Power converter and method for controlling same

Abstract

Provided is a power converter capable of enhancing accuracy of diode-mode detection. A power converter (1) comprises a primary-side circuit (10), a secondary-side circuit (20) having a plurality of synchronous rectification switches (21)-(24), and a controller (40). The secondary-side circuit (20) further has a detection circuit (100). The detection circuit (100): has a detection diode (101) and a detection transistor (102) connected in series; and detects, via the detection diode (101) and the detection transistor (102), the voltage across both ends of one main transistor (24) among the plurality of synchronous rectification switches (21)-(24). The detection transistor (102) has an antiparallel diode connected thereto. The detection circuit (100) detects, on the basis of a change in the voltage across both ends when the main transistor (24) is turned off, whether or not the main transistor (24) is in a diode mode when the main transistor (24) is turned off.

Description

Power converter and control method thereof

[0001] The present disclosure relates to a power converter and a control method thereof.

[0002] To improve the power conversion efficiency of a power converter, there is a synchronous rectification technology that replaces the rectifying section (diode) with a switching element (synchronous rectification switch). Synchronous rectification switches have lower conduction loss than diodes, improving efficiency. However, if the switching timing is not set appropriately, switching loss increases, resulting in a deterioration in power conversion efficiency. For example, Patent Document 1 discloses a technology that lengthens the on-period (called the synchronous rectification period) of a synchronous rectification switch when it is detected that the synchronous rectification switch is in a mode (called diode mode) in which current flows through the body diode of the synchronous rectification switch when the synchronous rectification switch is turned off. This reduces switching loss and improves power conversion efficiency.

[0003] U.S. Patent No. 7,495,934

[0004] However, in the technology disclosed in Patent Document 1, the detection accuracy of the diode mode depends on the performance of the synchronous rectifier switch, and therefore, if a synchronous rectifier switch that has low detection accuracy of the diode mode is used, there is a problem that synchronous rectification cannot be performed normally.

[0005] Therefore, the present disclosure provides a power converter that can improve the accuracy of detecting the diode mode, and a method for manufacturing the same.

[0006] A power converter according to the present disclosure includes a primary-side circuit, a secondary-side circuit, and a controller. The primary-side circuit includes a plurality of switches. The secondary-side circuit includes a plurality of synchronous rectification switches. The controller controls the primary-side circuit and the secondary-side circuit. The secondary-side circuit further includes a detection circuit. The detection circuit includes a detection diode and a detection transistor connected in series. The detection circuit detects a voltage across a main transistor via the detection diode and the detection transistor. The main transistor is one of the plurality of synchronous rectification switches. An anti-parallel diode is connected to the detection transistor. The detection circuit detects whether the main transistor is in diode mode when the main transistor is turned off, based on a change in the voltage across the main transistor when the main transistor is turned off. The diode mode is a mode in which current flows through the anti-parallel diode connected to the main transistor.

[0007] A control method according to the present disclosure is a control method for a power converter. The power converter includes a primary side circuit and a secondary side circuit. The primary side circuit has a plurality of switches. The secondary side circuit has a plurality of synchronous rectification switches. The secondary side circuit further includes a detection diode and a detection transistor connected in series. An anti-parallel diode is connected to the detection transistor. The control method detects a voltage across a main transistor via the detection diode and the detection transistor, and detects whether the main transistor is in diode mode when the main transistor is turned off based on a change in the voltage across the main transistor when the main transistor is turned off. The main transistor is one of a plurality of synchronous rectification switches. The diode mode is a mode in which a current flows through the anti-parallel diode connected to the main transistor.

[0008] These comprehensive or specific aspects may be realized as a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or may be realized as any combination of a system, a method, an integrated circuit, a computer program, and a recording medium.

[0009] According to a power converter and the like according to an aspect of the present disclosure, the accuracy of detecting the diode mode can be improved.

[0010] FIG. 1 is a circuit configuration diagram showing an example of a power converter according to an embodiment. FIG. 1 is a circuit configuration diagram showing a first example of a synchronous rectification unit according to an embodiment. FIG. 2 is a diagram for explaining an example of operation of the power converter when the synchronous rectification period becomes a first set value in the first example. FIG. 3 is a diagram for explaining turn-on and turn-off timings of a detection transistor that is in an off state in the first example. FIG. 4 is a diagram for explaining an example of operation of the power converter when the synchronous rectification period becomes a second set value in the first example. FIG. 5 is a diagram for explaining turn-off and turn-on timings of a detection transistor that is in an on state in the first example. FIG. 6 is a circuit configuration diagram showing a modified example of the first example of the synchronous rectification unit according to an embodiment. FIG. 7 is a diagram for explaining an example of operation of the power converter when the synchronous rectification period becomes a second set value in the modified example of the first example. FIG. 8 is a circuit configuration diagram showing a second example of a synchronous rectification unit according to an embodiment. FIG. 9 is a diagram for explaining an example of operation of the power converter when the synchronous rectification period becomes a first set value in the second example. FIG. 10 is a diagram for explaining an increase in the gain of the amplifier circuit and timing of its release in the second example. FIG. 11 is a diagram for explaining an example of operation of the power converter when the synchronous rectification period becomes a second set value in the second example. 10 is a diagram for explaining the timing of reduction in the amplification factor of the amplifier circuit and its release in a second example. FIG. 11 is a circuit configuration diagram showing a modified example of the second example of the synchronous rectification unit according to the embodiment. FIG. 12 is a circuit configuration diagram showing a third example of the synchronous rectification unit according to the embodiment. FIG. 13 is a diagram for explaining an example of the operation of the power converter when the synchronous rectification period becomes a first set value in the third example. FIG. 14 is a diagram for explaining an example of the operation of the power converter when the synchronous rectification period becomes a second set value in the third example. FIG. 15 is a flowchart showing an example of a control method according to another embodiment. FIG. 16 is a flowchart showing an example of a control method according to another embodiment.

[0011] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0012] The embodiments described below are all comprehensive or specific examples, and the numerical values, shapes, materials, components, arrangement and connection of the components, steps, and order of steps shown in the following embodiments are merely examples and are not intended to limit the present disclosure.

[0013] (Embodiment) Hereinafter, a power converter according to an embodiment will be described.

[0014] FIG. 1 is a circuit configuration diagram showing an example of a power converter 1 according to an embodiment.

[0015] The power converter 1 is an isolated DC-DC converter that boosts or bucks an input voltage to a predetermined output voltage. For example, the power converter 1 is an LLC converter that utilizes LLC resonance due to the leakage inductance, excitation inductance, and resonant capacitor of a transformer. In an LLC converter, frequency control is performed to change the switching frequency of each switch on the primary side, and phase shift control is performed to change the phase difference between the switching of each switch on the primary side, thereby changing the input / output voltage ratio (Gain), thereby enabling the desired power output. Note that the power converter 1 may be a resonant converter other than an LLC converter, or may be another type of buck, boost, or buck-boost converter.

[0016] The power converter 1 has terminals t1, t2, t3, and t4. The terminal t1 is an input terminal, and the terminal t2 is a ground terminal. The terminal t3 is an output terminal, and the terminal t4 is a ground terminal. Note that, since the power converter 1 is an isolated DC-DC converter, the terminals t2 and t4 are electrically isolated.

[0017] For example, the power converter 1 is mounted on a vehicle and applied to an electric vehicle system that drives auxiliary equipment. For example, a high-voltage lithium-ion battery or the like is connected to terminals t1 and t2, and a low-voltage lead-acid battery and auxiliary equipment are connected to terminals t3 and t4. For example, the voltage of a lithium-ion battery is 250 V to 450 V, and the voltage of a lead-acid battery is 10 V to 16 V. To convert a high voltage of 250 V to 450 V to a low voltage of 10 V to 16 V, for example, a power converter 1 such as an LLC converter that supports a wide input / output voltage ratio is used.

[0018] The power converter 1 includes a primary side circuit 10, a secondary side circuit 20, a transformer T, an inductor Lr, capacitors Cr, Cin and Cout, and a controller 40. The capacitors Cin and Cout do not necessarily have to be components of the power converter 1.

[0019] The capacitor Cin is an input capacitor connected between the terminal t1 and the terminal t2, and the capacitor Cout is an output capacitor (smoothing capacitor) connected between the terminal t3 and the terminal t4.

[0020] The primary circuit 10 is connected to the primary side of the transformer T. The primary circuit 10 has a plurality of switches. For example, the primary circuit 10 has switches 11, 12, 13, and 14 as the plurality of switches.

[0021] The switch 11 is a switch provided on a first path connecting the terminal t1 and the terminal t2. The switch 11 is, for example, an N-channel metal oxide semiconductor field effect transistor (MOSFET). The drain of the switch 11 is connected to the terminal t1, and the source of the switch 11 is connected to the drain of the switch 12.

[0022] The switch 12 is provided on the first path and is connected in series with the switch 11. The switch 12 is, for example, an N-channel MOSFET. The drain of the switch 12 is connected to the source of the switch 11, and the source of the switch 12 is connected to the terminal t2.

[0023] The switch 13 is provided on a second path that connects the terminal t1 and the terminal t2 and is different from the first path. The switch 13 is, for example, an N-channel MOSFET. The drain of the switch 13 is connected to the terminal t1, and the source of the switch 13 is connected to the drain of the switch 14.

[0024] The switch 14 is provided on the second path and connected in series with the switch 13. The switch 14 is, for example, an N-channel MOSFET. The drain of the switch 14 is connected to the source of the switch 13, and the source of the switch 14 is connected to the terminal t2.

[0025] The transformer T is an isolation transformer having a primary winding and a secondary winding that are insulated from each other. The primary winding of the transformer T is connected between a node N1 on the first path between the switches 11 and 12 and a node N2 on the second path between the switches 13 and 14.

[0026] The capacitor Cr and the inductor Lr are connected between the node N1 and the primary winding of the transformer T or between the node N2 and the primary winding of the transformer T. The capacitor Cr is a resonant capacitor, and the inductor Lr is a resonant inductor. For example, the capacitor Cr is connected to the node N2, the inductor Lr is connected to the node N1, and the capacitor Cr, the inductor Lr, and the primary winding of the transformer T are connected in series. The inductor Lr may be provided as a separate inductor, or may be provided by utilizing the leakage inductance of the transformer T.

[0027] The capacitor Cr and the inductor Lr may be connected in series at one end (e.g., node N1 side) of the primary winding of the transformer T, or may be connected in series at the other end (e.g., node N2 side) of the primary winding of the transformer T. In this way, the order in which the capacitor Cr, the inductor Lr, and the primary winding of the transformer T are connected between the node N1 and the node N2 is not particularly limited.

[0028] In FIG. 1, the excitation inductance of the transformer T is indicated by an inductor Lm.

[0029] The secondary-side circuit 20 is connected to the secondary side of the transformer T. The secondary-side circuit 20 includes a plurality of synchronous rectification switches. For example, the secondary-side circuit 20 includes switches 21, 22, 23, and 24 as the plurality of synchronous rectification switches. The switches 21, 22, 23, and 24 are each a switch for performing synchronous rectification. To perform synchronous rectification, it is necessary to detect the current flowing through the switch. For example, the current can be directly detected using a Hall sensor or a shunt resistor. However, the power converter 1 performs synchronous rectification by indirectly detecting the current without using a Hall sensor or a shunt resistor. The secondary-side circuit 20 includes, as a component for indirectly detecting the current, a synchronous rectification unit 30 provided corresponding to the switch 24, for example. Note that the synchronous rectification unit 30 may be provided corresponding to the switch 21, 22, or 23. Alternatively, the synchronous rectification unit 30 may be provided for each of two or more of the switches 21, 22, 23, and 24. That is, a plurality of synchronous rectification units 30 may be provided.

[0030] The switch 21 is a switch provided on the third path connecting the terminal t3 and the terminal t4. The switch 21 is, for example, an N-channel MOSFET. The drain of the switch 21 is connected to the terminal t3, and the source of the switch 21 is connected to the drain of the switch 22.

[0031] The switch 22 is provided on the third path and connected in series with the switch 21. The switch 22 is, for example, an N-channel MOSFET. The drain of the switch 22 is connected to the source of the switch 21, and the source of the switch 22 is connected to the terminal t4.

[0032] The switch 23 is a switch provided on a fourth path that connects the terminal t3 and the terminal t4 and is different from the third path. The switch 23 is, for example, an N-channel MOSFET. The drain of the switch 23 is connected to the terminal t3, and the source of the switch 23 is connected to the drain of the switch 24.

[0033] The switch 24 is provided on the fourth path and is connected in series with the switch 23. The switch 24 is, for example, an N-channel MOSFET. The drain of the switch 24 is connected to the source of the switch 23, and the source of the switch 24 is connected to the terminal t4. The switch 24 is an example of a main transistor, and the main transistor is one of the multiple synchronous rectification switches (switches 21, 22, 23, and 24).

[0034] The secondary winding of the transformer T is connected between a node N3 on the third path between the switches 21 and 22 and a node N4 on the fourth path between the switches 23 and 24 .

[0035] 1 shows an anti-parallel diode for each switch, and each anti-parallel diode is connected in parallel with the corresponding switch. Specifically, each anti-parallel diode has an anode connected to the source of the corresponding switch and a cathode connected to the drain of the corresponding switch. Each anti-parallel diode may be a body diode of the corresponding switch.

[0036] The secondary-side circuit 20 further includes a detection circuit 100. The detection circuit 100 detects whether the switch 24 is in the diode mode when the switch 24 is turned off. The diode mode is a mode in which current flows through an anti-parallel diode connected to the switch 24. The detection circuit 100 will be described in detail later.

[0037] The controller 40 controls the primary side circuit 10 and the secondary side circuit 20. Specifically, the controller 40 controls the switching of the switches 11, 12, 13, 14, 21, 22, 23, and 24. For example, the controller 40 controls gate drive circuits (not shown) connected to the gates of the switches 11, 12, 13, 14, 21, 22, 23, and 24, thereby controlling the switching of the switches 11, 12, 13, 14, 21, 22, 23, and 24. The controller 40 also controls the detection circuit 100.

[0038] The controller 40 is realized by, for example, a computer including a processor (microprocessor) and a memory. The memory may be a read-only memory (ROM) or a random access memory (RAM), and can store programs to be executed by the processor. For example, the controller 40 may be realized by a microcontroller.

[0039] Using the detection result of detection circuit 100, controller 40 shortens the synchronous rectification period, which is the on period of each of switches 21, 22, 23, and 24, until the diode mode is detected when switch 24 is turned off. In other words, if the diode mode of switch 24 is not detected when switch 24 is turned off, the synchronous rectification period may be too long, so the synchronous rectification period is shortened to search for a synchronous rectification period in which the diode mode is no longer detected.

[0040] Furthermore, using the detection result of detection circuit 100, controller 40 lengthens the synchronous rectification period, which is the on period of each of switches 21, 22, 23, and 24, until the diode mode is no longer detected when switch 24 is turned off. In other words, if the diode mode of switch 24 is detected when switch 24 is turned off, the synchronous rectification period is short and current is still flowing from the source to the drain of switch 24 when switch 24 is turned off (in other words, ZCS (zero current switching) has not been achieved), so the synchronous rectification period is extended until the current no longer flows.

[0041] Since current also flows through switches 21, 22, and 23 in the same manner, the synchronous rectification periods of all switches 21, 22, 23, and 24 can be controlled simply by detecting the diode mode of one synchronous rectification switch (switch 24 in this case).

[0042] The detection circuit 100 will be described in detail below with reference to first to third examples.

[0043] First, the first example will be described.

[0044] FIG. 2 is a circuit diagram showing a first example of the synchronous rectification unit 30 according to the embodiment.

[0045] In a first example, the detection circuit 100 includes a diode 101 and a transistor 102 connected in series. The diode 101 is an example of a detection diode, and the transistor 102 is an example of a detection transistor. The detection circuit 100 detects the voltage across the switch 24 via the diode 101 and the transistor 102. The detection circuit 100 detects whether the switch 24 is in the diode mode when the switch 24 is turned off, based on a change in the voltage across the switch 24 when the switch 24 is turned off.

[0046] The detection circuit 100 also includes a comparator 103 , a resistor 104 , and a capacitor 105 .

[0047] The diode 101 has a cathode connected to the drain of the switch 24 and an anode connected to the drain of the transistor 102 .

[0048] The transistor 102 is, for example, an N-channel MOSFET. The drain of the transistor 102 is connected to the anode of the diode 101, and the source of the transistor 102 is connected to the negative input terminal of the comparator 103 and one end of the resistor 104. The controller 40 controls a gate drive circuit (not shown) connected to the gate of the transistor 102, thereby controlling the on and off of the transistor 102.

[0049] An anti-parallel diode is connected to the transistor 102. The anti-parallel diode has an anode connected to the source of the transistor 102 and a cathode connected to the drain of the transistor 102. Note that the anti-parallel diode may be a body diode of the transistor 102.

[0050] One end of resistor 104 is connected to the source of transistor 102 and the negative input terminal of comparator 103, and the other end of resistor 104 is connected to one end of capacitor 105 and a power supply such as 3.3 V. Note that 3.3 V is just an example and is not particularly limited. One end of capacitor 105 is connected to resistor 104 and the power supply, and the other end of capacitor 105 is connected to ground. When switch 24 is in the off state, the voltage of the power supply (e.g., 3.3 V) is applied to the negative input terminal of comparator 103.

[0051] The negative input terminal of comparator 103 is connected to the source of transistor 102 and one end of resistor 104, the positive input terminal of comparator 103 is connected to ground, and the output terminal of comparator 103 is connected to controller 40. When a negative voltage smaller than the ground potential is applied to the negative input terminal of comparator 103, a signal indicating a High level is output to controller 40.

[0052] In FIG. 2, the voltage across the switch 24 is V ｄｓ , the gate-source voltage of the switch 24 is V ｇｓ , the forward voltage of the anti-parallel diode of the switch 24 is Vsd, and the current flowing through the switch 24 is I ｓｅｃ , the forward voltage of the diode 101 is Vf ＿Ｄｅｔ , the gate-source voltage of the transistor 102 is V ｇｓ＿Ｄｅｔ１ , the forward voltage of the anti-parallel diode of transistor 102 is Vsd ＿Ｄｅｔ１ , the voltage applied to the negative input terminal of the comparator 103 is V ｏ , the diode mode detection signal (signal that becomes High level when the diode mode is detected) by the detection circuit 100 is V Ｄｅｔ It is shown as follows.

[0053] When switch 24 is turned off and a current flows through the anti-parallel diode of switch 24, a voltage corresponding to the forward voltage of the anti-parallel diode of switch 24 is generated across switch 24. Without transistor 102, detection circuit 100 may not be able to correctly detect whether a voltage corresponding to the forward voltage of the anti-parallel diode of switch 24 is generated across switch 24, depending on whether the difference between the voltage generated across diode 101 (the forward voltage of diode 101) when switch 24 is turned off and the voltage generated across switch 24 has changed from positive to negative to exceed a threshold value (e.g., ground potential: 0 V). In other words, without transistor 102, detection circuit 100 may not be able to correctly detect whether switch 24 is in diode mode. This is because the difference may become unstable due to the influence of noise, and the difference may exceed the threshold value, resulting in the switch 24 being detected as being in diode mode even when it is not in diode mode.

[0054] The difference is the voltage applied to the negative input terminal of the comparator 103. Since the anode of the anti-parallel diode of the switch 24 is connected to the ground, a current (I ｓｅｃ ) flows, the voltage at the cathode of the anti-parallel diode becomes a negative voltage (-Vsd) by the forward voltage of the anti-parallel diode. Since the cathode of the diode 101 is connected to the cathode of the anti-parallel diode of the switch 24, the voltage at the anode of the diode 101 becomes a positive voltage (+Vf) by the forward voltage of the diode 101 with respect to the voltage at the cathode of the anti-parallel diode of the switch 24. ＿Ｄｅｔ Since the negative input terminal of the comparator 103 is connected to the anode side of the diode 101, the voltage at the negative input terminal of the comparator 103 is the sum of the positive voltage and the negative voltage, that is, the difference (Vf ＿Ｄｅｔ -Vsd).

[0055] Specifically, the forward voltage of the anti-parallel diode of switch 24 is 0.8 V, and the forward voltage of diode 101 is 0.4 V. When switch 24 is in the on state, the difference between the voltage (0.4 V) generated across diode 101 and the voltage (0 V) generated across switch 24 (i.e., the voltage applied to the negative input terminal of comparator 103) is 0.4 V. However, when switch 24 is in the on state, this difference (0.4 V) may be affected by switching noise and a voltage drop due to the on resistance of switch 24, causing the voltage applied to the negative input terminal of comparator 103 to drop by 0.4 V or more and become a negative voltage, which may result in switch 24 being detected as being in diode mode.

[0056] Therefore, in the first example, the transistor 102 is connected in series to the diode 101, and the detection circuit 100 detects the voltage across the switch 24 via the diode 101 and the transistor 102. In this case, the difference is the difference (Vf ＿Ｄｅｔ +Vsd ＿Ｄｅｔ１ By turning off transistor 102, the difference is increased by the voltage generated in the anti-parallel diode of transistor 102, making it less likely that the threshold will be exceeded even under the influence of noise, and it is possible to prevent switch 24 from being detected as being in diode mode when it is not (this is called erroneous detection).

[0057] For example, assume that the forward voltage of the anti-parallel diode of transistor 102 is 0.8 V. When switch 24 is in the on state and transistor 102 is in the off state, the difference between the sum (1.2 V) of the voltage generated across diode 101 (the forward voltage of diode 101) and the voltage generated across transistor 102 (the forward voltage of the anti-parallel diode of transistor 102) and the voltage across switch 24 (0 V) (i.e., the voltage applied to the negative input terminal of comparator 103) is 1.2 V. In this case, even if this 1.2 V voltage is affected by switching noise and the voltage drop due to the on resistance of switch 24, the voltage applied to the negative input terminal of comparator 103 can remain positive, thereby suppressing erroneous detection.

[0058] As a result, the accuracy of detecting the diode mode can be improved. By improving the accuracy of detecting the diode mode, synchronous rectification can be performed normally, and power conversion efficiency can be improved.

[0059] It is also possible to use a Hall sensor or a shunt resistor to detect that a current flows through the anti-parallel diode of the switch 24 when the switch 24 is turned off (i.e., the diode mode of the switch 24). However, if a Hall sensor is used, the size of the Hall sensor increases, resulting in a larger power converter. Furthermore, if a shunt resistor is used, loss occurs due to the insertion of the resistor. In the present disclosure, the diode mode can be detected without using a Hall sensor or a shunt resistor, thereby improving the accuracy of detecting the diode mode while achieving a smaller size and lower loss of the power converter 1.

[0060] Next, the operation of the power converter 1 in the first example will be described with reference to FIGS.

[0061] 3 is a diagram for explaining an example of the operation of the power converter 1 when the synchronous rectification period becomes the first set value in the first example. Ｄｅｔ ), the voltage (V ｏ ), the voltage across the switch 24 (V ｄｓ), the current flowing through the switch 24 (I ｓｅｃ ), the gate-source voltage of the switch 24 (V ｇｓ ), the gate-source voltage of the transistor 102 (V ｇｓ＿Ｄｅｔ１ ) are shown in the graphs. The same applies to Figures 4 to 6 described later. The first set value will be described later.

[0062] V in Figure 3 ｇｓ＿Ｄｅｔ１ As shown in V in FIG. ｇｓ As shown in Figure 3, when the switch 24 is in the off state, the voltage across the switch 24 is the voltage at the terminal t3 (output voltage). When the switch 24 is turned on, both ends of the switch 24 are short-circuited, so the voltage across the switch 24 is 0V. ｓｅｃ 3A, when the switch 24 is turned off while a current is flowing through the switch 24, the current continues to flow through the anti-parallel diode of the switch 24. Therefore, the voltage across the switch 24 becomes the forward voltage (−Vsd) of the anti-parallel diode of the switch 24.

[0063] However, as described above, the voltage (V ｏ ) is not affected by switching noise and the voltage drop due to the on-resistance of the switch 24. Therefore, as shown in FIG. 3B, the voltage (V ｏ ) is the sum of the forward voltage of the diode 101 and the forward voltage of the anti-parallel diode of the transistor 102 (Vf ＿Ｄｅｔ +Vsd ＿Ｄｅｔ１ ) and does not become a negative voltage. ｏ ) is only slightly below the threshold value (for example, 0 V), the detection accuracy of the comparator 103 is poor, and the voltage (V ｏ ) may not be able to detect that it is at a negative voltage.

[0064] 3C, even though the switch 24 is in the diode mode, it may not be possible to detect that the switch 24 is in the diode mode. The situation where the switch 24 is in the diode mode but the diode mode cannot be detected is also referred to as "non-detection."

[0065] As shown in (d) of FIG. 3 , the controller 40 shortens the synchronous rectification period, which is the on-period of the switch 24, until the diode mode is detected. However, if it is not detected that the switch 24 is in the diode mode at all, the controller 40 shortens the synchronous rectification period, and as shown in (e) of FIG. 3 , the synchronous rectification period is shortened to a first set value. The first set value is, for example, a value corresponding to the minimum value of the synchronous rectification period, which is determined from the switching frequency and phase of the switches 11, 12, 13, and 14 of the primary-side circuit 10. For example, the first set value may be the minimum value, or a value approximately 10% larger than the minimum value. When the synchronous rectification period has shortened to the first set value, the transistor 102 is in the off state, and the difference between the sum of the voltage generated in the diode 101 and the voltage generated in the transistor 102 and the voltage across the switch 24, that is, the voltage (V ｏ ) is too far from the threshold (for example, 0 V), and the detection circuit 100 may not be able to detect the diode mode correctly.

[0066] Therefore, when the controller 40 detects that the synchronous rectification period is equal to the first set value while the transistor 102 is in the off state, the controller 40 turns on the transistor 102 as shown in (f) of FIG. 3. This causes the voltage (V ｏ ) is the forward voltage (Vsd ＿Ｄｅｔ１ ) smaller.

[0067] As shown in (h) of FIG. 3, when the switch 24 is turned off while a current is flowing through the switch 24, the voltage (V ｏ ) is the forward voltage (Vf ＿Ｄｅｔ ) to the voltage across the switch 24 (Vｄｓ ) and becomes a negative voltage. As a result, the difference between the voltage generated in the diode 101 and the voltage across the switch 24, that is, the voltage (V ｏ ) is calculated by dividing the forward voltage (Vsd ＿Ｄｅｔ１ ) is no longer generated in the transistor 102, the difference is more likely to change to exceed the threshold (specifically, to fall below 0 V). Therefore, as shown in FIG. 3(j), the detection circuit 100 can detect that the switch 24 is in the diode mode. This prevents undetected cases.

[0068] Then, as shown in FIG. 3(k), controller 40 lengthens the synchronous rectification period until diode mode is no longer detected when switch 24 is turned off.

[0069] 3, the timing of turning on and off the transistor 102 is not particularly specified, but the transistor 102 may be turned on and off at a specific timing. This will be described with reference to FIG. 4.

[0070] FIG. 4 is a diagram for explaining the turn-on and turn-off timing of the transistor 102 that is in the off state in the first example.

[0071] 4, the controller 40 may turn on the transistor 102 in synchronization with the turning off of the switch 24 while keeping the transistor 102 in an off state. For example, if the transistor 102 is turned on before the switch 24 is turned off, the difference, i.e., the voltage (V ｏ ) may easily exceed the threshold when it is affected by switching noise and a voltage drop due to the on-resistance of switch 24, which may result in a false detection that it is in diode mode. Therefore, false detection can be suppressed by turning on transistor 102 in synchronization with the turning off of switch 24.

[0072] 4, the controller 40 may turn off the transistor 102 after the end of the dead time, that is, after the switch 23 on the high side of the switch 24 is turned on. If the diode mode is detected, the controller 40 may turn off the transistor 102 after the diode mode is detected.

[0073] 5 is a diagram for explaining an example of the operation of the power converter 1 when the synchronous rectification period becomes the second set value in the first example. The second set value will be described later.

[0074] V in Figure 5 ｇｓ＿Ｄｅｔ１ As shown in V in FIG. ｇｓ As shown in Figure 5, when the switch 24 is in the off state, the voltage across the switch 24 is the voltage (output voltage) at the terminal t3. When the switch 24 is turned on, both ends of the switch 24 are short-circuited, so the voltage across the switch 24 is 0V. ｓｅｃ When transistor 102 is turned on, current begins to flow through switch 24, as shown in ｏ ) is reduced by the amount corresponding to the absence of a forward voltage across the anti-parallel diode in transistor 102, and may become a negative voltage as shown in (a) of Fig. 5 due to the effects of switching noise and the voltage drop caused by the on-resistance of switch 24. This causes erroneous detection as shown in (b) of Fig. 5.

[0075] As shown in (c) of FIG. 5 , the controller 40 lengthens the synchronous rectification period, which is the on-period of the switch 24, until the diode mode is no longer detected. However, if the diode mode of the switch 24 continues to be detected, the controller 40 lengthens the synchronous rectification period, and as shown in (d) of FIG. 5 , the synchronous rectification period is lengthened to a second set value. The second set value is, for example, a value corresponding to the maximum value of the synchronous rectification period, which is determined from the switching frequency and phase of the switches 11, 12, 13, and 14 of the primary-side circuit 10. For example, the second set value may be the maximum value, or a value approximately 10% smaller than the minimum value. When the synchronous rectification period is lengthened to the second set value, the transistor 102 is in the on state, and the difference between the voltage generated in the diode 101 and the voltage across the switch 24, i.e., the voltage (V ｏ ) may become too close to the threshold (for example, 0 V) ​​and exceed (fall below) the threshold due to the influence of noise, causing the detection circuit 100 to erroneously detect the diode mode.

[0076] Therefore, when the controller 40 detects that the synchronous rectification period is equal to the second set value while the transistor 102 is in the on state, the controller 40 turns off the transistor 102 as shown in (e) of FIG. 5. This causes the voltage (V ｏ ) is the forward voltage (Vsd ＿Ｄｅｔ１ ) will be larger.

[0077] As shown in (g) of FIG. 5, when the switch 24 is turned off in a state where no current flows through the switch 24, the voltage (V ｏ ) is the sum of the forward voltage of the diode 101 and the forward voltage of the anti-parallel diode of the transistor 102 (Vf ＿Ｄｅｔ +Vsd ＿Ｄｅｔ１ ) is obtained. As a result, the difference between the sum of the voltage generated in the diode 101 and the voltage generated in the transistor 102 and the voltage across the switch 24, that is, the voltage (V ｏ) is less likely to exceed the threshold (specifically, is less likely to fall below 0 V) ​​even when affected by noise, making it possible to suppress false detection.

[0078] Then, when the diode mode is not detected as shown in (i) of FIG. 5, the controller 40 shortens the synchronous rectification period until the diode mode is detected when the switch 24 is turned off, as shown in (j) of FIG. 5, and searches for the optimal synchronous rectification period.

[0079] 5, the timing of turning on and off the transistor 102 is not particularly specified, but the transistor 102 may be turned on and off at specific timings. This will be described with reference to FIG. 6.

[0080] FIG. 6 is a diagram for explaining the turn-off and turn-on timing of the transistor 102 that is in the on state in the first example.

[0081] 6, when the controller 40 turns on the transistor 102, the controller 40 may turn off the transistor 102 in synchronization with the turning on of the switch 24, and may turn on the transistor 102 in synchronization with the turning off of the switch 24. For example, if the transistor 102 is in the on state after the switch 24 is turned on or before the switch 24 is turned off, the difference, i.e., the voltage (V ｏ ) may be more likely to exceed the threshold when it is affected by switching noise and a voltage drop due to the on-resistance of switch 24, which may result in a false detection that it is in diode mode. Therefore, false detection can be suppressed by turning off transistor 102 in synchronization with the turning on of switch 24 and turning on transistor 102 in synchronization with the turning off of switch 24.

[0082] The detection circuit 100 may have two or more detection transistors, which will be described with reference to FIGS.

[0083] 7 is a circuit configuration diagram showing a modification of the first example of the synchronous rectification unit 30 according to the embodiment. The following describes the circuit configuration of the detection circuit 100 in this modification, focusing on differences from the first example.

[0084] 7, the detection circuit 100 further includes a transistor 102a, which is an example of a detection transistor. The transistor 102a is connected in series with the diode 101 and the transistor 102.

[0085] The transistor 102a is, for example, an N-channel MOSFET. The drain of the transistor 102a is connected to the source of the transistor 102, and the source of the transistor 102a is connected to the negative input terminal of the comparator 103 and one end of the resistor 104. The controller 40 controls a gate drive circuit (not shown) connected to the gate of the transistor 102a, thereby controlling the on and off of the transistor 102a.

[0086] An anti-parallel diode is connected to the transistor 102a. The anti-parallel diode has an anode connected to the source of the transistor 102a and a cathode connected to the drain of the transistor 102a. The anti-parallel diode may be a body diode of the transistor 102a.

[0087] One end of the resistor 104 is connected to the source of the transistor 102 a and the negative input terminal of the comparator 103 , and the negative input terminal of the comparator 103 is connected to the source of the transistor 102 a and one end of the resistor 104 .

[0088] FIG. 7 further shows that the gate-source voltage of the transistor 102a is V ｇｓ＿Ｄｅｔ２ , the forward voltage of the anti-parallel diode of the transistor 102a is Vsd ＿Ｄｅｔ２ It is shown as follows.

[0089] The controller 40 controls the on and off of each of the two or more detection transistors (here, transistors 102 and 102a) depending on the diode mode detection state of the detection circuit 100. This will be described with reference to FIG.

[0090] 8 is a diagram for explaining an example of the operation of the power converter 1 when the synchronous rectification period becomes the second set value in the modification of the first example. From the top, FIG. 8 shows the detection signal (V Ｄｅｔ ), the voltage (V ｏ ), the voltage across the switch 24 (V ｄｓ ), the current flowing through the switch 24 (I ｓｅｃ ), the gate-source voltage of the switch 24 (V ｇｓ ), the gate-source voltage of the transistor 102 (V ｇｓ＿Ｄｅｔ１ ), the gate-source voltage of the transistor 102a (V ｇｓ＿Ｄｅｔ２ ) is shown. For example, the forward voltage (Vsd) of the anti-parallel diode of transistor 102a ＿Ｄｅｔ２ ) is the forward voltage of the anti-parallel diode of transistor 102 (Vsd ＿Ｄｅｔ１ ) is greater than

[0091] V in Figure 8 ｇｓ＿Ｄｅｔ１ and V ｇｓ＿Ｄｅｔ２ As shown in FIG. 8, the transistors 102 and 102a are in the ON state. ｇｓ As shown in Figure 8, when the switch 24 is in the off state, the voltage across the switch 24 is the voltage (output voltage) at the terminal t3. When the switch 24 is turned on, both ends of the switch 24 are short-circuited, so the voltage across the switch 24 is 0V. ｓｅｃ When transistors 102 and 102a are turned on, current begins to flow through switch 24, as shown in ｏ ) is reduced by the amount corresponding to the absence of the forward voltage of the anti-parallel diodes in transistors 102 and 102a, and may become a negative voltage as shown in (a) of Fig. 8 due to the effects of switching noise and the voltage drop caused by the on-resistance of switch 24. This causes erroneous detection as shown in (b) of Fig. 8.

[0092] As shown in (c) of FIG. 8, the controller 40 lengthens the synchronous rectification period, which is the on-period of the switch 24, until the diode mode is no longer detected. However, if it continues to be detected that the switch 24 is in the diode mode, the controller 40 lengthens the synchronous rectification period, and as shown in (d) of FIG. 8, the synchronous rectification period is lengthened to the second set value. When the synchronous rectification period is lengthened to the second set value, the transistors 102 and 102a are in the on-state, and the difference between the voltage generated in the diode 101 and the voltage across the switch 24, that is, the voltage (V ｏ ) may become too close to the threshold (for example, 0 V) ​​and exceed (fall below) the threshold due to the influence of noise, causing the detection circuit 100 to erroneously detect the diode mode.

[0093] Therefore, when the controller 40 detects that the synchronous rectification period is at the second set value while the transistor 102 is in the on state, the controller 40 turns off the transistors 102 and 102a, but does not turn off all of the transistors 102 and 102a, but turns off the transistors 102 and 102a one by one depending on the detected state of the diode mode.

[0094] For example, as shown in FIG. 8(e), the controller 40 turns off the transistor 102 whose anti-parallel diode has a small forward voltage. This causes the voltage (V ｏ ) is the forward voltage (Vsd ＿Ｄｅｔ１ ) will be larger.

[0095] If the diode mode is still falsely detected, as shown in FIG. 8(g), the controller 40 turns off both transistors 102 and 102a, as shown in FIG. 8(h). This causes the voltage (V ｏ ) is the forward voltage (Vsd ＿Ｄｅｔ１ +Vsd ＿Ｄｅｔ２ ) is increased by the voltage (V ｏ ) little by little to increase the voltage (V ｏ) can be prevented from straying too far from the threshold.

[0096] When an erroneous detection occurs, the number of detection transistors to be turned off is gradually increased, so that the difference between the sum of the voltage generated in the diode 101 and the voltage generated in two or more detection transistors and the voltage across the switch 24, that is, the voltage (V ｏ ) can be adjusted so that it is not too far from or too close to the threshold value, and false detection can be suppressed while also suppressing non-detection. Although not shown, if non-detection occurs, the number of detection transistors that are turned on can be gradually increased to ｏ ) can be adjusted so that it is not too close or too far from the threshold, thereby suppressing false detections while suppressing non-detections.

[0097] Next, a second example will be described.

[0098] FIG. 9 is a circuit diagram showing a second example of the synchronous rectification unit 30 according to the embodiment.

[0099] The second example differs from the first example in that the detection circuit 100 has an amplifier circuit 106 instead of the transistor 102, and detects the voltage across the switch 24 via the diode 101 and the amplifier circuit 106. The circuit configuration of the detection circuit 100 will be described below, focusing on the differences from the first example.

[0100] The amplifier circuit 106 is provided in the input stage or output stage of the detection circuit 100. An example in which the amplifier circuit 106 is provided in the output stage of the detection circuit 100 will be described below. In a second example, the transistor 102 is not provided, so the anode of the diode 101 is connected to the resistor 104 and the amplifier circuit 106. The amplifier circuit 106 amplifies the difference between the voltage generated in the diode 101 and the voltage across the switch 24. The amplifier circuit 106 has a variable gain function. For example, the amplifier circuit 106 changes the gain by being controlled by the controller 40. This function can be realized by a differential amplifier circuit as shown in FIG. 9. Specifically, the gain is determined by a resistor R １ and resistance R ２ａ , R ２ｂ , ...R ２ＮMore specifically, the resistance R ２ａ , R ２ｂ , ...R ２Ｎ The on and off of the switches connected in series with each of the resistors is controlled by a controller 40, and the amplification factor can be increased by reducing the number of resistors connected in parallel, i.e., increasing the combined resistance, and the amplification factor can be decreased by increasing the number of resistors connected in parallel, i.e., decreasing the combined resistance. ｏ ) is amplified, and a voltage (V ｏ ') is applied.

[0101] When the switch 24 is turned off and a current flows through the anti-parallel diode of the switch 24, a voltage corresponding to the forward voltage of the anti-parallel diode of the switch 24 is generated across the switch 24. If the amplifier circuit 106 is not provided, the detection circuit 100 may not be able to correctly detect whether a voltage corresponding to the forward voltage of the anti-parallel diode of the switch 24 is generated across the switch 24, depending on whether the difference between the voltage generated across the diode 101 (the forward voltage of the diode 101) when the switch 24 is turned off and the voltage generated across the switch 24 has changed to exceed a threshold value. In other words, if the amplifier circuit 106 is not provided, the detection circuit 100 may not be able to correctly detect whether the switch 24 is in diode mode. This is because the forward voltage of the anti-parallel diode of the switch 24 is small, and even if a voltage corresponding to the forward voltage of the anti-parallel diode of the switch 24 is generated across the switch 24, the difference only slightly exceeds the threshold value, and depending on the detection accuracy of the detection circuit 100, it may not be possible to detect that the switch 24 is in diode mode.

[0102] Specifically, the forward voltage of the anti-parallel diode of switch 24 is 0.6 V, and the forward voltage of diode 101 is 0.4 V. When switch 24 is in the off state, the difference between the voltage (0.4 V) generated in diode 101 and the voltage (0.6 V) generated in switch 24 is −0.2 V. At this time, this difference is a negative voltage and is below a threshold value (e.g., 0 V), so ideally, diode mode would be detected. However, because this difference is only slightly below the threshold value, diode mode may not be detected depending on the detection accuracy of detection circuit 100.

[0103] Therefore, in the second example, an amplifier circuit 106 is provided at the output stage of the detection circuit 100, and the detection circuit 100 detects the voltage across the switch 24 via the diode 101 and the amplifier circuit 106. When the amplifier circuit 106 is provided at the output stage of the detection circuit 100, the difference, i.e., the voltage (V ｏ ) is amplified, and the change in the difference can be increased. By increasing the change in the difference, the difference falls significantly below the threshold, and non-detection can be suppressed.

[0104] As a result, the accuracy of detecting the diode mode can be improved. By improving the accuracy of detecting the diode mode, synchronous rectification can be performed normally, and power conversion efficiency can be improved.

[0105] Next, the operation of the power converter 1 in the second example will be described with reference to FIGS.

[0106] 10 is a diagram for explaining an example of the operation of the power converter 1 when the synchronous rectification period becomes the first set value in the second example. Ｄｅｔ ), the difference voltage (V ｏ ), the voltage (V ｏ '), the voltage across the switch 24 (V ｄｓ ), the current flowing through the switch 24 (I ｓｅｃ ), the gate-source voltage of the switch 24 (V ｇｓ ), and a graph of the amplification factor of the amplifier circuit is shown. The same applies to Figures 11 to 13 described later.

[0107] As shown in the amplification factor of FIG. 10, the amplification factor of the amplifier circuit 106 is set to 1. When the amplification factor is 1, the voltage (V ｏ ) = voltage (V ｏ ') in Figure 10. ｇｓ As shown in Figure 10, when the switch 24 is in the off state, the voltage across the switch 24 is the voltage (output voltage) at the terminal t3. When the switch 24 is turned on, both ends of the switch 24 are short-circuited, so the voltage across the switch 24 is 0V. ｓｅｃ 10A, when the switch 24 is turned off while a current is flowing through the switch 24, the current continues to flow through the anti-parallel diode of the switch 24. Therefore, the voltage across the switch 24 becomes the forward voltage (−Vsd) of the anti-parallel diode of the switch 24.

[0108] As shown in FIG. 10(b), the voltage (V ｏ ) is only slightly below the threshold value (for example, 0 V), and if the detection accuracy of the comparator 103 is poor, the voltage (V ｏ 10C, even though the switch 24 is in the diode mode, it may not be possible to detect that the switch 24 is in the diode mode. In other words, there may be cases where the switch 24 is not detected.

[0109] As shown in (d) of Fig. 10, the controller 40 shortens the synchronous rectification period, which is the on-period of the switch 24, until the diode mode is detected, but if it is not detected at all that the switch 24 is in the diode mode, the controller 40 shortens the synchronous rectification period, and the synchronous rectification period is shortened to the first set value, as shown in (e) of Fig. 10. When the synchronous rectification period is shortened to the first set value, the difference is only slightly below the threshold value, and there is a possibility that the detection circuit 100 is not able to properly detect the diode mode.

[0110] Therefore, when the controller 40 detects that the synchronous rectification period is equal to the first set value, it increases the amplification factor of the amplifier circuit 106 as shown in (f) of FIG. 10. As a result, the voltage (V ｏ ) is amplified to produce a voltage (V ｏ ')

[0111] As shown in (h) of FIG. 10, when the switch 24 is turned off while a current flows through the switch 24, the difference, i.e., the voltage (V ｏ The change in voltage (V ｏ ') becomes significantly lower than the threshold value. In this way, by increasing the amplification factor of the amplifier circuit 106, the change in the difference can be increased, and the difference is more likely to change to significantly exceed the threshold value. Therefore, as shown in (j) of FIG. 10, the detection circuit 100 can detect that the switch 24 is in the diode mode. This prevents non-detection.

[0112] Then, as shown in FIG. 10(k), controller 40 lengthens the synchronous rectification period until diode mode is no longer detected when switch 24 is turned off.

[0113] 10, the timing of increasing the gain of the amplifier circuit 106 and canceling the increase is not specified, but the gain of the amplifier circuit 106 may be increased and canceled at a specific timing. This will be described with reference to FIG. 11.

[0114] FIG. 11 is a diagram for explaining the timing of increasing the amplification factor of the amplifier circuit 106 and canceling it in the second example.

[0115] 11, the controller 40 may increase the gain of the amplifier circuit 106 in synchronization with the turning off of the switch 24. For example, if the gain of the amplifier circuit 106 is increased before the switch 24 is turned off, the difference, i.e., the voltage (V ｏ) is affected by switching noise and a voltage drop due to the on-resistance of switch 24, these effects may also be amplified and the threshold may be exceeded, which may result in a false detection of the diode mode. Therefore, by increasing the amplification factor of amplifier circuit 106 in synchronization with the turn-off of switch 24, false detection can be suppressed.

[0116] 11 , the controller 40 may cancel the increase in the gain of the amplifier circuit 106 after the end of the dead time, that is, after the switch 23 on the high side of the switch 24 is turned on. If the diode mode is detected, the controller 40 may cancel the increase in the gain of the amplifier circuit 106 after the timing at which the diode mode is detected.

[0117] FIG. 12 is a diagram for explaining an example of the operation of the power converter 1 when the synchronous rectification period becomes the second set value in the second example.

[0118] As shown in the amplification factor of FIG. 12, the amplification factor of the amplifier circuit 106 is set to 1. ｇｓ As shown in Figure 12, when the switch 24 is in the off state, the voltage across the switch 24 is the voltage at the terminal t3 (output voltage). When the switch 24 is turned on, both ends of the switch 24 are short-circuited, so the voltage across the switch 24 is 0V. ｓｅｃ Current begins to flow through switch 24 as shown in ｏ ) may become a negative voltage as shown in (a) of Fig. 12 due to the effects of switching noise and the voltage drop caused by the on-resistance of the switch 24. This causes erroneous detection as shown in (b) of Fig. 12.

[0119] As shown in (c) of FIG. 12, the controller 40 lengthens the synchronous rectification period, which is the on-period of the switch 24, until the diode mode is no longer detected. However, if it continues to be detected that the switch 24 is in the diode mode, the controller 40 lengthens the synchronous rectification period, and as shown in (d) of FIG. 12, the synchronous rectification period is lengthened to the second set value. When the synchronous rectification period is lengthened to the second set value, the difference between the voltage generated in the diode 101 and the voltage across the switch 24, that is, the voltage (V ｏ ) may exceed the threshold (or fall below the threshold) due to the influence of noise, causing the detection circuit 100 to erroneously detect the diode mode.

[0120] Therefore, when the controller 40 detects that the synchronous rectification period is equal to the second set value, it reduces the amplification factor of the amplifier circuit 106 as shown in (e) of FIG. 12. This reduces the voltage (V ｏ ) is reduced to the voltage (V ｏ ')

[0121] As shown in (g) of FIG. 12, when the switch 24 is turned off with no current flowing through the switch 24, the difference, i.e., the voltage (V ｏ The change in voltage (V ｏ In this way, by reducing the amplification factor of the amplifier circuit 106, the influence of noise can be reduced, and the difference can be prevented from exceeding, for example, the hysteresis, which is the range in which the comparator 103 does not react, thereby suppressing false detection.

[0122] Then, when the diode mode is not detected as shown in FIG. 12(i), the controller 40 shortens the synchronous rectification period until the diode mode is detected when the switch 24 is turned off, as shown in FIG. 12(j), and searches for the optimal synchronous rectification period.

[0123] 12, the timing of the reduction in the gain of the amplifier circuit 106 and the timing of its cancellation are not specified, but the gain of the amplifier circuit 106 may be reduced and the reduction may be cancelled at a specific timing. This will be described with reference to FIG. 13.

[0124] FIG. 13 is a diagram for explaining the timing of the reduction and cancellation of the amplification factor of the amplifier circuit 106 in the second example.

[0125] 13, the controller 40 may decrease the gain of the amplifier circuit 106 in synchronization with the turning on of the switch 24, and cancel the decrease in the gain of the amplifier circuit 106 in synchronization with the turning off of the switch 24. For example, if the transistor 102 is in the on state after the switch 24 is turned on or before the switch 24 is turned off, the difference, i.e., the voltage (V ｏ ) may be more likely to exceed the threshold when it is affected by switching noise and a voltage drop due to the on-resistance of the switch 24, which may result in a false detection that the diode mode is being entered. Therefore, false detection can be suppressed by reducing the gain of the amplifier circuit 106 in synchronization with the turn-on of the switch 24 and canceling the reduction in the gain of the amplifier circuit 106 in synchronization with the turn-off of the switch 24.

[0126] As shown in FIG. 14, an amplifier circuit 106 may be provided at the input stage of the detection circuit 100.

[0127] FIG. 14 is a circuit configuration diagram showing a modification of the second example of the synchronous rectification unit 30 according to the embodiment.

[0128] Even in this case, the voltage (Vds) generated across the switch 24 can be amplified, and as a result, the difference, i.e., the voltage (V ｏ ) can be increased, and the same effect as when the amplifier circuit 106 is provided at the output stage of the detection circuit 100 can be achieved.

[0129] Next, a third example will be described.

[0130] FIG. 15 is a circuit configuration diagram showing a third example of the synchronous rectification unit 30 according to the embodiment.

[0131] 15 , the third example differs from the first and second examples in that the detection circuit 100 includes a transistor 102 and an amplifier circuit 106, and detects the voltage across the switch 24 via a diode 101, the transistor 102, and the amplifier circuit 106. The circuit configuration of the detection circuit 100 in the third example differs from the first and second examples only in that the detection circuit 100 includes both the transistor 102 and the amplifier circuit 106, and the other points are the same, so a description thereof will be omitted. Note that the third example may also include two or more detection transistors, and the amplifier circuit 106 may be provided in the input stage.

[0132] The operation of the power converter 1 in the third example will be described below with reference to FIGS. 16 and 17. FIG.

[0133] 16 is a diagram for explaining an example of the operation of the power converter 1 when the synchronous rectification period becomes the first set value in the third example. Ｄｅｔ ), the difference voltage between the sum of the voltage generated in the diode 101 and the voltage generated in the transistor 102 and the voltage across the switch 24 (V ｏ ), the voltage (V ｏ '), the voltage across the switch 24 (V ｄｓ ), the current flowing through the switch 24 (I ｓｅｃ ), the gate-source voltage of the switch 24 (V ｇｓ ), the gate-source voltage of the transistor 102 (V ｇｓ＿Ｄｅｔ１ ), and a graph of the amplification factor of the amplifier circuit is shown. The same applies to FIG. 17 described later.

[0134] V in FIG. ｇｓ＿Ｄｅｔ１ 16, the transistor 102 is in an off state. Also, as shown in the amplification factor of FIG. 16, the amplification factor of the amplifier circuit 106 is set to 1. ｇｓAs shown in Figure 16, when the switch 24 is in the off state, the voltage across the switch 24 is the voltage (output voltage) at the terminal t3. When the switch 24 is turned on, both ends of the switch 24 are short-circuited, so the voltage across the switch 24 is 0V. ｓｅｃ 16A, when the switch 24 is turned off while a current is flowing through the switch 24, the current continues to flow through the anti-parallel diode of the switch 24. Therefore, the voltage across the switch 24 becomes the forward voltage (−Vsd) of the anti-parallel diode of the switch 24.

[0135] However, the voltage applied to the negative input terminal of the comparator 103 (V ｏ ) is not affected by switching noise and the voltage drop due to the on-resistance of the switch 24. Therefore, as shown in FIG. 16(b), the voltage (V ｏ ) is the sum of the forward voltage of the diode 101 and the forward voltage of the anti-parallel diode of the transistor 102 (Vf ＿Ｄｅｔ +Vsd ＿Ｄｅｔ１ ) and falls just below the threshold (for example, 0 V), and if the detection accuracy of the comparator 103 is poor, ｏ 16C, even though the switch 24 is in the diode mode, it may not be possible to detect that the switch 24 is in the diode mode. In other words, there may be cases where the switch 24 is not detected.

[0136] As shown in (d) of FIG. 16, the controller 40 shortens the synchronous rectification period, which is the ON period of the switch 24, until the diode mode is detected. However, if it is not detected at all that the switch 24 is in the diode mode, the controller 40 shortens the synchronous rectification period, and as shown in (e) of FIG. 16, the synchronous rectification period is shortened to the first set value. When the synchronous rectification period is shortened to the first set value, the transistor 102 is in the OFF state, and the difference between the sum of the voltage generated in the diode 101 and the voltage generated in the transistor 102 and the voltage across the switch 24, that is, the voltage (Vｏ ) is only slightly below the threshold (e.g., 0 V), and the detection circuit 100 may not be able to properly detect the diode mode.

[0137] Therefore, when the controller 40 detects that the synchronous rectification period is equal to the first set value while the transistor 102 is in the off state, it turns on the transistor 102 as shown in (f) of FIG. 16 and increases the amplification factor of the amplifier circuit 106 as shown in (g) of FIG. 16. As a result, the voltage (V ｏ ) is the forward voltage (Vsd ＿Ｄｅｔ１ ) and, as shown in FIG. 16(i), the voltage (V ｏ ) is amplified to produce a voltage (V ｏ ')

[0138] As shown in (j) of FIG. 16, when the switch 24 is turned off while a current flows through the switch 24, the difference, i.e., the voltage (V ｏ The change in voltage (V ｏ ') becomes significantly lower than the threshold. In this way, by turning on the transistor 102 and increasing the amplification factor of the amplifier circuit 106, the change in the difference can be increased, and the difference is more likely to change to significantly exceed the threshold. Therefore, as shown in FIG. 16(l), the detection circuit 100 can detect that the switch 24 is in the diode mode. This prevents undetected states.

[0139] In this way, by providing both the transistor 102 and the amplifier circuit 106, the detection accuracy of the diode mode can be further improved.

[0140] Then, as shown in FIG. 16(m), controller 40 lengthens the synchronous rectification period until diode mode is no longer detected when switch 24 is turned off.

[0141] 16, the timing of turning on and off the transistor 102 is not particularly specified, but the transistor 102 may be turned on and off at specific timing, as in the first example. Also, in the example shown in Fig. 16, the timing of increasing the gain of the amplifier circuit 106 and releasing it is not particularly specified, but the gain of the amplifier circuit 106 may be increased and released at specific timing, as in the second example.

[0142] FIG. 17 is a diagram for explaining an example of the operation of the power converter 1 when the synchronous rectification period becomes the second set value in the third example.

[0143] V in FIG. ｇｓ＿Ｄｅｔ１ 17, the transistor 102 is in an ON state. Also, as shown in the amplification factor of FIG. 17, the amplification factor of the amplifier circuit 106 is set to 1. ｇｓ As shown in Figure 17, when the switch 24 is in the off state, the voltage across the switch 24 is the voltage at the terminal t3 (output voltage). When the switch 24 is turned on, both ends of the switch 24 are short-circuited, so the voltage across the switch 24 is 0V. ｓｅｃ When transistor 102 is turned on, current begins to flow through switch 24, as shown in ｏ ) is reduced by the amount that the forward voltage of the anti-parallel diode is not generated in transistor 102, and may become a negative voltage as shown in (a) of Fig. 17 due to the influence of switching noise and the voltage drop due to the on-resistance of switch 24. This causes erroneous detection as shown in (b) of Fig. 17.

[0144] As shown in (c) of FIG. 17, the controller 40 lengthens the synchronous rectification period, which is the on-period of the switch 24, until the diode mode is no longer detected. However, if it continues to be detected that the switch 24 is in the diode mode, the controller 40 lengthens the synchronous rectification period, and as shown in (d) of FIG. 17, the synchronous rectification period is lengthened to the second set value. When the synchronous rectification period is lengthened to the second set value, the transistor 102 is in the on-state, and the difference between the voltage generated in the diode 101 and the voltage across the switch 24, that is, the voltage (V ｏ ) may become too close to the threshold (for example, 0 V) ​​and exceed (fall below) the threshold due to the influence of noise, causing the detection circuit 100 to erroneously detect the diode mode.

[0145] Therefore, when the controller 40 detects that the synchronous rectification period is equal to the second set value while the transistor 102 is in the on state, it turns off the transistor 102 as shown in (e) of FIG. 17 and reduces the amplification factor of the amplifier circuit 106 as shown in (f) of FIG. 17. As a result, the voltage (V ｏ ) is the forward voltage (Vsd ＿Ｄｅｔ１ ) and, as shown in FIG. 17(h), the voltage (V ｏ ) is reduced to the voltage (V ｏ ')

[0146] As shown in (i) of FIG. 17, when the switch 24 is turned off in a state where no current flows through the switch 24, the difference, i.e., the voltage (V ｏ The change in voltage (V ｏ Even if the voltage Vcc is affected by noise, the voltage Vcc is less likely to exceed the threshold (specifically, is less likely to fall below 0 V), thereby suppressing false detection.

[0147] Then, if the diode mode is not detected as shown in (k) of FIG. 17, the controller 40 shortens the synchronous rectification period until the diode mode is detected when the switch 24 is turned off, as shown in (l) of FIG. 17, and searches for the optimal synchronous rectification period.

[0148] 17, the timing of turning on and off the transistor 102 is not particularly specified, but the transistor 102 may be turned on and off at specific timing, as in the first example. Also, in the example shown in Fig. 17, the timing of reducing the gain of the amplifier circuit 106 and releasing the reduction is not particularly specified, but the gain of the amplifier circuit 106 may be reduced and the reduction may be released at specific timing, as in the second example.

[0149] (Other Embodiments) As described above, the embodiments have been described as examples of the technology according to the present disclosure. However, the technology according to the present disclosure is not limited to these, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made as appropriate. For example, the following modifications are also included in one embodiment of the present disclosure.

[0150] For example, the present disclosure can be realized not only as a power converter, but also as a control method including steps (processing) performed by components that make up the power converter (for example, the detection circuit 100 and the controller 40).

[0151] 18 and 19 are flowcharts showing an example of a control method according to another embodiment.

[0152] The control method is a power converter control method, and the power converter includes a primary-side circuit having a plurality of switches and a secondary-side circuit having a plurality of synchronous rectifier switches. The secondary-side circuit further includes a detection diode and a detection transistor connected in series, and an anti-parallel diode connected to the detection transistor. As shown in Fig. 18 , the control method detects a voltage across a main transistor, which is one of the synchronous rectifier switches, via the detection diode and the detection transistor (step S11), and detects whether the main transistor is in diode mode when it is turned off based on a change in the voltage across the main transistor when it is turned off (step S12). The diode mode is a mode in which current flows through the anti-parallel diode connected to the main transistor.

[0153] The control method is a power converter control method, in which the power converter includes a primary-side circuit having a plurality of switches and a secondary-side circuit having a plurality of synchronous rectifier switches. The secondary-side circuit further includes a detection diode and an amplifier circuit. As shown in Fig. 19 , the control method detects the voltage across a main transistor, which is one of the synchronous rectifier switches, via the detection diode and the amplifier circuit (step S21), and detects whether the main transistor is in diode mode when it is turned off based on a change in the voltage across the main transistor when it is turned off (step S22). The diode mode is a mode in which current flows through an anti-parallel diode connected to the main transistor.

[0154] For example, the present disclosure can be realized as a program for causing a computer (processor) to execute steps included in the control method. Furthermore, the present disclosure can be realized as a non-transitory computer-readable recording medium, such as a CD-ROM, on which the program is recorded.

[0155] For example, when the present disclosure is realized as a program (software), each step is performed by running the program using hardware resources such as a computer's CPU, memory, input / output circuits, etc. In other words, each step is performed by the CPU acquiring data from memory or input / output circuits, etc., performing calculations, and outputting the calculation results to memory or input / output circuits, etc.

[0156] In the above-described embodiments, each component included in the power converter may be configured with dedicated hardware, or may be realized by executing a software program suitable for each component. Each component may be realized by a program execution unit such as a CPU or processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory.

[0157] Some or all of the functions of the power converter according to the above-described embodiments are typically realized as an LSI, which is an integrated circuit. These may be individually integrated into single chips, or some or all of them may be integrated into a single chip. Furthermore, the integrated circuit is not limited to an LSI, and may be realized using a dedicated circuit or a general-purpose processor. It is also possible to use an FPGA (Field Programmable Gate Array) that can be programmed after LSI manufacturing, or a reconfigurable processor that can reconfigure the connections and settings of circuit cells within the LSI.

[0158] Furthermore, if an integrated circuit technology that can replace LSI emerges due to advances in semiconductor technology or other derivative technologies, that technology may naturally be used to integrate the components included in the power converter.

[0159] In addition, this disclosure also includes forms obtained by making various modifications to the embodiments that a person skilled in the art would think of, and forms realized by arbitrarily combining the components and functions in each embodiment within the scope of the present disclosure.

[0160] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0161] (Technology 1) A power converter includes a primary-side circuit having a plurality of switches, a secondary-side circuit having a plurality of synchronous rectification switches, and a controller that controls the primary-side circuit and the secondary-side circuit. The secondary-side circuit further includes a detection circuit. The detection circuit has a detection diode and a detection transistor connected in series, and detects a voltage across a main transistor, which is one of the plurality of synchronous rectification switches, via the detection diode and the detection transistor. An anti-parallel diode is connected to the detection transistor. The detection circuit detects whether the main transistor is in diode mode when the main transistor is turned off, based on a change in the voltage across the main transistor when the main transistor is turned off. The diode mode is a mode in which current flows through the anti-parallel diode connected to the main transistor.

[0162] When the main transistor is turned off and a current flows through the anti-parallel diode of the main transistor, a voltage corresponding to the forward voltage of the anti-parallel diode of the main transistor is generated across the main transistor. Without a detection transistor, the detection circuit may not be able to correctly detect whether a voltage corresponding to the forward voltage of the anti-parallel diode of the main transistor is generated across the main transistor, depending on whether the difference between the voltage generated across the detection diode (forward voltage of the detection diode) when the main transistor is turned off and the voltage generated across the main transistor has changed to exceed a threshold value. That is, without a detection transistor, the detection circuit may not be able to correctly detect whether the main transistor is in diode mode. This difference may become unstable due to noise, and the difference may exceed the threshold value, resulting in the main transistor being detected as being in diode mode even when it is not. To address this issue, a detection transistor is connected in series with the detection diode. By turning off the detection transistor, the difference is increased by the voltage generated across the anti-parallel diode of the detection transistor, making it less likely to exceed the threshold value even when affected by noise. This prevents the main transistor from being detected as being in diode mode even when it is not (called a false detection). This improves the accuracy of diode mode detection, which allows synchronous rectification to be performed normally and improves power conversion efficiency.

[0163] It is also possible to detect the current flowing through the anti-parallel diode of the main transistor when the main transistor is turned off (i.e., diode mode) by using a Hall sensor or a shunt resistor. However, using a Hall sensor would result in a large power converter. Furthermore, using a shunt resistor would result in loss due to the insertion of the resistor. The present disclosure allows for diode mode detection without using a Hall sensor or a shunt resistor, thereby improving the accuracy of diode mode detection while miniaturizing and reducing loss in the power converter.

[0164] (Technology 2) In the power converter according to Technology 1, the controller shortens a synchronous rectification period, which is an on-period of each of the plurality of synchronous rectification switches, until the diode mode is detected when the main transistor is turned off, and turns on the detection transistor when it detects that the synchronous rectification period has reached a first set value while the detection transistor is in an off state.

[0165] If the controller does not detect that the main transistor is in diode mode, it shortens the synchronous rectification period until it reaches the first set value. In this case, the detection transistor of the detection circuit is off, which may cause the difference to deviate too far from the threshold, preventing the detection circuit from properly detecting diode mode. Therefore, by turning on the detection transistor in this case, the change in the difference can be increased, making it easier for the difference to exceed the threshold. This prevents the main transistor from being unable to detect diode mode even when it is in diode mode (referred to as "non-detection").

[0166] (Technology 3) The power converter according to Technology 2, wherein the controller turns on the detection transistor in synchronization with the turning off of the main transistor when the detection transistor is in an off state.

[0167] For example, if the detection transistor is turned on before the main transistor is turned off, the difference may easily exceed the threshold due to the effects of switching noise and the voltage drop due to the on-resistance of the main transistor, which may result in a false detection of diode mode. Therefore, by turning on the detection transistor in synchronization with the turn-off of the main transistor, false detection can be suppressed.

[0168] (Technology 4) In the power converter described in Technology 1, the controller lengthens a synchronous rectification period, which is an on-period of each of the plurality of synchronous rectification switches, until the diode mode is no longer detected when the main transistor is turned off, and turns off the detection transistor when it detects that the synchronous rectification period has reached a second set value while the detection transistor is in the on-state.

[0169] If the main transistor continues to be detected as being in diode mode, the controller lengthens the synchronous rectification period until the synchronous rectification period reaches the second set value. In this case, the detection transistor of the detection circuit is in the on state, and the difference may become too close to the threshold and exceed the threshold due to the influence of noise, causing the detection circuit to falsely detect diode mode. Therefore, by turning off the detection transistor in such a case, the difference moves away from the threshold, making it less likely to exceed the threshold even under the influence of noise, thereby suppressing false detection.

[0170] (Technology 5) A power converter described in Technology 4, wherein the controller, when the detection transistor is in an on state, turns off the detection transistor in synchronization with the turning on of the main transistor, and turns on the detection transistor in synchronization with the turning off of the main transistor.

[0171] For example, if the detection transistor is in the on state after the main transistor is turned on or before the main transistor is turned off, the difference may be more likely to exceed the threshold if it is affected by switching noise and the voltage drop due to the on-resistance of the main transistor, which could result in a false detection of diode mode. Therefore, by turning off the detection transistor in synchronization with the turn-on of the main transistor and turning on the detection transistor in synchronization with the turn-off of the main transistor, false detection can be suppressed.

[0172] (Technology 6) The detection circuit has two or more detection transistors, and the controller controls the on and off of each of the two or more detection transistors according to the detection state of the diode mode by the detection circuit. A power converter according to any one of technologies 1 to 5.

[0173] According to this, when a false detection occurs, the number of detection transistors to be turned off can be gradually increased to adjust the difference so that it is neither too far from nor too close to the threshold value, thereby suppressing false detection and also suppressing non-detection.Furthermore, when a non-detection occurs, the number of detection transistors to be turned on can be gradually increased to adjust the difference so that it is neither too close to nor too far from the threshold value, thereby suppressing false detection and also suppressing non-detection.

[0174] (Technology 7) A power converter includes a primary-side circuit having a plurality of switches, a secondary-side circuit having a plurality of synchronous rectification switches, and a controller that controls the primary-side circuit and the secondary-side circuit. The secondary-side circuit further includes a detection circuit. The detection circuit includes a detection diode and an amplifier circuit. The detection circuit detects the voltage across a main transistor, which is one of the plurality of synchronous rectification switches, via the detection diode and the amplifier circuit. The amplifier circuit has a variable gain function and is provided in the input stage or output stage of the detection circuit. The detection circuit detects whether the main transistor is in diode mode when the main transistor is turned off, based on a change in the voltage across the main transistor when the main transistor is turned off. The diode mode is a mode in which current flows through an anti-parallel diode connected to the main transistor.

[0175] When the main transistor is turned off and a current flows through the anti-parallel diode of the main transistor, a voltage corresponding to the forward voltage of the anti-parallel diode of the main transistor is generated across the main transistor. Without an amplifier circuit, the detection circuit may not be able to correctly detect whether a voltage corresponding to the forward voltage of the anti-parallel diode of the main transistor is generated across the main transistor, depending on whether the difference between the voltage generated across the detection diode (forward voltage of the detection diode) when the main transistor is turned off and the voltage generated across the main transistor has changed to exceed a threshold value. In other words, without an amplifier circuit, the detection circuit may not be able to correctly detect whether the main transistor is in diode mode. Because the forward voltage of the anti-parallel diode of the main transistor is small, even if a voltage corresponding to the forward voltage of the anti-parallel diode of the main transistor is generated across the main transistor, the difference only slightly exceeds the threshold value. Depending on the detection accuracy of the detection circuit, it may not be possible to detect that the main transistor is in diode mode. Therefore, an amplifier circuit is provided in the input or output stage of the detection circuit. If an amplifier circuit is provided in the input stage of the detection circuit, the voltage generated across the main transistor can be amplified, thereby increasing the change in the difference. If an amplifier circuit is provided at the output stage of the detection circuit, the difference is amplified, and the change in the difference can be increased. This can prevent the main transistor from being in diode mode when it is not detected (referred to as "non-detection"). This improves the accuracy of diode mode detection. The improved accuracy of diode mode detection allows for normal synchronous rectification, improving power conversion efficiency.

[0176] (Technology 8) A power converter according to Technology 7, wherein the controller shortens a synchronous rectification period, which is an on-period of each of the plurality of synchronous rectification switches, until the diode mode is detected when the main transistor is turned off, and increases the amplification factor of the amplifier circuit when it detects that the synchronous rectification period has reached a first set value.

[0177] If the main transistor is not detected as being in diode mode at all, the controller shortens the synchronous rectification period until it reaches the first set value. In this case, the difference only slightly exceeds the threshold, and the detection circuit may not be able to properly detect diode mode. Therefore, by increasing the amplification factor of the amplifier circuit in such a case, the change in the difference can be increased, making it easier for the difference to significantly exceed the threshold. This prevents non-detection.

[0178] (Technology 9) The power converter according to Technology 8, wherein the controller increases the gain of the amplifier circuit in synchronization with the turning off of the main transistor.

[0179] For example, if the gain of the amplifier circuit is increased before the main transistor is turned off, and the difference is affected by factors such as switching noise and a voltage drop due to the on-resistance of the main transistor, these effects may also be amplified, making it more likely to exceed the threshold, leading to a risk of false detection of diode mode. Therefore, false detection can be suppressed by increasing the gain of the amplifier circuit in synchronization with the turn-off of the main transistor.

[0180] (Technology 10) The power converter described in Technology 7, wherein the controller lengthens a synchronous rectification period, which is an on-period of each of the plurality of synchronous rectification switches, until the diode mode is no longer detected when the main transistor is turned off, and reduces the amplification factor of the amplifier circuit when it detects that the synchronous rectification period has reached a second set value.

[0181] If the main transistor continues to be detected as being in diode mode, the controller lengthens the synchronous rectification period until the synchronous rectification period reaches the second set value. In this case, the difference may exceed the threshold due to noise, causing the detection circuit to falsely detect diode mode. Therefore, by reducing the amplification factor of the amplifier circuit in such a case, the influence of noise can be reduced, and the difference can be prevented from exceeding the hysteresis, which is the range within which a comparator that compares the difference with a threshold does not react, thereby suppressing false detection.

[0182] (Technology 11) A power converter described in Technology 10, wherein the controller reduces the gain of the amplifier circuit in synchronization with the main transistor being turned on, and cancels the reduction in the gain of the amplifier circuit in synchronization with the main transistor being turned off.

[0183] For example, if the gain of the amplifier circuit is not reduced after the switch 24 is turned on or before the switch 24 is turned off, the difference may easily exceed the threshold when affected by switching noise and the voltage drop due to the on-resistance of the main transistor, which may result in a false detection of diode mode. Therefore, false detection can be suppressed by reducing the gain of the amplifier circuit in synchronization with the turn-on of the main transistor and canceling the reduction in the gain of the amplifier circuit in synchronization with the turn-off of the main transistor.

[0184] (Technology 12) The detection circuit further has an amplifier circuit, and detects the voltage across the main transistor via the detection diode, the detection transistor, and the amplifier circuit, and the amplifier circuit has a variable amplification factor function and is provided in the input stage or output stage of the detection circuit. This is a power converter described in Technology 1.

[0185] If an amplifier circuit is provided in the input stage of the detection circuit in addition to the detection transistor, the voltage generated in the main transistor can be amplified, thereby increasing the change in the difference. If an amplifier circuit is provided in the output stage of the detection circuit in addition to the detection transistor, the difference can be amplified, thereby increasing the change in the difference. This can reduce non-detection. By providing both the detection transistor and the amplifier circuit, the detection accuracy in the diode mode can be further improved.

[0186] (Technology 13) The power converter described in Technology 12, wherein the controller shortens a synchronous rectification period, which is an on-period of each of the plurality of synchronous rectification switches, until the diode mode is detected when the main transistor is turned off, and when the controller detects that the synchronous rectification period is at a first set value while the detection transistor is in an off state, turns on the detection transistor and increases the amplification factor of the amplifier circuit.

[0187] If the main transistor is not detected as being in diode mode at all, the controller shortens the synchronous rectification period until it reaches the first set value. In this case, the detection transistor of the detection circuit is in the off state, which may cause the difference to only slightly exceed the threshold, preventing the detection circuit from properly detecting diode mode. Therefore, by turning on the detection transistor and increasing the amplification factor of the amplifier circuit in such a case, the change in the difference can be increased, making it easier for the difference to exceed the threshold. This prevents undetected states.

[0188] (Technology 14) The power converter described in Technology 12, wherein the controller lengthens a synchronous rectification period, which is an on-period of each of the plurality of synchronous rectification switches, until the diode mode is no longer detected when the main transistor is turned off, and when the controller detects that the synchronous rectification period is at a second set value while the detection transistor is in the on-state, turns off the detection transistor and reduces the amplification factor of the amplifier circuit.

[0189] If the main transistor continues to be detected as being in diode mode, the controller lengthens the synchronous rectification period until it reaches the second set value. In this case, the detection transistor of the detection circuit is in the on state, and the difference may approach the threshold value too much and exceed the threshold value due to the influence of noise, causing the detection circuit to falsely detect diode mode. Therefore, by turning off the detection transistor and reducing the amplification factor of the amplifier circuit in such a case, the difference is less likely to exceed the threshold value even when affected by noise, thereby suppressing false detection.

[0190] (Technology 15) A control method for a power converter, the power converter comprising: a primary-side circuit having a plurality of switches; and a secondary-side circuit having a plurality of synchronous rectifier switches, the secondary-side circuit further comprising a detection diode and a detection transistor connected in series, and an anti-parallel diode connected to the detection transistor. The control method detects a voltage across a main transistor, which is one of the plurality of synchronous rectifier switches, via the detection diode and the detection transistor, and detects whether the main transistor is in diode mode when the main transistor is turned off based on a change in the voltage across the main transistor when the main transistor is turned off. The diode mode is a mode in which current flows through the anti-parallel diode connected to the main transistor.

[0191] This makes it possible to provide a control method that can improve the detection accuracy of the diode mode.

[0192] The power converter and the control method thereof according to the present disclosure can be applied to power converters such as LLC converters, etc. In this way, the power converter and the control method thereof according to the present disclosure are industrially useful.

[0193] REFERENCE SIGNS LIST 1 power converter 10 primary side circuit 11, 12, 13, 14, 21, 22, 23, 24 switch 20 secondary side circuit 30 synchronous rectification unit 40 controller 100 detection circuit 101 diode 102, 102a transistor 103 comparator 104, R １ , R ２ａ , R ２ｂ , R ２Ｎ Resistor 105, Cin, Cout, Cr Capacitor 106 Amplifier circuit Lr, Lm Inductors N1, N2, N3, N4 Node T Transformer t1, t2, t3, t4 Terminals

Claims

1. A power converter comprising: a primary side circuit having a plurality of switches; a secondary side circuit having a plurality of synchronous rectification switches; and a controller that controls the primary side circuit and the secondary side circuit, wherein the secondary side circuit further comprises a detection circuit having a detection diode and a detection transistor connected in series, the detection circuit detecting a voltage across a main transistor, which is one of the plurality of synchronous rectification switches, via the detection diode and the detection transistor, and an anti-parallel diode connected to the detection transistor, and the detection circuit detecting whether the main transistor is in diode mode when the main transistor is turned off based on a change in the voltage across both ends when the main transistor is turned off, and the diode mode is a mode in which a current flows through the anti-parallel diode connected to the main transistor.

2. The power converter according to claim 1, wherein the controller shortens a synchronous rectification period, which is an on-period of each of the plurality of synchronous rectification switches, until the diode mode is detected when the main transistor is turned off, and turns on the detection transistor when it detects that the synchronous rectification period is at a first set value while the detection transistor is in an off state.

3. The power converter according to claim 2, wherein the controller turns on the detection transistor in synchronization with the turning off of the main transistor when the detection transistor is in the off state.

4. The power converter according to claim 1, wherein the controller lengthens a synchronous rectification period, which is an on-period of each of the plurality of synchronous rectification switches, until the diode mode is no longer detected when the main transistor is turned off, and turns off the detection transistor when it detects that the synchronous rectification period is at a second set value while the detection transistor is in the on state.

5. The power converter according to claim 4, wherein the controller, when the detection transistor is in an on state, turns off the detection transistor in synchronization with the turning on of the main transistor, and turns on the detection transistor in synchronization with the turning off of the main transistor.

6. The power converter according to any one of claims 1 to 5, wherein the detection circuit has two or more detection transistors, and the controller controls the on and off of each of the two or more detection transistors according to the state of the diode mode detected by the detection circuit.

7. A power converter comprising: a primary side circuit having a plurality of switches; a secondary side circuit having a plurality of synchronous rectification switches; and a controller for controlling the primary side circuit and the secondary side circuit, wherein the secondary side circuit further comprises a detection circuit having a detection diode and an amplifier circuit, the detection circuit detecting a voltage across a main transistor which is one of the plurality of synchronous rectification switches via the detection diode and the amplifier circuit, the amplifier circuit having a variable amplification factor and being provided in an input stage or an output stage of the detection circuit, wherein the detection circuit detects whether the main transistor is in a diode mode when the main transistor is turned off based on a change in the voltage across both ends when the main transistor is turned off, and the diode mode is a mode in which a current flows through an anti-parallel diode connected to the main transistor.

8. The power converter according to claim 7, wherein the controller shortens a synchronous rectification period, which is an on-period of each of the plurality of synchronous rectification switches, until the diode mode is detected when the main transistor is turned off, and increases the amplification factor of the amplifier circuit when it is detected that the synchronous rectification period has reached a first set value.

9. The power converter according to claim 8, wherein the controller increases the gain of the amplifier circuit in synchronization with the turning off of the main transistor.

10. The power converter according to claim 7, wherein the controller lengthens a synchronous rectification period, which is an on-period of each of the plurality of synchronous rectification switches, until the diode mode is no longer detected when the main transistor is turned off, and reduces the amplification factor of the amplifier circuit when it detects that the synchronous rectification period has reached a second set value.

11. The power converter according to claim 10, wherein the controller reduces the gain of the amplifier circuit in synchronization with the main transistor being turned on, and cancels the reduction in the gain of the amplifier circuit in synchronization with the main transistor being turned off.

12. The power converter according to claim 1, wherein the detection circuit further includes an amplifier circuit, which detects the voltage across the main transistor via the detection diode, the detection transistor, and the amplifier circuit, and the amplifier circuit has a variable gain function and is provided in an input stage or an output stage of the detection circuit.

13. The power converter according to claim 12, wherein the controller shortens a synchronous rectification period, which is an on-period of each of the plurality of synchronous rectification switches, until the diode mode is detected when the main transistor is turned off, and when it detects that the synchronous rectification period has reached a first set value while the detection transistor is in an off state, turns on the detection transistor and increases the amplification factor of the amplifier circuit.

14. The power converter according to claim 12, wherein the controller lengthens a synchronous rectification period, which is an on-period of each of the plurality of synchronous rectification switches, until the diode mode is no longer detected when the main transistor is turned off, and when it detects that the synchronous rectification period has reached a second set value while the detection transistor is in the on state, turns off the detection transistor and reduces the amplification factor of the amplifier circuit.

15. A control method for a power converter, the power converter comprising: a primary side circuit having a plurality of switches; and a secondary side circuit having a plurality of synchronous rectifier switches; the secondary side circuit further having a detection diode and a detection transistor connected in series, with an anti-parallel diode connected to the detection transistor; the control method detecting, via the detection diode and the detection transistor, a voltage across a main transistor which is one of the plurality of synchronous rectifier switches; and detecting, based on a change in the voltage across both ends when the main transistor is turned off, whether the main transistor is in diode mode when the main transistor is turned off; the diode mode is a mode in which current flows through the anti-parallel diode connected to the main transistor.

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