JP2006129580A - Ac adapter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To lessen the current consumption in no-load state by a switch g cutting off the power line of a circuit part when a current monitoring circuit monitors a charge current and judges it to be in no-load state. <P>SOLUTION: When the current monitoring circuit 61 provided in the secondary circuit of an AC adaptor 10C monitors a charge current and judges it to be in no-load state, an analog switch SW3 cuts off the power line of a circuit part 60 which controls a voltage control circuit 42A. Hereby, this AC adaptor can lessen the current consumption in no-load state. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an AC adapter.

  This type of AC adapter is used to charge a secondary battery built in or attached to a main body such as a mobile phone. The secondary battery may be a lithium ion battery.

FIG. 1 shows a state where the AC adapter 10 is connected to a main body 20 such as a mobile phone. The AC adapter 10 is connected to the main body 20 via a cable having a resistance value. The AC adapter 10 has an anode (cathode) 11 and a cathode (anode) 12 and generates an adapter voltage V _ADP between its terminals.

On the other hand, the main body 20 includes a backflow prevention diode D, a charge control element Q such as a transistor, a secondary battery 21, and a charge control circuit 22. The charging control circuit 22 controls charging of the secondary battery 21 by controlling the charging control element Q. Although not shown, the charging control circuit 22 has a regulator therein. The secondary battery 21 generates a battery voltage (charging voltage) V _BATT .

  As shown in FIG. 2, the VI characteristic of the AC adapter has a constant current / constant voltage characteristic.

When charging control is performed on the secondary battery 21 of the main body 20, as is clear from FIG. 1, between the AC adapter 10 and the secondary battery 21, a cable loss, a loss due to contact resistance, and a backflow prevention diode are used. Since there is Vf of D and the like, the accuracy of the charging voltage V _BATT is not obtained. Therefore, as described above, the charging control circuit 22 has a regulator.

Further, the adapter voltage V _ADP of the AC adapter 10 is set to a higher voltage so that a voltage that can be charged can be supplied even if the factor causing the voltage loss varies to the maximum.

  This type of AC adapter has a primary side circuit that turns on and off a DC voltage applied to the primary winding of the transformer by a switching element, and a secondary output voltage that rectifies and smoothes the current induced in the secondary winding of the transformer. The secondary side circuit which outputs.

  In such an AC adapter, the primary circuit and the secondary circuit need to be electrically insulated and separated in order to prevent accidents such as electric shock. In general, a photocoupler or an insulating transformer is used as means for electrically insulating and separating. In the AC adapter, it is necessary to perform constant current control and constant voltage control. For this reason, it is necessary to return the change in the current flowing in the secondary side circuit as a constant current control signal and the change in the secondary side output voltage as a constant voltage control signal to the primary side circuit. In this case, the constant current control signal and the constant voltage control signal are returned (feedback) from the secondary side circuit to the primary side circuit via the photocoupler.

  Hereinafter, a conventional AC adapter will be described with reference to FIG. The illustrated switching AC adapter includes a rectifying / smoothing circuit 31, a primary winding Np of a transformer T, a switching control circuit 32, and a switching (SW) element 33 as a primary side circuit.

  The input AC voltage supplied from the AC power supply is rectified / smoothed by the rectifying / smoothing circuit 31 and converted to an input DC voltage. This input DC voltage is applied to the primary winding Np of the transformer T and turned on and off by the switching element 33. On / off of the switching element 33 is controlled by an on / off control signal supplied from the switching control circuit 32.

The illustrated AC adapter circuit includes a secondary winding Ns of the transformer T and a rectifying / smoothing circuit 41 as a secondary side circuit. The AC voltage induced in the secondary winding Ns of the transformer T is rectified / smoothed by the rectifying / smoothing circuit 41 and outputs the adapter voltage V _ADP .

The secondary circuit is provided with a constant voltage control circuit 42, a constant current control circuit 43, and a reference voltage generation circuit 44. The constant voltage control circuit 42 detects a change in the adapter voltage V _ADP and outputs a constant voltage control signal. This constant voltage control signal is fed back to the switching control circuit 32 provided in the primary side circuit as a feedback signal via the OR gate G and the photocoupler PC. The constant current control circuit 43 detects a current flowing through the secondary side circuit and outputs a constant current control signal. This constant current control signal is also fed back to the switching control circuit 32 provided in the primary circuit as a feedback signal via the OR gate G and the photocoupler PC. The reference voltage generation circuit 44 is for supplying a reference voltage to the constant voltage control circuit 42 and the constant current control circuit 43.

One end of resistors R 1 and R 2 is connected to the anode 12, and the other end of the resistor R 1 and the other end of the resistor R 2 are connected to a constant current control circuit 43. Further, resistors R3 and R4 for _dividing the adapter voltage V _ADP are connected in series between the cathode 11 and the other end of the resistor R2. A divided voltage of the adapter voltage V _ADP is supplied to the constant voltage control circuit 42 from a connection point between the resistors R3 and R4. The reference voltage generation circuit 44 is connected to the cathode 11, and resistors R5 and R6 for dividing the reference voltage are connected in series between the reference voltage generation circuit 44 and the other end of the resistor R2. Yes. A divided voltage of the reference voltage is supplied to the constant current control circuit 43 from the connection point between the resistors R5 and R6.

Incidentally, the transformer T is wound auxiliary winding N _B, one end of the auxiliary winding N _B, the switching element 33 is connected to the rectifying / smoothing circuit 31 and the switching control circuit 32, the auxiliary winding N _B Are connected to the switching control circuit 32 and the phototransistor collector of the photocoupler PC.

  In any case, the conventional AC adapter 10 performs constant voltage control using a fixed reference voltage.

FIG. 4 shows the charging characteristics of the conventional AC adapter 10. The horizontal axis represents time t [h], and the vertical axis represents voltage V and current I. While the battery voltage V _BATT is low, the battery is charged with a constant charging current Ic. When the battery voltage V _BATT reaches a predetermined voltage, constant voltage charging is performed. As shown in FIG. 4, the adapter voltage V _ADP is always higher than the battery voltage V _BATT .

However, in the configuration of the conventional AC adapter 10, a high voltage difference ΔV ′ is generated between the adapter voltage V _ADP and the battery voltage V _BATT in the constant voltage charging region, and the charge control transistor (charge control element) inside the main body 20 is generated. ) There is a problem of causing Q to generate heat. The jumping voltage (ΔV′−ΔV) is about 0.5 V, although it varies depending on the model / product.

  Next, with reference to FIG. 5, the reason why the voltage jumps when switching from the constant current charging region to the constant voltage charging region will be described. 5A, 5 </ b> B, and 5 </ b> C, the VI characteristic of the AC adapter 10 is indicated by a thick solid line, and the VI characteristic of the charge control circuit 22 is indicated by a thin solid line.

As shown in FIG. 5A, when the battery voltage V _BATT is low, the battery is in a constant current charging state, and the battery voltage V _BATT and the adapter voltage V _ADP gradually increase with a minimum potential difference ΔV. .

As shown in FIG. 5B, charging proceeds and the battery voltage V _BATT is changed to the corner of the VI characteristic of the charge control circuit 22 (the charge control mode is switched from the constant current charge control mode to the constant voltage charge control mode). The battery voltage V _BATT and the adapter voltage V _ADP gradually increase with a minimum necessary potential difference ΔV until the time of switching).

_Assume that the battery voltage V _BATT enters the constant voltage portion of the VI characteristic of the charge control circuit 22 as shown in FIG. In this case, since the charging current Ic of the AC adapter 10 and the charging current flowing through the secondary battery 21 are the same, the adapter voltage V _ADP naturally enters the constant voltage charging region of the AC adapter 10 with the VI characteristic. For this reason, the adapter voltage V _ADP jumps from the point of FIG. 5B to the point of FIG. 5C.

This is the reason why a high voltage difference ΔV ′ occurs between the adapter voltage V _ADP and the battery voltage V _BATT in the constant voltage charging region.

  In particular, at point A shown in FIG. 2 (the point at which the constant current charging region is switched to the constant voltage charging region), since the charging current Ic is maximum, the heat generation of the charge control transistor (charge control element) Q is maximum. It is a point.

  In order to solve the above problems, the applicant of the present application has already provided an AC adapter that can suppress the heat generation of the charge control element inside the main body (see Japanese Patent Application Nos. 2003-272169 and 2004-194825). ).

  However, since the proposed AC adapter does not consider low current consumption in terms of circuit, there is a problem that current consumption increases in a state where no load is connected (no load state).

  Accordingly, an object of the present invention is to provide an AC adapter that can reduce current consumption in a state where a load is not connected (no load state).

According to the present invention, the AC adapter (10C) used for charging the secondary battery (21) built in or attached to the main body (20), the primary winding (Np) of the transformer (T). A primary side circuit that turns on and off the input DC voltage applied by the switching element (33), and an AC voltage induced in the secondary winding (Ns) of the transformer is rectified and smoothed to output an adapter voltage (V _ADP ). A secondary side circuit, a voltage control circuit (42A) for detecting a change in adapter voltage and outputting a voltage control signal, and a constant current control circuit for detecting a charging current flowing through the secondary side circuit and outputting a constant current control signal (43), a photocoupler (PC) that feeds back a voltage control signal and a constant current control signal to a primary circuit as a feedback signal, and switching control that controls on / off of the switching element in response to the feedback signal In the AC adapter including the circuit (32), a current monitoring circuit (61) that is provided in the secondary side circuit and determines whether or not it is in a no-load state by monitoring the charging current, and the current monitoring circuit An AC adapter is provided, characterized by comprising switch means (SW3) for disconnecting the power supply line of the circuit section (60) for controlling the voltage control circuit when it is determined that the load is not loaded.

  In the AC adapter (10C), the current monitoring circuit (61) may determine that there is no load when the charging current becomes a predetermined current or less. The predetermined current is, for example, 80 mA. The main body may be a mobile phone, for example.

  In addition, the code | symbol in the said parenthesis is attached | subjected in order to make an understanding of this invention easy, and it is only an example, and of course is not limited to these.

  In the present invention, a current monitoring circuit is provided in the secondary side circuit, and when the current monitoring circuit monitors the charging current and determines that it is in the no-load state, the switch means controls the voltage control circuit. Since the power supply line is disconnected, the current consumption in the no-load state can be reduced.

  First, in order to facilitate understanding of the present invention, an AC adapter described in Japanese Patent Application No. 2004-194825 (hereinafter referred to as “prior application”) will be described.

  The first AC adapter 10A of the prior application will be described with reference to FIG. The illustrated AC adapter 10A uses a second reference voltage generation circuit 44A in addition to a conventional reference voltage generation circuit (hereinafter also referred to as "first reference voltage generation circuit") 44 and a constant voltage control circuit 42. 3 has the same configuration as that of the conventional AC adapter 10 shown in FIG. 3 except that the voltage control circuit 42A is used in place of the above and a −ΔI detection circuit 45 is added. Components having the same functions as those shown in FIG. 3 are denoted by the same reference numerals, and description thereof is omitted for the sake of simplicity.

The second reference voltage generation circuit 44A performs voltage adjustment so as to gradually lower the second reference voltage as a basic operation in the charged state. In response to the drop in the second reference voltage, the voltage control circuit 42A controls the adapter voltage V _ADP to decrease.

  The −ΔI detection circuit 45 is connected to the anode 12 via the resistor R7. The -ΔI detection circuit 45 detects that the charging current Ic has decreased below the set current value, and supplies a detection signal to the second reference voltage generation circuit 44A.

In response to this detection signal, the second reference voltage generation circuit 44A once raises the second reference voltage by a predetermined voltage. In response to the increase in the second reference voltage, the voltage control circuit 42A operates to temporarily increase the adapter voltage V _ADP by a predetermined voltage.

  Hereinafter, the operation of the AC adapter 10A will be described with reference to FIG. 7 in addition to FIG. FIG. 7 is a diagram showing the charging characteristics of the AC adapter 10A shown in FIG. The horizontal axis represents time t [h], and the vertical axis represents voltage V and current I.

  In the constant current charging region, the constant current control circuit 43 constantly monitors the charging current Ic. The constant current control circuit 43 outputs a constant current control signal so that the charging current Ic is constant. This constant current control signal is fed back to the switching control circuit 32 of the primary side circuit as a feedback signal through the OR gate G and the photocoupler PC.

At this time, the voltage control circuit 42A gradually decreases the adapter voltage V _ADP in response to the second reference voltage supplied from the second reference voltage generation circuit 44A. At this time, the charging current Ic is maintained at a constant value. However, if the potential difference (V _ADP −V _BATT ) between the adapter voltage V _ADP and the battery voltage V _BATT falls below the necessary minimum voltage ΔV, the charging current Ic cannot flow and the charging current Ic decreases rapidly. When the-[Delta] I detection circuit 45 detects that the charging current Ic has fallen below the set current value due to a rapid decrease in the charging current Ic, the-[Delta] I detection circuit 45 supplies a detection signal to the second reference voltage generation circuit 44A. In response to this detection signal, the second reference voltage generation circuit 44A once raises the second reference voltage by a predetermined voltage. The constant voltage control circuit 42A operates to increase the adapter voltage V _ADP by a predetermined voltage in response to the increase in the second reference voltage.

  Thereafter, the secondary battery 21 is charged while repeating this. As a result, the necessary minimum potential difference ΔV can always be maintained. Note that the repetition period is about 100 milliseconds, for example, and the predetermined voltage to be raised is about 100 mV, for example. The value of the sudden decrease in the charging current Ic is, for example, in the range of 30 to 50 mA.

For this reason, in the conventional AC adapter 10, the adapter voltage V _ADP has a specified voltage value in the constant voltage charging region (see FIG. 4). However, in the first AC adapter 10 A of the prior application, the minimum necessary as needed. Charging is performed while adjusting the potential difference ΔV. For this reason, in the first AC adapter 10A of the prior application, the adapter voltage V _ADP does not jump up when shifting from the constant current charging region to the constant voltage charging region, which is a problem in the conventional AC adapter 10. . In other words, the first AC adapter 10A of the prior application maintained a minimum voltage ΔV that is a potential difference (V _ADP −V _BATT ) between the adapter voltage V _ADP and the battery voltage V _BATT during constant current charging. Continue constant voltage charging. As a result, the heat generation of the charge control element Q inside the main body 20 can be suppressed.

  Next, the second AC adapter 10B of the prior application will be described with reference to FIG. However, in FIG. 8, since the primary side circuit is the same as the conventional one, its illustration is omitted. Components having the same functions as those shown in FIG. 6 are denoted by the same reference numerals, and only different points will be described below for simplification of description.

In the first AC adapter 10A of the above-mentioned prior application, the -ΔI detection circuit 45 cannot detect -ΔI when the charging current Ic is not flowing. Therefore, as shown in FIG. 9, the adapter voltage V _ADP gradually decreases.

Therefore, as shown in FIG. 10, the AC adapter 10 </ b> B includes a current monitoring circuit 51 that outputs an adapter voltage V _ADP equivalent to that of the conventional AC adapter 10 in a standby state after full charge detection. That is, when the main body 20 is connected and the charging current Ic flows more than a predetermined set value, the current monitoring circuit 51 performs control by the method in the AC adapter 10A shown in FIG. 6 (hereinafter referred to as “repetitive control”). Start. On the other hand, when the value of the charging current Ic becomes equal to or lower than the predetermined set value, the current monitoring circuit 51 stops the above-described repetitive control, and again the adapter voltage equivalent to the conventional AC adapter 10 shown in FIG. V _ADP is output. At any rate, the current monitoring circuit 51 stops the operation repeatedly at least in a standby state after detecting the full charge of the secondary battery 21.

  Next, “full charge detection” will be described. As shown in FIG. 11, when the secondary battery 21 is charged, when the secondary battery 21 is nearly fully charged, the secondary battery 21 is charged in the constant voltage charging mode, and the charging current Ic gradually decreases. . As the charging current Ic approaches zero as much as possible, the battery is fully charged. However, since the value of the charging current Ic becomes small, the charging time becomes long. Therefore, as shown in FIG. 12, when the current value of the charging current Ic becomes small to some extent, it is determined that the battery is fully charged, and the charging of the secondary battery 21 is terminated. The detected value of the current value of the charging current Ic at this time is called a full charge detection set current value.

  This is control on the main body (mobile phone) 20 side, not on the AC adapter.

  On the other hand, it is assumed that such charging control is performed on the main body (mobile phone) 20 side. Assume that charging is performed using the AC adapter 10 </ b> A illustrated in FIG. 6. In other words, it is assumed that the above repeated control is performed until full charge is detected using the AC adapter 10A.

  In this case, during the repeated control, the -ΔI detection circuit 45 always detects -ΔI. Therefore, when the repeated control is performed until full charge is detected, as shown in FIG. Full charge is detected earlier than the detection of.

  As a countermeasure, the current monitoring circuit 51 shown in FIG. 14 stops the above-described repetitive control with a value added by a certain voltage from the full charge detection set current value, and eliminates the fluctuation of −ΔI. The operation state is the same as that of the conventional AC adapter 10. As a result, full charge detection can be performed as in the prior art. In any case, the current monitoring circuit 51 stops the repetitive operation when the charging current Ic reaches a charging current value obtained by adding a predetermined value to the current value at the time of detecting full charge.

  FIG. 15 shows the operation of the AC adapter 10B. FIG. 15 is a diagram illustrating the charging characteristics of the AC adapter 10B illustrated in FIG. The horizontal axis represents time t [h], and the vertical axis represents voltage V and current I.

As shown in FIG. 15, when the charging current value obtained by adding a certain value to the full charge detection current value of the main body 20 is reached, the above repeated control is stopped, and the adapter voltage V _ADP at that time is maintained. . Thereby, in the vicinity of the full charge of the main body 20, the fluctuation of the charging current Ic due to repetitive control is eliminated, and the full charge can be accurately detected.

  The current monitoring circuit 51 sends a control signal for starting / stopping control to the second reference voltage generating circuit 44B.

  FIG. 16 shows the configuration of the current monitoring circuit 51. The current monitoring circuit 51 includes a current detection resistor R11, an amplifier circuit 511, and a current monitoring comparison determination circuit 512. The current detection resistor R11 is for detecting the charging current Ic. In other words, the current detection resistor R11 converts the charging current Ic into a detection voltage. Since the current detection resistor R11 is a small value to avoid power loss, the detection voltage is also a small value. Therefore, this detection voltage is amplified by the amplifier circuit 511.

  The amplifier circuit 511 includes resistors R12, R13, and R14 and an operational amplifier A1. One end of the current detection resistor R11 is connected to the non-inverting input terminal of the operational amplifier A1 via the resistor R12, and the other end of the current detection resistor R11 is connected to the inverting input terminal of the operational amplifier A1 via the resistor R13. Yes. The inverting input terminal of the operational amplifier A1 is connected to the output terminal of the operational amplifier A1 via the resistor R14. The amplifier circuit 511 amplifies the detection voltage and outputs the amplified detection voltage Va. The amplified detection voltage Va is supplied to the current monitoring comparison determination circuit 512.

  The current monitoring comparison determination circuit 512 includes resistors R15, R16, R17, R18, an operational amplifier A2, and an analog switch SW1. The amplified detection voltage Va is supplied to the inverting input terminal of the operational amplifier A2. Resistors R15, R16, and R17 are bleeder resistors connected in series. The resistors R15, R16, and R17 divide the reference voltage Vref and output a voltage Vb divided from the connection point between the resistors R15 and R16. This divided voltage Vb is supplied to the non-inverting input terminal of the operational amplifier A2. The connection point between the resistors R16 and R17 is connected to the contact 1 of the analog switch SW1. The output terminal of the operational amplifier A2 is connected to the control terminal of the analog switch SW1 via the resistor R18. The contact 2 of the analog switch SW1 is grounded. The analog switch SW1 has the logic of switch off at the control terminal high level and switch on at the control terminal low level.

  In the illustrated example, the current monitoring comparison determination circuit 512 outputs a logic high level signal as a control stop control signal, and outputs a logic low level signal as a control start control signal. The control start / stop threshold is set by dividing the reference voltage Vref by the bleeder resistors R15 to R17.

  More specifically, it is assumed that the current monitoring comparison determination circuit 51 outputs a control stop control signal at a logic high level. In this case, the analog switch SW1 is in an off state. Therefore, in this case, the bleeder resistors R15 to R17 output a voltage equal to Vref {(R16 + R17) / (R15 + R16 + R17)} as the divided voltage Vb. The divided voltage Vb at this time is a threshold voltage for starting control, and corresponds to, for example, when the charging current Ic flows through 300 mA.

  It is assumed that the current monitoring comparison determination circuit 51 outputs a control signal for starting control at a logic low level. In this case, the analog switch SW1 is in an on state. For this reason, the resistor R17 is short-circuited. Therefore, in this case, the bleeder resistors R15 to R17 are set to a voltage equal to Vref {(R16 / (R15 + R16)} as a divided voltage Vb, which is a threshold voltage for stopping control. For example, this corresponds to the case where the charging current Ic flows through 200 mA.

  That is, by providing an analog switch SW1 between the output terminal of the operational amplifier A2 and the bleeder resistors R15 to R17, hysteresis is applied to change the control start threshold voltage and the control stop threshold voltage. .

  FIG. 17 shows the operation of the current monitoring circuit 51. The current monitoring circuit 51 starts the control when the charging current Ic becomes 300 mA or more, and supplies the second reference voltage generation circuit 44B with a control start / stop control signal for stopping the control when the charging current Ic becomes 200 mA or less. .

  Further, the -ΔI detection signal is supplied from the -ΔI detection circuit 45A to the second reference voltage generation circuit 44B via the overvoltage prevention circuit 52. The overvoltage prevention circuit 52 outputs the -ΔI detection signal as it is while detecting no overvoltage.

  The operation of the second reference voltage generation circuit 44B will be described with reference to FIG. During the control stop period (that is, the period when the control signal for control stop at the logic high level is supplied from the current monitoring circuit 51), the second reference voltage generation circuit 44B outputs a constant voltage as the second reference voltage. In this example, this constant voltage is equal to the reference voltage of the conventional AC adapter 10 which is 1.25V.

  On the other hand, the second reference voltage generation circuit 44B performs the following operation during the control period (that is, the period when the control signal for starting control of the logic low level is supplied from the current monitoring circuit 51). That is, the second reference voltage generation circuit 44B gradually decreases the second reference voltage from the constant voltage (1.25V). When the -ΔI detection signal is input through the overvoltage prevention circuit 52, the second reference voltage generation circuit 44B increases the second reference voltage by the set voltage. After the −ΔI detection signal is input, the second reference voltage generation circuit 44B gradually decreases the second reference voltage again until the next −ΔI detection signal is input.

  The third reference voltage generation circuit 53 generates a third reference voltage Vref. The third reference voltage Vref is a constant voltage for determining a threshold voltage when inverting the output of the current monitoring circuit 51, as shown in FIG.

  As described above, the current monitoring circuit 51 divides the third reference voltage Vref into the threshold voltage at the start of control or the threshold voltage at the stop of control by the bleeder resistors R15 to R17, and the divided voltage Vb. The current monitoring comparison determination circuit 512 outputs a Low / High signal by comparing the detected voltage Va converted into a voltage by the current detection resistor R11 and amplified by the amplifier circuit 511.

  The AC adapter 10B shown in FIG. 8 includes, in addition to the −ΔI detection circuit 45A, a + ΔI detection circuit 54, a first comparison voltage generation circuit 55, a second comparison voltage generation circuit 56, and a comparison value fetch circuit 57. ing.

  That is, as shown in FIG. 19, when the load current Ic suddenly increases, the AC adapter 10B detects the increased current (+ ΔI detection), causes the −ΔI detection comparison value to follow the increased current, and performs charging. A decrease in current Ic is suppressed.

  FIG. 20 shows the + ΔI detection circuit 54. The + ΔI detection circuit 54 includes a current capturing hold unit 541, a + ΔI detection voltage setting unit 542, an inverting addition circuit 543, an inverting circuit 544, and a + ΔI detection unit 545.

  The current capturing and holding circuit 541 includes a switch SW, a capacitor C1, and an operational amplifier A3. The switch SW is turned on in response to a current capture trigger by + ΔI detection or −ΔI detection, and the current value at that time is held (held) by the capacitor C1. The hold voltage of the capacitor C1 is supplied to the non-inverting input terminal of the operational amplifier A3. The output terminal of the operational amplifier A3 is connected to the inverting input terminal of the operational amplifier A3. The current capture hold circuit 541 configured as described above outputs a charge current value (current capture hold value) that is captured and held immediately after + ΔI detection or −Δ detection.

  The + ΔI detection voltage setting unit 542 includes resistors R21, R22, and R23, an analog switch SW2, and an operational amplifier A4. The resistors R21 to R23 are connected in series between a reference voltage Vref terminal and a reference voltage (Vref / 2) terminal. A contact 1 of the analog switch SW2 is connected to a connection point between the resistors R22 and R23, and a contact 2 of the analog switch SW2 is connected to a reference voltage (Vref / 2) terminal. A control terminal of the analog switch SW2 is connected to an output terminal of a + ΔI detector 545 described later. The analog switch SW2 has a logic of switch on at the control terminal High level and switch off at the control terminal Low level. A connection point between the resistors R21 and R22 is connected to a non-inverting input terminal of the operational amplifier A4. The output terminal of the operational amplifier A4 is connected to the inverting input terminal of the operational amplifier A4. The + ΔI detection voltage setting unit 542 having such a configuration sets a + ΔI detection voltage level (+ ΔI detection voltage setting value). The analog switch SW2 is for providing a hysteresis so that the output is not violated by an increase in current near the set value. The + ΔI detection voltage setting unit 542 has an amplification factor of 1.

  The inverting adder circuit 543 includes resistors R24, R25, R26 and an operational amplifier A5. The inverting input terminal of the operational amplifier A5 is connected to the output terminal of the current capturing and holding unit 541 via the resistor R24, and is connected to the output terminal of the + ΔI detection voltage setting unit 542 via the resistor R25. The non-inverting input terminal of the operational amplifier A5 is connected to the reference voltage (Vref / 2) terminal. The output terminal of the operational amplifier A5 is connected to the inverting input terminal of the operational amplifier A5 via the resistor R26. The inverting addition circuit 543 having such a configuration adds the + ΔI detection voltage setting value to the current capture hold value and outputs a value obtained by inverting addition. This is because the phase is inverted due to the characteristics of the operational amplifier. The inversion adding circuit 543 has an amplification factor of 1.

  The inverting circuit 544 includes resistors R27 and R28 and an operational amplifier A6. The inverting input terminal of the operational amplifier A6 is connected to the output terminal of the inverting addition circuit 543 via the resistor R27. The non-inverting input terminal of the operational amplifier A6 is connected to the reference voltage (Vref / 2) terminal. The output terminal of the operational amplifier A6 is connected to the inverting input terminal of the operational amplifier A6 via the resistor R28. The inverting circuit 544 having such a configuration inverts the inverted addition value output from the inverting addition circuit 543 again, and outputs the added value. That is, since the phase is inverted in the previous stage, the inversion circuit 544 inverts again. The added value output from the inverting circuit 544 is a detected voltage comparison value of + ΔI. The amplification factor of the inverting circuit 544 is also 1 time.

  The + ΔI detection unit 545 includes an operational amplifier A7 and a resistor R29. A current waveform (current value) of the charging current Ic is supplied to the inverting input terminal of the operational amplifier A7. A detection voltage comparison value of + ΔI is supplied from the inverting circuit 544 to the non-inverting input terminal of the operational amplifier A7. The output terminal of the operational amplifier A7 is connected to the control terminal of the analog switch SW2 of the + ΔI detection voltage setting unit 542 via the resistor R29. The + ΔI detector 545 having such a configuration compares the + ΔI detection voltage comparison value with the current value of the charging current Ic and outputs a + ΔI detection signal.

  In any case, the + ΔI detection circuit 54 functions as additional detection means for detecting that the charging current Ic has increased beyond the additional set current value and outputting an additional detection signal. The combination of the comparison value fetch circuit 57 and the first comparison voltage generation circuit 55 operates as means for changing the set current value in the detection means (−ΔI detection circuit 45A) in response to the additional detection signal. .

  Next, referring to FIG. 21, in addition to the −ΔI detection circuit 45A of the AC adapter 10B illustrated in FIG. 8, the + ΔI detection circuit 54, the first comparison voltage generation circuit 55, and the second comparison voltage generation circuit 56 are illustrated. The operation of the comparison value fetch circuit 57 will be described.

  Based on the output voltage of the comparison value fetch circuit 57, the first comparison voltage generation circuit 55 generates a -ΔI detection comparison voltage, and the second comparison voltage generation circuit 56 generates a + ΔI detection comparison voltage.

  The comparison value capture circuit 57 generates a comparison value capture period signal in response to the −Δ detection signal or the + Δ detection signal, captures the current value of the charging current Ic only during that period, and captures the voltage during other periods. It is a circuit that maintains This taken-in voltage is also a reference voltage for the first comparison voltage generation circuit 55 and the second comparison voltage generation circuit 56.

  The first comparison voltage generation circuit 55 outputs a -ΔI detection comparison voltage that is lower than the voltage acquired by the comparison value acquisition circuit 57 by a voltage corresponding to -ΔI. The second comparison voltage generation circuit 56 outputs a + ΔI detection comparison voltage that is higher than the voltage acquired by the comparison value acquisition circuit 57 by a voltage corresponding to + ΔI.

  The AC adapter 10B further includes an overvoltage detection circuit 58 and an overvoltage prevention circuit 52.

By providing the overvoltage detection circuit 58 and the overvoltage prevention circuit 52, as shown in FIG. 22, when the adapter voltage V _ADP rises above a certain threshold value, the adapter voltage V _ADP caused by -ΔI detection is detected. Do not let the rise. Thereby, even if a pulse-like load is applied, it does not become an overvoltage. In any case, the combination of the overvoltage detection circuit 58 and the overvoltage prevention circuit 52 serves as a means for suppressing an increase in the adapter voltage V _ADP due to the detection signal when the adapter voltage V _ADP exceeds a predetermined threshold value.

  FIG. 23 shows an example of the overvoltage detection circuit 58 and the overvoltage prevention circuit 52. The overvoltage detection circuit 58 includes resistors R31 and R32 and an operational amplifier A8. The resistors R31 and R32 divide the reference voltage Vref and supply the divided voltage to the non-inverting input terminal of the operational amplifier A8 as an overvoltage detection threshold value. The second reference voltage is supplied from the second reference voltage generation circuit 44B to the inverting input terminal of the operational amplifier A8.

  The overvoltage detection circuit 58 having such a configuration compares the overvoltage detection threshold value with the second reference voltage and outputs a Low / High overvoltage detection circuit output signal.

  The illustrated overvoltage prevention circuit 52 includes an AND gate G1. When the overvoltage detection circuit output signal is high, the overvoltage prevention circuit 52 outputs the -ΔI detection signal output from the -ΔI detection circuit 45A as it is as an overvoltage prevention circuit output signal. On the other hand, when the overvoltage detection circuit output signal is low, the overvoltage prevention circuit 52 does not output the −ΔI detection signal.

  When the overvoltage prevention circuit output signal is input, the second reference voltage generation circuit 44B increases the second reference voltage by the set voltage. After the overvoltage prevention circuit output signal is input, the second reference voltage generation circuit 44B gradually lowers the second reference voltage again until the next overvoltage prevention circuit output signal is input.

  In the AC adapter of the prior application shown in FIG. 8, since low current consumption is considered in terms of circuit, the current consumption increases in a state where no load is connected. Therefore, in the present invention, the current consumption is reduced in a state where no load is connected (no load state) by adopting the configuration described below.

  With reference to FIG. 24, AC adapter 10C according to an embodiment of the present invention will be described. However, in FIG. 24, the primary side circuit is not different from the conventional one, and is not shown. Components having the same functions as those shown in FIG. 8 are denoted by the same reference numerals, and only different points will be described below for simplification of description.

  The illustrated AC adapter 10C further includes a current monitoring circuit 61, a fourth reference voltage generation circuit 62, and an analog switch SW3.

  The current monitoring circuit 61 connects the power supply line when the charging current flows to a predetermined current (for example, 90 mA) or more, and disconnects the power supply line when the charging current becomes a predetermined current (for example, 80 mA) or less. The switch control signal is output. In other words, the current monitoring circuit 61 monitors the charging current and determines whether or not it is in a no-load state. The fourth reference voltage generation circuit 62 supplies the fourth reference voltage Vref to the current monitoring circuit 61.

  As shown in FIG. 24, the circuit section 60 from which the power supply line is disconnected when there is no load includes a current monitoring circuit 51, a + ΔI detection circuit 54, a −ΔI detection circuit 45A, a comparison value capture circuit 57, and a first comparison voltage generation. A circuit 55, a second comparison voltage generation circuit 56, an overvoltage prevention circuit 52, and an overvoltage detection circuit 58. In other words, the circuit unit 60 is a part that controls the voltage control circuit 42A. The analog switch SW3 functions as a switch unit that disconnects the power supply line of the circuit unit 60 that controls the voltage control circuit 42A when the current monitoring circuit 61 determines that there is no load.

  FIG. 25 shows the configuration of the current monitoring circuit 61. The current monitoring circuit 61 includes a current detection resistor R41, an amplifier circuit 611, and a current monitoring comparison determination circuit 612. The current detection resistor R41 is for detecting the charging current Ic. In other words, the current detection resistor R41 converts the charging current Ic into a detection voltage. Since the current detection resistor R41 is a small value to avoid power loss, the detection voltage is also a small value. Therefore, this detection voltage is amplified by the amplifier circuit 611.

  The amplifier circuit 611 includes resistors R42, R43, R44 and an operational amplifier A11. One end of the current detection resistor R41 is connected to the non-inverting input terminal of the operational amplifier A11 via the resistor R42, and the other end of the current detection resistor R41 is connected to the inverting input terminal of the operational amplifier A11 via the resistor R43. Yes. The inverting input terminal of the operational amplifier A11 is connected to the output terminal of the operational amplifier A11 via the resistor R44. The amplifier circuit 611 amplifies the detection voltage and outputs the amplified detection voltage Vd. The amplified detection voltage Vd is supplied to the current monitoring comparison determination circuit 612.

  The current monitoring comparison determination circuit 612 includes resistors R45, R46, R47, and R48, an operational amplifier A12, and an analog switch SW4. The amplified detection voltage Vd is supplied to the non-inverting input terminal of the operational amplifier A12. Resistors R45, R46, and R47 are bleeder resistors connected in series. The resistors R45, R46, and R47 divide the reference voltage Vref and output the voltage Ve divided from the connection point between the resistors R45 and R46. The divided voltage Ve is supplied to the inverting input terminal of the operational amplifier A12. A connection point between the resistors R46 and R47 is connected to a fixed contact of the analog switch SW1. The output terminal of the operational amplifier A12 is connected to the control terminal of the analog switch SW1 via the resistor R48. The movable contact of the analog switch SW4 is grounded. The analog switch SW4 has a logic of switch on at the control terminal high level and switch off at the control terminal low level.

  In the illustrated example, the current monitoring comparison determination circuit 612 outputs a logic high level signal as a control signal for power supply line connection, and outputs a logic low level signal as a control signal for power supply line disconnection. By dividing the reference voltage Vref by the bleeder resistors R45 to R47, threshold values for power supply line connection / power supply line disconnection are set.

  More specifically, it is assumed that the current monitoring comparison determination circuit 612 outputs a control signal for disconnecting the power supply line at the logic low level. In this case, the analog switch SW4 is in an off state. Therefore, in this case, the bleeder resistors R45 to R47 output a voltage equal to Vref {(R46 + R47) / (R45 + R46 + R47)} as the divided voltage Ve. The divided voltage Ve at this time is a threshold voltage for power supply line connection, and corresponds to, for example, a case where the charging current Ic flows by 90 mA.

  It is assumed that the current monitoring comparison determination circuit 612 outputs a control signal for connecting a power supply line at a logic high level. In this case, the analog switch SW4 is in an on state. Therefore, the resistor R47 is short-circuited. Accordingly, in this case, the bleeder resistors R45 to R47 have a voltage equal to Vref {(R46 / (R45 + R46)} as the divided voltage Ve. The divided voltage Ve at this time is the threshold voltage for disconnecting the power supply line. For example, this corresponds to a case where the charging current Ic flows 80 mA.

  That is, by providing an analog switch SW4 between the output terminal of the operational amplifier A12 and the bleeder resistors R45 to R47, hysteresis is applied to change the threshold voltage for connecting the power supply line and the threshold voltage for disconnecting the power supply line. ing.

  FIG. 26 shows the operation of the current monitoring circuit 61. The current monitoring circuit 61 supplies a power supply line connection / disconnection control signal to the analog switch SW3 for connecting the power supply line when the charging current Ic becomes 90 mA or more and disconnecting the power supply line when the charging current Ic becomes 80 mA or less.

  As described above, the current monitoring circuit 61 divides the fourth reference voltage Vref into the threshold voltage when the power line is connected or the threshold voltage when the power line is disconnected by the bleeder resistors R45 to R47. The current monitoring comparison determination circuit 612 compares the voltage Ve and the detection voltage Vd converted into a voltage by the current detection resistor R41 and amplified by the amplifier circuit 611, thereby outputting a Low / High signal.

  As described above, the present invention has been described with reference to the embodiments, but the present invention is not limited to the above-described embodiments. For example, in the above-described embodiment, the case where the present invention is applied to an AC adapter for a mobile phone has been described as an example. However, the present invention can be applied to an AC adapter that supplies power to a charging circuit in addition to a mobile phone. It is.

It is a block diagram which shows the state by which the AC adapter was connected to the main body which incorporates a secondary battery. It is a characteristic view which shows the VI characteristic of AC adapter. It is a block diagram which shows the structure of the conventional AC adapter. It is a figure which shows the charge characteristic of the conventional AC adapter shown in FIG. FIG. 4 is a diagram for explaining the reason why a voltage jump occurs when the conventional AC adapter shown in FIG. 3 is switched from a constant current charging region to a constant voltage charging region. It is a block diagram which shows the structure of the 1st AC adapter of a prior application. It is a figure which shows the charge characteristic of the AC adapter shown in FIG. It is a block diagram which shows the structure of the secondary side circuit of the 2nd AC adapter of a prior application. It is a figure which shows the charge characteristic of an AC adapter at the time of repeating control by the AC adapter shown in FIG. 6 after full charge detection time. It is a figure which shows the charge characteristic of the AC adapter shown in FIG. It is a figure which shows the charge characteristic for demonstrating the constant current charge mode in the case of charging a secondary battery, and the constant voltage charge mode which does not perform full charge detection. It is a figure which shows the charge characteristic for demonstrating the constant current charge mode in the case of charging a secondary battery, and the constant voltage charge mode which performs full charge detection. It is a figure which shows the charge characteristic of the AC adapter of FIG. 6 for demonstrating the problem at the time of performing repeated control until full charge is detected using the AC adapter shown in FIG. It is a figure which shows the charge characteristic of the AC adapter shown in FIG. It is a figure which shows the charge characteristic of the AC adapter shown in FIG. It is a block diagram which shows the structure of the current monitoring circuit used for the AC adapter shown in FIG. FIG. 17 is a time chart showing a charging current and a current monitoring circuit output in order to explain the operation of the current monitoring circuit shown in FIG. 16. 9 is a time chart for explaining a relationship among a current monitoring circuit output, a second reference voltage, and an overvoltage prevention circuit output (−ΔI detection signal) in the AC adapter shown in FIG. 8. It is a figure which shows the charge characteristic of the AC adapter of FIG. It is a block diagram which shows the structure of the + (DELTA) I detection circuit used for the AC adapter shown in FIG. FIG. 9 is a time chart for explaining operations of a −ΔI detection circuit, a + ΔI detection circuit, a first comparison voltage generation circuit, a second comparison voltage generation circuit, and a comparison value capturing circuit of the AC adapter of FIG. 8; FIG. 9 is a diagram illustrating charging characteristics in a state where a pulse-like load is applied in the AC adapter of FIG. 8. It is a block diagram which shows the structure of the overvoltage detection circuit and overvoltage prevention circuit which are used for the AC adapter of FIG. It is a block diagram which shows the structure of the secondary side circuit of the AC adapter which concerns on one embodiment of this invention. It is a block diagram which shows the structure of the current monitoring circuit used for the AC adapter shown in FIG. FIG. 26 is a time chart showing a charging current and a current monitoring circuit output in order to explain the operation of the current monitoring circuit shown in FIG. 25. FIG.

Explanation of symbols

10C AC adapter 20 body (mobile phone)
DESCRIPTION OF SYMBOLS 21 Secondary battery 22 Charging control circuit 31 Rectification / smoothing circuit 32 Switching control circuit 33 SW element 41 Rectification / smoothing circuit 42A Voltage control circuit 43 Constant current control circuit 44 1st reference voltage generation circuit 44B 2nd reference voltage generation circuit 45A -ΔI detection circuit 51 Current monitoring circuit 52 Overvoltage prevention circuit 53 Third reference voltage generation circuit 54 + ΔI detection circuit 55 First comparison voltage generation circuit 56 Second comparison voltage generation circuit 57 Comparison value capture circuit 60 Voltage control Circuit section for controlling the circuit 61 Current monitoring circuit 62 Fourth reference voltage generating circuit SW3 Analog switch T transformer Np primary winding Ns secondary winding N _B auxiliary winding

Claims (4)

An AC adapter used for charging a secondary battery built in or attached to a main body, a primary side circuit for turning on and off an input DC voltage applied to a primary winding of a transformer by a switching element, and a second side of the transformer A secondary side circuit that rectifies and smoothes an AC voltage induced in the secondary winding and outputs an adapter voltage; a voltage control circuit that detects a change in the adapter voltage and outputs a voltage control signal; and the secondary side circuit A constant current control circuit that detects a charging current flowing through the output current and outputs a constant current control signal; a photocoupler that feeds back the voltage control signal and the constant current control signal to the primary circuit as a feedback signal; and In an AC adapter comprising a switching control circuit for controlling on / off of the switching element in response,
A current monitoring circuit provided in the secondary side circuit for monitoring the charging current to determine whether or not a no-load state;
An AC adapter comprising: switch means for disconnecting a power supply line of a circuit unit for controlling the voltage control circuit when it is determined by the current monitoring circuit that there is no load.   The AC adapter according to claim 1, wherein the current monitoring circuit determines the no-load state when the charging current becomes a predetermined current or less.   The AC adapter according to claim 1, wherein the predetermined current is 80 mA. The AC adapter according to any one of claims 1 to 3, wherein the main body is a mobile phone.

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