JP5301969B2 - Switching power supply circuit and electronic device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bootstrap type switching supply circuit of low cost, for higher oscillation frequency and wider range of input voltage. <P>SOLUTION: The switching supply circuit includes a switching element 1, a drive circuit 2 for driving the switching element 1, a bootstrap circuit to supply power to the drive circuit 2, and a constant voltage circuit 3 for acquiring a constant voltage by stepping down an input voltage V<SB>IN</SB>. The bootstrap circuit includes a mode (mode to turn off switch SW2) for boosting with a voltage outputted from a constant voltage circuit 3, and a mode (mode to turn on switch SW2) for boosting with the input voltage V<SB>IN</SB>. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a switching power supply circuit having a bootstrap circuit and an electronic apparatus using the same.

  Improvement of power conversion efficiency has the effects of energy saving, long battery life and reduced heat generation, and is the most important issue for switching power supply circuits. Further, with the recent promotion of energy saving, the voltage of devices supplied with power by the switching power supply circuit has been reduced, and those having a low voltage such as 2.5V system and 1.5V system are common. On the other hand, the input voltage of the switching power supply circuit is widely used from a low voltage to a high voltage, and the current required for the device tends to increase. In the switching power supply circuit, the power loss due to the on-resistance of the switching element increases in proportion to the increase in the current of the device that supplies the power, and the power loss due to the on-resistance of the switching element reduces the power conversion efficiency. It is the main factor. Therefore, in the switching power supply circuit, how to reduce the on-resistance of the switching element is an important issue.

  Further, in order to reduce the component size of external components (coils, capacitors), it is desired to increase the oscillation frequency.

  The on-resistance of the switching element is reduced by increasing the size of the switching element. However, the increase in size leads to an increase in cost, and must be minimized. Further, when an N-channel MOSFET or NPN transistor is compared with a P-channel MOSFET or PNP transistor as a switching element, the N-channel MOSFET or NPN transistor is preferable because the chip size can be reduced more than the P-channel MOSFET or PNP transistor. However, in order to drive an N-channel MOSFET or NPN transistor, a bootstrap circuit is required, and it is required to configure the bootstrap circuit at a low cost.

JP-A-5-304768 (FIG. 1) JP 2000-92822 A JP 2007-195361 A (FIG. 1)

  Here, FIG. 15 shows a configuration example of a conventional bootstrap type switching power supply circuit. The conventional bootstrap switching power supply circuit shown in FIG. 15 includes a bootstrap circuit configured by a bootstrap diode BD1 and a bootstrap capacitor BC1.

In the bootstrap circuit, when the input voltage V _IN applied to the terminal T1 is a value that does not exceed the gate breakdown voltage of the N-channel MOSFET 1 (hereinafter referred to as switching element 1) that is a switching element, the switching element 1 is off. The voltage V _{OUT at the} terminal T2 is −V _F (V _F is the forward voltage of the Zener diode ZD1), and the voltage V _{B at the} terminal T3 is V _IN −V _F1 (V _F1 is the forward voltage of the bootstrap diode BD1). The current flows from the terminal T1 to which the input voltage V _IN is applied to the bootstrap capacitor BC1 through the bootstrap diode BD1, and the bootstrap capacitor BC1 is charged.

When the switching element 1 is turned on, the voltage V _OUT of the terminal T2 -V _F from V _IN -V _DS (V _DS is the drain of the switching element 1 - source voltage) rises, only the rise terminals T3 The voltage V _B increases. Thereby, the level of the drive voltage of the drive circuit 2 that supplies the gate drive signal to the switching element 1 is increased, and the level of the gate drive signal can be increased.

In the conventional bootstrap type switching power supply circuit shown in FIG. 15 having such a configuration, the voltage V _{B at the} terminal T3 and the level of the gate drive signal for controlling the switching element 1 fluctuate according to the fluctuation of the input voltage V _IN . Further, since the conventional bootstrap type switching shown in FIG. 15 is a step-down chopper regulator, the input voltage V _{IN has} a wide range from a low voltage to a high voltage. However, if the input voltage V _IN is high, the bootstrap voltage (2V _IN + V _F −V _F1 −V _DS ) and the level of the gate drive signal for controlling the switching element 1 also increase, so that the gate breakdown voltage of the switching element 1 is not exceeded. Thus, it was necessary to set the upper limit of the input voltage V _IN . As shown in FIG. 15, the switching element 1, the bootstrap diode BD1, the drive circuit 2, and a control signal generation circuit for generating a control signal to be supplied to the drive circuit 2 are realized by a single chip IC 100. In this case, the switching element 1 is usually composed of LDMOS (Laterally Diffused MOS), and its gate breakdown voltage is often 10 V or less.

Patent Document 1 proposes a bootstrap type switching power supply circuit that can solve the above-mentioned problems relating to the setting of the input voltage V _IN . The bootstrap type switching power supply circuit proposed in Patent Document 1 is supplied from the gate drive circuit to the gate of the switching element (output power transistor) by providing a constant voltage circuit between the gate drive circuit and the input power supply terminal. The gate drive voltage to be applied is a constant value regardless of the value of the input voltage applied to the input power supply terminal. However, since the constant voltage circuit provided between the gate drive circuit and the input power supply terminal is a constant voltage circuit based on the source voltage of the switching element (output power transistor), it is proposed in Patent Document 1. The bootstrap type switching power supply circuit has a very complicated circuit configuration.

  FIG. 16 shows a configuration of a bootstrap switching power supply circuit in which the configuration of the constant voltage circuit is simplified as compared with the bootstrap type switching power supply circuit proposed in Patent Document 1. In FIG. 16, the same parts as those in FIG.

The conventional bootstrap type switching power supply circuit shown in FIG. 16 includes a bootstrap circuit including a constant voltage circuit 3 based on GND, a bootstrap diode BD1, and a bootstrap capacitor BC1. The constant voltage circuit 3 steps down the input voltage V _IN and generates a constant voltage V _C.

In the conventional bootstrap switching power supply circuit shown in FIG. 16, when the switching element 1 is off, the voltage V _{OUT at the} terminal T2 is −V _F , the voltage V _{B at the} terminal T3 is V _C −V _F1 , and a constant voltage A current flows from the circuit 3 to the bootstrap capacitor BC1 via the bootstrap diode BD1, and the bootstrap capacitor BC1 is charged. When the switching element 1 is turned on, the voltage V _OUT of the terminal T2 rises from -V _F to V _IN -V _DS, also increases the voltage V _B of the rise only terminal T3. Thereby, the level of the drive voltage of the drive circuit 2 that supplies the gate drive signal to the switching element 1 is increased, and the level of the gate drive signal can be increased.

In the conventional bootstrap type switching power supply circuit shown in FIG. 16, since the constant voltage circuit 3 based on GND is used, the circuit configuration is simple. Further, in the conventional bootstrap switching power supply circuit shown in FIG. 16, when the switching element 1 is on, the voltage V _{B at the} terminal T3 becomes V _C + V _IN + V _F −V _F1 −V _DS , and both ends of the drive circuit 2 Since the voltage is V _C + V _F −V _F1 , the gate drive signal for controlling the switching element 1 does not depend on the input voltage V _IN .

The constant voltage V _C output from the constant voltage circuit 3 is applied to the drive circuit 2 so that the voltage between the terminals T3 and T2 (V _B −V _OUT ) does not exceed the withstand voltage of the drive circuit 2 (usually using a 5V system). Set to the upper limit of pressure resistance. However, when it is desired to use the conventional bootstrap type switching power supply circuit shown in FIG. 16 with an input voltage V _{IN in} a wide range (for example, 4.5 V to 40 V, etc.), the input voltage V _IN is output from the constant voltage circuit 3. A problem arises when the voltage V _C falls below the set value. For example, when the constant voltage V _C output from the constant voltage circuit 3 is designed to be 5 V and the input voltage V _IN is supplied with 4.5 V, the output voltage of the constant voltage circuit 3 becomes 4 V or less ( The voltage supplied to the drive circuit 2 is further lower than 4 V in consideration of the forward voltage drop of the bootstrap diode BD. As a result, since only a low voltage can be supplied to the gate of the switching element 1, the on-resistance of the switching element 1 is lowered and the efficiency is lowered. In order to reduce the on-resistance of the switching element 1 sufficiently even when the input voltage V _IN falls below the set value of the constant voltage V _C output from the constant voltage circuit 3, the size of the switching element 1 is increased. It has to be designed, resulting in an increase in cost.

  If only a low voltage can be supplied to the drive circuit 2, the drive capability of the drive circuit 2 is limited, and a large switching element (power transistor) 1 corresponding to a large current of 5 A or more can be driven. It becomes impossible. In addition, even when the oscillation frequency is increased, the switching rise time, fall time, and delay time are delayed, and the switching operation cannot be performed.

  Note that the switching power supply proposed in Patent Document 3 controls on / off of the switch in the bootstrap circuit according to the source potential of the switching element (power transistor), and the power supply voltage supplied to the bootstrap circuit. And a switching power supply in which the power supply voltages supplied to the drains of the switching elements (power transistors) are different from each other, that is, a dual power supply type switching power supply. Therefore, the switching power supply proposed in Patent Document 3 is not applicable to the single power supply bootstrap switching power supply circuit that has been studied above.

  In addition, in order to provide a one-chip bootstrap chopper regulator including a switching element (power transistor) in order to cope with the recent price reduction, a bootstrap diode that requires bipolar technology (including an epi process) And a BiCDMOS (Bipolar Complementary Double-diffused MOS) process for generating an LDMOS transistor used as a power transistor and a CMOS (Complementary MOS) transistor constituting another circuit section in a single wafer is required. However, the power transistor does not need to be a discrete component, but the one-chip bootstrap chopper regulator is expensive. Further, in order to use a bootstrap diode as a Schottky barrier diode in order to cope with high-speed oscillation, a more expensive process is required.

  In view of the above situation, an object of the present invention is to provide an inexpensive bootstrap type switching power supply circuit capable of increasing the oscillation frequency and widening the input voltage and an electronic device using the same.

  To achieve the above object, a switching power supply circuit according to the present invention includes a switching element, a drive circuit for driving the switching element, a bootstrap circuit for supplying power to the drive circuit, and a step-down input voltage. A constant voltage circuit for obtaining a constant voltage, wherein the bootstrap circuit has a plurality of operation modes including a mode for booting with a voltage output from the constant voltage circuit and a mode for booting with the input voltage. .

  According to such a configuration, the bootstrap circuit can change the operation mode when the input voltage decreases, and the decrease in the supply voltage to the drive circuit and the increase in the on-resistance of the switching element can be suppressed. Higher frequency and wider input voltage can be achieved. In addition, since the circuit configuration is simple and there is no need to increase the size of the switching element, the cost can be reduced.

  The bootstrap circuit includes a first bootstrap diode whose anode is supplied with a voltage output from the constant voltage circuit, and a second bootstrap diode whose anode is supplied with the input voltage. You may make it prepare.

  Further, the bootstrap circuit may select one mode from the plurality of operation modes by an external control signal input from the outside.

  A voltage output from the constant voltage circuit when the input voltage detected by the input voltage detection circuit is greater than a set voltage. If the input voltage detected by the input voltage detection circuit is equal to or lower than a set voltage, the bootstrap circuit is in a mode other than the mode in which the boot is driven by the voltage output from the constant voltage circuit. A mode may be selected.

  The bootstrap circuit may include a first LDMOS instead of the first bootstrap diode, and may include a second LDMOS instead of the second bootstrap diode.

  The output voltage of the constant voltage circuit is supplied to the gate and source of the first LDMOS, the input voltage is supplied to the gate and source of the second LDMOS, and the first LDMOS and the second LDMOS The drain of the LDMOS is connected to the drive circuit, switching between connection / disconnection between the gate and source of the first LDMOS and the back gate, and switching between connection / disconnection between the drain and the back gate of the first LDMOS. The connection / disconnection between the gate and the source of the second LDMOS and the back gate and the connection / disconnection between the drain and the back gate of the second LDMOS may be switched.

  The input voltage detection circuit may include a comparison circuit for comparing the magnitude relationship between the input voltage and the set voltage.

  Further, the plurality of operation modes may include a mode in which booting is performed by an output voltage of the switching power supply circuit. In this case, the input voltage detection circuit compares the first comparison circuit for comparing the magnitude relationship between the input voltage and the set voltage, the output voltage of the constant voltage circuit, and the output voltage of the switching power supply circuit. You may make it provide the 2nd comparison circuit for comparing magnitude relationship.

  In order to achieve the above object, an electronic apparatus according to the present invention includes a switching power supply circuit having any one of the above configurations.

  According to the present invention, when the input voltage decreases, the bootstrap circuit changes the operation mode, and it is possible to suppress a decrease in the supply voltage to the drive circuit and an increase in the on-resistance of the switching element. In addition, the input voltage can be widened. In addition, since the circuit configuration is simple and there is no need to increase the size of the switching element, the cost can be reduced.

  Embodiments of the present invention will be described below with reference to the drawings. A bootstrap type switching power supply circuit according to the first embodiment of the present invention is shown in FIG. In FIG. 1, the same parts as those in FIG. 16 are denoted by the same reference numerals.

The switching power supply circuit shown in FIG. 1 includes a switching power supply IC100, a bootstrap capacitor BC1, which is an external component, a coil L1, a Schottky barrier diode SBD1, a resistor R1, a resistor R2, an output capacitor C1, and an output terminal T _O. A chopper regulator.

The internal configuration of the switching power supply IC 100 will be described below. The switching power supply IC 100 includes terminals T1 to T4, a switching element 1, a drive circuit 2, a constant voltage circuit 3 that outputs a constant voltage V _C (for example, a DC voltage of 5 [V]), a current detection unit 4, and the like. The main logic generator 5, the level shift circuit 6, bootstrap diodes BD1 and BD2, and a switch DW2.

  The terminal T1 is connected to the drain of the switching element 1 via the current detector 4, the cathode of the bootstrap diode 2 via the switch SW2, and the input terminal of the constant voltage circuit 3. The output terminal of the constant voltage circuit 3 is connected to the cathode of the bootstrap diode D1. The anode of the bootstrap diode D2 and the anode of the bootstrap diode D1 are connected to the terminal T3, and the source of the switching element 1 is connected to the terminal T2.

The main logic generation unit 5 includes an oscillator 51, an inverter gate 52, a reference voltage source 53, comparators 54 and 55, a flip-flop 56, and a NAND gate 57. The main logic generation unit 5 includes the voltage V _FB and the voltage at the terminal T4. A logic signal is generated based on the current detection signal of the current detection unit 4.

The level shift circuit 6 and the drive circuit 2 each use a voltage (V _B −V _OUT ) between the terminal T3 and the terminal T2 as a drive voltage. The level shift circuit 6 level-shifts the logic signal output from the main logic generation unit 5 and sends it to the drive circuit 2. The drive circuit 2 generates a gate drive signal according to the signal output from the level shift circuit 6 and sends the gate drive signal to the gate of the switching element 1.

Next, the configuration of the external parts will be described below. One end of the bootstrap capacitor BC1 is connected to the terminal T3, and the other end of the bootstrap capacitor BC1, one end of the coil L1, and the cathode of the Schottky barrier diode SBD1 are connected to the terminal T2. The anode of the Schottky barrier diode SBD1 is connected to the ground potential. The other end of the coil L1 is connected to one end of a resistor R1, one end of an output capacitor C1, and a terminal T _O that outputs an output voltage V _O. The other end of the resistor R1 is connected to the terminal T4 and one end of the resistor R2. The other end of the resistor R2 and the other end of the output capacitor C1 are connected to the ground potential.

  The bootstrap circuit of the switching power supply circuit shown in FIG. 1 includes a constant voltage circuit 3, a bootstrap diode BD1, a switch SW2, a bootstrap diode BD2, and a bootstrap capacitor BC1.

When the input voltage V _IN is equal to or higher than the constant voltage V _{C of} the constant voltage circuit 3, the voltage output from the constant voltage circuit 3 is the constant voltage V _C. On the other hand, when the input voltage V _IN is less than the constant voltage V _{C of} the constant voltage circuit 3, the voltage output from the constant voltage circuit 3 is less than the constant voltage V _C and further less than the input voltage V _IN . Therefore, the input voltage V _IN is larger than the set voltage (the input voltage at which the constant voltage circuit 3 can maintain the output of the constant voltage V _C and does not exceed the withstand voltage of the level shift circuit 6 and the drive circuit 2, for example, 6 V). In this case, the switch SW2 is turned off and booting is performed with the voltage output from the constant voltage circuit 3. Conversely, when the input voltage V _IN is equal to or lower than the set voltage, the switch SW2 is turned on and the input voltage is Boot with V _IN .

When the switch SW2 is turned off to boot with the constant voltage V _C output from the constant voltage circuit 3, the voltage (V _B −V _OUT ) between the terminal T3 and the terminal T2 is V _C −V _F1 + V. _f . V _f is the forward voltage of the Schottky barrier diode SBD1. The voltage (V _B −V _OUT ) between the terminal T3 and the terminal T2 is set as high as possible within a range not exceeding the breakdown voltage (for example, 5V) of the transistors in the level shift circuit 6 and the drive circuit 2. Thus, the gate voltage of the switching element 1 can be set high, the on-resistance of the switching element 1 is reduced, and the efficiency is improved. Further, the voltage (V _B −V _OUT ) between the terminal T3 and the terminal T2 is set as high as possible within a range not exceeding the breakdown voltage (for example, 5 V) of the transistors in the level shift circuit 6 and the drive circuit 2. As a result, the delay time of the level shift circuit 6 and the drive circuit 2 is suppressed, and the rise time and fall time of the switching element 1 are shortened, thereby making it possible to cope with higher oscillation frequencies.

On the other hand, when the switch SW2 is turned on to boot by the input voltage V _IN , the voltage (V _B −V _OUT ) between the terminal T3 and the terminal T2 becomes V _IN −V _F2 + V _f , and the constant voltage circuit Rather than booting with the voltage output from 3, the voltage (V _B −V _OUT ) between the terminal T3 and the terminal T2 can be suppressed from decreasing.

  With the above operation, it is possible to increase the oscillation frequency and widen the input voltage. Further, since the configuration of the constant voltage circuit is simple, it is inexpensive.

  Next, a bootstrap type switching power supply circuit according to the second embodiment of the present invention is shown in FIG. In FIG. 2, the same parts as those in FIG.

  In the switching power supply circuit shown in FIG. 2, the switch SW2 provided between the terminal T1 and the anode of the bootstrap diode BD2 in the switching power supply circuit shown in FIG. 1 is connected between the cathode of the bootstrap diode BD2 and the terminal T3. Further, the switch SW1 is provided between the cathode of the bootstrap diode BD1 and the terminal T3.

When the input voltage V _IN is higher than the set voltage (the input voltage that allows the constant voltage circuit 3 to maintain the output of the constant voltage V _C and does not exceed the withstand voltage of the level shift circuit 6 and the drive circuit 2, for example, 6 V). The switch SW1 is turned on, the switch SW2 is turned off, and when the input voltage V _IN is equal to or lower than the set voltage, the switch SW1 is turned off and the switch SW2 is turned on. With such an operation, the switching power supply circuit shown in FIG. 2 can achieve the same effects as the switching power supply circuit shown in FIG.

  Here, FIG. 3 shows a specific example of the switching power supply circuit shown in FIG. 1, that is, a configuration example including a switch control unit that controls ON / OFF of the switch SW2. In FIG. 3, the same parts as those in FIG.

In FIG. 3, the terminal T5, the inverter gate 7 and the inverter gate 8 correspond to the switch control unit and are the cheapest switch control unit. According to the configuration shown in FIG. 3, for example, by inputting either a high level signal or a low level signal to the terminal T5, it is determined whether the boot is performed by the input voltage V _IN or the output voltage of the constant voltage circuit 3. You can choose from. Therefore, in consideration of the input usage conditions, the user can select whether to boot by the input voltage V _IN or the output voltage of the constant voltage circuit 3. When booting the input voltage V _IN turns on the switch SW2, when booting the output voltage of the constant voltage circuit 3 turns off the switch SW 2.

  Next, FIG. 4 shows another specific example of the switching power supply circuit shown in FIG. 1, that is, another configuration example including a switch control unit that controls on / off of the switch SW2. In FIG. 4, the same parts as those in FIG.

Or in FIG. 4, the input voltage detection circuit 9, which correspond to the switch control unit, in accordance with the detection result of the input voltage V _IN, boots by either of the input voltage V _IN and the output voltage of the constant voltage circuit 3 Is selected.

An example of the input voltage detection circuit 9 is shown in FIG. The input voltage detection circuit shown in FIG. 5 includes resistors 91 and 92, a hysteresis comparator 93, a reference voltage source 94, and inverter gates 95 and 96. The reference voltage V _REF of the reference voltage source 94 and the input voltage are provided. the divided V _D of the V _iN and compares hysteresis comparator 93, the input voltage V _iN is set voltage (constant-voltage circuit 3 and an input voltage which can maintain the output of the constant voltage V _C, the level shift circuit 6 and When the voltage does not exceed the breakdown voltage of the drive circuit 2 (for example, 6 V) or less, the inverter gate 96 outputs a high level signal to turn on the switch SW2 (not shown in FIG. 5).

In the switching power supply circuit shown in FIG. 4, the waveforms of the voltage V _B at the terminal T3 and the voltage V _{OUT at} the terminal T2 and the states of the switch SW2 and the switching element 1 when the input voltage V _IN is higher than the set voltage are shown in FIG. The waveforms of the voltage V _B at the terminal T3 and the voltage V _{OUT at} the terminal T2 and the states of the switch SW2 and the switching element 1 when the input voltage V _IN is lower than the set voltage are as shown in FIG. .

  In the switching power supply circuit shown in FIGS. 1 to 4 described above, a bootstrap diode that is a diode element is used. However, by using an LDMOS instead of a bootstrap diode that is a diode element, a diode becomes unnecessary. Since the steps of epi and embedding can be reduced, it is possible to manufacture by an inexpensive process. Further, by using an LDMOS instead of a bootstrap diode that is a diode element, it is possible to cope with a high-speed response. Furthermore, since the LDMOS can also serve as a switch, it is possible to reduce the cost by reducing the switches SW1 and SW2.

The LDMOS is an element having a cross-sectional structure as shown in FIG. 8 and capable of realizing a high and medium breakdown voltage drain voltage and a low on-resistance. Generally, the drain breakdown voltage is large, but the gate breakdown voltage and the source breakdown voltage are low. Therefore, the drain of the LDMOS is connected to the terminal T3 to which the voltage V _B (see FIGS. 6 and 7) that becomes a high voltage due to the bootstrap is applied.

  FIG. 9 shows a modification of the switching power supply circuit shown in FIG. 3 in which the bootstrap diode is replaced with LDMOS, and FIG. 10 shows a modification of the switching power supply circuit shown in FIG. 4 in which the bootstrap diode is replaced with LDMOS.

  In the switching power supply circuit shown in FIGS. 9 and 10, the drain of the LDMOS 101 is connected to the terminal T3, the gate and source of the LDMOS 101 are connected to the output side of the constant voltage circuit 3, and the back gate of the LDMOS 101 is connected by the back gate control circuit 10. Control. The back gate of the LDMOS 101 is connected to the gate and source via the switch SW3 and is connected to the drain via the switch SW4.

  In the switching power supply circuit shown in FIGS. 9 and 10, the drain of the LDMOS 102 is connected to the terminal T3, the gate and source of the LDMOS 102 are connected to the terminal T1, and the back gate control circuit 10 controls the back gate of the LDMOS 102. The back gate of the LDMOS 102 is connected to the gate and source via the switch SW5, and is connected to the drain via the switch SW6.

When the switching element 1 is on, the back gate control circuit 10 turns on the switches SW3 and SW5, turns off the switches SW4 and SW6, and turns off the LDMOSs 101 and 102. When the switching element 1 is off and boots with the voltage output from the constant voltage circuit 3, the back gate control circuit 10 turns on the switches SW4 and SW5, turns off the switches SW6 and SW6, and turns the LDMOS 101 in the reverse direction. The LDMOS 102 is turned off. When the switching element 1 is off and boots with the input voltage _VIN , the back gate control circuit 10 turns on the switches SW3 and SW6, turns off the switches SW4 and SW5, turns off the LDMOS 101, and turns the LDMOS 102 in the reverse direction. Turn on.

The back gate control circuit 10 recognizes whether the switching element 1 is on or off based on the output of the boot unit control circuit 11. Further, the back gate control circuit 10 determines whether to boot with the voltage output from the constant voltage circuit 3 or with the input voltage V _IN based on the output of the inverter gates 7 and 8 or the output of the input voltage detection circuit 9. Has been decided. In the switching power supply circuit shown in FIG. 10, the input voltage V _IN is a set voltage (the constant voltage circuit 3 is an input voltage that can maintain the output of the constant voltage V _C , and the withstand voltages of the level shift circuit 6 and the drive circuit 2 are reduced. beyond not voltage, for example, booting the voltage output from the constant-voltage circuit 3 is higher than 6V), if the input voltage V _iN is set voltage or less, so that booting by the input voltage V _iN.

In the switching power supply circuit shown in FIG. 10 described above, the waveforms of the voltage V _B at the terminal T3 and the voltage V _{OUT at} the terminal T2 when the input voltage V _IN is higher than the set voltage, the switches SW3 to SW6, the LDMOSs 101 and 102, and the switching element. The state of 1 is as shown in FIG. 11. When the input voltage V _IN is lower than the set voltage, the waveforms of the voltage V _B at the terminal T3 and the voltage V _{OUT at} the terminal T2 and the switches SW3 to SW6 and the LDMOSs 101 and 102 are switched. The state of the element 1 is as shown in FIG.

  The switch SW3 and the switch SW5 can each use a Pch field effect transistor, and the switch SW4 and the switch SW6 can each use an Nch field effect transistor. However, both the Pch field effect transistor and the Nch field effect transistor must have a high and medium breakdown voltage in all of the gate, source, and drain.

  The back gates of the Pch field effect transistor (hereinafter referred to as Pch transistor S3) used as the switch SW3 and the Pch field effect transistor (hereinafter referred to as Pch transistor S5) used as the switch SW5 are connected to the output side of the constant voltage circuit 3, and the switch The back gates of the Nch field effect transistor (hereinafter referred to as Nch transistor S4) used as SW4 and the Nch field effect transistor (hereinafter referred to as Nch transistor S6) used as switch SW6 are connected to GND. Then, a signal synchronized with the output signal of the drive circuit 2 (the gate signal of the switching element 1) is supplied to each gate of the Pch transistor S3, Pch transistor S5, Nch transistor S4, and Nch transistor S6.

  When the gate signals of Pch transistor S3, Pch transistor S5, Nch transistor S4, and Nch transistor S6 are synchronized, the states of Pch transistor S3, Pch transistor S5, Nch transistor S4, and Nch transistor S6 are switched simultaneously. In this case, a time occurs when the Pch transistor S3, the Pch transistor S5, the Nch transistor S4, and the Nch transistor S6 are simultaneously turned on. The simultaneous ON time is as short as 1 ns or less, but the source-drain of the LDMOSs 101 and 102 penetrates at that time, and if the switching element 1 is penetrated, the output of the constant voltage circuit 3 A low withstand voltage system circuit (6 V or less) using the voltage as the power supply voltage will be destroyed. Therefore, a delayed signal (for example, the gate of the Pch transistor S5 with respect to the gate signal of the Pch transistor S3 so that the gate signals of the Pch transistor S3, the Pch transistor S5, the Nch transistor S4, and the Nch transistor S6 can be simultaneously turned off). It is preferable to avoid destruction of the low withstand voltage system circuit (6 V or less) by delaying the signal and delaying the gate signal of the Nch transistor S6 with respect to the gate signal of the Nch transistor S4.

  Next, a bootstrap type switching power supply circuit according to a third embodiment of the present invention is shown in FIG. In FIG. 13, the same parts as those in FIG.

The bootstrap type switching power supply circuit according to the third embodiment of the present invention shown in FIG. 13 inputs a 2-bit external control signal to the bootstrap type switching power supply circuit according to the second embodiment of the present invention shown in FIG. Terminals T6 and T7, a terminal T8 connected to the terminal T _O , a bootstrap diode BD3 whose cathode is connected to the terminal T3, and a switch provided between the anode of the bootstrap diode BD3 and the terminal T8 SW7 and a switch control circuit 12 that turns on one of the switches SW1, SW2, and SW7 according to a 2-bit external control signal input to the terminals T6 and T7 are newly provided, and a bootstrap diode The switch SW1 provided between the cathode of the BD1 and the terminal T3 is connected to the output side of the constant voltage circuit 3. A structure provided between the anode of the bootstrap diode BD1.

Bootstrap switching power supply circuit according to a second embodiment of the present invention shown in the bootstrap switching power circuit and 2 according to the first embodiment of the present invention shown in FIG. 1, the input voltage V _IN and a constant voltage circuit 3 The bootstrap type switching power supply circuit according to the third embodiment of the present invention shown in FIG. 13 is different from the input voltage V _IN and the constant voltage circuit 3. The boot is selected depending on either the output voltage or the output voltage V _O.

Therefore, in the bootstrap type switching power supply circuit according to the third embodiment of the present invention shown in FIG. 13, the input voltage V _IN falls below the set value of the constant voltage V _C output from the constant voltage circuit 3, and the constant voltage circuit This is suitable when the output voltage 3 is slightly lower than the constant voltage V _C and the output voltage V _O is larger than the output voltage of the constant voltage circuit 3. For example, when the input voltage V _IN that allows the constant voltage circuit 3 to output the constant voltage V _C is obtained, the switch SW 1 is turned on and the switches SW 2 and SW 7 are turned off, so that the constant voltage circuit 3 can output the constant voltage V _C. Do input voltage V _iN can not be obtained, when the output voltage of the constant voltage circuit 3 is greater than the output voltage V _O turns off the switch SW1 and SW 7 to turn on SW2, the constant voltage circuit 3 and the constant voltage V _C When the output voltage V _IN that can be output is not obtained and the output voltage of the constant voltage circuit 3 is not greater than the output voltage V _O, 2-bit external control that turns on the SW 7 and turns off the switches SW1 and SW2 A signal may be input to terminals T6 and T7.

  In the switching power supply circuit shown in FIGS. 1 to 4, the LDMOS can be used in place of the bootstrap diode which is a diode element, and the third embodiment of the present invention shown in FIG. Also in such a bootstrap switching power supply circuit, LDMOS can be used in place of the bootstrap diodes BD1 to BD which are diode elements.

  Further, in the bootstrap type switching power supply circuit according to the third embodiment of the present invention shown in FIG. 13, a switch control circuit shown in FIG. 14 may be provided in place of the terminals T6 and T7 and the switch control circuit 12. .

The switches SW1 , SW2 and SW7 are turned on by a high level control signal and turned off by a low level control signal. Further, an input voltage V _{IN at} which the constant voltage circuit 3 can output a constant voltage V _C is provided. When the _divided voltage V _D of the input voltage V _IN becomes larger than the reference voltage V _REF when the input voltage V _IN is obtained, and the input voltage V _IN that can output the constant voltage V _C cannot be obtained, the input voltage V partial pressure V _D of V _iN so becomes equal to or lower than the reference voltage V _REF, by setting the value of the resistance value and the reference voltage V _REF of the voltage dividing resistors for dividing the input voltage V _iN, the constant-voltage circuit 3 is constant voltage V when the input voltage V _iN can output a _C is obtained to turn off the switch SW2 and SW 7 to turn on the switch SW1. Constant voltage circuit 3 is not to obtain the input voltage V _IN can output a constant voltage V _C, the constant when the output voltage of the voltage circuit 3 is greater than the output voltage V _O turns on the SW2 off switches SW1 and SW 7 If the input voltage V _{IN from} which the constant voltage circuit 3 can output the constant voltage V _C is not obtained and the output voltage of the constant voltage circuit 3 is not larger than the output voltage V _O , the SW 7 is turned on and the switches SW1 and SW SW2 can be turned off.

The switching power supply circuit according to the present invention includes an LED driving circuit (for example, the resistor R1 is replaced with an LED). The switching power supply circuit according to the present invention can be mounted on all electronic devices, but is particularly suitable for use in the following electronic devices that require low cost and downsizing.
・ Vehicle equipment such as car audio ・ Various TVs such as LCD TVs, AV equipment such as DVD-Video ・ Computer peripherals such as CD-ROM devices, CD-R devices and DVD devices ・ LED drivers for LCD screen backlights of mobile phones Among the above preferred examples, electronic devices such as an optical storage device and a liquid crystal television are particularly suitable.

These are figures which show the structure of the bootstrap type | mold switching power supply circuit which concerns on 1st embodiment of this invention. These are figures which show the structure of the bootstrap type | mold switching power supply circuit which concerns on 2nd embodiment of this invention. These are figures which show the specific example of the switching power supply circuit shown in FIG. These are figures which show the other specific example of the switching power supply circuit shown in FIG. These are figures which show an example of an input voltage detection circuit. These are figures which show the state of each part voltage waveform and each element in case an input voltage is higher than a setting voltage. These are figures which show the state of each part voltage waveform and each element in case an input voltage is lower than a setting voltage. These are figures which show the cross-section of LDMOS. These are figures which show the modification of the switching power supply circuit shown in FIG. 3 which replaced the diode for bootstrap with LDMOS. These are figures which show the modification of the switching power supply circuit shown in FIG. 4 which replaced the diode for bootstrap with LDMOS. These are figures which show the state of each part voltage waveform and each element in case an input voltage is higher than a setting voltage. These are figures which show the state of each part voltage waveform and each element in case an input voltage is lower than a setting voltage. These are figures which show the structure of the bootstrap type | mold switching power supply circuit which concerns on 3rd embodiment of this invention. FIG. 3 is a diagram illustrating an example of a switch control circuit. These are figures which show the example of 1 structure of the conventional bootstrap type | mold switching power supply circuit. These are figures which show the other structural example of the conventional bootstrap type | mold switching power supply circuit. These are figures which show the input-output voltage characteristic of a constant voltage circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Switching element 2 Drive circuit 3 Constant voltage circuit 4 Current detection part 5 Main logic generation part 6 Level shift circuit 7, 8 Inverter gate 9 Input voltage detection circuit 10 Back gate control circuit 11 Boot part control circuit 12 Switch control circuit 51 Oscillator 52 Inverter gate 53 Reference voltage source 54, 55 Comparator 56 Flip-flop 57 NAND gate 91, 92 Resistor 93 Hysteresis comparator 94 Reference voltage source 95, 96 Inverter gate 100 Switching power supply IC
101, 102 LDMOS
BC1 Bootstrap capacitor BD1 to BD3 Bootstrap diode C1 Output capacitor L1 Coil R1, R2 Resistor SBD1 Schottky barrier diode SW1 to SW7 Switch T1 to T8 terminal T _O Output terminal

Claims (9)

A switching element;
A drive circuit for driving the switching element;
A bootstrap circuit for supplying power to the drive circuit;
And a constant voltage circuit that obtains a constant voltage by stepping down the input voltage,
The bootstrap circuit, the a mode to boot the voltage output from the constant voltage circuit, have a plurality of operation modes including a mode to boot by said input voltage,
The bootstrap circuit includes a first bootstrap diode whose anode is supplied with a voltage output from the constant voltage circuit, and a second bootstrap diode whose anode is supplied with the input voltage. A switching power supply circuit. The switching power supply circuit according to claim 1, wherein the bootstrap circuit selects one mode from the plurality of operation modes by an external control signal input from the outside. An input voltage detection circuit for detecting the input voltage;
When the input voltage detected by the input voltage detection circuit is larger than a set voltage, the bootstrap circuit selects a mode for booting with a voltage output from the constant voltage circuit,
2. The bootstrap circuit selects a mode other than a mode for booting with a voltage output from the constant voltage circuit when the input voltage detected by the input voltage detection circuit is equal to or lower than a set voltage. The switching power supply circuit described. 2. The switching power supply circuit according to claim 1, wherein the bootstrap circuit includes a first LDMOS instead of the first bootstrap diode, and includes a second LDMOS instead of the second bootstrap diode. . The output voltage of the constant voltage circuit is supplied to the gate and source of the first LDMOS, the input voltage is supplied to the gate and source of the second LDMOS, and the first LDMOS and the second LDMOS The drain is connected to the drive circuit;
Switching between connection / disconnection between the gate and source of the first LDMOS and the back gate, switching between connection / disconnection between the drain and the back gate of the first LDMOS, and gate / source and back gate of the second LDMOS 5. The switching power supply circuit according to claim 4, wherein connection / disconnection of the second LDMOS and connection / disconnection of the drain and back gate of the second LDMOS can be switched. The switching power supply circuit according to claim 3, wherein the input voltage detection circuit includes a comparison circuit for comparing a magnitude relationship between the input voltage and the set voltage. The switching power supply circuit according to any one of claims 1 to 6, wherein the plurality of operation modes include a mode of booting with an output voltage of the switching power supply circuit. The plurality of operation modes include a mode of booting with an output voltage of the switching power supply circuit,
  The input voltage detection circuit includes: a first comparison circuit for comparing a magnitude relationship between the input voltage and the set voltage; the output voltage of the constant voltage circuit; and the switching power supply circuit. The switching power supply circuit according to claim 3, further comprising a second comparison circuit for comparing a magnitude relationship with the output voltage. An electronic apparatus comprising the switching power supply circuit according to claim 1.

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