JP2010051066A - Switching supply circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the following problem associated with methods in which PFM method and PWM method, two prominent types of switching methods in switching power supplies, are switched during operation and their respective advantages are taken: in conventional technologies, the switching point is determined only by load current and the efficiency under light load is not necessarily maximized depending on operating conditions. <P>SOLUTION: Input current, input voltage, output current, and output voltage are measured and efficiency is computed using them and its maximum value is taken as the switching point. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a switching power supply circuit.

  There are roughly two types of switching systems in switching power supplies that maintain the voltage constant by controlling on and off of the switching element based on the error signal of the output voltage and the reference voltage. One is a PWM (Pulse Width Modulation) system that changes the on-duty ratio while fixing the switching frequency. The other is a PFM (pulse frequency modulation) system in which the switching ON time is fixed and the frequency is changed.

The PWM method is excellent in responsiveness and ripple voltage, and the PFM method is excellent in efficiency at light load. Furthermore, a method for switching between the PWM method and the PFM method during the operation according to the operating condition is attracting attention by taking advantage of the features of these methods. For example, the PWM method is normally used, but when the load current becomes smaller than a certain threshold, the PFM method is used to prevent the efficiency from being lowered (see Patent Documents 1 and 2).
Japanese Patent Laid-Open No. 10-014217 JP 2006-149067 A

  However, in the conventional proposed technique, switching between the PWM method and the PFM method is determined based only on the load current. In this case, depending on the operating conditions, the switching point is not always at the maximum efficiency when the load is light. First, since the efficiency characteristics vary depending on the input voltage, a switching point corresponding to the input voltage is required.

  To cope with this with the proposed technology, it is necessary to memorize switching points for both combinations of input voltage and load current. However, in order to realize a highly accurate switching point, the number of input voltage conditions must be set. I have to do more. As a result, the memory area is expanded and the control logic is complicated.

  Further, even if the number of input voltage conditions is increased, individual differences due to variations in the wiring pattern of the substrate cannot be handled, and there may be a case where the efficiency is not maximized even at the same switching point. In order to cope with this, it is necessary to store switching points for each substrate by adjustment work before shipment, etc., but the increase in man-hours due to this is inevitable.

  The present invention for solving the above-described problems is a switching that can operate at an optimum switching point regardless of a change in input voltage or an individual difference of boards without adjusting work, and can obtain high efficiency at a light load. An object is to provide a power supply circuit.

The present invention for solving the above problems is a switching power supply circuit that supplies power to a load so that an output voltage to a connected load matches a reference voltage.
An inductor for voltage conversion;
A switch for switching on and off the current flowing through the inductor;
Output voltage measuring means for measuring the output voltage;
Input voltage measuring means for measuring an input voltage to the switching power supply circuit;
Load current measuring means for measuring a load current flowing through the load;
Input current detection means for detecting an input current to the switching power supply circuit;
Pulse width modulation signal generating means for generating a pulse width modulation signal based on an error signal between the output voltage and the reference voltage;
Pulse frequency modulation signal generating means for generating a pulse frequency modulation signal based on the error signal;
The load current measured by the load current measuring means is compared with a switching threshold, and when the load current is smaller than the switching threshold, the pulse frequency modulation signal generating means is selected, and the load current is smaller than the switching threshold. A selection means for selecting the pulse width modulation signal generation means if not small,
Control means for controlling on and off of the switch based on the modulation signal supplied from the signal generation means selected by the selection means,
The power supply efficiency in the switching power supply circuit further includes setting means for setting the switching threshold as a load current measured by the load current measuring means.

  According to the present invention, it is possible to provide a switching power supply circuit that can operate at an optimal switching point regardless of a change in input voltage or an individual difference of boards without performing an adjustment operation and can obtain high efficiency at a light load. Can do.

[First Embodiment]
Hereinafter, an example in which the first embodiment of the present invention is applied to a voltage mode switching power supply circuit of an information processing device will be described with reference to FIGS. The information processing apparatus includes electronic devices such as a digital camera, a digital video camera, and a mobile phone. Hereinafter, a case where the present invention is applied to a digital camera will be described as an example.

  First, a configuration example of an information processing apparatus having a voltage mode switching power supply circuit corresponding to the first embodiment of the invention will be described with reference to the block diagram of FIG. The information processing apparatus of the present invention includes a battery 1 that supplies power, a load 2 such as a sensor, a power supply unit 3 that supplies a voltage to the load 2, a CPU 7 that performs system control and image processing, and an operation unit 8. The operation unit 8 receives a power on / off operation, a shooting mode switching operation, and the like from the user.

  The power supply unit 3 is a voltage mode switching power supply circuit of the present invention, and supplies power to the load so that the output voltage to the connected load 2 matches the reference voltage. The power supply unit 3 includes a controller IC 4 for controlling output of a stable voltage, a power inductor 5 for voltage conversion, a smoothing capacitor 6, an input current detection resistor 12 for detecting an input current, and a load current detection resistor 13 for detecting a load current. Consists of.

  The controller IC 4 includes a logic control unit 9 that controls the operation of the entire controller IC 4 in accordance with the IC control signal, and a feedback control unit 10 that generates a control signal for outputting an output voltage at a constant level. Further, it has a switch unit 14 for turning on and off the current flowing through the power inductor 5 in accordance with the control signal, and a communication I / F 11 for performing communication with the CPU 7 and recording a set voltage or the like in the set data recording unit 17.

  Further, the voltage at both ends of the input current detection resistor 12 is converted into digital data, the voltage at both ends of the first input A / D 24, the second input A / D 25 and the load current detection resistor 13 is converted into digital data, and the output voltage It has a first output A / D 26 and a second output A / D 27 for measuring. Furthermore, it has 1st input A / D24, 2nd input A / D25, 1st output A / D26, and 2nd output A / D27. The first input A / D 24 and the second input A / D 25 are used to measure the input voltage by converting the voltage across the input current detection resistor 12 into digital data. The first output A / D 26 and the second output A / D 27 are for converting the voltage at both ends of the load current detection resistor 13 into digital data and measuring the output voltage.

  The controller IC 4 has an efficiency calculation unit 30 that is a feature of the present invention, and a variable pseudo load unit 29 that causes a constant current to flow in a pseudo manner according to a command from the efficiency calculation unit 30. The variable pseudo load unit 29 is connected to the output side terminal of the power supply unit 3 and can change the load current. The efficiency calculation unit 30 calculates the power supply efficiency at the load current from the voltage data from the first input A / D 24, the second input A / D 25, the first output A / D 26, and the second output A / D 27.

  The feedback control unit 10 includes a reference data register 15 that temporarily stores reference data that is a reference voltage of the output voltage, and a setting data recording unit 17 that holds the reference data when the power is turned off. The setting data recording unit 17 also holds a switching point (switching threshold) described later. In addition, an output voltage comparison unit 16 that compares output voltage data with reference data, a pulse width modulation signal generation unit (PWM signal generation unit) 18, and a pulse frequency modulation signal generation unit (PFM signal generation unit) 21 are included. The PWM signal generation unit 18 and the PFM signal generation unit 21 generate a digital pulse width modulation (PWM) signal and a digital pulse frequency modulation (PFM) signal from the output of the output voltage comparison unit 16, respectively.

  Further, a switching point register 22 that temporarily stores switching points of the PWM signal generation unit 18 and the PFM signal generation unit 21, and a load current that calculates a load current from data of the first output A / D 26 and the second output A / D 27 A measurement unit 28 is included. Furthermore, the load current value measured by the load current measuring unit 28 is compared with the value of the switching point register 22, and either the PWM signal generating unit 18 or the PFM signal generating unit 21 is selected to output a switching signal. / PFM switching unit 23.

  The switch unit 14 includes a main switch driver 19 that generates a control signal to the main switch 20 in accordance with a switching signal supplied according to the selection by the PWM / PFM switching unit 23. In addition, the main switch 20 that performs an on / off operation of a current flowing through the power inductor 5 according to a control signal of the main switch driver 19 is provided.

  In the present embodiment, a variable pseudo load is realized by connecting a signal obtained by converting a PWM signal into a direct current by LPF as a variable pseudo load to a constant current circuit of two transistors and changing the duty of PWM.

  Next, an example of the operation of the information processing apparatus corresponding to the first embodiment of the invention will be described with reference to FIGS. First, the flow of control from the start of the apparatus will be described with reference to the flowchart of FIG.

  When the logic control unit 9 receives the activation control signal from the operation unit 8, the logic control unit 9 starts a series of operations (referred to as scanning) for measuring the switching point to the efficiency calculation unit 30 in step ST201 (scan). Send). The details of the scanning operation will be described later with reference to the flowchart of FIG.

Next, in step ST202, the logic control unit 9 reads the reference data V _ref and the switching point data I _Lm from the setting data recording unit 17. In step ST203, the read data is developed in the reference data register 15 and the switching point register 22, respectively.

Next, in step ST 204, and I acquire the second input A / D25, the first output A / D26 and second output A / D27 voltage data V _ADI2 from, V _ADo1, V _ADo2. Next, in step ST205, V _i which is V _ADi2 at the time of the previous scan is compared with the current V _ADi2, and it is determined whether or not the difference is larger than a predetermined threshold value V _ith . When the determination result is false (“NO” in step ST205), the process proceeds to step ST206. In step ST206, the output voltage comparison unit 16 calculates the error signal V _err according to Equation 1 using the reference data V _ref and V _ADo2 .

[Formula 1]
V _err = f (V _ADo2 −V _ADo1 )
Here, f (x) is a function for applying a gain or an offset to x and fulfills the function of phase compensation.

If the determination result in step ST205 is true (“YES” in step S205), the process proceeds to step ST207. In step ST207, a scan start signal is transmitted again, thereby resetting the switching point data I _Lm . In the subsequent step ST208, the reset switching point data I _Lm is read from the setting data recording unit 17. In the subsequent step ST209, the switching point data I _Lm is developed in the switching point register 22, and the process proceeds to step ST206. After step ST 206, the process proceeds to step ST210, the load current I _L is calculated in accordance with Equation 2.

[Formula 2]
I _L = (V _ADo2 −V _ADo1 ) / R _o
Next, in step ST211, the PWM / PFM switching unit 23 compares the load current I _L with I _{Lm of the} switching point register 22. If the load current value I _L is equal to or greater than point current I _Lm switch ( "NO" in step ST 211), the process proceeds to step ST212. In step ST212, PWM / PFM switching unit 23 selects the PWM signal generator 18 generates a PWM signal by the PWM signal generating unit 18 based on the V _err. Thereafter, the process proceeds to step ST214.

On the other hand, if the load current value I _L point current I _Lm smaller switch ( "YES" at step ST 211), the process proceeds to step S213. In step ST 213, PWM / PFM switching unit 23 selects the PFM signal generator 21 generates the PFM signal of the PFM signal generating unit 21 based on the V _err. Thereafter, the process proceeds to step ST214.

  In step ST214, the logic control unit 9 confirms the state of the protection function and the soft start function, and masks or changes the switching signal as necessary. The main switch 20 is turned on / off via the main switch driver 19 in accordance with the PWM signal or the PFM signal. Then, returning to step ST204, the output voltage is kept constant by performing a series of operations repeatedly.

  Next, the contents of the scan executed in step ST201 and step ST207 will be described using the flowchart of FIG.

When receiving the scan start signal from the logic control unit 9, the efficiency calculation unit 30 initializes each variable in step ST301. Variables include V _ADi1 , V _ADi2 , V _ADo1 , V _ADo2 , V _i , η, ηm, n, and I _Lm .

Next, in step ST <b> 302, the efficiency calculation unit 30 passes the nth pseudo load current to the variable pseudo load unit 29. In step ST303, the efficiency calculating unit 30 outputs voltage data V _ADi1 and V _ADi2 from the first input A / D 24, the second input A / D 25, the first output A / D 26, and the second output A / D 27 at that _time. , V _ADo1 and V _ADo2 are acquired. Next, in step ST304, the acquired V _ADi2 is stored in V _i .

  In step ST305, the efficiency η is calculated from the acquired data according to Equation 3.

[Formula 3]
η = {V _ADo2 · R _i (V _ADo2 −V _ADo1 } / {V _ADi2 · R _o (V _ADi2 −V _ADi1 })
Here, R _i and R _o are the resistance value of the input current detection resistor 12 and the resistance value of the load current detection resistor 13, respectively. Next, in step ST306, the calculated efficiency η is compared with the maximum efficiency ηm. When η> ηm (“YES” in step ST306), the process proceeds to step ST307. When η ≦ ηm (“NO” in step ST306), the process proceeds to step ST311.

In step ST307, η is set as a new ηm. In step ST308, the value of the switching point I _Lm at this time is calculated. Since the value of I _Lm here corresponds to the load current at that time, it can be calculated according to Equation 2. In subsequent step ST309, it is determined whether or not the switching point I _Lm calculated in ST308 exceeds a predetermined upper limit I _Lmth of the switching current.

If it exceeds the upper limit (“YES” in step ST309), the process proceeds to step ST310. In step ST310, I _Lmth is set to the value of the switching point I _Lm , and then the _{process proceeds} to step ST311. If the value of the switching point I _Lm does not exceed the upper limit value I _Lmth of the switching current (“NO” in step ST309), the process proceeds to ST311 as it is.

In step ST311, n is incremented by 1, and it is determined in step ST312 whether n has reached a predetermined number of measurement points nm. If n has not reached nm (“NO” in step ST312), the process returns to step ST302. On the other hand, when n reaches nm (“YES” in step ST312), the process proceeds to step ST313. In step ST313, the value of I _Lm calculated most recently at that time is recorded in the setting data recording unit 17 as the actual value of the switching point I _Lm .

In the flowchart of FIG. 3, the efficiency η is sequentially calculated, and the maximum efficiency η is set to ηm. At this time, the value of the switching point I _Lm is updated while the maximum efficiency ηm is being updated. However, when the maximum efficiency ηm is not updated, the value of the switching point I _Lm is not updated. In this way, it is possible to determine the value of the switching point I _Lm that maximizes the efficiency η. In the process of the flowchart of FIG. 2, control using the switching point determined in this way is performed.

7, in the efficiency maximum load current I _L is a diagram for explaining a state where switching between PWM method and PFM system. The horizontal axis represents the load current I _L and the vertical axis represents the efficiency η.

  According to the present embodiment, by setting the point at which efficiency is autonomously maximized during operation as a switching point, it is always optimal even if there is a change in input voltage or individual differences in the board without performing adjustment work. It becomes possible to operate at various switching points. Thereby, a switching power supply circuit capable of obtaining high efficiency at light load can be provided.

[Second Embodiment]
Next, an example in which the second embodiment of the present invention is applied to a voltage mode switching power supply circuit of an information processing apparatus will be described with reference to FIGS. The information processing apparatus includes electronic devices such as a digital camera, a digital video camera, and a mobile phone. Hereinafter, a case where the present invention is applied to a digital camera will be described as an example.

  First, FIG. 4 is a diagram showing a configuration example of an information processing apparatus having a voltage mode switching power supply circuit corresponding to the second embodiment of the invention. 4 has substantially the same configuration as the information processing apparatus corresponding to the first embodiment shown in FIG. In the first embodiment described above, the variable pseudo load unit 29 is provided, and a configuration in which the maximum value of efficiency is actively acquired by actively using the variable pseudo load unit 29 is employed. On the other hand, this embodiment is different in that the variable pseudo load unit 29 is not provided and a configuration in which the maximum value of efficiency is passively acquired by the actual operation of the load is employed.

  Next, an example of the operation of the information processing apparatus corresponding to the second embodiment of the invention will be described with reference to FIGS. First, the flow of control from the start of the apparatus will be described with reference to the flowchart of FIG.

When the logic control unit 9 receives the activation control signal from the operation unit 8, the logic control unit 9 reads the reference data V _ref and the switching point data I _Lm from the setting data recording unit 17 in step ST501. In the subsequent step ST502, the read data is developed in the reference data register 15 and the switching point register 22, respectively.

Next, in step ST503, voltage data V _ADi1 , V _ADi2 , V _ADo1 , V _ADo2 are obtained from the first input A / D 24, the second input A / D 25, the first output A / D 26, and the second output A / D 27. To do. In subsequent step ST504, the current efficiency η is calculated using these data. Details of the efficiency η calculation will be described later with reference to the flowchart of FIG. Next, in step ST505, the output voltage comparison unit 16 calculates the error signal V _{err according} to the above equation 1 using the reference data V _ref and V _ADo2 .

Next, in step ST506, the load current I _L is calculated according to the above equation 2. Next, in step ST507, the PWM / PFM switching unit 23 compares the load current I _L with I _{Lm of the} switching point register 22. If load current value I _L is greater than or equal to switching point current I _Lm (“NO” in step ST507), the process proceeds to step ST508. In step ST 508, PWM / PFM switching unit 23 selects the PWM signal generator 18 generates a PWM signal by the PWM signal generating unit 18 based on the V _err. Thereafter, the process proceeds to step ST510.

On the other hand, when the load current value I _L point current I _Lm smaller switch ( "YES" in step ST 507), the process proceeds to step ST 509. In step ST 509, PWM / PFM switching unit 23 selects the PFM signal generator 21 generates a PFM signal at PFM signal generating unit 21 based on the V _err. Thereafter, the process proceeds to step ST510.

  In step ST510, next, the logic control unit 9 checks the state of the protection function and the soft start function, and masks or changes the switching signal as necessary. In step ST511, on / off control of the main switch 20 is performed via the main switch driver 19 in accordance with the PWM signal or the PFM signal. Thereafter, the process returns to step ST503, and the output voltage is kept constant by repeatedly performing a series of operations.

  Next, details of the efficiency calculation process in step ST504 of FIG. 5 will be described with reference to the flowchart of FIG.

When the process of step ST503 is completed, the efficiency calculation section 30, the variable η in step ST 601, [eta] m, initializes the I _Lm. Next, in step ST602, the efficiency η is calculated from the data of V _ADi1 , V _ADi2 , V _ADo1 , and V _ADo2 acquired in step ST503 according to the above-described equation 3. Here, R _i and R _o are the resistance value of the input current detection resistor 12 and the resistance value of the load current detection resistor 13, respectively.

  Next, in step ST603, the calculated η is compared with the maximum efficiency ηm set at that time. When η> ηm (“YES” in step ST603), the process proceeds to step ST604. On the other hand, if η ≦ ηm (“NO” in step ST603), the process proceeds to ST608.

In step ST604, the calculated efficiency η is set to a new maximum efficiency ηm. Also, the process proceeds to step S605, and the switching point I _Lm at this time is calculated. Since the value of I _Lm here corresponds to the load current at that time, it can be calculated according to Equation 2. In step ST606, it determines whether the calculated I _L exceeds the upper limit I _LMTH switching current predetermined. If the load current exceeds the upper limit (“YES” in step ST606), I _Lmth is set as the value of the switching point I _Lm , and the process proceeds to step ST608. On the other hand, if the upper limit is not exceeded, the process proceeds to step ST608.

In step ST608, the value of I _Lm calculated most recently at that time is recorded as the actual value of the switching point I _{Lm in} the setting data recording unit 17, and the process proceeds to step ST505 in FIG.

5 and 6, the efficiency η is sequentially calculated every time voltage data is acquired from the first input A / D 24, the second input A / D 25, the first output A / D 26, and the second output A / D 27. To go. In this process, the maximum efficiency η is set to ηm, and the value of the switching point I _Lm is updated while the maximum efficiency ηm is updated. However, when the maximum efficiency ηm is not updated, the switching point I _Lm is not updated. In this way, it is possible to determine the value of the switching point I _Lm that maximizes the efficiency η. In step ST507 and the subsequent steps in the flowchart of FIG. 5, switching control using the switching points determined in this way is performed.

In the control method of this embodiment, as shown in FIG. 7, it is possible to switch the PWM method and the PFM system in the efficiency maximum load current I _L.

  Although the present invention has been described in detail based on the embodiments, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope described in the claims. For example, in the present embodiment, an example is shown in which the present invention is applied to a voltage mode switching power supply, but application to current mode control and other control methods is also possible. In the current mode, the switch current measuring unit of the current control loop can be used as the load current measuring unit of the present invention.

  In the present embodiment, an example is shown in which the present invention is applied to a step-down power supply circuit. In the present embodiment, an example is shown in which the present invention is applied to a digital control power supply. In this embodiment, an example is shown in which the efficiency calculation is performed by software calculation. However, an alternative value of efficiency can also be performed by hardware calculation.

In this embodiment, the variable pseudo load unit is realized by a constant current circuit using a PWM signal, an LPF, and a transistor, but other means may be used as long as an equivalent function can be realized. For example, analog control may be directly performed by a PWM signal and a DAC instead of the LPF. In the first embodiment, an example of measuring the switching point scanning hard when vary by more than a predetermined value from V _i during startup and previous scan, the scan for further reduction in power consumption It is also possible to perform only the first time.

It is a block diagram of the information processing apparatus corresponding to the 1st Embodiment of this invention. It is a flowchart which shows an example of the process in the 1st Embodiment of this invention. It is a flowchart which shows an example of the scanning process in the 1st Embodiment of this invention. It is a block diagram of the information processing apparatus corresponding to the 2nd Embodiment of this invention. It is a flowchart which shows an example of the process in the 2nd Embodiment of this invention. It is a flowchart which shows an example of the efficiency calculation process in the 2nd Embodiment of this invention. In the load current I _L to be maximum efficiency in the embodiment of the present invention is a diagram for explaining a state where switching between PWM method and PFM system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Battery 2 ... Load 3 ... Power supply part 4 ... Controller IC
5 ... Power inductor 6 ... Smoothing capacitor 7 ... CPU
8 ... Operation unit 9 ... Logic control unit 10 ... Feedback control unit 11 ... Communication I / F
12 ... Input current detection resistor 13 ... Load current detection resistor 14 ... Switch unit 15 ... Reference data register 16 ... Output voltage comparison unit 17 ... Set voltage recording unit 18 ... PWM Signal generation unit 19 ... main switch driver 20 ... main switch 21 ... PFM signal generation unit 22 ... switching point register 23 ... PWM / PFM switching unit 24 ... first input A / D
25 ... Second input A / D
26: First output A / D
27 ... Second output A / D
28 ... Load current measurement unit 29 ... Variable pseudo load unit 30 ... Efficiency calculation unit

Claims (4)

A switching power supply circuit that supplies power to a load so that an output voltage for a connected load matches a reference voltage,
An inductor for voltage conversion;
A switch for switching on and off the current flowing through the inductor;
Output voltage measuring means for measuring the output voltage;
Input voltage measuring means for measuring an input voltage to the switching power supply circuit;
Load current measuring means for measuring a load current flowing through the load;
Input current detection means for detecting an input current to the switching power supply circuit;
Pulse width modulation signal generating means for generating a pulse width modulation signal based on an error signal between the output voltage and the reference voltage;
Pulse frequency modulation signal generating means for generating a pulse frequency modulation signal based on the error signal;
The load current measured by the load current measuring means is compared with a switching threshold, and when the load current is smaller than the switching threshold, the pulse frequency modulation signal generating means is selected, and the load current is smaller than the switching threshold. A selection means for selecting the pulse width modulation signal generation means if not small,
Control means for controlling on and off of the switch based on the modulation signal supplied from the signal generation means selected by the selection means,
The switching power supply circuit further comprising setting means for setting the switching threshold as the load current measured by the load current measuring means when the power supply efficiency in the switching power supply circuit is maximized. The power supply efficiency is
The output voltage measured by the output voltage measuring means;
The load current measured by the load current measuring means;
The input voltage measured by the input voltage measuring means;
2. The switching power supply circuit according to claim 1, wherein the switching power supply circuit is calculated using the input current detected by the input current detecting means. A pseudo load unit connected to the output side terminal of the switching power supply circuit and capable of changing the load current;
The switching threshold is set as the load current when the power supply efficiency becomes maximum when the load current is changed by the pseudo load unit. Switching power supply circuit.   4. The switching power supply circuit according to claim 3, wherein the switching threshold is reset when the input voltage when set using the pseudo load unit changes by a predetermined value or more. 5. .

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