JP4974653B2 - Step-up switching regulator control circuit, step-up switching regulator using the same, and electronic equipment using them - Google Patents

Description

  The present invention relates to a switching power supply, and more particularly to a current detection technique.

  In recent mobile phones, PDAs (Personal Digital Assistance), digital still cameras, and small information terminals such as audio players, for example, light emitting diodes (hereinafter referred to as LEDs) used for liquid crystal backlights. There are devices that require a voltage higher than the output voltage of the battery. When a voltage higher than the battery voltage is required, the battery voltage is boosted using a switching power supply such as a boost switching regulator to obtain a voltage necessary for driving a load circuit such as an LED. In some cases, a step-down switching regulator is used to supply an appropriate drive voltage to a device that operates at a voltage lower than the battery voltage, such as a microcomputer.

The step-up switching regulator includes a switching transistor having one end grounded. An inductor is connected to the other end of the switching transistor. When the switching transistor is intermittently turned on and off, energy is stored in the inductor, and the output capacitor is charged via the rectifier diode, thereby boosting the voltage. Is generated. Patent Document 1 describes a related technique.
JP 2004-70827 A

  Here, if an overcurrent flows through the inductor, the inductor may be saturated and the boosting operation may be hindered. Further, if an overcurrent flows through the switching transistor, the reliability of the element may be affected. Therefore, it is necessary to monitor the current flowing through the switching transistor and the inductor and perform a protection process such as turning off the switching transistor when a predetermined current is exceeded. The overcurrent protection circuit is provided not only in the step-up switching regulator but also in the step-down switching regulator and other switching power supplies. Therefore, a technique for detecting the current with high accuracy is required. Further, a technique for detecting the current flowing through the switching transistor with high accuracy is also required in a switching power supply that monitors the current flowing through the switching transistor and switches the switching transistor on and off.

  The present invention has been made in view of such a problem, and one of its purposes is to provide a control circuit for a switching power supply capable of highly accurate current detection.

  According to an aspect of the present invention, a switching power supply control circuit is provided. In this control circuit, a predetermined fixed voltage is applied to the first terminal, and a switching voltage generated at the second terminal which is the other end of the first terminal is supplied to an output circuit externally attached to the control circuit. A driver circuit for generating a drive signal to be supplied to the control terminal of the switching transistor based on a pulse modulation signal whose duty ratio is controlled so that the output voltage of the output circuit approaches a predetermined target voltage; The voltage source that generates the threshold voltage of the switching transistor and the voltage across the switching transistor are compared with the threshold voltage. When the voltage across the switching transistor exceeds the threshold voltage, a comparison signal of a predetermined level is output. A comparator, and a protection circuit that forcibly turns off the switching transistor when the comparison signal reaches a predetermined level.The voltage source is the same type as the switching transistor, and is connected to a reference transistor to which a fixed voltage is applied to the first terminal and a second terminal which is the other end of the first terminal of the reference transistor, and a predetermined constant is applied to the reference transistor. A constant current source for supplying current, and outputs a voltage at a connection point between the reference transistor and the constant current source as a threshold voltage.

  At both ends of the switching transistor, a product of the current flowing through the switching transistor (hereinafter also referred to as switching current) and the on-resistance of the switching transistor is generated as a voltage drop. Further, the product of the on-resistance of the reference transistor and the constant current is generated as a voltage drop at both ends of the reference transistor, and is used as a threshold voltage. By comparing the voltage drop between the switching transistor and the reference transistor by the comparator, the switching current and the constant current (threshold current) are converted into a voltage and indirectly compared, and an overcurrent state is detected. According to this aspect, since the switching transistor and the reference transistor are the same type of transistor, the on-resistances of the switching transistor and the reference transistor fluctuate following each other when the temperature and the fixed voltage fluctuate. As a result, the switching current can be compared with a stable threshold current, and the accuracy of overcurrent detection can be increased.

  The switching transistor and the reference transistor may be formed by pairing. By pairing and forming the two transistors, the correlation between the respective on-resistances can be increased, and the accuracy of overcurrent detection can be further increased.

A predetermined bias voltage is applied to the control terminal of the reference transistor, and the predetermined bias voltage is equal to the voltage to be supplied to the control terminal of the switching transistor during the period in which the switching transistor is to be turned on.
In this case, since the bias states of the reference transistor and the switching transistor match, the correlation of the on-resistance can be further increased.

  In one aspect, the switching power supply may be a step-up switching regulator. The output circuit may include an inductor to which an input voltage is applied at one end. A ground voltage may be applied as a fixed voltage to the first terminal of the switching transistor, and the second terminal of the switching transistor may be connected to the other end of the inductor.

  The switching transistor and the reference transistor may be an N-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor).

  In one aspect, the switching power supply may be a step-down switching regulator. The output circuit may include an inductor having one end connected to the output terminal of the step-down switching regulator. The input voltage of the step-down switching regulator may be applied as a fixed voltage to the first terminal of the switching transistor, and the second terminal of the switching transistor may be connected to the other end of the inductor.

  The switching transistor and the reference transistor may be a P-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor).

  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 control circuit as one LSI, the circuit area can be reduced and the characteristics of the circuit elements can be kept uniform.

  Another aspect of the present invention is a step-up switching regulator. This step-up switching regulator includes an output circuit and the control circuit described above. The output circuit includes an output capacitor having one end grounded, an inductor having an input voltage applied to one end, and a rectifying element provided between the other end of the output capacitor and the other end of the inductor. The control circuit supplies a switching voltage to the other end of the inductor. The switching regulator outputs the voltage at the other end of the output capacitor as an output voltage.

  Yet another embodiment of the present invention is a step-down switching regulator. This step-down switching regulator includes an output circuit and the control circuit described above. The output circuit includes an output capacitor having one end grounded, and an inductor having one end connected to the other end of the output capacitor. The control circuit supplies a switching voltage to the other end of the inductor. Switching outputs the voltage at the other end of the output capacitor as an output voltage.

Yet another embodiment of the present invention is an electronic device. This electronic device includes a battery and the switching regulator according to any one of the above-described aspects that increases or decreases the voltage of the battery.
According to this aspect, when the load is short-circuited, the overcurrent state of the switching regulator can be suppressed, so that the stability of the device can be improved.

  According to still another aspect of the present invention, there is provided a current detection circuit that detects that a monitoring current to be monitored exceeds a predetermined threshold current. The current detection circuit is provided on the monitoring current path, and is the same type as the first transistor having a predetermined fixed voltage supplied to the first terminal, and the fixed voltage is supplied to the first terminal. The second transistor, a constant current source connected to the second terminal which is the other end of the first terminal of the second transistor and supplying a predetermined constant current to the second transistor, and a voltage at the second terminal of the second transistor And a comparator that compares the voltage of the second terminal of the first transistor.

  The first and second transistors may be formed by pairing. Further, the same bias voltage may be supplied to the control terminals of the first and second transistors.

  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, etc. are also effective as an aspect of the present invention.

  According to the switching power supply control circuit of the present invention, highly accurate current detection can be realized.

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 where the member A and the member B are connected” means that the member A and the member B are physically directly connected, or the member A and the member B are electrically connected. It includes the case of being indirectly connected through another member that does not affect the connection state.

(First embodiment)
FIG. 1 is a circuit diagram showing a configuration of a switching power supply 200 according to the first embodiment. The switching power supply 200 is a step-up type switching regulator, and includes a control circuit 100 and a switching regulator output circuit (hereinafter simply referred to as an output circuit) 110. The control circuit 100 is an LSI chip integrated on a single semiconductor substrate, and a switching transistor M1 functioning as a switching element is built in the control circuit 100. The switching power supply 200 boosts the input voltage Vin applied to the input terminal 202, stabilizes the input voltage Vin to a predetermined target voltage, and outputs the output voltage Vout from the output terminal 204.

  The output circuit 110 includes an output capacitor C1, an inductor L1, and a diode D1 that is a rectifying element. The output capacitor C1 has one end grounded and the other end connected to the output terminal 204. One end of the inductor L1 is connected to the input terminal 202, and the input voltage Vin is applied thereto. The diode D1 is provided between the other end of the inductor L1 and the output terminal 204, the anode is connected to the other end of the inductor L1, and the cathode is connected to the output terminal 204. The other end of the inductor L1 is connected to the switching terminal 104 of the control circuit 100. In the case of the synchronous rectification method, the diode D1 may be a transistor.

  The switching power supply 200 controls the current flowing through the inductor L1 by the control circuit 100, boosts the input voltage Vin by charging the output capacitor C1, and the voltage appearing at the output capacitor C1 is connected to the output terminal 204. Supply to a load (not shown). The control circuit 100 includes a feedback terminal 102 and a switching terminal 104 as input / output terminals. An output voltage Vout supplied to the load is fed back to the feedback terminal 102.

  The control circuit 100 includes a switching transistor M1, a driver circuit 10, a pulse modulation unit 12, and a current detection circuit 20. In the present embodiment, the switching transistor M1 is an N-channel MOS transistor, and a ground voltage GND is applied as a predetermined fixed voltage to the source which is the first terminal. The second terminal at the other end of the first terminal of the switching transistor M 1, that is, the drain is connected to the switching terminal 104. The switching transistor M1 supplies the switching voltage Vsw1 appearing at the drain to the output circuit 110 externally attached to the control circuit 100 via the switching terminal 104.

  The pulse modulation unit 12 generates a pulse modulation signal Sp whose duty ratio is controlled so that the output voltage Vout of the switching power supply 200 output from the output circuit 110 approaches a predetermined target voltage Vref. As a pulse modulation method by the pulse modulation unit 12, any method such as a pulse width modulation method and a pulse frequency modulation method can be applied. A known technique may be used as the pulse modulation unit 12. For example, the pulse modulator 12 can be configured to include an error amplifier, a triangular wave generator, and a PWM comparator. The error amplifier amplifies an error between the voltage corresponding to the output voltage Vout and the reference voltage Vref, and generates an error voltage. The triangular wave generator generates a periodic voltage having a triangular wave shape or a sawtooth wave shape. The PWM comparator may compare the periodic voltage with the error voltage and generate a pulse signal that switches between a high level and a low level according to the magnitude relationship.

  The driver circuit 10 generates a drive signal Sd to be supplied to the gate, which is a control terminal of the switching transistor M1, based on the pulse signal Sp output from the pulse modulation unit 12. The driver circuit 10 may include an inverter having a sufficient driving capability for driving the switching transistor M1. In this embodiment, the driver circuit 10 is supplied with the power supply voltage Vdd, and the driver circuit 10 swings the voltage level of the drive signal Sd between the power supply voltage Vdd and the ground voltage GND.

  When the drive signal Sd becomes the power supply voltage Vdd, that is, the high level, the switching transistor M1 is turned on. When the drive signal Sd becomes the ground voltage GND, that is, the low level, the switching transistor M1 is turned off. When the switching transistor M1 is turned on, the switching current Isw flows from the input terminal 202 via the inductor L1 and the switching transistor M1, and energy is stored in the inductor L1. When the switching transistor M1 is turned off, a current is supplied from the input terminal 202 to the output capacitor C1 via the inductor L1 and the diode D1. As the switching transistor M1 is repeatedly turned on and off, the output voltage Vout is stabilized at the reference voltage Vref.

  The current detection circuit 20 monitors the switching current Isw that flows while the switching transistor M1 is on, and compares it with a predetermined threshold current Ith. When the current detection circuit 20 detects an overcurrent state where Isw> Ith, the protection circuit 30 forcibly turns off the switching transistor M1 to perform circuit protection.

The current detection circuit 20 includes a threshold voltage source 22 and a comparator 24.
The threshold voltage source 22 generates a predetermined threshold voltage Vth1. The comparator 24 compares the voltage across the switching transistor M1, that is, the switching voltage Vsw1 corresponding to the voltage drop, with the threshold voltage Vth1. When the voltage Vsw1 across the switching transistor M1 exceeds the threshold voltage Vth1, the comparator 24 outputs a comparison signal Scmp of a predetermined level (hereinafter referred to as high level).
The protection circuit 30 forcibly turns off the switching transistor M1 when the comparison signal Scmp becomes high level. The protection circuit 30 may be a circuit that fixes the gate voltage of the switching transistor M1, that is, the level of the drive signal Sd to a low level when the comparison signal Scmp is at a high level, and may be configured integrally with the driver circuit 10. However, it may be configured integrally with the pulse modulator 12.

The switching voltage Vsw1 is given by Expression (1) using the on-resistance Ron1 of the switching transistor M1 and the switching current Isw.
Vsw1 = Isw × Ron1 (1)
The current detection circuit 20 determines that an overcurrent state occurs when Vsw1> Vth1.
Isw × Ron1> Vth1 (2)
When it satisfies, it is determined as an overcurrent state. Therefore, the threshold current Ith is
Ith = Vth1 / Ron1 (3)
Given in.

  If both the on-resistance Ron1 and the threshold voltage Vth1 are constant values, the threshold current Ith is kept constant. However, in reality, the on-resistance Ron1 of the switching transistor M1 varies depending on the temperature. Further, the on-resistance Ron1 varies depending on the gate voltage. As described above, the drive voltage Sd supplied to the gate of the switching transistor M1 is the power supply voltage Vdd, and this power supply voltage Vdd is often supplied from a battery or the like. Therefore, the on-resistance Ron1 of the switching transistor M1 varies depending on the power supply voltage Vdd. Furthermore, the on-resistance Ron1 of the switching transistor M1 is also affected by process variations. Therefore, when the threshold voltage Vth1 is generated using a band gap reference circuit or the like, the threshold current Ith varies because Vth1 and Ron1 vary independently.

  On the other hand, in the control circuit 100 according to the present embodiment, the threshold voltage source 22 generates the threshold voltage Vth1 that changes following the change in the on-resistance Ron1 of the switching transistor M1. The threshold voltage source 22 includes a reference transistor M2 and a constant current source 26. The reference transistor M2 is of the same type as the switching transistor M1, that is, an N-channel MOSFET. The same fixed voltage as the source of the switching transistor M1, that is, the ground voltage GND is applied to the source which is the first terminal of the reference transistor M2. The reference transistor M2 is preferably configured by pairing with the switching transistor M1. A predetermined bias voltage is applied to the control terminal, that is, the gate of the reference transistor M2. This bias voltage is preferably equal to the voltage to be supplied to the gate of the switching transistor M1, that is, the power supply voltage Vdd during the period in which the switching transistor M1 is to be turned on.

The constant current source 26 is connected to a second terminal that is the other end of the source of the reference transistor M2, that is, a drain, and supplies a predetermined constant current Ic1 to the reference transistor M2. The threshold voltage source 22 outputs the voltage at the connection point between the reference transistor M2 and the constant current source 26 as the threshold voltage Vth1. That is, the threshold voltage Vth1 is a voltage across the reference transistor M2, that is, a voltage drop. Therefore, in the present embodiment, the threshold voltage Vth1 is determined by using the on-resistance Ron2 of the reference transistor M2.
Vth1 = Ron2 × Ic1 (4)
Given in.

By substituting equation (4) into equation (3), equation (5) can be obtained as threshold current Ith in the present embodiment.
Ith = Ic1 × Ron2 / Ron1 (5)

  Here, the on-resistances Ron1 and Ron2 of the switching transistor M1 and the reference transistor M2 will be considered. As described above, since the switching transistor M1 and the reference transistor M2 are composed of the same type of transistors, the on-resistance depends on temperature. In addition, when two transistors are formed by pairing, the matching of on-resistance is further improved. Furthermore, since the same bias voltage, that is, the power supply voltage Vdd is applied to the gates of the switching transistor M1 and the reference transistor M2, the bias state also matches.

  Therefore, the on-resistances Ron1 and Ron2 follow each other even when temperature fluctuations, power supply voltage fluctuations, and process variations occur. That is, although the values of the on-resistances Ron1 and Ron2 vary, it can be considered that the ratio is kept constant, and Ron2 / Ron1 in the equation (5) is a constant value.

  If the constant current Ic1 is generated as a current independent of temperature and power supply voltage using a reference voltage obtained from a bandgap circuit, the threshold current Ith in Expression (5) becomes a constant value. The constant current Ic1 varies depending on process variations, but this may be adjusted using trimming or the like.

  According to the control circuit 100 according to the present embodiment, since Ic1 and Ron2 / Ron1 are both maintained at a constant value, the threshold current Ith compared with the switching current Isw is set to the temperature, power supply voltage, process It can be kept constant regardless of variations, and highly accurate overcurrent detection can be realized.

(Second Embodiment)
In the first embodiment, the case where the switching power supply 200 is a step-up switching regulator has been described. In the second embodiment, a case where the current detection technique is applied to a step-down switching regulator will be described.

  FIG. 2 is a circuit diagram showing a configuration of a switching power supply 200a according to the second embodiment. In the following description, components that are the same as or equivalent to the components in FIG. 1 are not shown, and description thereof is omitted as appropriate. The switching power supply 200a is a synchronous rectification step-down switching regulator. The switching power supply 200a includes a control circuit 100a and an output circuit 110a.

  The output circuit 110a includes an inductor L2 and an output capacitor C2. The output capacitor C2 has one end grounded and the other end connected to the output terminal 204. The inductor L2 has one end connected to the output terminal 204 and the other end connected to the switching terminal 104 of the control circuit 100a. The control circuit 100a supplies the switching voltage Vsw2 to the inductor L2 connected to the switching terminal 104.

The control circuit 100a includes a switching transistor M3, a synchronous rectification transistor M4, a driver circuit 10a, a pulse modulation unit (not shown), a current detection circuit 20a, and a protection circuit 30a.
The switching transistor M3 is a P-channel MOSFET, a source which is a first terminal is connected to the input terminal 106, and the input voltage Vin is applied as a fixed voltage. The drain which is the second terminal of the switching transistor M3 is connected to the inductor L2 via the switching terminal 104. The switching transistor M3 is a switch corresponding to the switching transistor M1 in FIG. 1, and a voltage drop generated at both ends thereof is compared with the threshold voltage Vth2.

The synchronous rectification transistor M4 is an N-channel MOSFET, the source is grounded, and the drain is connected to the switching terminal 104 and the drain of the switching transistor M3. The synchronous rectification transistor M4 may be replaced with a diode.
The driver circuit 10a generates drive signals SdH and SdL to be supplied to the gates of the switching transistor M3 and the synchronous rectification transistor M4 based on the pulse signal Sp output from the pulse modulation unit. The drive signals SdH and SdL are switched between a high level and a low level in a complementary manner. Each drive signal SdH, SdL becomes the power supply voltage Vdd at the high level and the ground voltage GND at the low level. The switching transistor M3 is turned on when the drive signal SdH is at a low level, and turned off when the drive signal SdH is at a high level. The synchronous rectification transistor M4 is turned on when the drive signal SdL is at a high level and turned off when the drive signal SdL is at a low level. When the switching transistor M3 and the synchronous rectification transistor M4 are alternately turned on and off, the input voltage Vin is stepped down and a stabilized output voltage Vout is generated.

The current detection circuit 20a detects the overcurrent state by comparing the switching voltage Vsw2 appearing at the drain of the switching transistor M3 with the threshold voltage Vth2. The current detection circuit 20a includes a threshold voltage source 22a and a comparator 24a.
The threshold voltage source 22a generates a predetermined threshold voltage Vth2. The comparator 24a compares the switching voltage Vsw2 with the threshold voltage Vth2. The comparator 24a outputs a comparison signal Scmp that becomes a predetermined level (high level) when the switching voltage Vsw2 falls below the threshold voltage Vth2.

  The protection circuit 30a forcibly turns off the switching transistor M3 and the synchronous rectification transistor M4 when the comparison signal Scmp becomes a high level. When the comparison signal Scmp is at a high level, the protection circuit 30a fixes the gate voltage of the switching transistor M3, that is, the level of the drive signal SdH at a high level, and sets the gate voltage of the synchronous rectification transistor M4, that is, the level of the drive signal SdL at a low level. Any circuit may be used as long as it is fixed to the level, and may be integrated with the driver circuit 10a or may be integrated with a pulse modulation unit (not shown).

The switching voltage Vsw2 is obtained by using the on-resistance Ron3 of the switching transistor M3 and the switching current Isw flowing through the switching transistor M3.
Vsw2 = Vin−Isw × Ron3 (6)
It is represented by

The threshold voltage source 22a includes a reference transistor M5 and a constant current source 26a. The reference transistor M5 is composed of the same type of P-channel MOSFET as the switching transistor M3. The same fixed voltage as the source of the switching transistor M3, that is, the input voltage Vin is applied to the source which is the first terminal of the reference transistor M5. The reference transistor M5 is preferably configured by pairing with the switching transistor M3.
A predetermined bias voltage is applied to the gate of the reference transistor M5. This bias voltage is preferably the voltage to be supplied to the gate of the switching transistor M3, that is, the ground voltage GND during the period in which the switching transistor M3 is to be turned on.

The constant current source 26a is connected to a second terminal (drain) which is the other end of the first terminal (source) of the reference transistor M5, and supplies a predetermined constant current Ic2 to the reference transistor M5. The threshold voltage source 22a outputs the voltage at the connection point between the reference transistor M5 and the constant current source 26a as the threshold voltage Vth2. Therefore, in the present embodiment, the threshold voltage Vth2 is determined by using the on-resistance Ron4 of the reference transistor M5.
Vth2 = Vin−Ron4 × Ic2 (7)
Given in.

Since the current detection circuit 20a determines that Vsw2 <Vth2 is an overcurrent state, in the overcurrent state,
Vin-Isw × Ron3 <Vin-Ron4 × Ic2 (8)
Holds. Therefore, the threshold current Ith2 is
Ith2 = Ic2 × Ron4 / Ron3 (9)
Given in.

  For the same reason as described in the first embodiment, the on-resistances Ron3 and Ron4 of the switching transistor M3 and the reference transistor M5 vary in conjunction with each other. Therefore, also in the present embodiment, the threshold current Ith2 is maintained at a substantially constant value regardless of fluctuations in the power supply voltage, temperature, and process variations, and highly accurate overcurrent detection can be realized.

  In the second embodiment, as a modification thereof, the synchronous rectification transistor M4 may be used for overcurrent detection. The current detection circuit 20a may generate the threshold voltage Vth2 to be compared with the switching voltage Vsw2 by the threshold voltage source 22 of FIG.

FIG. 3 is a block diagram showing a configuration of an electronic device equipped with the switching regulator according to the first and second embodiments. The electronic device 300 is a small information terminal such as a mobile phone terminal, portable audio player, or PDA, and includes a battery 310, a power supply device 320, an analog circuit 330, a digital circuit 340, a microcomputer 350, and an LED 360.
Taking a mobile phone terminal as an example, the battery 310 is, for example, a lithium ion battery, and outputs about 3 to 4 V as the battery voltage Vbat. The analog circuit 330 includes high-frequency circuits such as a power amplifier, an antenna switch, an LNA (Low Noise Amplifier), a mixer, and a PLL (Phase Locked Loop), and includes a circuit block that stably operates at a power supply voltage Vcc = 3.4V. . The digital circuit 340 includes various DSPs (Digital Signal Processors) and the like, and includes a circuit block that stably operates at a power supply voltage Vdd = 3.4V. The microcomputer 350 is a block that comprehensively controls the entire electronic device 300 and operates with a power supply voltage of 1.5V. The LED 360 includes RGB three-color LEDs (Light Emitting Diodes) and is used as a liquid crystal backlight or illumination, and a driving voltage of 4 V or more is required for driving.

  The power supply device 320 is a multi-channel switching power supply, and includes a switching regulator for stepping down or stepping up the battery voltage Vbat as necessary for each channel. For the analog circuit 330, the digital circuit 340, the microcomputer 350, and the LED 360, Supply an appropriate power supply voltage. The switching power supply 200 according to the first and second embodiments can be suitably used for such a power supply apparatus 320, and the reliability of the electronic device 300 can be improved.

  Those skilled in the art will understand that the above-described embodiment is an exemplification, and that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

In the embodiment, the current detection technique according to the present invention has been described using a step-up or step-down switching regulator as an example, but the application of the present invention is not limited to this. For example, in the switching power supply 200 of FIG. 1, the present invention can be applied to other switching power supplies such as a DC / DC converter, a DC / AC converter, an inverter, a capacitor charging circuit, a battery charging circuit, etc. The invention is applicable.
For example, in a capacitor charging circuit for strobe light emission or a battery charging circuit, the current flowing through the switching transistor may be monitored, and this current may be compared with a threshold value to switch the on / off state of the switching transistor. Even in such applications, the current detection technique of the present invention can be suitably used, and is included in the technical scope of the present invention.

  In the embodiment, the case where a MOSFET is used as a switching transistor has been described. However, a bipolar transistor may be used. In this case, the reference transistor used for the threshold voltage source 22 may also be composed of the same type of bipolar transistor.

  In the embodiment, the case where the control circuit 100 is integrated in one LSI has been described. However, the present invention is not limited to this, and some components are provided as discrete elements or chip components outside the LSI. Or you may comprise by several LSI. What part and how much to integrate can be determined by cost, occupied area, and the like.

  In the embodiment, the setting of the logical values of the high level and the low level is an example, and can be freely changed by appropriately inverting it with an inverter or the like.

Furthermore, the current detection techniques according to the first and second embodiments can be grasped as follows from another viewpoint. In the parentheses, the correspondence with the first embodiment is illustrated.
A current detection circuit according to an embodiment is a circuit that detects that a monitoring current (Isw) to be monitored exceeds a predetermined threshold current (Ith).
This current detection circuit
A first transistor (M1) provided on a path of the monitoring current Isw and supplied with a predetermined fixed voltage (Vdd) to a first terminal (source);
A second transistor (M2) having the same type as the first transistor (M1) and having a fixed voltage supplied to the first terminal (source);
A constant current source (26) connected to a second terminal (drain) which is the other end of the first terminal (source) of the second transistor (M2) and supplying a predetermined constant current (Ic1) to the second transistor (M2). )When,
A comparator (24) for comparing the voltage (Vth1) of the second terminal (drain) of the second transistor (M2) with the voltage (Vsw1) of the second terminal (drain) of the first transistor (M1).

  From this point of view, the application of the current detection technique according to the present invention is not limited to a switching power supply, and can be suitably used for various circuits using switching transistors that repeatedly turn on and off. Examples of such a circuit include an H-bridge circuit and a half-bridge circuit, which can be applied to a motor driver or the like.

  Although the present invention has been described based on the embodiments, the embodiments merely illustrate the principle and application of the present invention, and the embodiments are intended to include the idea of the present invention defined in the claims. Many modifications and changes in arrangement are possible within the range not leaving.

It is a circuit diagram which shows the structure of the switching power supply which concerns on 1st Embodiment. It is a circuit diagram which shows the structure of the switching power supply which concerns on 2nd Embodiment. It is a block diagram which shows the structure of the electronic device carrying the switching regulator which concerns on 1st, 2nd embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 Control circuit, 102 Feedback terminal, 104 Switching terminal, 106 Input terminal, 110 Output circuit, 200 Switching power supply, 202 Input terminal, 204 Output terminal, 10 Driver circuit, 12 Pulse modulation part, 20 Current detection circuit, 22 Threshold value Voltage source, 24 comparator, 26 constant current source, 30 protection circuit, M1 switching transistor, M2 reference transistor, M3 switching transistor, M4 synchronous rectification transistor, M5 reference transistor, C1 output capacitor, C2 output capacitor, L1 inductor, L2 inductor, D1 diode, 300 electronic device, 310 battery, 320 power supply device, 330 analog circuit, 340 digital circuit, 350 microcomputer, 3 60 LEDs.

Claims (5)

A control circuit for a step-up switching regulator having an inductor with an input voltage applied to the inductor at one end ,
A switching transistor which is an N-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor) for supplying a switching voltage generated at the drain to the other end of the inductor externally attached to the control circuit;
A pulse modulator that generates a pulse modulation signal whose duty ratio is controlled such that the output voltage of the step-up switching regulator approaches a predetermined target voltage ;
A power supply voltage supplied from the battery is applied to the upper power supply terminal, a ground voltage is applied to the lower power supply terminal, and a drive signal that takes the power supply voltage and the ground voltage in accordance with the pulse modulation signal a driver circuit for outputting to the gate of the switching transistor,
A voltage source for generating a predetermined threshold voltage;
Comparing the voltage across the switching transistor with the threshold voltage, and when the voltage across the switching transistor exceeds the threshold voltage, a comparator that outputs a comparison signal of a predetermined level;
A protection circuit for forcibly turning off the switching transistor when the comparison signal reaches the predetermined level;
With
The voltage source is
A reference transistor, which is an N-channel MOSFET, the source of which is grounded and the power supply voltage applied to the gate ;
A constant current source connected to the drain of the reference transistor and supplying a predetermined constant current to the reference transistor;
And a voltage at a connection point between the reference transistor and the constant current source is output as the threshold voltage.   The control circuit according to claim 1, wherein the switching transistor and the reference transistor are formed by pairing.   The control circuit according to claim 1 or 2, wherein the control circuit is integrated on a single semiconductor substrate. An output circuit including: an output capacitor having one end grounded; an inductor having an input voltage applied to one end; and a rectifier provided between the other end of the output capacitor and the other end of the inductor;
The control circuit according to any one of claims 1 to 3 , wherein the switching voltage is supplied to the other end of the inductor;
And a voltage at the other end of the output capacitor is output as the output voltage. Battery,
The step-up switching regulator according to claim 4 that boosts the voltage of the battery;
An electronic device comprising:

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