JP2010252564A - Switching power supply circuit and electronic equipment having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply circuit which easily prevents noise or the like caused by a switching operation from adversely affecting the switching operation as much as possible even when a light load is connected. <P>SOLUTION: The switching power supply circuit includes: a circuit for generating a first signal according to a current flowing through a switching element; a circuit for generating a second signal according to a voltage in an output terminal; a switch control circuit for controlling on/off of the switching element; and an addition circuit for adding a predetermined value to the first signal or the second signal to reduce a difference between the first signal and the second signal. The switch control circuit turns off the switching element every time a value of the first signal reaches that of the second signal. The addition circuit detects the timing at which the switching element is turned on, and is used as a switching power supply circuit which starts addition when a predetermined first delay time elapses from the detection timing. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a switching power supply circuit used for a power supply device of an electronic apparatus.

  2. Description of the Related Art Conventionally, switching power supply circuits that adjust output power by a switching operation have been widely used in power supply devices for electronic devices. The switching power supply has a relatively high power conversion efficiency, and can contribute to energy saving, a longer battery life, and reduced heat generation. Further, in recent years, with the promotion of energy saving, the voltage of devices to which the switching power supply supplies power has been reduced, and low voltage devices such as 2.5V system, 1.5V system, and 1.0V system have become common.

  In switching power supplies, in order to reduce the size and cost of products, it is desired to increase the oscillation frequency (for example, 900 kHz or more) that can be configured with a small coil size. Therefore, a switching power supply that can operate in a short on-time (for example, 150 ns or less) is required. Furthermore, although the current required for the device tends to increase, when it is unnecessary, the current consumption of the device is reduced, so from the case of a high load (for example, 1 A or more) to the case of a light load (for example, 100 mA or less) There is a need for a switching power supply that operates stably.

  In addition, it is necessary to reduce the output capacitor and coil for miniaturization, and it is relatively easy to design a stable feedback circuit for the switching power supply. Current control type (current detection and voltage detection are used to determine the switching timing. Switching power supply is attracting attention. Note that a current control type switching power supply is disclosed in Patent Literature 1, Patent Literature 2, and the like.

  Here, as an example of the current control type switching power supply, the one shown in FIG. 5 is cited, and its operation will be briefly described.

  The DC voltage supplied to the input terminal IN is smoothed by the input capacitor C1 to become the input voltage Vin, and then converted into a pulse voltage by the switching operation of the switching element 12. When the switching element 12 is on, a current flows from the input terminal IN to the coil L1, whereby energy is accumulated in the coil L1 and energy is supplied to the load connected to the output terminal OUT.

  On the other hand, when the switching element 12 is off, the energy accumulated in the coil L1 is supplied to the load. The output voltage Vout smoothed by the output capacitor C2 is supplied to the output terminal OUT. Further, the switching element 12 is controlled via the drive circuit 17b so that it is turned on when the flip-flop circuit (RS flip-flop circuit) 17a is in the set state and turned off when it is in the reset state.

  On the other hand, at the non-inverting input terminal of the comparator 16, a compensation current Isens (current corresponding to the magnitude of the switch current Isw flowing through the switching element 12) detected by the current detection circuit 11 is compensated by the current compensation circuit 13. The current to which Ic is added (compensated current Icc) is input. The output signal of the comparator 16 is input to the input terminal R of the flip-flop circuit 17a, and the output signal from the transmitter 18 is input to the input terminal S.

  Here, the switching operation in the switching power supply will be described with reference to the timing chart of FIG. 6 (when a standard load is connected to the output terminal OUT). FIG. 6A shows the waveform of the pulse signal output from the transmitter 18. 6B shows the waveform of the output signal from the output terminal Q of the flip-flop circuit 17a, and FIG. 6C shows the waveform of the switch current Isw. Further, (d) in FIG. 6 represents the waveform of the detection current Isens, and (e) in FIG. 6 represents the waveform of the compensation current Ic.

  As shown in these figures, the flip-flop circuit 17a receives the pulse signal from the transmitter 18, is set at the fall timing, and turns on the switching element 12. On the other hand, when the signal from the comparator 16 becomes H (High) level, the signal is reset and the switching element 12 is turned off.

  In this way, the switching element 12 is turned on / off, and a switching current Isw having a waveform as shown in FIG. Note that the timing when the switching element 12 is turned off, that is, the timing when the output of the comparator 16 becomes the H level is determined as follows.

  As shown in FIG. 6F, the comparator 16 compares the compensated current Icc obtained by adding the compensation current Ic to the detection current Isens and the error current Ie output from the voltage detection circuit 15. Then, at the timing (the timing indicated by A) when the level of the compensated current Icc reaches the level of the error current Ie, the comparator 16 sets the output signal to the H level and resets the flip-flop circuit 17a. When the error current Ie is larger, the comparator 16 sets the output signal to L (Low) level so as not to reset the flip-flop circuit 17a.

  Here, as shown in FIG. 6D, the detection current Isens is provided with a predetermined offset α1. Thereby, even when the switch current Isw does not flow, the compensated current Icc maintains the level of α1. Further, the difference between the offset α1 and the error current Ie is α2, as shown in FIG.

  Here, the error current Ie from the voltage detection circuit 15 is a current corresponding to an error between the feedback voltage Vadj obtained by dividing the output voltage Vout by the voltage dividing resistors R1 and R2 and the reference voltage Vref. Therefore, the output voltage Vout is maintained at a constant voltage according to the reference voltage Vref by the switching operation of the switching element 12.

  Note that the addition of the compensation current Ic described above is performed so that the fluctuation generated in the switch current Isw is converged and the switching operation is stabilized. That is, the current compensation circuit 13 increases the slope of the compensated current Icc by adding the compensation current Ic that increases with time to the detection current Isens when the switching element 12 is turned on. By performing such an operation, the output voltage Vout is stably maintained even when the load connected to the output terminal OUT varies.

JP 2005-184991 A JP 2004-40856 A

  Here, it is assumed that the load connected to the output terminal OUT of the switching power supply described above is light (when a light load is connected). At this time, the level of the switch current Isw decreases as shown in FIG. 7C, and the level of the error current Ie and the compensated current Icc also decreases as shown in FIG. 7F. As a result, α2 which is the difference between the offset α1 and the error current Ie is also reduced.

  As a result, the switching operation in the switching element 12 is easily affected by noise and the like resulting from the switching operation itself (particularly switching from off to on). For example, as shown in FIG. 7F, the noise may be superimposed on the compensated current Icc. In this case, since α2 is relatively small, the level of the compensated current Icc may reach the level of the error current Ie at an unintended timing (timing indicated by B in FIG. 7F).

  In this case, an inappropriate signal is output from the comparator 16, and consequently, the switching operation in the switching element 12 is adversely affected. Such a phenomenon occurs more remarkably in a switching power supply circuit that operates in a short on-time.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a switching power supply circuit that makes it easy to suppress, as much as possible, noise caused by a switching operation from adversely affecting the switching operation even when a light load is connected. To do.

  In order to achieve the above object, a switching power supply circuit according to the present invention includes a switching element between an input terminal and an output terminal, and adjusts the power input to the input terminal through on / off switching of the switching element. In the switching power supply circuit that outputs the adjusted power from the output terminal, a first signal generation circuit that generates a first signal indicating a value corresponding to a current flowing through the switching element, and A second signal generating circuit for generating a second signal indicating a value corresponding to the voltage; a switching control circuit for controlling on / off switching of the switching element; and adding a predetermined value to the first signal or the second signal And an addition circuit that reduces a difference between the values of the first signal and the second signal, and the switching control circuit is configured so that each time the value of the first signal reaches the value of the second signal, The switching element is turned off, and the adder circuit detects timing when the switching element is turned on, and starts the addition at a timing when a predetermined first delay time has elapsed from the detected timing. The configuration is as follows.

  According to this configuration, if a time during which noise due to the switching operation is sufficiently attenuated is set as the first delay time, it is possible to suppress the noise from adversely affecting the switching operation as much as possible.

  More specifically, the addition circuit may be configured to detect the timing at which the switching element is switched off and stop the addition at a timing according to the detection result.

  More specifically, the addition circuit may be configured to stop the addition at a timing when a predetermined second delay time has elapsed from a timing at which the switching element is switched off.

  In the above-described configuration, a compensation circuit is provided for acquiring a timing specifying signal indicating a timing at which the switching element is turned on / off, and increasing the slope of the first signal during the period when the switching element is on. The timing specifying signal is also supplied to the adder circuit, and the adder circuit may detect a timing at which the switching element is turned on / off based on the timing specifying signal.

  According to this configuration, it is possible to share the path for transmitting the timing specifying signal (corresponding to the output signal Sc in the embodiment) to the compensation circuit and the path for transmitting the timing specifying signal to the adding circuit. Become.

  More specifically, the configuration includes a DMAX circuit that turns off the switching element in a predetermined period, and the adder circuit acquires a signal indicating the predetermined period and responds to the acquired signal. Thus, the addition may be started or stopped.

  A switching power supply circuit according to the present invention has one end connected to an input terminal to which a DC voltage is applied, a switching element that switches the DC voltage into a pulse voltage, and the other end of the switching element and an output terminal. A coil connected to smooth the pulse voltage to make a DC voltage different from the DC voltage, and an output capacitor connected between the output terminal and the ground, and smoothing the DC voltage from the coil to make an output voltage And a rectifying element that is connected between a connection point between the switching element and the coil and the ground, and flows a current through the coil during an off period of the switching element. A current detection circuit for generating a first signal corresponding to the magnitude of the output voltage, and a feedback current generated by dividing the output voltage And a voltage detection circuit for generating a second signal representing an error between the predetermined reference voltage and the pulse signal generated by the oscillator, the switching element is turned on, and the value of the first signal is the second signal. The switching control circuit that turns off the switching element each time the value reaches the value, and an addition that adds a predetermined value to the first signal or the second signal and reduces the difference between the values of the first signal and the second signal The addition circuit detects a timing at which the switching element is turned on / off, and starts the addition at a timing when a predetermined first delay time has elapsed from the timing at which the switching element is turned on. On the other hand, the addition is stopped at a timing when switched off or when a predetermined delay time has elapsed from the timing when switched off.

  According to this configuration, if a time during which noise due to the switching operation is sufficiently attenuated is set as the predetermined delay time, it is possible to suppress the noise from adversely affecting the switching operation as much as possible.

  Moreover, if it is an electronic device provided with the switching power supply circuit which concerns on the said structure, it will become possible to enjoy the advantage which concerns on the said structure.

  As described above, according to the switching power supply circuit according to the present invention, if the time that noise due to the switching operation is sufficiently attenuated is set as the first delay time, the noise adversely affects the switching operation. It is possible to suppress as much as possible. As a result, it is possible to realize a highly efficient switching power supply circuit that can suppress malfunction as much as possible and supply power stably even under short on-time and light load conditions.

It is a block diagram of the switching power supply circuit which concerns on Example 1 of this invention. It is a timing chart which concerns on Example 1 of this invention. It is a block diagram of the switching power supply circuit which concerns on Example 2 of this invention. It is a timing chart which concerns on Example 2 of this invention. It is a block diagram regarding the conventional switching power supply circuit. It is a timing chart regarding the conventional switching power supply circuit (when standard load is connected). It is a timing chart regarding the conventional switching power supply circuit (when a light load is connected).

  Embodiments of the present invention will be described below with reference to switching power supply circuits according to Example 1 and Example 2.

[Example 1]
First, an embodiment (Example 1) of the present invention will be described. FIG. 1 is a configuration diagram of a switching power supply device according to the first embodiment. As shown in the figure, the switching power supply device 1 includes a current detection circuit 11, a switching element 12, a current compensation circuit 13, a current addition circuit 14, a voltage detection circuit 15, a comparator 16, a control circuit 17, a transmitter 18, an input terminal. IN, an output terminal OUT, an input capacitor C1, an output capacitor C2, a coil L1, a diode D1, a voltage dividing resistor (R1, R2), and the like.

  An input terminal IN to which a DC voltage is supplied from the outside is connected to an output terminal OUT via each of the current detection circuit 11, the switching element 12, and the coil L1. The output terminal OUT is connected to an external load (not shown). Thereby, the switching power supply 1 can supply electric power to the load.

  The current detection circuit 11 is provided between the input terminal IN and the switching element 12 and is connected to the non-inverting input terminal of the comparator 16. Thereby, the current detection circuit 11 detects the magnitude of the current (switch current Isw) flowing through the switching element 12 and outputs a current (detection current Isens) corresponding to the detection result to the non-inverting input terminal of the comparator 16. .

  More specifically, the current detection circuit 11 sets a current obtained by adding a predetermined offset α1 to a current proportional to the switch current Isw as a detection current Isens. As a result, the detection current Isw has a waveform as shown in FIG. An input capacitor C1 having one end grounded is connected between the input terminal IN and the current detection circuit 11.

  The switching element 12 is formed of a transistor or the like, and performs a switching operation (switching on / off) so as to switch between conduction / non-conduction of a power path connecting the input terminal IN and the output terminal OUT. This switching operation is controlled by a signal input from the control circuit 17.

  The cathode of the diode D1 is connected between the switching element 12 and the coil L1, and the anode side of the diode D1 is grounded. An output capacitor C2 having one end grounded is connected between the coil L1 and the output terminal OUT. Further, the coil L1 and the output terminal OUT are grounded via voltage dividing resistors (R1, R2).

  The voltage dividing resistor R1 and the voltage dividing resistor R2 are connected to the inverting input terminal of the voltage detection circuit 15. As a result, a voltage (adjusted voltage Vadj) corresponding to the voltage (output voltage Vout) output from the output terminal OUT is input to the inverting input terminal of the voltage detection circuit 15. A voltage of a predetermined value (reference voltage Vref) is input to the non-inverting input terminal of the voltage detection circuit 15.

  The voltage detection circuit 15 is formed as a differential amplifier circuit, and outputs a current (error current Ie) corresponding to a difference between voltages (adjustment voltage Vadj and adjustment voltage Vadj) input to both input terminals. This error current Ie is output to the inverting input terminal of the comparator 16.

  The current compensation circuit 13 generates a compensation current Ic and adds it to the detection current Isens. The current compensation circuit 13 generates the compensation current Ic so that it becomes zero while the switching element 12 is off and gradually increases while the switching element 12 is on. As a result, the compensation current Ic has a waveform as shown in FIG. By adding such a compensation current Ic, the switching operation can be stabilized as will be described later.

  The current compensation circuit 13 is supplied with a signal (an output signal Sc described later) output from the flip-flop circuit 17a to the drive circuit 17b. By monitoring the state of the output signal Sc, the switching element 12 is turned on / off. Detect the switching timing. However, this is only an example, and it may be detected by other methods.

  The current addition circuit 14 generates an addition current Iad having a constant value α3 and adds (adds) the detection current Isens to the detection current Isens. The current adding circuit 14 detects the timing when the switching element 12 is turned on, and starts generation and addition (addition) of the addition current Iad at a timing delayed by a predetermined time T1 from this timing. The current adding circuit 14 detects the timing when the switching element 12 is turned off, and stops generation and addition (addition) of the addition current Iad at this timing. That is, the addition current Iad is added to the detection current Isens during a period from the timing when T1 has elapsed after the switching element 12 is turned on to the timing when the switching element 12 is turned off.

  As a result, the addition current Iad has a waveform as shown in FIG. By adding the addition current Iad, as will be described later, it is possible to prevent noise generated mainly due to the switching operation from adversely affecting the switching operation. Note that the timing at which generation and addition (addition) of the addition current Iad is stopped may be a timing delayed from the timing at which the switching element 12 is turned off (a timing at which a predetermined delay time has elapsed). However, even in this case, the addition of the addition current Iad is stopped by the next timing when the switching element 12 is turned on.

  Further, the current addition circuit 14 is supplied with the output signal Sc as in the case of the current compensation circuit 13, and monitors the state of the output signal Sc to detect the timing when the switching element 12 is switched on / off. . As described above, the current compensation circuit 13 and the current addition circuit 14 use a common signal in order to detect the switching timing of the switching element 12.

  That is, the current addition circuit 14 is also operated by a signal for operating the current compensation circuit 13, and a path (circuit) for transmitting the signal can be shared and simplified. . As a result, it is easy to reduce the cost of the switching power supply circuit 1. Note that the output signal Sc can also be regarded as a signal (timing specifying signal) indicating the timing at which the switching element 12 is switched on / off.

  Further, a current (compensated / added current Imix) obtained by adding the compensation current Ic and the addition current Iad to the detection current Isens is input to the non-inverting input terminal of the comparator 16. The comparator 16 outputs a signal corresponding to the magnitude relationship between the currents (compensated / added current Imix and error current Ie) input to both input terminals to the control circuit 17.

  The control circuit 17 includes a flip-flop circuit (RS flip-flop circuit) 17a and a drive circuit 17b. In the flip-flop circuit 17a, an output signal from the comparator 16 is input to the R terminal, and an oscillation signal generated by the transmitter 18 is input to the S terminal.

  The flip-flop circuit 17a outputs an output signal Sc corresponding to these inputs to the drive circuit 17b. The drive circuit 17b switches on / off of the switching element 12 according to the state of the output signal Sc (controls the switching operation).

  With the above-described configuration, the switching power supply circuit 1 operates as follows. The DC voltage supplied to the input terminal IN is smoothed by the input capacitor C1 to become the input voltage Vin, and then converted into a pulse voltage by the switching operation of the switching element 12. When the switching element 12 is on, a current flows from the input terminal IN to the coil L1, whereby energy is accumulated in the coil L1 and energy is supplied to the load connected to the output terminal OUT. .

  On the other hand, when the switching element 12 is off, the energy stored in the coil L1 is supplied to the load connected to the output terminal OUT. Note that the output voltage Vout smoothed by the output capacitor C2 is supplied to the output terminal OUT. The switching element 12 is controlled via the drive circuit 17b so that it is turned on when the flip-flop circuit 17a is in the set state and turned off when it is in the reset state. In this way, the switching power supply circuit 1 adjusts the power input to the input terminal IN through on / off switching of the switching element 12, and outputs the adjusted power from the output terminal OUT.

  Here, more detailed contents of the switching operation will be described with reference to each timing chart (when a light load is connected) shown in FIG. 2A shows the waveform of a pulse signal output from the transmitter 18. FIG. FIG. 2B shows the waveform of the output signal Sc output from the output terminal Q of the flip-flop circuit 17a. 2C shows a waveform of the switch current Isw flowing through the switching element 12, and FIG. 2D shows a waveform of the detection current Isens. FIG. 2E shows the waveform of the compensation current Ic, and FIG. 2F shows the waveform of the addition current Iad.

  As shown in these figures, the flip-flop circuit 17a receives the pulse signal from the transmitter 18, is set at the fall timing, and turns on the switching element 12. On the other hand, when the signal from the comparator 16 becomes H (High) level, the signal is reset and the switching element 12 is turned off.

  In this way, the switching element 12 is turned on / off, and a switching current Isw as shown in FIG. Note that the timing when the switching element 12 is turned off, that is, the timing when the output of the comparator 16 becomes the H level is determined as follows.

  As described above, the compensated and added current Imix is input to the non-inverting input terminal of the comparator 16, and the error current Ie is input to the inverting input terminal. As a result, the comparator 16 compares the compensated / added current Imix with the error current Ie as shown in FIG.

  Then, at the timing when the level of the compensated / added current Imix reaches the level of the error current Ie, the comparator 16 sets the output signal to the H level and resets the flip-flop circuit 17a. When the level of the error current Ie is larger, the comparator 16 sets the output signal to L (Low) level so that the flip-flop circuit 17a is not reset.

  Here, the error current Ie from the voltage detection circuit 15 is a current corresponding to an error between the feedback voltage Vadj obtained by dividing the output voltage Vout by the voltage dividing resistors R1 and R2 and the reference voltage Vref. Therefore, the output voltage Vout is maintained at a constant voltage according to the reference voltage Vref by the switching operation of the switching element 12.

  The compensation current Ic increases with time when the switching element 12 is turned on, and the slope of the compensated / added current Imix is increased. Therefore, the output voltage Vout is stably maintained even when the switching operation is stable and the size of the load connected to the output terminal OUT varies.

  Further, the addition current Iad gives an offset of α3 to the compensated / added current Imix after the delay time T1 has elapsed since the switching element 12 was turned on, and calculates the difference between the compensated / added current Imix and the error current Ie. Make it smaller. Thereby, it is possible to prevent noise generated mainly due to the switching operation from adversely affecting the switching operation.

  That is, as shown in FIG. 2 (g), even if noise caused by the switching operation (noise generated when switching from off to on) is superimposed on the compensated / added current Imix, the noise is superimposed. During this period, the offset of α3 is not given to the compensated / added current Imix. Therefore, the level of the compensated / added current Imix reaches the level of the error current Ie at an unintended timing due to the influence of the noise (being in a state as shown in FIG. 7 (f)). Prevented in advance.

  This is because the period in which noise is superimposed on the compensated / added current Imix (the period in which noise is not sufficiently attenuated and the influence of noise is assumed to be relatively large) is the period in which noise is not superimposed (noise is It can be seen that the difference between the level of the compensated and added current Imix and the level of the error current Ie is larger than the period of time when the attenuation is sufficiently attenuated and the influence of noise is assumed to be relatively small. it can. This prevents the influence of noise on the magnitude relationship between the two currents (Imix and Ie).

  In the switching power supply circuit 1, the compensated / added current Imix and the error current Ie are compared by the comparator 16. Therefore, adding the addition current Iad to the detection current Isens is equivalent to adding a current having the same magnitude and different polarity as the addition current Iad to the error current Ie. Actually, instead of the addition current Iad being added to the detection current Isens, a current having the same magnitude and different polarity as the addition current Iad may be added to the error current Ie.

  Further, the above-described delay time T1 can be arbitrarily set. However, in order to surely prevent the above-described adverse effects, the time that the noise caused by the switching operation is sufficiently attenuated (the magnitude of the noise is below a predetermined reference value) or slightly longer than this time It is desirable to be set to.

  Also, the magnitude α3 of the addition current Iad can be arbitrarily set, but is set sufficiently larger than the magnitude of noise due to the switching operation in order to surely prevent the above-described adverse effects. Is desirable.

[Example 2]
Next, another embodiment (Example 2) of the present invention will be described. The present embodiment is basically the same as the first embodiment except for the point where a DMAX circuit is provided and the point relating to the generation of the addition current Iad, and redundant description is omitted.

  FIG. 3 is a configuration diagram of the switching power supply circuit 1 according to the present embodiment. As shown in the figure, the switching power supply circuit 1 has a DMAX circuit 19. The DMAX circuit 19 appropriately plays a role of turning off the switching element 12 for a certain period of time for the purpose of preventing magnetic saturation in the coil L1.

  More specifically, the DMAX circuit 19 outputs a signal for turning off the switching element 12 (off switching signal) to the R terminal of the flip-flop circuit 17a. Thereby, the switching element 12 is turned off during the period when the off-switching signal is at the H level. The timing at which the DMAX circuit 19 is operated can be arbitrarily set so as to prevent magnetic saturation and the like.

  The DMAX circuit 19 also outputs the above-described OFF switching signal to the current adding circuit 14, and the current adding circuit 14 acquires this. Thereby, the current addition circuit 14 detects the timing when the switching element 12 is turned off by the off switching signal. Further, the current addition circuit 14 generates an addition current Iad according to the detection result and adds it to the detection current Isens. The off switching signal can also be regarded as a signal indicating a period during which the switching element 12 is turned off by the DMAX circuit 19.

  Here, the waveform and the like of the addition current Iad will be described with reference to the timing chart of FIG. 4A shows the waveform of the pulse signal output from the transmitter 18, and FIG. 4B shows the waveform of the output signal Sc output from the output terminal Q of the flip-flop circuit 17a. Represents. FIG. 4C shows the waveform of the off switching signal output from the DMAX circuit 19. Moreover, (d) of FIG. 4 represents the waveform of the addition current Iad.

  As shown in this figure, during the period in which the OFF switching signal is at the H level, the output signal Sc is in the L level state even when the pulse fall (Ta timing) at the transmitter 18 arrives. Reference numeral 12 denotes an off state. When the OFF switching signal becomes L level (when the timing of Tb has arrived), the output signal Sc becomes H level and the switching element 12 is switched ON.

  On the other hand, generation and addition of the addition current Iad is started at the timing when the delay time T1 has elapsed from the timing of Tb. The generation and addition of the addition current Iad are stopped at the timing when the off switching signal becomes H level. In this way, the generation or addition of the addition current Iad is started or stopped in accordance with the OFF switching signal output from the DMAX circuit 19.

  For this reason, the addition current Iad can be added at an appropriate timing even when the timing at which the switching element 12 is turned on by the OFF signal varies, and the timing at which noise due to the switching operation occurs is also varied. ing. Note that the waveforms of the off signal and the addition current described here are examples, and other waveforms may be adopted.

[Summary]
As described above, the switching power supply circuit 1 according to the embodiment of the present invention includes the switching element 12 between the input terminal IN and the output terminal OUT, and converts the power input to the input terminal IN to the switching operation of the switching element 12. Adjustment is performed through (on / off switching), and the adjusted electric power is output from the output terminal OUT.

  Further, the switching power supply circuit 1 includes a functional unit (such as the current detection circuit 11) that generates a detection current Isens (first signal) having a magnitude corresponding to the current flowing through the switching element 12, and a voltage at the output terminal OUT. A functional unit (such as the voltage detection circuit 15) that generates an error current Ie (second signal) of a large magnitude, and a functional unit (such as the comparator 16 and the control circuit 17) that controls on / off switching of the switching element 12, A functional unit (adder circuit 14) that adds a predetermined value to the detection current Isens (or error current Ie) and reduces the difference between the current values.

The comparator 16 and the control circuit 17 turn off the switching element 12 every time the value of the detection current Isens reaches the value of the error current Ie. The adder circuit 14
The timing at which the switching element 12 is switched on is detected, and the addition of the addition current Iad is started at the timing when the delay time T1 has elapsed from the detected timing.

  Therefore, by setting the time for which the noise caused by the switching operation is sufficiently attenuated as the delay time T1, it is possible to suppress the noise from adversely affecting the switching operation as much as possible.

  Note that the switching power supply circuit 1 described above can be used for general electronic devices, general-purpose power supplies, and the like. In particular, switching power supplies are used as power supply devices for devices that require miniaturization and short on-time (for example, in-vehicle devices such as car audio, AV devices such as liquid crystal televisions and DVD videos, and PC peripheral devices such as CD drivers and DVD drivers). Circuit 1 is preferred.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this content. The present invention can be implemented with various modifications without departing from the spirit of the present invention.

  The present invention can be used in the field of switching power supplies.

DESCRIPTION OF SYMBOLS 1 Switching power supply circuit 11 Current detection circuit 12 Switching element 13 Current compensation circuit 14 Current addition circuit 15 Voltage detection circuit 16 Comparator 17 Control circuit 17a Flip-flop circuit 17b Drive circuit 18 Oscillator 19 DMAX circuit IN Input terminal OUT Output terminal C1 Input capacitor C2 Output capacitor D1 Diode L1 Coil R1, R2 Voltage dividing resistor

Claims (7)

A switching device comprising a switching element between an input terminal and an output terminal, adjusting power input to the input terminal through on / off switching of the switching element, and outputting the adjusted power from the output terminal In the power circuit,
A first signal generation circuit for generating a first signal indicating a value corresponding to a current flowing through the switching element;
A second signal generation circuit for generating a second signal indicating a value corresponding to a voltage at the output terminal;
A switching control circuit for controlling on / off switching of the switching element;
An adding circuit for adding a predetermined value to the first signal or the second signal and reducing a difference between the values of the first signal and the second signal;
With
The switching control circuit includes:
Each time the value of the first signal reaches the value of the second signal, the switching element is turned off.
The adder circuit
A switching power supply circuit comprising: detecting a timing at which the switching element is turned on; and starting the addition at a timing at which a predetermined first delay time has elapsed from the detected timing. The adder circuit
2. The switching power supply circuit according to claim 1, wherein a timing at which the switching element is switched off is detected, and the addition is stopped at a timing according to a result of the detection. The adder circuit
3. The switching power supply circuit according to claim 2, wherein the addition is stopped at a timing when a predetermined second delay time has elapsed from a timing at which the switching element is switched off. A timing specifying signal indicating a timing for switching on / off of the switching element is supplied, and a compensation circuit is provided to increase a slope of the first signal in a period in which the switching element is on;
The timing specifying signal is also supplied to the adding circuit,
The adder circuit
4. The switching power supply circuit according to claim 2, wherein a timing at which the switching element is turned on / off is detected based on the timing specifying signal. A DMAX circuit for turning off the switching element for a predetermined period;
The adder circuit
4. The switching power supply circuit according to claim 2, wherein a signal indicating the predetermined period is acquired, and the addition is started or stopped according to the acquired signal. 5. One end is connected to an input terminal to which a DC voltage is applied, and the switching element that switches the DC voltage to a pulse voltage, and
A coil connected between the other end of the switching element and an output terminal, and smoothing the pulse voltage to make a DC voltage different from the DC voltage;
An output capacitor connected between the output terminal and the ground, and smoothing a DC voltage from the coil to be an output voltage;
A rectifying element that is connected between a connection point between the switching element and the coil and the ground, and causes a current to flow through the coil during an off period of the switching element;
In a switching power supply circuit comprising:
A current detection circuit that generates a first signal corresponding to the magnitude of the current flowing through the switching element;
A voltage detection circuit that generates a second signal representing an error between a feedback voltage generated by dividing the output voltage; and a predetermined reference voltage;
A switching control circuit that turns on the switching element for each period of a pulse signal generated by an oscillator and turns off the switching element each time the value of the first signal reaches the value of the second signal;
An adding circuit for adding a predetermined value to the first signal or the second signal and reducing a difference between the values of the first signal and the second signal;
With
The adder circuit
Detecting the switching timing of the switching element;
While starting the addition at a timing when a predetermined delay time has elapsed from the timing of switching on,
The addition is stopped at a timing when the switch is turned off or when a predetermined first delay time has elapsed from the timing when the switch is turned off.   An electronic apparatus comprising the switching power supply circuit according to any one of claims 1 to 6.

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