JP2010068638A - Ac adaptor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve power saving by reducing power consumption when in a no-load power supply state in an AC adaptor having a switching power supply configuration. <P>SOLUTION: When in a no-load power supply state, the detection result of a voltage detecting part 22y is corrected by a detection/correction part 27. On the basis of the correction, a switching control part 13 controls a switching part 11 such that the DC power supply for power feeding of an output processing part 18 has a lower voltage than a voltage before the correction. Output of a fourth winding 10d formed by additional winding of a winding wire to a third winding of a transformer 10y is rectified and smoothed by an auxiliary power supply part 37 so as to form the DC auxiliary power supply that has a voltage equal to or over a minimum operating voltage of the switching control part 13. Instead of the control power supply of a control power supply part 26, the auxiliary power supply of the auxiliary power supply part 37 is supplied to a power-supply terminal Vdd of the switching control part 13 so as to reduce power consumption by preventing the switching control part 13 from being restarted due to injection of the DC power supply on the input side of an input processing part 7 in a no-load power supply state. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an AC adapter having a switching power supply configuration, and more particularly to power reduction at no load.

  2. Description of the Related Art Conventionally, various electronic devices such as printers and projectors supply DC power from an AC adapter to a power supply target device such as a main device. In addition, in these electronic devices, a portable type such as an ink jet printer for photo printing (hereinafter referred to as a photo printer) is detachably mounted with a battery unit (also referred to as a battery pack) having a secondary battery configuration. When a battery unit is mounted, DC power is supplied from the AC adapter and the battery unit to the main body device that is a power supply target with priority given to power supply from the AC adapter (see, for example, Patent Document 1). .

  In order to improve the conversion efficiency, this type of AC adapter is generally formed in a switching power supply for a flyback converter or a forward converter.

JP 2003-72057 A (paragraphs [0024]-[0026], FIG. 3 etc.)

  If the DC power source that supplies power to the power supply target device from the AC adapter is set to the power supply voltage of the power supply target device, the power supply target device does not have to be provided with a DC-DC converter or the like that steps up and down the DC power supplied from the AC adapter. Therefore, it is possible to reduce the size and cost of the power supply target device.

  When the input side (AC power supply side) and the output side are electrically insulated and the DC power supply of the power supply voltage is supplied to the power supply target device, the AC adapter is, for example, a switching power supply for a flyback converter as shown in FIG. It is conceivable that they are formed.

  The AC adapter shown in FIG. 3 is an AC power source of 230 V, for example, 230 V AC power plug 1 inserted into a power outlet 1 via a fuse 3 and an AC filter 6 formed by a capacitor 4 and a coil 5. The AC power is input to the rectifier circuit 8 and rectified and smoothed by the rectifier circuit 8 and the smoothing capacitor 9 to form a high voltage input-side DC power source. Further, the DC power supply on the input side is fed to the first winding 10a on the primary side of the transformer 10x. The N-channel MOS type FET 12 of the switching unit 11 connected in series with the first winding 10a is high-frequency switched by the switching control unit 13 to interrupt the input side DC power supply, and the secondary side of the transformer 10x A pulse output of a voltage corresponding to the winding ratio of the windings 10a and 10b is induced in the second winding 10b. The FET 12 has a drain connected to the first winding 10a, a source grounded via the overcurrent detection resistor 14, and a gate connected to the control terminal G of the switching control unit 13 via the resistor 15. . A series circuit of a resistor 16 for gate discharge and a diode 17 is connected to the resistor 15 in parallel. The transformer 10x is provided with a third winding 10c for control power supply on the primary side, the circles of the windings 10a to 10c of the transformer 10x indicate the start of winding, and the outputs of the second and third windings 10b and 10c. Are of the same polarity.

  The pulse output of the second winding 10b is rectified and smoothed by the diode 19 and the smoothing capacitor 20 of the output processing unit 18, and the power supply voltage (for example, 42V) of the power supply target device (not shown) is supplied as a DC output for power supply. An output-side DC power supply is formed, and the output-side DC power supply is supplied to the power supply target device from the output terminals 21p and 21n. Further, the voltage of the output side DC power source is detected by a voltage detection unit 22x subsequent to the output processing unit 18, and the detection result is detected by a light emitting diode (light emitting element) 23a and a phototransistor (light receiving element) 23b of the photocoupler 23. The optical signal is fed back to the switching control unit 13. Then, the switching control unit 13 feedback-controls the high-frequency switching of the FET 12 so that the voltage of the detection result becomes a setting voltage for feedback control, and controls the output-side DC power supply to the power supply voltage of the power supply target device. Note that the collector of the phototransistor 23b is connected to the feedback terminal FB of the switching control unit 13, and the emitter is grounded.

  By the way, the switching control unit 13 can be formed by various control ICs for switching power supplies. For example, when the switching control unit 13 is formed by a control IC of the FA5540 series of Fuji Electric Device Technology Co., Ltd. having a built-in activation element, the switching control unit 13 Is activated by the high-voltage DC power supply on the input side injected to the high-voltage terminal Vh, and thereafter, the power supply terminal Vdd is supplied from the control power supply unit 26 formed by the diode 24 and the smoothing capacitor 25 to around 10-20V. The high frequency switching of the FET 12 is feedback controlled by operating with the control power source. The control power supply unit 26 rectifies and smoothes the output of the third winding 10c of the transformer 10y by the diode 24 and the smoothing capacitor 25 to form the control power supply. Further, the switching control unit 13 monitors the overcurrent of the first winding 10a from the terminal voltage of the resistor 14 applied to the overcurrent detection terminal OC, and turns off the FET 12 and detects the primary side of the transformer 10x when the overcurrent is detected. It also has a function to prevent overcurrent.

  In the AC adapter of FIG. 3, when the power supply target device connected to the output terminals 21p and 21n is turned off, or when the power supply target device is disconnected from the output terminals 21p and 21n, the AC adapter is This is a so-called no-load power supply state. When the output-side DC power supply is maintained at the power supply voltage of the power supply target device even in this no-load power supply state, power is wasted by the high-speed switching operation of the FET 12 during that time.

  The switching control unit 13 formed by the FA5540 series control IC or the like increases the switching frequency of the FET 12 by the flyback of the quasi-resonant operation when the AC adapter is in a no-load power supply state, and the detection result of the voltage detection unit 22x. The voltage of the photodiode 12a increases and the amount of light emitted from the photodiode 23a increases. Therefore, when the amount of light emitted increases, the collector voltage of the phototransistor 23b (the voltage at the feedback terminal FB) decreases to the threshold voltage. Stop switching control. Furthermore, when the switching control is stopped and the voltage of the detection result decreases and the voltage of the feedback terminal FB becomes higher than the threshold voltage, the switching control of the FET 12 is resumed. By repeating this operation, the FET 12 is intermittently switched in the no-load power supply state to lower the switching frequency (oscillation frequency), thereby reducing the power consumption of the AC adapter.

  However, when the switching control of the FET 12 is stopped, the pulse output of the windings 10b and 10c of the transformer 10x decreases, and not only the voltage of the DC power supply on the output side that supplies power to the power supply target device but also the power supply terminal Vdd of the switching control unit 13. The voltage of the control power supply that supplies power also decreases. When the voltage of the control power supply at the power supply terminal Vdd is lower than the minimum operating voltage at which the switching control unit 13 can operate, the switching control unit 13 stops operating and returns to the initial state. It is restarted by power supply injection and starts switching control of the FET 12. At this time, if the AC adapter continues to be in a no-load power supply state, the voltage of the detection result rises, the feedback terminal FB becomes lower than the threshold voltage, and the switching control unit 13 controls the switching of the FET 12. As a result, the control power supply voltage at the power supply terminal Vdd drops below the minimum operating voltage at which the switching control unit 13 can operate, and the switching control unit 13 stops operating and returns to the initial state. Thereafter, the same operation is repeated.

  Therefore, the AC adapter of FIG. 3 uses a high voltage input side DC power source formed by a linear regulator operation with a large power loss of the input processing unit 7 in the no-load power supply state to the switching control unit 13 as a starting power source. And the switching control unit 13 is repeatedly activated. Therefore, the power consumption in the no-load power supply state increases on the contrary. This power consumption increases as the voltage of the DC power supply on the input side increases. In particular, when the control IC of the switching control unit 13 has a built-in low voltage malfunction prevention (UVLO) function and the minimum operating voltage at which the switching control unit 13 can operate is relatively high, the switching control unit 13 is repeatedly activated. The power consumption associated with is a problem.

  Even when the AC adapter is formed in a switching regulator configuration of a forward converter, the same power consumption as when the AC adapter is in a no-load power supply state becomes a problem.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to reduce power consumption in a no-load power supply state in an AC adapter having a switching power supply configuration to save power. In the present invention, the “no-load power supply state” includes a state in which the power supply device state connected to the AC adapter is turned off and a state in which the power supply target device is disconnected from the AC adapter. .

  In order to achieve the above object, an AC adapter according to the present invention feeds power to a first winding of a transformer by intermittently connecting a DC output of the input processing unit that rectifies and smoothes an input AC power source. A switching unit, an output processing unit configured to rectify and smooth the output of the second winding of the transformer to form a DC output for feeding, and feed the DC output from the output terminal to the power supply target device; and A voltage detection unit that detects a voltage; a control power supply unit that rectifies and smoothes the output of the third winding of the transformer to form a control power supply; and a power supply terminal to which the control power supply is fed. In the AC adapter including a switching control unit that feedback-controls the switching of the switching unit so that the detection voltage of the voltage detection unit becomes a set voltage while the voltage of is maintained at the minimum operating voltage or higher, A detection correction unit that corrects the detection result of the voltage detection unit to reduce the voltage of the DC output for power supply when the load enters a power supply state, and a fourth winding formed by adding to the third winding And rectifying and smoothing the output of the fourth winding, forming an auxiliary power supply that is equal to or higher than the minimum operating voltage when the no-load power supply state is established, and supplying power to the power supply terminal instead of the control power supply A power supply unit.

  Therefore, according to the AC adapter of the present invention, in the no-load power supply state, the detection correction unit corrects the detection result of the voltage detection unit, and based on this correction, the DC power supply for power supply has a lower voltage than the voltage before correction. A switching control part controls a switching part so that it may become. At this time, a higher voltage output than the output of the third winding is generated in the fourth winding formed by adding to the third winding of the transformer. Further, the output of the fourth winding is rectified and smoothed by the auxiliary power supply unit to form a DC auxiliary power supply that is equal to or higher than the minimum operating voltage of the switching control unit.

  Then, instead of the DC control power supply of the control power supply unit based on the output of the third winding reduced by the correction, a DC auxiliary power supply that is equal to or higher than the minimum operating voltage of the auxiliary power supply unit is fed to the power supply terminal of the switching control unit. The switching control unit is not activated by the DC power supply on the input side of the input processing unit, and continues to operate with the auxiliary power supplied to the power supply terminal to interrupt the switching unit. In this case, the switching control unit is not restarted by injection of the DC power supply on the input side of the input processing unit in the no-load power supply state, and the power consumption in the no-load power supply state of the AC adapter is reduced and saved. Electricity can be achieved.

  The AC adapter of the present invention further includes a power supply control terminal whose level changes depending on whether the power supply state is loaded or unloaded, and the detection correction unit detects the unloaded power supply state from the level of the power supply control terminal. Therefore, it is possible to easily detect the no-load power supply state from the level of the power supply control terminal, reduce the power consumption in the no-load power supply state, and save power.

  The switching control unit of the AC adapter of the present invention is formed by a control IC having a low voltage malfunction prevention (UVLO) function that stops the control operation when the voltage of the power supply terminal becomes lower than the minimum operating voltage. That is preferable. In this case, in the no-load power supply state, instead of the control power supply of the control power supply unit based on the output of the third winding, an auxiliary power supply that is equal to or higher than the minimum operating voltage of the auxiliary power supply unit is supplied to the power supply terminal of the switching control unit. For this reason, the switching control unit does not operate the low-voltage malfunction prevention function and is not restarted by injection of the DC power supply on the input side of the input processing unit. For this reason, power consumption can be reduced by reducing the power consumption of this type of AC adapter having a function of preventing low-voltage malfunction when no load is supplied.

  In the AC adapter of the present invention, it is also preferable that the voltage detection unit and the switching control unit are coupled by a photocoupler. In this case, the power consumption in the no-load power supply state of this type of AC adapter in which the primary side (AC power supply side) and secondary side (DC output side) of the transformer are electrically insulated by a photocoupler is reduced. Less power consumption can be achieved.

  Furthermore, the auxiliary power supply unit of the AC adapter according to the present invention includes a regulator unit that rectifies and smoothes the output of the fourth winding, a collector connected to the regulator unit, and an emitter via a diode for preventing backflow. A power supply control transistor connected to a power supply terminal and having a base connected to the regulator unit via a bias resistor, and the control power supply until the base voltage of the power supply control transistor is in a no-load power supply state It is practically preferable to provide a Zener diode that maintains a lower voltage.

  In this case, the voltage of the control power supply of the control power supply unit based on the output of the third winding of the transformer is defined by the Zener diode until the no-load power supply state is reached, that is, when the AC adapter is loaded with a load. The voltage becomes higher than the base voltage of the power supply control transistor of the auxiliary power supply unit, the transistor and the backflow prevention diode are turned off, and the control power supply of the control power supply unit is supplied to the power supply terminal of the switching control unit. Next, in a no-load power supply state, the base voltage of the power supply control transistor of the auxiliary power supply unit becomes higher than the voltage of the control power supply of the control power supply unit, and this transistor and the backflow prevention diode are turned on, and the auxiliary power supply The auxiliary power supply of the unit is fed to the power supply terminal of the switching control unit instead of the control power supply.

  Therefore, the auxiliary power supply unit is formed in a simple and specific configuration including a regulator unit that rectifies and smoothes the output of the fourth winding, a power supply control transistor, a backflow prevention diode, and a Zener diode. be able to.

  An embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2. FIG. 1 is a connection diagram of the AC adapter of this embodiment, and FIG. 2 is a waveform diagram for explaining the operation. In these drawings, the same reference numerals as those in FIG. 3 denote the same or corresponding parts.

  The AC adapter according to the present embodiment shown in FIG. 1 includes a control IC in which the switching control unit 13 incorporates, for example, the FA5540 series undervoltage malfunction prevention (UVLO) function. The control power supplied to Vdd is about 12V, and the minimum operating voltage of the power supply terminal Vdd is about 9V.

  The AC adapter of this embodiment shown in FIG. 1 is different from the AC adapter of FIG. 3 in the following first to fourth points.

  The first is that a transformer 10y is provided instead of the transformer 10x of FIG. The transformer 10y is further provided with a fourth winding 10d formed by adding to the third winding 10c, and this fourth winding 10d provides an auxiliary power source of about 12V higher than the minimum operating voltage in a no-load power supply state. The number of turns is set so that power is supplied to the power supply terminal Vdd.

  Second, the output processing unit 18 is provided with a voltage detection unit 22y and a detection correction unit 27 instead of the voltage detection unit 22x in FIG. In the voltage detector 22y, a resistor 28, a forward photodiode 23a, a collector and emitter of an NPN transistor 29 for current adjustment, and a reverse Zener diode 30 for correcting temperature characteristics are connected in series between output terminals 21p and 21n. A bias voltage obtained by dividing the output voltage of the output processing unit 18 by resistors 31 and 32 is applied to the base of the transistor 29. Then, the voltage of the DC power supply on the output side of the output processing unit 18 (that is, the DC output for power supply between the output terminals 21p and 21n) is detected, and the amount of current flowing through the photodiode 23a (and further according to the detected voltage) The light emission amount) is controlled. The detection correction unit 27 connects the drain and source of the N-channel CMOS type FET 33 to the cathode of the photodiode 23a and the output terminal 21n, and in the reverse direction for setting the gate voltage via the resistor 34 between the output terminals 21p and 21n. A Zener diode 35 is provided, and the FET 33 has a gate to which the voltage of the cathode of the Zener diode 35 is applied.

  Thirdly, a power supply control terminal 36 whose level changes depending on whether the power supply is loaded or not is provided, and this power supply control terminal 36 is connected to the gate of the FET 33. The control power supply terminal 36 forms a connector terminal portion that is detachably connected to the power supply target device such as the main body of the photo printer together with the output terminals 21p and 21n, and is shown by a broken line in the drawing when there is no load. The equivalent circuit switch in the power supply target apparatus is turned off, and the power supply control terminal 36 changes in level from the low level (hereinafter referred to as L) in the ground state to the high level (hereinafter referred to as H) in the open state (non-ground state). .

  Fourth, the output of the fourth winding 10d is rectified and smoothed to form an auxiliary power supply that is equal to or higher than the minimum operating voltage when a no-load power supply state is established, and the power supply of the switching control unit 13 is used instead of the control power supply. The auxiliary power supply unit 37 that supplies power to the terminal Vdd is provided. The auxiliary power supply unit 37 is connected to a regulator unit 40 formed by a rectifying diode 38 and a smoothing capacitor 39, and a collector connected to a connection point 40 a between the cathode of the diode 38, which is the output terminal of the regulator unit 40, and the capacitor 39. The NPN power supply control transistor 41, the backflow prevention diode 42 provided between the emitter of the transistor 41 and the power supply terminal Vdd, and the connection point 40a and the base of the transistor 41 are provided. A bias resistor 43 and a Zener diode 44 provided between the base of the transistor 41 and the ground are provided. Based on the setting of the Zener voltage, the Zener diode 44 holds the base voltage of the transistor 41 at a lower voltage than the control power supply on the emitter side in a loaded power supply state, and maintains the base voltage of the transistor 41 in a no-load power supply state. Set higher than the control power supply on the emitter side.

  The operation of the AC adapter of the present embodiment configured as described above will be described. First, when a power supply target device is connected to the output terminals 21p and 21n and the power supply is turned on, the power supply control is performed. Since the terminal 36 is held at L and the FET 33 is turned off, the detection correction unit 27 detects that the power supply state is loaded. At this time, the detection correction unit 27 does not act on the voltage detection unit 22y.

  The voltage detection unit 22y detects the voltage of the DC power supply for load power supply by changing the collector-emitter voltage of the transistor 29 opposite to the output voltage of the output processing unit 18 (DC output voltage for load power supply). When the load is in a power supply state, the energization current of the photodiode 23a changes in proportion to the voltage of the detection result based on the change in the collector-emitter voltage of the transistor 29, the light emission amount of the photodiode 23a, and further the photo The amount of light received by the transistor 23 b changes in proportion to the output voltage of the output processing unit 18. At this time, the feedback terminal FB of the switching control unit 13 changes in level (voltage) opposite to the output voltage of the output processing unit 18.

  Then, the switching control unit 13 activated by the DC power supply on the input side of the input processing unit 7 outputs the output of the output processing unit 18 based on the error between the level of the feedback terminal FB and the level of the feedback control setting voltage (42V). The high frequency switching of the FET 12 of the switching unit 11 is feedback-controlled so that the voltage becomes the set voltage, and the input side DC power source fed from the input processing unit 7 to the first winding 10a of the transformer 10y is intermittently connected. The pulse output of the second winding 10b based on the interruption is rectified and smoothed by the output processing unit 18 to form a DC power source on the output side of the set voltage, and this DC power source is supplied from the output terminals 21p and 21n to the power supply target device. Power is supplied.

  Further, due to the intermittent DC power supply on the input side, pulse outputs corresponding to the number of turns are also generated in the third and fourth windings 10c and 10d of the transformer 10y. Then, the pulse output of the third winding 10c is rectified and smoothed by the control power supply unit 26, and a control power supply having a specified voltage of about 12 V is formed in a loaded power supply state. This control power supply is fed to the power supply terminal Vdd of the switching control unit 13, and the switching control unit 13 operates with the control power supply.

  On the other hand, the pulse output of the fourth winding 10d is rectified and smoothed by the regulator section 40 of the auxiliary power supply section 37, thereby forming an auxiliary power supply having a higher voltage than the control power supply. When the load is in a power supply state, the control power supply is about 12V, while the auxiliary power supply is about 120V.

  Further, the Zener diode 44 to which the auxiliary power source is applied to the cathode via the bias resistor 43 is set to 10 V whose Zener voltage is slightly lower than the control power source of the specified voltage. For this reason, the base voltage of the transistor 41 in a loaded power supply state is lower than the voltage of the control power supply. At this time, the backflow prevention diode 42 provided between the emitter of the transistor 41 and the power supply terminal Vdd is reverse-biased and turned off, and the auxiliary power supply of the auxiliary power supply unit 37 is not supplied to the switching control unit 13.

  Therefore, when the load is in the power supply state, the control power supply of about 12V of the control power supply unit 26 based on the output of the third winding 10c of the transformer 10y is supplied to the switching control unit 13 and switched by the control power supply of the control power supply unit 26. The controller 13 operates to control the high frequency switching of the FET 12, so that the DC power of the set voltage (42 V) is supplied to the power supply target device. At this time, the voltage of the control power source is higher than the minimum operating voltage (about 9 V) of the switching control unit 13, and the switching control unit 13 is not restarted by the high-voltage input side DC power source of the input processing unit 7.

  Next, since the power supply control terminal 36 becomes H in the no-load power supply state, the detection correction unit 27 detects that it is in the no-load power supply state. At this time, the FET 33 is turned on by the Zener voltage (about 5 V) of the Zener diode 35, and the FET 33 forms a bypass path in parallel with the current path of the transistor 29 and the Zener diode 3 on the cathode side of the photodiode 23 a.

  Then, the cathode potential of the photodiode 23a decreases due to the formation of the bypass path, the energization current of the photodiode 23a increases, and the detection result of the voltage detection unit 22y is corrected, specifically, the detection of the voltage detection unit 22y. The resulting voltage is corrected to be higher than the actual output voltage of the output processing unit 18. This correction increases the light emission amount of the photodiode 23a and increases the light reception amount of the phototransistor 23b. Further, the switching control unit 13 activated by the DC power supply on the input side of the input processing unit 7 feedback-controls the high frequency switching of the FET 12 so that the level of the feedback terminal FB based on the corrected detection voltage becomes the set voltage level. Then, the DC power supply on the input side fed to the first winding 10a is interrupted.

  At this time, the pulse output of the second to fourth windings 10b to 10d is decreased by an amount corresponding to the correction, and the output output formed by rectifying and smoothing the pulse output of the second winding 10b by the output processing unit 18. The voltage of the DC power supply on the side decreases to about 4.2 V, which is 1/10 of the set voltage (42 V), for example. In addition, since the switching frequency of the FET 12 decreases with a decrease in the voltage of the DC power supply on the output side, waste of power due to the switching operation of the FET 12 and the like is prevented.

  In addition, the voltage of the control power supply of the control power supply unit 26 formed by rectifying and smoothing the pulse output of the third winding 10c is also reduced to about 2.3V, which is 1/10. Similarly, the voltage of the fourth winding 10c The voltage of the auxiliary power supply of the regulator unit 40 of the auxiliary power supply unit 37 formed by rectifying and smoothing the pulse output also decreases to about 12V, which is 1/10.

  Then, the auxiliary power supply of the regulator unit 40 is applied to the Zener diode 44 of the base of the transistor 41 through the resistor 43, and the base voltage of the transistor 41 is maintained at 10V by the Zener voltage of the Zener diode 44 even in a no-load power supply state. The base voltage of the transistor 41 is higher than the control voltage on the emitter side. Therefore, the transistor 41 and the diode 42 are turned on, and instead of the control power supply, the auxiliary power supply of about 12 V of the regulator unit 40 is supplied to the power supply terminal Vdd of the switching control unit 13 via the transistor 41 and the diode 42.

  Even if the voltage drop of the transistor 41 and the diode 42 is taken into consideration, the switching control unit 13 is supplied with an auxiliary power supply having a voltage higher than the minimum operating voltage (about 9 V) of the switching control unit 13 to the power supply terminal Vdd. The operation is not stopped when the power supply state is.

  Therefore, in the no-load power supply state, the voltage of the output-side DC power source that supplies power to the power supply target device from the output terminals 21p and 21n is based on the voltage boost correction of the detection result of the voltage detection unit 22y by the detection correction unit 27. The switching frequency of the FET 12 is lowered by reducing it to 1/10, and the auxiliary power supply of the auxiliary power supply unit 37 based on the output of the fourth winding 10d of the transformer 10y is supplied to the power supply terminal Vdd of the switching control unit 13, and the power supply terminal By maintaining Vdd above the minimum operating voltage at which the low voltage malfunction prevention (UVLO) function operates, and avoiding the situation where the switching control unit 13 is restarted by the high-voltage input side DC power supply of the input processing unit 7 As a result, power consumption can be saved by reducing wasteful power consumption.

  Note that the voltages across the terminals of the capacitors 39, 25, and 20 are summarized when the power supply control terminal 36 is L (in a loaded power supply state) and when the power supply control terminal 36 is H (in a no-load power supply state). Is shown in Table 1 below.

  Further, according to an experiment, as shown in FIG. 2A, when the control terminal 36 is in a no-load power supply state where the L is L, the power supply terminal Vdd of the switching control unit 13 is as indicated by a solid line in FIG. The AC adapter of this embodiment maintained at a constant voltage higher than the minimum operating voltage Vα and the power supply terminal Vdd from the minimum operating voltage Vα as shown by the broken line in FIG. When the AC adapter that periodically repeats the rise to the starting voltage (upper limit voltage) Vβ and the opposite drop is compared with the power consumption in the no-load power supply state, the latter AC adapter is 0.3 W On the other hand, it was confirmed that the AC adapter of this embodiment is reduced to 0.2 W. Therefore, by using the AC adapter of this embodiment as an AC adapter as an external power source of a device such as a photo printer, the power consumption of the device such as a photo printer during standby (when the power is off) can be reduced. ) External power supply standard value (0.3 W).

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit thereof. For example, in the above-described embodiment, feedback of the detection voltage is possible. The primary side (AC power supply side) and the secondary side (output side) of the transformer 10y are electrically insulated from each other using a photocoupler 23, but the primary side of the transformer 10y and 2 The structure may be such that the secondary side is electrically insulated, and further, when electrical insulation between the primary side and the secondary side of the transformer 10y is unnecessary, the photocoupler 23 or the like is not used. Alternatively, the detection voltage may be fed back by an electrical signal.

  In the above-described embodiment, the no-load power supply state is detected from the level change of the power supply control terminal 36. However, the level change of terminals and contacts in place of the power supply control terminal 36 and the connection / separation of the power supply target device. The no-load power supply state may be detected from the switch change or the like associated with. Further, the number of turns of each of the windings 10a to 10d of the transformer 10y may be set in accordance with the input side and output side DC power supply, control power supply, auxiliary power supply voltage, and the like.

  Next, the switch control unit 13 can be formed by various control ICs for switching power supplies. In this case, the control IC may not have a built-in low voltage malfunction prevention (UVLO) function. Further, the switch control unit 13 is not limited to one formed by a control IC for switching power supply.

  Moreover, in the said embodiment, although applied to the AC adapter formed in the switching power supply of the flyback converter, this invention is applicable similarly to the AC adapter etc. which were formed in the switching power supply of the forward converter. .

  The present invention can be applied to an AC adapter that charges a main device or the like of various electronic devices.

The connection diagram of one Embodiment of this invention. The wave form diagram of operation | movement description of FIG. The connection diagram of an example of the AC adapter of a switching power supply structure.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 7 ... Input processing part, 10y ... Transformer, 10a ... 1st winding, 10b ... 2nd winding, 10c ... 3rd winding, 10d ... 4th winding, 11 ... Switching part, 13 ... Switching control part, 18 Output processing unit, 21p, 21n ... Output terminal, 22y ... Voltage detection unit, 23 ... Photocoupler, 26 ... Control power supply unit, 27 ... Detection correction unit, 36 ... Power supply control terminal, 37 ... Auxiliary power supply unit, 40 ... Regulator , 41 ... transistor for power supply control, 42 ... diode for backflow prevention, 43 ... resistor for bias, 44 ... zener diode, Vdd ... power supply terminal

Claims (5)

An input processing unit for rectifying and smoothing the input AC power supply;
A switching unit for intermittently supplying a direct current output of the input processing unit to supply power to the first winding of the transformer;
An output processing unit for rectifying and smoothing the output of the second winding of the transformer to form a DC output for power feeding, and feeding the DC output from an output terminal to a power feeding target device;
A voltage detector for detecting the voltage of the output terminal;
A control power supply unit that forms a control power supply by rectifying and smoothing the output of the third winding of the transformer;
The control power supply has a power supply terminal to which power is supplied, and while the voltage of the power supply terminal is maintained at a minimum operating voltage or more, the switching section is fed back so that the detection voltage of the voltage detection section becomes a set voltage. In an AC adapter including a switching control unit for controlling,
A detection correction unit that corrects the detection result of the voltage detection unit to reduce the voltage of the DC output for power supply when it enters a no-load power supply state;
A fourth winding formed by winding around the third winding;
Auxiliary power supply unit that rectifies and smoothes the output of the fourth winding and forms an auxiliary power supply that is equal to or higher than the minimum operating voltage when the load is in a no-load power supply state and supplies power to the power supply terminal instead of the control power supply AC adapter with   The AC adapter according to claim 1, further comprising a power supply control terminal that changes in level depending on whether the power supply state is loaded or not, and wherein the detection correction unit detects the no-load power supply state from the level of the power supply control terminal.   The switching control unit is activated by a DC output of the input processing unit, and is formed by a control IC having a low voltage malfunction prevention function that stops the control operation when the voltage of the power supply terminal becomes lower than the minimum operating voltage. The AC adapter according to claim 1 or 2.   The AC adapter according to claim 1, wherein the voltage detection unit and the switching control unit are coupled by a photocoupler. The auxiliary power unit is
A regulator unit for rectifying and smoothing the output of the fourth winding;
A power supply control transistor having a collector connected to the regulator unit, an emitter connected to the power supply terminal via a backflow prevention diode, and a base connected to the regulator unit via a bias resistor;
5. The AC adapter according to claim 1, further comprising: a Zener diode that holds a base voltage of the power supply control transistor at a lower voltage than the control power supply until a no-load power supply state is achieved.

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