JP2007135277A - Switching power supply device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce power consumption at standby without making the switching operation of a switching power supply device unstable. <P>SOLUTION: This switching power supply device is provided with: an output voltage adjustment circuit (33) that imparts a control signal to a control circuit (10) by receiving a detection signal of an output voltage detection circuit (8) at normal operation, shortens an on-period of a MOSFET (3) when an output voltage is high, and extends the on-period of the MOSFET (3) when the output voltage is low; a current adjustment circuit (41) that controls the impedance of a current that drives the output voltage adjustment circuit (33); and a standby-state detection circuit (34) that detects the standby operation of a load (7), and generates a standby signal. Since the impedance is increased by the current adjustment circuit (41) when the standby signal is generated by the standby-state detection circuit (34), not only the power consumption of the output voltage adjustment circuit (33) is reduced but also the power consumption of the switching power supply device itself is reduced by extending an off-period of the MOSFET (3) by using the output voltage adjustment circuit (33). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a switching power supply device that improves power conversion efficiency, and in particular, reduces power consumption during standby.

  In order to improve the power conversion efficiency of a switching power supply device, it has recently become important to reduce power consumption during standby. For the purpose of reducing switching loss by reducing the switching frequency during standby, or switching by intermittent operation (burst operation), and reducing driving power, detection during standby, frequency reduction and intermittent operation methods, etc. Various methods have been proposed.

For example, Patent Document 1 below shows a switching power supply device that reduces power consumption and improves conversion efficiency during light loads such as when waiting for a load. As shown in FIG. 4, this switching power supply device includes a DC power source (1) composed of a rectifying / smoothing circuit (1b) connected to an AC power source (1a), a primary winding (2a), and a secondary winding. Transformer (2) having line (2b) and auxiliary winding (2c), MOSFET (MOS field effect transistor) (3) as a switching element, output rectifier diode (4) and output smoothing capacitor (5) a rectifying and smoothing circuit (6) comprising, a load (7) the output voltage detection circuit (8) for detecting the voltage V _O of, and a MOSFET (3) the on-off control to the control circuit (10).

The primary winding (2a) of the transformer (2) and the MOSFET (3) are connected in series to the DC power supply (1). The rectifying / smoothing circuit (6) is connected to the secondary winding (2b) of the transformer (2) and supplies DC power of voltage V _O to the load (7). The auxiliary winding (2c) is connected to the power supply terminal (V _CC ) of the control circuit (10) via the auxiliary rectifier diode (11) and the auxiliary smoothing capacitor (12). The control circuit (10) is driven by a voltage applied from the auxiliary winding (2c) to the power supply terminal (V _CC ), and is connected to the gate terminal of the MOSFET (3) via the drive circuit (14). a signal generating circuit for applying a _G (13), the output voltage detection circuit (8) of the detection signal by the on-period control circuit for controlling the pulse width of the on-off signal V _G that are output from the signal generating circuit (13) ( 18).

ON period control circuit (18), when the detection voltage of the output voltage detection circuit (8) is lower than the target value, by extending the pulse width of the on-off signal V _G that are output from the signal generating circuit (13), opposite when higher than the target value, to shorten the pulse width of the on-off signal V _G that are output from the signal generating circuit (13), the transformer rectifier smoothing circuit from the secondary winding of the (2) (2b) (6) The level of the DC output voltage V _O applied to the load (7) via the is maintained constant. In addition, the current flowing from the DC power supply (1) during startup via the startup resistor (16) connected between the positive terminal of the DC power supply (1) and the power supply terminal (V _CC ) of the control circuit (10) By charging the auxiliary smoothing capacitor (12) using the voltage, the control circuit (10) is activated by the voltage applied to the power supply terminal (V _CC ) of the control circuit (10), and the gate terminal of the MOSFET (3) is turned on / off. An off signal V _G is applied.

As shown in FIG. 5, the control circuit (10) has a signal generation circuit (13) as a signal generation means and a detection signal output from the output voltage detection circuit (8) as the load (7) becomes lighter. a frequency control circuit (17) as frequency control means for reducing the frequency of the output signal V ₄ generation circuit (13), and on-period control circuit for an on period control means (18), as the minimum oN period output means A minimum on-period output circuit (19), an on-period comparison circuit (20) as an on-period comparison means constituted by a D flip-flop, and a frequency control circuit (17) by an output signal of the on-period comparison circuit (20) A switching means (26) for switching to a driving state or a stopping state and a driving circuit (14) are provided.

The signal generation circuit (13) is driven by a voltage applied to the power supply terminal (V _CC ), and an output signal having a long pulse width when the output voltage detection circuit (8) detects the low voltage V _O of the load (7). When V ₄ is generated and the output voltage detection circuit (8) detects the high voltage V _O of the load (7), an output signal V ₄ having a short pulse width is generated. ON period control circuit (18), the output voltage detection circuit in a state in which there is a high frequency of the output signal V ₄ of the signal generator from the light load (13) when the state heavier load than the light load (7) (8) The pulse width of the output signal V ₄ of the signal generation circuit 13 is controlled by the detection signal. The minimum on-period output circuit 19 outputs the pulse signals V ₁ and V ₂ of the first minimum on-period T ₁ or the second minimum on-period T ₂ corresponding to a light load state or a load state heavier than a light load. Output. ON period comparison circuit (20) the minimum ON period output circuit (19) a pulse signal V _1, the first minimum on period of the V ₂ T ₁ or second minimum ON period T ₂ and a signal generating circuit which is output from the Compared with the ON period of the output signal V _{4 in} (13), it is determined whether the load is light or heavier than the light load. The drive circuit (14) includes an OR gate (14a) that outputs a logical sum signal of the pulse signals V ₁ and V ₂ of the minimum on-period output circuit (19) and the output signal V ₄ of the signal generation circuit (13); and a driver (14b) to be applied to the gate terminal of the MOSFET (3) an output signal of the OR gate (14a) as the on-off signal V _G. Minimum ON period output circuit (19) and the on-period comparison circuit (20), the signal generating circuit (13) load state determines heavier load conditions than either light load or light load by pulse width of the output signal V ₄ of A determination unit is configured.

The minimum on-period output circuit (19) includes a first pulse generation circuit (23), a second pulse generation circuit (24), and a minimum on-period switching circuit (25). The first pulse generation circuit (23) outputs a _first pulse signal V ₁ that defines a _first minimum on-period T ₁ . The second pulse generation circuit (24) outputs a _second pulse signal V ₂ that defines a _second minimum on-period T ₂ shorter than the first minimum on-period T ₁ . When the load (7) is in a light load state, the minimum on-period switching circuit (25) outputs the first pulse signal V ₁ by the output signal of the on-period comparison circuit (20), and the load (7) is less than the light load. outputting a second pulse signal V ₂ by the output signal of the oN period comparison circuit (20) when the heavy load state. That is, the minimum ON period output circuit (19) is longer than the signal generating circuit (13) minimum ON period T ₂ output ON period of the signal V ₄ is a second when the second shorter than the minimum ON period T ₂ of the of the outputting a first pulse signal V ₁ having a minimum oN period T ₁ of the 1, the oN period of the output signal V ₄ of the signal generating circuit (13) is first when longer than the minimum on-period T ₁ first It has a hysteresis characteristic that outputs a _second pulse signal V ₂ having a _second minimum on-period T ₂ shorter than the minimum on-period T ₁ .

First minimum ON period T ₁ of the first pulse signal V ₁ output from the first pulse generation circuit (23), even if the frequency of the on-off signal V _G at light load is lowered to the audible region The value is set so that the magnetostrictive sound of the transformer (2) cannot be heard. ON period comparison circuit (20), second second minimum on period of the pulse signal V ₂ that the ON period of the output signal V ₄ is outputted from the minimum ON period output circuit (19) of the signal generating circuit (13) when less than T _2, together with imparting an output signal indicative of the light load state to minimize the minimum oN period switching circuit oN period output circuit (19) in (25), the frequency control circuit by applying to the switching means (26) (17) switching the drive state, the first first minimum oN period of the pulse signal V ₁ to the oN period of the output signal V ₄ of the signal generating circuit (13) is outputted from the minimum oN period output circuit (19) when longer than T _1, and applied to the switching means (26) while applying an output signal indicating a heavy load condition than the light load to the minimum oN period switching circuit of the minimum oN period output circuit (19) in (25) Stop the frequency control circuit (17).

As shown in FIG. 5, the signal generating circuit (13) includes the oscillation frequency setting capacitor (21) and the charging time of the oscillation frequency setting capacitor (21), that is, the charging voltage V of the oscillation frequency setting capacitor (21). An oscillation circuit (22) as an oscillating means for outputting a pulse signal having a frequency determined by the time until _CF reaches the maximum value from the minimum value, and an oscillation circuit (22) by the output signal of the on-period control circuit (18) a pulse signal having a PWM (pulse width modulation) control to generate an output signal V ₄ PWM control circuit (27). The PWM control circuit (27) is set by the pulse signal of the oscillation circuit (22), and is reset by the output signal of the ON period control circuit (18), and the RS-FF (RS flip-flop) (27a) constructed from a NOR gate (27b) for outputting an inverted signal V ₄ of the logical sum of the pulse signal and the output signal of the RS-FF (27a) of the circuit (22). ON period comparison circuit (20) is inputted in synchronism with the falling of the output signal V ₃ of the minimum ON period output circuit (19) which is input to the control signal input terminal (D) to the clock signal input terminal (CLK) And a D flip-flop that outputs a voltage level signal of the output signal V ₄ of the signal generation circuit 13 and its inverted signal.

The minimum on time switching circuit (25), the output signal V ₅ of the inverted signal output terminal of the first pulse signal V ₁ and the ON period comparison circuit output from the first pulse generator (23) (20) first aND gate (25a), the non-inverted signal output terminal of the second pulse signal V ₂ and the oN period comparison circuit output from the second pulse generating circuit (24) (20) for outputting a logical product signal logical sum of the second aND gate for outputting a logical product signal (25b), and the output signal of the output signal of the first aND gate (25a) and a second aND gate (25b) between the output signal V ₆ of and an OR gate (25c) for outputting a signal V _3. The frequency control circuit (17) is a current mirror circuit that directly discharges the charge of the oscillation frequency setting capacitor (21) in the signal generation circuit (13) with a current signal proportional to the detection signal of the output voltage detection circuit (8). Composed. The switching means (26) composed of a MOSFET connected between the control terminal of the frequency control circuit (17) and the ground terminal is connected to the non-inverting output terminal of the on-period comparison circuit (20) in a light load state. The low voltage (L) level signal V _{6 is} turned off to switch the frequency control circuit (17) to the driving state. When the load is heavier than a light load, the non-inverted output terminal of the on period comparison circuit (20) Is turned on by a high voltage (H) level signal V ₆ output from the frequency control circuit 17 to switch the frequency control circuit 17 to a stopped state.

When the switching power supply shown in FIGS. 4 and 5 is operated, if a voltage is applied from the DC power supply (1) to the power supply terminal (V _CC ) of the control circuit (10) via the starting resistor (16), control circuit (10) is activated the signal generating circuit a high voltage from the (13) (H) level of the on-off signal V _G is output, MOSFET (3) becomes conductive. As a result, the voltage E of the DC power source (1) is applied to the primary winding (2a) of the transformer (2), and a voltage is generated in the auxiliary winding (2c). The voltage generated in the auxiliary winding (2c) is applied to the power supply terminal (V _CC ) of the control circuit (10) via the auxiliary rectifier diode (11) and the auxiliary smoothing capacitor (12). The control circuit (10) is driven by the voltage generated on the line (2c).

A high voltage (H) level of the on-off signal V _G is applied through the drive circuit (14) from the signal generating circuit of the control circuit (10) in (13) to the gate terminal of the MOSFET (3), MOSFET (3 ) Is turned on, current flows from the DC power source (1) through the primary winding (2a) of the transformer (2) and the MOSFET (3), and energy is stored in the transformer (2). At this time, since a reverse voltage is applied to the output rectifying diode (4) constituting the rectifying / smoothing circuit (6) and a non-conducting state is established, no current flows through the output rectifying diode (4), and the transformer (2 ) Is not transmitted to the secondary winding (2b). At the same time, a reverse voltage is applied to the auxiliary rectifier diode (11) connected to the auxiliary winding (2c) of the transformer (2), and the non-conducting state is applied. The charging voltage of the auxiliary smoothing capacitor (12) is applied to the power supply terminal (V _CC ) of the control circuit (10).

Next, the on / off signal V _G applied from the control circuit (10) to the gate terminal of the MOSFET (3) changes from the high voltage (H) level to the low voltage (L) level, and the MOSFET (3) turns from on to off. Then, a forward voltage is applied from the secondary winding (2b) of the transformer (2) to the output rectifier diode (4) of the rectifying / smoothing circuit (6) and becomes conductive, so that it accumulates in the transformer (2). The energy thus supplied is supplied from the secondary winding (2b) to the load (7) via the rectifying and smoothing circuit (6), and the transformer (2) is reset. At the same time, since a forward voltage is applied to the auxiliary rectifier diode (11) connected to the auxiliary winding (2c) of the transformer (2) to be in a conductive state, during the off period of the MOSFET (3) A voltage is applied from the auxiliary winding (2c) to the power supply terminal (V _CC ) of the control circuit (10) through the auxiliary rectifier diode (11) and the auxiliary smoothing capacitor (12). When a predetermined time elapses, a high voltage (H) level on / off signal is sent from the signal generation circuit (13) in the control circuit (10) to the gate terminal of the MOSFET (3) via the drive circuit (14). V _G is applied, and the MOSFET (3) is turned on again.

When the load (7) has a high impedance and a light load, the output voltage detection circuit (8) detection voltage is higher than the target value, so the on-period control circuit (18) in the control circuit (10) generates a signal. It is controlled so that the pulse width of the on-off signal V _G which is output through the circuit (13) from the drive circuit (14) is narrowed, the oN period of the MOSFET (3) is shortened. Conversely, when the load (7) impedance is low and the load is heavy, the detection voltage of the output voltage detection circuit (8) is lower than the target value, so the on-period control circuit (18) in the control circuit (10) the pulse width of the signal generating circuit (13) on-off signal is output via the drive circuit (14) from the V _G is controlled to become wide, the oN period of the MOSFET (3) is prolonged.

When the load (7) is heavier load condition than the light load (time t ₁ ~t ₇ shown in FIG. 6), the pulse width of the signal generating circuit (13) of the output signal V ₄ shown in FIG. 6 (B), longer than the pulse width of the output signal V ₃ of the minimum oN period output circuit (19) shown in FIG. 6 (C), the on-off signal V _G applied from the drive circuit (14) to the MOSFET (3) is, as shown in FIG. 6 (H), the signal generating circuit shown in long Figure 6 pulse width than the output signal V ₃ of the minimum oN period output circuit (19) shown in FIG. 6 (C) (B) (13) The waveform is substantially the same as that of the output signal V ₄ . On the other hand, the high voltage (H) level signal V ₆ shown in FIG. 6 (F) is output from the non-inverting output terminal of the on period comparison circuit (20), and the low voltage (L) level shown in FIG. 6 (G). Since the signal V ₅ is output from the inverting output terminal, the second pulse signal V ₂ of the second pulse generation circuit (24) shown in FIG. 6 (D) becomes the minimum ON period output circuit (19) minimum ON. output period switching circuit from (25) as an output signal V ₃ shown in FIG. 6 (C).

Further, since the output signal V ₆ of the non-inverting output terminal of the on period comparison circuit (20) is at a high voltage (H) level, the switching means (26) is turned on and the frequency control circuit (17) is not driven. The charging time of the oscillation frequency setting capacitor (21), that is, the time until the charging voltage _VCF reaches the maximum value is constant. Therefore, the frequency of the voltage V _CF of the oscillation frequency setting capacitor (21) of the signal generation circuit (13) becomes constant as shown in FIG. 6 (A), and the signal generation circuit is determined by the output signal of the ON period control circuit (18). The pulse width of the signal V ₄ output from the PWM control circuit (27) in (13) is controlled as shown in FIG. 6 (B).

When the load at time t ₇ (7) is a light load state, the output signal V of the signal generating circuit (13) FIG. 6 (B) the pulse width of the output signal V ₄ shown in the minimum ON period output circuit (19) since shorter than the pulse width shown in ₃ of FIG. 6 (C), the on-off signal V _G shown in FIG. 6 (H) applied from the drive circuit (14) to the MOSFET (3), the signal generating circuit ( The waveform is substantially the same as that of the output signal V ₃ shown in FIG. 6C of the minimum on-period output circuit 19 having a longer pulse width than the output signal V ₄ shown in FIG. On the other hand, at the time t ₈ after the _second minimum on-period T ₂ has elapsed from the time t ₇ , the on-period comparison circuit (20) outputs the second pulse signal V ₂ of the second pulse generation circuit (24). Since the output signal V ₄ of the signal generation circuit 13 shorter than the pulse width of the output signal V ₄ is detected, the output signals V ₅ and V ₆ of the on-period comparison circuit 20 are respectively shown in FIGS. 6G and 6F. As shown in FIG. 4, the low voltage (L) level is converted to the high voltage (H) level, and the high voltage (H) level is converted to the low voltage (L) level.

For this reason, after time t ₈ , the first pulse signal V ₁ of the first pulse generation circuit (23) shown in FIG. 6 (E) is minimum on as the output signal V ₃ shown in FIG. 6 (C). simultaneously output from the period switching circuit (25), the output signal V ₆ of the oN period comparison circuit (20) is a low voltage (L) level, the switching means (26) is turned off from on, the frequency control circuit ( 17) is driven. As a result, since the electric charge of the oscillation frequency setting capacitor (21) is directly discharged by the current signal proportional to the detection signal of the output voltage detection circuit (8), the lighter the load (7), the lower the oscillation frequency setting capacitor. (21) Charging time is extended. Thus, after time t _7, the load (7) enough to become lighter, as shown in FIG. 6 (A), since the voltage V _CF oscillation frequency setting capacitor (21) is reduced, FIG. 6 (B ), The frequency of the output signal V ₄ of the PWM control circuit (27) is controlled.

Thereafter, when the load at time t ₁₂ (7) is made somewhat heavier a light load state, the signal generating circuit (13) FIG. 6 (B) are shown the output signal V ₄ of the pulse width is the minimum ON period output circuit (19) 6 for longer than the pulse width of the output signal V ₃ of (C), the pulse of FIG. 6 (H) to indicate on-off signal V _G applied to the MOSFET (3) from the drive circuit (14) The width is longer than the output signal V _{3 of the} minimum on-period output circuit (19) shown in FIG. 6 (C) and is substantially the same as the output signal V ₄ shown in FIG. 6 (B) of the signal generation circuit (13). It becomes a waveform. On the other hand, the time t ₁₄ from the time t ₁₂ minimum ON period T ₁ first has elapsed, the ON period comparison circuit (20), the first of the first pulse signal V ₁ of the pulse of the pulse generating circuit (23) Since the output signal V ₄ of the signal generation circuit 13 longer than the width is detected, the output signals V ₅ and V ₆ of the on period comparison circuit 20 are shown in FIGS. 6G and 6F, respectively. As described above, the high voltage (H) level changes to the low voltage (L) level, and the low voltage (L) level changes to the high voltage (H) level.

Therefore, after time t ₁₄ , the second pulse signal V ₂ shown in FIG. 6D of the second pulse generation circuit 24 is transferred from the minimum ON period switching circuit 25 to FIG. 6C. Is output as the output signal V ₃ shown. The output signal V ₆ of the ON period comparison circuit (20), because after time t ₁₄ becomes a high voltage (H) level, the switching means (26) is turned on from off, the frequency control circuit (17) Operation stops. Since the frequency of the voltage V _CF shown in FIG. 6 (A) of the capacitor oscillation frequency set to the time t ₁₂ after (21) is constant, PWM control circuit by an output signal of the on-period control circuit (18) The pulse width of the output signal V ₄ from (27) is controlled as shown in FIG. 6 (B).

Load (7) the period t ₁ ~t ₇ and time t ₁₂ after serving as the somewhat heavier state, the frequency control circuit (17) is stopped, shown in Figure of the PWM control circuit (27) 6 (B) The pulse width of the output signal V ₄ is controlled by the output signal of the ON period control circuit (18). The load during the period t ₇ ~t ₁₂ (7) is a light load, frequency control circuit (17), the signal generating circuit by the detection signal of the output voltage detection circuit (8) of the output signal V ₄ (13) While lowering the frequency, the detection signal of the output voltage detection circuit (8) is also input to the on-period control circuit (18) at the same time, the pulse width of the output signal V ₄ is also on-period control signal generating circuit (13) Control is performed as shown in FIG. 6B by the output signal of the circuit (18). However, when the load is light, the first pulse signal V ₁ having the first minimum on-period T ₁ is output from the first pulse generation circuit (23), and the output signal V of the minimum on-period output circuit (19). to be input together with the output signal V ₄ of the signal generating circuit to the OR gate (14a) (13) as _3, MOSFET on and off signal V _G shown in FIG. 6 (H) applied to the gate terminal of the (3) The on period is equal to the first minimum on period T ₁ . For this reason, the MOSFET (3) is forcibly maintained in an on state for a longer period than necessary, so that the feedback amount of the detection signal of the output voltage detection circuit (8) increases, and the signal generation circuit (13) The pulse width of the output signal V ₄ shown in FIG. 6B is further shorter than the second minimum on-period T ₂ immediately before the control method is switched from on-period control to frequency control.

Thus, on the ON period of the light load to the on-off signal V _G is the ON period of the on-off signal V _G so as not to be shortened to a first minimum on period T ₁ of the following isochronous load stand as constant because lowering the frequency of the off signal V _G, and reducing the switching losses of the MOSFET (3), it can improve the conversion efficiency. Further, when the load (7) is somewhat heavier, a second pulse signal having a minimum ON period output circuit (19) the minimum ON period T ₂ output signal V ₃ is a second shorter than the minimum ON period T ₁ first of It is switched to V _2, the on-period is in a state of high frequency of the light load on-off signal V _G than is controlled, to heavy load from the normal load without upsizing the transformer (2), etc. High conversion efficiency can be realized. The minimum ON period output circuit (19), because it has a hysteresis characteristic, the control circuit (10) facilitates the frequency control and the on period control of the on-off signal V _G to be applied to the gate terminal of the MOSFET (3) from Can be switched to. Furthermore, since the current peaks flowing through the transformer (2) even at light loads the frequency of the on-off signal V _G decreases to audible range can be suppressed, thereby preventing noise etc. magnetostrictive sound transformer (2).

  By the way, in the switching power supply device shown in Patent Document 1, the controller IC constituting the control circuit (10) has been changed from the bipolar process to the C-MOS process, and the current consumption has been greatly reduced. If a C-MOS type IC is used instead of a bipolar IC that consumes a current of about 20 mA, the current becomes about 1 mA. Further, when the controller IC is driven at 15 V, the power consumption of about 0.3 W is consumed in the bipolar IC, whereas it is reduced to about 0.015 W in the recent C-MOS type IC.

  In most types of isolated switching power supply devices, an error signal from an output voltage detection circuit obtained by comparing an output voltage with a reference voltage is transmitted to the primary side via a photocoupler and converted into a control voltage by a resistor. To the control circuit. Since this method operates stably even when the load fluctuates, for example, if the current flowing through the light receiving portion of the photocoupler at the maximum load is set to 0.1 mA, a current of about 1 mA flows through the control circuit during standby. At this time, if the control circuit is driven at 15 V, 0.015 W of power is consumed during standby. This is comparable to the power consumption of the controller IC used for the control circuit. Similarly, the maximum current flows in the light emitting portion of the photocoupler during standby. Considering the current transfer rate of the photocoupler and the conversion efficiency of the switching power supply, the power consumption further increases.

  For example, even a 21-inch color television that consumes about 80 to 100 W during viewing requires low power consumption during standby, which is reduced to 0.1 to 0.2 W. Since the power consumed by the load during standby is about 0.01 to 0.05 W, the power consumed by the light receiving unit and the resistor of the photocoupler is comparable to the power consumed by the load.

Japanese Patent No. 3525436

  By the way, in order to realize standby power consumption of 0.1 to 0.2 W, it is difficult to use one switching power supply device even if the switching frequency is lowered or the burst operation is performed at the standby time of the switching power supply device. Therefore, it was necessary to provide another switching power supply device. Further, the power consumed by the photocoupler and the resistor reaches a level that cannot be ignored with respect to the power consumption required during standby. In order to reduce this power consumption, if the current flowing through the photocoupler is reduced, the control system from the detection of the output voltage to the operation of the control circuit is operated with a high gain, so that the current flowing at the maximum load is reduced. This causes a problem that the switching operation becomes unstable.

  Therefore, an object of the present invention is to provide a switching power supply device that can reduce power consumption during standby without making the switching operation unstable.

  The switching power supply device of the present invention includes a DC power supply (1), a primary winding (2a) and a switching element (3) of a transformer (2) connected in series to the DC power supply (1), and a switching element (3 ) A control circuit (10) for applying a drive signal to the control terminal of), a rectifying / smoothing circuit (6) connected to the secondary winding (2b) of the transformer (2) and supplying DC power to the load (7); The output voltage detection circuit (8) that detects the voltage of the DC power supplied to the load (7) and generates a detection signal, and the control circuit that receives the detection signal of the output voltage detection circuit (8) during normal operation An output that gives a control signal to (10) and shortens the ON period of the switching element (3) when the DC power voltage is high, and extends the ON period of the switching element (3) when the DC power voltage is low And a voltage adjustment circuit (33). This switching power supply includes a current adjustment circuit (41) that controls the impedance of the current that drives the output voltage adjustment circuit (33), and a standby state detection circuit that detects a standby operation of the load (7) and generates a standby signal (34). When the standby state detection circuit (34) generates a standby signal, the current adjustment circuit (41) increases the impedance, so not only the power consumed by the output voltage adjustment circuit (33) is reduced, but also the output By extending the OFF period of the switching element (3) by the voltage adjustment circuit (33), the power consumption of the switching power supply device itself can be reduced. Further, since the impedance of the current adjustment circuit (41) is increased only during standby, even if the load (7) increases, the switching element (3) can be reliably switched with low power.

  In the switching power supply according to the present invention, power consumption during standby can be reduced, and the running cost of the switching power supply and the amount of heat generated can be suppressed.

  Embodiments of a switching power supply device according to the present invention will be described below with reference to FIGS. In FIG. 1 and FIG. 3, the same parts as those shown in FIG.

  As shown in FIG. 1, a DC power source (1) includes a rectifying / smoothing circuit (1b) connected to an AC power source (1a) via a line filter (1c). The rectifying / smoothing circuit (1b) (1c) Full-wave rectifier circuit (1d) connected to the latter stage, one end is connected to the positive output terminal of full-wave rectifier circuit (1d) via inrush current limiting resistor (28), and the other end is all And an input smoothing capacitor (29) connected to the negative terminal of the wave rectifier circuit (1d). The positive output terminal of the full-wave rectifier circuit (1d) is full-wave rectified through the inrush current limiting resistor (28), the primary winding (2a) of the transformer (2), the MOSFET (3), and the current detection resistor (9). Connected to the negative terminal of the circuit (1d). When the power is turned on, the AC voltage from the AC power source (1a) is full-wave rectified by the full-wave rectifier circuit (1d) via the line filter (1c), smoothed by the input smoothing capacitor (29), and converted to a DC voltage. Converted. The inrush current limiting resistor (28) limits the inrush current flowing through the input smoothing capacitor (29) when the power is turned on.

  One end of the secondary winding (2b) of the transformer (2) is connected to the positive input terminal of the load (7) via the output rectifier diode (4) constituting the rectifying and smoothing circuit (6). The other end of the line (2b) is connected to the negative terminal of the load (7). An output smoothing capacitor (5) constituting a rectifying / smoothing circuit (6) is connected between the cathode terminal of the output rectifier diode (4) and the other end of the secondary winding (2b). An output voltage detection circuit (8) is connected in parallel with the load (7). The output voltage detection circuit (8) has a voltage dividing resistor (54, 55) connected in parallel with the output smoothing capacitor (5) and a base terminal connected to the voltage dividing point of the voltage dividing resistor (54, 55). Transistor (error amplification circuit) (52), and a Zener diode (threshold setting circuit) connected between the emitter terminal (one main terminal) of the transistor (52) and the other end of the secondary winding (2b) (53) and a resistor (51) connected between the output rectifier diode (4) and the Zener diode (53). The collector terminal (the other main terminal) of the transistor (52) is connected to the output rectifier diode (4) via the light emitting part (light emitting diode) (31) and the resistor (56) constituting the photocoupler (30). .

One end of the auxiliary winding (2c) of the transformer (2) is connected to the input terminal of the regulator (50) via the current limiting resistor (15) and the auxiliary rectifier diode (11). The regulator (50) supplies DC power of a constant voltage V _REG to each device in the control circuit (10). In order to activate the control circuit (10), the input terminal of the regulator (50) is connected to the full-wave rectifier circuit (1d) via the activation resistor (16). An auxiliary smoothing capacitor (12) is connected between the auxiliary rectifier diode (11) and the regulator (50) and between the other end of the auxiliary winding (2c). The collector terminal of the phototransistor constituting the light receiving section (32) of the photocoupler (30) is connected to the auxiliary rectifier diode (11), the emitter terminal is connected to the non-inverting input terminal of the comparator (37), and the base terminal is Light from the light emitting part (31) of the photocoupler (30) is received. A pair of adjustment resistors (35, 36) are connected in parallel between the emitter terminal of the phototransistor of the light receiving unit (32) and the other end of the auxiliary winding (2c).

The light receiving section (32) and adjustment resistor (35, 36) of the photocoupler (30) function as a receiving means for receiving the detection signal of the output voltage detection circuit (8), and errors from the output voltage detection circuit (8). A current based on the signal flows to the light receiving section (32) of the photocoupler (30), and a control voltage V _FB based on the error signal is generated in the adjustment resistors (35, 36). This control voltage V _FB is input to the non-inverting input terminal of the comparator (37). That is, the photocoupler (30) and the adjustment resistors (35, 36) function as transmission means. The inverting input terminal of the comparator (37) is connected to the voltage dividing point of the voltage dividing resistor (42, 43), and one end of one voltage dividing resistor (42) is connected to the regulator (50) and is constant at 8V, for example. The other voltage- _dividing resistor (43) is connected to the negative terminal of the full-wave rectifier circuit (1d). Therefore, the divided voltage V _{DT obtained} by dividing the output voltage V _REG of the regulator (50) by the voltage dividing resistors (42, 43) is input to the inverting input terminal of the comparator (37). The output terminal of the comparator (37) is connected to the reset terminal of the RS-FF (38), and the output terminal of the RS-FF (38) is connected to the gate terminal (control terminal) of the MOSFET (3). The output voltage detection circuit (8), the photocoupler (30), and the comparator (37) constitute an output voltage adjustment circuit (33).

  The current adjustment circuit (41) is connected in series with a pair of adjustment resistors (35, 36) connected in parallel between the light receiver (32) and the comparator (37), and one adjustment resistor (35). Switch 44, first and second oscillators 39 and 40, and first and second oscillators 39 and 40 are selectively connected to the set terminal of RS-FF 38. And a selection switch (45) having an output terminal. One end of the adjusting resistor (35, 36) is connected to the light receiving part (32) of the photocoupler (30), and the other end of one adjusting resistor (35) is connected to the auxiliary winding (2c) via the changeover switch (44). The other end of the other adjustment resistor (36) is directly connected to the other end of the auxiliary winding (2c). The other end of the auxiliary winding (2c) is connected to a connection point between the MOSFET (3) and the current detection resistor (9), and becomes a reference potential of the primary circuit (ground potential in FIG. 1). The input terminals of the first and second oscillators (39, 40) are connected to the output terminal of the RS-FF (38), and the output terminals of the first and second oscillators (39, 40) are the selection switch (45). Are connected to the first and second input terminals, respectively. Therefore, the selection switch (45) selects either the input signal from the first oscillator (39) or the input signal from the second oscillator (40) according to the output signal from the standby state detection circuit (34). Output to the set terminal of the RS-FF (38), set the RS-FF (38), and turn on the MOSFET (3). At the same time, the changeover switch (44) is also opened / closed by the output signal from the standby state detection circuit (34) to switch the range of the adjustment resistors (35, 36). When the first and second oscillators (39, 40) receive the output signal from the RS-FF (38), the first and second oscillators (39, 40) each generate a pulse after a predetermined period of time, but the oscillation frequency of the second oscillator (40) Is lower than the oscillation frequency of the first oscillator (39), the interval between pulses generated from the second oscillator (40) is longer than the interval between pulses generated from the first oscillator (39). Therefore, when the pulse output from the second oscillator (40) is selected by the selection switch (45), the period during which the RS-FF (38) is set becomes longer and the off period of the MOSFET (3) becomes longer. . The standby state detection circuit (34), the changeover switch (44), and the selection switch (45) constitute a mode changeover circuit (46).

When the switching power supply shown in FIG. 1 is turned on, the input smoothing capacitor (29) is switched from the AC power supply (1a) through the line filter (1c), the full-wave rectifier circuit (1d), and the inrush current limiting resistor (28). In addition to being charged, the auxiliary smoothing capacitor (12) is charged via the starting resistor (16). At the same time, DC power is supplied to the regulator (50) in the control circuit (10) via the starting resistor (16). When the charging voltage of the auxiliary smoothing capacitor (12) reaches the starting voltage of the control circuit (10) configured by the integrated circuit, the regulator (50) detects the starting voltage and the operation of the control circuit (10) is started. The The regulator (50) in the control circuit (10) detects the voltage V _CC applied to the power supply terminal of the control circuit (10), starts or stops each internal device, and constantly supplies a stable voltage. Applied to each device in the control circuit (10).

When the control circuit (10) starts operating in the state shown in FIG. 1, the RS-FF (38) generates a drive signal by the pulse output from the first oscillator (39), and the MOSFET (3) is turned on. Can be switched to. When the MOSFET (3) is turned on, the primary winding (2a) of the transformer (2) from the input smoothing capacitor (29) of the DC power source (1), the MOSFET (3), the current detection resistor (9) and the DC power source (1 ) Current I _D flows through the full-wave rectifier circuit (1d). At this time, as shown in FIG. 2, the current _ID flowing in the MOSFET (3) has a predetermined slope determined by the voltage of the input smoothing capacitor (29) and the inductance of the primary winding (2a) of the transformer (2). Corresponding to this current _ID , the divided voltage V _DT is a predetermined voltage from a voltage (eg, 1.5 V) obtained by dividing the output voltage V _REG of the regulator (50) by the voltage dividing resistors (42, 43). Decrease with the slope of. At this time, the voltage of the level corresponding to the current I _D flowing through the MOSFET (3) is generated in the current detecting resistor (9), trans by the current I _D flowing through the primary winding of the transformer (2) (2a) ( Although energy is stored in 2), no current flows through the secondary winding (2b) because the output rectifier diode (4) is biased in the reverse direction.

  The output voltage detection circuit (8) divides the output voltage applied to the load (7) by the voltage dividing resistor (54, 55), and the divided voltage is applied to the base terminal of the transistor (52). Then, an error signal corresponding to the difference between the base-emitter voltage of the transistor (52) and the threshold value of the Zener diode (53) flows to the light emitting section (31) of the photocoupler (30). Therefore, when the output voltage applied to the base terminal of the transistor (52) is high, a large amount of current flows between the emitter and collector of the transistor (52), increasing the amount of light emitted from the light emitting unit (31). When the output voltage applied to the base terminal of the transistor (52) is low, a small amount of current flows between the emitter and collector of the transistor (52), and the light emission amount of the light emitting section (31) decreases.

On the other hand, depending on the voltage charged in the auxiliary smoothing capacitor (12), the path of the auxiliary smoothing capacitor (12), the light receiving part (32) of the photocoupler (30), the adjusting resistor (35, 36), and the auxiliary smoothing capacitor (12) The current flows through the adjustment resistor (35, 36), whereby the control voltage V _FB is applied to the non-inverting input terminal of the comparator (37). The comparator (37) compares the divided voltage V _{DT of the} voltage dividing resistor (42, 43) applied to the inverting input terminal with the control voltage V _FB, and the divided voltage V _DT becomes the control voltage V _FB . When it reaches or falls below, it produces a high voltage (H) level output.

As shown in FIG. 2, the minimum voltage of the _divided voltage V _DT is determined by the control voltage V _FB applied to the adjustment resistors (35, 36). When the divided voltage V _DT reaches or falls below the control voltage V _FB applied to the non-inverting input terminal of the comparator (37), the output of the comparator (37) is inverted to the high voltage (H) level. Therefore, the RS-FF (38) is reset by the high voltage (H) level output of the comparator (37). For this reason, the output (Q) of the RS-FF (38) becomes a low voltage (L) level, the MOSFET (3) is switched off, and simultaneously, a reset signal is sent to the first oscillator (39). At this time, the energy stored in the transformer (2) is supplied from the secondary winding (2b) to the load (7) via the output rectifier diode (4) and the output smoothing capacitor (5). Corresponding to the rapid decrease in current _ID, the divided voltage _VDT also increases rapidly. The first oscillator (39) that has received the reset signal outputs a start pulse after a predetermined time has elapsed, and the RS-FF (38) is set by this start pulse. Therefore, the output signal of the RS-FF (38) becomes a high voltage (H) level, and the MOSFET (3) is turned on. By repeating the above operation, the output voltage to the load (7) is controlled so as to be stabilized at a predetermined voltage level.

When the output voltage from the secondary winding (2b) rises, the current flowing through the light emitting unit (31) increases, so the current flowing through the light receiving unit (32) also increases. For this reason, the control voltage V _FB generated in the adjustment resistor (35, 36) rises close to 1.5V as shown on the right side of FIG. Therefore, even if the MOSFET (3) is switched on, the divided voltage V _DT reaches the control voltage V _FB in a short time, so that the MOSFET (3) is switched from on to off in a short time, and the MOSFET ( The on period of 3) is shortened and the output voltage is lowered. Conversely, when the output voltage from the secondary winding (2b) decreases, the current flowing through the light emitting section (31) decreases, and the current flowing through the light receiving section (32) also decreases. For this reason, the control voltage V _FB generated in the adjustment resistor (35, 36) decreases away from 1.5V. For this reason, when the MOSFET (3) is switched on, it takes time for the divided voltage V _DT to reach the control voltage V _FB. Therefore, the MOSFET (3) is switched from on to off in a long time, The on period of the MOSFET (3) is extended, and the output voltage to the load (7) increases.

During standby, the current flowing through the primary winding (2a) and secondary winding (2b) of the load (7) and transformer (2) decreases, so that the standby state detection circuit (34) By connecting a current detection sensor such as a current detection resistor (not shown) to the primary winding (2a) or secondary winding (2b) and measuring the amount of current that decreases, the current that decreases during standby is reduced. Can be detected. For example, the standby time may be determined by detecting the level of the current _IO flowing to the load (7). Further, the standby time may be determined by detecting the level of the current _ID flowing through the current detection resistor (9). Except during standby, the current flowing through the load (7) increases, and the current flowing through the primary winding (2a) and the secondary winding (2b) of the transformer (2) increases correspondingly. Therefore, the standby state detection circuit (34) detects the reduced current flowing in any of the load (7), the primary winding (2a) and the secondary winding (2b) by the current detection sensor during standby, A signal may be generated.

When the load (7) enters the standby operation, the standby state detection circuit (34) generates a standby signal and switches the changeover switch (44) from on to off. As a result, the current of the light receiving unit (32) flows through the adjustment resistor (35, 36) during normal operation, whereas the current of the light receiving unit (32) flows through only the adjustment resistor (36) during standby, so that the output is output during standby. The impedance of the voltage adjustment circuit (33) increases and the control voltage V _FB rises. At the same time, the standby state detection circuit (34) switches the selection switch (45) from the first input terminal shown in the figure to the second input terminal. By switching the selection switch (45), the first oscillator (39) is disconnected from the RS-FF (38), and the second oscillator (40) is connected to the set terminal of the RS-FF (38). The interval between pulses generated from the second oscillator (40) is longer than the interval between pulses generated from the first oscillator (39), and therefore the off period of the MOSFET (3) becomes longer. The switching frequency is lowered, and the power conversion efficiency during standby can be improved. Further, the current flowing through the light receiving part (32) of the photocoupler (30) flows only through the other adjustment resistor (36), and no current flows through the separated adjustment resistor (35). Normally, when a current flows from the light receiving part (32) of the photocoupler (30) through the adjusting resistor (35, 36), the level of the voltage V _FB generated in the adjusting resistor (35, 36) _{depends on} the level of the MOSFET (3). The ON period width is determined and the output voltage to the load (7) is controlled to a constant level.However, during standby, current flows only through the other adjustment resistor (36), so the photocoupler (30) The current flowing through the light receiving unit (32) can be reduced. In this way, not only the power consumed by the output voltage adjustment circuit (33) is reduced, but also by extending the off period of the switching element (3) by the output voltage adjustment circuit (33), the switching power supply device itself Power consumption can be reduced.

  When the load (7) is in normal operation, the standby state detection circuit (34) does not generate a standby signal, so that the changeover switch (44) is switched from off to on and the selection switch (45) is the second input terminal. Is switched to the first input terminal to return to the state shown in the figure.

In the embodiment shown in FIG. 1, since the ON period of the MOSFET (3) is short during standby, the control voltage V _FB rises to approximately 1.5V. At this time, a current of 1 mA is required for the light receiving portion (32) of the photocoupler (30) in the normal mode in which the adjustment resistors (35, 36) are used simultaneously. If only the other adjustment resistor (36) is used, the current flowing through the light receiving section (32) of the photocoupler (30) decreases, so that the standby current may be 300 μA, and the light receiving section (32 of the photocoupler (30) may be used. ) Current can be reduced to 1/3 or less.

  If the current that flows to the load (7) increases from the standby state, the current that flows to the light receiver (32) of the photocoupler (30) decreases, so the comparator (37) may become unstable. Because both adjustment resistors (35, 36) are used by the mode switching circuit (46), the impedance of the output voltage adjustment circuit (33) is reduced and the current flowing through the light receiving part (32) of the photocoupler (30) is increased. Therefore, the operation of the comparator (37) and the switching operation of the MOSFET (3) can be stabilized. Changing the resistance value of the adjustment resistor (35, 36) that converts the current of the light receiving part (32) of the photocoupler (30) into a voltage changes the gain of the control system that stabilizes the output voltage of the switching power supply. However, since the load current is very small and there is almost no load fluctuation during standby, there is no problem in operation.

  When the control circuit (10) is operated at 15V, the power consumed by the adjusting resistors (35, 36) connected in series with the light receiving section (32) of the photocoupler (30) is 0.015 W in normal times. However, it is reduced to 0.0045 W which is 1/3 or less in the standby mode of the present invention. The same applies to the light emitting section (31) of the photocoupler (30). When the current transfer rate (CTR) of the photocoupler (30) is 50 and the output voltage is 15 V, the output voltage is normally 0.03 W. The standby time of the present invention is 0.009W. Since power consumption in the light emitting section (31) of the photocoupler (30) is consumed on the secondary side, it is necessary to consider the power conversion efficiency of the power consumption transformer (2). Assuming that the power conversion efficiency during standby, that is, during light load, is 50%, the power consumption (input power) caused by the current flowing through the light emitting section (31) of the photocoupler (30) is 0.06 W during normal operation. However, it is 0.018 W during the standby operation. The total power consumption (input power) due to the current flowing through the light receiving part (32) and light emitting part (31) of the photocoupler (30) is 0.075W during normal operation, while waiting. The power consumption during operation is 0.0225W. During standby operation according to the present invention, power consumption can be reduced to 0.05 W. Since the power consumption required when the switching power supply is on standby is 0.1 to 0.2 W, this effect is significant. However, since the current transfer rate of the photocoupler (30) tends to decrease as the current of the light emitting unit (31) decreases, the actually obtained effect may be slightly less.

The embodiment of the present invention shown in FIG. 1 can be modified. For example, the changeover switch (44) can be changed to a semiconductor switch such as a transistor. In this case, as shown in FIG. 3, the changeover switch (44) is replaced with a transistor (47), a standby signal from the standby state detection circuit (34) is applied to the base terminal of the transistor (47), and the transistor (47 The current flowing between the emitter and the collector of the transistor (47) is adjusted according to the magnitude of the base current of the transistor (47), so that the current flowing through the light receiving section (32), that is, the control voltage V _FB can be continuously adjusted. it can. Further, a discharge resistor (48) is connected between the first oscillator (39) and the ground, and an oscillation frequency adjusting capacitor (49) is connected in parallel to the discharge resistor (48), so that a standby state detection circuit ( 34) Apply the standby signal from the oscillation frequency adjustment capacitor (49) to the oscillation frequency adjustment capacitor (49), and adjust the charging voltage level of the oscillation frequency adjustment capacitor (49), thereby making the oscillation frequency of the first oscillator (39) continuous. The MOSFET (3) can be switched off at various oscillation frequencies. Further, the photocoupler (30) may be omitted, and the output signal of the output voltage detection circuit (8) may be applied to the non-inverting input terminal of the comparator (37) without changing the level or without changing the level. . Other semiconductor switching elements such as bipolar transistors and IGBTs (insulated gate bipolar transistors) can be used instead of the MOSFET (3).

  In the above embodiment, the present invention is applied to a flyback type separately excited switching power supply, but the present invention can also be applied to a forward type, resonant type, or self-excited type switching power supply.

Electrical circuit diagram showing an embodiment of a switching power supply device according to the present invention The graph which shows the characteristic of the switching current of the electric circuit diagram shown in FIG. 1, a divided voltage, and a control voltage Electric circuit diagram showing another embodiment of the present invention Electric circuit diagram showing a conventional switching power supply Electrical circuit diagram showing details of internal configuration of control circuit shown in FIG. Timing chart of operation signal of each part of conventional switching power supply

Explanation of symbols

  (1) ・ ・ DC power supply, (1a) ・ ・ AC power supply, (1b) ・ ・ Rectification smoothing circuit, (1c) ・ ・ Line filter, (1d) ・ ・ Full wave rectification circuit, (2) ・ Transformer, (2a) ・ ・ Primary winding, (2b) ・ ・ Secondary winding, (2c) ・ ・ Auxiliary winding, (3) ・ ・ MOSFET (switching element), (4) ・ ・ Output rectifier diode, ( 5) ... Output smoothing capacitor, (6) ... Rectifier smoothing circuit, (7) ... Load, (8) ... Output voltage detection circuit, (9) ... Current detection resistor, (10) ... Control circuit (11) ・ ・ Auxiliary rectifier diode, (12) ・ ・ Auxiliary smoothing capacitor, (13) ・ ・ Signal generation circuit, (14) ・ ・ Drive circuit, (14a) ・ ・ OR gate, (14b) ・ ・ Driver (15) ... Current limiting resistor, (16) ... Starting resistor, (17) ... Frequency control circuit, (18) ... On period control circuit, (19) ... Minimum on period output circuit, (20 .. ON period comparison circuit (D flip-flop ), (21) ... Oscillation frequency setting capacitor, (22) ... Oscillation circuit, (23) ... First pulse generation circuit, (24) ... Second pulse generation circuit, (25) ... (25a) .. first AND gate, (25b) .. second AND gate, (25c) .. OR gate, (26) .. switching means, (27) .. PWM Control circuit, (27a) ・ ・ RS-FF (RS flip-flop), (27b) ・ ・ NOR gate, (28) ・ ・ Inrush current limiting resistor, (29) ・ ・ Input smoothing capacitor, (30) ・ ・ Photo Coupler, (31) ... Light emitting part, (32) ... Light receiving part, (33) ... Output voltage adjustment circuit, (34) ... Standby detection circuit, (35,36) ... Adjustment resistor, (37・ ・ Comparator, (38) ・ ・ RS-FF, (39) ・ ・ First oscillator, (40) ・ ・ Second oscillator, (41) ・ ・ Current adjustment circuit, (42,43) ・・ Partial resistance, (44) ・ ・ Switch, (45) ・ ・Selection switch, (46) ... mode switching circuit, (47) ... transistor (semiconductor switch), (48) ... discharge resistor, (49) ... oscillation frequency adjusting capacitor, (50) ... regulator, (51) ... Resistance, (52) ... Transistor, (53) ... Zener diode, (54, 55) ... Voltage divider resistor, (56) ... Resistance,

Claims (5)

A DC power supply, a primary winding and a switching element of a transformer connected in series to the DC power supply, a control circuit for applying a drive signal to a control terminal of the switching element, and a secondary winding of the transformer A rectifying / smoothing circuit that supplies DC power to the load, an output voltage detection circuit that detects a voltage of the DC power supplied to the load and generates a detection signal, and a detection signal of the output voltage detection circuit during normal operation. Receive and apply a control signal to the control circuit, shorten the on-period of the switching element when the voltage of the DC power is high, and extend the on-period of the switching element when the voltage of the DC power is low In a switching power supply device comprising an output voltage adjustment circuit,
A current adjusting circuit for controlling an impedance of a current for driving the output voltage adjusting circuit;
A standby state detection circuit that detects a standby operation of the load and generates a standby signal;
The switching power supply device according to claim 1, wherein when the standby state detection circuit generates a standby signal, the current adjustment circuit increases impedance. The current adjustment circuit includes a plurality of adjustment resistors for determining a current value of a current flowing through the output voltage adjustment circuit, and a changeover switch for selecting an operation of the adjustment resistor,
2. The switching power supply device according to claim 1, wherein when the standby state detection circuit generates a standby signal, the adjustment resistor is selected by the changeover switch to adjust the impedance of the current adjustment circuit. The current adjustment circuit includes a plurality of oscillators having different oscillation frequencies that determine the ON timing of the switching element,
3. The switching power supply device according to claim 1, wherein when the standby state detection circuit generates a standby signal, the switching element is switched on by an output of an oscillator having a lower oscillation frequency among the plurality of oscillators. The current adjustment circuit includes a regulation resistor that regulates a current value of a current that flows through the output voltage regulation circuit, and a switch that controls a current that flows through the regulation resistor by regulating a current that flows through the semiconductor switch. With a switch,
2. The switching power supply device according to claim 1, wherein the change-over switch continuously changes the impedance of the current adjustment circuit when the standby state detection circuit generates a standby signal. The current adjustment circuit includes an oscillator that determines the ON timing of the switching element,
3. The switching power supply device according to claim 1, wherein an oscillation frequency of the oscillator is continuously changed by a standby signal of the standby state detection circuit, and the switching element is turned on at different timings.

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