CN100502213C - Resonance converter and method for realizing light load and no-load voltage stabilization thereof - Google Patents

Abstract

The present invention refers to a resonant converter and a method for achieving light-load and no-load voltage stabilization thereof. The resonant converter includes a conversion circuit stage, a diode rectifier circuit stage, a filter and load circuit stage, a logic circuit, a driver and an energy feedback circuit. The method is that when the filter and load circuit stage is light-loaded or no-loaded, energy is fed back from the filter and load circuit stage to the conversion circuit stage.

Description

Resonant converter and its light-load and no-load regulation method

technical field

The invention relates to a resonant converter and a method for realizing its light-load and no-load voltage stabilization, in particular to a resonant DC-DC converter applied to a power supply.

Background technique

The development trend of DC-DC converters, like most power products, is towards high efficiency (High Efficiency), high power density (High Power Density), high reliability (High Reliability) and low cost (Low Cost). . Please refer to FIG. 1, which is a block diagram of an existing DC-DC converter. In FIG. Its working principle is that the DC voltage Vin first passes through the conversion circuit stage 11 to receive high-frequency chopping, then passes through the diode rectification circuit stage 12 to receive rectification, and finally is sent to the filter and load circuit stage 13 to receive filtering and then to the load.

In this kind of DC-DC converter, since the energy is transmitted from the conversion circuit stage 11 to the filter and load circuit stage 13, it is a one-way transmission path, so when the circuit works under light load or no load, there will be output For the situation of unstable voltage, refer to Fig. 2(a) as an example.

Figure 2(a) is a circuit diagram of a typical traditional full-bridge LLC (inductance-inductance-capacitance) converter, which generally uses Pulse Frequency Modulation (PFM) technology. In FIG. 2(a), the full-bridge LLC converter 20 mainly includes a conversion circuit stage composed of switches Q1~Q4, resonant capacitor C1, resonant inductance L1, magnetizing inductance L2, and transformer T1, and diodes D1~D2. There are three parts: the rectifier circuit stage, and the filter and load circuit stage composed of the filter capacitor Cout. Wherein, Q1 and Q2, Q3 and Q4 respectively constitute two bridge arms, and the driving signals of Q1 and Q4, Q3 and Q2 each perform a switching action at a duty cycle close to 50%. The resonant capacitor C1, the resonant inductance L1 and the primary side of the transformer T1 are connected in series at the midpoint of the two bridge arms, and the magnetizing inductance L2 is connected in parallel with the primary side of the transformer T1. On the other hand, the secondary side of the transformer T1 adopts a center tap structure, using two diodes D1 and D2 to adopt a full-wave rectification mode, and the output terminal directly uses a capacitor Cout for filtering and voltage stabilization.

For a resonant converter using diode rectification, there is a minimum voltage gain within its operating frequency range; the above-mentioned minimum voltage gain of the full-bridge LLC converter 20 at the highest operating frequency is an example. Generally, the gain of the converter within its operating range is designed to be greater than the above-mentioned minimum voltage gain. At this time, the converter can theoretically achieve a completely stable operation with no load. However, in fact, due to the existence of parasitic oscillations caused by the parasitic parameters of the components (such as the parasitic capacitance of the primary and secondary sides of the transformer, etc.), if the converter uses a unidirectional conductivity diode (such as: Figure 2 ( As shown in a)), then too much energy will be injected into the output terminal and cause the output voltage to rise. As a result, the system often becomes unstable when it is light-loaded or no-loaded.

In view of the above problems, at least the following four solutions appear in the prior art to try to solve them.

The first method is to dissipate the excess energy injected into the output. The practical way is to add an appropriate dummy load to the output. However, the existence of dummy load will reduce the efficiency of the system, increase the no-load loss, and increase the cost and volume accordingly.

The second method is to add an independent auxiliary circuit, which shuts down the main circuit at no load or light load, and uses this auxiliary circuit to maintain the output voltage. Although this method will not increase additional loss, it needs to judge the load voltage and switch between the auxiliary circuit and the main circuit in the control, which not only increases the difficulty of control, but also greatly reduces the dynamic performance of the system. At the same time, the cost will increase.

The third method is to use the intermittent working mode (Burst Mode) to control the amount of energy from input to output.

The fourth method is to prevent excessive energy from being injected into the output terminal at no-load, which can be achieved by changing the resonance parameters or resonance impedance, etc. There are three known solutions:

(1) Invention No. US5,388,040

Please refer to Fig. 2 (b), which is a circuit diagram of a traditional full-bridge LLC converter disclosed by No. US5,388,040 invention. display symbol.

US5,388,040 invention adopts the method of changing the resonance parameters, as shown in Fig. 2(b), which is to add a switch Sa in series with the excitation inductance L2 in the main circuit. By controlling the switch Sa to adjust the size of the equivalent magnetizing inductance, in the case of light load or no load, after the switch Sa is turned on, the equivalent magnetizing inductance of the entire main circuit will be reduced, so in a certain working In the frequency range, the minimum voltage gain of the entire main circuit will decrease, and the entire main circuit can work stably.

(2) JP8,033,329 invention

Please refer to Fig. 2(c), which is a circuit diagram of a traditional full-bridge LLC converter disclosed in invention No. JP8,033,329, and the same components as those in the aforementioned Fig. 2(a) in the full-bridge LLC converter 22 are marked with the same figure display symbol.

JP8,033,329 invention adopts the method of changing the resonance impedance, as shown in Fig. 2(c). It is to add a parallel resonant unit composed of inductance L2 and capacitor C2 to the resonant circuit formed by resonant capacitor C1, resonant inductance L1 and the primary side of transformer T1, so as to increase the resonance of converter 22 when it is no-load or light-loaded. The impedance of the loop, so as to achieve the effect of stabilizing the system. But its disadvantage is that when the main circuit works under light load or no load, the parallel resonant unit will bear great voltage and current stress.

(3) Invention No. JP2,106,164

Please refer to Fig. 2 (d), which is a circuit diagram of a traditional full-bridge LLC converter disclosed by No. JP2, 106, and No. 164 invention. In the full-bridge LLC converter 23, the same components as in the aforementioned Fig. 2 (a) are marked with the same figure display symbol.

The method adopted in JP2,106,164 invention is shown in Fig. 2(d). It is a series circuit composed of an auxiliary switch S and a resistor R connected in parallel at the resonant capacitor C1. Through this series circuit, the energy on the resonant capacitor C1 can be consumed at no-load to avoid excessive energy being injected into the output end.

In view of the defects of the prior art, the applicant finally conceived the present invention after careful testing and research, and a persistent spirit. The following is a brief description of the present invention.

Contents of the invention

The main purpose of the present invention is to propose a resonant converter and its light-load and no-load voltage stabilization method to solve the problem of unstable operation of the entire circuit due to the influence of parasitic parameters when the converter is light-loaded or no-loaded .

The main idea of the present invention is to propose a resonant converter, which additionally has an energy feedback circuit compared with the prior art, which can refeed back the excess energy injected into the output end of the converter through the rectifier diode to the input end of the converter , the loss caused by this circuit structure is very small, and it can be realized with a relatively simple control.

The present invention proposes a resonant converter, comprising: a conversion circuit stage; a diode rectification circuit stage coupled in series to the conversion circuit stage to rectify the output of the conversion circuit stage; a filter and load circuit stage , coupled in series to the diode rectifier circuit stage, filtering the output of the diode rectifier circuit stage; a logic circuit, coupled to the conversion circuit stage, generating a logic signal in response to the conversion circuit stage; a driver, coupled in series to the logic circuit, receiving the logic signal and generating a drive signal; and an energy feedback circuit, coupled to the conversion circuit stage, the filter and load circuit stage and the driver, when When the filter and load circuit stage is light-loaded or unloaded, the energy feedback circuit receives the driving signal and feeds back energy from the filter and load circuit stage to the conversion circuit stage.

The secondary idea of the present invention is to propose a method for realizing light-load and no-load voltage regulation of a resonant converter, which feeds back the energy at the output end of the converter to the input end of the converter through a physical circuit path or an inductive circuit path, so as to realize the complete conversion of the converter. Stable operation with no load.

The present invention proposes a method for realizing light-load and no-load voltage regulation of a resonant converter, wherein the resonant converter includes a conversion circuit stage, a diode rectification circuit stage, a filter and load circuit stage, and a logic circuit, The diode rectification circuit stage is coupled in series to the conversion circuit stage to rectify the output of the conversion circuit stage, and the filter and load circuit stage is coupled in series to the diode rectification circuit stage to rectify the diode The output of the circuit stage is filtered, and the logic circuit is coupled to the conversion circuit stage and generates a logic signal in response to the conversion circuit stage. The method includes the following steps: when the filter and load circuit stage is lightly loaded or At no load, an energy is fed back from the filter and load circuit stage to the conversion circuit stage in response to the logic signal.

The present invention needs to pass through following accompanying drawing and detailed description, so that understand more deeply:

Description of drawings

Figure 1: Block diagram of a conventional DC-DC converter.

Figure 2(a): Circuit diagram of a traditional full-bridge LLC converter.

Fig. 2(b): The circuit diagram of the traditional full-bridge LLC converter disclosed in US5,388,040 invention.

Fig. 2(c): The circuit diagram of the traditional full-bridge LLC converter disclosed in JP8,033,329 invention.

Fig. 2(d): The circuit diagram of the traditional full-bridge LLC converter disclosed in JP2,106,164 invention.

Figure 3: Block diagram of a preferred embodiment of the resonant converter of the present invention.

Figure 4: Circuit diagram of a preferred embodiment of the resonant converter of the present invention.

Figure 5(a)~(f): Circuit diagrams of various configurations of the energy feedback circuit of the present invention.

Fig. 6(a)-(e): Circuit diagrams of multiple configurations of the stage coupling of the energy feedback circuit and the diode rectification circuit of the present invention. Figure 7: Waveform diagram of the resonant converter of Figure 4.

Fig. 8: A circuit diagram of another configuration of the energy feedback circuit of the present invention.

FIG. 9 is a circuit diagram of another preferred embodiment of the present invention adopting the architecture of FIG. 8 .

Detailed ways

Please refer to FIG. 3 , which is a block diagram of a preferred embodiment of the present invention. In addition, in FIG. 3 , the same blocks as those in FIG. 1 are denoted by the same symbols. Wherein, the converter 30 is composed of a conversion circuit stage 11 , a diode rectification circuit stage 12 , a filter and load circuit stage 13 , a logic circuit 31 , a driver 32 and an energy feedback circuit 33 .

In FIG. 3 , the diode rectification circuit stage 12 is coupled in series to the conversion circuit stage 11 to rectify the output of the conversion circuit stage 11, and the filter and load circuit stage 13 is coupled in series to the diode rectification circuit stage 12 to rectify the output of the conversion circuit stage 11. The output of the diode rectification circuit stage 12 is filtered, the logic circuit 31 is coupled to the conversion circuit stage 11 to generate a logic signal in response to the conversion circuit stage 11, and the driver 32 is connected in series to the logic circuit 31 to receive The logic signal generates a drive signal, and the energy feedback circuit 33 is coupled to the conversion circuit stage 11, the filter and load circuit stage 13 and the driver 32; and when the filter and load circuit stage 13 is light-loaded or unloaded , the energy feedback circuit 33 receives the driving signal and feeds back energy from the filter and load circuit stage 13 to the conversion circuit stage 11 .

For the actual circuit configuration, please refer to FIG. 4 , which is a circuit diagram of a preferred embodiment of the present invention. In FIG. 4 , the same blocks as in the aforementioned FIG. 3 are denoted by the same symbols. Wherein, the resonant converter 40 is a series resonant converter, which is composed of a conventional DC-DC converter 10 , a logic circuit 31 , a driver 32 and an energy feedback circuit 33 .

In FIG. 4 , the conversion circuit stage includes: an input voltage generating circuit composed of transistor switches Q1 ˜ Q4 , a resonant capacitor C1 , a resonant inductor L1 , a magnetizing inductor L2 and a transformer T1 . The magnetizing inductance L2 is connected in parallel to the primary side of the transformer T1 and then connected in series with the resonant circuit. Although this embodiment uses a full bridge circuit composed of four transistor switches Q1~Q4 as the input voltage generation circuit, two A half-bridge circuit composed of transistor switches is used as the input voltage generating circuit.

In FIG. 4 , the diode rectifier circuit stage, filter and load circuit stage are coupled to the secondary side of the transformer T1 in sequence. In this embodiment, although the diode rectifier circuit stage is a diode full-wave rectifier circuit composed of diodes D1 and D2, it can also be a diode half-wave rectifier circuit or a diode full-bridge rectifier circuit. The filter and load circuit stage includes a capacitor Cout, and the load is not drawn.

In Fig. 4, although the configuration circuit of logic circuit 31 is made with components such as resistance Ra, diode Da1, capacitor Ca and AND gate, its configuration mode is not limited to this example, and those of ordinary skill in the art can satisfy the same function Other types of logic circuits 31 can be easily conceived under the premise.

In FIG. 4, although the energy feedback circuit 33 is made of a transistor switch Sa and a diode Da opposite to the diode D1, its configuration is not limited to this example, and those skilled in the art can achieve the same function under the premise of Other types of energy feedback circuits 33 are readily conceivable. With the technology of the present invention, the configuration of the energy feedback circuit 33 includes at least one switch, therefore, the configuration of the energy feedback circuit 33 can be a single switch shown in Figure 5 (a), a single switch shown in Figure 5 (b) Transistor switch Sa, the series connection of single transistor switch Sa and diode Da shown in Figure 5(c), the series connection of single transistor switch Sa and resistor Ra shown in Figure 5(d), the A series connection of a single transistor switch Sa with a resistor Ra and a diode Da, or a series connection of two transistor switches Sa as shown in FIG. 5( f ). As long as energy can be transferred from the output end to the input end, the energy feedback circuit 33 can be a single switch or a combination of multiple switches, and it can be a one-way switch or a two-way switch. These switches can have internal resistance, An external series resistor can also be used, but its basic feature is to provide a controllable energy channel from point B to point A in Figure 5.

As mentioned earlier, the diode rectifier circuit stage can be a diode half-wave rectifier circuit, a diode full-wave rectifier circuit or a diode full-bridge rectifier circuit. The circuit diagram of the configuration as an energy feedback circuit coupled with three diode rectification circuit stages. As shown in Figure 6(a)~(c), the energy feedback circuit is a single physical circuit path, and the frequency of the energy feedback circuit is at most equal to the switching frequency of the conversion circuit stage, that is, within one switching cycle, at most An energy feedback from output to input can of course also be realized with multiple switching cycles. Figure 6(d) and Figure 6(e) provide two physical circuit paths, which are connected in parallel with a switch tube on each diode of the diode rectification circuit stage, and are realized by adding an energy feedback unit (switch) Energy can be fed back twice in one switching cycle;

The operation mode of the above-mentioned FIG. 4 is described below with the waveform diagram of FIG. 7 .

The input signal of the logic circuit 31 is the driving signal gQ1 of the transistor switches Q1 and Q4, and the driving signal gQ2 of the transistor switches Q3 and Q2. The falling edge of the driving signal gQ2 is delayed through the network of resistor Ra, diode Da1 and capacitor Ca to obtain the signal u1, and then ANDed with the driving signal gQ1 to obtain a rising edge synchronous with the driving signal gQ1, but the pulse width is not greater than the driving Signal gQ1 logic signal u2. The logic signal u2 is amplified by the driver 32 and used to drive the transistor switch Sa of the energy feedback circuit 33 . The transistor switch Sa is connected in series with the diode Da and then connected in parallel with the main power diode D1, which can provide unidirectional energy transfer in the opposite direction to the diode D1, so as a whole, the unit composed of the transistor switch Sa, diode Da and diode D1 can realize energy two-way transmission. When the voltage u3 of the secondary side winding of the transformer T1 where the diode D1 is located rises to be positive, the transistor switch Sa is turned on at this moment. If too much energy is transferred to the output terminal at no-load, the voltage at the output terminal will be greater than the voltage u3 at this time, so a current flows from the output terminal to the primary side of the transformer T1, thereby realizing energy feedback. And when the load increases, the voltage u3 is greater than the output terminal voltage, and the current flows from the diode D1 to the output at this time. Because of the existence of the diode Da, there is no current passing through the transistor switch Sa. Therefore, the energy transfer circuit 33 is important for the main circuit when the load is increased. There is no influence on the working state of , and the transistor switch Sa and the diode Da can use components with smaller specifications.

Please refer to Fig. 8, which is a circuit diagram of another configuration mode of the energy feedback circuit of the present invention, which is different from the physical circuit path in Fig. 5, what is adopted in Fig. 8 is an inductive circuit path; that is, an auxiliary two The secondary winding and a switch S form an energy feedback circuit 81 to control energy feedback to the primary side. The energy feedback circuit 81 can be used in converters with various output filtering modes. If the output filtering mode also adopts capacitor direct filtering, the architecture is equivalent to the architecture shown in FIG. 6( b ). In addition, the switch S can also be replaced by the configuration shown in Fig. 5(a)-(f), as long as it can provide a controllable energy channel from the output end to the input end. For a diode full-bridge rectifier circuit as shown in Figure 6(c), this architecture can save a switching element.

Please refer to FIG. 9 , which is a circuit diagram of another preferred embodiment of the present invention adopting the architecture of FIG. 8 , and its waveform diagram is the same as that shown in FIG. 7 .

In FIG. 9 , the blocks that are the same as those in the aforementioned FIG. 3 , FIG. 4 , and FIG. 8 are denoted by the same symbol. Wherein, the resonant converter 90 is a series resonant converter, which is composed of a conventional DC-DC converter 10 , a logic circuit 31 , a driver 32 and an energy feedback circuit 81 . However, at this time, the input voltage generation circuit is a half-bridge circuit composed of two transistor switches Q1 and Q2, the diode rectification circuit stage is a diode full-wave rectification circuit, and the energy feedback circuit 81 is composed of an auxiliary secondary winding, transistor It is composed of a switch Sa and a diode Da.

The logic circuit 31 is exactly the same as the logic circuit in FIG. 4 , and finally generates a logic signal u2 whose rising edge is synchronous with the drive signal gQ1, but the pulse width is not greater than the drive signal gQ1; of course, the existing flyback circuit can also be used for synchronous rectification control methods to generate control signals. And when the voltage u3 of the auxiliary winding on the secondary side of the transformer rises to be positive, the transistor switch Sa is turned on at this time. If too much energy is transferred to the output terminal at no-load, the voltage at the output terminal is greater than the voltage u3 at this time, and current flows from the output terminal to the primary side of the transformer T1, thereby realizing energy feedback and ensuring stable operation at no-load . Similarly, when the load is heavier, the voltage u3 is greater than the output terminal voltage, and because of the presence of the diode Da, there is no current passing through the transistor switch Sa, therefore, the energy transfer circuit 81 has no influence on the working state of the main circuit when the load is heavier, and The transistor switch Sa and the diode Da can use components with smaller specifications.

To sum up, the present invention provides a resonant converter and a method for realizing its light-load and no-load voltage stabilization. The feedback circuit is used to realize the two-way transmission of energy, and the excessive energy injected into the output terminal through the rectifier diode is fed back to the input terminal, so as to ensure the stable operation of the system. The added energy feedback circuit not only has no effect on the working state of the main circuit when the load is increased , and the used transistor switches and diodes can use smaller size components. .

The present invention can be modified in various ways by those of ordinary skill in the art, all without departing from what is intended to be protected by the claims.

Claims (12)

1. A resonant converter, characterized in that, comprising: a conversion circuit stage; A diode rectification circuit stage, coupled in series with the conversion circuit stage, rectifies the output of the conversion circuit stage; a filter and load circuit stage, coupled in series with the diode rectifier circuit stage, for filtering the output of the diode rectifier circuit stage; a logic circuit, coupled to the conversion circuit stage, generating a logic signal in response to the conversion circuit stage; A driver, coupled in series with the logic circuit, receives the logic signal and generates a drive signal; and An energy feedback circuit, coupled to the conversion circuit stage, the filter and load circuit stage and the driver, when the filter and load circuit stage is light-loaded or unloaded, the energy feedback circuit receives the drive The signal feeds an energy from the filter and load circuit stage to the conversion circuit stage. 2. The resonant converter as claimed in claim 1, wherein the diode rectification circuit stage is selected from one of a diode half-wave rectification circuit, a diode full-wave rectification circuit and a diode full-bridge rectification circuit. 3. The resonant converter according to claim 1, wherein the energy feedback circuit is composed of at least one switch unit. 4. The resonant converter according to claim 3, wherein the switch unit is connected in parallel with a diode of the diode rectifier circuit stage to form a recombination unit, and the resonant converter comprises at least one recombination unit, Feedback energy from the filter and load circuit stage to the conversion circuit stage. 5 . The resonant converter according to claim 3 , wherein the energy feedback circuit further comprises a transformer secondary side auxiliary winding, and the transformer secondary side auxiliary winding is connected in series with the switching unit. 6. The resonant converter according to claim 4 or 5, characterized in that: The switch unit is a switch tube connected in series with a resistor; The switch unit is a switch tube connected in series with a diode; The switch unit is a switch tube; The switch unit is a switch tube connected in series with a diode and a resistor; or The switch unit is a switch tube connected in series with another switch tube. 7. The resonant converter as claimed in claim 1, wherein the resonant converter is a series resonant converter. 8. The resonant converter according to claim 7, characterized in that: The conversion circuit stage includes an input voltage generating circuit, a resonant circuit, a magnetizing inductance and a transformer, the input voltage generating circuit is coupled to the resonant circuit, the magnetizing inductance is connected in parallel to the primary side of the transformer and then connected in series with the resonant circuit, and the input voltage generating circuit is selected from one of a half-bridge circuit and a full-bridge circuit, the resonant circuit includes a resonant capacitor and a resonant inductance connected in series with each other; The filtering and loading circuit stage includes a capacitor; and/or The logic circuit includes a resistor, a diode, a capacitor and an AND gate, wherein the AND gate is coupled to the resistor, the diode and the capacitor. 9. A method for realizing light-load and no-load voltage regulation of a resonant converter, wherein the resonant converter includes a conversion circuit stage, a diode rectification circuit stage, a filter and load circuit stage, and a logic circuit, The diode rectification circuit stage is coupled in series to the conversion circuit stage to rectify the output of the conversion circuit stage, and the filter and load circuit stage is coupled in series to the diode rectification circuit stage to rectify the diode The output of the circuit stage is filtered, the logic circuit is coupled to the conversion circuit stage and generates a logic signal in response to the conversion circuit stage, and the method includes the following steps: When the filter and load circuit stage is lightly loaded or unloaded, an energy is fed back from the filter and load circuit stage to the conversion circuit stage in response to the logic signal. 10. The method for realizing light-load and no-load voltage regulation of a resonant converter as claimed in claim 9, further comprising a step of: At least one physical circuit path is provided between the conversion circuit stage and the filter and load circuit stage for feeding energy from the filter and load circuit stage to the conversion circuit stage. 11. The method for realizing light-load and no-load voltage regulation of a resonant converter according to claim 10, wherein the diode rectification circuit stage includes at least one diode, and the physical circuit path is connected in parallel with the diode to A recombination unit is formed, and the resonant converter at least includes the recombination unit to realize energy feedback from the filter and load circuit stage to the conversion circuit stage. 12. The method for realizing light-load and no-load voltage regulation of a resonant converter as claimed in claim 10, further comprising a step of: An inductive circuit path is provided between the conversion circuit stage and the filter and load circuit stage for the energy to be fed back from the filter and load circuit stage to the conversion circuit stage.

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