High-precision drain-source voltage detection circuit for synchronous rectification of LLC resonant converter

Abstract

The application discloses a high-precision drain-source voltage detection circuit for synchronous rectification of an LLC resonant converter, one end of a drain-source off voltage blocking circuit is connected with a drain electrode of a synchronous rectification tube to be detected, the other end of the drain-source off voltage blocking circuit is connected with a cathode of a compensation diode, an anode of a clamping diode and a same-direction input end of an operational amplifier, one end of a first current-limiting resistor is connected with an anode of the compensation diode, the other end of the first current-limiting resistor is connected with a cathode of the clamping diode and a constant-current source circuit, one end of a first compensation resistor is connected with the anode of the compensation diode, the other end of the first compensation resistor is connected with a reverse input end of the operational amplifier, a cathode of a stabilizing tube is connected with the cathode of the clamping diode, an anode of the stabilizing tube is grounded, and an output end of the operational amplifier is used as a final output signal end; and the circuit can accurately detect the drain-source voltage of the LLC resonant converter.

Description

Technical Field

[0001] This invention belongs to the field of DC / DC converter technology and relates to a high-precision drain-source voltage detection circuit for synchronous rectification of LLC resonant converters. Background Technology

[0002] In recent years, with the continuous development of new energy electric vehicles and aerospace industries, LLC resonant converters have received widespread attention from industry and academia due to their advantages such as achieving ZVS soft switching across the entire load range. Improving the efficiency and power density of LLC resonant converters across a wide voltage regulation range has become a key research focus. Among these, synchronous rectification control of the secondary rectifier diodes is one of the important aspects of improving the operating efficiency of LLC resonant converters.

[0003] Currently, synchronous rectifier drain-source voltage detection schemes are widely used in synchronous rectification control of LLC resonant converters due to their lossless and small sampling circuits, independence from resonant parameters, and ability to directly reflect the on / off state of the secondary rectifier diode. However, existing synchronous rectifier drain-source voltage detection schemes suffer from low detection accuracy and limited applicable voltage levels, thus requiring urgent improvement. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a high-precision drain-source voltage detection circuit for synchronous rectification of LLC resonant converters. This circuit can detect the drain-source voltage of LLC resonant converters more accurately.

[0005] To achieve the above objectives, this invention discloses a high-precision drain-source voltage detection circuit for synchronous rectification of an LLC resonant converter, comprising a drain-source turn-off voltage blocking circuit, a drain-source turn-on voltage compensation circuit, a drain-source turn-off voltage clamping circuit and a constant current source circuit, a first compensation resistor and a Zener diode; the drain-source turn-on voltage compensation circuit includes a compensation diode, a first current-limiting resistor, a first compensation resistor and an operational amplifier; the drain-source turn-off voltage clamping circuit includes a clamping diode and a Zener diode;

[0006] One end of the drain-source turn-off voltage blocking circuit is connected to the drain of the synchronous rectifier being tested, and the other end of the drain-source turn-off voltage blocking circuit is connected to the cathode of the compensation diode, the anode of the clamping diode, and the non-inverting input terminal of the operational amplifier. One end of the first current-limiting resistor is connected to the anode of the compensation diode, and the other end of the first current-limiting resistor is connected to the cathode of the clamping diode and the constant current source circuit. One end of the first compensation resistor is connected to the anode of the compensation diode, and the other end of the first compensation resistor is connected to the inverting input terminal of the operational amplifier. The cathode of the Zener diode is connected to the cathode of the clamping diode, the anode of the Zener diode is grounded, and the output terminal of the operational amplifier serves as the final output signal terminal.

[0007] The drain-source turn-off voltage blocking circuit consists of several N blocking diodes of the same type connected in series.

[0008] The constant current source circuit includes a second current-limiting resistor and a voltage source. The cathode of the clamping diode is connected to one end of the second current-limiting resistor, and the other end of the second current-limiting resistor is connected to the voltage source.

[0009] It also includes a second compensation resistor and a compensation capacitor. One end of the second compensation resistor is connected to the inverting input terminal of the operational amplifier, and the other end of the second compensation resistor is connected to the output terminal of the operational amplifier. The compensation capacitor is connected in parallel with the second compensation resistor.

[0010] The output of the operational amplifier is connected to a synchronous rectification control circuit.

[0011] All blocking diodes and compensation diodes are Schottky diodes of the same type.

[0012] The clamping diode is a Schottky diode.

[0013] When the synchronous rectifier tube being tested (S) s1 When the circuit is turned on, the first sampling voltage V1 is:

[0014]

[0015] Among them, V F(Da) For a single blocking diode (D ax Forward conduction pressure drop.

[0016] When the synchronous rectifier tube being tested (S) s1 When the circuit is turned on, the second sampling voltage V2 is:

[0017]

[0018] Among them, V F(Db) For compensation diode (D) b Forward conduction pressure drop.

[0019] When the synchronous rectifier tube being tested (S) s1 When the op-amp (U1) is turned on, the output voltage V at the output terminal is... s for:

[0020]

[0021] When the synchronous rectifier tube being tested (S) s1 When turned off, the output voltage V at the output terminal of the operational amplifier (U1) is... s for:

[0022]

[0023] The present invention has the following beneficial effects:

[0024] The high-precision drain-source voltage detection circuit for synchronous rectification of LLC resonant converters described in this invention does not require resistor voltage division of the drain-source voltage during operation, thus avoiding the problem of excessive noise due to low drain-source voltage. Secondly, based on the traditional reverse series diode sampling method, this invention adds a drain-source on-state voltage compensation circuit. This circuit uses a differential compensation circuit to accurately compensate for the voltage offset caused by the reverse series diode, thereby accurately sampling the drain-source on-state voltage of the synchronous rectifier. Furthermore, this invention can expand the applicable voltage range by increasing the number N of blocking diodes in the drain-source turn-off voltage blocking circuit. Simultaneously, a corresponding compensation coefficient is applied to the drain-source on-state voltage compensation circuit to obtain an accurate drain-source on-state voltage. In addition, the constant current source circuit provides a suitable static current when the clamping diode is reverse-biased, ensuring that the Zener diode always operates in the reverse breakdown region, while simultaneously providing current to the detection circuit. This circuit features high drain-source on-state voltage detection accuracy and expandable applicable voltage levels, making it highly suitable for synchronous rectification control of LLC resonant converters at various voltage levels. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of the present invention;

[0026] Figure 2 This is a schematic diagram of the current path when the synchronous rectifier tube being tested is turned on, according to the present invention.

[0027] Figure 3 This is a schematic diagram of the current path when the detected synchronous rectifier is turned off, according to the present invention.

[0028] Figure 4 This is a waveform diagram of the present invention when it operates in the LLC sub-resonant region. Detailed Implementation

[0029] To enable those skilled in the art to better understand the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, not all embodiments, and are not intended to limit the scope of the present invention. Furthermore, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion regarding the concepts disclosed in the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort should fall within the scope of protection of the present invention.

[0030] The accompanying drawings show structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not drawn to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0031] refer to Figure 1 , Figure 2 and Figure 3 The high-precision drain-source voltage detection circuit for synchronous rectification of LLC resonant converters described in this invention includes a drain-source turn-off voltage blocking circuit, a drain-source conduction voltage compensation circuit, a drain-source turn-off voltage clamping circuit, and a constant current source circuit.

[0032] The drain-source turn-off voltage blocking circuit consists of several N blocking diodes of the same type D. a1 ~D an It is connected in series;

[0033] The drain-source on-voltage compensation circuit includes a compensation diode D. b First current-limiting resistor R s First compensation resistor R1, second compensation resistor R f Compensation capacitor C f And op-amp U1;

[0034] The drain-source turn-off voltage clamping circuit includes a clamping diode D. c and Zener diode D cc ;

[0035] The constant current source circuit includes a second current-limiting resistor R. cc and voltage source LDO.

[0036] Blocking diode D a1 The cathode and the synchronous rectifier tube S being tested s1 The drains of the diodes are connected, blocking diode D. an anode and compensation diode D b Cathode, clamping diode D c The anode of the circuit is connected to the non-inverting input terminal of operational amplifier U1, and the first current-limiting resistor R is connected to the non-inverting input terminal of operational amplifier U1. s One end is connected to the compensation diode D b The anode is connected to the first current-limiting resistor R. s The other end is connected to the clamping diode D c cathode and second current-limiting resistor R cc One end is connected to the second current-limiting resistor R. ccThe other end is connected to the voltage source LDO, and one end of the first compensation resistor R1 is connected to the compensation diode D. b The anode of the first compensation resistor R1 is connected to the inverting input terminal of the operational amplifier U1, and the other end of the first compensation resistor R is connected to the inverting input terminal of the operational amplifier U1. f One end is connected to the inverting input of operational amplifier U1, and the second compensation resistor R f The other end is connected to the output of operational amplifier U1, and the compensation capacitor C f With the second compensation resistor R f Parallel connection, Zener diode D cc Cathode and clamping diode D c The cathode is connected, Zener diode D cc The anode is grounded. The output of operational amplifier U1 is sent to the synchronous rectification control circuit as the final output signal of the detection circuit.

[0037] The working principle of the high-precision drain-source voltage detection circuit for synchronous rectification of LLC resonant converter described in this invention is as follows:

[0038] The drain-source turn-off voltage blocking circuit is used to cut off the synchronous rectifier diode S. s1 High drain-source voltage during turn-off; drain-source on-state voltage compensation circuit is used for synchronous rectifier S s1 The circuit compensates for the voltage shift caused by the drain-source turn-off voltage blocking circuit during turn-on, enabling accurate detection of the drain-source turn-on voltage. This includes the first compensation resistor R1 and the second compensation resistor R... f Compensation capacitor C f The operational amplifier U1 and the operational amplifier U1 form a differential amplifier with low-pass filtering; the drain-source turn-off voltage clamping circuit is used to clamp the synchronous rectifier S. s1 When turned off, the output of the drain-source voltage detection circuit is clamped to a voltage of appropriate amplitude to prevent it from damaging the subsequent synchronous rectification control circuit; the constant current source circuit is used to provide a suitable quiescent current to ensure the Zener diode D cc It always operates in the reverse breakdown region while simultaneously supplying current to the detection circuit.

[0039] When the synchronous rectifier S being tested s1 When turned on, the synchronous rectifier S s1 Drain-source voltage V ds Much smaller than the regulated voltage V cc N blocking diodes D a1 ~D an and compensation diode D b Both are in the forward conducting state, and the current in this path is controlled by the first current-limiting resistor R. s Decision, clamping diode D c When in reverse cutoff state, the first sampling voltage V1 is:

[0040]

[0041] Among them, V F(Da) For a single blocking diode D ax The forward conduction voltage drop, and the second sampling voltage V2 are:

[0042]

[0043] Among them, V F(Db) To compensate diode D b The forward conduction voltage drop, in this invention, the compensation diode D b With blocking diode D ax They are Schottky diodes of the same type, and the second compensation resistor R f The resistance of the resistor is N times that of the first compensation resistor R1, therefore the following condition is met:

[0044]

[0045] R f =N·R1

[0046] After differential amplification of the first sampling voltage V1 and the second sampling voltage V2, the detection output voltage V is obtained. s for:

[0047]

[0048] Therefore, this invention can accurately sample the drain-source on-state voltage V. ds When the synchronous rectifier tube S being tested s1 When turned off, its drain-source voltage V ds Much greater than the regulated voltage V cc N blocking diodes D a1 ~D an and compensation diode D b Both are in reverse cutoff state, clamping diode D c When the circuit is in the forward conduction state, the first sampling voltage V1 is:

[0049]

[0050] Among them, V F(Dc) Clamping diode D c The forward conduction voltage drop, and the second sampling voltage V2 are:

[0051]

[0052] After differential amplification of the first sampling voltage V1 and the second sampling voltage V2, the detection output voltage V is obtained. s for:

[0053]

[0054] Therefore, the present invention can effectively cut off and clamp the drain-source turn-off voltage V. ds .

[0055] In this embodiment, the N blocking diodes D a1 ~D an and compensation diode D b Using the same type of Schottky diodes ensures they have the same forward voltage drop when the same current flows through them. Additionally, the clamping diode D... c It is a Schottky diode, and there are N blocking diodes D a1 ~D an Compensation diode D b and clamping diode D c The reverse recovery time should be as small as possible, and its junction capacitance at high frequencies should be as small as possible, in order to minimize the phase lag effect of the detection circuit.

[0056] In this embodiment, the first current-limiting resistor R s The resistance value should be appropriate; if it is too large, the synchronous rectifier diode S... s1 When the circuit is turned on, the current in the detection circuit is too small, causing the detection circuit to be unable to effectively suppress the clamping diode D. c The impact of the reverse leakage current and the input bias current of operational amplifier U1 on the accuracy of drain-source voltage detection; if their values ​​are too small, the first current-limiting resistor R... s The losses on the synchronous rectifier S increase, and the synchronous rectifier tube S s1 Detection output voltage V during shutdown s This will increase, potentially causing it to exceed the maximum input voltage range of the subsequent synchronous rectification control circuit.

[0057] In this embodiment, the Zener diode D cc Zener voltage V cc The value of should be appropriate; if the Zener voltage V cc If it is too large, then the synchronous rectifier S s1 Detection output voltage V during shutdown s This may exceed the maximum input voltage range of the subsequent synchronous rectification control circuit; if the Zener voltage V cc If it's too small, then the synchronous rectifier S s1 When the circuit is turned on, the current in the detection circuit is too small, even with N blocking diodes D. a1 ~D an and compensation diode D b Neither of them can conduct, causing the drain-source conduction voltage detection function of this invention to fail.

[0058] In this embodiment, the voltage source LDO and the second current-limiting resistor R ccTogether they form a constant current source circuit, which is used to power the Zener diode (D). cc Provide sufficient current to ensure the Zener diode D cc It can always operate in the reverse breakdown region, therefore the output voltage V of the voltage source LDO is... LDO It should be greater than the regulated voltage V. cc The second current-limiting resistor R cc The value of should ensure that the current flows through the second current-limiting resistor R. cc The current is greater than that of the Zener diode D. cc The minimum Zener current.

[0059] In this embodiment, the operational amplifier U1 has a sufficiently high unity-gain bandwidth product, a sufficiently small input bias current, and a sufficiently small input capacitance to maximize the high-frequency dynamic performance and detection accuracy of the detection circuit.

[0060] The schematic diagram of the working waveform of the present invention under typical working conditions is shown below. Figure 4 As shown, it describes a typical waveform diagram of the present invention under light load in the LLC sub-resonant region.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A high-precision drain-source voltage detection circuit for synchronous rectification of an LLC resonant converter, characterized in that, This includes a drain-source turn-off voltage blocking circuit, a drain-source turn-on voltage compensation circuit, a drain-source turn-off voltage clamping circuit, a constant current source circuit, and a Zener diode (D). cc The drain-source on-state voltage compensation circuit includes a compensation diode (D). b ), first current-limiting resistor (R) s The circuit includes a first compensation resistor (R1) and an operational amplifier (U1); the drain-source turn-off voltage clamping circuit includes a clamping diode (D... c ) and Zener diode (D) cc ); One end of the drain-source turn-off voltage blocking circuit is connected to the synchronous rectifier (S) being tested. s1 The drain of the circuit is connected to the source-drain cutoff voltage blocking circuit, and the other end of the circuit is connected to the compensation diode (D). b Cathode and clamping diode (D) c The anode of the amplifier is connected to the non-inverting input of the operational amplifier (U1), and the first current-limiting resistor (R) is connected to the non-inverting input of the operational amplifier (U1). s One end of the diode is connected to the compensation diode (D). b The anode of the first current-limiting resistor (R) is connected to the first current-limiting resistor (R). s The other end of the diode is connected to the clamping diode (D). c The cathode and constant current source circuit of the first compensation resistor (R1) are connected together, and one end of the first compensation resistor (R1) is connected to the compensation diode (D). b The anode of the first compensation resistor (R1) is connected to the inverting input terminal of the operational amplifier (U1), and the other end of the first compensation resistor (R1) is connected to the inverting input terminal of the operational amplifier (U1). The Zener diode (D) cc The cathode and clamping diode (D) c The cathode of the diode is connected to the Zener diode (D). cc The anode of the operational amplifier (U1) is grounded, and the output terminal of the operational amplifier (U1) is used as the final output signal terminal. The drain-source turn-off voltage blocking circuit is composed of several N blocking diodes of the same type connected in series; The constant current source circuit includes a second current-limiting resistor (R). cc ) and voltage source (LDO), clamping diode (D) c The cathode of the second current-limiting resistor (R) cc One end of the first current-limiting resistor is connected to the second current-limiting resistor (R). cc The other end of the circuit is connected to a voltage source (LDO); It also includes a second compensation resistor (R) f ) and compensation capacitor (C f ), second compensation resistor (R) f One end of the resistor is connected to the inverting input of the operational amplifier (U1), and the second compensation resistor (R) is connected to the inverting input of the operational amplifier (U1). f The other end of the capacitor is connected to the output of the operational amplifier (U1), and the compensation capacitor (C) is connected to the output of the operational amplifier (U1). f ) and the second compensation resistor (R) f )in parallel.

2. The high-precision drain-source voltage detection circuit for synchronous rectification of an LLC resonant converter according to claim 1, characterized in that, The output of the operational amplifier (U1) is connected to a synchronous rectification control circuit.

3. The high-precision drain-source voltage detection circuit for synchronous rectification of an LLC resonant converter according to claim 1, characterized in that, Each blocking diode and compensation diode (D b ( ) are Schottky diodes of the same type.

4. The high-precision drain-source voltage detection circuit for synchronous rectification of an LLC resonant converter according to claim 1, characterized in that, Clamping diode (D) c () is a Schottky diode.

5. The high-precision drain-source voltage detection circuit for synchronous rectification of an LLC resonant converter according to claim 1, characterized in that, When the synchronous rectifier tube being tested (S) s1 When the op-amp (U1) is turned on, the output voltage V at the output terminal is... s for: Where V2 is the second sampling voltage, V F(Da) For a single blocking diode (D ax The forward conduction voltage drop, V F(Db) For compensation diode (D) b The forward conduction voltage drop of V1 is the first sampling voltage.

6. The high-precision drain-source voltage detection circuit for synchronous rectification of an LLC resonant converter according to claim 5, characterized in that, When the synchronous rectifier tube being tested (S) s1 When the op-amp (U1) is turned off, the output voltage V at the output terminal is... s for: 。

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