JP2006311646A - Switching regulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching regulator which can prevent over-current from flowing into a switching element, even when the connection between a control circuit section controlling the switching element and a negative side power source voltage is interrupted, in the switching regulator controlling the switching of a switching element to convert input voltage to a prescribed voltage to output the same. <P>SOLUTION: The switching regulator comprises the control circuit section which operates when a prescribed positive side power source voltage and a negative side power source voltage are supplied and controls the switching of the switching element so that the output voltage of the switching regulator is constant at a prescribed value, a detecting circuit section which detects whether the control circuit section is connected to the negative side power source voltage or not, and a connection switching circuit section which connects the control circuit section to the negative side power source voltage using other channels when the detecting circuit section detects the interruption between the control circuit section and the negative side power source voltage. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a switching regulator that converts an input voltage into a predetermined voltage and outputs it by controlling switching of a switching element.

  For example, in a portable digital device represented by a mobile phone or the like, a step-up switching regulator using an inductor is often used as a step-up circuit. This step-up switching regulator controls the output voltage by switching the switching element at a high frequency.

  FIG. 4 is a circuit diagram showing a configuration example of a conventional switching regulator. As shown in FIG. 4, the switching regulator 101 includes an inductor L100, a switching element TR100, a diode D100, a smoothing capacitor C100, and a switching control IC 110 (hereinafter simply referred to as “control IC 110”) on the same semiconductor substrate. , And a plurality of resistors R101 to R104. The switching regulator 101 converts the input voltage Vin0 into a predetermined voltage Vout0 higher than the input voltage Vin0 by driving the switching element TR100 using PWM (Pulse Width Modulation) control using the control IC 110. And output. Hereinafter, switching element TR100 will be described as an N-channel MOS (Metal Oxide Semiconductor) transistor.

  The control IC 110 includes a UVLO (Under Voltage Lock Out) circuit 111, a reference voltage generation circuit 112, a duty limiting circuit 113, an oscillation circuit 114, a PWM comparison circuit 115, an error amplification circuit 116, a reference voltage generation circuit 117, an output circuit 118, And a short-circuit protection circuit 119. The control IC 110 includes a power supply terminal 131, a ground terminal 132, a reference voltage output terminal 133, a DTC (Dead Time Control) terminal 134, an FB terminal 135, and an EXT terminal 136. A voltage Vin0 is supplied from the DC power supply to the power supply terminal 131, and a voltage Vfb0 obtained by dividing the output voltage Vout0 by the resistors R101 and R102 is input to the FB terminal 135. The reference voltage Vr0 generated by the reference voltage generation circuit 112 is output to the reference voltage output terminal 133, and the voltage Vdtc0 obtained by dividing the reference voltage Vr0 by the resistors R103 and R104 is input to the DTC terminal 134. A drive signal Sg0 for driving the switching element TR100 is output from the output circuit 118 to the EXT terminal 136.

  As described above, the control IC 110 that controls the switching of the switching element TR100 is provided with various protection circuits in order to prevent a malfunction at the time of abnormality. The UVLO circuit 111 is a circuit for fixing the switching of the switching element TR100 in the off state when the input voltage Vin0 decreases. Specifically, the UVLO circuit 111 outputs a predetermined control signal S101 to the output circuit 118 when the input voltage Vin0 becomes equal to or lower than a predetermined voltage. When the control signal S101 is input, the output circuit 118 sets the EXT terminal 136 to the voltage Vgnd0 and turns off the switching element TR100. The duty limiting circuit 113 limits the duty cycle in the PWM control of the switching element TR100 to prevent the switching element TR100 from being held in the on state. Further, the short circuit protection circuit 119 is used to fix the switching element TR100 in the off state when the on state continues for a predetermined time or more. In addition to these, examples of the protection circuit include a circuit that detects a current flowing through the switching element TR100 and turns off the switching element TR100 when the detected current value is equal to or greater than a predetermined value.

  Some conventional switching regulators prevent thermal destruction by detecting an overvoltage generated at a predetermined terminal and turning off the switching element (see, for example, Patent Document 1).

Also, conventional switching regulators distinguish between cases where an overcurrent that leads to a short circuit flows as an output current and cases where an overcurrent that does not lead to a short circuit flows, and provides optimum protection in each case. Some have an overcurrent protection function (see, for example, Patent Document 2).
JP 2004-166391 A JP 2002-171749 A

  However, the conventional control IC 110 has no protection function when the ground terminal 132 is opened. When the ground terminal 132 is opened, a current flows from the power supply terminal 131 to the ground terminal 132, and the voltage of the ground terminal 132 rises with time. FIG. 5 is a graph showing a change in the voltage Vgnd0 of the ground terminal 132 when the ground terminal 132 is opened in the conventional control IC 110. In FIG. As shown in FIG. 5, when the voltage Vgnd0 of the ground terminal 132 increases, the circuit inside the control IC 110 does not operate normally, and the voltage of the drive signal Sg0 that drives the switching element TR100 becomes the voltage Vgnd0 of the ground terminal 132. To the voltage Vin0 of the power supply terminal 131. Therefore, when the voltage of the drive signal Sg0 that drives the switching element TR100 is held at the voltage Vin0 of the power supply terminal 131 for a long time, there is a problem that an overcurrent flows through the switching element TR100. Further, even if the control IC 110 outputs the voltage Vgnd0 of the ground terminal 132 to the switching element TR100 in order to turn off the switching element TR100, the voltage Vgnd0 of the ground terminal 132 is increased, so that the switching element TR100. Has a problem that it is not completely turned off and overcurrent flows.

  The present invention has been made to solve the above problems, and in a switching regulator including a control circuit unit that controls switching of the switching element, the connection between the control circuit unit and the negative power supply voltage is provided. It is an object of the present invention to provide a switching regulator capable of preventing an overcurrent from flowing through a switching element even when it is interrupted.

  The first switching regulator according to the present invention converts the input voltage into a predetermined voltage and outputs it as an output voltage by controlling switching of the switching element. The switching regulator operates by being supplied with a predetermined positive power supply voltage and a negative power supply voltage, and controls the switching of the switching element so that the output voltage is constant at a predetermined value; A detection circuit unit that detects whether or not the control circuit unit is connected to a negative power supply voltage, and the detection circuit unit cuts off the connection between the control circuit unit and the negative power supply voltage. A connection switching circuit unit that connects the control circuit unit to the negative power supply voltage using another path.

  Preferably, in the first switching regulator, the connection switching circuit unit connects the control circuit unit to the negative power supply voltage via a resistor. Hereinafter, this switching regulator is referred to as a “second switching regulator”.

  Preferably, in the first or second switching regulator, the control circuit unit receives a proportional voltage generation unit that generates and outputs a proportional voltage proportional to the output voltage, and the negative power supply voltage. A negative power supply input terminal. The detection circuit unit compares the proportional voltage with the voltage at the negative power supply input terminal, and when the voltage at the negative power supply input terminal is equal to or higher than the proportional voltage, the control circuit It detects that the connection between the circuit unit and the negative power supply voltage is cut off. Hereinafter, this switching regulator is referred to as a “third switching regulator”.

  Preferably, in the third switching regulator, when the voltage of the negative power supply input terminal is equal to or higher than a voltage obtained by adding a predetermined voltage to the proportional voltage, the control circuit unit Detects that the connection between the power supply voltage and the negative power supply voltage is broken. Hereinafter, this switching regulator is referred to as a “fourth switching regulator”.

  Preferably, in the third or fourth switching regulator, the connection switching circuit unit includes a resistance connection terminal connected to the negative power supply voltage via the resistor, and the negative power supply input terminal. When it is detected that the connection between the control circuit unit and the negative power supply voltage is interrupted by the detection circuit unit and the transistor connected between the resistance connection ends, A transistor control circuit portion for turning on the transistor. Hereinafter, this switching regulator is referred to as a “fifth switching regulator”.

  Preferably, in any one of the third to fifth switching regulators, the control circuit unit is disconnected from the control circuit unit and the negative power supply voltage by the detection circuit unit. Is detected, the voltage at the negative power supply input terminal is output to the control electrode of the switching element. Hereinafter, this switching regulator is referred to as a “sixth switching regulator”.

  Preferably, in any one of the third to sixth switching regulators, the control circuit unit, the detection circuit unit, and the connection switching circuit unit excluding the proportional voltage generation unit are integrated in one IC.

  According to the switching regulator of the present invention, the control circuit operates by being supplied with the predetermined positive power supply voltage and the negative power supply voltage, and controls the switching of the switching element so that the output voltage of the switching regulator becomes constant at a predetermined value. A detection circuit unit that detects whether the control circuit unit is connected to the negative power supply voltage, and the detection circuit unit interrupts the connection between the control circuit unit and the negative power supply voltage. When detected, when the connection between the control circuit unit and the negative power supply voltage is interrupted because it includes a connection switching circuit unit that connects the control circuit unit to the negative power supply voltage using another path However, it is possible to prevent an overcurrent from flowing through the switching element.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
(Embodiment 1)
FIG. 1 shows a configuration example of a switching regulator according to Embodiment 1 of the present invention. The switching regulator 1 is a step-up switching regulator. As shown in FIG. 1, the switching regulator 1 includes an inductor L1, a switching element TR1, a diode D1, a smoothing capacitor C1, a switching control integrated circuit 10 (hereinafter simply referred to as “control IC 10”), and a plurality of switching regulators. Resistors R1 to R4 are provided. The inductor L1, the switching element TR1, the diode D1, the smoothing capacitor C1, the control IC 10, and the resistors R1 to R4 are mounted on the same semiconductor substrate.

  One end of the inductor L1 is connected to the DC power supply, and the other end is connected to the anode of the diode D1. A switching element TR1 is connected between the anode of the diode D1 and the ground voltage. Two resistors R1 and R2 connected in series are connected between the cathode of the diode D1 and the ground voltage, and a capacitor C1 is connected in parallel with the resistors R1 and R2. The switching regulator 1 uses the control IC 10 to drive the switching element TR1 using PWM control, thereby converting the input voltage Vin to a predetermined voltage Vout that is higher than the voltage Vin and outputting it. In the switching regulator 1, when the switching element TR1 is turned on, a current flows from the DC power source to the switching element TR1 via the inductor L1, and when the switching element TR1 is turned off, a counter electromotive force is generated in the inductor L1, thereby causing the diode D1 and the capacitor A current flows through C1. The switching regulator 1 outputs the voltage of the capacitor C1 as the output voltage Vout.

  The control IC 10 includes an ULVO circuit 11, a reference voltage generation circuit 12, a duty limiting circuit 13, an oscillation circuit 14, a PWM comparison circuit 15, an error amplification circuit 16, a reference voltage generation circuit 17, an output circuit 18, a short circuit protection circuit 19, and a ground. A terminal open detection circuit 20, a transistor TR2, and an internal control circuit 21 are provided. The control IC 10 includes a power supply terminal 31, a ground terminal 32, a reference voltage output terminal 33, a DTC terminal 34, an FB terminal 35, and an EXT terminal 36. A voltage Vin is supplied from the DC power supply to the power supply terminal 31, and a voltage Vfb obtained by dividing the output voltage Vout by the resistors R1 and R2 is input to the FB terminal 35. The reference voltage Vr generated by the reference voltage generation circuit 12 is output to the reference voltage output terminal 33, and the voltage Vdtc obtained by dividing the reference voltage Vr by the resistors R3 and R4 is input to the DTC terminal 34. A drive signal Sg for driving the switching element TR <b> 1 is output from the output circuit 18 to the EXT terminal 36. Note that the oscillation circuit 14, the PWM comparison circuit 15, the error amplification circuit 16, the reference voltage generation circuit 17, and the output circuit 18 form a control circuit unit that controls switching of the switching element TR1. The ground terminal open detection circuit 20 forms a detection circuit unit, and the transistor TR2 and the internal control circuit 21 form a connection switching circuit unit. Further, the ground terminal 32 and the DTC terminal 34 form a negative power supply input terminal and a resistance connection terminal, respectively.

  The resistors R1 and R2 are provided for detecting the output voltage Vout. Specifically, the output voltage Vout is divided at a predetermined ratio by the resistors R1 and R2, and the divided voltage Vfb is input to the FB terminal 35. One end of the resistor R2 is grounded, and the other end is connected to the resistor R1 and the FB terminal 35. Thereby, the output voltage Vout of the switching regulator 1 is fed back to the control IC 10. The resistors R3 and R4 are provided for dividing the reference voltage Vr output to the reference voltage output terminal 33 at a predetermined ratio. Here, one end of the resistor R3 is connected to the reference voltage output terminal 33, and the other end is connected to one end of the resistor R4. One end of the resistor R4 is connected to the resistor R3 and the DTC terminal 34, and the other end is grounded. As a result, the voltage Vdtc obtained by dividing the reference voltage Vr by the resistors R3 and R4 is input to the DTC terminal 34. The voltage Vdtc input to the DTC terminal 34 is used to set the maximum value of the duty cycle allowed in the PWM control of the switching element TR1. Here, the duty cycle is a value obtained by dividing the pulse width time of the pulse signal Sg output from the output circuit 18 in the active state, that is, the time during which the switching element TR1 is turned on by the period of the pulse signal Sg. .

  Hereinafter, the configuration and operation of the control IC 10 will be described in detail. The oscillation circuit 14, the PWM comparison circuit 15, the error amplification circuit 16, the reference voltage generation circuit 17, and the output circuit 18 constitute a drive unit that drives the switching element TR1 using PWM control. The error amplification circuit 16 amplifies and outputs an error between the voltage Vfb at the FB terminal 35 and the reference voltage Vref generated by the reference voltage generation circuit 17. The PWM comparison circuit 15 compares the voltage of the triangular wave signal output from the oscillation circuit 14 with the output voltage of the error amplification circuit 16, and generates and outputs a pulse signal having a different pulse width depending on the magnitude relationship. The output circuit 18 generates a drive signal Sg for driving the transistor TR1 based on the pulse signal output from the PWM comparison circuit 15, and outputs the drive signal Sg to the EXT terminal 36.

  Since the above-described driving unit feedback-controls the output voltage Vout of the switching regulator 1 using the error amplifier circuit 16, the switching element TR1 can be stably driven, and thus the output voltage Vout is predetermined. Can be held at a voltage of Here, the drive unit increases the duty cycle in the PWM control of the switching element TR1 when the output voltage Vout decreases, and decreases the duty cycle when the output voltage Vout increases.

  The ULVO circuit 11 is a circuit for fixing the switching of the switching element TR1 in the off state when the input voltage Vin decreases. Specifically, the UVLO circuit 11 outputs a predetermined control signal S1 to the output circuit 18 when the input voltage Vin becomes equal to or lower than a predetermined voltage. When the control signal S1 is input, the output circuit 18 sets the voltage at the EXT terminal 36 to the voltage Vgnd and turns off the switching element TR1.

  The reference voltage generation circuit 12 generates a predetermined reference voltage Vr and outputs it to the reference voltage output terminal 33. The duty limiting circuit 13 receives the voltage Vdtc input to the DTC terminal 34, the triangular wave signal output from the oscillation circuit 14, and the output voltage of the PWM comparison circuit 15. The duty limiting circuit 13 generates a pulse signal from the triangular wave signal output from the oscillation circuit 14 and the voltage Vdtc input to the DTC terminal 34. The generation method is the same as the method in which the PWM comparison circuit 15 generates a pulse signal using the voltage of the triangular wave signal and the output voltage of the error amplification circuit 16. Further, the duty limiting circuit 13 compares the generated pulse signal with the output signal of the PWM comparison circuit 15, and when the duty cycle of the output signal of the PWM comparison circuit 15 is larger than the duty cycle of the generated pulse signal. Then, it is determined that the duty cycle at the time of PWM control of the switching element TR1 exceeds the maximum value, and the control signal S2 is output to the output circuit 18. When the control signal S2 is input, the output circuit 18 sets the EXT terminal 36 to the voltage Vgnd and turns off the switching element TR1.

  The output voltage of the error amplifier circuit 16 is input to the short circuit protection circuit 19. The short-circuit protection circuit 19 outputs a control signal S3 to the output circuit 18 when a certain period of time has passed with the output voltage of the error amplifier circuit 16 exceeding a predetermined voltage. When the control signal S3 is input, the output circuit 18 sets the EXT terminal 36 to the voltage Vgnd and turns off the switching element TR1. Here, the short circuit protection circuit 19 is used to fix the switching element TR100 in the off state when the on state of the switching element TR1 continues for a predetermined time or more. If the ON state of the switching element TR1 continues, the voltage Vfb input to the FB terminal 35 decreases and the output voltage of the error amplifier circuit 16 increases. Therefore, by detecting the output voltage of the error amplifier circuit 16, the switching element TR1 is detected. It is possible to detect whether TR1 is in an on state.

  Next, the ground terminal open detection circuit 20, the transistor TR2, and the internal control circuit 21 will be described in detail. The ground terminal open detection circuit 20 detects whether the ground terminal 32 is open by comparing the voltage Vfb input to the FB terminal 35 with the voltage Vgnd. When it is detected that the ground terminal 32 is open, a control signal S4 is output to the internal control circuit 21. When the control signal S4 is input, the internal control circuit 21 outputs the control signal S5 to the gate of the transistor TR2 and the output circuit 18, respectively. The transistor TR2 is turned on when the voltage of the control signal S5 is applied to the gate. Further, when the control signal S5 is input, the output circuit 18 sets the EXT terminal 36 to the voltage Vgnd and turns off the switching element TR1.

  Hereinafter, the operation of the ground terminal open detection circuit 20 will be described in detail. When the ground terminal 32 is opened, a current flows from the power supply terminal 31 to the ground terminal 32, and the voltage Vgnd of the ground terminal 32 increases. When the voltage Vgnd of the ground terminal 32 increases, normal switching control of the switching element TR1 becomes impossible and the output voltage Vout cannot be maintained, so that the output voltage Vout decreases. Therefore, if the resistance values of the resistors R1 and R2 are set so that the feedback voltage Vfb is 1V, the voltage Vfb of the FB terminal 24 is lower than 1V. The ground terminal open detection circuit 20 compares the increased voltage Vgnd of the ground terminal 32 with the voltage Vfb of the FB terminal 24. When the voltage Vgnd of the ground terminal 32 becomes equal to or higher than the voltage Vfb, the ground terminal 32 is opened. This is detected and a control signal S4 is output.

  When the control signal S4 is input from the ground terminal open detection circuit 20, the internal control circuit 21 outputs a control signal S5 to the output circuit 18, and a transistor connected between the ground terminal 32 and the DTC terminal 34. The control signal S5 is also output to TR2 to turn on the transistor TR2. As a result, the current flowing from the power supply terminal 31 to the ground terminal 32 flows to the DTC terminal 34 via the transistor TR2, and flows from the DTC terminal 34 to the outside of the control IC 10 via the resistor R4. Therefore, an increase in the voltage Vgnd of the ground terminal 32 of the control IC 10 can be suppressed. When the control signal S5 is input, the output circuit 18 outputs the ground terminal voltage Vgnd to the gate of the switching element TR1, and stops the switching of the switching element TR1.

  Here, the change in the voltage Vgnd when the ground terminal 32 is open differs depending on the resistance value of the resistor R4. FIG. 2 is a graph showing a change in the voltage Vgnd of the ground terminal 32 when the ground terminal 32 is opened when the resistance value of the resistor R4 is large, and FIG. 3 shows a sufficiently small resistance value of the resistor R4. It is a graph which shows the change of the voltage Vgnd of the grounding terminal 32 when the grounding terminal 32 becomes open. When the resistance value of the resistor R4 is large, as shown in FIG. 2, the voltage Vgnd of the ground terminal 32 is finally a voltage determined by the current flowing through the ground terminal 32 and the resistance value of the resistor R4, that is, the current of the current. It stabilizes at a voltage represented by the product of the value and the resistance value of the resistor R4. On the other hand, when the resistance value of the resistor R4 is sufficiently small, the voltage Vgnd of the ground terminal 32 decreases to a voltage lower than the voltage Vfb of the FB terminal 35 as shown in FIG. When the voltage at the ground terminal 32 becomes lower than the voltage Vfb at the FB terminal 35, the ground terminal open detection circuit 20 stops outputting the control signal S4 and cancels the ground terminal open detection state. When the ground terminal open detection circuit 20 cancels the ground terminal open detection state, the transistor TR2 connected between the ground terminal 32 and the DTC terminal 34 is turned off, so that the voltage Vgnd of the ground terminal 32 is supplied from the power supply terminal 31. It rises again with current. When the voltage Vgnd of the ground terminal 32 becomes equal to or higher than the voltage Vfb of the FB terminal 35, the ground terminal open detection circuit 20 detects again that the ground terminal 32 is open and outputs the control signal S4. The open detection state is entered, and the voltage at the ground terminal 32 decreases again. When the resistance value of the resistor R4 is sufficiently small, this operation is repeated. Therefore, when the resistance value of the resistor R4 is sufficiently small, the voltage Vgnd of the ground terminal 32 is always suppressed to the vicinity of the voltage of the FB terminal 24.

  As described above, when the resistance value of the resistor R4 is sufficiently small, the voltage Vgnd of the ground terminal 32 is always suppressed to the vicinity of the voltage of the FB terminal 24. Therefore, the voltage Vgnd rises more than when the resistance value of the resistor R4 is large. It can be said that the effect is great in that it suppresses. However, if the resistance value of the resistor R4 cannot be made sufficiently small due to circuit design restrictions, etc., the voltage Vgnd represented by the product of the current value of the current flowing through the ground terminal 32 and the resistance value of the resistor R4 A somewhat large resistance value can be determined so that the difference from the voltage Vfb is within an allowable range.

  When the ground terminal 32 is open, the switching regulator according to the first embodiment detects the state and turns on the transistor TR2 between the ground terminal 32 and the DTC terminal 34. Therefore, a current that attempts to flow from the power supply terminal 31 to the ground terminal 32 flows to the outside of the control IC 10 via the transistor TR2, and an increase in the voltage Vgnd of the ground terminal 32 of the control IC 10 can be suppressed. Further, since the voltage Vgnd of the ground terminal 32 is applied to the gate of the switching element TR1, the switching element TR1 is turned off, and an overcurrent can be prevented from flowing through the switching element TR1.

  In the switching regulator according to the first embodiment, the ground terminal open detection circuit 20 does not operate with the voltage Vgnd of the ground terminal 32 as a reference, and compares the voltage Vgnd of the ground terminal 32 with the voltage Vfb of the FB terminal 24. Thus, it is detected whether or not the ground terminal 32 is open. Therefore, even if the voltage Vgnd of the ground terminal 32 increases, the detection operation can be performed normally. If the control signal S4 is output from the ground terminal open detection circuit 20, the internal control circuit 21, the transistor TR2, and the output circuit 18 perform the above-described operations. Therefore, even if the ground terminal 32 is open, the ground terminal The open detection circuit 20, the internal control circuit 21, the transistor TR 2, and the output circuit 18 operate stably and can suppress an increase in the voltage at the ground terminal 32.

  Further, when the ground terminal 32 is open, the voltage Vgnd of the ground terminal 32 rises and the control IC 10 cannot operate normally and cannot hold the output voltage. Therefore, the voltage Vfb of the FB terminal 24 cannot be maintained during normal operation. Less than. In the switching regulator according to the first embodiment, the ground terminal open detection circuit 20 compares the lowered voltage Vfb of the FB terminal 24 with the voltage Vgnd of the ground terminal 32 to detect an increase in the voltage of the ground terminal 32. When the rise of the ground terminal 32 is small, it can be detected that the ground terminal 32 is open, and an overcurrent of the switching element TR1 can be prevented.

  In the switching regulator according to the first embodiment, the voltage Vgnd of the ground terminal 32 is applied to the gate of the switching element TR1, thereby preventing an overcurrent from flowing through the switching element TR1, but the voltage Vgnd of the ground terminal 32 is prevented. If the rise of the voltage is suppressed, the internal circuit of the control IC 110 operates normally, and the drive signal Sg output from the output circuit 18 is not fixed for a long time in the active state. Therefore, the voltage Vgnd is not necessarily changed to the switching element. Even if it is not applied to the gate of TR1, it is possible to prevent an overcurrent from flowing through the switching element TR1.

  In the switching regulator according to the first embodiment, the ground terminal open detection circuit 20 compares the voltage Vgnd of the ground terminal 32 with the voltage Vfb of the FB terminal 24. The voltage Vgnd and the voltage Vfb of the ground terminal 32 are set to a predetermined value. The voltage Vfb1 obtained by adding the above voltage may be compared. In this case, when the voltage Vgnd of the ground terminal 32 becomes equal to or higher than the voltage Vfb1, the ground terminal open detection circuit 20 detects that the ground terminal 32 is open and outputs the control signal S4.

  Further, in the switching regulator according to the first embodiment, the control IC 10 controls the switching of the external switching element TR1, but even when controlling the switching of the internal switching element TR1, the ground terminal 32 is controlled. Increase in the voltage Vgnd of the current can be suppressed, and an overcurrent can be prevented from flowing through the switching element TR1.

It is the circuit diagram which showed the structural example of the switching regulator by Embodiment 1 of this invention. It is a graph which shows the change of the voltage Vgnd of the ground terminal 32 when the ground terminal 32 is opened when the resistance value of the resistor R4 is large. It is a graph which shows the change of the voltage Vgnd of the ground terminal 32 when the ground terminal 32 becomes open when the resistance value of the resistor R4 is sufficiently small. It is the circuit diagram which showed the structural example of the conventional switching regulator. In the conventional switching regulator, it is a graph which shows the change of the voltage Vgnd0 of the ground terminal 132 when the ground terminal 132 becomes open.

Explanation of symbols

1 Switching regulator 10 Control IC
DESCRIPTION OF SYMBOLS 11 UVLO circuit 12 Reference voltage generation circuit 13 Duty limit circuit 14 Oscillation circuit 15 PWM comparison circuit 16 Error amplification circuit 17 Reference voltage generation circuit 18 Output circuit 19 Short-circuit protection circuit 20 Ground terminal open detection circuit 21 Internal control circuit 31 Power supply terminal 32 Ground Terminal 33 Reference voltage output terminal 34 DTC terminal 35 FB terminal 36 EXT terminal TR1 Switching element (transistor)
TR2 Transistor L1 Inductor D1 Diode C1 Smoothing capacitor R1-R4 Resistance

Claims (7)

In a switching regulator that converts the input voltage into a predetermined voltage and outputs it as an output voltage by controlling the switching of the switching element.
A control circuit unit that operates by being supplied with a predetermined positive power supply voltage and a negative power supply voltage, and controls switching of the switching element so that the output voltage is constant at a predetermined value;
A detection circuit unit for detecting whether the control circuit unit is connected to a negative power supply voltage;
When the detection circuit unit detects that the connection between the control circuit unit and the negative power supply voltage is interrupted, the control circuit unit is connected to the negative power supply voltage using another path. A switching regulator comprising: a connection switching circuit unit.   The switching regulator according to claim 1, wherein the connection switching circuit unit connects the control circuit unit to the negative power supply voltage via a resistor. The control circuit unit is
A proportional voltage generator that generates and outputs a proportional voltage proportional to the output voltage;
A negative power supply input terminal to which the negative power supply voltage is input,
The detection circuit unit compares the proportional voltage with the voltage at the negative power source input terminal, and when the voltage at the negative power source input terminal is equal to or higher than the proportional voltage, the control circuit unit and the negative power source The switching regulator according to claim 1, wherein the switching regulator detects that the connection with the voltage is cut off.   When the voltage at the negative power supply input terminal is equal to or higher than a voltage obtained by adding a predetermined voltage to the proportional voltage, the detection circuit unit is disconnected from the control circuit unit and the negative power supply voltage. The switching regulator according to claim 3, wherein the switching regulator is detected. The connection switching circuit unit is
A resistance connection terminal connected to the negative power supply voltage via the resistor;
A transistor connected between the negative power supply input terminal and the resistance connection terminal;
And a transistor control circuit unit that turns on the transistor when the detection circuit unit detects that the connection between the control circuit unit and the negative power supply voltage is cut off. 5. The switching regulator according to 3 or 4.   When the control circuit unit detects that the connection between the control circuit unit and the negative power supply voltage is interrupted by the detection circuit unit, the negative power supply input terminal is connected to the control electrode of the switching element. The switching regulator according to any one of claims 3 to 5, wherein the voltage is output. 7. The switching regulator according to claim 3, wherein the control circuit unit, the detection circuit unit, and the connection switching circuit unit excluding the proportional voltage generation unit are integrated in one IC.

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