Power conversion device and synchronous rectification controller thereof

Abstract

The present application provides a power conversion device and a synchronous rectification controller thereof. At least one of a differential operation and an integral operation is performed on a drain voltage signal of a synchronous rectification transistor. Whether to turn on the synchronous rectification transistor when a next drain voltage signal is less than or equal to a turn-on threshold voltage is determined according to at least one of a differential signal obtained by performing the differential operation and an integral signal obtained by performing the integral operation.

Description

Technical Field

[0001] This invention relates to a power supply device, and more particularly to a power conversion device and its synchronous rectification controller. Background Technology

[0002] Power conversion devices are indispensable components in modern electronic devices. In power conversion devices based on pulse width modulation (PWM) control, the secondary side typically has rectifier diodes. Since rectifier diodes consume a significant amount of power when in the on-state, synchronous rectifier transistors with lower on-resistance can be used instead. In this architecture, a synchronous rectifier controller is still required to control the switching on and off of the synchronous rectifier transistors on the secondary side.

[0003] When the secondary inductor current of a power converter discharges to zero, the drain voltage of the synchronous rectifier transistor (SRRT) will begin to oscillate accordingly. In the prior art, the SRRT's conduction timing could be determined by detecting the slope of the drain voltage drop, thus preventing the SRRT from turning on during inductor-capacitor oscillation and causing current backflow at the power converter's output, which could damage the power converter and reduce its safety. However, with the increasing operating frequency of modern power systems, the slope of the SRRT's drain voltage drop during inductor current discharge and inductor-capacitor oscillation is becoming increasingly similar, making this method inaccurate in determining the SRRT's turn-on timing. Summary of the Invention

[0004] This invention provides a power conversion device and its synchronous rectification controller, which can effectively improve the accuracy of controlling the switching of the conduction state of the synchronous rectification transistor.

[0005] The synchronous rectification controller of the present invention is used to control the conduction state of a synchronous rectification transistor. The synchronous rectification controller includes a conduction control circuit and a turn-off control circuit. The conduction control circuit is coupled to the drain terminal of the synchronous rectification transistor and performs at least one of a differentiation operation and an integration operation on the drain voltage signal of the synchronous rectification transistor. Based on at least one of the differential signal obtained by the differentiation operation and the integral signal obtained by the integration operation, it determines whether to turn on the synchronous rectification transistor when the drain voltage signal is less than or equal to the conduction threshold voltage. The turn-off control circuit is coupled to the drain terminal of the synchronous rectification transistor and compares the drain voltage signal with the turn-off threshold voltage. When the drain voltage signal is greater than the turn-off threshold voltage, the turn-off control circuit turns off the synchronous rectification transistor.

[0006] In one embodiment of the present invention, if the drain voltage signal is greater than or equal to a preset voltage, and the signal value of the differential signal is equal to 0 for a preset time during the period when the drain voltage signal is greater than or equal to the preset voltage, the conduction control circuit conducts the synchronous rectifier transistor when the drain voltage signal is less than or equal to the conduction threshold voltage. If the drain voltage signal is not greater than or equal to the preset voltage, or the signal value of the differential signal is equal to 0 for a preset time during the period when the drain voltage signal is greater than or equal to the preset voltage, the conduction control circuit does not conduct the synchronous rectifier transistor when the drain voltage signal is less than or equal to the conduction threshold voltage.

[0007] In one embodiment of the present invention, if the signal value of the differential signal is greater than or equal to a preset differential value, and the signal value of the differential signal decreases from greater than or equal to the preset differential value to 0 and remains at 0 for a preset time, the conduction control circuit conducts the synchronous rectifier transistor when the drain voltage signal is less than or equal to the conduction threshold voltage in the next instance. If the signal value of the differential signal is not greater than or equal to the preset differential value, or the signal value of the differential signal decreases from greater than or equal to the preset differential value to 0 and does not remain at 0 for a preset time, the conduction control circuit does not conduct the synchronous rectifier transistor when the drain voltage signal is less than or equal to the conduction threshold voltage in the next instance.

[0008] In one embodiment of the present invention, if the drain voltage signal is greater than or equal to a preset voltage, and the signal value of the integral signal during the period when the drain voltage signal is greater than or equal to the preset voltage is greater than or equal to a preset integral value, the turn-on control circuit turns on the synchronous rectifier transistor when the drain voltage signal is less than or equal to the turn-on threshold voltage in the next instance. If the drain voltage signal is not greater than or equal to the preset voltage, or the signal value of the integral signal during the period when the drain voltage signal is greater than or equal to the preset voltage is not greater than or equal to the preset integral value, the turn-on control circuit does not turn on the synchronous rectifier transistor when the drain voltage signal is less than or equal to the turn-on threshold voltage in the next instance.

[0009] In one embodiment of the present invention, during a period when the drain voltage signal is greater than or equal to a preset voltage, if the signal value of the differential signal is greater than or equal to a preset differential value and the signal value of the integral signal is greater than or equal to a preset integral value, the conduction control circuit conducts the synchronous rectifier transistor when the drain voltage signal is less than or equal to the conduction threshold voltage. If the signal value of the differential signal is not greater than or equal to the preset differential value, or if the signal value of the integral signal is not greater than or equal to the preset integral value during the period when the drain voltage signal is greater than or equal to the preset voltage, the conduction control circuit does not conduct the synchronous rectifier transistor when the drain voltage signal is less than or equal to the conduction threshold voltage.

[0010] In one embodiment of the present invention, the aforementioned preset integral value is equal to the integral value of the drain voltage signal over a preset time period during the period when the drain voltage signal is greater than or equal to a preset voltage.

[0011] In one embodiment of the present invention, the above-mentioned synchronous rectification controller further includes a logic circuit coupled to the turn-on control circuit, the turn-off control circuit and the gate terminal of the synchronous rectification transistor, and is controlled by the turn-on control circuit and the turn-off control circuit to generate a synchronous rectification control signal to the gate terminal of the synchronous rectification transistor.

[0012] In one embodiment of the present invention, the above-mentioned logic circuit includes an SR flip-flop, the set terminal and the reset terminal of which are respectively coupled to a conduction control circuit and a turn-off control circuit, and the output terminal of the SR flip-flop is coupled to the gate terminal of a synchronous rectifier transistor.

[0013] In one embodiment of the present invention, the aforementioned turn-off threshold voltage is greater than the turn-on threshold voltage.

[0014] The present invention also provides a power conversion device, including a transformer, a synchronous rectifier transistor, and a synchronous rectifier controller. The transformer has a primary side and a secondary side, wherein a first terminal of the primary side is used to receive an input voltage, and a first terminal of the secondary side is used to provide an output voltage to a load. The drain terminal of the synchronous rectifier transistor is coupled to a second terminal of the secondary side, and the source terminal of the synchronous rectifier transistor is coupled to ground. The synchronous rectifier controller is coupled between the drain terminal and the gate terminal of the synchronous rectifier transistor to control the conduction state of the synchronous rectifier transistor. The synchronous rectifier controller includes a conduction control circuit and a turn-off control circuit. The conduction control circuit is coupled to the drain terminal of the synchronous rectifier transistor and performs at least one of a differentiation operation and an integration operation on the drain voltage signal of the synchronous rectifier transistor. Based on at least one of the differential signal obtained from the differentiation operation and the integral signal obtained from the integration operation, it determines whether to turn on the synchronous rectifier transistor when the next drain voltage signal is less than or equal to a conduction threshold voltage. The shutdown control circuit is coupled to the drain terminal of the synchronous rectifier transistor and compares the drain voltage signal with the shutdown threshold voltage. When the drain voltage signal is greater than the shutdown threshold voltage, the shutdown control circuit shuts down the synchronous rectifier transistor.

[0015] Based on the above, the conduction control circuit of this embodiment can perform at least one of differentiation and integration operations on the drain voltage signal of the synchronous rectifier transistor. Based on at least one of the differential signal obtained by performing the differentiation operation and the integral signal obtained by performing the integration operation, it determines whether to turn on the synchronous rectifier transistor when the drain voltage signal is less than or equal to the conduction threshold voltage. In this way, by judging the change of the drain voltage signal of the synchronous rectifier transistor through the differential signal and the integral signal, the difference between the discharge period of the inductor current and the oscillation period of the inductor capacitor can be accurately distinguished, thereby effectively improving the accuracy of controlling the switching of the conduction state of the synchronous rectifier transistor.

[0016] To make the above features and advantages of the present invention more apparent and understandable, specific embodiments are described below in conjunction with the accompanying drawings. Attached Figure Description

[0017] Figure 1 This is a circuit block diagram of a power conversion device according to an embodiment of the present invention;

[0018] Figure 2 This is a circuit diagram of a synchronous rectifier controller according to an embodiment of the present invention;

[0019] Figure 3 This is a circuit diagram of a synchronous rectifier controller according to another embodiment of the present invention;

[0020] Figure 4 This is a signal timing diagram of a synchronous rectifier controller according to an embodiment of the present invention;

[0021] Figure 5 This is a signal timing diagram of a synchronous rectifier controller according to another embodiment of the present invention;

[0022] Figure 6 This is a circuit diagram of a synchronous rectifier controller according to another embodiment of the present invention;

[0023] Figure 7 This is a signal timing diagram of a synchronous rectifier controller according to another embodiment of the present invention;

[0024] Figure 8 This is a circuit diagram of a synchronous rectifier controller according to another embodiment of the present invention;

[0025] Figure 9 This is a signal timing diagram of a synchronous rectifier controller according to another embodiment of the present invention. Detailed Implementation

[0026] To make the content of this invention more readily apparent, the following specific embodiments are provided as examples on which this invention can indeed be practiced. Furthermore, wherever possible, components / members referred to by the same reference numerals in the drawings and embodiments represent the same or similar parts.

[0027] Figure 1 This is a circuit block diagram of a power conversion device according to an embodiment of the present invention. In this embodiment, the power conversion device 10 is a flyback architecture, but it is not limited thereto. In other embodiments, the architecture of the power conversion device may be, for example, a push-pull, forward, half-bridge, full-bridge, or other types of architecture. The operation of the power conversion device with other architectures can be deduced from the operation of this embodiment.

[0028] The power conversion device 10 includes, but is not limited to, a transformer T, a synchronous rectifier transistor MSR, a synchronous rectifier controller 102, a power switch Mp, and a pulse width modulation signal generator 110. The transformer T includes a primary side Np and a secondary side Ns. The first terminal of the primary side Np (e.g., the common-polarity terminal, i.e., the dotted point) is used to receive the input voltage VIN, while the first terminal of the secondary side Ns (e.g., the opposite-polarity terminal, i.e., the undotted point) is used to provide the output voltage VOUT to the load RL (e.g., an electronic device) and to charge the capacitor Co, but is not limited to this.

[0029] The first terminal of the power switch Mp is coupled to the second terminal (e.g., a different name terminal) of the primary side Np. The second terminal of the power switch Mp is coupled to the second ground terminal GND2. The control terminal of the power switch Mp is coupled to the pulse width modulation signal generator 110 to receive the pulse width modulation signal Spwm. The pulse width modulation signal generator 110 can generate and adjust the pulse width modulation signal Spwm according to the state of the load RL (or power supply requirements).

[0030] The drain terminal of the synchronous rectifier transistor MSR is coupled to the second terminal (e.g., the same-name terminal) of the secondary side Ns, and the source terminal and body terminal of the synchronous rectifier transistor MSR are coupled to the first ground terminal GND1. A parasitic diode Dr is present between the drain terminal and the body terminal of the synchronous rectifier transistor MSR. In one embodiment of the present invention, the synchronous rectifier transistor MSR may be an N-type metal-oxide-semiconductor field-effect transistor, but the present invention is not limited thereto; the choice depends on the actual application or design requirements. The synchronous rectification controller 102 is coupled to the drain terminal of the synchronous rectifier transistor MSR to receive the drain voltage signal VD. The synchronous rectification controller 102 can generate a synchronous rectification control signal VG corresponding to the voltage level of the drain voltage signal VD and send it to the gate terminal of the synchronous rectifier transistor MSR to control the conduction state of the synchronous rectifier transistor MSR.

[0031] The synchronous rectification controller 102 includes a turn-on control circuit 104 and a turn-off control circuit 106, which are coupled to the drain terminals of the synchronous rectification transistor MSR.

[0032] The turn-on control circuit 104 can perform at least one of differentiation and integration operations on the drain voltage signal VD, and determine whether to turn on the synchronous rectifier transistor MSR when the drain voltage signal VD is less than or equal to the turn-on threshold voltage Vonth based on at least one of the differential signal obtained from the differentiation operation and the integral signal obtained from the integration operation. Furthermore, the turn-off control circuit 106 can compare the drain voltage signal VD with the turn-off threshold voltage Voffth. When the drain voltage signal VD is greater than the turn-off threshold voltage Voffth, the turn-off control circuit 106 can turn off the synchronous rectifier transistor MSR, wherein the turn-off threshold voltage Voffth is greater than the turn-on threshold voltage Vonth.

[0033] By using at least one of the differential and integral signals of the drain voltage signal VD to determine the change in the drain voltage signal VD of the synchronous rectifier transistor MSR, it is possible to accurately distinguish whether the secondary side of the power conversion device 10 is in the period of inductor current discharge or inductor-capacitor oscillation, thereby effectively improving the accuracy of controlling the switching of the synchronous rectifier transistor's conduction state.

[0034] In some embodiments, the synchronous rectification controller 102 may further include logic circuitry coupled to the turn-on control circuit 104, the turn-off control circuit 106, and the gate of the synchronous rectification transistor MSR. This logic circuitry is controlled by the turn-on control circuit 104 and the turn-off control circuit 106 to generate a synchronous rectification control signal to the gate of the synchronous rectification transistor. For example… Figure 2 As shown, in this embodiment, the logic circuit is implemented using an SR flip-flop 202, but it is not limited to this. The set terminal S and reset terminal R of the SR flip-flop 202 are coupled to the turn-on control circuit 104 and the turn-off control circuit 106, respectively, and the output terminal Q of the SR flip-flop 202 is coupled to the gate terminal of the synchronous rectifier transistor MSR. The SR flip-flop 202 can output a synchronous rectification control signal VG according to the turn-on control signal output by the turn-on control circuit 104 and the turn-off control signal output by the turn-off control circuit 106, so as to control the conduction state of the synchronous rectifier transistor MSR.

[0035] For example, Figure 3 This is a circuit diagram of a synchronous rectifier controller according to another embodiment of the present invention. Figure 4 This is a signal timing diagram of the synchronous rectifier controller. Please refer to it. Figure 3 and Figure 4The turn-on control circuit 104 can perform a differentiating operation on the drain voltage signal VD. More specifically, the turn-on control circuit 104 may include a differentiating circuit 302, a comparator circuit 304, and an AND gate 306. The differentiating circuit 302 is coupled between the drain terminal of the synchronous rectifier transistor MSR and one input terminal of the AND gate 306. The comparator circuit 304 is coupled between the drain terminal of the synchronous rectifier transistor MSR and the other input terminal of the AND gate 306. The output terminal of the AND gate 306 is coupled to the setting terminal S of the SR flip-flop 202.

[0036] Differentiating circuit 302 can perform a differentiating operation on drain voltage signal VD to obtain differential signal VD1. For example... Figure 4 As shown, when the power switch Mp is turned on, the input voltage VIN provides power to the coil of the primary side Np of the transformer T for energy storage. At this time, the drain voltage VD is rapidly pulled up to K×VIN, resulting in a positive surge in the differential signal VD1, where K is the coil ratio of the secondary side Ns to the primary side Np of the transformer T. Meanwhile, the parasitic diode Dr of the synchronous rectifier transistor MSR is reverse-biased and turned off. Furthermore, when the power switch Mp is turned off in response to the pulse width modulation signal Spwm generated by the pulse width modulation signal generator 110, based on Lenz's law, the energy stored in the primary side Np of the transformer T is transferred to the secondary side Ns of the transformer T. Simultaneously, the parasitic diode Dr of the synchronous rectifier transistor MSR is forward-biased and turned on. Since the body terminal of the synchronous rectifier transistor MSR is coupled to the first ground terminal GND1, the voltage level at the drain terminal of the synchronous rectifier transistor MSR (i.e., the drain voltage VD) will drop sharply from K×VIN to a negative voltage value, thus causing a negative surge in the differential signal VD1.

[0037] Differentiator circuit 302 can determine whether the drain voltage signal VD is greater than or equal to a preset voltage Vth (i.e., whether the voltage of the positive surge is greater than or equal to the preset voltage Vth), and whether the time during which the drain voltage signal VD is greater than or equal to the preset voltage Vth is equal to the time during which the signal value of the differential signal VD1 is equal to 0 reaches a preset time Tth (i.e., during the period from the time of the occurrence of the positive surge to the time of the occurrence of the negative surge, whether the voltage value of the positive surge remains at 0 for a preset time Tth after returning to 0). When the drain voltage signal VD is greater than or equal to the preset voltage Vth and the time during which the signal value of the differential signal VD1 is equal to 0 reaches the preset time Tth, differentiator circuit 302 outputs a first control signal with a high voltage level to AND gate 306. If the drain voltage signal VD is not greater than or equal to the preset voltage Vth, or if the time during which the drain voltage signal VD is greater than or equal to the preset voltage Vth is less than or equal to the preset time Tth, the differentiating circuit 302 outputs a first control signal with a low voltage level to the AND gate 306.

[0038] Furthermore, the comparator circuit 304 compares the drain voltage signal VD with the turn-on threshold voltage Vonth. When the drain voltage signal VD is less than or equal to the turn-on threshold voltage Vonth, the comparator circuit 304 outputs a second control signal with a high voltage level to the AND gate 306. If the drain voltage signal VD is not less than or equal to the turn-on threshold voltage Vonth, the comparator circuit 304 outputs a second control signal with a low voltage level to the AND gate 306. The AND gate 306 can generate a turn-on control signal based on the first and second control signals and send it to the setting terminal S of the SR flip-flop 202.

[0039] Additionally, the shutdown control circuit 106 compares the drain voltage signal VD with the shutdown threshold voltage Voffth. When the drain voltage signal VD is greater than the shutdown threshold voltage Voffth, the shutdown control circuit 106 outputs a shutdown control signal with a high voltage level to the reset terminal R of the SR flip-flop 202. If the drain voltage signal VD is not greater than the shutdown threshold voltage Voffth, the shutdown control circuit 106 outputs a shutdown control signal with a low voltage level to the reset terminal R of the SR flip-flop 202.

[0040] Thus, if the differentiating circuit 302 determines that the drain voltage signal VD is greater than or equal to the preset voltage Vth, and the signal value of the differentiating signal VD1 is equal to 0 for a preset time during the period when the drain voltage signal VD is greater than or equal to the preset voltage Vth, the conduction control circuit 104 can conduct the synchronous rectifier transistor MSR (so that the synchronous rectifier control signal VG turns to a high voltage level) when the drain voltage signal VD is less than or equal to the conduction threshold voltage Vonth next time. If the differentiating circuit 302 determines that the drain voltage signal VD is not greater than or equal to the preset voltage Vth, or if the time during which the signal value of the differentiating signal VD1 is equal to 0 during the period when the drain voltage signal VD is greater than or equal to the preset voltage Vth does not reach the preset time Tth, the conduction control circuit 104 will not conduct the synchronous rectifier transistor MSR when the drain voltage signal VD is less than or equal to the conduction threshold voltage Vonth next time. This is to avoid conducting the synchronous rectifier transistor MSR during the oscillation period of the drain voltage signal VD of the synchronous rectifier transistor MSR, which would cause the current at the output terminal of the power conversion device 10 to flow back and thus damage the power conversion device 10.

[0041] It is worth noting that, in some embodiments, the differentiating circuit 302 can also determine whether to turn on the synchronous rectifier transistor MSR based on whether the signal value of the differential signal VD1 is greater than or equal to a preset differential value. For example... Figure 5 As shown, in Figure 5 In this embodiment, if the differentiating circuit 302 determines that the signal value of the differential signal VD1 is greater than or equal to the preset differential value Vrth, and the signal value of the differential signal VD1 decreases from greater than or equal to the preset differential value Vrth to 0 and remains at 0 for a preset time Tth, the conduction control circuit 104 may conduct the synchronous rectifier transistor MSR when the drain voltage signal VD is less than or equal to the conduction threshold voltage Vonth in the next instance. However, if the differentiating circuit 302 determines that the signal value of the differential signal VD1 is not greater than or equal to the preset differential value Vrth, or the signal value of the differential signal VD1 decreases from greater than or equal to the preset differential value Vrth to 0 and remains at 0 for a time less than the preset time Tth, the conduction control circuit 104 will not conduct the synchronous rectifier transistor MSR when the drain voltage signal VD is less than or equal to the conduction threshold voltage Vonth in the next instance.

[0042] Figure 6 This is a circuit diagram of a synchronous rectifier controller according to another embodiment of the present invention. Figure 7 yes Figure 6 Please refer to the signal timing diagram of the synchronous rectifier controller in the embodiment. Figure 6 and Figure 7 . Figure 6 Examples and Figure 3 The difference in the embodiments is that, Figure 3In this embodiment, the differentiating circuit is replaced by an integrating circuit 602. The integrating circuit 602 performs an integration operation on the drain voltage signal VD to obtain an integrated signal VD2, and determines whether the drain voltage signal VD is greater than or equal to a preset voltage Vth, and whether the signal value of the integrated signal VD2 is greater than or equal to a preset integration value Ath during the period when the drain voltage signal VD is greater than or equal to the preset voltage Vth. The preset integration value Ath can, for example, be the integral value of the drain voltage signal within a preset time T1 during the period when the drain voltage signal VD is greater than or equal to the preset voltage.

[0043] When the drain voltage signal VD is greater than or equal to the preset voltage Vth and the signal value of the integral signal VD2 during the period when the drain voltage signal VD is greater than or equal to the preset voltage Vth is greater than or equal to the preset integral value Ath, the integrator circuit 602 outputs a first control signal with a high voltage level to the AND gate 306. Conversely, if the drain voltage signal VD is not greater than or equal to the preset voltage Vth, or the signal value of the integral signal VD2 during the period when the drain voltage signal VD is greater than or equal to the preset voltage Vth is not greater than or equal to the preset integral value Ath, the integrator circuit 602 outputs a first control signal with a low voltage level to the AND gate 306. The implementation details of the comparator circuit 304 and the shutdown control circuit 106 are as follows... Figure 3 The implementation methods are the same, so they will not be repeated here.

[0044] Thus, if the drain voltage signal VD is greater than or equal to the preset voltage Vth, and the signal value of the integral signal VD2 during the period when the drain voltage signal VD is greater than or equal to the preset voltage Vth is greater than or equal to the preset integral value Ath, the turn-on control circuit 104 can turn on the synchronous rectifier transistor MSR when the drain voltage signal VD is less than or equal to the turn-on threshold voltage Vonth. However, if the drain voltage signal VD is not greater than or equal to the preset voltage Vth, or the signal value of the integral signal VD2 during the period when the drain voltage signal VD is greater than or equal to the preset voltage Vth is not greater than or equal to the preset integral value Ath, the turn-on control circuit 104 will not turn on the synchronous rectifier transistor MSR when the drain voltage signal VD is less than or equal to the turn-on threshold voltage Vonth, to avoid turning on the synchronous rectifier transistor MSR during the oscillation period of the drain voltage signal VD of the synchronous rectifier transistor MSR.

[0045] Figure 8 This is a circuit diagram of a synchronous rectifier controller according to another embodiment of the present invention. Figure 9 yes Figure 8 Please refer to the signal timing diagram of the synchronous rectifier controller in the embodiment. Figure 8 and Figure 9 . Figure 8 Examples and Figure 3 The difference in the embodiments is that, Figure 3In this embodiment, the differentiating circuit is replaced by a differentiating-integrating circuit 802. The differentiating-integrating circuit 802 can perform differentiating and integrating operations on the drain voltage signal VD to obtain a differential signal VD1 and an integral signal VD2. During the period when the drain voltage signal VD is greater than or equal to a preset voltage Vth, it determines whether the signal value of the differential signal VD1 is greater than or equal to a preset differential value Vrth, and whether the signal value of the integral signal VD2 is greater than or equal to a preset integral value Ath.

[0046] When the drain voltage signal VD is greater than or equal to the preset voltage Vth, the signal value of the differential signal VD1 is greater than or equal to the preset differential value Vrth, and the signal value of the integral signal VD2 is greater than or equal to the preset integral value Ath, the differential-integral circuit 802 outputs a first control signal with a high voltage level to the AND gate 306. Conversely, if the signal value of the differential signal VD1 is not greater than or equal to the preset differential value Vrth, or the signal value of the integral signal VD2 is not greater than or equal to the preset integral value Ath, the differential-integral circuit 802 outputs a first control signal with a low voltage level to the AND gate 306. The implementation details of the comparator circuit 304 and the shutdown control circuit 106 are as follows... Figure 3 The implementation methods are the same, so they will not be repeated here.

[0047] Thus, if the signal value of the differential signal VD1 is greater than or equal to the preset differential value Vrth during the period when the drain voltage signal VD is greater than or equal to the preset voltage Vth, and the signal value of the integral signal VD2 is greater than or equal to the preset integral value Ath, the turn-on control circuit 104 can turn on the synchronous rectifier transistor MSR when the drain voltage signal VD is less than or equal to the turn-on threshold voltage Vonth. However, if the signal value of the differential signal VD1 is not greater than or equal to the preset differential value Vrth during the period when the drain voltage signal VD is greater than or equal to the preset voltage Vth, or the signal value of the integral signal VD2 is not greater than or equal to the preset integral value Ath, the turn-on control circuit 104 will not turn on the synchronous rectifier transistor MSR when the drain voltage signal VD is less than or equal to the turn-on threshold voltage Vonth, to avoid turning on the synchronous rectifier transistor MSR during the oscillation period of the drain voltage signal VD of the synchronous rectifier transistor MSR.

[0048] In summary, the conduction control circuit of this embodiment can perform at least one of differentiation and integration operations on the drain voltage signal of the synchronous rectifier transistor. Based on at least one of the differential signal obtained from the differentiation operation and the integral signal obtained from the integration operation, it determines whether to turn on the synchronous rectifier transistor when the drain voltage signal is less than or equal to the conduction threshold voltage. In this way, by judging the change of the drain voltage signal of the synchronous rectifier transistor through the differential signal and the integral signal, the difference between the inductor current discharge period and the inductor-capacitor oscillation period can be accurately distinguished, effectively improving the accuracy of controlling the switching of the synchronous rectifier transistor's conduction state. This avoids turning on the synchronous rectifier transistor during the inductor-capacitor oscillation period, which would cause current backflow at the output of the power conversion device and damage the power conversion device.

[0049] Although the present invention has been disclosed above with reference to embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A synchronous rectification controller for controlling the conduction state of a synchronous rectification transistor, characterized in that, The synchronous rectification controller includes: A turn-on control circuit, coupled to the drain terminal of the synchronous rectifier transistor, performs at least one of a differentiation operation and an integration operation on the drain voltage signal of the synchronous rectifier transistor. Based on at least one of the differential signal obtained from the differentiation operation and the integral signal obtained from the integration operation, it determines whether to turn on the synchronous rectifier transistor when the drain voltage signal is less than or equal to the turn-on threshold voltage next time. A shutdown control circuit, coupled to the drain terminal of the synchronous rectifier transistor, compares the drain voltage signal with a shutdown threshold voltage. When the drain voltage signal is greater than the shutdown threshold voltage, the shutdown control circuit shuts off the synchronous rectifier transistor. If the drain voltage signal is greater than or equal to a preset voltage, and the signal value of the differential signal is equal to 0 for a preset time during the period when the drain voltage signal is greater than or equal to the preset voltage, the turn-on control circuit turns on the synchronous rectifier transistor the next time the drain voltage signal is less than or equal to the turn-on threshold voltage. If the drain voltage signal is not greater than or equal to the preset voltage, or the signal value of the differential signal is equal to 0 for a preset time during the period when the drain voltage signal is greater than or equal to the preset voltage, the turn-on control circuit does not turn on the synchronous rectifier transistor the next time the drain voltage signal is less than or equal to the turn-on threshold voltage.

2. The synchronous rectifier controller according to claim 1, characterized in that, Also includes: A logic circuit, coupled to the turn-on control circuit, the turn-off control circuit, and the gate terminal of the synchronous rectifier transistor, is controlled by the turn-on control circuit and the turn-off control circuit to generate a synchronous rectification control signal to the gate terminal of the synchronous rectifier transistor.

3. The synchronous rectification controller according to claim 2, characterized in that, The logic circuit includes an SR flip-flop, whose set terminal and reset terminal are respectively coupled to the turn-on control circuit and the turn-off control circuit, and the output terminal of the SR flip-flop is coupled to the gate terminal of the synchronous rectifier transistor.

4. The synchronous rectifier controller according to claim 1, characterized in that, The shut-off threshold voltage is greater than the turn-on threshold voltage.

5. A synchronous rectification controller for controlling the conduction state of a synchronous rectification transistor, characterized in that, The synchronous rectification controller includes: A turn-on control circuit, coupled to the drain terminal of the synchronous rectifier transistor, performs at least one of a differentiation operation and an integration operation on the drain voltage signal of the synchronous rectifier transistor. Based on at least one of the differential signal obtained from the differentiation operation and the integral signal obtained from the integration operation, it determines whether to turn on the synchronous rectifier transistor when the drain voltage signal is less than or equal to the turn-on threshold voltage next time. A shutdown control circuit, coupled to the drain terminal of the synchronous rectifier transistor, compares the drain voltage signal with a shutdown threshold voltage. When the drain voltage signal is greater than the shutdown threshold voltage, the shutdown control circuit shuts off the synchronous rectifier transistor. If the value of the differential signal is greater than or equal to a preset differential value, and the value of the differential signal decreases from greater than or equal to the preset differential value to 0 and remains at 0 for a preset time, the turn-on control circuit turns on the synchronous rectifier transistor the next time the drain voltage signal is less than or equal to the turn-on threshold voltage. If the value of the differential signal is not greater than or equal to the preset differential value, or the value of the differential signal decreases from greater than or equal to the preset differential value to 0 and remains at 0 for less than the preset time, the turn-on control circuit does not turn on the synchronous rectifier transistor the next time the drain voltage signal is less than or equal to the turn-on threshold voltage.

6. A synchronous rectification controller for controlling the conduction state of a synchronous rectification transistor, characterized in that, The synchronous rectification controller includes: A turn-on control circuit, coupled to the drain terminal of the synchronous rectifier transistor, performs at least one of a differentiation operation and an integration operation on the drain voltage signal of the synchronous rectifier transistor. Based on at least one of the differential signal obtained from the differentiation operation and the integral signal obtained from the integration operation, it determines whether to turn on the synchronous rectifier transistor when the drain voltage signal is less than or equal to the turn-on threshold voltage next time. A shutdown control circuit, coupled to the drain terminal of the synchronous rectifier transistor, compares the drain voltage signal with a shutdown threshold voltage. When the drain voltage signal is greater than the shutdown threshold voltage, the shutdown control circuit shuts off the synchronous rectifier transistor. If the drain voltage signal is greater than or equal to a preset voltage, and the signal value of the integral signal is greater than or equal to a preset integral value during the period when the drain voltage signal is greater than or equal to the preset voltage, the turn-on control circuit turns on the synchronous rectifier transistor the next time the drain voltage signal is less than or equal to the turn-on threshold voltage. If the drain voltage signal is not greater than or equal to the preset voltage, or the signal value of the integral signal is not greater than or equal to the preset integral value during the period when the drain voltage signal is greater than or equal to the preset voltage, the turn-on control circuit does not turn on the synchronous rectifier transistor the next time the drain voltage signal is less than or equal to the turn-on threshold voltage.

7. The synchronous rectification controller according to claim 6, characterized in that, The preset integral value is equal to the integral value of the drain voltage signal over a preset time period during the period when the drain voltage signal is greater than or equal to the preset voltage.

8. A synchronous rectification controller for controlling the conduction state of a synchronous rectification transistor, characterized in that, The synchronous rectification controller includes: A turn-on control circuit, coupled to the drain terminal of the synchronous rectifier transistor, performs at least one of a differentiation operation and an integration operation on the drain voltage signal of the synchronous rectifier transistor. Based on at least one of the differential signal obtained from the differentiation operation and the integral signal obtained from the integration operation, it determines whether to turn on the synchronous rectifier transistor when the drain voltage signal is less than or equal to the turn-on threshold voltage next time. A shutdown control circuit, coupled to the drain terminal of the synchronous rectifier transistor, compares the drain voltage signal with a shutdown threshold voltage. When the drain voltage signal is greater than the shutdown threshold voltage, the shutdown control circuit shuts off the synchronous rectifier transistor. During the period when the drain voltage signal is greater than or equal to a preset voltage, if the value of the differential signal is greater than or equal to a preset differential value and the value of the integral signal is greater than or equal to a preset integral value, the turn-on control circuit turns on the synchronous rectifier transistor the next time the drain voltage signal is less than or equal to the turn-on threshold voltage. If the value of the differential signal is not greater than or equal to the preset differential value, or if the value of the integral signal is not greater than or equal to the preset integral value during the period when the drain voltage signal is greater than or equal to the preset voltage, the turn-on control circuit does not turn on the synchronous rectifier transistor the next time the drain voltage signal is less than or equal to the turn-on threshold voltage.

9. The synchronous rectifier controller according to claim 8, characterized in that, The preset integral value is equal to the integral value of the drain voltage signal over a preset time period during the period when the drain voltage signal is greater than or equal to the preset voltage.

10. A power conversion device, comprising: A transformer has a primary side and a secondary side, wherein a first terminal of the primary side is used to receive an input voltage, and a first terminal of the secondary side is used to provide an output voltage to a load; A synchronous rectifier transistor, wherein the drain terminal of the synchronous rectifier transistor is coupled to the second terminal of the secondary side, and the source terminal of the synchronous rectifier transistor is coupled to the ground terminal; as well as A synchronous rectification controller, coupled between the drain and gate terminals of the synchronous rectification transistor, is used to control the conduction state of the synchronous rectification transistor. The synchronous rectification controller includes: A turn-on control circuit, coupled to the drain terminal of the synchronous rectifier transistor, performs at least one of a differentiation operation and an integration operation on the drain voltage signal of the synchronous rectifier transistor, and determines whether to turn on the synchronous rectifier transistor when the drain voltage signal is less than or equal to the turn-on threshold voltage next time based on at least one of the differential signal obtained by performing the differentiation operation and the integral signal obtained by performing the integration operation. as well as A shutdown control circuit, coupled to the drain terminal of the synchronous rectifier transistor, compares the drain voltage signal with a shutdown threshold voltage. When the drain voltage signal is greater than the shutdown threshold voltage, the shutdown control circuit shuts off the synchronous rectifier transistor. If the drain voltage signal is greater than or equal to a preset voltage, and the signal value of the differential signal is equal to 0 for a preset time during the period when the drain voltage signal is greater than or equal to the preset voltage, the turn-on control circuit turns on the synchronous rectifier transistor the next time the drain voltage signal is less than or equal to the turn-on threshold voltage. If the drain voltage signal is not greater than or equal to the preset voltage, or the signal value of the differential signal is equal to 0 for a preset time during the period when the drain voltage signal is greater than or equal to the preset voltage, the turn-on control circuit does not turn on the synchronous rectifier transistor the next time the drain voltage signal is less than or equal to the turn-on threshold voltage.

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