JP5513735B2 - Boost switching power supply - Google Patents

Description

  The present invention relates to a step-up switching power supply device (chopper type power supply device) that boosts an input voltage to generate an output voltage.

  FIG. 4 is a circuit diagram showing a conventional example of a step-up switching power supply device. As an example of the related art related to the switching power supply device, Patent Literature 1 can be cited.

JP 2004-32875 A

  Certainly, in the conventional step-up switching power supply, the input transistor (power supply voltage Vcc in FIG. 4) is boosted by turning on and off the output transistor M2 and the synchronous rectification transistor M1 in a complementary manner. Output voltage Vout can be obtained.

  However, the synchronous rectification step-up switching power supply device has a problem that the conversion efficiency decreases because a backflow current flows from the output side to the input side via the synchronous rectification transistor M1 at light load.

  The prior art disclosed in Patent Document 1 is a technique that achieves conversion efficiency improvement at light load by switching the rectification method according to the magnitude of the load current. Embodiment disclosed in Patent Document 1 These are all premised on application to a step-down switching power supply, and are not directly applicable to a step-up switching power supply.

  In view of the above problems, an object of the present invention is to provide a step-up switching power supply device that can improve conversion efficiency.

  In order to achieve the above object, a step-up switching power supply apparatus according to the present invention includes an output transistor, a synchronous rectification transistor, and a control unit that complementarily turns on / off the output transistor and the synchronous rectification transistor. The synchronous switching rectifier transistor has a drain connected to an input terminal of the input voltage via an inductor, and a source and a back gate. A P-channel field effect transistor connected to an output terminal of the output voltage, wherein the control unit is configured to output the output transistor based on at least one of an externally input control signal and a direction of a current flowing in the output transistor. And a first operation mode in which the synchronous rectification transistor is complementarily turned on and off, and As always off period rectification transistor is a second operation mode in which only the on / off the output transistor, and the switching configuration (first configuration).

  In the step-up switching power supply device having the first configuration, the control unit includes a parasitic diode attached between the drain and the back gate of the synchronous rectification transistor that is always turned off in the second operation mode. A configuration used as a rectifying element (second configuration) may be used.

  The step-up switching power supply device having the second configuration includes a first back gate control transistor connected between a back gate of the synchronous rectification transistor and an output terminal of the output voltage; A second back gate control transistor connected between the back gate and the drain or between the back gate of the synchronous rectification transistor and the input terminal of the input voltage (third configuration) ).

  Further, the step-up switching power supply device having any one of the first to third configurations includes an error amplifier that amplifies a difference between a feedback voltage that varies according to the output voltage and a predetermined reference voltage to generate an error voltage. And an oscillator that generates a predetermined triangular wave voltage, and a PWM comparator that generates a PWM signal by comparing the error voltage and the triangular wave voltage, and the control unit is based on the PWM signal, The output transistor and the synchronous rectification transistor may be complementarily turned on / off (fourth configuration).

  With the step-up switching power supply device according to the present invention, it is possible to prevent reverse current at light load and improve conversion efficiency.

  FIG. 1 is a circuit diagram showing an embodiment of a step-up switching power supply device according to the present invention. As shown in FIG. 1, the step-up switching power supply of this embodiment includes a control unit 1, an error amplifier 2, an oscillator 3, a PWM [Pulse Width Modulation] comparator 4, a synchronous rectification transistor M1, and an output transistor M2. And a first back gate control transistor M3, a second back gate control transistor M4, an inductor L1, an output capacitor C1, a resistor R1 and a resistor R2.

  Of the above components, components other than the inductor L1, the output capacitor C1, and the resistors R1 and R2 may be integrated in the semiconductor device 100. At that time, other circuit blocks (such as a low voltage lockout circuit and a temperature protection circuit) may be appropriately incorporated in the semiconductor device 100 in addition to the above-described components.

  The transistor M1 is a P-channel MOS [Metal-Oxide-Semiconductor] field effect transistor, and its drain is connected to an external terminal T1 (switch terminal). The source of the transistor M1 is connected to the external terminal T2 (output terminal). The gate of the transistor M1 is connected to the first gate signal output terminal of the control unit 1. A parasitic diode D1 is attached between the drain of the transistor M1 and the back gate, with the anode connected to the drain and the cathode connected to the back gate.

  The transistor M2 is an N-channel MOS field effect transistor, and its drain is connected to the external terminal T1. The source and back gate of the transistor M2 are connected to the external terminal T3 (ground terminal). The gate of the transistor M2 is connected to the second gate signal output terminal of the control unit 1.

  The transistor M3 is a P-channel MOS field effect transistor, and its drain is connected to the external terminal T2. The source and back gate of the transistor M3 are connected to the back gate of the transistor M1. The gate of the transistor M3 is connected to the third gate signal output terminal of the control unit 1.

  The transistor M4 is a P-channel MOS field effect transistor, and its drain is connected to the external terminal T1. The source and back gate of the transistor M4 are connected to the back gate of the transistor M1. The gate of the transistor M4 is connected to the fourth gate signal output terminal of the control unit 1. Note that the drain of the transistor M4 may be connected to the external terminal T0 (power supply terminal).

  The control unit 1 includes a logic circuit 11 and a driver 12. The logic circuit 11 includes a first operation mode (synchronous rectification mode) in which the transistors M1 and M2 are complementarily turned on / off based on a switching signal SEL input via the external terminal T5 (switching signal input terminal). The transistor M1 always functions as a main body for switching between the second operation mode (asynchronous rectification mode) in which only the transistor M2 is turned on / off. The driver 12 is means for generating gate signals of the transistors M1 to M4 based on the instruction from the logic unit 11 and the PWM signal S1 input from the PWM comparator 4.

  The inverting input terminal (−) of the error amplifier 2 is connected to the external terminal T4 (feedback terminal). The non-inverting input terminal (+) of the error amplifier 2 is connected to the application terminal for the reference voltage Vref. The non-inverting input terminal (+) of the PWM comparator 4 is connected to the output terminal of the error amplifier 2. The inverting input terminal (−) of the PWM comparator 4 is connected to the output terminal of the oscillator 3. The output terminal of the PWM comparator 4 is connected to the PWM signal input terminal of the control unit 1.

  Outside the semiconductor device 100, one end of the external terminal T0 and the inductor L1 is connected to the input end of the input voltage (power supply voltage Vcc in FIG. 1). Note that the power supply voltage Vcc applied to the external terminal T0 is supplied to the circuit blocks integrated in the semiconductor device 100 (in FIG. 1, the control unit 1, the error amplifier 2, the oscillator 3, and the PWM comparator 4). Used for driving. The external terminal T1 is connected to the other end of the inductor L1. The external terminal T2 is connected to a load (not shown), and is connected to the ground terminal via a path via the output capacitor C1 and a path via a voltage dividing circuit including the resistors R1 and R2. The external terminal T3 is connected to the ground terminal. The external terminal T4 is connected to a connection node between the resistor R1 and the resistor R2. The external terminal T5 is connected to a switching signal output terminal of a host (not shown) (such as a set side CPU [Central Processing Unit]). The switching signal SEL given to the external terminal T5 is input to the control unit 1 and used for operation mode switching control of the transistors M1 and M2.

  First, the basic operation (step-up operation) of the step-up switching power supply device configured as described above will be described.

  The transistor M2 is an output transistor that is switching controlled (opening / closing control) according to the second gate voltage from the control unit 1, and the transistor M1 is switching controlled (opening / closing control) according to the first gate voltage from the control unit 1. ) Synchronous rectification transistor.

  When boosting the power supply voltage Vcc to obtain the output voltage Vout, the control unit 1 turns on the transistor M3, turns off the transistor M4, and performs complementary switching control on the transistor M1 and the transistor M2.

  Note that the term “complementary” used in this specification refers to the case where the transistors M1 and M2 are turned on / off in addition to the case where the on / off of the transistors M1 and M2 are completely reversed. The case where a predetermined delay is given to the off transition timing is also included.

  When the transistor M2 is turned on, the inductor current IL flows through the inductor L1 toward the ground terminal via the transistor M2, and the electrical energy is stored. Note that if the charge has already been accumulated in the output capacitor C1 during the ON period of the transistor M2, the current from the output capacitor C1 flows through the load (not shown) connected to the external terminal T2. At this time, the transistor M1, which is a synchronous rectifier, is turned off in a complementary manner to the on state of the transistor M2, so that no current flows from the output capacitor C1 toward the transistor M2.

  On the other hand, when the transistor M2 is turned off, the electric energy stored therein is released by the back electromotive voltage generated in the inductor L1. At this time, since the transistor M1 is turned on complementarily to the off state of the transistor M2, the current flowing from the external terminal T1 through the transistor M1 flows into the load from the external terminal T2 and the output capacitor C1. Then, it also flows into the ground terminal and charges the output capacitor C1. By repeating the above operation, the output voltage Vout smoothed by the output capacitor C1 is supplied to the load.

  As described above, the step-up switching power supply according to this embodiment boosts the input voltage Vin and generates the output voltage Vout by switching control of the transistors M1 and M2.

  Next, feedback control of the step-up switching power supply device having the above configuration will be described.

  The error amplifier 2 includes an output feedback voltage Vfb (corresponding to an actual value of the output voltage Vout) drawn from a connection node between the resistors R1 and R2, and a predetermined reference voltage Vref (corresponding to a target value of the output voltage Vout). The difference is amplified to generate an error voltage Verr. That is, the voltage level of the error voltage Verr becomes higher as the output voltage Vout is lower than the target value. On the other hand, the oscillator 3 generates a triangular wave voltage (sawtooth voltage) Vsaw having a predetermined frequency.

  The PWM comparator 4 compares the error voltage Verr and the triangular wave voltage Vsaw to generate a PWM signal S1. That is, the on-duty (ratio of the on-period of the transistor M2 in the unit period) of the PWM signal S1 sequentially varies according to the relative level of the error voltage Verr and the triangular wave voltage Vsaw. More specifically, as the output voltage Vout is lower than its target value, the on-duty of the PWM signal S1 increases. As the output voltage Vout approaches the target value, the on-duty of the PWM signal S1 decreases.

  When boosting the power supply voltage Vcc to obtain the output voltage Vout, the control unit 1 performs complementary switching control on the transistors M1 and M2 in accordance with the PWM signal S1. More specifically, the control unit 1 turns on the transistor M2 and turns off the transistor M1 during the high level period of the PWM signal S1, while turning off the transistor M2 during the low level period of the PWM signal S1. The transistor M1 is turned on.

  As described above, the step-up switching power supply according to the present embodiment can adjust the output voltage Vout to the target value by the output feedback control based on the error voltage Verr.

  Next, the back gate control operation of the step-up switching power supply device configured as described above will be described.

  Until the step-up operation is started after the power supply voltage Vcc is turned on, the control unit 1 turns on only the transistor M4 and turns off the remaining transistors M1, M2, and M3. By such back gate control, it is possible to reliably block all current leak paths from the external terminal T1 to the external terminal T2, including the current leak path via the parasitic diode associated with the transistor M1.

  Further, by turning on the transistor M4, the back gates of the transistors M1, M3, and M4 can be connected to the highest potential point (switch voltage Vsw (= power supply voltage Vcc)) at that time, so that the transistors M1, M3 It becomes possible to make the OFF state of the more reliable.

  Thereafter, when the boosting operation is started, the control unit 1 turns on the transistor M3 and turns off the transistor M4 as described above, and performs switching control on the transistors M1 and M2 in a complementary manner. As a result, the step-up switching power supply device can boost the input voltage Vin to generate the output voltage Vout.

  Next, the operation mode switching control of the step-up switching power supply device configured as described above will be described in detail with reference to FIGS. 2A and 2B. 2A and 2B are waveform diagrams showing the gate voltages and the inductor current IL of the transistors M1 and M2 in the first and second operation modes, respectively. The inductor current IL is depicted with the direction flowing from the input terminal of the power supply voltage Vcc toward the external terminal T1 being positive.

  When the first operation mode (synchronous rectification mode) is selected by the switching signal SEL, the control unit 1 generates each gate voltage so that the transistors M1 and M2 are complementarily turned on / off (FIG. 2A). See). That is, in the first operation mode, the output voltage Vout is generated from the power supply voltage Vcc by the synchronous rectification method by using the transistor M1 having a small on-resistance value as the synchronous rectification element.

  On the other hand, when the second operation mode (asynchronous rectification mode) is selected by the switching signal SEL, the control unit 1 sets each gate voltage so that the transistor M1 is always turned off and only the transistor M2 is turned on / off. Generate (see FIG. 2B). That is, in the second operation mode, the output voltage Vout is generated from the power supply voltage Vcc by the diode rectification method by using the parasitic diode D1 attached between the drain and the back gate of the transistor M1 that is always turned off as a rectifier. Generated.

  As described above, in the step-up switching power supply device of the present embodiment, the first operation mode in which the transistors M1 and M2 are complementarily turned on / off based on the externally input switching signal SEL, and the transistor M1 are always set. The second operation mode in which the transistor M2 is turned off and only the transistor M2 is turned on / off is switched. With such a configuration, the first operation mode of the synchronous rectification method is selected in order to give priority to the reduction of resistance loss generated in the rectifier element at the time of heavy load, and priority is given to prevention of backflow of the inductor current IL at the time of light load. Therefore, since the second operation mode of the diode rectification method can be selected, it is possible to improve the conversion efficiency of the step-up switching power supply device.

  The configuration of the present invention can be variously modified in addition to the above-described embodiment without departing from the gist of the invention.

  For example, in the above-described embodiment, the configuration in which the operation mode switching control is performed based on the switching signal SEL input via the external terminal T5 has been described as an example. However, the configuration of the present invention is not limited thereto. Instead of this, as shown in FIG. 3, a current detection unit 5 that detects the direction of the current flowing through the transistor M2 may be provided, and the operation mode switching control may be performed spontaneously based on the detection signal S2. . That is, the control unit 1 performs switching control of the operation mode so that the first operation mode is selected if the direction of the current flowing through the transistor M2 is the positive direction, and the second operation mode is selected if the direction of the current flowing in the transistor M2 is the reverse direction. Good. With such a modification, it is possible to perform the operation mode switching control spontaneously without requiring an external switching signal SEL.

  The current detection unit 5 may be configured such that an aluminum wiring connecting the source of the transistor M2 and the external terminal T3 is used as a sense resistor and the voltage at both ends thereof is monitored, or in parallel with the transistor M2. A mirror transistor for current detection may be provided to monitor the current flowing through the mirror transistor.

  The present invention is a technique useful for increasing the conversion efficiency of a step-up switching power supply device, and is used for all electronic devices that require an output voltage higher than the input voltage (for example, an optical disc drive such as a Blu-ray disc drive, a digital still camera, / Digital video camera / portable equipment such as a mobile phone).

These are the circuit diagrams which show one Embodiment of the switching power supply device which concerns on this invention. These are waveform diagrams showing the gate voltages of the transistors M1 and M2 and the inductor current IL in the first operation mode. These are waveform diagrams showing the gate voltages of the transistors M1 and M2 and the inductor current IL in the second operation mode. These are circuit diagrams which show the modification of the switching power supply device which concerns on this invention. These are the circuit diagrams which show one prior art example of a switching power supply device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control part 2 Error amplifier 3 Oscillator 4 PWM comparator 5 Current detection part 11 Logic circuit 12 Driver 100 Semiconductor device M1 Synchronous rectification transistor (P channel type MOS transistor)
M2 output transistor (N-channel MOS transistor)
M3 First back gate control transistor (P-channel MOS transistor)
M4 Second back gate control transistor (P-channel MOS transistor)
L1 Inductor C1 Output capacitor R1 to R2 Resistance D1 Parasitic diode T1 to T5 External terminal

Claims (3)

An output transistor, a synchronous rectification transistor, a control unit that complementarily turns on and off the output transistor and the synchronous rectification transistor, and a current detection unit that detects a current direction flowing through the output transistor, A step-up switching power supply that boosts an input voltage to generate an output voltage,
The synchronous rectification transistor is a P-channel field effect transistor having a drain connected to an input terminal of the input voltage via an inductor, and a source and a back gate connected to an output terminal of the output voltage.
The step-up switching power supply device further includes a first back gate control transistor connected between a back gate of the synchronous rectification transistor and an output terminal of the output voltage; a back gate and a drain of the synchronous rectification transistor; Or a second back gate control transistor connected between a back gate of the synchronous rectification transistor and an input terminal of the input voltage,
The control unit includes a first operation mode in which the output transistor and the synchronous rectification transistor are complementarily turned on / off based on a detection result of the current detection unit, and the synchronous rectification transistor is always turned off, and the output transistor And a second operation mode for switching only on / off, and a current flowing through the output transistor when a direction flowing from the input terminal of the input voltage toward the output transistor is defined as a positive direction. The first operation mode is selected if the direction is the positive direction, the second operation mode is selected if the direction is the reverse direction , and the drain of the synchronous rectification transistor that is always turned off in the second operation mode. And a parasitic diode associated with the back gate as a rectifying element, and the input voltage The second back gate control transistor is turned on and the output transistor, the synchronous rectification transistor, and the first back gate control transistor are all turned off until the boosting operation is started after being turned on. is there,
A step-up switching power supply device characterized by the above. An error amplifier that generates an error voltage by amplifying a difference between a feedback voltage that varies according to the output voltage and a predetermined reference voltage, an oscillator that generates a predetermined triangular wave voltage, and the error voltage and the triangular wave voltage are compared. And a PWM comparator for generating a PWM signal,
2. The step-up switching power supply device according to claim 1 , wherein the control unit complementarily turns on / off the output transistor and the synchronous rectification transistor based on the PWM signal. An electronic apparatus comprising the step-up switching power supply device according to claim 1 .

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