non-isolated topologies are available. Correspondingly, in order to ensure that the branch between the input end and the output end of the second-stage voltage conversion circuit maintains a through state, the other branches maintain the off state to stop the voltage conversion operation, and in the second operation state, the synchronous buck The main power transistor in the circuit maintains the on state, and the synchronous transistor maintains the off state; when the non-synchronous boost circuit is used, the main power transistor remains in the off state; when the synchronous boost circuit is used, the main power transistor remains In the off state, the synchronous transistor remains in the on state.

In the embodiment shown in FIG. 3, the flyback converter adopts the secondary side control mode, and the feedback signal sampling by the optical coupler is not only disadvantageous to circuit integration, but also increases the volume and cost of the circuit, and the embodiment shown in FIG. The flyback converter adopts a primary side control mode to control the flyback converter by sampling an output voltage of the auxiliary winding of the flyback converter The working state, without the use of optocoupler components, etc., is conducive to circuit integration. The topology of the second-stage voltage conversion circuit is preferably a non-isolated synchronous buck circuit, and further includes a PWM control circuit, a detection circuit, and a logic circuit; wherein the detection signal outputs a valid signal in the second working state; The PWM control signal output by the PWM control circuit and the effective signal output by the detection circuit control the switching action of the transistor in the second-stage voltage conversion circuit through the logic circuit.

In the first operating state, the first stage of the voltage converting circuit using a flyback converter primary side control, and the primary side of the preferred control transistor S ₁ is quasi-resonant control mode. The logic circuit controls the switching operation of the main power transistor S ₄ and the synchronous transistor S ₅ in the synchronous buck circuit according to the PWM control signal; in the second working state, the logic circuit outputs an effective signal according to the detecting circuit. The main power transistor S _{4 is controlled to} remain in an on state, and the synchronous transistor S _{5 is} kept in an off state. At the same time, the effective signal is inverted to control the transistor S _{3 to be} turned off. At this time, the first output voltage V _out1 is divided by the resistor R ₂₁ and the resistor R ₂₂ , and the first output is characterized by the connection change of the voltage dividing resistor. The feedback signal of the voltage V _out1 is correspondingly increased. Through the control of the duty cycle of the primary side transistor S ₁ , the first output voltage V _out1 is decreased compared with the normal operation, and the load can be normally supplied with power.

The AC-DC voltage conversion circuit in accordance with the preferred embodiment of the present invention has been described above, and the various embodiments are not described in detail, and the invention is not limited to the specific embodiments. Obviously, according to Many modifications and variations are possible in the above description. Related improvements made by the skilled person in the art based on the circuit disclosed in the embodiments of the present invention, a combination of a plurality of embodiments, and a circuit structure using the same function realized by other techniques, circuit layouts or components are also Within the scope of protection of the embodiments of the invention. The invention is limited only by the scope of the claims and the full scope and equivalents thereof.

Claims (9)

A high-efficiency AC-DC voltage conversion circuit, comprising: a first-stage voltage conversion circuit and a second-stage voltage conversion circuit, wherein the first-stage voltage conversion circuit is an isolated topology with power factor correction function a structure for converting the received AC power to a first output voltage; the second stage voltage conversion circuit is a non-isolated topology for converting the received first output voltage into a constant electrical signal; In the first working state, the AC power source sequentially passes through the first-stage voltage conversion circuit and the second-stage voltage conversion circuit to generate the constant electrical signal to drive the subsequent load; in the second working state, the second-stage voltage The conversion circuit does not perform a voltage conversion operation, and the first stage voltage conversion circuit performs voltage conversion on the AC power source according to the current desired electrical signal to match the output electrical signal of the first stage voltage conversion circuit with the current desired electrical signal; And the first stage voltage conversion circuit comprises a bridge rectifier, a flyback converter and a power factor correction control circuit The flyback converter adopts a primary side control mode to control the operating state of the flyback converter by sampling an output voltage of the auxiliary winding of the flyback converter. The AC-DC voltage conversion circuit according to Item 1, wherein the bridge rectifier is connected to the AC power source to convert the AC power source into a DC voltage; and the flyback converter is respectively associated with the Bridge rectifier and the power factor A positive control circuit is coupled to receive the DC voltage, and the power factor correction control circuit controls the input voltage and the input current of the flyback converter to be in phase. The AC-DC voltage conversion circuit according to claim 1, wherein in the second operating state, the feedback voltage of the feedback circuit in the first-stage voltage conversion circuit or a reference value thereof is adjusted to make the The output electrical signal of the first stage voltage conversion circuit matches the current desired electrical signal. The AC-DC voltage conversion circuit according to claim 1, wherein in the first operating state, the second-stage voltage conversion circuit operates in a PWM mode to maintain an output electrical signal by controlling a duty cycle of the transistor. Constant; in the second operating state, the branch between the input and output of the second stage voltage conversion circuit remains in a through state, and the other branches remain in an off state to stop the voltage conversion operation. The AC-DC voltage conversion circuit according to Item 4 of the patent application scope, wherein the topology of the second-stage voltage conversion circuit is a non-isolated non-synchronous step-down circuit, and in the second working state, the main power is The crystal remains on. The AC-DC voltage conversion circuit according to claim 4, wherein the topology of the second-stage voltage conversion circuit is a non-isolated synchronous buck circuit, and in the second operating state, the main power transistor Keeping on, the synchronous power transistor remains off. The AC-DC voltage conversion circuit according to claim 5 or 6, wherein: further comprising: selecting circuit, PWM control a circuit and a linear adjustment circuit, in the first working state, the selection circuit selects the PWM control circuit to control a switching action of the transistor in the second-stage voltage conversion circuit; in the second working state, the selection circuit selects the linear adjustment The circuit controls the switching action of the transistor in the second stage voltage conversion circuit. The AC-DC voltage conversion circuit according to Item 5 or 6, wherein the method further includes: a PWM control circuit, a detection circuit, and a logic circuit; wherein the detection circuit outputs a valid signal in the second operating state; The PWM control signal output by the PWM control circuit and the effective signal output by the detection circuit control the switching state of the transistor in the second-stage voltage conversion circuit through the logic circuit. The AC-DC voltage conversion circuit of claim 2, wherein the flyback converter further includes a primary side transistor, the primary side of the flyback converter and the primary side transistor phase Connected, the power factor correction control circuit controls the switching action of the primary side transistor by a quasi-resonant control method.