Switching device, insulated dc / dc converter, and ac / dc converter

Abstract

To achieve a suppression of generation loss and radiation noise in a well-balanced manner.SOLUTION: A switching device (10) includes a switching transistor (M1) provided between a first terminal (TM1) and a second terminal (TM2) connected to an inductive load (W1), and turns on and off the switching transistor. A driver (110) turns on the switching transistor by supplying a charging current to a gate of the switching transistor, and turns off the switching transistor by discharging accumulated charges in the gate of the switching transistor. The driver discharges the accumulated charge through an external resistor (RADJ) provided between the resistor connection terminal and the ground outside the switching device.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a switching device, an isolated DC / DC converter, and an AC / DC converter. [Background technology]

[0002] BACKGROUND ART Devices that control a current flowing through an inductive load by switching a switching transistor connected to the inductive load are widely known (see, for example, Patent Document 1 below). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-163461

[0004] [overview] In this type of device, it is desirable to minimize the loss generated in the switching transistor, while also reducing the radiation noise. However, there is often a trade-off between the loss and the radiation noise, so a technology that can achieve a good balance between suppressing the loss and the radiation noise is needed.

[0005] A switching device according to one embodiment of the present disclosure comprises a first terminal connected to an inductive load, a second terminal, a switching transistor provided between the first terminal and the second terminal, a resistor connection terminal, and a control drive circuit configured to control the current flowing from a wiring to which an input voltage is applied to ground through the inductive load and the switching transistor by turning the switching transistor on or off through control of the gate voltage of the switching transistor, wherein the control drive circuit has a driver configured to turn on the switching transistor by supplying a charging current to the gate of the switching transistor and to turn off the switching transistor by discharging accumulated charge in the gate of the switching transistor, and the driver discharges the accumulated charge through an external resistor provided outside the switching device between the resistor connection terminal and ground. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a diagram illustrating the overall configuration of an AC / DC converter according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a diagram showing the overall configuration of a DC / DC converter provided in the AC / DC converter of FIG. [Figure 3] FIG. 3 is an external perspective view of the primary-side control device according to the embodiment of the present disclosure. [Figure 4] FIG. 4 is a schematic diagram of the reference device. [Figure 5] FIG. 5 shows some signal waveforms in the reference device. [Figure 6] FIG. 6 shows some signal waveforms in the reference device. [Figure 7] FIG. 7 is an explanatory diagram of a method for adjusting the slew rate in the reference device. [Figure 8] FIG. 8 is an explanatory diagram of a method for adjusting the slew rate in the reference device. [Figure 9]FIG. 9 is a diagram illustrating some signal waveforms in a primary side controller according to an embodiment of the present disclosure. [Figure 10] FIG. 10 is a waveform diagram of the drain voltage when the switching transistor is turned off according to an embodiment of the present disclosure.

[0007] [Detailed explanation] Hereinafter, examples of embodiments of the present disclosure will be described in detail with reference to the drawings. In each of the drawings, identical parts are designated by the same reference numerals, and redundant descriptions of identical parts will be omitted as a general rule. For the sake of brevity, in this specification, symbols or signs referring to information, signals, physical quantities, functional units, circuits, elements, or components may be used, and the names of the information, signals, physical quantities, functional units, circuits, elements, or components corresponding to the symbols or signs may be omitted or abbreviated. For example, a switching transistor referred to by "M1" (see FIG. 2) described below may be written as a switching transistor M1 or abbreviated as a transistor M1, but these all refer to the same thing.

[0008] First, some terms used in describing the embodiments of the present disclosure will be explained: A level refers to a level of potential, and a high level has a higher potential than a low level for any signal or voltage of interest.

[0009] For any transistor configured as a FET (field-effect transistor), such as a MOSFET, the on state refers to a state in which the drain and source of the transistor are conductive, and the off state refers to a state in which the drain and source of the transistor are non-conductive (cut-off state). The same applies to transistors not classified as FETs. Unless otherwise specified, MOSFETs are understood to be enhancement-type MOSFETs. MOSFET is an abbreviation for "metal-oxide-semiconductor field-effect transistor." Additionally, unless otherwise specified, the back gate of any MOSFET can be considered shorted to the source.

[0010] Hereinafter, for any transistor, the on-state and off-state may be simply expressed as on and off. For any transistor, the switching from the off-state to the on-state is expressed as turn-on, and the switching from the on-state to the off-state is expressed as turn-off. Also, for any transistor, the period during which the transistor is in the on-state is referred to as the on-period, and the period during which the transistor is in the off-state is referred to as the off-period.

[0011] The connection between a plurality of parts forming a circuit, such as any circuit element, wiring, node, etc., may be understood to refer to an electrical connection unless otherwise specified.

[0012] When any two voltages to be compared are voltage v1 and v2, "v1>v2" represents that voltage v1 is higher than voltage v2, "v1<v2" represents that voltage v1 is lower than voltage v2, and "v1=v2" represents that the value of voltage v1 is the same as the value of voltage v2. The same applies to other expressions including physical quantities other than voltage. <0*********278> FIG. 1 is an overall configuration diagram of an AC / DC converter 1 according to this embodiment. The AC / DC converter 1 includes a filter 2, a rectifier circuit 3, a DC / DC converter 4 which is an isolated DC / DC converter 4, an input capacitor C , , OUT , <00000*********3>, IN , IN , OUT , ,

[0014] and an output capacitor C OUT and. The output capacitor C OUT may be understood to be included in the components of the DC / DC converter 4. Although details will become clear from the following description, in the AC / DC converter 1, a secondary output voltage V IN is generated from the primary input voltage V OUT by using a transformer in a switching manner.

[0014] The AC / DC converter 1 comprises a primary circuit arranged on the primary side of the AC / DC converter 1 and a secondary circuit arranged on the secondary side of the AC / DC converter 1, and the primary circuit and the secondary circuit are electrically isolated from each other. In this specification, isolation means that the transmission of DC signals and power is blocked. The filter 2, the rectifier circuit 3, and the input capacitor C IN is placed in the primary circuit, and the output capacitor C OUT is arranged in the secondary side circuit. The DC / DC converter 4 is arranged across the primary side circuit and the secondary side circuit. When focusing on the DC / DC converter 4, the primary side circuit may be understood as a circuit arranged on the primary side of the circuits that make up the DC / DC converter 4, and the secondary side circuit may be understood as a circuit arranged on the secondary side of the circuits that make up the DC / DC converter 4.

[0015] The ground in the primary circuit is referenced to "GND1", and the ground in the secondary circuit is referenced to "GND2". Primary input voltage V IN Any voltage or signal in the primary circuit, including the secondary output voltage V, is a voltage or signal referenced to ground GND1 and has a potential seen by ground GND1. OUT Any voltage or signal in the secondary circuit, including the above, is a voltage or signal referenced to ground GND2 and has a potential as seen from ground GND2. In each of the primary circuit and secondary circuit, ground refers to a reference conductor having a reference potential of 0V (zero volts) or refers to the reference potential itself. However, since ground GND1 and ground GND2 are insulated from each other, they may have different potentials. The reference conductor is made of a conductor such as metal. Any circuit provided in the primary circuit and requiring a power supply voltage is connected to the primary input voltage V IN Any circuit that is provided on the secondary side and requires a power supply voltage can be driven using a voltage based on the secondary side output voltage V OUT The voltage based on the above can be used as the power supply voltage.

[0016] Filter 2 converts the AC voltage V input to AC / DC converter 1 into AC Removes noise from AC voltage V AC The rectifier circuit 3 converts the AC voltage V supplied through the filter 2 into AC The input capacitor C IN generates a DC voltage by smoothing the full-wave rectified voltage. For this reason, the input capacitor C IN The input capacitor C can also be called a smoothing capacitor. IN The DC voltage generated by the primary input voltage V IN It functions as the primary input voltage V IN is a pair of input terminals IN P and IN N In detail, the input capacitor C IN The low potential terminal is connected to the ground GND1 and the input terminal IN N connected to the input capacitor C IN The high potential terminal of the input terminal IN P and connected to the input terminal IN N The potential at the input terminal IN P to the primary input voltage V IN Strictly speaking, the primary input voltage V IN is the AC voltage V AC It is a pulsating voltage with a frequency corresponding to the frequency of

[0017] DC / DC converter 4 operates on the primary input voltage V IN By converting the power (DC-DC conversion) using a switching method, the specified target voltage V TG The secondary output voltage V is regulated by OUT The secondary output voltage V OUT is the DC voltage equivalent to the output voltage of the AC / DC converter 1, and is connected to the pair of output terminals OUT P and OUT N In detail, the output capacitor C OUT The low-potential terminal is connected to the ground GND2 and the output terminal OUT N connected to the output capacitor C OUTThe high potential terminal is the output terminal OUT P And the output terminal OUT N The output terminal OUT P to the secondary output voltage V OUT A pair of input terminals IN P and IN N can be considered to correspond to the input terminal pair in the DC / DC converter 4, and the pair of output terminals OUT P and OUT N can be considered to correspond to the output terminal pair in the AC / DC converter 1 or the DC / DC converter 4.

[0018] A load LD is also shown in Figure 1. The load LD can be considered to be the load of the AC / DC converter 1, or, if we focus on the DC / DC converter 4, it can also be considered to be the load of the DC / DC converter 4. The load LD is connected to a pair of output terminals OUT P and OUT N The secondary output voltage V OUT For example, the load LD is a microcomputer, a DSP (Digital Signal Processor), a power supply circuit, a lighting device, an analog circuit, or a digital circuit.

[0019] Figure 2 shows the internal configuration of the DC / DC converter 4 provided in the AC / DC converter 1. The DC / DC converter 4 includes a transformer TR, which is a power transformer having a primary winding W1 and a secondary winding W2. The DC / DC converter 4 in Figure 2 employs a flyback topology, in which the primary winding W1 and secondary winding W2 of the transformer TR are electrically insulated from each other but magnetically coupled with each other in opposite polarity. The transformer TR also has an auxiliary winding W3 on the primary side.

[0020] The primary side circuit of the DC / DC converter 4 (in other words, the primary side circuit of the AC / DC converter 1) includes, in addition to the primary side winding W1 and the auxiliary winding W3, a primary side control device 10, which is an example of a switching device, and an input capacitor C INa rectifier diode D11, capacitors C11 to C13, voltage dividing resistors R11 and R12, and a sense resistor R CS and the adjustment resistor R ADJ As described above, the input terminal IN P and IN N Between the input capacitor C IN and an input capacitor C IN The primary input voltage V IN is added.

[0021] FIG. 3 shows an external perspective view of the primary-side control device 10. The primary-side control device 10 is an electronic component including a semiconductor chip having a semiconductor integrated circuit formed on a semiconductor substrate, a housing (package) CS that houses the semiconductor chip, and multiple external terminals exposed to the outside of the primary-side control device 10 from the housing CS. The primary-side control device 10 is formed by encapsulating the semiconductor chip in the housing CS made of resin. Note that the number of external terminals of the primary-side control device 10 and the type of housing for the primary-side control device 10 shown in FIG. 3 are merely examples and can be designed as desired. Terminals TM1 to TM7 shown in FIG. 2 are external terminals provided on the primary-side control device 10. Other external terminals may also be provided on the primary-side control device 10. Note that terminal TM1 may be formed of two or more external terminals. The same applies to terminals TM2 to TM7.

[0022] 2 again, the primary-side control device 10 includes a switching transistor M1, a driver 110, a control circuit 120, a startup circuit 130, and an internal power supply circuit 140. A semiconductor chip on which the switching transistor M1 is formed and a semiconductor chip on which the driver 110, the control circuit 120, the startup circuit 130, and the internal power supply circuit 140 are formed are housed in a housing CS. However, the switching transistor M1, the driver 110, the control circuit 120, the startup circuit 130, and the internal power supply circuit 140 may be formed on a single semiconductor chip.

[0023] The driver 110 includes a high-side transistor MH and a low-side transistor ML. The transistors M1 and ML are configured as N-channel MOSFETs. The transistor MH is configured as a P-channel MOSFET.

[0024] Input terminal IN P connected to the primary input voltage V IN The first end of the primary winding W1 is connected to the wiring WR11 to which the primary input voltage V IN is applied to the primary winding W1. A second end of the primary winding W1 is connected to a terminal TM1. A drain of the switching transistor M1 is connected to the terminal TM1, and a source of the switching transistor M1 is connected to a terminal TM2. That is, the switching transistor M1 is connected in series to the primary winding W1. A sense resistor R is connected between the terminal TM2 and ground GND1 outside the primary control device 10. CS Specifically, a sense resistor R CS The first end of the resistor R is connected to the terminal TM2. CS The second end of the transistor is connected to ground GND1.

[0025] The voltage at terminal TM1 is V D The voltage at terminal TM2 is called voltage V S Voltage V D corresponds to the drain voltage of the switching transistor M1, and the voltage V S corresponds to the source voltage of the switching transistor M1. The current flowing through the primary winding W1 is the primary current I P During the ON period of the switching transistor M1, the primary current I P is the input terminal IN P The voltage V flows from the primary winding W1 through the channel of the switching transistor M1. S is the sense resistor R CS The voltage developed across the sense resistor R CS (voltage drop at the drain of the switching transistor M1) and the drain current ID (more precisely, the drain current I D The voltage has a value proportional to the instantaneous value of

[0026] A first end of the auxiliary winding W3 is connected to the anode of a rectifier diode D11, and a second end of the auxiliary winding W3 is connected to ground GND1. A cathode of the rectifier diode D11 is connected to a first end of a capacitor C11 and to a terminal TM3. A second end of the capacitor C11 is connected to ground GND1. A voltage VCC at the terminal TM3 functions as a power supply voltage for the primary-side control device 10. A terminal TM4 is a ground terminal connected to ground GND1.

[0027] A first terminal of the voltage dividing resistor R11 is connected to the wiring WR11. A second terminal of the voltage dividing resistor R11 is connected to the terminal TM5, a first terminal of the voltage dividing resistor R12, and a first terminal of the capacitor C12. A second terminal of the voltage dividing resistor R12 and a second terminal of the capacitor C12 are connected to the ground GND1. The voltage V at the terminal TM5 BR is the primary input voltage V IN The terminal TM6 is connected to the first terminal of the capacitor C13, and the second terminal of the capacitor C13 is connected to the ground GND1. The voltage at the terminal TM6 is FB An external resistor, an adjustment resistor R, is connected between the terminal TM7 and the ground GND1 outside the primary side control device 10. ADJ That is, outside the primary side control device 10, an adjusting resistor R ADJ The first end of the resistor R is connected to the terminal TM7. ADJ The second end of the terminal TM7 is connected to the ground GND1. The terminal TM7 is an example of a resistor connection terminal.

[0028] In the primary side control device 10, the source of the transistor MH is connected to a node to which the internal power supply voltage VDD is applied, the drains of the transistors MH and ML are commonly connected to the gate of the switching transistor M1, and the source of the transistor ML is connected to a terminal TM7. Therefore, the terminal TM7 and the adjustment resistor R are connected between the source of the transistor ML and the ground GND1. ADJThe gate voltage of the switching transistor M1 is represented by the symbol "V G " for reference.

[0029] The control circuit 120 is connected to the terminals TM2, TM4, TM5, and TM6, and also to the gates of the transistors MH and ML. The control circuit 120 controls the internal power supply voltage V REG The DC / DC converter 4 is driven based on the voltage V at the terminal TM1. The primary side circuit of the DC / DC converter 4 is provided with a self-power supply circuit that generates a power supply voltage VCC, and the self-power supply circuit is formed by the auxiliary winding W3, the rectifier diode D11, the capacitor C11 and the start-up circuit 130. The start-up circuit 130 is connected to the terminals TM1 and TM3. Before the switching drive of the switching transistor M1 starts, the start-up circuit 130 generates the voltage V at the terminal TM1. D As mentioned above, the power supply voltage VCC is the voltage at the terminal TM3. The power supply voltage VCC is the primary side input voltage V IN After the switching transistor M1 starts to be switched, the voltage induced in the auxiliary winding W3 based on the magnetic flux generated in the primary winding W1 is rectified and smoothed by the rectifier diode D11 and the capacitor C11, and the power supply voltage VCC continues to be applied to the terminal TM3.

[0030] The internal power supply circuit 140 is connected to the terminal TM3 and generates an internal power supply voltage V REG and VDD. Internal power supply voltage V REG and VDD each have a positive DC voltage value (and therefore are higher than the potential of ground GND1). REG is supplied to the control circuit 120, and the internal power supply voltage VDD is supplied to the driver 110. REG and VDD may be a common voltage.

[0031] The secondary side circuit of the DC / DC converter 4 (in other words, the secondary side circuit of the AC / DC converter 1) includes, in addition to the secondary side winding W2, a secondary side control device 20, a rectifier diode D21, and an output capacitor COUT The secondary winding W2 has a first end connected to the anode of the rectifier diode D21, and a cathode of the rectifier diode D21 is connected to a wiring WR21. The secondary winding W2 has a second end connected to a wiring WR22. The wiring WR21 is connected to the output terminal OUT P and the wire WR22 is connected to the output terminal OUT N and ground GND2. As mentioned above, the output terminal OUT P and OUT N Between the output capacitor C OUT and an output capacitor C OUT Between both terminals (and therefore between wires WR21 and WR22) is the secondary output voltage V OUT The current flowing through the secondary winding W2 is called the secondary current I S During all or part of the off period of the switching transistor M1, a secondary current I flows from the wiring WR22 through the secondary winding W2 and the rectifier diode D21 toward the wiring WR21. S is playing.

[0032] A first end of a voltage dividing resistor R21 is connected to the wiring WR21. A second end of the voltage dividing resistor R21 is connected to a first end of a voltage dividing resistor R22, and a second end of the voltage dividing resistor R22 is connected to ground GND2. A connection node between the voltage dividing resistors R21 and R22 is connected to the secondary-side control device 20. The secondary-side control device 20 is also connected to ground GND2 and the wiring WR21. The secondary-side control device 20 calculates the secondary-side output voltage V with respect to the potential of ground GND2. OUT The voltage V at the connection node between the voltage dividing resistors R21 and R22 is DIV is the secondary output voltage V OUT is the partial pressure of

[0033] In the DC / DC converter 4, a photocoupler PC is provided across the primary side circuit and the secondary side circuit. The photocoupler PC has a light emitting element PCa provided in the secondary side circuit and a light receiving element PCb provided in the primary side circuit. The secondary side output voltage V OUTA first end of a resistor R23 is connected to a node to which this voltage is applied, and a light-emitting element PCa is provided between a second end of the resistor R23 and the secondary-side control device 20. The light-receiving element PCb is connected in parallel to a capacitor C13.

[0034] The operation of the DC / DC converter 4 configured as above will now be described. The control circuit 120 controls the voltage V BR When V is less than a predetermined brownout threshold voltage, the switching transistor M1 is not switched on. BR is maintained above the brownout threshold voltage and the power supply voltage VCC is high enough to allow the primary side control device 10 to operate normally.

[0035] The control circuit 120 controls the gate potentials of the transistors MH and ML to alternately turn the transistors MH and ML on and off, thereby switching the switching transistor M1. In particular, the control circuit 120 controls the gate potentials of the transistors MH and ML individually to set the state of the driver 110 to one of an output high state, an output low state, and a both-off state. In the output high state, the transistor MH is on and the transistor ML is off. In the output low state, the transistor MH is off and the transistor ML is on. In the both-off state, the transistors MH and ML are both off. The control circuit 120 never turns on the transistors MH and ML simultaneously.

[0036] The control circuit 120 controls the transistor MH to be off by supplying a high-level signal to the gate of the transistor MH, and controls the transistor MH to be on by supplying a low-level signal to the gate of the transistor MH. The control circuit 120 controls the transistor ML to be on by supplying a high-level signal to the gate of the transistor ML, and controls the transistor ML to be off by supplying a low-level signal to the gate of the transistor ML. The high-level signal that the control circuit 120 supplies to the gate of the transistor MH or ML is a voltage signal that is supplied to the internal power supply voltage VREG The low-level signal supplied by the control circuit 120 to the gate of the transistor MH or ML has the potential of the ground GND1.

[0037] When the driver 110 is switched from the output low state to the output high state starting from the state in which the switching transistor M1 is off, the gate voltage V G As the internal power supply voltage VDD rises toward the internal power supply voltage VDD, the state of the switching transistor M1 switches from the off state to the on state. The internal power supply voltage VDD is higher than the gate threshold voltage of the switching transistor M1. Then, when the driver 110 switches from the output high state to the output low state, the gate voltage V of the switching transistor M1 G As the voltage of the switching transistor M1 decreases toward the voltage of the ground GND1, the state of the switching transistor M1 switches from the on state to the off state. In the switching drive of the switching transistor M1, the state of the switching transistor M1 repeatedly switches between on and off. In the switching drive of the switching transistor M1, when the control circuit 120 changes the driver 110 from one of the output low state and the output high state to the other, the control circuit 120 may set the driver 110 to a both-off state for a small dead time to reliably prevent the transistors MH and ML from being turned on simultaneously.

[0038] The driver 110 and the control circuit 120 form a control drive circuit. The control drive circuit (110, 120) controls the gate voltage of the switching transistor M1 by turning on or off the transistors MH and ML, thereby turning on or off the switching transistor M1. During the on period of the switching transistor M1, a signal is transmitted from the wire WR11 to the primary coil W1, the terminal TM1, the channel (between the drain and source) of the switching transistor M1, the terminal TM2, and the sense resistor R CS The primary current I P During the off period of the switching transistor M1, the primary side current I PThat is, the control drive circuit (110, 120) performs switching drive to turn on or off the switching transistor M1, thereby preventing the primary side current I P Control.

[0039] During the on-period of the switching transistor M1, the primary current I P increases, and the primary current I P The stored energy is then released from the secondary winding W2 during the off period of the switching transistor M1 (more specifically, the secondary current I S flows through the rectifier diode D21 during the off period of the switching transistor M1), OUT is charged and the secondary output voltage V OUT is obtained.

[0040] The secondary side control device 20 detects the voltage V generated at the connection node between the voltage dividing resistors R21 and R22. DIV A current corresponding to the amount of current supplied to the light-emitting element PCa of the photocoupler PC is then generated in the light-receiving element PCb of the photocoupler PC, and a feedback voltage V FB At this time, the secondary side control device 20 controls the voltage V DIV The amount of current supplied to the light emitting element PCa is controlled so that the voltage V DIV Feedback voltage V according to FB is generated in the primary side circuit. FB The switching transistor M1 is switched based on the OUT is the target voltage V TG It is stabilized at

[0041] More specifically, the secondary side controller 20 controls the voltage V DIV a predetermined reference voltage V REF20 (not shown), the voltage V DIV is the reference voltage VREF20 If it is higher than the voltage V DIV is the reference voltage V REF20 If the current supply amount to the light emitting element PCa is lower than the feedback voltage V FB The decrease in the amount of current supplied to the light-emitting element PCa leads to a decrease in the feedback voltage V FB The control circuit 120 can drive the switching transistor M1 by pulse width modulation. In this case, the control circuit 120 controls the feedback voltage V FB As the feedback voltage V FB As the voltage V increases, the on-duty of the switching transistor M1 increases. DIV and the reference voltage V REF20 Feedback control is realized to maintain the error between V and V at zero or close to zero. DIV =V REF20 "When "V OUT =V TG The on-duty of the switching transistor M1 refers to the ratio of the length of the on-period of the switching transistor M1 to the length of the switching period in each switching period of the switching transistor M1. Note that the control method of the switching transistor M1 by the control circuit 120 is not limited to the pulse width modulation method. Therefore, for example, the control circuit 120 may control the feedback voltage V FB The switching transistor M1 may be switched at a switching frequency according to the above.

[0042] Also, the control circuit 120 supplies a voltage V S The control circuit 120 receives the voltage V S Specifically, for example, the control circuit 120 controls the voltage V S When the voltage V exceeds a predetermined overcurrent determination voltage, the control circuit 120 performs an overcurrent protection process by immediately turning off the switching transistor M1. SWhen it is determined that the switching transistor M1 is in an overcurrent state based on the above, the switching drive of the switching transistor M1 can be stopped for a certain period of time to keep the switching transistor M1 in an off state.

[0043] Here, several reference devices will be described for comparison with the configuration of FIG. 2. FIG. 4 is a schematic diagram of a reference device 910A. The reference device 910A includes a switching transistor 930 in addition to a primary-side control device 920 formed using a semiconductor integrated circuit. The switching transistor 930 is an N-channel MOSFET. An AC / DC converter can be formed using the reference device 910A. In the reference device 910A, a primary-side input voltage Vin obtained by rectifying an AC voltage is connected to a first terminal of a primary-side winding 941 of a transformer 940, and a second terminal of the primary-side winding 941 is connected to the drain of the switching transistor 930. The source of the switching transistor 930 is connected to ground. The primary-side control device 920 switches the switching transistor 930 by controlling the gate voltage Vg of the switching transistor 930. The drain voltage and drain current of the switching transistor 930 are referred to as "Vd" and "Id," respectively.

[0044] The primary-side control device 920 supplies a charge (positive charge) to the gate of the switching transistor 930, thereby increasing the gate voltage Vg and turning on the switching transistor 930. Thereafter, the primary-side control device 920 discharges the accumulated charge on the gate of the switching transistor 930, thereby decreasing the gate voltage Vg and turning off the switching transistor 930.

[0045] 5 shows some signal waveforms of the reference device 910A when the charging and discharging currents of the gate of the switching transistor 930 are relatively large. FIG. 6 shows some signal waveforms of the reference device 910A when the charging and discharging currents of the gate of the switching transistor 930 are relatively small. Note that the loss generated in the switching transistor 930 is expressed as the product of the drain voltage Vd and the drain current Id.

[0046] A large amount of noise occurs due to a sudden change in the drain voltage Vd. By reducing the charging current to the gate of the switching transistor 930, the rate at which the drain voltage Vd decreases is reduced, thereby reducing radiation noise. On the other hand, the loss generated when the switching transistor 930 is turned on does not increase at all or very little even if the rate at which the drain voltage Vd decreases is reduced. In other words, the sum of the products (Vd × Id) in portion 961 of FIG. 5 is almost the same as the sum of the products (Vd × Id) in portion 962 of FIG. 6. For this reason, reducing the slew rate when the drain voltage Vd decreases is effective for both improving power conversion efficiency and reducing radiation noise.

[0047] Furthermore, reducing the discharge current from the gate of the switching transistor 930 also reduces the rate of rise of the drain voltage Vd, which also reduces radiation noise. However, the loss generated when the switching transistor 930 is turned off significantly increases in conjunction with the decrease in the slew rate when the drain voltage Vd rises. This corresponds to the sum of the products (Vd × Id) in portion 972 of FIG. 6 being larger than the sum of the products (Vd × Id) in portion 971 of FIG. 5, and is due to the fact that the drain current Id when the switching transistor 930 is turned off is relatively large. In other words, there is a trade-off between the loss and radiation noise when the switching transistor 930 is turned off. Therefore, from the perspectives of both power conversion efficiency and radiation noise, the slew rate when the drain voltage Vd rises must be carefully designed.

[0048] A first reference method and a second reference method are considered as methods for reducing and adjusting radiation noise caused by fluctuations in the drain voltage Vd.

[0049] The reference device 910B in FIG. 7 employs the first reference method. Based on the reference device 910A in FIG. 4, the reference device 910B is obtained by providing a capacitor 950 between the drain and source of the switching transistor 930. By adjusting the capacitance value of the capacitor 950, the slew rate of the drain voltage Vd when the switching transistor 930 is turned on and off can be adjusted to a desired slew rate. However, when generating the primary-side input voltage Vin by full-wave rectifying a commercial AC voltage, the required withstand voltage of the capacitor 950 is approximately 600 V. As a result, the reference device 910B requires an expensive and large-sized capacitor 950.

[0050] The second reference method is applied to reference device 910C in Figure 8. Based on reference device 910A in Figure 4, reference device 910C is obtained by inserting a slew rate adjustment circuit 960 between primary-side control device 920 and the gate of switching transistor 930. The slew rate adjustment circuit 960 comprises a resistor (gate resistor) 961 provided between the input / output terminals of primary-side control device 920 and the gate of switching transistor 930, and a series circuit of resistor (gate resistor) 962 and diode 963 provided between the input / output terminals of primary-side control device 920 and the gate of switching transistor 930. In this case, the anode of diode 963 is connected to the gate of switching transistor 930, and the cathode of diode 963 is connected to the input / output terminals of primary-side control device 920 via resistor 962.

[0051] In the reference device 910C, the charge stored in the gate of the switching transistor 930 is supplied to the gate of the switching transistor 930 from the input / output terminal of the primary-side control device 920 through a resistor 961. Therefore, the slew rate of the drain voltage Vd (the slew rate when the drain voltage Vd drops) when the switching transistor 930 is turned on is determined by the value of the resistor 961. On the other hand, when the primary-side control device 920 drops the gate voltage Vg, the charge stored in the gate of the switching transistor 930 is drawn into the input / output terminal of the primary-side control device 920 through resistors 961 and 962. Here, if the value of the resistor 962 is set sufficiently smaller than the value of the resistor 961, the slew rate of the drain voltage Vd (the slew rate when the drain voltage Vd rises) when the switching transistor 930 is turned off is determined approximately by the value of the resistor 962. Therefore, by adjusting the value of the resistor 962, the slew rate of the drain voltage Vd (the slew rate when the drain voltage Vd rises) when the switching transistor 930 is turned off can be adjusted to a desired slew rate.

[0052] When the switching transistor 930 and the primary-side control device 920 are mounted on a board as separate components, as in the reference device 910C, the slew rate of the drain voltage Vd can be easily and arbitrarily adjusted by adjusting the value of resistor 962, taking into account the power required on the secondary side and the results of EMI tests, etc. However, when forming a primary-side control device with a built-in switching transistor (corresponding to the switching transistor 930), adjusting the slew rate of the drain voltage Vd is not easy, and the gate resistance of the switching transistor must be determined at the time of designing the primary-side control device. When incorporating a primary-side control device with a built-in switching transistor into an AC / DC converter, it is not possible to reduce the gate resistance to improve efficiency or increase the gate resistance to reduce radiated noise.

[0053] Considering these points, in the DC / DC converter 4 of FIG. 2, an adjustment resistor R ADJWhen the transistor ML is on and the transistor MH is off, the gate voltage V G Starting from a state where V is 0V, when the control circuit 120 turns off the transistor ML and then turns on the transistor MH, the driver 110 supplies a charging current from the node to which the internal power supply voltage VDD is applied to the gate of the switching transistor M1 through the transistor MH, thereby increasing the gate voltage V of the switching transistor M1. G The gate voltage V is increased from 0V to the internal power supply voltage VDD (on voltage). G When the voltage rises from 0V to the internal power supply voltage VDD, the switching transistor M1 is turned on. After that, when the control circuit 120 turns off the transistor MH and then turns on the transistor ML, the driver 110 transfers the accumulated charge at the gate of the switching transistor M1 to the transistor ML and the adjustment resistor R. ADJ This discharges the gate voltage V of the switching transistor M1 to the ground GND1. G The internal power supply voltage VDD is decreased towards 0V. The gate voltage V G During the process of the internal power supply voltage Vdd decreasing to 0V, the switching transistor M1 is turned off.

[0054] FIG. 9 shows a schematic diagram of some signal waveforms in the DC / DC converter 4. As an example, consider that the control circuit 120 switches the switching transistor M1 using pulse width modulation. Signals SET and RST are generated within the control circuit 120. The signals SET and RST are each binary signals having a high level or a low level. In principle, the signals SET and RST have a low level. An oscillator (not shown) provided in the control circuit 120 causes the signal SET to have a high level for only a short time at a predetermined switching frequency. In response to the level of the signal SET switching from a low level to a high level, the control circuit 120 switches the state of the driver 110 from an output low state to an output high state. When the state of the driver 110 switches from the output low state to the output high state, a charging current is supplied to the gate of the switching transistor M1 through the transistor MH from a node to which the internal power supply voltage VDD is applied, and the supply of this charging current is controlled by the gate voltage V G This continues until the drain voltage V reaches the internal power supply voltage VDD. D During the period when the gate voltage V G is generally kept close to the gate threshold voltage of the switching transistor M1.

[0055] After that, a reset circuit (not shown) provided in the control circuit 120 sets the level of the signal RST to a high level for a very short time. In response to the level of the signal RST switching from a low level to a high level, the control circuit 120 switches the state of the driver 110 from an output high state to an output low state. When the state of the driver 110 switches from the output high state to the output low state, the accumulated charge in the gate of the switching transistor M1 is transferred to the transistor ML and the adjustment resistor R ADJ A discharge current is generated that discharges the gate voltage V G This continues until the drain voltage V drops to 0V. D During the period when the gate voltage V Gis generally kept near the gate threshold voltage of the switching transistor M1. The reset circuit determines the timing at which the level of the signal RST switches from low to high by the feedback voltage V FB The time difference between the timing when the signal SET changes to high level and the timing when the signal RST changes to high level is determined based on the feedback voltage V FB As the feedback voltage V FB increases as .

[0056] When the switching transistor M1 is turned on, the drain voltage V D The rate of decrease of the drain voltage V D By reducing the rate at which the drain voltage V decreases, the radiation noise when the switching transistor M1 is turned on can be reduced. D Therefore, there is no or almost no increase in the drain voltage V D In order to achieve both improved power conversion efficiency and reduced radiation noise, it is necessary to set the on-resistance of the transistor MH high enough to sufficiently reduce radiation noise. D The slew rate at the time of the drop becomes smaller.

[0057] On the other hand, when turning off the switching transistor M1, the drain voltage V D Therefore, by reducing the discharge current when the switching transistor M1 is turned off, it is possible to reduce the radiation noise when the switching transistor M1 is turned off. However, as described above with respect to the reference configuration, the loss that occurs when the switching transistor M1 is turned off is proportional to the drain voltage V DIn other words, there is a trade-off between the loss and the radiation noise when the switching transistor M1 is turned off. Therefore, from the viewpoints of both power conversion efficiency and radiation noise, D The rising slew rate must be carefully designed.

[0058] In this regard, the DC / DC converter 4 in Figure 2 has an adjustment resistor R ADJ By adjusting the resistance value of D The slew rate at the time of rise can be easily and arbitrarily adjusted. ADJ By adjusting the resistance value of D Therefore, it is possible to achieve a good balance between power conversion efficiency and radiation noise characteristics according to the power required on the secondary side.

[0059] The on-resistance of the transistor ML may be any value, but in order to make the above adjustment function effectively, it is preferable that the on-resistance of the transistor ML is not too high. The on-resistance of the transistor ML may be smaller than the on-resistance of the transistor MH.

[0060] In FIG. 10, a solid line waveform 610 and a dashed line waveform 620 represent the drain voltage V when the switching transistor M1 is turned off. D The waveform of the broken line 620 is shown. ADJ The resistance value of the adjustment resistor R when the solid line waveform 610 is observed is ADJ The resistance value of the adjustment resistor R ADJ The drain voltage V D It can be seen that the slew rate increases and decreases when the power conversion efficiency increases. The radiation noise corresponding to the dashed waveform 620 is smaller than the radiation noise corresponding to the solid waveform 610, but the loss corresponding to the dashed waveform 620 is larger than the loss corresponding to the solid waveform 610. From the viewpoints of both power conversion efficiency and radiation noise, it is necessary to select an adjustment resistor R with an appropriate resistance value.ADJ It is best to adopt this.

[0061] Here, the configuration of the DC / DC converter 4 employing the diode rectification method is taken as an example. However, the DC / DC converter 4 also uses the primary voltage V applied to the primary winding W1. P The secondary voltage V on the secondary side of the transformer TR is generated by switching S For example, a synchronous rectification type DC / DC converter 4 may be configured by providing a synchronous rectification transistor (not shown) in place of the rectification diode D21 in the secondary circuit. In this case, one end of the secondary winding W2 and the output terminal OUT P or OUT N A synchronous rectification transistor is inserted between the switch transistor M1 and the secondary-side control device 20, and the synchronous rectification transistor is turned on during all or part of the off period of the switch transistor M1. Furthermore, for example, the DC / DC converter 4 may be configured as a forward-type isolated DC / DC converter, and in this case too, either a synchronous rectification type or a diode rectification type may be adopted.

[0062] The primary winding W1 is an example of an inductive load connected to the drain of the switching transistor M1 through the terminal TM1. Although the embodiment in which the technology according to the present disclosure is applied to the AC / DC converter 1 has been described above, the application of the technology according to the present disclosure is not limited to the AC / DC converter 1. The technology according to the present disclosure can be applied to any application in which an arbitrary inductive load (coil) is connected to the drain of the switching transistor M1 through the terminal TM1, and the current flowing through the inductive load and the switching transistor M1 is controlled by turning the switching transistor M1 on and off.

[0063] The channel types of the FETs (field effect transistors) shown in the above embodiments are merely examples, and the channel type of any FET may be changed between P-channel and N-channel types without departing from the spirit of the above.

[0064] Any of the transistors described above may be any type of transistor, provided that no disadvantages arise. For example, any of the transistors described above as MOSFETs may be replaced with junction field effect transistors (FETs), insulated gate bipolar transistors (IGBTs), or bipolar transistors, provided that no disadvantages arise. Any of the transistors has a first electrode, a second electrode, and a control electrode. In an FET, one of the first and second electrodes is the drain, the other is the source, and the control electrode is the gate. In an IGBT, one of the first and second electrodes is the collector, the other is the emitter, and the control electrode is the gate. In a bipolar transistor that is not an IGBT, one of the first and second electrodes is the collector, the other is the emitter, and the control electrode is the base.

[0065] The embodiments of the present disclosure can be modified in various ways as appropriate within the scope of the technical ideas set forth in the claims. The above-described embodiments are merely examples of the present disclosure, and the meanings of the terms of the present disclosure and each constituent element are not limited to those described in the above-described embodiments. The specific numerical values ​​shown in the above description are merely examples, and as a matter of course, they can be changed to various numerical values.

[0066] <<Additional Notes>> A supplementary note will be provided for the present disclosure, the specific configuration examples of which have been shown in the above-described embodiments.

[0067] A switching device (10) according to one aspect of the present disclosure includes a first terminal (TM1) connected to an inductive load (W1), a second terminal (TM2), a switching transistor (M1) provided between the first terminal and the second terminal, a resistor connection terminal (TM7), and a gate voltage (V G ) to turn on or off the switching transistor, INand a control drive circuit (110, 120) configured to control a current flowing from a wiring (WR11) to which a current is applied through the inductive load and the switching transistor to ground, the control drive circuit having a driver (110) configured to supply a charging current to the gate of the switching transistor to turn on the switching transistor and to discharge accumulated charges in the gate of the switching transistor to turn off the switching transistor, the driver having an external resistor (R ADJ ) to discharge the accumulated charge (first configuration).

[0068] This makes it possible to achieve a good balance between loss and noise that occurs when the switching transistor is turned off by adjusting the resistance value of the external resistor.

[0069] In the switching device according to the first configuration, the driver may have a high-side transistor (MH) provided between a node to which an on-voltage (VDD) higher than the ground voltage is applied and the gate of the switching transistor, and a low-side transistor (ML) provided between the gate of the switching transistor and the resistor connection terminal, the control drive circuit turns on the switching transistor by turning off the low-side transistor and turning on the high-side transistor so that the gate voltage of the switching transistor is directed toward the on-voltage, and turns off the switching transistor by turning off the high-side transistor and turning on the low-side transistor so that the gate voltage of the switching transistor is directed toward the ground voltage, and the resistor connection terminal and the external resistor may be interposed between the low-side transistor and ground (second configuration).

[0070] In the switching device according to the first or second configuration, the device may be configured (third configuration) to include a housing (CS) that houses the switching transistor and the control drive circuit, and a plurality of external terminals exposed from the housing, the plurality of external terminals including the first terminal, the second terminal, and the resistor connection terminal.

[0071] In a switching device according to any of the first to third configurations, a fourth configuration may be adopted in which the slew rate of the voltage increase at the first terminal when the switching transistor is switched from an on state to an off state is adjusted by adjusting the resistance value of the external resistor.

[0072] An isolated DC / DC converter according to one aspect of the present disclosure uses a power transformer (TR) having a primary winding (W1) and a secondary winding (W2) that are insulated from each other to generate a primary voltage (V IN ) to the secondary voltage (V OUT ), and is provided with a switching device according to any one of the first to fourth configurations, wherein the inductive load is the primary winding, and the input voltage is the primary voltage (fifth configuration).

[0073] An AC / DC converter according to one aspect of the present disclosure is AC ) and a smoothing capacitor (C IN ) and the isolated DC / DC converter according to the fifth configuration, wherein the isolated DC / DC converter is configured to generate the secondary side voltage from the primary side voltage as the DC voltage (sixth configuration). [Explanation of symbols]

[0074] 1 AC / DC converter 2. Filters 3 Rectifier circuit 4 DC / DC converters IN P , IN N Input terminal C IN Input Capacitor V IN Primary Input Voltage OUT P , OUT N Output terminal C OUT Output Capacitor V OUT Secondary Output Voltage LD load 10 Primary side control device 20 Secondary control device TR transformer W1 Primary winding W2 Secondary winding W3 Auxiliary winding D11, D21 rectifier diodes C11~C13 capacitors R11, R12, R21, R22 voltage dividing resistors R23 resistance R CS Sense Resistor R ADJ adjustment resistance PC photocoupler PCa light emitting element PCB light receiving element M1 Switching transistor 110 Driver MH, ML transistors 120 control circuit 130 Starter Circuit 140 Internal power supply circuit V D Voltage (Drain voltage) V S Voltage (source voltage) VCC power supply voltage VDD, V REG Internal Power Supply Voltage

Claims

1. a first terminal connected to an inductive load; A second terminal; a switching transistor provided between the first terminal and the second terminal; A resistor connection terminal; a control drive circuit configured to control a current flowing from a wiring to which an input voltage is applied to ground through the inductive load and the switching transistor by turning the switching transistor on or off through control of a gate voltage of the switching transistor; the control and drive circuit includes a driver configured to supply a charging current to a gate of the switching transistor to turn on the switching transistor and to discharge a stored charge on the gate of the switching transistor to turn off the switching transistor; The driver discharges the accumulated charge through an external resistor provided between the resistor connection terminal and ground outside the switching device. , switching device.

2. the driver has a high-side transistor provided between a node to which an on-voltage higher than a ground voltage is applied and a gate of the switching transistor, and a low-side transistor provided between the gate of the switching transistor and the resistor connection terminal; the control drive circuit turns on the switching transistor by causing the gate voltage of the switching transistor to approach the on-voltage through turning off the low-side transistor and turning on the high-side transistor; turning off the switching transistor by directing a gate voltage of the switching transistor toward the ground voltage through turning off the high-side transistor and turning on the low-side transistor; The resistor connection terminal and the external resistor are interposed between the low-side transistor and ground.

10. The switching device of claim 1.

3. a housing that houses the switching transistor and the control drive circuit; a plurality of external terminals exposed from the housing; The plurality of external terminals include the first terminal, the second terminal, and the resistor connection terminal.

3. A switching device according to claim 1 or 2.

4. The slew rate of the voltage rise at the first terminal when the switching transistor is switched from an on state to an off state is adjusted by adjusting the resistance value of the external resistor.

3. A switching device according to claim 1 or 2.

5. 1. An isolated DC / DC converter configured to generate a secondary voltage on a secondary side from a primary voltage on a primary side using a power transformer having a primary winding and a secondary winding that are insulated from each other, A switching device according to claim 1 or 2, The inductive load is the primary winding, and the input voltage is the primary voltage. , isolated DC / DC converter

6. a rectifier circuit configured to full-wave rectify an AC voltage; a smoothing capacitor configured to generate a DC voltage by smoothing the full-wave rectified voltage; an isolated DC / DC converter according to claim 5; The isolated DC / DC converter generates the secondary voltage from the primary voltage as the DC voltage. , AC / DC converter.

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