JP2019140752A - Switching circuit, dc/dc converter, and control circuit thereof - Google Patents

Abstract

To reduce cost of a switching circuit.SOLUTION: A switching circuit 200 using an N channel transistor as a high side transistor Mcomprises a power supply circuit 300 for bootstrap. A reference voltage source 310 generates a reference voltage V. An output transistor 304 receives the reference voltage Vat a control electrode that is a gate or a base, and a source or an emitter is connected to an output node. A feedback circuit 320 (i) clamps a difference in a voltage between the control electrode of an output transistor 304 and an output node 302, and (ii), when a voltage Vof the output node 302 increases, increases a voltage Vof the control electrode of the output transistor 304 following the above.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a switching circuit.

A switching circuit is used for a DC / DC converter, an inverter, or the like. FIG. 1 is a circuit diagram of a switching circuit. The switching circuit 100 includes a high side transistor M ₁ provided between the input terminal (VCC) and the switching terminal (LX), and a low side transistor M ₂ provided between the LX terminal and the ground terminal (GND). High-side transistor _{M 1} is turned on, the low side transistor _{M 2} is in the state of off, (voltage _{V CC} is generated between the VCC pin) and the LX pin high, the high-side transistor _{M 1} is turned off, the low side transistor _{M 2} is turned on In the state, a low level (voltage V _{GND of the} GND terminal) is generated at the LX terminal. Instead of the low-side transistor M _2, it may be provided rectifying element such as a Schottky diode.

As high-side transistor _{M 1,} there is the use of the transistor of the N-channel (or NPN type). In this case, in order to turn on the high side transistor M ₁ has, on its gate, it is necessary to apply a higher gate voltage V _HG than the input voltage V _CC. A bootstrap circuit is used to generate a gate voltage V _HG that is higher than the input voltage _VCC .

A bootstrap capacitor C _BST is connected between the bootstrap terminal (BST) and the LX terminal. The power supply circuit 110 for the bootstrap circuit generates a constant voltage V _HREG . The constant voltage V _HREG is determined to be higher than the threshold voltage V _{GS (th)} between the gate and the source of the high side transistor M1. The constant voltage V _HREG is applied to the bootstrap capacitor C _BST via the diode D1 and the BST terminal.

In a state where the LX terminal is low (0 V), the bootstrap capacitor C _BST is charged with ΔV = V _HREG −Vf. Vf is the forward voltage of the diode _{D 1.} The voltage V _{BST at the} BST terminal is V _LX + ΔV. The voltage V _BST at the _BST terminal is supplied to the upper power supply terminal of the high side driver 102. The lower power supply terminal of the high side driver 102 is connected to the LX terminal. The high side driver 102 outputs V _BST when the control signal _SH is on level (eg, high), and outputs V _LX when it is off level (eg, low).

JP 2011-014738 A

The high-side transistor _{M 1} is turned on, when it is LX _{= V CC,} voltage _{V BST} of BST _terminal, the _{V CC} + _ΔV. Voltage of LX terminal depending on the state of the load, there is a case where jumping further beyond the input voltage V _CC.

The output HREG of the power supply circuit 110 is coupled to the BST terminal via a parasitic capacitance between the anode and cathode of the diode D1. Therefore, the jump of the voltage V _{BST at} the BST terminal increases the voltage V _HREG of the output HREG of the power supply circuit 110. When the power supply circuit 110 is configured with an element having a low breakdown voltage of about 5 V, the increase in the voltage V _HREG should not be allowed.

FIGS. 2A and 2B are diagrams for explaining measures for suppressing an increase in voltage V _HREG . In FIG. 2A, a capacitor 104 having a large capacitance (in the order of several hundreds pF to nF) is connected to the output HREG of the power supply circuit 110 to suppress an increase in the voltage V _HREG . If the capacitor 104 is to be built in the IC, the chip area increases, which increases the cost. When the capacitor 104 is externally attached, a new additional terminal is required in addition to the chip component, which also increases the cost.

  As another approach, as shown in FIG. 2B, a voltage clamp circuit 106 may be provided on the output HREG of the power supply circuit 110. However, if the voltage clamp circuit 106 is added, the chip size also increases, and an increase in cost is inevitable. Further, since the voltage clamp circuit 106 discards current, it causes another problem of increased power consumption.

  SUMMARY An advantage of some aspects of the invention is that it lowers the cost of a switching circuit.

  One embodiment of the present invention relates to a switching circuit. The switching circuit includes an input terminal, a switching terminal, a bootstrap terminal, a high-side transistor provided between the input terminal and the switching terminal, a bootstrap capacitor provided between the switching terminal and the bootstrap terminal, a power supply A circuit, and a first rectifier element provided between the output node of the power supply circuit and the bootstrap terminal. The power supply circuit includes: a reference voltage source that generates a reference voltage; an output transistor that receives a reference voltage at a control electrode that is a gate or a base, a source or an emitter connected to an output node; and (i) a control electrode of the output transistor A feedback circuit that clamps the voltage difference of the output node and (ii) increases the voltage of the control electrode of the output transistor following the rise of the voltage of the output node.

  Another aspect of the present invention relates to a control circuit for a DC / DC converter. The control circuit includes a switching terminal and a bootstrap terminal, and a pulse modulator that generates a pulse signal that instructs on / off of the high-side transistor so that a feedback signal according to the state of the DC / DC converter or the load approaches a target value; A power supply circuit; a first rectifying element provided between the output node of the power supply circuit and the bootstrap terminal; a driver that receives the voltage of the bootstrap terminal at the upper power supply terminal and drives the high-side transistor based on the pulse signal; Is provided. The power supply circuit includes: a reference voltage source that generates a reference voltage; an output transistor that receives a reference voltage at a control electrode that is a gate or a base, a source or an emitter connected to an output node; and (i) a control electrode of the output transistor A feedback circuit that clamps the voltage difference of the output node and (ii) increases the voltage of the control electrode of the output transistor following the increase of the voltage of the output node.

  Another aspect of the present invention relates to a DC / DC converter. The DC / DC converter includes the above-described control circuit.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, and the like are also effective as an aspect of the present invention.

  According to an aspect of the present invention, the reliability of a bootstrap power supply circuit can be improved.

It is a circuit diagram of a switching circuit. FIGS. 2A and 2B are diagrams for explaining measures for suppressing an increase in voltage V _HREG . It is a circuit diagram of the switching circuit concerning an embodiment. It is a circuit diagram of the 1st example of composition of a power circuit. It is an operation | movement waveform diagram of a switching circuit provided with the power supply circuit of FIG. It is a circuit diagram of the 2nd example of composition of a power circuit. FIG. 7A is an operation waveform diagram of the switching circuit including the power supply circuit of FIG. 6, and FIG. 7B is an operation waveform diagram of the switching circuit including the power supply circuit of FIG. It is a circuit diagram of a DC / DC converter.

(Outline of the embodiment)
One embodiment disclosed herein relates to a switching circuit. The switching circuit includes an input terminal, a switching terminal, a bootstrap terminal, a high-side transistor provided between the input terminal and the switching terminal, a bootstrap capacitor provided between the switching terminal and the bootstrap terminal, a power supply A circuit, and a first rectifier element provided between the output node of the power supply circuit and the bootstrap terminal. The power supply circuit includes: a reference voltage source that generates a reference voltage; an output transistor that receives a reference voltage at a control electrode that is a gate or a base, a source or an emitter connected to an output node; and (i) a control electrode of the output transistor A feedback circuit that clamps the voltage difference of the output node and (ii) increases the voltage of the control electrode of the output transistor following the rise of the voltage of the output node.

  In this embodiment, by allowing the voltage jump at the output node, a clamp circuit and a large-capacitance capacitor for suppressing the voltage rise at the output node become unnecessary, and the cost can be reduced. However, if only the voltage at the output node rises, an overvoltage occurs between the gate and source of the output transistor (between the base and emitter), so a feedback circuit is provided to follow the voltage rise at the output node (source / emitter). The voltage of the control electrode (gate, base) of the output transistor was increased. As a result, the output transistor can be protected.

The feedback circuit may include a Zener diode provided between the control electrode of the output transistor and the output node. Thus, in a higher than the voltage of it is the output node of the voltage of the control electrode of the output transistor, the potential difference between the gate and the source of the output node (base-emitter), can be clamped so as not to exceed the Zener voltage V _Z. When the switching terminal transitions to high and the output node voltage V _HREG rises, the voltage of the control electrode can be raised to V _HREG -V _F following that. V _F is the forward voltage of the Zener diode.

The feedback circuit may include two Zener diodes connected in reverse series between the control electrode of the output transistor and the output node. In this case, in a state where the voltage of the control electrode of the output transistor is higher than the voltage of the output node, the potential difference between the gate and source (between the base and emitter) of the output node can be clamped so as not to exceed V _Z + V _F. When the switching terminal transitions to high and the output node voltage V _HREG rises, the control electrode voltage rises to V _HREG − (V _F + V _Z ). That is, the voltage peak of the control electrode can be suppressed. This prevents the output transistor from turning on when the switching terminal transitions to low.

  The power supply circuit may further include a second rectifier element provided between the reference voltage source and the control electrode of the output transistor. As a result, the control electrode of the output transistor and the reference voltage source can be separated, and a jump in the voltage of the control electrode can be prevented from being applied to the reference voltage source. This produces the advantage that the reference voltage source can be configured with a low voltage process.

  The second rectifying element may include a diode. The second rectifying element may include a transistor that is controlled in synchronization with the switching of the high-side transistor.

  Another aspect of the present invention relates to a control circuit for a DC / DC converter. The control circuit includes a switching terminal and a bootstrap terminal, and a pulse modulator that generates a pulse signal that instructs on / off of the high-side transistor so that a feedback signal according to the state of the DC / DC converter or the load approaches a target value; A power supply circuit; a first rectifying element provided between the output node of the power supply circuit and the bootstrap terminal; a driver that receives the voltage of the bootstrap terminal at the upper power supply terminal and drives the high-side transistor based on the pulse signal; Is provided. The power supply circuit includes: a reference voltage source that generates a reference voltage; an output transistor that receives a reference voltage at a control electrode that is a gate or a base, a source or an emitter connected to an output node; and (i) a control electrode of the output transistor A feedback circuit that clamps the voltage difference of the output node and (ii) increases the voltage of the control electrode of the output transistor following the increase of the voltage of the output node.

  The control circuit may be integrated on a single semiconductor substrate. “Integrated integration” includes the case where all of the circuit components are formed on a semiconductor substrate and the case where the main components of the circuit are integrated. A resistor, a capacitor, or the like may be provided outside the semiconductor substrate. By integrating the circuit on one chip, the circuit area can be reduced and the characteristics of the circuit elements can be kept uniform.

(Embodiment)
The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. The embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

  In this specification, “the state in which the member A is connected to the member B” means that the member A and the member B are electrically connected to each other in addition to the case where the member A and the member B are physically directly connected. It includes cases where the connection is indirectly made through other members that do not substantially affect the general connection state, or that do not impair the functions and effects achieved by their combination.

  Similarly, “the state in which the member C is provided between the member A and the member B” refers to the case where the member A and the member C or the member B and the member C are directly connected, as well as their electric It includes cases where the connection is indirectly made through other members that do not substantially affect the general connection state, or that do not impair the functions and effects achieved by their combination.

  “Signal A (voltage, current) is in response to signal B (voltage, current)” means that signal A has a correlation with signal B. Specifically, (i) signal A Is signal B, (ii) signal A is proportional to signal B, (iii) signal A is obtained by level shifting signal B, and (iv) signal A is obtained by amplifying signal B. If (v) signal A is obtained by inverting signal B, it means (vi) or any combination thereof. It will be understood by those skilled in the art that the “depending” range is determined depending on the type and application of the signals A and B.

FIG. 3 is a circuit diagram of the switching circuit 200 according to the embodiment. The switching circuit 200 includes a high side transistor M ₁ , a low side transistor M ₂ , a high side driver 202, a low side driver 204, a bootstrap capacitor C _BST , a rectifier element D ₁ , and a power supply circuit 300.

Among the components of the switching circuit 200, the bootstrap capacitor C _BST is externally attached, and the remaining components are integrated in the control circuit 400 which is an integrated circuit. Note that discrete elements may be employed for the high-side transistor M ₁ and the low-side transistor M ₂ and externally attached to the control circuit 400.

The input (VCC) terminal, a DC voltage _{V CC} from the outside is supplied. The ground (GND) terminal is grounded. A load, an inductor, and a transformer (not shown) are connected to the switching terminal LX. The switching circuit 200 generates a switching signal V _LX that transitions between high (V _CC ) and low (V _GND ) at the switching terminal LX.

A bootstrap capacitor C _BST is externally connected between the bootstrap (BST) terminal and the LX terminal. High-side transistor _{M 1} is provided between VCC and LX terminal. Low-side transistor _{M 2} is provided between the LX terminal and the GND terminal.

In this embodiment, although the high-side transistor M ₁ and the low-side transistor M ₂ and MOSFET (Metal Oxide Semiconductor Field Effect Transistor ) not the type of the transistor is limited, the use of the IGBT (Insulated Gate Bipolar Transistor), a bipolar transistor You can also. High-side driver 202 drives the high-side transistor _{M 1} based on the high-side pulse _{S H.} The upper power supply terminal of the high side driver 202 is connected to the BST terminal and receives the voltage V _BST . The lower power supply terminal of the high side driver 202 is connected to the LX terminal and receives the switching voltage V _LX . Low-side driver 204 drives the low-side transistor M ₂ on the basis of the low-side pulse S _L.

The power supply circuit 300 generates a power supply voltage V _HREG for bootstrap. First rectifying element _{D 1} is provided between the output node 302 and BST terminal of the power supply circuit 300. The power supply circuit 300 has a source follower (emitter follower) type output.

  The power supply circuit 300 includes an output transistor 304, a reference voltage source 310, a feedback circuit 320, and a second rectifier element 330.

The reference voltage source 310 generates a reference voltage _VREF . The output transistor 304 is an N-channel MOSFET and receives a reference voltage V _REF at a control electrode which is a gate (or base), and a source (or emitter) is connected to the output node 302. A bipolar transistor may be used as the output transistor 304.

  The second rectifying element 330 is a diode provided between the output of the feedback circuit 320 and the gate of the output transistor 304. The forward voltage of the second rectifying element 330 is set to Vf. The resistor 332 is provided between the gate of the output transistor 304 and the ground, and forms a discharge path.

In the steady state, V _REF −Vf is given to the gate of the output transistor 304, and the voltage V _HREG of the source (output node) 302 of the output transistor 304 is expressed by the following equation.
V _HREG = V _REF -Vf-V _gs
V _gs is a gate-source voltage of the output transistor 304.

  The feedback circuit 320 (i) clamps the voltage difference between the control electrode (gate) of the output transistor 304 and the output node 302 so as not to exceed a predetermined voltage (clamp level). The predetermined voltage may be defined in consideration of the breakdown voltage between the gate and source (between the base and emitter) of the output transistor 304. Specifically, the clamp level may be set smaller than the breakdown voltage in consideration of a margin.

Further, the feedback circuit 320 (ii) raises the voltage V _G of the gate of the output transistor 304 following the rise of the voltage V _HREG of the output node 302. At this time, the relationship of V _HREG > V _G is maintained so that the output transistor 304 is not turned on.

Hereinafter, a specific configuration of the feedback circuit 320 will be described. FIG. 4 is a circuit diagram of a first configuration example (300A) of the power supply circuit 300. The feedback circuit 320 </ b> A includes a Zener diode 322 provided between the control electrode (gate) of the output transistor 304 and the output node 302. The Zener voltage of the Zener diode 322 and _{V Z.} Further distinguishing the forward voltage of the zener diode 322 and the forward voltage Vf of the second rectifying element 330 as _{V F.}

FIG. 5 is an operation waveform diagram of the switching circuit 200 including the power supply circuit 300A of FIG. Prior to time t ₀ , the high-side transistor M ₁ is off and the low-side transistor M ₂ is on, and the voltage V _{LX at the} LX terminal is low (0 V).

The gate voltage V _G of the output transistor 304 is V _REF −Vf, and the voltage V _{HREG at the} output node is V _G −V _gs . For ease of understanding, Assuming the voltage drop of the rectifying element _{D 1} is ignored, the output voltage _{V HREG} voltage _{V BST} and the power supply circuit 300 of BST terminals are equal, across bootstrap capacitor _{C BST} is , _{ΔV≈V HREG} is charged.

The high-side transistor _{M 1} is turned on at time _{t 0,} the low-side transistor _{M 2} is turned off, the voltage _{V LX} of the LX terminal rises to high _{V CC.} The voltage V _{BST at the} BST terminal rises while maintaining the relationship of V _BST = V _LX + ΔV. Due to the influence of the parasitic capacitance of the rectifying element D ₁ , the increase in the voltage V _BST causes the voltage V _{HREG at} the output node 302 to increase. When the voltage _{V HREG} exceeds the gate voltage _{V G,} the gate voltage _{V G rises} while maintaining the relationship between _{V G =} V _HREG -V _F.

At time _{t 1,} the high-side transistor _{M 1} is turned off, the low side transistor _{M 2} is turned on, the voltage _{V LX} of LX terminal begins to decrease toward the low (0V). The slope of voltage V _HREG at output node 302 is substantially equal to the slope of switching voltage V _LX . On the other hand, the gate voltage V _G decreases with a slope corresponding to the impedance of the resistor 332 and the feedback circuit 320.

Gate voltage _{V G} is decreased to the original voltage level _V REF -Vf. On the other hand, the voltage V _{HREG at} the output node 302 _decreases to a voltage level V _G −V _gs = V _REF −Vf−V _gs defined by the gate voltage V _G.

The above is the operation of the switching circuit 200. Next, the advantages will be described.
According to the switching circuit 200, _since the voltage jump of the output node V _HREG is allowed, a clamp circuit and a large-capacitance capacitor for suppressing the voltage rise of the output node 302 are unnecessary, and the cost can be reduced. The output node 302 may be connected with a capacitor having a small capacity that does not significantly increase the cost.

On the other hand if only the voltage V _HREG remains output node 302 and maintains the voltage V _G of the control electrode is increased, so that the overvoltage is generated between the gate and source of the output transistor (base-emitter). Therefore, the feedback circuit 320 is provided to increase the voltage V _G of the control electrode (gate, base) of the output transistor 304 in accordance with the voltage increase of the output node (source / emitter). Thereby, the output transistor 304 can be protected.

  Next, another configuration of the feedback circuit 320 will be described. FIG. 6 is a circuit diagram of a second configuration example (300B) of the power supply circuit 300. The feedback circuit 320B further includes a Zener diode 324 connected in reverse series to the Zener diode 322 in addition to the Zener diode 322 of the feedback circuit 320A. Others are the same as the first configuration example.

  Subsequently, the operation of the switching circuit 200 including the power supply circuit 300B will be described. FIG. 7A is an operation waveform diagram of the switching circuit 200 including the power supply circuit 300B of FIG. FIG. 7B is an operation waveform diagram of the switching circuit 200 including the power supply circuit 300A of FIG.

First, a problem that may occur in the switching circuit 200 will be described with reference to FIG. The slope when the switching voltage V _{LX at the} LX terminal transitions from high to low depends on the size of the low-side transistor M ₂ and the driving capability of the low-side driver 204. The slope of the switching voltage V _LX at the LX terminal is different between FIG. 7B and FIG. 5, and the slope of the switching voltage V _LX is steep in FIG. 7B.

As described above, the slope of the gate voltage V _G is reduced is dependent on the impedance of the resistor 332 and the feedback circuit 320. As shown in FIG. 7B, when the switching voltage V _LX decreases rapidly, there may occur a situation in which the magnitude relationship between V _G and V _LX is reversed while the gate voltage V _G is higher than the reference voltage V _REF . If V _G −V _LX > V _{gs (th) in a} state where the gate voltage V _G is high, the output transistor 304 is turned on, and the output node 302 which should be lowered to ΔV = V _REF −Vf−V _gs originally. voltage _{V HREG} of, only drops to ΔV _'= V G _{-V gs} as shown by the solid line. As a result, the bootstrap capacitor C _BST is charged with a high voltage ΔV ′. In the next switching cycle, when the switching voltage V _LX transitions high, the bootstrap voltage V _BST rises to V _CC + ΔV ′, causing an overvoltage condition. The above is a problem that may occur in the switching circuit 200.

  This problem can be solved by using the power supply circuit 300B according to the second configuration example. This will be described with reference to FIG.

While the switching voltage V _LX is high, the gate voltage V _G rises to V _G = V _HREG − (V _Z + V _F ). This is lower than _{V HREG} -V _F of FIG. 7 (b), the difference between the reference voltage _{V REF} is smaller. Therefore, when the switching voltage V _LX transitions to low, the time required for the gate voltage V _G to drop to the reference voltage V _REF can be shortened. Therefore, in the state of V _G > V _REF , V _HREG can be prevented from becoming lower than V _G , and the problem shown in FIG. 7B can be solved.

Those skilled in the art can understand from the above description that the configuration of the feedback circuit 320 is not limited to those shown in FIGS. 4 and 6. Feedback circuit 320, when the voltage _{V HREG} output node 302 is jumped, as appropriate potential difference _{V DIFF} between the gate voltage _{V G} is generated, it can be seen that it is sufficient in the feedback circuit 320. The potential difference V _DIFF can be adjusted by the number of diodes and Zener diodes, or can be adjusted by using other constant voltage elements.

Subsequently, a DC / DC converter using the switching circuit according to the embodiment will be described. FIG. 8 is a circuit diagram of the DC / DC converter 500. The DC / DC converter 500 includes a control circuit 400C, a bootstrap capacitor C _BST , an inductor L ₁ , an output capacitor C ₁ , and resistors R ₁₁ and R ₁₂ . The control circuit 400C is a functional IC integrated on one semiconductor substrate.

The DC / DC converter 500 is a constant voltage output and supplies an output voltage _VOUT stabilized to a predetermined level to a load (not shown). A feedback signal V _FB obtained by dividing the output voltage _VOUT of the DC / DC converter 500 by the resistors R ₁₁ and R ₁₂ is input to the feedback (FB) terminal of the control circuit 400C. In a constant current output converter, a feedback signal _VFB corresponding to the output current is fed back.

The pulse modulator 410 generates a pulse signal S _PWM that instructs on / off of the high-side transistor M ₁ so that the feedback signal V _FB approaches the target value V _REF . The logic circuit 420 generates pulse signals S _PWMH and S _PWML for controlling the high-side transistor M ₁ and the low-side transistor M ₂ in accordance with the pulse signal S _PWM . Pulse signal _{S PWMH} the high side is converted into a high-side pulse _{S H} by the level shifter 504 is supplied to the high-side driver 202. Low-side pulse signal _{S PWML} is supplied to the low-side driver 204 as a low-side pulse _{S L.}

  The application of the switching circuit 200 is not limited to a DC / DC converter, and can be used for a power converter such as an inverter or a converter.

In an embodiment, the rectifying element shown as a diode can be replaced by a transistor. For example, the second rectifying element 330 can be a transistor that is controlled in synchronism with the switching of the high side transistor M _1. Similarly, the same first be rectifying element D _1.

  Although the present invention has been described using specific terms based on the embodiments, the embodiments only illustrate the principles and applications of the present invention, and the embodiments are defined in the claims. Many variations and modifications of the arrangement are permitted without departing from the spirit of the present invention.

M ₁ high side transistor M ₂ low side transistor C _BST bootstrap capacitor 200 switching circuit 202 high side driver 204 low side driver 300 power supply circuit 302 output node 304 output transistor 310 reference voltage source 320 feedback circuit 322, 324 Zener diode 330 second rectifier element 400 Control Circuit 410 Pulse Modulator D ₁ Rectifier 500 DC / DC Converter

Claims (14)

An input terminal;
A switching terminal;
A bootstrap terminal,
A high-side transistor provided between the input terminal and the switching terminal;
A bootstrap capacitor provided between the switching terminal and the bootstrap terminal;
A power circuit;
A first rectifying element provided between an output node of the power supply circuit and the bootstrap terminal;
With
The power supply circuit is
A reference voltage source for generating a reference voltage;
An output transistor that receives the reference voltage at a control electrode that is a gate or a base, and whose source or emitter is connected to the output node;
(I) Clamps the voltage difference between the control electrode of the output transistor and the output node, and (ii) increases the voltage of the control electrode of the output transistor following the increase in the voltage of the output node. A feedback circuit;
A switching circuit comprising:   The switching circuit according to claim 1, wherein the feedback circuit includes a Zener diode provided between the control electrode of the output transistor and the output node.   2. The switching circuit according to claim 1, wherein the feedback circuit includes two Zener diodes connected in reverse series between the control electrode of the output transistor and the output node.   4. The switching circuit according to claim 1, wherein the power supply circuit further includes a second rectifier element provided between the reference voltage source and the control electrode of the output transistor. 5.   The switching circuit according to claim 4, wherein the second rectifying element includes a diode.   The switching circuit according to claim 4, wherein the second rectifying element includes a transistor controlled in synchronization with switching of the high-side transistor. A control circuit for a DC / DC converter,
A switching terminal and a bootstrap terminal;
A pulse modulator that generates a pulse signal that instructs on / off of the high-side transistor so that a feedback signal according to a state of the DC / DC converter or the load approaches a target value;
A power circuit;
A first rectifying element provided between an output node of the power supply circuit and the bootstrap terminal;
A driver that receives the voltage of the bootstrap terminal at an upper power supply terminal and drives the high-side transistor based on the pulse signal;
With
The power supply circuit is
A reference voltage source for generating a reference voltage;
An output transistor that receives the reference voltage at a control electrode that is a gate or a base, and whose source or emitter is connected to the output node;
(I) Clamps the voltage difference between the control electrode of the output transistor and the output node, and (ii) increases the voltage of the control electrode of the output transistor following the increase in the voltage of the output node. A feedback circuit;
A control circuit comprising:   The control circuit according to claim 7, wherein the feedback circuit includes a Zener diode provided between the control electrode of the output transistor and the output node.   The control circuit according to claim 7, wherein the feedback circuit includes two Zener diodes connected in reverse series between the control electrode of the output transistor and the output node.   The control circuit according to claim 7, wherein the power supply circuit further includes a second rectifying element provided between the reference voltage source and the control electrode of the output transistor.   The control circuit according to claim 10, wherein the second rectifying element includes a diode.   The control circuit according to claim 10, wherein the second rectifier element includes a transistor controlled in synchronization with switching of the high-side transistor.   The control circuit according to claim 7, wherein the control circuit is integrated on a single semiconductor substrate.   A DC / DC converter comprising the control circuit according to claim 7.

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