A control circuit and feedback circuit for a multi-output circuit

Abstract

This invention discloses a control circuit and its feedback circuit for a multi-output switching circuit. The switching circuit includes an energy storage element with multiple windings and a primary-side switch. The control circuit is powered by a rectified power supply voltage from one of the windings. In this invention, the voltage of the power supply winding and the power supply voltage of the control circuit are weighted and superimposed to form a feedback voltage, which is used for loop control of the control circuit to adjust the duty cycle of the control signal of the primary-side switch, thereby effectively regulating each output. The weighted feedback control circuit and control method proposed in this invention have a simple circuit structure and can effectively regulate multiple outputs, improving the accuracy of each output.

Description

[0001] This application is a divisional application of patent application No. CN 202011519080.3, filed on December 21, 2020, entitled "A Control Circuit and Feedback Circuit for a Multi-output Circuit". Technical Field

[0002] This invention relates to electronic circuits, and more specifically to multi-output circuits and their feedback circuits. Background Technology

[0003] In switching power supply circuits, such as Figure 1 The flyback converter shown can generate multiple output voltages by adding a secondary winding to the transformer. Since this type of switching power supply circuit has only a single control loop, when it has multiple outputs, we need to select the output to be regulated as the feedback signal to participate in the control loop regulation. This feedback output can be the output with the highest power or a low-power output requiring higher precision. However, this feedback only provides precise regulation for its own output; for other outputs, only coarse regulation or no regulation is performed.

[0004] To enhance the regulation of each output, a common solution is to weight the feedback from multiple outputs to achieve regulation of all outputs. In some applications, such as flyback converters with partial primary-side control, optocouplers and other coupling devices are omitted for cost reasons, making it difficult to feed back the secondary-side outputs to the primary side, let alone provide feedback and regulation of multiple secondary-side outputs. In these applications, providing feedback signals to effectively regulate each output becomes a challenge. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned technical problems of the prior art, and to propose a feedback control circuit and control method for a multi-output switching power supply circuit.

[0006] According to an embodiment of the present invention, a control circuit is used to control a multi-output switching circuit having at least two secondary rectifier diodes. The control circuit includes: a sample-and-hold circuit that samples and holds the power supply winding voltage during the on-state of any one of the secondary rectifier diodes and outputs a power supply winding sample-and-hold signal; and a feedback circuit that receives the power supply voltage and the power supply winding sample-and-hold signal from the control circuit, and outputs the power supply winding sample-and-hold signal as a feedback voltage to control the output of the multi-output switching circuit when the value of the power supply winding sample-and-hold signal is between a third proportional voltage and a fourth proportional voltage. The ratio of the third proportional voltage to the power supply voltage is a third proportional coefficient, the ratio of the fourth proportional voltage to the power supply voltage is a fourth proportional coefficient, the value of the third proportional coefficient is greater than 1 and less than 2, and the value of the fourth proportional coefficient is greater than 0 and less than 1.

[0007] In one embodiment, the control circuit further comprises: an error amplifier receiving the feedback voltage and a reference signal, outputting a compensation signal, the compensation signal being an error amplified signal of the feedback voltage and the reference signal; and a pulse control circuit receiving the compensation signal, outputting a switch control signal for controlling the primary side switch of the multi-output switching circuit based on the compensation signal.

[0008] In one embodiment, the feedback circuit comprises: a third proportional circuit receiving the supply voltage, outputting a third proportional voltage, the third proportional voltage being in a third proportional ratio to the supply voltage, the third proportional ratio having a value greater than 1 and less than 2; a fourth proportional circuit receiving the supply voltage, outputting a fourth proportional voltage, the fourth proportional voltage being in a fourth proportional ratio to the supply voltage, the fourth proportional ratio having a value greater than 0 and less than 1; a hysteretic comparison circuit receiving the third proportional voltage, the fourth proportional voltage and the supply winding sample hold signal, outputting a selection signal based on a comparison result of the three, wherein when the value of the supply winding sample hold signal is between the third proportional voltage and the fourth proportional voltage, the value of the selection signal is a first level, otherwise, the value of the selection signal is a second level; and a selection circuit receiving the selection signal, the supply voltage and the supply winding sample hold signal, outputting the supply winding sample hold signal as the feedback voltage when the value of the selection signal is the first level, outputting the supply voltage as the feedback voltage when the value of the selection signal is the second level.

[0009] According to an embodiment of the present application, a control circuit for controlling a multi-output switching circuit having at least two secondary side rectifier tubes, the control circuit comprising: a sample hold circuit sampling and holding a supply winding voltage during a turn-on period of any of the secondary side rectifier tubes, outputting a supply winding sample hold signal; a feedback circuit receiving a supply voltage of the control circuit, the supply winding sample hold signal, a compensation signal and a threshold signal, outputting the supply voltage or the supply winding sample hold signal as a feedback voltage based on a comparison result of the compensation signal and the threshold signal; and an error amplifier receiving the feedback voltage and a reference signal, outputting the compensation signal for controlling the multi-output switching circuit, the compensation signal being an error amplified signal of the feedback voltage and the reference signal.

[0010] According to an embodiment of the present application, a flyback switching circuit comprising the aforementioned control circuit, further comprising: a primary side switch coupled between a primary side winding and a primary side ground.

[0011] According to an embodiment of the present application, a control circuit for a Flybuck circuit comprises: a sample-and-hold circuit, which samples a primary winding voltage of the Flybuck circuit during a turn-on period of a secondary rectifier tube of the Flybuck circuit, and outputs a primary winding sample-and-hold signal; and a feedback circuit, which receives a power supply voltage of the control circuit and the primary winding sample-and-hold signal, and outputs the primary winding sample-and-hold signal as a feedback voltage for controlling an output of a multi-output switching circuit when a value of the primary winding sample-and-hold signal is between a third proportional voltage and a fourth proportional voltage, wherein a ratio of the third proportional voltage to the power supply voltage is a third proportional coefficient, a ratio of the fourth proportional voltage to the power supply voltage is a fourth proportional coefficient, the third proportional coefficient has a value greater than 1 and less than 2, and the fourth proportional coefficient has a value greater than 0 and less than 1.

[0012] In one embodiment, the control circuit further comprises an error amplifier, which receives the feedback voltage and a reference signal, and outputs a compensation signal which is an error amplified signal of the feedback voltage and the reference signal; and a pulse control circuit, which receives the compensation signal, and outputs a switching control signal of a primary switch based on the compensation signal.

[0013] According to an embodiment of the present application, a Flybuck circuit comprises the control circuit of the Flybuck circuit, and further comprises: an energy storage element comprising a primary winding and a secondary winding; a primary switch coupled between an input voltage of the Flybuck circuit and a control ground; a freewheeling tube coupled between a first end of the primary winding and a primary ground, a second end of the primary winding providing a first output voltage; and a secondary rectifier tube coupled between the secondary winding and a second output voltage.

[0014] The feedback circuit and the control circuit provided by the present application have simple circuit structures, and can effectively regulate multi-output and improve output accuracy of each output. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 A circuit structure schematic diagram of an existing primary control flyback switching circuit 10 is shown;

[0016] Figure 2 A circuit structure schematic diagram of a control circuit 20 according to an embodiment of the present application is shown;

[0017] Figure 3 Voltage waveform schematic diagrams of a power supply voltage Vcc1, a supply winding sample-and-hold signal Vs&h1 and a supply winding voltage VL1 of the flyback switching circuit 10 are shown;

[0018] Figure 4 A circuit structure schematic diagram of a control circuit 40 according to an embodiment of the present application is shown;

[0019] Figure 5 A schematic diagram of the circuit structure of a control circuit 50 according to an embodiment of the present invention is shown;

[0020] Figure 6 A schematic diagram of the circuit structure of a control circuit 60 according to an embodiment of the present invention is shown;

[0021] Figure 7 A schematic diagram of the existing Flybuck circuit 70 is shown;

[0022] Figure 8 The diagram shows the voltage waveforms of the power supply voltage Vcc2, the primary winding voltage VL2, and the primary winding sample-and-hold signal Vs&h2 in the Flybuck circuit 70.

[0023] Figure 9 A schematic diagram of the circuit structure of a control circuit 90 according to an embodiment of the present invention is shown;

[0024] Figure 10 A schematic diagram of the circuit structure of a control circuit 100 according to an embodiment of the present invention is shown;

[0025] Figure 11 A schematic diagram of the circuit structure of a control circuit 110 according to an embodiment of the present invention is shown. Detailed Implementation

[0026] Specific embodiments of the present invention will now be described in detail. It should be noted that the embodiments described herein are for illustrative purposes only and are not intended to limit the invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other instances, well-known circuits, materials, or methods have not been specifically described to avoid obscuring the invention.

[0027] Throughout this specification, references to “an embodiment,” “an example,” or “an example” mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases “in an embodiment,” “in an embodiment,” “an example,” or “an example” appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. Moreover, those skilled in the art will understand that the accompanying drawings provided herein are for illustrative purposes and are not necessarily drawn to scale. It should be understood that when an element is referred to as “connected to” or “coupled to” another element, it can be a direct connection or coupling to the other element or there may be intermediate elements. Conversely, when an element is referred to as “directly connected to” or “directly coupled to” another element, there are no intermediate elements. The same reference numerals indicate the same elements. The term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0028] Figure 1 A schematic diagram of the circuit structure of a conventional primary-side controlled flyback switching circuit 10 is shown. Figure 1 As shown, the flyback switching circuit 10 includes: an energy storage element T1, comprising a primary winding Lp1, a first secondary winding Ls11, a second secondary winding Ls12, and a power supply winding Lt1; a primary-side switch PM1, coupled between the primary winding Lp1 and primary ground PGND; a first secondary-side rectifier D11, coupled between the first secondary winding Ls11 and the first output terminal 102 of the flyback switching circuit 10; a second secondary-side rectifier D12, coupled between the second secondary winding Ls12 and the second output terminal 103 of the flyback switching circuit 10; a power supply winding rectifier D13, coupled between one end of the power supply winding Lt1 and the power supply voltage Vcc1; and a control circuit 105, receiving the power supply voltage Vcc1 and the power supply winding voltage VL1, and outputting a switch control signal G1 to control the primary-side switch PM1. The control circuit 105 and the primary-side switch PM1 can be integrated into a primary-side control chip, or they can be integrated into different chips. Figure 1 As shown, the first output terminal 102 of the flyback switching circuit 10 is coupled to capacitor Co11, which provides a first output voltage Va1; the second output terminal 103 is coupled to capacitor Co12, which provides a second output voltage Va2; and capacitor Ct1 is coupled between the power supply voltage Vcc1 and the primary ground PGND, and the power supply voltage Vcc1 is generated by the power supply winding Lt1 to supply power to the control circuit 105.

[0029] The flyback switching circuit 10 utilizes the alternating switching of the primary-side switch PM1 and the first secondary-side rectifier D11 and the second secondary-side rectifier D12 to transfer energy from the primary side to the secondary side. By setting the turns ratio of the primary and secondary windings and the duty cycle of the primary-side switch PM1, the flyback switching circuit 10 can provide the required first output voltage Va1 and second output voltage Va2.

[0030] In the primary-side controlled flyback switching circuit 10, since the primary and secondary sides are isolated and there are no optocouplers or other coupling devices to provide feedback to the secondary output, in the prior art, the voltage VL1 of the power supply winding Lt1 is typically sampled and held as a feedback voltage during the freewheeling period of the secondary rectifier diode to adjust the duty cycle of the primary-side switch PM1 to adapt to the load changes of the first output terminal 102 and the second output terminal 103. However, in some cases, such as when the loads of each output differ significantly, the overall system load is light, or the accuracy requirements of the light-load output are high, using the sampled power supply winding voltage VL1 as a feedback voltage to adjust the control loop usually cannot effectively and timely adjust the light-load output.

[0031] Figure 2 A schematic diagram of the circuit structure of a control circuit 20 according to an embodiment of the present invention is shown. Figure 2 As shown, the control circuit 20 includes: a sample-and-hold circuit 24, which samples and holds the power supply winding voltage VL1 during the on-state of either the secondary rectifier diodes D11 and D12, and outputs a power supply winding sample-and-hold signal Vs&h1; a feedback circuit 21, which receives the power supply voltage Vcc1 and the power supply winding sample-and-hold signal Vs&h1, and outputs a weighted voltage Vmix1 as the feedback voltage Vfb1; an error amplifier 22, which receives the feedback voltage Vfb1 and the reference signal Vref1, and outputs a compensation signal Vcomp1, wherein the compensation signal Vcomp1 is an error amplification signal of the feedback voltage Vfb1 and the reference signal Vref1; and a pulse control circuit 23, which receives the compensation signal Vcomp1 and outputs a switching control signal G1 for the primary-side switch PM1 based on the compensation signal Vcomp1.

[0032] The sample-and-hold circuit 24 receives the power supply winding voltage VL1 and samples and holds its value during the period after the power supply winding voltage VL1 stops oscillating, when any secondary rectifier diode is turned on, to output a power supply winding sample-and-hold signal Vs&h1. In practical applications, those skilled in the art can calculate the turn-on time of the secondary rectifier diode based on the parameters of the specific application, and estimate the oscillation time of the power supply winding voltage VL1 after the primary switch PM1 is turned off and the secondary rectifier diodes D11 and D12 are turned on, thereby avoiding this oscillation time to select a suitable sampling point.

[0033] The pulse control circuit 23 can be any existing circuit used to generate a switching control signal G1 with a certain duty cycle, such as a pulse width modulation (PWM) circuit, a pulse frequency modulation (PFM) circuit, or a combination of both. In one embodiment, when the feedback voltage Vfb1 decreases, the compensation signal Vcomp1 increases. Through the adjustment of the pulse control circuit 23, the duty cycle of the control signal G1 increases, thereby transferring more energy from the primary side to the secondary side. When the feedback voltage Vfb1 increases, the compensation signal Vcomp1 decreases. Through the adjustment of the pulse control circuit 23, the duty cycle of the control signal G1 decreases, thereby reducing the energy transferred from the primary side to the secondary side.

[0034] Figure 2 In this embodiment, the feedback circuit 21 is also called a weighting circuit, comprising: a first proportional circuit 201, which receives the power supply voltage Vcc1 and outputs a first proportional voltage K1×Vcc1 proportional to the power supply voltage Vcc1, where K1 is a first proportional coefficient with a value greater than 0 and less than 1; a second proportional circuit 202, which receives the power supply winding sample-and-hold signal Vs&h1 and outputs a second proportional voltage K2×Vs&h1 proportional to the power supply winding sample-and-hold signal Vs&h1, where K2 is a second proportional coefficient with a value greater than 0 and less than 1; and an arithmetic circuit 203, which receives the first proportional voltage K1×Vcc1 and the second proportional voltage K2×Vs&h1 and outputs a weighted voltage Vmix, wherein the weighted voltage Vmix1 is the sum of the first proportional voltage K1×Vcc1 and the second proportional voltage K2×Vs&h1, i.e., Vmix1=K1×Vcc1+K2×Vs&h1; where K1+K2=1.

[0035] Figure 3 The diagram shows the voltage waveforms of the power supply voltage Vcc1, the power supply winding voltage VL1, and the power supply winding sample-and-hold signal Vs&h1 of the flyback switching circuit 10. The following is a related explanation. Figure 1 , Figure 2 and Figure 3 To explain the working principle of control circuit 20. For example Figure 3As shown, at time t0, the primary-side switch PM1 is turned off, and the first secondary-side rectifier D11, the second secondary-side rectifier D12, and the power supply winding rectifier D13 are turned on. The power supply winding voltage VL1 rises, oscillating at the initial moment. The capacitor Ct1 is charged, and the power supply voltage Vcc1 rises to a certain extent. After the power supply voltage Vcc1 is greater than the power supply winding voltage VL1, the power supply winding rectifier D13 is turned off, and the power supply voltage Vcc1 remains on the capacitor Ct1, supplying power to the control circuit 105. Before the power supply winding voltage VL1 stops oscillating and all secondary-side rectifiers are turned off (at time t1), the sample-and-hold circuit 24 samples the power supply winding voltage VL1 and holds its value, outputting the power supply winding sample-and-hold signal Vs&h1. At time t2, the primary-side switch PM1 is turned on, and the value of the power supply winding sample-and-hold signal Vs&h1 remains unchanged. Because the control circuit 105 is powered while the rectifier diode D13 of the power supply winding is off, the power supply voltage Vcc1 slowly decreases. At time t3, the primary-side switch PM1 turns off again, and a new switching cycle begins, repeating continuously.

[0036] The power supply voltage Vcc1 supplies power to the control circuit 105, and its load condition is close to that of the light-load output circuit. However, the power supply winding sample-and-hold signal Vs&h1 better reflects the output of the heavy-load output circuit. Figure 2 The feedback circuit 21 in the middle superimposes the two after weighting, which can adjust the output of both the heavy-load output path and the light-load output path, so that each of the multi-output paths can be effectively regulated. Figure 2 In this configuration, the values ​​of the proportional coefficients K1 and K2 can be set according to the specific application requirements. For example, in a specific application, if the load of the heavy-load output circuit requires higher power accuracy, then the value of K2 can be appropriately larger, while the value of K1 can be appropriately smaller. If the load of the light-load output circuit requires higher power accuracy, then the value of K1 can be appropriately larger, while the value of K2 can be appropriately smaller. In one embodiment, K1 = 0.2 and K2 = 0.8.

[0037] Figure 4 A schematic diagram of the circuit structure of a control circuit 40 according to an embodiment of the present invention is shown. Figure 4As shown, the control circuit 40 includes: a sample and hold circuit 24 that samples and holds the supply winding voltage VL1 during the conduction of any one of the secondary rectifier diodes D11 and D12, and outputs a supply winding sample and hold signal Vs&h1; a feedback circuit 41 that receives the power supply voltage Vcc1 and the supply winding voltage VL1, and outputs a feedback voltage Vfb1 based on the power supply voltage Vcc1 and the supply winding voltage VL1; an error amplifier 22 that receives the feedback voltage Vfb1 and a reference signal Vref1, and outputs a compensation signal Vcomp1, where the compensation signal Vcomp1 is an error amplified signal of the feedback voltage Vfb1 and the reference signal Vref1; and a pulse control circuit 23 that receives the compensation signal Vcomp1, and outputs a switching control signal G1 for the primary switch PM1 based on the compensation signal Vcomp1.

[0038] In Figure 4 In an embodiment, the feedback circuit 41 includes: a third proportional circuit 401 that receives the power supply voltage Vcc1 and outputs a third proportional voltage K3×Vcc1 proportional to the power supply voltage Vcc1, where K3 is a third proportionality coefficient and 1 < K3 < 2; a fourth proportional circuit 402 that receives the power supply voltage Vcc1 and outputs a fourth proportional voltage K4×Vcc1 proportional to the power supply voltage Vcc1, where K4 is a fourth proportionality coefficient and 0 < K4 < 1; a hysteresis comparison circuit 403 that receives the third proportional voltage K3×Vcc1, the fourth proportional voltage K4×Vcc1, and the supply winding sample and hold signal Vs&h1, and outputs a selection signal S1 based on the comparison result of the three. Among them, when the value of the supply winding sample and hold signal Vs&h1 is between the third proportional voltage K3×Vcc1 and the fourth proportional voltage K4×Vcc1, the value of the selection signal S1 is the first level; otherwise, the value of the selection signal S1 is the second level; and a selection circuit 42 that receives the selection signal S1, the power supply voltage Vcc1, and the supply winding sample and hold signal Vs&h1, and selectively outputs the power supply voltage Vcc1 or the supply winding sample and hold signal Vs&h1 as the feedback voltage Vfb1 under the control of the selection signal S1.

[0039] The level state of the selection signal S1 can be determined according to the specific application circuit situation. For example, the first level of the selection signal S1 can be a high level, the second level can be a low level, or vice versa.

[0040] The third proportional voltage K3×Vcc1 and the fourth proportional voltage K4×Vcc1 are the hysteresis intervals of the supply winding sample and hold signal Vs&h1. In Figure 4In the embodiment, when the value of the supply winding sample-and-hold signal Vs&h1 is between the third proportional voltage K3×Vcc1 and the fourth proportional voltage K4×Vcc1, that is, K4×Vcc1 < Vs&h1 < K3×Vcc1, the supply winding sample-and-hold signal Vs&h1 is selected by the selection circuit 407 as the feedback voltage Vfb1. When the value of the supply winding sample-and-hold signal Vs&h1 is greater than the third proportional voltage K3×Vcc1 or less than the fourth proportional voltage K4×Vcc1, the sampling point of the supply winding voltage VL1 may be at its oscillation position, and the supply winding sample-and-hold signal Vs&h1 cannot truly reflect the load. In this case, the power supply voltage Vcc1 is selected as the feedback voltage Vfb1.

[0041] In Figure 4 In the embodiment, the hysteresis comparison circuit 403 includes: a first comparator 404 that receives the third proportional voltage K3×Vcc1 and the supply winding sample-and-hold signal Vs&h1 and outputs a first comparison signal CR1 based on the comparison result of the two; a second comparator 405 that receives the fourth proportional voltage K4×Vcc1 and the supply winding sample-and-hold signal Vs&h1 and outputs a second comparison signal CR2 based on the comparison result of the two; and a logic circuit 406 that receives the first comparison signal CR1 and the second comparison signal CR2 and outputs a selection signal S1 based on the logical operation of the two.

[0042] In one embodiment, K3 = 1.2 and K4 = 0.8. When 0.8×Vcc1 < Vs&h1 < 1.2×Vcc1, the first comparison signal CR1 and the second comparison signal CR2 are at a high level. After passing through the logic circuit 406, the selection signal S1 is at a high level. Under the control of the selection signal S1, the selection circuit 407 selects and outputs the supply winding sample-and-hold signal Vs&h1 as the feedback voltage Vfb1. When Vs&h1 ≤ 0.8×Vcc1 or Vs&h1 ≥ 1.2×Vcc1, the second comparison signal CR2 or the first comparison signal CR1 is at a low level. After passing through the logic circuit 406, the selection signal S1 is at a low level. Under the control of the selection signal S1, the selection circuit 407 selects and outputs the power supply voltage Vcc1 as the feedback voltage Vfb1.

[0043] In Figure 4 the logic circuit 406 is an AND gate circuit. Those of ordinary skill in the art should be clear that when the level state of the input signal or output signal changes, in order to achieve the same function, the logic circuit 406 may include other gate circuits.

[0044] Figure 5 shows a schematic circuit diagram of the control circuit 50 according to an embodiment of the present invention. As Figure 5As shown, the control circuit 50 includes: a sample-and-hold circuit 24 that samples and holds the supply winding voltage VL1 during the conduction of any one of the secondary rectifier diodes D11 and D12, and outputs a supply winding sample-and-hold signal Vs&h1; a feedback circuit 51 that receives the power supply voltage Vcc1 and the supply winding sample-and-hold signal Vs&h1, and outputs a feedback voltage Vfb1 based on the power supply voltage Vcc1 and the supply winding sample-and-hold signal Vs&h1; an error amplifier 22 that receives the feedback voltage Vfb1 and a reference signal Vref1, and outputs a compensation signal Vcomp1, where the compensation signal Vcomp1 is an error amplified signal of the feedback voltage Vfb1 and the reference signal Vref1; and a pulse control circuit 23 that receives the compensation signal Vcomp1, and outputs a switching control signal G1 for the primary switch PM1 based on the compensation signal Vcomp1.

[0045] In Figure 5 the embodiment, the feedback circuit 51 includes: a third proportional circuit 401 that receives the power supply voltage Vcc1 and outputs a third proportional voltage K3×Vcc1 proportional to the power supply voltage Vcc1, where K3 is a third proportionality coefficient and 1 < K3 < 2; a fourth proportional circuit 402 that receives the power supply voltage Vcc1 and outputs a fourth proportional voltage K4×Vcc1 proportional to the power supply voltage Vcc1, where K4 is a fourth proportionality coefficient and 0 < K4 < 1; a hysteresis comparison circuit 403 that receives the third proportional voltage K3×Vcc1, the fourth proportional voltage K4×Vcc1, and the supply winding sample-and-hold signal Vs&h1, and outputs a selection signal S1 based on the comparison result of the three. Among them, when the value of the supply winding sample-and-hold signal Vs&h1 is between the third proportional voltage K3×Vcc1 and the fourth proportional voltage K4×Vcc1, the value of the selection signal S1 is a first level; otherwise, the value of the selection signal S1 is a second level; a feedback circuit 21 that receives the power supply voltage Vcc1 and the supply winding sample-and-hold signal Vs&h1, and outputs a weighted voltage Vmix1; and a selection circuit 42 that receives the selection signal S1, the power supply voltage Vcc1, and the weighted voltage Vmix1, and selects and outputs the power supply voltage Vcc1 or the weighted voltage Vmix1 as the feedback voltage Vfb1 under the control of the selection signal S1.

[0046] The third proportional voltage K3×Vcc1 and the fourth proportional voltage K4×Vcc1 are the hysteresis interval of the supply winding sample-and-hold signal Vs&h1. In Figure 5In an embodiment, when the value of the supply winding sample-and-hold signal Vs&h1 is between the third proportional voltage K3×Vcc1 and the fourth proportional voltage K4×Vcc1, that is, when K4×Vcc1 < Vs&h1 < K3×Vcc1, the weighted voltage Vmix1 is selected by the selection circuit 407 as the feedback voltage Vfb1. When the value of the supply winding sample-and-hold signal Vs&h1 is greater than the third proportional voltage K3×Vcc1 or less than the fourth proportional voltage K4×Vcc1, it is possible that the sampling point of the supply winding sample-and-hold signal Vs&h on the supply winding voltage VL1 is at its oscillation position. In this case, the power supply voltage Vcc1 is selected as the feedback voltage Vfb1.

[0047] Figure 6 FIG. shows a schematic circuit diagram of a control circuit 60 according to an embodiment of the present invention. As Figure 6 shown, the control circuit 60 includes: a sample-and-hold circuit 24 that samples and holds the supply winding voltage VL1 during the conduction of any one of the secondary rectifier diodes D11 and D12, and outputs a supply winding sample-and-hold signal Vs&h1; a feedback circuit 61 that receives a compensation signal Vcomp1, a threshold signal Vth, a power supply voltage Vcc1, and the supply winding sample-and-hold signal Vs&h1, and outputs a feedback voltage Vfb1 based on the compensation signal Vcomp1, the threshold signal Vth, the power supply voltage Vcc1, and the supply winding sample-and-hold signal Vs&h1; an error amplifier 22 that receives the feedback voltage Vfb1 and a reference signal Vref1, and outputs a compensation signal Vcomp1, where the compensation signal Vcomp1 is an error amplified signal of the feedback voltage Vfb1 and the reference signal Vref1; and a pulse control circuit 23 that receives the compensation signal Vcomp1, and outputs a switching control signal G1 for the primary switch PM1 based on the compensation signal Vcomp1.

[0048] In Figure 6 the embodiment, the feedback circuit 61 includes: a load comparison circuit 601 that receives the compensation signal Vcomp1 and the threshold signal Vth, and outputs a selection signal S2 based on the comparison result of the two; and a selection circuit 407 that receives the selection signal S2, the power supply voltage Vcc1, and the supply winding sample-and-hold signal Vs&h1, and selectively outputs the power supply voltage Vcc1 or the supply winding sample-and-hold signal Vs&h1 as the feedback voltage Vfb1 under the control of the selection signal S2.

[0049] In Figure 6In the above circuit, when the value of the compensation signal Vcomp1 is greater than the threshold signal Vth, the system is determined to be in a heavy load state. The selection signal S2 is at the first level, and the selection circuit 407 selects the output power supply winding sample and hold signal Vs&h1 as the feedback voltage Vfb1 under the control of the selection signal S2. When the value of the compensation signal Vcomp1 is less than or equal to the threshold signal Vth, the system is determined to be in a light load state. The selection signal S2 is at the second level, i.e., low level, and the selection circuit 407 selects the output power supply voltage Vcc1 as the feedback voltage Vfb1 under the control of the selection signal S2.

[0050] Under the control of the feedback circuit 61, the control circuit 60 selects the power supply winding sampling and holding signal Vs&h1 as the feedback voltage Vfb1 when the system is under heavy load, so as to focus on adjusting the heavy load output path. When the system is under light load, it selects the power supply voltage Vcc1 as the feedback voltage Vfb1, so as to focus on adjusting the light load output path. This allows both the heavy load output path and the light load output path of the system to be effectively adjusted.

[0051] The threshold signal Vth is used to determine the system's light or heavy load, and its value can be set according to the parameters and requirements of the specific application.

[0052] Figure 7 A schematic diagram of the existing Flybuck circuit 70 is shown. Figure 7 As shown, the Flybuck circuit 70 includes: an energy storage element T2, comprising a primary winding Lp2 and a secondary winding Ls2; a freewheeling diode D21, coupled between a first terminal of the primary winding Lp2 and primary ground GND21, the second terminal of the primary winding Lp2 providing a first output voltage Vb1; a primary switch PM2, coupled between the input voltage VIN and control ground CGND (i.e., the switching terminal of the Flybuck circuit 70); a secondary rectifier diode D22, coupled between the secondary winding Ls2 and the second output voltage Vb2; and a control circuit 705, receiving a power supply voltage Vcc2 and outputting a switch control signal G2 to the primary switch PM2. Figure 7As shown, a capacitor Co21 is coupled between the first output terminal 701 and the primary-side ground GND21, and the capacitor Co21 provides the first output voltage Vb1; a capacitor Co22 is coupled between the second output terminal 702 and the secondary-side ground GND22, and the capacitor Co22 provides the second output voltage Vb2; and a capacitor Ct is coupled between the power supply voltage Vcc2 and the control ground CGND, and the power supply voltage Vcc2 is used to power the control circuit 705. By controlling the on / off state of the primary-side switch PM2 and the freewheeling diode D21, the secondary-side rectifier diode D22, and the power supply winding rectifier diode D23, the Flybuck circuit 70 converts the input voltage VIN into the required first output voltage Vb1, second output voltage Vb2, and power supply voltage Vcc2. The control circuit 705 and the primary-side switch PM2 can be integrated into the primary-side control chip, or they can be integrated into different chips.

[0053] In the prior art, the power supply voltage Vcc2 is used as a feedback voltage to provide to the control circuit 705, participating in the control loop to regulate the output of the Flybuck circuit 70. However, when the output path of the second output voltage Vb2 is heavily loaded, the control circuit 705 can no longer quickly and effectively regulate the output of each load path by adjusting the control loop based on the power supply voltage Vcc2. Figure 8 The diagram shows the voltage waveforms of the power supply voltage Vcc2, primary winding voltage VL2, and primary winding sample-and-hold signal Vs&h2 in the Flybuck circuit 70. The primary winding sample-and-hold signal Vs&h2 is obtained by sampling and holding the primary winding voltage VL2 during the period when any one of the freewheeling diode D21, secondary rectifier diode D22, or primary winding rectifier diode D23 is conducting. Figure 8 As shown, when the secondary side is heavily loaded, that is, when the output terminal 702 is heavily loaded, the second output voltage Vb2 drops, and at the same time, the conduction time of the freewheeling diode D21 is short, so that the primary winding voltage VL2 drops, and the primary winding sampling and holding signal Vs&h2 and the first output voltage Vb1 drop accordingly.

[0054] In order to quickly restore the first output voltage Vb1 and the second output voltage Vb2 to their set values ​​under heavy load on the secondary side, the primary winding sample-and-hold signal Vs&h2 needs to participate in the feedback control.

[0055] Figure 9 A schematic diagram of the circuit structure of a control circuit 90 according to an embodiment of the present invention is shown. The control circuit 90 can be used to replace... Figure 7 The control circuit 705 of the Flybuck circuit 70 shown. Figure 9 The control circuit 90 shown is Figure 2 The control circuit 20 shown is similar, in Figure 9In the circuit, the primary winding sampling and holding signal Vs&h2 and the power supply voltage Vcc2 are input to the feedback circuit 21 to obtain the fifth proportional voltage K1×Vcc2 and the sixth proportional voltage K2×Vs&h2, and finally obtain the weighted voltage Vmix2=K1×Vcc2+K2×Vs&h2. The weighted voltage Vmix2 is used as the feedback voltage Vfb2 to regulate the control loop. The output switch control signal G2 controls the primary side switch PM2, which enables the output voltage of each channel to be quickly and effectively regulated. The proportional coefficients K1 and K2 can be set according to the specific application requirements.

[0056] Figure 10 A schematic diagram of the circuit structure of a control circuit 100 according to an embodiment of the present invention is shown. The control circuit 100 can be used to control... Figure 7 The Flybuck circuit 70 shown. Figure 10 The control circuit 100 shown is Figure 4 The control circuit 40 shown is similar. In Figure 10 In the process, when the value of the primary winding sample-and-hold signal Vs&h2 is between the seventh proportional voltage K3×Vcc2 and the eighth proportional voltage K4×Vcc2, the power supply voltage Vcc2 is selected by the selection circuit 1007 as the feedback voltage Vfb2. Otherwise, the primary winding sample-and-hold signal Vs&h2 is selected as the feedback voltage Vfb2 to regulate the control loop. The output switch control signal G2 is used to control the primary switch PM2, so that the output voltage of each path can be quickly and effectively regulated.

[0057] Figure 11 A schematic diagram of the circuit structure of a control circuit 110 according to an embodiment of the present invention is shown. The control circuit 110 can be used to control... Figure 7 The Flybuck circuit 70 shown. Figure 11 The control circuit 110 shown is Figure 5 The control circuit 50 shown is similar. In Figure 11 In the process, when the value of the primary winding sampling and holding signal Vs&h2 is between the seventh proportional voltage K3×Vcc2 and the eighth proportional voltage K4×Vcc2, the power supply voltage Vcc2 is selected by the selection circuit 1007 as the feedback voltage Vfb2. Otherwise, the weighted voltage Vmix2 output by the feedback circuit 21 is selected as the feedback voltage Vfb2 to regulate the control loop, and outputs the switch control signal G2 to control the primary side switch PM2, so that the output voltage of each path can be quickly and effectively regulated.

[0058] When the control circuit 110 is used to control the Flybuck circuit 70, when the value of the power supply winding sample-and-hold signal Vs&h2 is between the seventh proportional voltage K3×Vcc2 and the eighth proportional voltage K4×Vcc2, the power supply voltage Vcc2 is selected as the feedback voltage Vfb1 for loop control; otherwise, the weighted voltage Vmix2 of the power supply winding sample-and-hold signal Vs&h2 and the power supply voltage Vcc2 is selected as the feedback voltage Vfb2.

[0059] For ease of understanding, this manual uses a two-output switching circuit, namely... Figure 1 flyback switching circuit 10 and Figure 7 The working principle of this invention is illustrated using the Flybuck circuit 70. However, it should be understood that this invention can also be applied to switching circuits with two or more outputs.

[0060] Figure 3 The waveforms of various signals are shown when the flyback switching circuit 10 operates in discontinuous current mode (DCM). Figure 8 The waveforms of various signals are shown when the Flybuck circuit 70 operates in discontinuous current mode (DCM). Those skilled in the art, upon understanding this invention, will realize that the operating mode of the flyback switching circuit 10 and the Flybuck circuit 70 does not affect the essence of this invention.

[0061] In this invention, for clarity of signal correspondence, the power supply voltage, power supply winding voltage, power supply winding sample-and-hold signal, primary winding voltage, and primary winding sample-and-hold signal used for feedback control are schematically input to the control circuit. In practical applications, to match the input voltage range of the control circuit and its subsequent circuits, the power supply voltage, power supply winding voltage, power supply winding sample-and-hold signal, primary winding voltage, and primary winding sample-and-hold signal can all be provided to the control circuit for feedback control after voltage division processing.

[0062] Although the invention has been described with reference to several exemplary embodiments, it should be understood that the terminology used is descriptive and exemplary, and not restrictive. Since the invention can be embodied in many forms without departing from the spirit or essence of the invention, it should be understood that the above embodiments are not limited to any of the foregoing details, but should be interpreted broadly within the spirit and scope defined by the appended claims. Therefore, all variations and modifications falling within the scope of the claims or their equivalents should be covered by the appended claims.

Claims

1. A control circuit for controlling a multi-output switching circuit having at least two secondary-side rectifier tubes, the control circuit comprising: a sample-and-hold circuit for sampling and holding a supply winding voltage during an on period of any of the secondary-side rectifier tubes, and outputting a supply winding sample-and-hold signal; and a feedback circuit for receiving a supply voltage of the control circuit and the supply winding sample-and-hold signal, and outputting the supply winding sample-and-hold signal as a feedback voltage for controlling an output of the multi-output switching circuit when a value of the supply winding sample-and-hold signal is between a third proportional voltage and a fourth proportional voltage, wherein a ratio of the third proportional voltage to the supply voltage is a third proportional coefficient, a ratio of the fourth proportional voltage to the supply voltage is a fourth proportional coefficient, a value of the third proportional coefficient is greater than 1 and less than 2, and a value of the fourth proportional coefficient is greater than 0 and less than 1. 2.The control circuit of claim 1, further comprising: an error amplifier for receiving the feedback voltage and a reference signal, and outputting a compensation signal which is an error amplified signal of the feedback voltage and the reference signal; and a pulse control circuit for receiving the compensation signal, and outputting a switching control signal for controlling a primary-side switch of the multi-output switching circuit based on the compensation signal. 3.The control circuit of claim 1, wherein the feedback circuit comprises: a third proportional circuit for receiving the supply voltage, and outputting the third proportional voltage, wherein a ratio of the third proportional voltage to the supply voltage is the third proportional coefficient, and a value of the third proportional coefficient is greater than 1 and less than 2; a fourth proportional circuit for receiving the supply voltage, and outputting the fourth proportional voltage, wherein a ratio of the fourth proportional voltage to the supply voltage is the fourth proportional coefficient, and a value of the fourth proportional coefficient is greater than 0 and less than 1; a hysteretic comparison circuit for receiving the third proportional voltage, the fourth proportional voltage and the supply winding sample-and-hold signal, and outputting a selection signal based on a comparison result of the third proportional voltage, the fourth proportional voltage and the supply winding sample-and-hold signal, wherein a value of the selection signal is a first level when a value of the supply winding sample-and-hold signal is between the third proportional voltage and the fourth proportional voltage, and a value of the selection signal is a second level otherwise; and a selection circuit for receiving the selection signal, the supply voltage and the supply winding sample-and-hold signal, and selecting to output the supply winding sample-and-hold signal as the feedback voltage when the value of the selection signal is the first level, and selecting to output the supply voltage as the feedback voltage when the value of the selection signal is the second level. 4.A control circuit for controlling a multi-output switching circuit having at least two secondary-side rectifier tubes, the control circuit comprising: a sample-and-hold circuit for sampling and holding a supply winding voltage during an on period of any of the secondary-side rectifier tubes, and outputting a supply winding sample-and-hold signal; a feedback circuit for receiving a supply voltage of the control circuit and the supply winding sample-and-hold signal, and outputting the supply winding sample-and-hold signal as a feedback voltage when a value of the supply winding sample-and-hold signal is between a third proportional voltage and a fourth proportional voltage, wherein a ratio of the third proportional voltage to the supply voltage is a third proportional coefficient, and a ratio of the fourth proportional voltage to the supply voltage is a fourth proportional coefficient; and a hysteretic comparison circuit for receiving the third proportional voltage, the fourth proportional voltage and the supply winding sample-and-hold signal, and outputting a selection signal based on a comparison result of the third proportional voltage, the fourth proportional voltage and the supply winding sample-and-hold signal, wherein a value of the selection signal is a first level when a value of the supply winding sample-and-hold signal is between the third proportional voltage and the fourth proportional voltage, and a value of the selection signal is a second level otherwise. ​ An error amplifier receives the feedback voltage and the reference signal, and outputs a compensation signal for controlling the multi-output switch circuit, the compensation signal being an error amplified signal of the feedback voltage and the reference signal.

5. The control circuit of claim 4, further comprising: a pulse control circuit receiving the compensation signal, and outputting a switch control signal for controlling the primary side switch of the multi-output switch circuit based on the compensation signal.

6. The control circuit of claim 4, wherein, The feedback circuit comprises: a load comparison circuit receiving the compensation signal and a threshold signal, and outputting a selection signal based on a comparison result of the two; a selection circuit receiving the selection signal, the supply voltage and the supply winding sample hold signal, and selecting to output the supply voltage or the supply winding sample hold signal as the feedback voltage under control of the selection signal.

7. A flyback switching circuit comprising the control circuit of any one of claims 1-6, further comprising: a primary side switch coupled between a primary side winding and a primary side ground of the flyback switching circuit.

8. The flyback switching circuit of claim 7, further comprising: an energy storage element comprising the primary side winding, the supply winding and at least two secondary side windings.

9. The flyback switching circuit of claim 8, further comprising: at least two secondary side rectifier tubes, each coupled between a corresponding secondary side winding and an output terminal; and a supply winding rectifier tube coupled between one end of the supply winding and the supply voltage of the control circuit.

10. A control circuit for a Flybuck circuit, comprising: a sample hold circuit sampling a primary side winding voltage of the Flybuck circuit during a turn-on period of a secondary side rectifier tube of the Flybuck circuit, and outputting a primary side winding sample hold signal; and a feedback circuit receiving a supply voltage of the control circuit and the primary side winding sample hold signal, and outputting the primary side winding sample hold signal as a feedback voltage for controlling an output of a multi-output switch circuit when a value of the primary side winding sample hold signal is between a seventh proportional voltage and an eighth proportional voltage, the seventh proportional voltage being a third proportional coefficient of the supply voltage, the eighth proportional voltage being a fourth proportional coefficient of the supply voltage, the third proportional coefficient having a value greater than 1 and less than 2, and the fourth proportional coefficient having a value greater than 0 and less than 1.

11. The control circuit of claim 10, further comprising: an error amplifier receiving the feedback voltage and a reference signal, and outputting a compensation signal, the compensation signal being an error amplified signal of the feedback voltage and the reference signal; and a pulse control circuit receiving the compensation signal, and outputting a switch control signal for controlling a primary side switch of the Flybuck circuit based on the compensation signal.

12. The control circuit of claim 10, wherein the feedback circuit comprises: a third proportional circuit receiving the supply voltage, and outputting the seventh proportional voltage, the seventh proportional voltage being a third proportional coefficient of the supply voltage, the third proportional coefficient having a value greater than 1 and less than 2; a fourth proportional circuit receiving the supply voltage, and outputting the eighth proportional voltage, the eighth proportional voltage being a fourth proportional coefficient of the supply voltage, the fourth proportional coefficient having a value greater than 0 and less than 1. ​ a hysteresis comparison circuit receiving the seventh proportional voltage, the eighth proportional voltage and the primary winding sample hold signal, and outputting a selection signal based on a comparison result of the three, wherein when a value of the primary winding sample hold signal is between the seventh proportional voltage and the eighth proportional voltage, a value of the selection signal is a first level, otherwise, the value of the selection signal is a second level; and a selection circuit receiving the selection signal, a power supply voltage and the primary winding sample hold signal, when the value of the selection signal is the first level, outputting the power supply voltage as a feedback voltage, when the value of the selection signal is the second level, outputting the primary winding sample hold signal as the feedback voltage.

13. A Flybuck circuit comprising the control circuit of any one of claims 10-12, further comprising: a storage element comprising a primary winding and a secondary winding; a primary switch coupled between an input voltage of the Flybuck circuit and a control ground; a freewheeling diode coupled between a first end of the primary winding and a primary ground, a second end of the primary winding providing a first output voltage; and a secondary rectifier coupled between the secondary winding and a second output voltage.

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