Rectification circuit and ac / DC converter

Abstract

To downsize an AC / DC converter.SOLUTION: In a rectification circuit 200, a bridge circuit 210 rectifies an AC voltage VAC. A voltage clamp circuit 220 includes a clamp transistor Q3 and a smoothing capacitor C1 connected sequentially in series between an output terminal of the bridge circuit 210 and a ground line, and controls turn-on and turn-off of the clamp transistor Q3 in accordance with an output voltage VRECT of the bridge circuit 210. A post-stage DC / DC converter 300 is connected in parallel to the smoothing capacitor C1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a rectifier circuit and an AC / DC converter. [Background technology]

[0002] AC / DC converters are used to supply power from commercial AC power sources to electronic devices. An AC / DC converter includes a rectifier circuit that rectifies the AC voltage, and a DC / DC converter that converts the output voltage of the rectifier circuit to a voltage level suitable for the load.

[0003] AC / DC converters of 75W or less that do not require power factor correction (PFC) typically use an AC rectifier circuit that combines a diode bridge and an electrolytic capacitor. In this configuration, the electrolytic capacitor generates a voltage that is approximately √2 times the AC input voltage. This means that it is necessary to select an electrolytic capacitor with a high voltage resistance of, for example, 400V. This electrolytic capacitor has been an obstacle to miniaturizing and reducing the cost of AC / DC converters. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2024-001433

[0005] [overview] The present disclosure has been made in view of the above circumstances, and one of its exemplary purposes is to reduce the size of an AC / DC converter.

[0006] One aspect of the present disclosure relates to a rectifier circuit. The rectifier circuit includes a bridge circuit that rectifies an AC voltage, and a voltage clamp circuit that includes a clamp transistor and a smoothing capacitor connected in series between an output terminal of the bridge circuit and a ground line, and that controls the on / off of the clamp transistor in accordance with the output voltage of the bridge circuit. The ground line is shared with the ground line of a downstream DC / DC converter.

[0007] Any combination of the above elements, or mutual substitution of elements or expressions between methods, devices, systems, etc., are also valid aspects of the present invention or the present disclosure. Furthermore, the description in this section (Means for Solving the Problems) does not explain all essential features of the present invention, and therefore, subcombinations of the described features may also constitute the present invention. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a circuit diagram of an AC / DC converter according to an embodiment. [Figure 2] FIG. 2 is a waveform diagram illustrating the operation of the AC / DC converter of FIG. [Figure 3] FIG. 3 is a circuit diagram of an AC / DC converter according to a comparative technique. [Figure 4] FIG. 4 is a circuit diagram of an AC / DC converter according to an embodiment. [Figure 5] FIG. 5 is a waveform diagram illustrating the operation of the AC / DC converter of FIG.

[0009] [Detailed explanation] (Outline of the embodiment) A summary of some exemplary embodiments of the present disclosure is provided. This summary is intended to provide a simplified overview of some concepts of one or more embodiments in order to provide a basic understanding of the embodiments as a prelude to the more detailed description that follows. It is not intended to limit the scope of the invention or disclosure. This summary is not an exhaustive overview of all possible embodiments, and is not intended to identify key elements of all embodiments or to delineate the scope of some or all aspects. For convenience, the term "one embodiment" may refer to one embodiment (example or variant) or multiple embodiments (examples or variants) disclosed herein.

[0010] A rectifier circuit according to one embodiment includes a bridge circuit that rectifies an AC voltage, and a voltage clamp circuit that includes a clamp transistor and a smoothing capacitor connected in series between an output terminal of the bridge circuit and a ground line, and that controls the on / off of the clamp transistor in accordance with the output voltage of the bridge circuit. The ground line is shared with the ground line of a downstream DC / DC converter.

[0011] With this configuration, clamping the voltage across the smoothing capacitor reduces the voltage resistance required of the smoothing capacitor. This allows the use of a small electrolytic capacitor as the smoothing capacitor, resulting in a more compact and cost-effective device. Furthermore, since the reference voltage of the smoothing capacitor and the downstream DC / DC converter are common (ground common), driving and controlling the downstream DC / DC converter becomes easier.

[0012] In one embodiment, the DC / DC converter may have a first bootstrap circuit including a first rectifying element, a first bootstrap line, and a first bootstrap capacitor. The clamp transistor may be an N-type transistor. The voltage clamp circuit may include a gate driver having an output connected to a control terminal of the N-type transistor, an output node connected to the control terminal of the N-type transistor, a lower power supply node connected to the capacitor, and an upper power supply node, a second bootstrap circuit including a second bootstrap line connected to the upper power supply node of the gate driver, a second bootstrap capacitor connected between the second bootstrap line and the capacitor, and a second rectifying element connected between the second bootstrap line and the first bootstrap line.

[0013] According to this configuration, the gate high voltage required to drive the clamp transistor can be generated simply by adding the second bootstrap circuit, without adding a separate power supply.

[0014] An AC / DC converter according to one embodiment may include any of the rectifier circuits described above, and a DC / DC converter connected in parallel to the capacitor of the rectifier circuit and having a common ground line.

[0015] In one embodiment, the DC / DC converter may include a high-side transistor, a low-side transistor, and a non-isolated gate drive circuit that drives the high-side transistor and the low-side transistor. As described above, the smoothing capacitor of the rectifier circuit and the DC / DC converter share a common reference voltage (ground common), so the drive circuit for the switching element of the DC / DC converter in the subsequent stage can be configured as a simple, non-isolated circuit.

[0016] (Embodiment) Preferred embodiments will be described below with reference to the drawings. The same or equivalent components, parts, and processes shown in each drawing will be given the same reference numerals, and redundant explanations will be omitted as appropriate. Furthermore, the embodiments are examples and do not limit the disclosure and invention, and all features and combinations thereof described in the embodiments are not necessarily essential to the disclosure and invention.

[0017] In this specification, "a state in which component A is connected to component B" includes not only a case in which component A and component B are directly physically connected to each other, but also a case in which component A and component B are indirectly connected to each other via other components that do not substantially affect the electrical connection between them or that do not impair the function or effect achieved by their connection.

[0018] Similarly, "a state in which component C is provided between component A and component B" includes not only cases in which components A and C, or components B and C, are directly connected, but also cases in which they are indirectly connected via other components that do not substantially affect the electrical connection state between them or impair the functions or effects achieved by their combination.

[0019] 1 is a circuit diagram of an AC / DC converter 100 according to an embodiment. The AC / DC converter 100 receives an AC voltage V AC DC voltage V OUT Convert to.

[0020] The AC / DC converter 100 includes a rectifier circuit 200 and a DC / DC converter 300 .

[0021] The rectifier circuit 200 outputs AC voltage V AC is rectified and the DC input voltage V IN The DC / DC converter 300 converts the DC input voltage V IN , the DC output voltage V OUT Convert to.

[0022] The rectifier circuit 200 includes a bridge circuit 210 and a voltage clamp circuit 220. The bridge circuit 210 is a diode bridge circuit that converts an AC voltage V AC is full-wave rectified.

[0023] The voltage clamp circuit 220 includes a clamp transistor Q3 and a smoothing capacitor C1 connected in series between the output terminal of the bridge circuit 210 and the ground line 102. The voltage clamp circuit 220 regulates the output voltage (called a rectified voltage) V RECT The clamp transistor Q3 is turned on and off in response to the voltage V generated across the smoothing capacitor C1. C1 is the input voltage V IN is supplied to the subsequent DC / DC converter 300. That is, the switching circuit (half-bridge circuit) of the DC / DC converter 300 is connected in parallel with the smoothing capacitor C1.

[0024] The voltage clamp circuit 220 includes a controller 222 and a gate driver 224. The controller 222 controls the output voltage V RECT The controller 222 generates a control signal S1 that instructs the clamp transistor Q3 to be turned on or off based on the voltage V between both ends of the smoothing capacitor C1. C1 However, at a certain threshold voltage V TH It is sufficient to generate it so that it does not exceed .

[0025] For example, the controller 222 may RECT is the threshold voltage V TH When the rectified voltage V exceeds the threshold voltage V, the controller 222 changes the control signal S1 to a level corresponding to turning off the clamp transistor Q3. RECT is the input voltage V IN When the voltage Vcc drops below 0 V, the control signal S1 is changed to a level corresponding to turning on the clamp transistor Q3.

[0026] The gate driver 224 controls the gate voltage V of the clamp transistor Q3 based on the control signal S1.G3 Control.

[0027] There are no particular limitations on the topology of the DC / DC converter 300, and an isolated or non-isolated converter can be used. For example, the DC / DC converter 300 may be an asymmetrical half-bridge (AHB) converter.

[0028] The DC / DC converter 300 includes a half-bridge circuit 310, a transformer T1, a resonant capacitor C2, a diode D1, an output capacitor C3, a controller 320, and a gate driver 330. The half-bridge circuit 310 includes a high-side transistor Q1 and a low-side transistor Q2. The controller 320 controls the output voltage V OUT The gate driver 330 generates a control signal S2, which is a pulse signal, so that the gate voltage V of the high-side transistor Q1 and the low-side transistor Q2 approaches a target level. The method for generating the control signal S2 is not particularly limited, and pulse width modulation, pulse frequency modulation, etc. may be used. The gate driver 330 controls the gate voltage V of the high-side transistor Q1 and the low-side transistor Q2 in response to the control signal S2. G1 ,V G2 occurs.

[0029] The controller 222, the gate driver 224, the controller 320, and the gate driver 330 may be integrated on a single semiconductor substrate to form a control IC (Integrated Circuit) 400. The controller 222, the controller 320, and the gate driver 330 are connected to the voltage clamp circuit 220 and a common ground line 102, and operate based on a common reference voltage (ground voltage).

[0030] The above is the configuration of the AC / DC converter 100. Next, the operation thereof will be described.

[0031] 2 is a waveform diagram illustrating the operation of the AC / DC converter 100 of FIG. 2. From the top, the waveform diagram shows the rectified voltage V RECT and the voltage V of the smoothing capacitor C1C1 (Input voltage V IN ), the charging current I flowing through the smoothing capacitor C1 C , the voltage V of the ground line 102 GND , a control signal S1 is shown which instructs the clamp transistor Q3 to be on or off.

[0032] Rectified voltage V RECT is the AC voltage V AC The control signal S1 is high, that is, the clamp transistor Q3 is on during the period T ON , V RECT >V C When this occurs, the clamp transistor Q3 is charged and the voltage V of the smoothing capacitor C1 C is the rectified voltage V RECT It rises following the

[0033] At time t1, the rectified voltage V RECT is the threshold voltage V TH When the voltage V reaches 1 V, the control signal S1 goes low and the clamp transistor Q3 turns off. OFF The smoothing capacitor C1 is discharged by the input current of the DC / DC converter 300 and decreases over time.

[0034] At time t2, the rectified voltage V RECT is the voltage V of the smoothing capacitor C1 C1 When the voltage V goes lower than V, the control signal S1 goes high and the clamp transistor Q3 turns on. Immediately after the clamp transistor Q3 turns on, V RECT <V C Therefore, the smoothing capacitor C1 is not charged. At time t3, V RECT >V C This causes the smoothing capacitor C1 to start charging. The AC / DC converter 100 repeats the above operations.

[0035] Next, advantages of the AC power supply 2 according to the embodiment will be described. The advantages of the AC / DC converter 100 will become clear when compared with a comparative technique. Therefore, the comparative technique will be described.

[0036] 3 is a circuit diagram of an AC / DC converter 100R according to the comparative technology. In a voltage clamp circuit 220R according to the comparative technology, the positions of a smoothing capacitor C1R and a clamp transistor Q3R are interchanged, with the smoothing capacitor C1R being placed on the higher potential side than the clamp transistor Q3R.

[0037] The voltage V across the smoothing capacitor C1R C1 is the input voltage V IN The voltage V is supplied to the DC / DC converter 300R at the subsequent stage. Therefore, the ground line 202 of the rectifier circuit 200R and the ground line 302 of the DC / DC converter 300R have different potentials. Furthermore, the ground line 302 of the DC / DC converter 300R is floating, and its voltage V GND2 fluctuates over time.

[0038] The controller 320 of the DC / DC converter 300R controls the ground voltage V GND1 , while the gate driver 330 of the DC / DC converter 300R operates based on a floating ground voltage V GND2 It operates based on the standard.

[0039] In this configuration, the DC / DC converter 300R is connected to a floating ground voltage V GND2 Depending on the routing (ground pattern) of the ground line 302 on the printed circuit board, there is a problem that common mode noise increases.

[0040] Furthermore, the control signals S2H and S2L generated by the controller 320 cannot be directly transmitted to the gate driver 330, and an insulated gate drive circuit 330R must be used, which results in a complex circuit and high costs.

[0041] In contrast, in the AC / DC converter 100 of FIG. 1, the rectifier circuit 200 and the DC / DC converter 300 are connected to a common ground line 102, and a common, non-floating, fixed ground voltage V GND Therefore, the DC / DC converter 300 can reduce the influence of common mode noise.

[0042] Furthermore, in the AC / DC converter 100 of FIG. 1, a non-insulated gate driver 330 can be employed, which reduces the number of circuit components and enables cost reduction.

[0043] The present disclosure covers various devices and methods that can be understood as the block diagram or circuit diagram of Figure 1 or derived from the above description, and is not limited to a specific configuration. Below, more specific configuration examples and examples will be described not to narrow the scope of the present disclosure, but to aid in understanding and clarify the essence and operation of the present disclosure and the present invention.

[0044] 4 is a circuit diagram of an AC / DC converter 100A according to one embodiment. First, a DC / DC converter 300A will be described.

[0045] In the DC / DC converter 300A, the high-side transistor Q1 is an N-type transistor (NMOS transistor), and the DC / DC converter 300A has a first bootstrap circuit 340. A first bootstrap capacitor C4 is connected between a first bootstrap line 342 and a switching node 312, which is the output of the half-bridge circuit 310.

[0046] The power supply circuit 240 outputs a rectified voltage V RECT When the power supply voltage V CC1 The power supply circuit 240 is a source follower type power supply circuit, and includes an N-type transistor, i.e., an NPN bipolar transistor or an NMOS transistor, and a constant voltage circuit 242. CC1can be set to, for example, about 12V.

[0047] The anode of the first rectifier element D4 of the first bootstrap circuit 340 is connected to the power supply voltage V CC1 is supplied, and its cathode is connected to the first bootstrap line 342.

[0048] The first bootstrap line 342 is connected to a first bootstrap voltage V BST1 occurs. V BST1 =V SW +V CC1 -Vf …(1) V SW is the switching voltage generated at the switching node 312, and Vf is the forward voltage of the first rectifier element D4.

[0049] The gate driver 330 includes a high-side driver 332, a level shifter 334, and a low-side driver 336. The upper power supply node of the high-side driver 332 is connected to a first bootstrap voltage V BST1 The control signal S2 generated by the controller 320 is level-shifted up via a level shifter 334 and supplied to the high-side driver 332. When the control signal S2 is at an on level (for example, high), the high-side driver 332 applies a first bootstrap voltage V BST1 This supplies a gate high voltage equivalent to V CC1 This results in -Vf, turning on the high-side transistor Q1.

[0050] The low-side driver 336 drives the low-side transistor Q2 based on the control signal S2. When the control signal S2 is at an off level (for example, low), the low-side driver 336 applies the power supply voltage V CC1This supplies a gate high voltage equivalent to V CC1 As a result, the low-side transistor Q2 turns on.

[0051] Next, the rectifier circuit 200A will be described. Since the clamp transistor Q3 is an N-type transistor, in order to turn on the clamp transistor Q3, the voltage V C1 A higher gate high voltage is required. To generate this gate high voltage, the voltage clamp circuit 220A is provided with a second bootstrap circuit 230. The second bootstrap circuit 230 generates the gate high voltage of the clamp transistor Q3 by utilizing the switching of the DC / DC converter 300A in the subsequent stage.

[0052] An output node of the gate driver 224 is connected to the control terminal (gate) of the clamp transistor Q3. A lower power supply node of the gate driver 224 is connected to an output line 226 of the voltage clamp circuit 220A.

[0053] The second bootstrap circuit 230 includes a second bootstrap line 232, a second rectifier element D5, and a second bootstrap capacitor C5. The second bootstrap line 232 is connected to the upper power supply node of the gate driver 224. The second bootstrap capacitor C5 is connected between the second bootstrap line 232 and the output line 226. The cathode of the second rectifier element D5 is connected to the second bootstrap line 232, and the anode of the second rectifier element D5 is connected to the first bootstrap line 342 of the first bootstrap circuit 340. A second bootstrap voltage V generated on the second bootstrap line 232 is connected to the upper power supply node of the gate driver 224. BST2 is supplied to the upper power supply node of the gate driver 224 as a gate high voltage.

[0054] The above is the configuration of the AC / DC converter 100A. Next, the operation of the AC / DC converter 100A will be described.

[0055] 5 is a waveform diagram illustrating the operation of the AC / DC converter 100A of FIG. 4. From the top, the waveform diagram shows the rectified voltage V RECT and the voltage V of the smoothing capacitor C1 C1 (Input voltage V IN ), power supply voltage V CC1 , a control signal S2 of the DC / DC converter 300A, and a control signal S1 of the voltage clamp circuit 220A are shown.

[0056] First bootstrap voltage V BST1 is expressed by equation (1). V BST1 =V SW +V CC1 -Vf …(1) When the high-side transistor Q1 is high, V SW =V IN Therefore, the first bootstrap voltage V BST1 is expressed by equation (2). V BST1 =V IN +V CC1 -Vf …(2)

[0057] When the high-side transistor Q1 is on, the second bootstrap capacitor C5 is connected to the first bootstrap voltage V BST1 The voltage V across the second bootstrap capacitor C5 is C5 is expressed by equation (3). V C5 =V CC1 -2 × Vf …(3) 2×Vf is the sum of the forward voltages of the first rectifier element D4 and the second rectifier element D5.

[0058] That is, the second bootstrap voltage V BST2 is expressed by equation (4). V BST2 =V IN +V C5 =V IN +V CC1 -2 × Vf …(4)

[0059] When the control signal S1 is at an on level (high), the gate driver 224 applies the second bootstrap voltage V to the gate of the clamp transistor Q3 as a gate high voltage. BST2 At this time, the gate-source voltage V of the clamp transistor Q3 GS3 is expressed by equation (5). V GS3 =V BST2 -V IN =V CC1 -2 × Vf …(5) This allows the clamp transistor Q3 to be turned on.

[0060] 4, the gate high voltage required to drive the clamp transistor Q3 can be generated simply by adding the second bootstrap circuit 230. This eliminates the need to add a separate power supply with a large circuit scale, thereby reducing the number of components and costs.

[0061] Although the embodiments of the present disclosure have been described using specific terms, this description is merely an example to facilitate understanding and does not limit the scope of the present disclosure or the claims, and the scope of the present invention is defined by the claims. Furthermore, not only the embodiments but also embodiments, examples, and modifications not described herein are included in the scope of the present invention.

[0062] (Variation 1) The circuit topology of the DC / DC converter 300 is not particularly limited, and can be selected to suit the power and application of the AC / DC converter 100. For example, the DC / DC converter 300 may be a flyback converter, a forward converter, or a full-bridge converter. In applications that do not require isolation, the DC / DC converter 300 can be a non-insulated converter such as a buck converter, a boost converter, or a buck-boost converter.

[0063] (Variation 2) 4, a technique for generating the gate high voltage of the gate driver 224 using the second bootstrap circuit 230 has been described, but the present disclosure is not limited to this. If an increase in the number of components or cost is acceptable, another power supply circuit may be added.

[0064] (Variation 3) In the embodiment, a full-wave rectifier circuit including a diode full-bridge circuit has been described as the bridge circuit 210, but a half-wave rectifier circuit may also be used. Furthermore, instead of the diode bridge circuit, a synchronous rectifier bridge circuit including four transistors may also be used, or a hybrid type of diodes and transistors may also be used.

[0065] (Addendum) One aspect of the technology disclosed in this specification can be understood as follows.

[0066] (Item 1) a bridge circuit that rectifies AC voltage; a voltage clamp circuit including a clamp transistor and a smoothing capacitor connected in series in this order between the output terminal of the bridge circuit and a ground line, the voltage clamp circuit being configured to control the on / off of the clamp transistor in accordance with the output voltage of the bridge circuit, wherein the ground line of the bridge circuit is common to the ground line of a downstream DC / DC converter.

[0067] (Item 2) the DC / DC converter has a first bootstrap circuit including a first rectifying element, a first bootstrap line, and a first bootstrap capacitor; the clamp transistor is an N-type transistor; The voltage clamp circuit a gate driver whose output is connected to the control terminal of the N-type transistor; a gate driver having an output node connected to a control terminal of the N-type transistor, a lower power supply node connected to the smoothing capacitor, and an upper power supply node; a second bootstrap circuit including: a second bootstrap line connected to the upper power supply node of the gate driver; a second bootstrap capacitor connected between the second bootstrap line and the smoothing capacitor; and a second rectifying element connected between the second bootstrap line and the first bootstrap line; Item 2. The rectifier circuit of item 1, comprising:

[0068] (Item 3) Item 1 or 2, and a rectifier circuit; a DC / DC converter connected in parallel to the smoothing capacitor of the rectifier circuit and to which the ground line is commonly connected; An AC / DC converter comprising:

[0069] (Item 4) The DC / DC converter a high-side transistor and a low-side transistor; a non-insulated gate drive circuit that drives the high-side transistor and the low-side transistor; 4. The AC / DC converter according to item 3, comprising: [Explanation of symbols]

[0070] 2...AC power supply, 100...AC / DC converter, 102...ground line, 200...rectifier circuit, 210...bridge circuit, 220...voltage clamp circuit, Q3...clamp transistor, C1...smoothing capacitor, 222...controller, 224...gate driver, 230...second bootstrap circuit, C5...second bootstrap capacitor, D5...second rectifier element, C2...resonant capacitor, C3...output capacitor, T1...transformer, Q1...high-side transistor, Q2...low Side transistor, 300...DC / DC converter, 302...ground line, 310...half bridge circuit, 312...switching node, S1...control signal, 320...controller, 330...gate driver, 332...high side driver, 334...level shifter, 336...low side driver, 340...first bootstrap circuit, 342...first bootstrap line, C4...first bootstrap capacitor, D4...first rectifier element, 400...control IC.

Claims

1. a bridge circuit that rectifies AC voltage; a voltage clamp circuit including a clamp transistor and a smoothing capacitor connected in series between the output terminal of the bridge circuit and a ground line, the voltage clamp circuit being configured to control the on / off of the clamp transistor in accordance with the output voltage of the bridge circuit; wherein the ground line is common to a ground line of a DC / DC converter in a subsequent stage.

2. the DC / DC converter has a first bootstrap circuit including a first rectifying element, a first bootstrap line, and a first bootstrap capacitor; the clamp transistor is an N-type transistor; The voltage clamp circuit a gate driver whose output is connected to the control terminal of the N-type transistor; a gate driver having an output node connected to a control terminal of the N-type transistor, a lower power supply node connected to the smoothing capacitor, and an upper power supply node; a second bootstrap circuit including: a second bootstrap line connected to the upper power supply node of the gate driver; a second bootstrap capacitor connected between the second bootstrap line and the smoothing capacitor; and a second rectifying element connected between the second bootstrap line and the first bootstrap line; 2. The rectifier circuit of claim 1, comprising:

3. A rectifier circuit according to claim 1 or 2; a DC / DC converter connected in parallel to the smoothing capacitor of the rectifier circuit and having the ground line connected in common; An AC / DC converter comprising:

4. The DC / DC converter a high-side transistor and a low-side transistor; a non-insulated gate drive circuit that drives the high-side transistor and the low-side transistor; 4. The AC / DC converter of claim 3, comprising:

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