Control circuit

Abstract

A control circuit is used for a flyback converter and comprises a feedback circuit, a first current mirror, a second current mirror, a compensation resistor and a pole adjuster. The feedback circuit generates a feedback current based on an output voltage of the flyback converter. The first current mirror maps the feedback current to a first mapped current. The second current mirror maps the first mapping current to a second mapping current. The compensation resistor is coupled to the internal node, and the second mapping current flows through the compensation resistor to generate an internal voltage at the internal node. The pole adjuster generates a compensation voltage based on the internal voltage. The flyback converter increases the output power of the output voltage based on an increase in the compensation voltage.

Description

Technical Field

[0001] The present invention relates to a control circuit of a flyback converter, and more particularly to a control circuit of a flyback converter with low current loss. Background Art

[0002] A flyback converter is a voltage conversion circuit derived from a buck-boost converter. The buck-boost converter's single-winding inductor is replaced with a two-winding transformer. The output voltage is then rectified using a rectifier (e.g., a diode). However, to accurately control the flyback converter's output voltage, closed-loop control is required.

[0003] In flyback converter designs, the closed-loop control circuit often consumes some current. To increase the flyback converter's conversion efficiency, it's essential to reduce the current consumption of the closed-loop control circuit. However, reducing the current often has other effects, making this a significant challenge. Summary of the Invention

[0004] The present invention proposes a control circuit for a flyback converter that reduces current consumption while maintaining stability. Furthermore, the control circuit not only shifts the dominant pole, which is too low, to a higher frequency but also generates a new dominant pole through a pole adjuster, thereby making the stability of the control circuit more easily controllable.

[0005] In view of this, the present invention provides a control circuit for a flyback converter, comprising a feedback circuit, a first current mirror, a second current mirror, a compensation resistor, and a pole adjuster. The feedback circuit generates a feedback current based on an output voltage of the flyback converter. The first current mirror maps the feedback current into a first mirrored current. The second current mirror maps the first mirrored current into a second mirrored current. The compensation resistor is coupled to an internal node, wherein the second mirrored current flows through the compensation resistor to generate an internal voltage at the internal node. The pole adjuster generates a compensation voltage based on the internal voltage, wherein the flyback converter increases the output power of the output voltage based on an increase in the compensation voltage.

[0006] According to one embodiment of the present invention, the pole adjuster includes a pole resistor and a pole capacitor. The pole resistor is coupled between the internal node and the compensation voltage. The pole capacitor is coupled between the compensation voltage and a ground terminal. The sum of the resistance values ​​of the compensation resistor and the pole resistor, and the capacitance value of the pole capacitor, determines a dominant pole of the control circuit.

[0007] According to an embodiment of the present invention, the first current mirror and the compensation resistor are both coupled to a bias voltage, the second mirrored current flows from the bias voltage to the internal node, and the second current mirror is coupled to a ground terminal.

[0008] According to an embodiment of the present invention, the control circuit further includes a connecting resistor coupled to the first current mirror, wherein the feedback current flows through the connecting resistor.

[0009] According to one embodiment of the present invention, the feedback circuit includes a voltage divider circuit, a voltage stabilizing element, a first resistor, and an optocoupler element. The voltage divider circuit divides the output voltage to generate a divided voltage. The voltage stabilizing element draws an optocoupled current from an optocoupler node based on the divided voltage. The first resistor is coupled to the output voltage, wherein the optocoupled current flows through the first resistor. The optocoupler element is coupled between the first resistor and the optocoupler node. The optocoupler element generates the feedback current based on the optocoupled current. The optocoupled current increases as the divided voltage increases.

[0010] According to another embodiment of the present invention, the feedback circuit includes a voltage divider circuit, a first transconductance amplifier, a zero-point adjuster, a second transconductance amplifier, an optocoupler element, and a second resistor. The voltage divider circuit divides the output voltage to generate a divided voltage. The first transconductance amplifier compares the divided voltage with a reference voltage to generate a first current. The first current flows through the zero-point adjuster to generate a first voltage and a zero point. The second transconductance amplifier generates an optocoupler current based on the first voltage. The optocoupler element generates the feedback current based on the optocoupler current. The second resistor is coupled between the second transconductance amplifier and the optocoupler element. The optocoupler current flows through the second resistor.

[0011] According to one embodiment of the present invention, when the divided voltage exceeds the reference voltage, the first transconductance amplifier increases the first current, and when the divided voltage does not exceed the reference voltage, the first transconductance amplifier decreases the first current.

[0012] According to one embodiment of the present invention, the zero-point adjuster includes a zero-point resistor and a zero-point capacitor. The zero-point resistor is coupled to the first voltage. The zero-point capacitor is coupled between the zero-point resistor and a ground terminal. The zero point is used to increase the stability of the control circuit.

[0013] The present invention further provides a control circuit for a flyback converter, comprising a first transistor, a feedback circuit, an amplifier, a first resistor, a first transconductance amplifier, and a second resistor. The first transistor includes a gate terminal, a drain terminal, and a source terminal, wherein the gate terminal receives a control voltage. The feedback circuit draws a feedback current from the source terminal based on an output voltage of the flyback converter. The amplifier includes a positive terminal, a negative terminal, and an output terminal, wherein the positive terminal receives a first reference voltage, the negative terminal is coupled to the source terminal, and the output terminal generates the control voltage. The first resistor is coupled between a bias voltage and the drain terminal. The first transconductance amplifier generates a first current based on a voltage difference across the first resistor. The second resistor is coupled between the bias voltage and a compensation voltage. The first current flows through the second resistor to generate the compensation voltage. The flyback converter increases the output power of the output voltage based on an increase in the compensation voltage.

[0014] According to one embodiment of the present invention, the feedback circuit includes a voltage divider circuit, a voltage stabilizing element, a third resistor, and an optocoupler element. The voltage divider circuit divides the output voltage to generate a divided voltage. The voltage stabilizing element draws an optocoupled current from an optocoupler node based on the divided voltage. The third resistor is coupled to the output voltage, wherein the optocoupled current flows through the third resistor. The optocoupler element is coupled between the third resistor and the optocoupler node. The optocoupler element generates the feedback current based on the optocoupled current. The optocoupled current increases as the divided voltage increases.

[0015] According to another embodiment of the present invention, the feedback circuit includes a voltage divider circuit, a second transconductance amplifier, a zero-point adjuster, a third transconductance amplifier, an optical coupling element, and a fourth resistor. The voltage divider circuit divides the output voltage to generate a divided voltage. The second transconductance amplifier compares the divided voltage with a second reference voltage to generate a first current. The first current flows through the zero-point adjuster to generate a first voltage and a zero point. The third transconductance amplifier generates an optical coupling current based on the first voltage. The optical coupling element generates the feedback current based on the optical coupling current. The fourth resistor is coupled between the second transconductance amplifier and the optical coupling element. The zero point is used to increase the stability of the control circuit.

[0016] According to one embodiment of the present invention, when the divided voltage exceeds the reference voltage, the first transconductance amplifier increases the first current, and when the divided voltage does not exceed the reference voltage, the first transconductance amplifier decreases the first current.

[0017] The present invention further provides a control circuit for a flyback converter, comprising a feedback circuit, a first current mirror, a second current mirror, a compensation resistor, and a pole adjuster. The feedback circuit generates an optocoupler current based on an output voltage of the flyback converter, wherein the feedback circuit further includes an optocoupler element. The optocoupler element generates the feedback current based on the optocoupler current. The first current mirror maps the feedback current into a first mirrored current. The second current mirror maps the first mirrored current into a second mirrored current. The compensation resistor is coupled to an internal node, wherein the second mirrored current flows through the internal resistor, generating an internal voltage at the internal node. The pole adjuster generates a compensation voltage based on the internal voltage. The flyback converter increases the output power of the output voltage based on an increase in the compensation voltage.

[0018] According to one embodiment of the present invention, the pole adjuster includes a pole resistor and a pole capacitor. The pole resistor is coupled between the first node and the compensation voltage. The pole capacitor is coupled between the compensation voltage and a ground terminal. The sum of the resistance values ​​of the pole resistor and the compensation resistor, and the capacitance value of the pole capacitor determine a main pole of the control circuit.

[0019] According to an embodiment of the present invention, the first current mirror and the first resistor are both coupled to a bias voltage, the second mirrored current flows from the bias voltage to the first node, and the second current mirror is coupled to a ground terminal.

[0020] According to an embodiment of the present invention, the control circuit further includes a connecting resistor coupled to the first current mirror, wherein the feedback current flows through the connecting resistor.

[0021] According to one embodiment of the present invention, the feedback circuit includes a voltage divider circuit, a voltage stabilizing element, and a first resistor. The voltage divider circuit divides the output voltage to generate a divided voltage. The voltage stabilizing element draws the optocoupled current from an optical coupling node based on the divided voltage. The first resistor is coupled to the output voltage, wherein the optocoupled current flows through the first resistor. The optocoupler element is coupled between the optocoupler node and the first resistor. The optocoupled current increases as the divided voltage increases.

[0022] According to another embodiment of the present invention, the feedback circuit includes a voltage divider circuit, a first transconductance amplifier, a zero-point adjuster, a second transconductance amplifier, and a second resistor. The voltage divider circuit divides the output voltage to generate a divided voltage. The first transconductance amplifier compares the divided voltage with a reference voltage to generate a first current. The first current flows through the zero-point adjuster to generate a first voltage and a zero point. The second transconductance amplifier generates the optically coupled current based on the first voltage. The second resistor is coupled between the second transconductance amplifier and the optically coupled element. The optically coupled current flows through the second resistor.

[0023] According to one embodiment of the present invention, when the divided voltage exceeds the reference voltage, the first transconductance amplifier increases the first current, and when the divided voltage does not exceed the reference voltage, the first transconductance amplifier decreases the first current.

[0024] According to one embodiment of the present invention, the zero-point adjuster includes a zero-point resistor and a zero-point capacitor. The zero-point resistor is coupled to the first voltage. The zero-point capacitor is coupled between the zero-point resistor and a ground terminal. The zero point is used to increase the stability of the control circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1A A block diagram of a flyback converter according to an embodiment of the present invention is shown;

[0026] Figure 1B A block diagram of a flyback converter according to another embodiment of the present invention is shown;

[0027] Figure 2 A circuit diagram showing a control circuit according to an embodiment of the present invention;

[0028] Figure 3 A circuit diagram showing a control circuit according to another embodiment of the present invention;

[0029] Figure 4 A circuit diagram showing a control circuit according to another embodiment of the present invention;

[0030] Figure 5 A circuit diagram showing a control circuit according to another embodiment of the present invention;

[0031] Figure 6 A circuit diagram showing a control circuit according to another embodiment of the present invention;

[0032] Figure 7 A circuit diagram showing a control circuit according to another embodiment of the present invention; and

[0033] Figure 8 A circuit diagram showing a control circuit according to another embodiment of the present invention.

[0034] Explanation of symbols

[0035] 100A, 100B: Flyback Converter

[0036] 110,200,300,400,500,600,700,800: Control circuit

[0037] QH: Upper bridge transistor

[0038] QL: low bridge transistor

[0039] TM: Transformer

[0040] CR: resonant capacitor

[0041] RS: Sense resistor

[0042] CO: output capacitance

[0043] DR: Rectifier

[0044] HS: upper bridge drive signal

[0045] LS: lower bridge drive signal

[0046] PS: Primary coil

[0047] SS: Secondary coil

[0048] VO: output voltage

[0049] VCOMP: compensation voltage

[0050] VIN: input voltage

[0051] 210, 310, 410, 510, 610, 710, 810: Feedback circuit

[0052] 211: Voltage divider circuit

[0053] DRG: voltage stabilizing element

[0054] R1: first resistor

[0055] PD: Optical Coupler Component

[0056] RZ1: First zero point resistance

[0057] CZ1: First zero point capacitor

[0058] RD1: The first voltage divider resistor

[0059] RD2: Second voltage divider resistor

[0060] VD: divided voltage

[0061] IPD: Optocoupler Current

[0062] IFB: Feedback current

[0063] NPD1: first optical coupling node

[0064] NPD2: Second optical coupling node

[0065] LED: Light Emitting Diode

[0066] Q: Transistor

[0067] RCOMP: compensation resistor

[0068] CCOMP: compensation capacitor

[0069] VBIAS: bias voltage

[0070] ICOMP: Compensation current

[0071] CT: total capacitance

[0072] CD: parasitic capacitance

[0073] RZ2: Second zero point resistance

[0074] CZ2: Second zero point capacitor

[0075] GM1: First transconductance amplifier

[0076] 412: Zero point adjuster

[0077] GM2: Second transconductance amplifier

[0078] R2: Second resistor

[0079] VREF1: first reference voltage

[0080] I1: first current

[0081] V1: first voltage

[0082] RZ3: The third zero point resistor

[0083] CZ3: The third zero point capacitor

[0084] RZ4: Fourth zero point resistor

[0085] CZ4: Fourth zero point capacitor

[0086] CM1: First current mirror

[0087] CM2: Second current mirror

[0088] RINT: Connection resistance

[0089] 620: Pole Adjuster

[0090] IM1: first mapping current

[0091] IM2: Second mirror current

[0092] NI: Internal Node

[0093] VI: Internal voltage

[0094] RPL: Pole resistance

[0095] CPL: Pole Capacitance

[0096] T1: first transistor

[0097] AMP: amplifier

[0098] R3: The third resistor

[0099] GM3: Third transconductance amplifier

[0100] R4: the fourth resistor

[0101] D: Drain terminal

[0102] S: Source terminal

[0103] G: Gate terminal

[0104] VC: control voltage

[0105] INP: positive input terminal

[0106] INN: negative input terminal

[0107] OT: output terminal

[0108] VREF2: Second reference voltage

[0109] I2: Second current DETAILED DESCRIPTION

[0110] The following descriptions are examples of the present disclosure. Their purpose is to illustrate the general principles of the present disclosure and should not be considered as limiting the present disclosure, the scope of which should be determined by the scope of the claims.

[0111] It is worth noting that the following disclosure provides multiple embodiments or examples for practicing different features of the present disclosure. The specific component examples and arrangements described below are intended only to briefly illustrate the spirit of the present disclosure and are not intended to limit the scope of the present disclosure. In addition, the following description may reuse the same component symbols or characters in multiple examples. However, this repetition is intended only to provide simplified and clear descriptions and is not intended to define the relationship between the various embodiments and / or configurations discussed below.

[0112] In addition, the description below of a feature being connected to, coupled to, and / or formed on another feature may actually include multiple different embodiments, including direct contact between these features, or including other additional features formed between these features, etc., so that these features are not in direct contact.

[0113] In addition, relative terms such as "lower" or "bottom" and "upper" or "top" may be used in the embodiments to describe the relative relationship of one element to another element in the drawings. It is understood that if the device in the drawings is turned upside down, the element described as being on the "lower" side will become the element on the "upper" side.

[0114] It is understood that although the terms "first," "second," "third," etc. may be used herein to describe various elements, components, regions, layers, and / or parts, these elements, components, regions, layers, and / or parts should not be limited by these terms, and these terms are merely used to distinguish different elements, components, regions, layers, and / or parts. Thus, a first element, component, region, layer, and / or part discussed below may be referred to as a second element, component, region, layer, and / or part without departing from the teachings of some embodiments of the present disclosure.

[0115] Some embodiments of the present disclosure can be understood in conjunction with the accompanying drawings, which are considered part of the description of the present disclosure. It should be noted that the drawings of the present disclosure are not drawn to scale for actual devices and components. The shapes and thicknesses of the embodiments may be exaggerated in the drawings to clearly illustrate the features of the present disclosure. Furthermore, the structures and devices in the drawings are schematically illustrated to clearly illustrate the features of the present disclosure.

[0116] Here, the terms "about," "approximately," and "substantially" generally mean within 20%, preferably within 10%, and more preferably within 5%, or within 3%, or within 2%, or within 1%, or within 0.5% of a given value or range. The quantities given here are approximate quantities, that is, in the absence of specific description of "about," "approximately," or "substantially," the meaning of "about," "approximately," or "substantially" may still be implied.

[0117] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meanings as commonly understood by those skilled in the art. It is understood that these terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning consistent with the background or context of the relevant technology and this disclosure, and should not be interpreted in an idealized or overly formal manner unless specifically defined in the present disclosure.

[0118] In some embodiments of the present disclosure, terms such as "connected" and "interconnected," unless otherwise specified, may refer to two structures being in direct contact, or may refer to two structures not being in direct contact, with another structure positioned between them. Furthermore, such terms may include situations where both structures are movable or both structures are fixed.

[0119] In the drawings, similar elements and / or features may have the same reference numerals. Various elements of the same type may be distinguished by adding letters or numbers after the reference numerals to distinguish similar elements and / or similar features.

[0120] Figure 1A FIG. 2 shows a block diagram of a flyback converter according to an embodiment of the present invention. Figure 1A As shown, a flyback converter 100A includes a low-bridge transistor QL, a transformer TM, an output capacitor CO, a rectifier element DR, and a control circuit 110. When the low-bridge transistor QL is conducting based on a low-bridge drive signal LS, the input voltage VIN stores energy in the transformer TM. When the low-bridge transistor QL is off, the transformer TM releases energy. The transformer TM includes a primary winding PS and a secondary winding SS, where the primary winding PS is electrically connected to the low-bridge transistor QL.

[0121] The output capacitor CO is coupled to both ends of the secondary winding SS. The rectifier element DR is coupled between the output capacitor CO and the secondary winding SS, thereby converting the energy stored in the transformer TM into the output voltage VO. The control circuit 110 is configured to generate a compensation voltage VCOMP based on the output voltage VO.

[0122] According to one embodiment of the present invention, when the compensation voltage VCOMP increases, the flyback converter 100A uses the low-bridge drive signal LS to increase the output power of the output voltage VO. According to another embodiment of the present invention, when the compensation voltage VCOMP decreases, the flyback converter 100A uses the low-bridge drive signal LS to decrease the output power of the output voltage VO.

[0123] Figure 1B A block diagram of a flyback converter according to another embodiment of the present invention is shown. Figure 1BAs shown, a flyback converter 100B includes a high-bridge transistor QH, a low-bridge transistor QL, a transformer TM, a resonant capacitor CR, a sense resistor RS, an output capacitor CO, a rectifier element DR, and a control circuit 110. High-bridge transistor QH charges transformer TM and resonant capacitor CR using input voltage VIN based on a high-bridge drive signal HS. Low-bridge transistor QL discharges transformer TM and resonant capacitor CR based on a low-bridge drive signal LS.

[0124] Transformer TM includes a primary coil PS and a secondary coil SS. Primary coil PS is electrically connected to high-bridge transistor QH and low-bridge transistor QL. Resonant capacitor CR is coupled to transformer TM. Sense resistor RS is used to detect current flowing through primary coil PS and resonant capacitor CR.

[0125] The output capacitor CO is coupled to both ends of the secondary winding SS. The rectifier element DR is coupled between the output capacitor CO and the secondary winding SS, thereby converting the energy stored in the transformer TM into the output voltage VO. The control circuit 110 is configured to generate a compensation voltage VCOMP based on the output voltage VO.

[0126] According to one embodiment of the present invention, when the compensation voltage VCOMP increases, the flyback converter 100B utilizes the high-bridge drive signal HS and the low-bridge drive signal LS to increase the output power of the output voltage VO. According to another embodiment of the present invention, when the compensation voltage VCOMP decreases, the flyback converter 100B utilizes the high-bridge drive signal HS and the low-bridge drive signal LS to decrease the output power of the output voltage VO. According to one embodiment of the present invention, the flyback converter 100B is an asymmetrical half-bridge flyback converter.

[0127] Figure 2 A circuit diagram of a control circuit according to an embodiment of the present invention is shown. According to an embodiment of the present invention, the control circuit 200 may correspond to Figure 1A as well as Figure 1B The control circuit 110. Figure 2 As shown, the control circuit 200 includes a feedback circuit 210, a compensation resistor RCOMP, and a compensation capacitor CCOMP. The feedback circuit 210 includes a voltage divider circuit 211, a rectifier element DR, a first resistor R1, an optical coupling element PD, a first zero point resistor RZ1, and a first zero point capacitor CZ1.

[0128] The voltage divider circuit 211 includes a first voltage divider resistor RD1 and a second voltage divider resistor RD2, configured to divide the output voltage VO to generate a divided voltage VD. A voltage regulator DRG draws an optocoupler current IPD from a first optocoupler node NPD1 based on the divided voltage VD. According to some embodiments of the present invention, the voltage regulator DRG may be a TL431. According to one embodiment of the present invention, the optocoupler current IPD increases as the divided voltage VD increases. According to another embodiment of the present invention, the optocoupler current IPD decreases as the divided voltage VD decreases. A first resistor R1 is coupled to the output voltage VO, and the optocoupler current IPD flows through the first resistor R1.

[0129] Based on the optical coupling current IPD, the optical coupling device PD draws a feedback current IFB from a second optical coupling node NPD2. The optical coupling device PD includes a light-emitting diode LED and a transistor Q. The light-emitting diode LED is coupled between a first resistor R1 and the optical coupling node NPD, and the optical coupling current IPD flows through the light-emitting diode LED. When the optical coupling current IPD flows through the light-emitting diode LED, causing the light-emitting diode LED to emit light, the light generated by the light-emitting diode LED causes the transistor Q to draw a feedback current IFB from the second optical coupling node NPD2. The feedback current IFB is positively correlated with the optical coupling current IPD.

[0130] According to some embodiments of the present invention, the ground terminal coupled to the light-emitting diode LED of the optical coupling element PD and the ground terminal coupled to the transistor Q are electrically isolated from each other. A first zero-point resistor RZ1 and a first zero-point capacitor CZ1 are connected in series between the first optical coupling node NPD1 and the divided voltage VD to generate a zero point to stabilize the control circuit 200.

[0131] like Figure 2 As shown, the control circuit 200 further includes a compensation resistor RCOMP and a compensation capacitor CCOMP. The compensation resistor RCOMP is coupled between the bias voltage VBIAS and the compensation voltage VCOMP. The compensation capacitor CCOMP is coupled between the compensation voltage VCOMP and ground. A compensation current ICOMP flows through the compensation resistor RCOMP. The compensation voltage VCOMP is electrically connected to the second optical coupling node NPD2.

[0132] According to one embodiment of the present invention, the main pole from the output voltage VO to the compensation voltage VCOMP is determined by the compensation resistor RCOMP and the total capacitor CT. The zero point created by the sum of the first zero-point capacitor CZ1, the first zero-point resistor RZ1, and the first voltage-divider resistor RD1 is used to maintain loop stability. The total capacitor CT is equal to the sum of the compensation capacitor CCOMP and the parasitic capacitance CD of the transistor Q. According to one embodiment of the present invention, the sum of the first zero-point capacitor CZ1, the first zero-point resistor RZ1, and the first voltage-divider resistor RD1 determines the location of the zero point.

[0133] According to one embodiment of the present invention, to reduce the current consumption of control circuit 200, compensation resistor RCOMP must be added to reduce compensation current ICOMP. However, the added compensation resistor RCOMP shifts the dominant pole to a lower frequency position and also increases the gain from output voltage VO to compensation voltage VCOMP. Therefore, additional measures must be taken to ensure the stability of control circuit 200.

[0134] Figure 3 A circuit diagram of a control circuit according to another embodiment of the present invention is shown. Figure 3 The control circuit 300 and Figure 2 Compared to the control circuit 200, the feedback circuit 310 of the control circuit 300 further includes a second zero-point resistor RZ2 and a second zero-point capacitor CZ2, wherein the second zero-point resistor RZ2 and the second zero-point capacitor CZ2 are connected in series between the output voltage VO and the light-emitting diode LED of the optical coupling device PD.

[0135] According to one embodiment of the present invention, reducing the feedback current IFB helps reduce the optocoupler current IPD, thereby reducing the current consumption of the control circuit 300 and improving conversion efficiency. As the feedback current IFB decreases, the compensation current ICOMP also decreases, causing the compensation resistor RCOMP to increase. This causes the dominant pole generated by the compensation resistor RCOMP to shift toward lower frequencies, thereby causing instability in the control circuit 300. The sum of the second zero capacitor CZ2, the first resistor R1, and the second zero resistor RZ2 is used to generate an additional zero to compensate for the phase shift caused by the increased compensation resistor RCOMP, thereby ensuring the stability of the control circuit 300.

[0136] Figure 4 A circuit diagram of a control circuit according to another embodiment of the present invention is shown. Figure 4 The control circuit 400 and Figure 2 Compared with the control circuit 200, Figure 2 The feedback circuit 210 is replaced by the feedback circuit 410. Figure 4 As shown, the feedback circuit 410 includes a voltage divider circuit 211 , a first transconductance amplifier GM1 , a zero-point adjuster 412 , a second transconductance amplifier GM2 , a second resistor R2 , and an optical coupling element PD.

[0137] The voltage divider circuit 211 is configured to divide the output voltage VO to generate a divided voltage VD. The first transconductance amplifier GM1 generates a first current I1 based on the difference between the divided voltage VD and the first reference voltage VREF1. The first current I1 flows through the zero-point adjuster 412 to generate a first voltage V1.

[0138] like Figure 4 As shown, the zero adjuster 412 includes a third zero resistor RZ3 and a third zero capacitor CZ3. The third zero resistor RZ3 and the third zero capacitor CZ3 are connected in series between the first voltage V1 and ground, and the first current I1 flows through the third zero resistor RZ3 and the third zero capacitor CZ3. Subsequently, the second transconductance amplifier GM2 generates an optical coupling current IPD based on the first voltage V1.

[0139] The optical coupling element PD generates a feedback current IFB flowing through the transistor Q from the second optical coupling node NPD2 based on the optical coupling current IPD flowing through the light emitting diode LED. Figure 4 As shown, the control circuit 400 further includes a compensation resistor RCOMP and a compensation capacitor CCOMP, wherein the compensation resistor RCOMP is coupled between the bias voltage VBIAS and the compensation voltage VCOMP, and the compensation capacitor CCOMP is coupled between the compensation voltage VCOMP and the ground.

[0140] According to one embodiment of the present invention, the dominant pole of the control circuit 400 is determined by the sum of the compensation resistor RCOMP, the compensation capacitor CCOMP, and the parasitic capacitance CD of the transistor Q. The third zero-point resistor RZ3 and the third zero-point capacitor CZ3 are used to determine the zero point, thereby controlling the stability of the control circuit 400. To reduce the current consumption of the control circuit 400, the compensation resistor RCOMP can be increased to reduce the compensation current ICOMP. However, increasing the compensation resistor RCOMP will cause the dominant pole to shift to a lower frequency, thereby causing instability in the control circuit 400.

[0141] Figure 5 A circuit diagram of a control circuit according to another embodiment of the present invention is shown. Figure 5 The control circuit 500 and Figure 4 Compared to the control circuit 400, the feedback circuit 510 further includes a fourth zero-point resistor RZ4 and a fourth zero-point capacitor CZ4, wherein the fourth zero-point resistor RZ4 and the fourth zero-point capacitor CZ4 are connected in series between the second transconductance amplifier GM2 and the light-emitting diode LED of the optical coupling element PD, and are connected in parallel with the second resistor R2.

[0142] According to one embodiment of the present invention, the sum of the fourth zero-point capacitor CZ4, the fourth zero-point resistor RZ4, and the second resistor R2 determines an additional zero point to compensate for the main pole derived from the compensation resistor RCOMP added to reduce the compensation current ICOMP, which moves to a lower frequency, thereby increasing the stability of the control circuit 500.

[0143] Figure 6 A circuit diagram of a control circuit according to another embodiment of the present invention is shown. Figure 6 As shown, the control circuit 600 includes a feedback circuit 610, a first current mirror CM1, a connecting resistor RINT, a second current mirror CM2, a compensation resistor RCOMP and a pole adjuster 620, wherein the feedback circuit 610 and the Figure 2 The feedback circuit 210 is the same as that of FIG. 1 , and will not be repeated here.

[0144] The first current mirror CM1 is coupled to a bias voltage VBIAS and is configured to mirror the feedback current IFB into a first mirrored current IM1. A connecting resistor RINT is coupled between the first current mirror CM1 and the transistor Q of the optical coupling device PD. According to one embodiment of the present invention, the connecting resistor RINT and the first current mirror CM1 are configured to shift the pole generated at the second optical coupling node NPD2 (as shown in Figures 2 and 3) to a very high frequency position. According to other embodiments of the present invention, the connecting resistor RINT may be omitted.

[0145] The second current mirror CM2 is coupled to ground and configured to map the first mirrored current IM1 to a second mirrored current IM2. A compensation resistor RCOMP is coupled between a bias voltage VBIAS and an internal node NI, and a compensation current ICOMP flows through the compensation resistor RCOMP. The second current mirror CM2 draws the second mirrored current IM2 from the internal node NI.

[0146] Pole adjuster 620 is coupled between internal node NI and compensation voltage VCOMP and generates compensation voltage VCOMP based on internal voltage V1 at internal node NI. Pole adjuster 620 includes a pole resistor RPL and a pole capacitor CPL. Pole resistor RPL is coupled between internal node NI and compensation voltage VCOMP, and pole capacitor CPL is coupled between compensation voltage VCOMP and ground. According to one embodiment of the present invention, when pole resistor RPL is large, compensation current ICOMP is equal to second mirrored current IM2.

[0147] According to one embodiment of the present invention, the sum of the pole capacitor CPL, the pole resistor RPL, and the compensation resistor RCOMP is used to determine the dominant pole of the control circuit 600. In other words, when the compensation resistor RCOMP is increased to reduce the current consumption of the control circuit 600, the dominant pole of the control circuit 600 can be moved toward higher frequencies by reducing the capacitance of the pole capacitor CPL, thereby increasing the stability of the control circuit 600.

[0148] In other words, Figure 6 The control circuit 600 and Figure 3Compared with the control circuit 300, the control circuit 600 uses the first current mirror CM1, the connection resistor RINT and the second current mirror CM2 to move the pole generated at the second optical coupling node NPD2 to a very high frequency position, and then uses the pole adjuster 620 to generate a suitable main pole. Therefore, the control circuit 600 does not need Figure 3 The second zero-point resistor RZ2 and the second zero-point capacitor CZ2 can obtain sufficient phase margin and ensure the stability of the control circuit 600.

[0149] Figure 7 A circuit diagram of a control circuit according to another embodiment of the present invention is shown. Figure 7 As shown, the control circuit 700 includes a feedback circuit 710, a first current mirror CM1, a connecting resistor RINT, a second current mirror CM2, a compensation resistor RCOMP and a pole adjuster 720, wherein the feedback circuit 710 and the Figure 4 The feedback circuit 410 is the same as that of FIG. 4 , and will not be repeated here.

[0150] also, Figure 7 The first current mirror CM1, the connection resistor RINT, the second current mirror CM2, the compensation resistor RCOMP and the pole adjuster 720 are respectively connected to Figure 6 The first current mirror CM1, the connecting resistor RINT, the second current mirror CM2, the compensation resistor RCOMP and the pole adjuster 620 are the same and are not repeated here.

[0151] According to one embodiment of the present invention, Figure 4 The main pole of the control circuit 400 is formed at the second optical coupling node NPD2, Figure 7 The first current mirror CM1 and the connected resistor RINT move the pole of the second optical coupling node NPD2 to a very high frequency position, and utilize the pole adjuster 720 to generate a suitable dominant pole, thereby improving the stability of the control circuit 700.

[0152] Figure 8 A circuit diagram of a control circuit according to another embodiment of the present invention is shown. Figure 8 As shown, the control circuit 800 includes a feedback circuit 810, a first transistor T1, an amplifier AMP, a third resistor R3, a third transconductance amplifier GM3 and a fourth resistor R4. According to one embodiment of the present invention, the feedback circuit 810 can be Figure 2 The feedback circuit 210 is configured to draw a feedback current IFB from the second optical coupling node NPD2. According to another embodiment of the present invention, the feedback circuit 810 may be Figure 4 The feedback circuit 410 is configured to draw a feedback current IFB from the second optical coupling node NPD2.

[0153] The first transistor T1 includes a drain terminal D, a source terminal S, and a gate terminal G, wherein the gate terminal G receives a control voltage VC. The source terminal S is coupled to a second optical coupling node NPD2. The amplifier AMP includes a positive input terminal INP, a negative input terminal INN, and an output terminal OT. The negative input terminal INN is coupled to the source terminal S, the positive input terminal INP receives a second reference voltage VREF2, and the output terminal OT generates the control voltage VC, thereby controlling the first transistor T1. The third resistor R3 is coupled between the bias voltage VBIAS and the drain terminal D.

[0154] The third transconductance amplifier GM3 generates a second current I2 based on the voltage difference across the third resistor R3. The fourth resistor R4 is coupled between the bias voltage VBIAS and the compensation voltage VCOMP. The second current I2 flows from the bias voltage VBIAS through the fourth resistor R4 to the compensation voltage VCOMP. According to one embodiment of the present invention, the main pole of the control circuit 800 is located at the second optical coupling node NPD2.

[0155] According to one embodiment of the present invention, when the feedback current IFB decreases, the resistance value of the third resistor R3 increases accordingly. Since the source terminal S of the first transistor T1 is a low impedance node and is coupled to the second optical coupling node NPD2, even if the third resistor R3 increases as the feedback current IFB decreases, Figure 8 The pole of the second optical coupling node NPD2 is still maintained at a very high frequency position.

[0156] The present invention proposes a control circuit for a flyback converter that reduces current consumption while maintaining stability. Furthermore, the control circuit not only shifts the dominant pole, which is too low, to a higher frequency but also generates a new dominant pole through a pole adjuster, thereby making the stability of the control circuit more easily controllable.

[0157] Although the embodiments of the present disclosure and their advantages have been disclosed as above, it should be understood that any person skilled in the art may make changes, substitutions and modifications without departing from the spirit and scope of the present disclosure. In addition, the scope of protection of the present disclosure is not limited to the processes, machines, manufacturing, material compositions, devices, methods and steps in the specific embodiments described in the specification. Any person skilled in the art can understand from the disclosure of some embodiments of the present disclosure that the processes, machines, manufacturing, material compositions, devices, methods and steps currently or in the future are developed. As long as they can implement substantially the same functions or obtain substantially the same results in the embodiments described herein, they can be used according to some embodiments of the present disclosure. Therefore, the scope of protection of the present disclosure includes the above-mentioned processes, machines, manufacturing, material compositions, devices, methods and steps. In addition, each claim constitutes a separate embodiment, and the scope of protection of the present disclosure also includes the combination of each claim and embodiment.

Claims

1. A control circuit, characterized in that: For a flyback converter comprising: a feedback circuit generating a feedback current based on an output voltage of the flyback converter; a first current mirror, mapping the feedback current into a first mapped current; a second current mirror, mapping the first mapped current into a second mapped current; a compensation resistor coupled to an internal node, wherein the second mirrored current flows through the compensation resistor to generate an internal voltage at the internal node; and a pole adjuster generating a compensation voltage based on the internal voltage; The flyback converter increases the output power of the output voltage based on the increase of the compensation voltage.

2. The control circuit according to claim 1, wherein: The pole adjuster mentioned above includes: a pole resistor coupled between the internal node and the compensation voltage; and a pole capacitor coupled between the compensation voltage and a ground terminal; The sum of the resistance value of the compensation resistor and the resistance value of the pole resistor and the capacitance value of the pole capacitor determines a main pole of the control circuit.

3. The control circuit according to claim 1, wherein: The first current mirror and the compensation resistor are both coupled to a bias voltage; wherein the second mirrored current flows from the bias voltage to the internal node; The second current mirror is coupled to a ground terminal.

4. The control circuit according to claim 1, wherein: Also includes: a connecting resistor coupled to the first current mirror; The feedback current flows through the connection resistor.

5. The control circuit according to claim 4, wherein: The above feedback circuit includes: a voltage divider circuit for dividing the output voltage to generate a divided voltage; a voltage stabilizing element, which draws an optical coupling current from an optical coupling node based on the divided voltage; a first resistor coupled to the output voltage, wherein the optically coupled current flows through the first resistor; and an optical coupling element coupled between the first resistor and the optical coupling node; wherein the optical coupling element generates the feedback current based on the optical coupling current; The optical coupling current increases as the divided voltage increases.

6. The control circuit according to claim 4, wherein: The above feedback circuit includes: a voltage divider circuit for dividing the output voltage to generate a divided voltage; a first transconductance amplifier, comparing the divided voltage with a reference voltage to generate a first current; a zero-point adjuster, wherein the first current flows through the zero-point adjuster to generate a first voltage and a zero point; a second transconductance amplifier, generating a photocoupled current based on the first voltage; an optical coupling element, generating the feedback current based on the optical coupling current; and a second resistor coupled between the second transconductance amplifier and the optical coupling element; The optical coupling current flows through the second resistor.

7. The control circuit according to claim 6, wherein: When the divided voltage exceeds the reference voltage, the first transconductance amplifier increases the first current; When the divided voltage does not exceed the reference voltage, the first transconductance amplifier reduces the first current.

8. The control circuit according to claim 6, wherein: The above-mentioned zero point adjuster includes: a zero-point resistor coupled to the first voltage; and a zero-point capacitor coupled between the zero-point resistor and a ground terminal; The zero point is used to increase the stability of the control circuit.

9. A control circuit, characterized in that: For a flyback converter comprising: a first transistor comprising a gate terminal, a drain terminal, and a source terminal, wherein the gate terminal receives a control voltage; a feedback circuit, which draws a feedback current from the source terminal based on an output voltage of the flyback converter; An amplifier comprising a positive terminal, a negative terminal, and an output terminal, wherein the positive terminal receives a first reference voltage, the negative terminal is coupled to the source terminal, and the output terminal generates the control voltage; a first resistor coupled between a bias voltage and the drain terminal; a first transconductance amplifier, generating a first current based on a voltage difference between two ends of the first resistor; and a second resistor coupled between the bias voltage and a compensation voltage; wherein the first current flows through the second resistor to generate the compensation voltage; The flyback converter increases the output power of the output voltage based on the increase of the compensation voltage.

10. The control circuit according to claim 9, wherein: The above feedback circuit includes: a voltage divider circuit for dividing the output voltage to generate a divided voltage; a voltage stabilizing element, which draws an optical coupling current from an optical coupling node based on the divided voltage; a third resistor coupled to the output voltage, wherein the optical coupling current flows through the third resistor; and an optical coupling element coupled between the third resistor and the optical coupling node; wherein the optical coupling element generates the feedback current based on the optical coupling current; The optical coupling current increases as the divided voltage increases.

11. The control circuit according to claim 9, wherein: The above feedback circuit includes: a voltage divider circuit for dividing the output voltage to generate a divided voltage; a second transconductance amplifier, comparing the divided voltage with a second reference voltage to generate a first current; a zero-point adjuster, wherein the first current flows through the zero-point adjuster to generate a first voltage and a zero point; a third transconductance amplifier, generating a photocoupled current based on the first voltage; an optical coupling element, generating the feedback current based on the optical coupling current; and a fourth resistor coupled between the second transconductance amplifier and the optical coupling element; The zero point is used to increase the stability of the control circuit.

12. The control circuit according to claim 11, wherein: When the divided voltage exceeds the reference voltage, the first transconductance amplifier increases the first current; When the divided voltage does not exceed the reference voltage, the first transconductance amplifier reduces the first current.

13. A control circuit, characterized in that: For a flyback converter comprising: a feedback circuit, generating an optically coupled current based on an output voltage of the flyback converter, wherein the feedback circuit further comprises: an optical coupling element, generating a feedback current based on the optical coupling current; a first current mirror, mapping the feedback current into a first mapped current; a second current mirror, mapping the first mapped current into a second mapped current; a compensation resistor coupled to an internal node, wherein the second mirrored current flows through the compensation resistor to generate an internal voltage at the internal node; and a pole adjuster generating a compensation voltage based on the internal voltage; The flyback converter increases the output power of the output voltage based on the increase of the compensation voltage.

14. The control circuit according to claim 13, wherein: The pole adjuster mentioned above includes: a pole resistor coupled between the internal node and the compensation voltage; and a pole capacitor coupled between the compensation voltage and a ground terminal; The sum of the resistance value of the pole resistor and the resistance value of the compensation resistor and the capacitance value of the pole capacitor determines a main pole of the control circuit.

15. The control circuit according to claim 13, wherein: The first current mirror and the compensation resistor are both coupled to a bias voltage; wherein the second mirrored current flows from the bias voltage to the internal node; The second current mirror is coupled to a ground terminal.

16. The control circuit according to claim 13, wherein: Also includes: a connecting resistor coupled to the first current mirror; The feedback current flows through the connection resistor.

17. The control circuit according to claim 16, wherein: The above feedback circuit includes: a voltage divider circuit for dividing the output voltage to generate a divided voltage; a voltage stabilizing element, which draws the optical coupling current from an optical coupling node based on the divided voltage; and a first resistor coupled to the output voltage, wherein the optically coupled current flows through the first resistor; wherein the optical coupling element is coupled between the optical coupling node and the first resistor; The optical coupling current increases as the divided voltage increases.

18. The control circuit according to claim 16, wherein: The above feedback circuit includes: a voltage divider circuit for dividing the output voltage to generate a divided voltage; a first transconductance amplifier, comparing the divided voltage with a reference voltage to generate a first current; a zero-point adjuster, wherein the first current flows through the zero-point adjuster to generate a first voltage and a zero point; a second transconductance amplifier, generating the optically coupled current based on the first voltage; and a second resistor coupled between the second transconductance amplifier and the optical coupling element; The optical coupling current flows through the second resistor.

19. The control circuit according to claim 18, wherein: When the divided voltage exceeds the reference voltage, the first transconductance amplifier increases the first current; When the divided voltage does not exceed the reference voltage, the first transconductance amplifier reduces the first current.

20. The control circuit according to claim 18, wherein: The above-mentioned zero point adjuster includes: a zero-point resistor coupled to the first voltage; and a zero-point capacitor coupled between the zero-point resistor and a ground terminal; The zero point is used to increase the stability of the control circuit.

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