Power supply control circuit and control method thereof

Abstract

The invention discloses a power supply control circuit of an isolated switching circuit. The power supply control circuit is provided with a first voltage output circuit, a second voltage output circuit and a power supply voltage output circuit. The first voltage output circuit is used for outputting a first voltage representing an input voltage of the isolated switching circuit, and the second voltage output circuit is used for outputting a second voltage representing an output voltage of the isolated switching circuit. The power supply voltage output circuit outputs power supply voltage to supply power to the power supply control circuit based on the first voltage and the second voltage. According to the power supply control circuit, the change range of the power supply voltage can be effectively reduced, and the situation that the power loss of the circuit is too large during wide-range input or wide-range output is avoided.

Description

Technical Field

[0001] Embodiments of the present invention relate to electronic circuits, and more particularly, to a power supply control circuit. Background Art

[0002] In isolated switched power supply technology, an auxiliary winding is usually used to supply power to the power supply control circuit of the isolated switched power supply. As Figure 1 shown, taking the asymmetrical half-bridge flyback converter 10 as an example, the power supply control circuit 101 is powered by the auxiliary winding Na. Among them, the supply voltage Vcc provided by the auxiliary winding Na is proportional to the output voltage Vout, and the proportionality coefficient is determined by the turn ratio of the auxiliary winding Na and the secondary winding Ns. To ensure the normal operation of the power supply control circuit 101, the turn ratio of the auxiliary winding Na and the secondary winding Ns should meet a certain multiple (for example, Na:Ns > 3:1). However, when the output voltage Vout range is wide (for example, 5V - 48V), the change range of the supply voltage Vcc provided by the auxiliary winding Na is very large, resulting in a large power loss in the circuit. Summary of the Invention

[0003] To solve the above technical problems, the present invention provides a power supply control circuit, which outputs a supply voltage based on the input voltage and output voltage of an isolated switching circuit to supply power to the power supply control circuit, so as to reduce the change range of the supply voltage, thereby reducing the circuit loss of the isolated switching circuit.

[0004] According to an embodiment of the present invention, a power supply control circuit for an isolated switching circuit is provided, including: a first voltage output circuit, receiving a first auxiliary winding voltage provided by a first auxiliary winding of the isolated switching circuit, and outputting a first voltage representing the input voltage of the isolated switching circuit based on the first auxiliary winding voltage; a second voltage output circuit, receiving a second auxiliary winding voltage provided by a second auxiliary winding of the isolated switching circuit, and outputting a second voltage representing the output voltage of the isolated switching circuit based on the second auxiliary winding voltage; and a supply voltage output circuit, outputting a supply voltage based on the first voltage and the second voltage.

[0005] According to an embodiment of the present invention, an isolated switching circuit is further provided, including the power supply control circuit as described above, and further including: a transformer, including a primary winding, a secondary winding, a first auxiliary winding, and a second auxiliary winding.

[0006] According to an embodiment of the present invention, a power supply control method for an isolated switching circuit is also proposed, including: receiving a first auxiliary winding voltage provided by a first auxiliary winding of the isolated switching circuit, and outputting a first voltage representing the input voltage of the isolated switching circuit based on the first auxiliary winding voltage; receiving a second auxiliary winding voltage provided by a second auxiliary winding of the isolated switching circuit, and outputting a second voltage representing the output voltage of the isolated switching circuit based on the second auxiliary winding voltage; and outputting a power supply voltage based on the first voltage and the second voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] For a better understanding of the present invention, the present invention will be described in detail according to the following drawings:

[0008] Figure 1 FIG. shows a schematic structural diagram of an existing asymmetric half-bridge flyback converter 10;

[0009] Figure 2 FIG. shows a schematic structural diagram of an asymmetric half-bridge flyback converter 20 according to an embodiment of the present invention;

[0010] Figure 3 FIG. shows a schematic circuit diagram of a power supply control circuit 31 according to an embodiment of the present invention;

[0011] Figure 4 FIG. shows a schematic circuit diagram of a power supply control circuit 41 according to an embodiment of the present invention;

[0012] Figure 5 FIG. shows a schematic circuit diagram of a power supply control circuit 51 according to an embodiment of the present invention;

[0013] Figure 6 FIG. shows a schematic circuit diagram of a power supply control circuit 61 according to an embodiment of the present invention;

[0014] Figure 7 FIG. shows a schematic circuit diagram of a power supply control circuit 71 according to an embodiment of the present invention;

[0015] Figure 8 FIG. shows a schematic circuit diagram of a power supply control circuit 81 according to an embodiment of the present invention;

[0016] Figure 9 FIG. shows a schematic circuit diagram of a power supply control circuit 91 according to an embodiment of the present invention;

[0017] Figure 10 FIG. shows a schematic flow diagram of a power supply control method 100 for an isolated switching circuit according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] Specific embodiments of the present invention will be described in detail below. It should be noted that the embodiments described here are only for illustrative purposes and do not limit the present invention. In the following description, in order to provide a thorough understanding of the present invention, a large number of specific details are set forth. However, it will be apparent to those of ordinary skill in the art that the present invention does not have to employ these specific details. In other instances, well-known circuits, materials, or methods have not been described in detail in order to avoid obscuring the present invention.

[0019] Throughout the specification, the mention of "one embodiment", "an embodiment", "one example", or "an example" means that a particular feature, structure, or characteristic described in connection with the embodiment or example is included in at least one embodiment of the present invention. Thus, the phrases "in one embodiment", "in an embodiment", "one example", or "an example" appearing throughout the specification do not necessarily all refer to the same embodiment or example. Additionally, the particular features, structures, or characteristics may be combined in any suitable combination and / or sub-combination in one or more embodiments or examples. Moreover, those of ordinary skill in the art should understand that the drawings provided herein are for illustrative purposes only and that the drawings are not necessarily drawn to scale. Like reference numerals indicate like elements. The term "and / or" used herein includes any and all combinations of one or more of the associated listed items.

[0020] An isolated switching power supply often uses an auxiliary winding to supply power to its power control circuit. Take Figure 1 the existing asymmetric half-bridge flyback converter 10 shown as an example. In Figure 1 it, the auxiliary winding Na of the asymmetric half-bridge flyback converter 10 is wound on the same magnetic core as the primary winding Np and the secondary winding Ns. The auxiliary winding Na provides the supply voltage Vcc to the power control circuit 101. The value of the supply voltage Vcc is related to the turns ratio between the output voltage Vout, the secondary winding Ns, and the auxiliary winding Na, that is, Vcc:Vout = Na:Ns. For example, when the turns ratio between the auxiliary winding Na and the secondary winding Ns is 1:1, the value of the supply voltage Vcc is equal to the value of the output voltage Vout. When the range of the output voltage Vout of the asymmetric half-bridge flyback converter 10 is relatively large, such as 5V - 48V, since the power control circuit 101 has a minimum voltage limit (e.g., 15V), the turns ratio between the auxiliary winding Na and the secondary winding Ns must reach at least 3:1 to ensure the normal operation of the power control circuit 101. However, in the case where the turns ratio between the auxiliary winding Na and the secondary winding Ns is 3:1, if the output voltage Vout is 48V, the supply voltage Vcc will be as high as 144V, which results in a large power loss in the circuit. Thus, simply supplying power to the power control circuit based on the output voltage Vout or the input voltage Vin is difficult to meet the demand for low power loss in practical applications.

[0021] Figure 2 FIG. Figure 2 shows a schematic structural diagram of an asymmetric half-bridge flyback converter 20 according to an embodiment of the present invention. The asymmetric half-bridge flyback converter 20 includes: an upper pull switch Q1 and a lower pull switch Q2 serially coupled between an input terminal IN and a primary ground PGND; a transformer T1 having a primary winding Np, a secondary winding Ns, a first auxiliary winding Na1, and a second auxiliary winding Na2; a resonant capacitor Cr serially coupled with the primary winding Np between a switching terminal SW and the primary ground PGND; a secondary switch Ds serially coupled with the secondary winding Ns; and an output capacitor Co and a load Ro. In Figure 2 , the input terminal IN is configured to receive an input voltage Vin. The input voltage Vin is a DC voltage and can be obtained by rectifying an AC voltage. In Figure 2 the embodiment, the upper pull switch Q1 and the lower pull switch Q2 are implemented by MOSFETs (metal oxide semiconductor field effect transistors). In other embodiments, the upper pull switch Q1 and the lower pull switch Q2 can be implemented by other switches, such as BJTs (bipolar junction transistors), IGBTs (insulated gate bipolar transistors), etc. In Figure 2 , the resonant inductor Lr is the leakage inductance of the primary winding Np, that is, it is only an equivalent schematic device rather than an actual inductor device. In some applications, an independent inductor device can also be additionally added as the resonant inductor according to the needs of the application. In Figure 2 , the secondary switch Ds is a diode. It should be understood that the secondary switch Ds can also be implemented by a controllable switch tube, such as a MOSFET. And in some applications, the secondary switch Ds can be coupled between the secondary winding Ns and a secondary ground SGND.

[0022] In Figure 2 , the asymmetric half-bridge flyback converter 20 further includes a power control circuit 201 for controlling the upper pull switch Q1 and the lower pull switch Q2 to alternately turn on and off, transferring the energy on the primary side to the secondary side, and forming an output voltage Vout on the output capacitor Co to supply energy to the load Ro. Specifically, when the upper pull switch Q1 is turned on and the lower pull switch Q2 is turned off, the primary winding Np and the resonant capacitor Cr store energy, and the output capacitor Co supplies energy to the load Ro. When the upper pull switch Q1 is turned off and the lower pull switch Q2 is turned on, the energy stored in the primary winding Np and the resonant capacitor Cr is transferred to the secondary winding Ns, and the secondary winding Ns charges the output capacitor Co and supplies energy to the load Ro.

[0023] In Figure 2In an embodiment, the asymmetric half-bridge flyback converter 20 further includes a power supply control circuit 21 for supplying power to the power control circuit 201. The power supply control circuit 21 includes: a first voltage output circuit 202, a second voltage output circuit 203, and a power supply voltage output circuit 204. Among them, the first voltage output circuit 202 receives the first auxiliary winding voltage VNa1 provided by the first auxiliary winding Na1, and provides a first voltage V1 representing the input voltage Vin based on the first auxiliary winding voltage VNa1. The second voltage output circuit 203 receives the second auxiliary winding voltage Va2 provided by the second auxiliary winding Na2, and provides a second voltage V2 representing the output voltage Vout based on the second auxiliary winding voltage VNa2. The power supply voltage output circuit 204 receives the first voltage V1 and the second voltage V2, and outputs a power supply voltage Vcc based on the first voltage V1 and the second voltage V2 for supplying power to the power control circuit 201.

[0024] That is to say, the power supply voltage output circuit 204 outputs the power supply voltage Vcc based on both the first voltage V1 representing the input voltage Vin and the second voltage V2 representing the output voltage Vout. For example, in the case where the output voltage Vout of the asymmetric half-bridge flyback converter 20 is very large and the input voltage Vin is very small, the power supply voltage output circuit 204 supplies power to the power control circuit 201 based on the first voltage V1 representing the input voltage Vin. Conversely, in the case where the output voltage Vout of the asymmetric half-bridge flyback converter 20 is very small and the input voltage Vin is very large, the power supply voltage output circuit 204 supplies power to the power control circuit 201 based on the second voltage V2 representing the output voltage Vout. In some embodiments, the power supply voltage output circuit 204 outputs the minimum value of the first voltage V1 and the second voltage V2 as the power supply voltage Vcc, that is, when the first voltage V1 is less than the second voltage V2, the power supply voltage Vcc is equal to the first voltage V1; when the first voltage V1 is greater than the second voltage V2, the power supply voltage is equal to the second voltage V2, thereby effectively limiting the variation range of the power supply voltage Vcc.

[0025] It should be understood that the asymmetric half-bridge flyback converter 20 is only for illustrative purposes to explain the working principle of the power supply control circuit. The power supply control circuit of the present invention is also applicable to other isolated switching circuits, such as flyback circuits, forward circuits, LLC circuits, etc.

[0026] In summary, the power supply control circuit of the embodiment of the present invention supplies power to the power control circuit based on the input voltage and output voltage of the isolated switching circuit, which can effectively reduce the variation range of the power supply voltage, thereby reducing the power loss of the isolated switching circuit with a wide range of input or wide range of output.

[0027] Figure 3The schematic circuit diagram of the power supply control circuit 31 according to an embodiment of the present invention is shown. In Figure 3 In the embodiment, the power supply control circuit 31 includes a first voltage output circuit 302, a second voltage output circuit 303, and a power supply voltage output circuit 304. Among them, the first voltage output circuit 302 includes a first auxiliary winding capacitor Ca, a first switch D1, a second switch D2, and a first capacitor C1. Among them, the first auxiliary winding capacitor Ca has a first end and a second end, and the first end is connected to the first auxiliary winding Na1 of the isolated switch circuit. The first switch D1 has a first end and a second end, where the first end is coupled to the output end of the first voltage output circuit 302, and the second end is coupled to the second end of the first auxiliary winding capacitor Ca; the second switch D2 has a first end and a second end, where the first end is coupled to the connection point of the first switch D1 and the first auxiliary winding capacitor Ca, and the second end is coupled to the primary ground PGND; and the first capacitor C1 is coupled between the output end of the first voltage output circuit 302 and the primary ground PGND.

[0028] The second voltage output circuit 303 includes a third switch D3 and a second capacitor C2. Among them, the third switch D3 has a first end and a second end, where the first end is coupled to the output end of the second voltage output circuit 303, and the second end is coupled to the second auxiliary winding Na2 of the isolated switch circuit. The second capacitor C2 is coupled between the output end of the second voltage output circuit 303 and the primary ground PGND.

[0029] In Figure 3 In the embodiment, the first switch D1, the second switch D2, and the third switch D3 are all diodes. In other embodiments, the first switch D1, the second switch D2, and the third switch D3 may be other suitable switch elements, such as MOSFETs.

[0030] When the pull-up switch transistor Q1 is turned on and the pull-down switch transistor Q2 is turned off, the first auxiliary winding capacitor Ca, the first auxiliary winding Na1, and the second switch D2 form an energy storage loop, and the current flows from the first auxiliary winding Na1 through the primary ground PGND and the second switch D2 to the first auxiliary winding capacitor Ca to supply power to the first auxiliary winding capacitor Ca. The voltage VCa across the first auxiliary winding capacitor Ca is equal to the negative of the voltage VNa1 across the first auxiliary winding Na1, that is, VCa = -VNa1, and the first auxiliary winding Na1 then induces the voltage VNp of the primary winding Np. As Figure 3As shown, define the direction of the voltage VNa1 across the first auxiliary winding Na1 as from the terminal of opposite name to the terminal of the same name (i.e., positive at the top and negative at the bottom). Then, the voltage VNa1 across the first auxiliary winding Na1 = -VNp / (Np / Na1). Thus, the voltage across the first auxiliary winding capacitor Ca is VCa = -VNa1 = VNp / (Np / Na1). Among them, the voltage VNp of the primary winding Np = Vin - VCr, where VCr is the voltage across the resonant capacitor Cr, and it is approximately VCr = Vout / (Ns / Np).

[0031] When the pull-up switch Q1 is turned off and the pull-down switch Q2 is turned on, the first auxiliary winding Na1, the first auxiliary winding capacitor Ca, the first switch D1, and the first capacitor C1 form an energy storage loop. The current flows from the first auxiliary winding Na1 through the first auxiliary winding capacitor Ca, the first switch D1 to the first capacitor C1 to charge the first capacitor C1. At this time, the charging voltage VC1 of the first capacitor C1 is equal to the voltage VNa1 of the first auxiliary winding Na1. The first auxiliary winding Na1 induces the voltage of the secondary winding Ns. Thus, the charging voltage VC1 of the first capacitor C1 = VNa1 = Vout / (Ns / Na1). Therefore, the first voltage V1 output by the first voltage output circuit 302 is equal to the sum of the voltage VCa across the first auxiliary winding capacitor and the charging voltage VC1 of the first capacitor C1. It can be calculated that V1 = VCa + VC1 = Vin / (Np / Na1). Therefore, the first voltage V1 output by the first voltage output circuit 302 = Vin / (Np / Na1).

[0032] Similarly, when the pull-up switch Q1 is turned off and the pull-down switch Q2 is turned on, the second auxiliary winding Na2, the third switch D3, and the second capacitor C2 form an energy storage loop. The current flows from the second auxiliary winding Na2 through the third switch D3 to the second capacitor C2 to charge the second capacitor C2. At this time, the second auxiliary winding Na2 induces the voltage of the secondary winding Ns, that is, VNa2 = Vout / (Ns / Na2). Therefore, the second voltage V2 output by the second voltage output circuit 303 = VNa2 = Vout / (Ns / Na2).

[0033] It can be seen that the first voltage V1 output by the first voltage output circuit 302 characterizes the magnitude of the input voltage Vin, and the second voltage V2 output by the second voltage output circuit 303 characterizes the magnitude of the output voltage Vout. Since there is a voltage drop in the switches D1 - D3 during actual conduction, the values of the first voltage V1 and the second voltage V2 obtained according to the equations V1 = Vin / (Np / Na1) and V2 = Vout / (Ns / Na2) are both approximate values.

[0034] Figure 4 shows a schematic circuit diagram of the power supply control circuit 41 according to an embodiment of the present invention. InFigure 4 In an embodiment, the power supply voltage output circuit 404 includes a power supply capacitor Cvcc, a first controllable switch S1, a second controllable switch S2, a first voltage limiting circuit 4041 and a second voltage limiting circuit 4042. The power supply capacitor Cvcc has a first terminal and a second terminal, wherein the first terminal is coupled to the output terminal of the power supply voltage output circuit 404, and the second terminal is coupled to the primary ground PGND. The first controllable switch S1 includes a first terminal a, a second terminal b and a third terminal c, wherein the first terminal a is coupled to the first terminal of the power supply capacitor Cvcc, and the second terminal b is used to receive a first voltage V1. The first voltage limiting circuit 4041 is configured to receive a second voltage V2 and provide a first control voltage VS1 to the third terminal c of the first controllable switch S1 based on the second voltage V2. The second controllable switch S2 includes a first terminal d, a second terminal e and a third terminal f, wherein the first terminal d is coupled to the first terminal of the power supply capacitor Cvcc, and the second terminal f is used to receive the second voltage V2. The second voltage limiting circuit 4042 is configured to receive the first voltage V1 and provide a second control voltage VS2 to the third terminal f of the second controllable switch S2 based on the first voltage V1.

[0035] In Figure 4 an embodiment, the controllable switches S1 and S2 are BJTs, and their first terminals a (d) are emitters, second terminals b (e) are collectors, and third terminals c (f) are bases. In other embodiments, other suitable controllable switches can be used as the controllable switches S1 and S2, such as MOSFETs. When the controllable switches S1 and S2 are MOSFETs, their first terminals a (d) are source terminals, second terminals b (e) are drain terminals, and third terminals c (f) are gate terminals.

[0036] When the first voltage V1 is greater than the first limiting voltage VL1, the second control voltage VS2 provided by the second voltage limiting circuit 4042 is equal to the first limiting voltage VL1. When the first voltage V1 is less than the first limiting voltage VL1, the second control voltage VS2 is equal to the first voltage V1. That is, Vf = VS2 = MIN(V1, VL1).

[0037] When the second voltage V2 is greater than the second limiting voltage VL2, the first control voltage VS1 provided by the first voltage limiting circuit 4041 is equal to the second limiting voltage VL2. When the second voltage V2 is less than the second limiting voltage VL2, the first control voltage VS1 is equal to the second voltage V2. That is, Vc = VS1 = MIN(V2, VL2). Wherein, the first limiting voltage VL1 is less than the second limiting voltage VL2.

[0038] In other embodiments, the first (second) voltage limiting circuit may include a comparator configured to compare the received voltage with a limiting voltage. When the received voltage is less than the limiting voltage, the received voltage is output; when the received voltage is greater than the limiting voltage, the limiting voltage is output, so as to limit the output voltage value within a certain range. Those of ordinary skill in the art should understand that any circuit that can limit the voltage within a certain threshold range can be used as the voltage limiting circuit of the present invention.

[0039] In Figure 4 the embodiment, when the third terminal voltages Vc (Vf) of the controllable switches S1, S2 are greater than the second terminal voltages Vb (Ve), the first terminal voltages Va (Vd) of the controllable switches S1, S2 are equal to the second terminal voltages Vb (Ve); when the third terminal voltages Vc (Vf) of the controllable switches S1, S2 are less than the second terminal voltages Vb (Ve), the first terminal voltages Va (Vd) of the controllable switches S1, S2 are equal to Vc (Vf) - Vth, where Vth is the conduction threshold voltage of the controllable switches S1, S2. The first controllable switch S1 is equivalent to outputting the first terminal voltage Va based on the minimum value of the first voltage V1 and the first control voltage VS1, that is, Va = MIN(V1, VS1) = MIN(V1, MIN(V2, VL2)). Similarly, the second controllable switch S2 is equivalent to outputting the first terminal voltage Vd based on the minimum value of the second voltage V2 and the second control voltage VS2, that is, Vd = MIN(V2, VS2) = MIN(V2, MIN(V1, VL1)). The power supply capacitor Cvcc outputs the power supply voltage Vcc based on the smaller value between the first voltage V1 and the first control voltage VS1 and the smaller value between the second voltage V2 and the second control voltage VS2. For ease of understanding, an example will be given below.

[0040] In one embodiment, the turns ratio of the primary winding Np, secondary winding Ns, first auxiliary winding Na1 and second auxiliary winding Na2 is set to Np:Ns:Na1:Na2 = 16:4:1:10, the controllable switches S1, S2 are NPN type BJTs, and the first limiting voltage VL1 is 15V and the second limiting voltage VL2 is 16V.

[0041] When the input voltage Vin is small (e.g., 128V) and the output voltage Vout is also small (e.g., 5V), it can be calculated that the first voltage V1 = Vin / (Np / Na1) = 8V, and the second voltage V2 = Vout / (Ns / Na2) = 12.5V. In this case, the third-terminal voltage Vc of the first controllable switch S1 is equal to MIN(V2, VL2) = V2 = 12.5V, the second-terminal voltage Vb is equal to V1, i.e., 8V, then the first-terminal voltage Va of the first controllable switch S1 is equal to 8V. At the same time, the third-terminal voltage Vf of the second controllable switch S2 is equal to MIN(V1, VL1) = V1 = 8V, the second-terminal voltage Ve is equal to V2, i.e., 12.5V, then the first-terminal voltage Vd of the second controllable switch S2 is equal to Vc - Vth = MIN(V2, MIN(V1, VL1)) - Vth = V1 - Vth. It can be obtained that the supply voltage Vcc provided by the power supply voltage output circuit 404 is equal to V1 = 8V. In other words, in this case, the power supply voltage output circuit 404 supplies power to the power supply control circuit 201 based on the first voltage V1 representing the input voltage Vin.

[0042] When the input voltage Vin is large (e.g., 320V) and the output voltage Vout is small (e.g., 5V), it can be calculated that the first voltage V1 = Vin / (Np / Na1) = 20V, and the second voltage V2 = Vout / (Ns / Na2) = 12.5V. In this case, the third-terminal voltage Vc of the first controllable switch S1 is equal to MIN(V2, VL2) = V2 = 12.5V, the second-terminal voltage Vb is equal to V1, i.e., 20V, then the first-terminal voltage Va of the first controllable switch S1 is equal to V2 - Vth. At the same time, the third-terminal voltage Vf of the second controllable switch S2 is equal to MIN(V1, VL1) = 15V, the second-terminal voltage Ve is equal to V2, i.e., 12.5V, then the first-terminal voltage Vd of the second controllable switch S2 is equal to V2 = 12.5V. It can be obtained that the supply voltage Vcc provided by the power supply voltage output circuit 404 is equal to V2 = 12.5V. In other words, in this case, the power supply voltage output circuit 404 supplies power to the power supply control circuit 201 based on the second voltage V2 representing the output voltage Vout.

[0043] When the input voltage Vin is small (e.g., 128V) and the output voltage Vout is large (e.g., 48V), it can be calculated that the first voltage V1 = Vin / (Np / Na1) = 8V, and the second voltage V2 = Vout / (Ns / Na2) = 120V. In this case, the third terminal voltage Vc of the first controllable switch S1 is equal to MIN(V2, VL2) = VL2 = 16V, the second terminal voltage Vb is equal to V1, i.e., 8V, then the first terminal voltage Va of the first controllable switch S1 is equal to V1 = 8V. At the same time, the third terminal voltage Vf of the second controllable switch S2 is equal to MIN(V1, VL1) = V1 = 8V, the second terminal voltage Ve is equal to V2, i.e., 120V, then the first terminal voltage Vd of the second controllable switch S2 is equal to V1 - Vth. It can be obtained that the supply voltage Vcc provided by the supply voltage output circuit 304 is equal to V1 = 8V. In other words, in this case, the supply voltage output circuit 404 supplies power to the power control circuit 201 based on the first voltage V1 representing the input voltage Vin.

[0044] When the input voltage Vin is large (e.g., 320V) and the output voltage Vout is also large (e.g., 48V), it can be calculated that the first voltage V1 = Vin / (Np / Na1) = 20V, and the second voltage V2 = Vout / (Ns / Na2) = 120V. In this case, the third terminal voltage Vc of the first controllable switch S1 is equal to MIN(V2, VL2) = VL2 = 16V, the second terminal voltage Vb is equal to V1, i.e., 20V, then the first terminal voltage Va of the first controllable switch S1 is equal to VL1 - Vth. At the same time, the third terminal voltage Vf of the second controllable switch S2 is equal to MIN(V1, VL1) = VL1 = 15V, the second terminal voltage Ve is equal to V2, i.e., 120V, then the first terminal voltage Vd of the second controllable switch S2 is equal to VL2 - Vth. Since the first limit voltage VL1 is less than the second limit voltage VL2, the supply voltage output by the supply capacitor Cvcc is equal to the first limit voltage VL1. In other words, when both the input voltage Vin and the output voltage Vout are large, the supply voltage output circuit 404 supplies power to the power control circuit 201 based on the first limit voltage VL1, that is, the supply voltage Vcc is limited to the first limit voltage VL1.

[0045] Therefore, the power supply voltage output circuit 404 controls the first controllable switch S1 and the second controllable switch S2 based on the first voltage V1 and the second voltage V2 to achieve an output of the power supply voltage Vcc with a relatively small variation range. Meanwhile, when both the input voltage Vin and the output voltage Vout are very large, the voltage limiting circuits 4041 and 4042 limit the power supply voltage Vcc within a certain voltage limit range (e.g., the first limit voltage VL1). Even if the variation range of the input voltage or the output voltage of the isolated switching circuit is very large, the power supply control circuit of the embodiment of the present invention can still provide the power supply voltage Vcc with a relatively small variation range, thereby reducing the power loss of the isolated switching circuit.

[0046] Figure 5 FIG. shows a schematic circuit diagram of a power supply control circuit 51 according to an embodiment of the present invention. In the embodiment as Figure 5 shown, the first voltage limiting circuit 5041 includes a first Zener diode ZD1 and a first protection resistor R1. Among them, the cathode terminal of the first Zener diode ZD1 is coupled to the third terminal c of the first controllable switch S1, the anode terminal is coupled to the primary ground PGND, and the second limit voltage VL2 of the first voltage limiting circuit 5041 is equal to the Zener voltage Vzd1 of the first Zener diode ZD1. The second voltage limiting circuit 5042 includes a second Zener diode ZD2 and a second protection resistor R2. Among them, the cathode terminal of the second Zener diode ZD2 is coupled to the third terminal f of the second controllable switch S2, the anode terminal is coupled to the primary ground PGND, and the first limit voltage VL1 of the second voltage limiting circuit 5042 is equal to the Zener voltage Vzd2 of the second Zener diode ZD2. Among them, on the basis of ensuring that Vzd1 is greater than Vzd2, the Zener voltages Vzd1 and Vzd2 of the Zener diodes ZD1 and ZD2 can be set according to actual application requirements.

[0047] In Figure 5 the embodiment, the power supply voltage output circuit 504 further includes a first output diode Da1 and a second output diode Da2 for preventing current from flowing from the first terminal of the charging capacitor Cvcc to the first controllable switch S1 and the second controllable switch S2. The first output diode Da1 has a first terminal (cathode terminal) and a second terminal (anode terminal), where the first terminal is coupled to the first terminal of the power supply capacitor Cvcc, and the second terminal is coupled to the first terminal a of the first controllable switch S1. The second output diode Da2 has a first terminal (cathode terminal) and a second terminal (anode terminal), where the first terminal is coupled to the first terminal of the power supply capacitor Cvcc, and the second terminal is coupled to the first terminal d of the second controllable switch S2.

[0048] It should be understood that the first output diode Da1 and the second output diode Da2 are non-essential components, that is, the power supply voltage output circuit 504 may not include the first output diode Da1 and the second output diode Da2. In one embodiment, the power supply voltage output circuit 504 only includes the second output diode Da2.

[0049] Figure 6 FIG. shows a schematic circuit diagram of a power supply control circuit 61 according to an embodiment of the present invention. Different from Figure 5 that, Figure 6 the first voltage output circuit 602 of also includes a current limiting circuit 6021, which is serially coupled to the first auxiliary winding capacitor Ca. In Figure 6 the embodiment shown, the current limiting circuit 6021 includes a resistor R3. In other embodiments, the current limiting circuit 6021 includes an inductor. At the same time, in Figure 6 the embodiment of, the power supply voltage output circuit 604 further includes a supplementary voltage output circuit 6042A, which is coupled to the third terminal f of the second controllable switch S2.

[0050] The supplementary voltage output circuit 6042A is used to provide a supplementary voltage Vadd to ensure the normal operation of the power supply control circuit 201. In one embodiment, the supplementary voltage Vadd is less than the first limit voltage VL1 and the second limit voltage VL2. As described above, when the value of the first voltage V1 is at its minimum (i.e., less than the second voltage V2, the first limit voltage VL1, and the second limit voltage VL2), the power supply voltage Vcc is equal to the first voltage V1. In one embodiment, when the value of the first voltage V1 is less than the minimum operating voltage of the power supply control circuit 201, the supplementary voltage output circuit 6042A outputs the supplementary voltage Vadd, increasing the power supply voltage Vcc to the minimum operating voltage of the power supply control circuit 201, thus ensuring the normal operation of the power supply control circuit 201.

[0051] Figure 7 FIG. shows a schematic circuit diagram of a power supply control circuit 71 according to an embodiment of the present invention. Different from Figure 4 that, Figure 7The first voltage output circuit 702 includes a first switch D1 and a first capacitor C1. The first switch D1 has a first end and a second end, where the first end is coupled to the output end of the first voltage output circuit 702, and the second end is coupled to the first auxiliary winding Na1 of the isolated switch circuit. The first capacitor C1 is coupled between the output end of the first voltage output circuit 702 and the primary ground PGND. In this case, the charging voltage VC1 of the first capacitor C1 is equal to the voltage across the first auxiliary winding Na1, that is, VC1 = VNa1. The first auxiliary winding Na1 senses the voltage VNp of the primary winding Np, and then the first voltage V1 = VC1 = (Vin - VCr) / (Np / Na1) can be obtained, that is, the first voltage output circuit 702 outputs the first voltage V1 representing the input voltage Vin. Except that the value of the first voltage V1 output by the first voltage output circuit 702 is different, the working principle of the power supply control circuit 71 is the same as that of the power supply control circuit 41, which will not be elaborated here.

[0052] Figure 8 FIG. shows a schematic circuit diagram of a power supply control circuit 81 according to an embodiment of the present invention. Different from Figure 7 In the embodiment shown in Figure 8 the first voltage limiting circuit 8041 includes a first Zener diode ZD1 and a first protection resistor R1. Among them, the cathode end of the first Zener diode ZD1 is coupled to the third end c of the first controllable switch S1, the anode end is coupled to the primary ground PGND, and the second limiting voltage VL2 of the first voltage limiting circuit 8041 is equal to the Zener voltage Vzd1 of the first Zener diode ZD1. The second voltage limiting circuit 8042 includes a second Zener diode ZD2 and a second protection resistor R2. Among them, the cathode end of the second Zener diode ZD2 is coupled to the third end f of the second controllable switch S2, the anode end is coupled to the primary ground PGND, and the first limiting voltage VL1 of the second voltage limiting circuit 8042 is equal to the Zener voltage Vzd2 of the second Zener diode ZD2. Among them, on the basis of ensuring that Vzd1 is greater than Vzd2, the Zener voltages Vzd1 and Vzd2 of the Zener diodes ZD1 and ZD2 can be set according to actual application requirements.

[0053] In Figure 8In an embodiment, the power supply voltage output circuit 804 further includes a first output diode Da1 and a second output diode Da2, which are used to prevent current from flowing from the first end of the charging capacitor Cvcc to the first controllable switch S1 and the second controllable switch S2. Among them, the first output diode Da1 has a first end (cathode end) and a second end (anode end), where the first end is coupled to the first end of the power supply capacitor Cvcc, and the second end is coupled to the first end a of the first controllable switch S1. Among them, the second output diode Da2 has a first end (cathode end) and a second end (anode end), where the first end is coupled to the first end of the power supply capacitor Cvcc, and the second end is coupled to the first end d of the second controllable switch S2.

[0054] It should be understood that the first output diode Da1 and the second output diode Da2 are non-essential components, that is, the power supply voltage output circuit 804 may not include the first output diode Da1 and the second output diode Da2. In one embodiment, the power supply voltage output circuit 804 only includes the second output diode Da2.

[0055] Figure 9 FIG. shows a schematic circuit diagram of a power supply control circuit 91 according to an embodiment of the present invention. Different from Figure 8 is that Figure 9 the first voltage output circuit 902 of further includes a current limiting circuit 9021, which is serially coupled with the first switch D1. In Figure 9 the shown embodiment, the current limiting circuit 9021 includes a resistor R3. In other embodiments, the current limiting circuit 9021 includes an inductor. At the same time, Figure 9 the power supply voltage output circuit 904 of further includes a supplementary voltage output circuit 9042A, which is coupled to the third end f of the second controllable switch S2, and its function is the same as that of the supplementary voltage output circuit 6042A, and will not be described here again.

[0056] In this paper, the working principle of the power supply control circuit of the present invention is described by taking an asymmetric half-bridge flyback converter as an example. It should be understood that the power supply control circuit of the present invention is also applicable to other isolated switching circuits, such as general flyback circuits, forward circuits, LLC circuits, etc.

[0057] Figure 10 FIG. shows a schematic flow chart of a power supply control method 100 for an isolated switching circuit according to an embodiment of the present invention. The isolated switching circuit includes an isolation device (such as a transformer), a primary circuit, and a secondary circuit. The primary circuit includes at least one switching tube. By controlling the on and off of the primary switching tube, the energy received by the primary circuit is transferred to the secondary circuit to supply power to the load, that is, the input voltage received by the primary circuit is converted into the output voltage required by the load. The isolation device includes a first auxiliary winding and a second auxiliary winding. The dual auxiliary winding power supply control method 100 includes:

[0058] Step 1001: Receive a first auxiliary winding voltage provided by a first auxiliary winding of an isolated switching circuit, and output a first voltage representing an input voltage of the isolated switching circuit based on the first auxiliary winding voltage.

[0059] Step 1002: Receive a second auxiliary winding voltage provided by a second auxiliary winding of the isolated switching circuit, and output a second voltage representing an output voltage of the isolated switching circuit based on the second auxiliary winding voltage.

[0060] Step 1003: Output a supply voltage based on the first voltage and the second voltage.

[0061] In one embodiment, step 1003 includes:

[0062] Receive the second voltage and provide a first control voltage based on the second voltage;

[0063] Receive the first voltage and provide a second control voltage based on the first voltage; and

[0064] Output a supply voltage based on the smaller value between the first voltage and the first control voltage and the smaller value between the second voltage and the second control voltage;

[0065] Where when the first voltage is greater than a first limit voltage, the second control voltage is equal to the first limit voltage, and when the first voltage is less than the first limit voltage, the second control voltage is equal to the first voltage;

[0066] Where when the second voltage is greater than a second limit voltage, the first control voltage is equal to the second limit voltage, and when the second voltage is less than the second limit voltage, the first control voltage is equal to the second voltage; wherein, the first limit voltage is less than the second limit voltage.

[0067] Note that in the flowchart described above, the functions marked in the boxes can also occur in an order different from that shown in the flowchart. For example, two consecutive boxes shown can actually be executed substantially in parallel, and they can sometimes be executed in the reverse order, depending on the specific functions involved.

[0068] In the specification, relative terms such as "first" and "second" may be used solely to distinguish one entity or action from another entity or action, and do not necessarily or imply any relationship or order among such entities or actions. Numerical sequences such as "first", "second", "third", etc. merely refer to different individuals among a plurality, and do not imply any order or sequence, unless the claim language specifically limits it. The order of the text in any one claim does not imply that the processing steps must be carried out in a temporal or logical order according to such order, unless the claim language specifically states so. Without departing from the scope of the present invention, these processing steps may be interchanged in any order, as long as such interchange does not render the claim language contradictory and does not result in logical absurdity.

[0069] While the invention has been described with reference to several exemplary embodiments, it should be understood that the terms used are descriptive and exemplary rather than restrictive. Since the present 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 broadly construed 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 power supply control circuit for an isolated switching circuit, comprising: a first voltage output circuit receiving a first auxiliary winding voltage provided by a first auxiliary winding of the isolated switch circuit and outputting a first voltage representing an input voltage of the isolated switch circuit based on the first auxiliary winding voltage; a second voltage output circuit receiving a second auxiliary winding voltage provided by a second auxiliary winding of the isolated switch circuit and outputting a second voltage representing an output voltage of the isolated switch circuit based on the second auxiliary winding voltage; as well as The power supply voltage output circuit outputs a power supply voltage based on the first voltage and the second voltage.

2. The power supply control circuit according to claim 1, wherein the first voltage output circuit comprises: a first auxiliary winding capacitor having a first end and a second end, wherein the first end is connected to the first auxiliary winding of the isolated switching circuit; a first switch having a first terminal and a second terminal, wherein the first terminal is coupled to the output terminal of the first voltage output circuit, and the second terminal is coupled to the second terminal of the first auxiliary winding capacitor; a second switch having a first end and a second end, wherein the first end is coupled to a connection point between the first switch and the first auxiliary winding capacitor, and the second end is coupled to the primary ground; as well as The first capacitor is coupled between the output terminal of the first voltage output circuit and the primary ground.

3. The power supply control circuit according to claim 2, wherein the first voltage output circuit further comprises: The current limiting circuit is coupled in series with the first auxiliary winding capacitor.

4. The power supply control circuit according to claim 1 , wherein the first voltage output circuit comprises: A first switch having a first end and a second end, wherein the first end is coupled to the output end of the first voltage output circuit, and the second end is coupled to the first auxiliary winding of the isolation switch circuit; as well as The first capacitor is coupled between the output terminal of the first voltage output circuit and the primary ground.

5. The power supply control circuit according to claim 4, wherein the first voltage output circuit further comprises: The current limiting circuit is coupled in series with the first switch.

6. The power supply control circuit according to claim 1 , wherein the second voltage output circuit comprises: a third switch having a first end and a second end, wherein the first end is coupled to the output end of the second voltage output circuit, and the second end is coupled to the second auxiliary winding of the isolation switch circuit; as well as The second capacitor is coupled between the output terminal of the second voltage output circuit and the primary ground.

7. The power supply control circuit according to claim 1, wherein the power supply voltage output circuit comprises: A power supply capacitor having a first terminal and a second terminal, wherein the first terminal is coupled to the output terminal of the power supply voltage output circuit, and the second terminal is coupled to the primary ground; A first controllable switch comprises a first end, a second end and a third end, wherein the first end is coupled to the first end of the power supply capacitor, and the second end is used to receive a first voltage; a first voltage limiting circuit, receiving the second voltage and providing a first control voltage to a third terminal of the first controllable switch based on the second voltage; A second controllable switch comprises a first end, a second end and a third end, wherein the first end is coupled to the first end of the power supply capacitor, and the second end is used to receive a second voltage; as well as a second voltage limiting circuit, receiving the first voltage and providing a second control voltage to a third terminal of the second controllable switch based on the first voltage; in When the first voltage is greater than the first limiting voltage, the second control voltage provided by the second voltage limiting circuit is equal to the first limiting voltage; when the first voltage is less than the first limiting voltage, the second control voltage is equal to the first voltage; as well as When the second voltage is greater than the second limiting voltage, the first control voltage provided by the first voltage limiting circuit is equal to the second limiting voltage; when the second voltage is less than the second limiting voltage, the first control voltage is equal to the second voltage; wherein the first limiting voltage is less than the second limiting voltage.

8. The power supply control circuit according to claim 7, wherein the first voltage limiting circuit comprises: a first Zener diode, comprising a cathode terminal and an anode terminal, wherein the cathode terminal is coupled to the third terminal of the first controllable switch, and the anode terminal is coupled to the primary ground; as well as The first protection resistor includes a first end and a second end, wherein the first end is coupled to the third end of the first controllable switch, and the second end is used to receive a second voltage.

9. The power supply control circuit according to claim 7, wherein the second voltage limiting circuit comprises: a second Zener diode, comprising a cathode terminal and an anode terminal, wherein the cathode terminal is coupled to the third terminal of the second controllable switch, and the anode terminal is coupled to the primary ground; as well as The second protection resistor includes a first end and a second end, wherein the first end is coupled to the third end of the second controllable switch, and the second end is used to receive the first voltage.

10. The power supply control circuit according to claim 7, wherein the power supply voltage output circuit further comprises: The first output diode has a first end and a second end, wherein the first end is coupled to the first end of the power supply capacitor, and the second end is coupled to the first end of the first controllable switch.

11. The power supply control circuit according to claim 7, wherein the power supply voltage output circuit further comprises: The second output diode has a first end and a second end, wherein the first end is coupled to the first end of the power supply capacitor, and the second end is coupled to the first end of the second controllable switch.

12. The power supply control circuit according to claim 7, wherein the second voltage limiting circuit further comprises: The supplementary voltage output circuit is coupled to the third terminal of the second controllable switch. 13 . The power supply control circuit according to claim 12 , wherein the supplementary voltage provided by the supplementary voltage output circuit is smaller than the first limit voltage and the second limit voltage.

14. An isolated switch circuit, comprising the power supply control circuit according to any one of claims 1 to 13, further comprising: The transformer includes a primary winding, a secondary winding, a first auxiliary winding and a second auxiliary winding.

15. The isolated switch circuit of claim 14, further comprising: Pull-up switch tube; A pull-down switch tube is coupled in series with the pull-up switch tube between the input end of the isolation switch circuit and the primary ground; as well as The resonant capacitor is coupled in series with the primary winding between a connection point between the pull-up switch tube and the pull-down switch tube and the primary ground.

16. A power supply control method for an isolated switching circuit, comprising: receiving a first auxiliary winding voltage provided by a first auxiliary winding of the isolated switch circuit, and outputting a first voltage representing an input voltage of the isolated switch circuit based on the first auxiliary winding voltage; receiving a second auxiliary winding voltage provided by a second auxiliary winding of the isolated switch circuit, and outputting a second voltage representing an output voltage of the isolated switch circuit based on the second auxiliary winding voltage; as well as A supply voltage is output based on the first voltage and the second voltage.

17. The power supply control method according to claim 16, wherein outputting the power supply voltage based on the first voltage and the second voltage comprises: receiving a second voltage and providing a first control voltage based on the second voltage; receiving a first voltage and providing a second control voltage based on the first voltage; as well as outputting a supply voltage based on a smaller value between the first voltage and the first control voltage, or a smaller value between the second voltage and the second control voltage; When the first voltage is greater than the first limiting voltage, the second control voltage is equal to the first limiting voltage; and when the first voltage is less than the first limiting voltage, the second control voltage is equal to the first voltage; and When the second voltage is greater than the second limiting voltage, the first control voltage is equal to the second limiting voltage; when the second voltage is less than the second limiting voltage, the first control voltage is equal to the second voltage; wherein the first limiting voltage is less than the second limiting voltage.

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