JP2006296081A - Charging system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain reductions of allowable power of a charging control element as well as the size of the charging control element by relieving power concentration to the charging control element in a series regulator type charging system. <P>SOLUTION: A charging path from an external power source 1 to a secondary battery 2 includes the charging control element 4 composed of a MOSFET controlled by a charging control circuit 7, and a reverse current prevention element 5 composed of the MOSFET. A reverse current prevention control circuit 8 wherein the reverse current prevention element 5 is turned on at charging within such a range that an input voltage Vi is a battery voltage Vb or more and the input voltage Vi is a voltage (Vb+Vos) of which a battery voltage Vb is added to an offset voltage Vos or less, and the reverse current prevention element 5 is turned off without the range. Thus, when the input voltage Vi from the external power source 1 is lower than the battery voltage Vb, the reverse current is prevented by the reverse current prevention element 5 and its body diode, and during the charging where the input voltage Vi is much higher than the battery voltage Vb, the power concentration to the charging control element 4 is dispersed by power consumption in the body diode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a series regulator type charging system that charges a secondary battery such as a lithium ion battery using an external power source.

  In recent years, charging of secondary batteries such as lithium-ion batteries has been increasingly performed by switching and pulse methods with an emphasis on efficiency, but low noise, ease of control, and parts saving There are also many series regulator type charging systems due to the advantages such as low price. An example of the circuit configuration of a series regulator charging system described in Patent Document 1 is shown in FIG. 8, and the operation thereof will be described below.

  In FIG. 8, reference numeral 1 denotes an external power source such as an AC adapter. Reference numeral 2 denotes a secondary battery such as a lithium ion battery. Reference numeral 31 denotes a charging circuit. The charging circuit 31 includes a charging control element 4 composed of a P-channel MOSFET, a backflow prevention diode 51, a current detection resistor 6, and a charging control circuit 7.

  The charge control element 4, the backflow prevention diode 51, and the current detection resistor 6 are connected in series, and the charging circuit 31 controls the DC power supplied from the external power source 1 to a constant current or a constant voltage to control the secondary battery 2. To charge.

  The charging control circuit 7 detects the charging current to the secondary battery 2 by the current detection resistor 6, and also detects the battery voltage Vb of the secondary battery 2, and applies the gate voltage to the charging control element 4 to Adjust the impedance. Generally, when the battery voltage Vb of the secondary battery 2 is low, constant current charging is performed by adjusting the impedance of the charge control element 4 so as to stabilize the voltage across the current detection resistor 6. When the battery voltage Vb of the secondary battery 2 rises and approaches full charge, constant voltage charging is performed by adjusting the impedance of the charge control element 4 so as to stabilize the battery voltage of the secondary battery 2.

  The backflow prevention diode 51 is connected to prevent current from flowing from the secondary battery 2 via the charge control element 4 when the external power source 1 is not charged, such as when it is not connected. For this reason, the supply voltage Vi from the external power supply 1 drops to the output voltage (battery voltage of the secondary battery 2) Vb of the charging circuit 31 at the time of constant voltage charging, and the voltage drop between the charging control element 4 and the current detection resistor 6. And a forward voltage drop of about 0.7 V by the backflow prevention diode 51 must be set.

Further, prior to the constant current charging by the charge control element 4 described above, when the external power source 1 has a constant current drooping characteristic, the charge control element 4 is turned on in the initial charging stage when the battery voltage of the secondary battery 2 is low. The secondary battery 2 may be rapidly charged with a constant current determined by the external power source 1. That is, this is a charging mode in which the external power source 1 is actively used in order to suppress the power loss in the charging circuit 31 and to rapidly charge the secondary battery 2 with a constant current exceeding the capacity of the charging circuit 31. In such a quick charge mode, the power loss due to the forward voltage drop in the backflow prevention diode 51 becomes large.
JP 2003-92843 A

  A problem of the conventional series regulator type charging system is that large power consumption occurs in the charging control element 4 during constant current charging by the charging control element 4. Moreover, when a load circuit (not shown) supplied with power from the secondary battery 2 is operated, the charging current to the secondary battery 2 is reduced by the supply current to the load circuit, so that the charging time is extended. That is, the period during which large power consumption is generated in the charge control element 4 becomes long. In order to reduce heat generation and secure the element life, it is necessary to use an element having a large allowable power or size as the charge control element 4.

  In view of the above problems, the charging system of the present invention aims to reduce the allowable power and reduce the size of the charging control element by reducing the power concentration on the charging control element.

  In order to solve the above-described problems, a charging system according to the present invention includes a series regulator type charging circuit in which power is input from an external power source to an input terminal and a charging current is output from the output terminal to a secondary battery. . In the charging circuit, a charging control element that adjusts the charging current to the secondary battery and a backflow prevention element that can control the magnitude of the voltage generated at both ends of the element when conducting are connected in series to the charging path from the external power source to the secondary battery. Have. The backflow prevention element has an operating state that blocks a backflow of current from the secondary battery to the input terminal and exhibits a predetermined impedance during charging.

  With the above configuration, the power consumption concentrated on the charge control element is also borne by the backflow prevention element due to the voltage drop at the backflow prevention element during charging. As a result, it is possible to disperse thermal stress, reduce the allowable power of the charge control element, and reduce the size.

  Furthermore, in the charging system according to the present invention, the backflow prevention element is a MOSFET whose body diode is forward with respect to the charging current, and the charging circuit has a backflow prevention control circuit that controls the backflow prevention element. The backflow prevention control circuit turns on the backflow prevention element when the absolute value of the input voltage of the charging circuit is within a predetermined range that is equal to or greater than the absolute value of the output voltage of the charging circuit, and prevents backflow when it is outside the predetermined range. The device is configured to be in an off state.

  Thus, during constant current charging by the charge control element, the power consumption concentrated on the charge control element can be borne by the backflow prevention element due to the voltage drop at the body diode of the backflow prevention element. In addition, you may connect the diode which becomes a forward direction with respect to a charging current in parallel with a backflow prevention element.

  In addition, the predetermined range higher than the absolute value of the output voltage of the charging circuit described above is the absolute value of the output voltage of the charging circuit, the absolute value of the output voltage of the charging circuit, It is good to set between the voltage value more than the voltage value which added the direction voltage drop.

  In the charging system according to the present invention, the backflow prevention element is a MOSFET, and the charging circuit includes a backgate voltage setting circuit that sets a backgate voltage of the backflow prevention element, and a drain-source voltage of the backflow prevention element. The back gate voltage setting circuit includes a comparator that compares the absolute value of the input voltage of the charging circuit and the absolute value of the output voltage, and a backflow prevention element based on the output of the comparator. A switch that connects the back gate to the input voltage of the charging circuit and the output voltage that has a larger absolute value. The on-voltage control circuit has an absolute value of the input voltage of the charging circuit that is When the value is equal to or greater than the value, the drain-source voltage of the backflow prevention element may be adjusted to a predetermined value.

  With this configuration, by adjusting the voltage drop at the backflow prevention element during charging, the power consumption concentrated on the charge control element is also borne by the backflow prevention element, the thermal stress is dispersed, and the charge control element The allowable power can be reduced and the size can be reduced.

  Further, in the above configuration, the on-voltage control circuit uses the drain-source voltage of the backflow prevention element when the absolute value of the input voltage of the charging circuit is equal to or larger than the absolute value of the output voltage of the charging circuit. By having the operation state of adjusting the voltage value of the inter-voltage to a predetermined magnification, it is possible to cause the backflow prevention element to bear a predetermined ratio of the power consumption concentrated on the charge control element. Further, the power sharing between the charge control element and the backflow prevention element may be made equal.

  According to the charging system of the present invention, in the series regulator type charging system, when the input voltage from the external power source is lower than the battery voltage of the secondary battery, the voltage drop of the backflow prevention element that prevents backflow is reduced during charging. By adjusting in step, a part of the power consumption concentrated on the charge control element can be borne by the backflow prevention element having a size comparable to the charge control element. As a result, thermal stress is dispersed, and the allowable power of the charge control element can be reduced and downsized. In other words, during constant current charging by the charging control element of the series regulator type charging system, the power consumption concentrated on the charging control element can be shared with the backflow prevention element having the same size as the charging control element. It is possible to reduce the size of the charge control element by reducing the allowable power and to improve the reliability by extending the life.

  Hereinafter, a charging system according to the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 shows a circuit configuration of a charging system according to Embodiment 1 of the present invention.

  In FIG. 1, reference numeral 1 denotes an external power source such as an AC adapter. Reference numeral 2 denotes a secondary battery such as a lithium ion battery. Reference numeral 3 denotes a charging circuit.

  The charging circuit 3 includes a charge control element 4 made of a P-channel MOSFET, a backflow prevention element 5 made of a P-channel MOSFET, a current detection resistor 6, a charge control circuit 7, and a backflow prevention control circuit 8.

  The charge control element 4, the backflow prevention element 5, and the current detection resistor 6 are connected in series. The charging circuit 3 charges the secondary battery 2 by controlling the DC power supplied from the external power source 1 to a constant current or a constant voltage. The charge control element 4 and the backflow prevention element 5 are installed facing each other with their drain terminals connected to each other.

  The charge control circuit 7 includes a charge state switching reference voltage source 71 that generates the first voltage Vb1, a battery voltage detection comparator 72, a charge control circuit switch 73, a constant current charge control operational amplifier 74, a constant current charge. Constant voltage charging reference voltage source 75 for generating voltage Viref corresponding to the current value of time, constant voltage charging control operational amplifier 76, and constant voltage charging reference voltage source 77 for generating second voltage Vb2. The

  The charging control circuit 7 detects the charging current Ib to the secondary battery 2 by the current detection resistor 6 and also detects the battery voltage Vb of the secondary battery 2, applies a gate voltage to the charging control element 4, Adjust its impedance.

  In the present embodiment, when the battery voltage Vb of the secondary battery 2 is equal to or lower than the first voltage Vb1 (= 3V), the charge control circuit 7 detects the charge using the battery voltage detection comparator 72 and performs charging. The control circuit changeover switch 73 is switched to ignore the voltage drop in the current detection resistor 6 and set the charge control element 4 to the full-on state. When the charge control element is a PMOS device as shown in this figure, the gate voltage is set to the ground level which is the lowest voltage by switching the charge control circuit changeover switch 73. At this time, the charging control circuit 7 is in a quick charging mode based on the constant current characteristic of the external power source 1. The constant current output of the external power supply 1 is assumed to be Ib0 (= 1A).

  Next, when the battery voltage Vb of the secondary battery 2 becomes higher than the first voltage Vb1, the charging control circuit 7 switches the charging control circuit changeover switch 73 so that the charging control circuit 7 keeps the voltage drop in the current detection resistor 6 constant. The control is switched to the control by the operational amplifier 74 for current charge control, thereby adjusting the gate voltage of the charge control element 4. That is, the charging control circuit 7 is in a constant current charging mode. The charging current at this time is Ib1 (= 0.5 A).

  When the battery voltage Vb of the secondary battery 2 reaches the second voltage Vb2 (= 4.2V), the constant voltage charge control operational amplifier 76 maintains the voltage by switching the charge control circuit changeover switch 73. The control is switched to thereby adjusting the gate voltage of the charge control element 4. That is, the charging control circuit 7 is in a constant voltage charging mode.

  The switching between the constant current charging operation and the constant voltage charging operation is represented by the charge control circuit switching switch 73. As a more specific configuration example, the battery voltage Vb of the secondary battery 2 is measured, and the second It may be compared with a voltage slightly smaller than the voltage Vb2 of the current voltage, or the output of the constant voltage charging operational amplifier 76 and the output of the constant current charging operational amplifier 74 are input to select the larger control signal for charging. A maximum value circuit that is applied to the gate of the control element 4 may be used. In the operation using the maximum value circuit, when the battery voltage Vb of the secondary battery 2 reaches the second voltage Vb2 by constant current charging by the constant current charging operational amplifier 74, the constant voltage is smoothly applied. The operation proceeds to constant voltage charging by the charging operational amplifier 76.

  In FIG. 1, the backflow prevention control circuit 8 detects the input / output voltages Vi and Vb of the charging circuit 3 and applies a gate voltage to the backflow prevention element 5 according to the magnitude relation between the input / output voltages Vi and Vb.・ Control off. The backflow prevention control circuit 8 includes a first comparator 81, a second comparator 82, an offset voltage source 83 having an offset voltage Vos (= 1.5 V), and a NAND gate 84.

  In the backflow prevention control circuit 8, in the first comparator 81, the input voltage Vi of the charging circuit 3 is input to the non-inverting input terminal, and the output voltage Vb of the charging circuit 3 is input to the inverting input terminal. In the second comparator 82, the input voltage Vi of the charging circuit 3 is input to the inverting input terminal, and the voltage (Vb + Vos) obtained by adding the offset voltage Vos of the offset voltage source 83 to the output voltage Vb of the charging circuit 3 is the non-inverting input terminal. Is input. Each output of the first comparator 81 and the second comparator 82 is input to the NAND gate 84, and the output is given to the gate terminal of the backflow prevention element 5 made of a P-channel MOSFET. The backflow prevention control circuit 8 turns on the backflow prevention element 5 at the time of charging when the input voltage Vi is equal to or higher than the battery voltage Vb and within the range of the battery voltage Vb plus the offset voltage Vos (Vb + Vos). Outside the range, it is in the off state.

  Thus, when the input voltage Vi from the external power source 1 is lower than the battery voltage Vb, the backflow prevention element 5 and its body diode prevent backflow, and when the input voltage Vi is sufficiently higher than the battery voltage Vb, the body diode The power concentration on the charge control element 4 is dispersed by the power consumption at.

  The internal circuit of the charging control circuit 7 is only an example. The circuit configuration differs depending on the type of the secondary battery, and it goes without saying that various configurations are possible even with the same secondary battery.

  Here, the operation power supplies of the charge control circuit 7 and the backflow prevention control circuit 8 will be described. The power source of the charging control circuit 7 is basically taken from the external power source 1. The power source of the backflow prevention control circuit 8 is basically taken from the secondary battery 2 because the backflow prevention element 5 is controlled to be turned off when the external power source 1 is not present. However, in the charging control circuit 7, there is a possibility that power is supplied from the secondary battery 2 as necessary, such as an input portion from the secondary battery 2. In addition, it is assumed that the voltage of the secondary battery 2 has dropped to a level at which the backflow prevention control circuit 8 cannot operate. In some cases, the power supply can be switched from the secondary battery 2 to the external power supply 1. In short, it is necessary to devise how to supply power as a whole system. The control circuit 800 of the prior art is the same as the control circuit 8 described above.

  FIG. 2 is an operation waveform diagram showing a change over time when the secondary battery 2 is charged in the charging system according to the first embodiment shown in FIG. The figure shows the input voltage Vi (broken line) of the charging circuit 3, the output voltage of the charging circuit 3, that is, the battery voltage Vb of the secondary battery 2, the charging current Ib to the secondary battery 2, and the output of the first comparator 81. Vc1, the output Vc2 of the second comparator 82, the output of the NAND gate 84, that is, the gate voltage Vg of the backflow prevention element 5 are shown. Hereinafter, the operation of the charging system according to Embodiment 1 of the present invention shown in FIG. 1 will be described with reference to FIG.

  In the period T1 of FIG. 2, the battery voltage Vb of the secondary battery 2 is lower than the first voltage Vb1, but the external power source 1 is not connected or stopped, and the input voltage Vi of the charging circuit 3 is zero voltage or 2 It is in a state lower than the battery voltage Vb of the secondary battery 2. At this time, the output Vc1 of the first comparator 81 is L level, and the output Vc2 of the second comparator 82 is H level. Therefore, the gate voltage Vg of the backflow prevention element 5 becomes H level, and the backflow prevention element 5 that is a P-channel MOSFET is turned off. Thereby, the backflow from the secondary battery 2 is prevented. Since the body diode is in the forward direction with respect to the direction of the charging current, the backflow prevention element 5 naturally prevents the backflow from the secondary battery 2 even in the path of the body diode.

  On the other hand, the charge control circuit 7 does not operate when the external power source is not connected, and does not control the charge control element 4. In this case, since the reverse current in the direction from the secondary battery 2 to the external power source 1 is interrupted by the reverse current element 5, the state of the charge control element 4 is arbitrary. Therefore, the charge control circuit 7 is required to consume current from the input portions at both ends of the current detection resistor 6 when the external power source 1 is not applied and the voltage Vb of the secondary battery 2 is applied. It is only not to do.

  A period T <b> 2 in FIG. 2 is a period of the quick charge mode in which the supply voltage from the external power supply 1 is input to the charging circuit 3. First, since the battery voltage Vb of the secondary battery 2 is lower than the first voltage Vb1, when the supply voltage from the external power source 1 is input to the charging circuit 3, the charging control element 4 is turned on by the charging control circuit 7. The external power supply 1 → the charge control element 4 → the body diode of the backflow prevention element 5 → the current detection resistor 6 → the secondary battery 2 and the charging current flow. At this time, the input voltage Vi of the charging circuit 3 is compared with the battery voltage Vb of the secondary battery 2 at the ON resistance (0.2Ω) of the charge control element 4 and the current detection resistor 6 (resistance value 0.2Ω). The voltage drop (0.4V) due to the constant current output Ib0 (= 1A) of the external power supply 1 and the forward voltage drop (0.7V) of the body diode of the backflow prevention element 5 are added. That is, (Vi = Vb + 1.1V).

  Therefore, since the voltage difference between the input voltage Vi of the charging circuit 3 and the battery voltage Vb of the secondary battery 2 is smaller than the offset voltage Vos (= 1.5 V), the output Vc1 of the first comparator 81 and the second voltage Both outputs Vc2 of the comparator 82 are at the H level. Therefore, the output of the NAND gate 84, that is, the gate voltage Vg of the backflow prevention element 5 becomes L level, and the backflow prevention element 5 which is a P-channel MOSFET is turned on. Even if the backflow prevention element 5 is turned on and the voltage drop due to the on-resistance (0.2Ω) of the backflow prevention element 5 is 0.2 V, the on-resistance of the charge control element 4 and the voltage drop at the current detection resistor 6 In addition, since it is 0.6 V, the output Vc1 of the first comparator 81 and the output Vc2 of the second comparator 82 are both at the H level, and the quick charge mode is maintained.

  In addition, the numerical value in the above description is an example, and is not limited to this numerical value.

  A period T3 in FIG. 2 is a constant current charging mode period in which the charging of the secondary battery 2 has progressed and the battery voltage Vb has become higher than the first voltage Vb1 (= 3 V). When the constant current charging mode is entered, the external power supply 1 leaves the constant current operation of the external power supply 1 and supplies a predetermined output voltage Vi (= 5.5 V). For this reason, a voltage difference of 5.5-3 = 2.5V is generated between the input / output voltages Vi and Vb of the charging circuit 3, which is higher than the offset voltage Vos (= 1.5V). Therefore, the output Vc1 of the first comparator 81 becomes H level, the output Vc2 of the second comparator 82 becomes L level, the gate voltage Vg of the backflow prevention element 5 becomes H level, and the backflow prevention element which is a P-channel MOSFET. 5 is off.

  The charging current Ib is adjusted to a constant current Ib1 (= 0.5 A), and flows from the external power source 1 → the charge control element 4 → the body diode of the backflow prevention element 5 → the current detection resistor 6 → the secondary battery 2. When the forward voltage drop in the body diode of the backflow prevention element 5 is 0.7 V, the power consumption in the backflow prevention element 5 is 0.7 × 0.5 = 0.35 W. On the other hand, since the voltage drop at the current detection resistor 6 is 0.1V, the voltage applied to the charge control element 4 is 2.5−0.7−0.1 = 1.7V. Therefore, the power consumption in the charge control element 4 is 1.7 × 0.5 = 0.85W.

  When the backflow prevention element 5 is in the on state (on resistance 0.2Ω) as in the conventional case, the power consumption in the backflow prevention element 5 is 0.2 × 0.5 × 0.5 = 0.05 W, and charging The applied voltage to the control element 4 was 2.5−0.1−0.1 = 2.3 V, and the power consumption in the charge control element 4 was 2.3 × 0.5 = 1.15 W. . Compared to such a conventional configuration, the backflow prevention element 5 shares the power consumption of 0.3 W, so that the power consumption in the charge control element 4 is reduced.

  In the period T3 of FIG. 2, when the secondary battery 2 is further charged and the battery voltage Vb increases to exceed 4 V, the voltage difference generated between the input and output of the charging circuit 3 is offset voltage Vos (= 1). .5V). Then, the output Vc1 of the first comparator 81 and the output Vc2 of the second comparator 82 both become H level, the gate voltage Vg of the backflow prevention element 5 becomes L level, and the backflow prevention element 5 is turned on. . For this reason, although the power consumption in the backflow prevention element 5 is 0.05 W, the voltage difference between the input and output of the charging circuit 3 is also reduced to 1.5 V. Therefore, the voltage applied to the charging control element 4 is 1. 3V and power consumption is 0.65W.

  A period T4 in FIG. 2 is a constant voltage charging mode in which the battery voltage Vb of the secondary battery 2 is increased to reach the second voltage Vb2 (= 5 V). The charging current Ib is a small current determined by the voltage difference between the battery voltage Vb of the secondary battery 2 and the net battery voltage Vbx and the internal resistance of the secondary battery 2. When this current falls below a predetermined value of several tens of mA, the charging operation is terminated and overcharging is prevented. At this time, both the output Vc1 of the first comparator 81 and the output Vc2 of the second comparator 82 are at the H level, and the backflow prevention element 5 is in the ON state.

  As described above, during constant current charging by the charging control element 4, when the voltage difference between the input and output of the charging circuit 3 is large, the backflow prevention element 5 is turned off, causing a voltage drop due to the body diode of the backflow prevention element 5. A part of the power consumption concentrated on the charge control element 4 is also shared with the backflow prevention element 5. As a result, thermal stress is dispersed, and the allowable power of the charge control element 4 can be reduced and the size can be reduced.

  In the first embodiment, the body diode of the backflow prevention element 5 for preventing the backflow from the output of the charging circuit 3 to the input is used. However, the backflow prevention element 5 is a diode that is forward with respect to the charging current. And may be connected in parallel separately. For example, when a Schottky barrier diode is connected, the forward voltage is smaller than that of the body diode of the backflow prevention element 5, so that most of the current flows through the Schottky barrier diode. Fever can be shared. When a silicon PN junction diode is used, the forward voltage is almost equal to that of the body diode of the backflow prevention element 5, so that the current is distributed according to the size of the body diode and the heat generation is dispersed.

(Embodiment 2)
The charging system according to Embodiment 1 of the present invention has a simple configuration, but the voltage application to the backflow prevention element is up to a voltage drop (about 0.7 V) due to the body diode, so that sufficient power distribution cannot be performed. There is. The charging system according to Embodiment 2 described below can improve the effect of power distribution by adding a little more control.

  Here, differences from the first embodiment will be described. Also in the second embodiment, the state of the backflow prevention element is changed. However, it is different in that the change in state is not only two states, on and off, but continuous. In the first embodiment, when the backflow prevention element 5 is turned on, a voltage corresponding to a voltage drop due to an on-resistance is generated, and when it is turned off, a voltage corresponding to a body diode is generated. On the other hand, in the second embodiment, the on-resistance is continuously controlled by changing the gate voltage of the backflow prevention element 5, and any voltage other than the forward voltage of the diode is generated in the backflow prevention element 5 portion. By doing so, the power consumption in the backflow prevention element 5 is controlled. Therefore, depending on conditions, it is an obstacle to connect the body diodes in parallel. The back gate voltage setting circuit 10 is for invalidating the body diode of the backflow prevention element 5.

  FIG. 3 shows a circuit configuration of a charging system according to Embodiment 2 of the present invention.

  In FIG. 3, the same reference numerals are given to the same configurations as those of the charging system according to Embodiment 1 shown in FIG. 1, and the description thereof is omitted. The charging system according to Embodiment 2 shown in FIG. 3 is different from the charging system according to Embodiment 1 shown in FIG. 1 in that a backflow prevention element 9 is connected instead of the backflow prevention element 5 in FIG. A back gate voltage setting circuit 10 and an on-voltage control circuit 11 are added in place of the backflow prevention control circuit 8.

  Here, the operating power supply of the charge control circuit 7 is basically taken from the external power supply 1. The back gate voltage setting circuit 10 and the on-voltage control circuit 11 are basically taken from the secondary battery 2. However, when the back gate voltage control of the backflow prevention element 5 is performed as in this embodiment, it is necessary to devise a circuit for how to supply power to the back gate voltage setting circuit 10.

  The backflow prevention element 9 is the same P-channel MOSFET as the backflow prevention element 5 of FIG. 1, but the backgate voltage can be switched by the backgate voltage setting circuit 10, and not only as a switch by the on-voltage control circuit 11. The impedance can also be adjusted.

  In FIG. 3, the back gate voltage setting circuit 10 compares the input / output voltage of the charging circuit 3 with the comparator 101, and the back gate of the backflow prevention element 9 according to the output of the comparator 101. The switch 102 is connected to the higher one of Vi and Vb.

  The on-voltage control circuit 11 is a series circuit of a diode 111, a resistor 112, a resistor 113, and a diode 114 connected between the source of the charge control element 4 and the connection point of the backflow prevention element 9 and the current detection resistor 6. And an operational amplifier 115. The operational amplifier 115 receives the potential at the connection point between the resistors 112 and 113 and the potential at the connection point between the charge control element 4 and the backflow prevention element 9 in the series circuit. The resistance values of the resistor 112 and the resistor 113 are set equal. The diode 111 and the diode 114 prevent backflow.

  First, the operation when the external power supply 1 is connected and the charging circuit 3 is supplied with an input voltage Vi higher than the battery voltage Vb of the secondary battery 2 will be described. At this time, since the comparator 101 outputs the H level in the back gate voltage setting circuit 10, the switch 102 applies the input voltage Vi of the charging circuit 3 as the back gate voltage of the backflow prevention element 9. That is, the backflow prevention element 9 has a configuration of a P-channel MOSFET connected in series with the charge control element 4 in the same direction.

On the other hand, in the on-voltage control circuit 11, an intermediate potential of the series circuit of the charge control element 4 and the backflow prevention element 9 is generated at the connection point between the resistor 112 and the resistor 113. The operational amplifier 115 adjusts the gate potential of the backflow prevention element 9 so that this intermediate potential is equal to the connection point potential of the charge control element 4 and the backflow prevention element 9. As a result, the voltage applied to the charge control element 4 and the voltage applied to the backflow prevention element 9 are equal, and the power consumption due to the charging current is also equal. For example, if the charging current Ib = 0.5 A, the input voltage Vi of the charging circuit 3 is 5.5 V, the battery voltage Vb of the secondary battery 2 is 3 V, and the voltage drop of the current detection resistor 6 is 0.1 V, the charging control element 4 and the backflow prevention element 9,
0.5 × (5.5-3-0.1) /2=0.6W
It becomes. This relationship is maintained in the charging operation in which the input voltage Vi of the charging circuit 3 is higher than the battery voltage Vb of the secondary battery 2, and the power of the charge control element 4 and the backflow prevention element 9 is ideally shared. As a result, thermal stress is dispersed, and the allowable power of the charge control element 4 can be reduced and the size can be reduced.

  Next, the operation when the input voltage Vi of the charging circuit 3 is lower than the battery voltage Vb of the secondary battery 2 because the external power source 1 is not connected or stopped will be described. At this time, since the comparator 101 outputs L level in the back gate voltage setting circuit 10, the switch 102 applies the output voltage Vb of the charging circuit 3 to the back gate voltage of the backflow prevention element 9. That is, the backflow prevention element 9 has a configuration of a P-channel MOSFET connected to the charge control element 4 so as to face each other. This configuration is the same as the configuration of the conventional example and the backflow prevention element of the first embodiment.

  On the other hand, in the on-voltage control circuit 11, the diode 111 and the diode 114 are in an open state due to the reverse voltage, but the charging control element 4 is connected to the connection point of the resistor 112 and the resistor 113 due to their parasitic capacitance and leakage current. And the intermediate potential of the series circuit of the backflow prevention element 9 is generated. The charging control circuit 7 adjusts the impedance of the charging control element 4 in order to flow a charging current. When the input voltage Vi of the charging circuit 3 is low, it is not possible to sufficiently apply the gate voltage to the charging control element 4, but charging is performed because the body diode of the charging control element 4 exists in the forward direction with respect to the external power supply 1. As a result, the connection point potential between the control element 4 and the backflow prevention element 9 becomes a value close to the input voltage Vi of the charging circuit 3. Therefore, the operational amplifier 115 outputs the H level, and the backflow prevention element 9 is turned off. The body diode of the backflow prevention element 9 is in a direction to prevent backflow from the secondary battery 2 by the back gate voltage setting circuit 10, and the backflow prevention element 9 is in the off state, so that backflow is prevented.

  In the charging system according to the second embodiment, the applied voltages of the charging control element 4 and the backflow prevention element 9 are equal during charging, that is, the power consumption is equally shared. However, the present invention is not limited to this sharing. Absent. The heat sharing may be set to a ratio other than 1: 1 in consideration of the heat radiation performance depending on the shape and size of each of the charge control element 4 and the backflow prevention element 9.

  In the charging system of the second embodiment shown in FIG. 3, the back gate voltage setting circuit 10 connects the back gate of the backflow prevention element 9 to the input or output of the charging circuit 3, but the present invention is limited to this configuration. Is not to be done. For example, when the input voltage Vi of the charging circuit 3 is higher than the battery voltage Vb of the secondary battery 2, the back gate of the backflow prevention element 9 is connected to the connection point between the charge control element 4 and the backflow prevention element 9. If the input voltage Vi of the charging circuit 3 is lower than the battery voltage Vb of the secondary battery 2, the back gate of the backflow prevention element 9 is connected to the connection point between the current detection resistor 6 and the backflow prevention element 9. Also good.

  In short, when the input voltage Vi of the charging circuit 3 is higher than the battery voltage Vb of the secondary battery 2, the back gate voltage setting circuit 10 uses the same body diode as that of the charging control element 4 by shortcutting the body diode in the direction of preventing the backflow. When the input voltage Vi of the charging circuit 3 is lower than the battery voltage Vb of the secondary battery 2, the charging control element 4 is opposed to take advantage of the body diode in the direction of preventing reverse flow. That's fine.

(Embodiment 3)
FIG. 4 shows a circuit configuration of a charging system according to Embodiment 3 of the present invention.

  In FIG. 4, the same reference numerals are assigned to the same configurations as those of the charging system according to Embodiment 2 shown in FIG. 2, and the description thereof is omitted. The charging system according to Embodiment 3 shown in FIG. 4 is different from the charging system according to Embodiment 2 shown in FIG. 3 in the following points.

  When the input voltage Vi of the charging circuit 3 is lower than the battery voltage Vb of the secondary battery 2, in order to perform the backflow prevention operation by reliably turning off the backflow prevention element 9, for example, as shown in FIG. When the comparator 101 in the setting circuit 10 outputs an L level, a circuit for turning off the backflow prevention element 9 in preference to the operation of the on-voltage control circuit 11 is added.

  In FIG. 4, the switch 116 connects the gate of the control element 9 to the output of the on-voltage control circuit 11 when the output of the comparator 101 is at the H level, and switches the control element 9 when the output of the comparator 101 is at the L level. The gate is connected to the output of the charging circuit 3.

  With this configuration, when the input voltage Vi of the charging circuit 3 is lower than the battery voltage Vb of the secondary battery 2, the backflow prevention element 9 can be reliably turned off. Other effects are the same as those of the second embodiment.

(Embodiment 4)
In the charging system of each embodiment of the present invention described above, the system is configured with the negative electrode of the secondary battery 2 as the common potential, but it goes without saying that the positive electrode of the secondary battery 2 can also be configured as the common potential.

  For example, when the charging system is configured with the positive electrode of the secondary battery 2 as a common potential corresponding to the configuration of the first embodiment of the present invention, the configuration is as shown in FIG. Although a detailed description is omitted, the charging circuit 30 includes a charge control element 40 made of an N-channel MOSFET, a backflow prevention element 50 made of an N-channel MOSFET, a current detection resistor 60, a charge control circuit 70, and a backflow prevention control. Circuit 80.

  The backflow prevention control circuit 80 includes a first comparator 801, a second comparator 802, a voltage source 803 having an offset voltage Vos (= 1.5 V), and an AND gate 804. In the backflow prevention control circuit 80, in the first comparator 801, the input voltage (−Vi) of the charging circuit 30 is input to the inverting input terminal, and the output voltage (−Vb) of the charging circuit 30 is input to the non-inverting input terminal. The In the second comparator 802, the input voltage (−Vi) of the charging circuit 30 is input to the non-inverting input terminal, and the offset voltage (Vos) of the voltage source 803 from the output voltage (−Vb) of the charging circuit 30 (= 1. A voltage (−Vb−Vos) obtained by subtracting 5V) is input to the inverting input terminal. Each output of the first comparator 801 and the second comparator 802 is input to the AND gate 804, and the output is given to the gate terminal of the backflow prevention element 50 formed of an N-channel MOSFET. That is, with respect to the circuit configuration of FIG. 1, the P-channel MOSFET becomes an N-channel MOSFET, the offset voltage is subtracted from addition, the input of the comparator is reversed, and the NAND gate becomes an AND gate.

  Similarly, FIG. 6 shows a charging system in which the positive electrode of the secondary battery 2 is configured as a common potential corresponding to the second embodiment of the present invention described with reference to FIG. 6, the on-voltage control circuit 110 corresponding to the on-voltage control circuit 11 shown in FIG. 3 is used, but the two elements of the diode 1104 and the diode 1101 have opposite polarities to those in FIG. . Further, the back gate voltage setting circuit 100 having the comparator 1001 whose input is inverted corresponds to the comparator 101 of the back gate voltage setting circuit 10 of the backflow prevention element of FIG. This is because it is necessary to connect the back gate of the backflow prevention element 90 in FIG. 6 to the lowest potential of the circuit in response to setting the back gate potential of the backflow prevention element 9 in FIG. 3 to the maximum potential of the circuit. is there. Reference numeral 1002 denotes a switch corresponding to the switch 102.

  Further, FIG. 7 shows a charging system in which the positive electrode of the secondary battery 2 is configured as a common potential corresponding to the third embodiment of the present invention described with reference to FIG. This configuration also has a portion of polarity inversion as in FIGS. 5 and 6, but the basic operation is the same as in FIG.

  5, 6, and 7, a switch 703 is illustrated as a switch corresponding to the charge control circuit switching switch 73 for switching between constant current charging and constant voltage charging in FIGS. 1, 3, and 4. As a switch corresponding to the maximum value circuit described in the configuration example of the changeover switch 73, the switch 703 uses a minimum value circuit. This is because the polarity of the gate voltage that controls the charge control element 40 is inverted.

  In addition to the MOSFET, for example, a combination of a mechanical switch and a diode (parallel circuit) configured by MEMS technology (micromachine technology) can be considered as the backflow prevention element. The switch may be an electromagnetic relay. It is only necessary to have a low resistance switch and a voltage generating element (in this case, a diode) for generating heat “intentionally” under certain conditions when conducting in the backflow prevention element portion. The gist of the present invention is to distribute power by causing a part of the power concentrated on other elements (charge control elements) to take over the backflow prevention elements.

  As described above, the present invention is useful as a series regulator type charging system.

It is a circuit block diagram of the charging system which concerns on Embodiment 1 of this invention. It is an operation | movement waveform diagram of the charging system which concerns on Embodiment 1 of this invention. It is a circuit block diagram of the charging system which concerns on Embodiment 2 of this invention. It is a circuit block diagram of the charging system which concerns on Embodiment 3 of this invention. It is a circuit block diagram of the charging system which concerns on Embodiment 4 of this invention. It is a circuit block diagram of the charging system which concerns on Embodiment 4 of this invention. It is a circuit block diagram of the charging system which concerns on Embodiment 4 of this invention. It is a circuit block diagram of the conventional series regulator type charging system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 External power supply 2 Secondary battery 3 Charging circuit 4 Charging control element 5 Backflow prevention element 6 Current detection resistor 7 Charging control circuit 71 Reference voltage source for charging state switching 72 Battery voltage detecting comparator 73 Charging control circuit switching switch 74 Constant current Operational amplifier for charging control 75 Reference voltage source for constant current charging 76 Operational amplifier for constant voltage charging control 77 Reference voltage source for constant voltage charging 8 Backflow prevention control circuit 81 First comparator 82 Second comparator 83 Offset voltage source 84 NAND gate

Claims (7)

An external power source, a secondary battery, and a series regulator type charging circuit that receives power from the external power source at an input terminal and outputs a charging current from an output terminal to the secondary battery;
The charging circuit includes a charge control element that adjusts a charging current to the secondary battery in a charging path from the external power source to the secondary battery, and a backflow prevention that can control the magnitude of the voltage generated at both ends of the element when conducting. With the element in series,
The said backflow prevention element is a charging system which interrupts | blocks the backflow of an electric current from the said secondary battery to the said input terminal, and has the operation state which shows predetermined | prescribed impedance at the time of charge. The backflow prevention element is a MOSFET whose body diode is in a forward direction with respect to a charging current, and the charging circuit has a backflow prevention control circuit for controlling the backflow prevention element,
The backflow prevention control circuit turns on the backflow prevention element when the absolute value of the input voltage of the charging circuit is within a predetermined range equal to or larger than the absolute value of the output voltage of the charging circuit, and is outside the predetermined range. The charging system according to claim 1, wherein the backflow prevention element is turned off.   The charging system according to claim 2, wherein a diode that is forward with respect to a charging current is connected in parallel with the backflow prevention element.   The predetermined range higher than the absolute value of the output voltage of the charging circuit is the absolute value of the output voltage of the charging circuit, the absolute value of the output voltage of the charging circuit, The charging system according to claim 2, wherein the charging system is between a voltage value equal to or higher than a voltage value obtained by adding a forward voltage drop. The backflow prevention element is a MOSFET, and the charging circuit includes a backgate voltage setting circuit that sets a backgate voltage of the backflow prevention element, and an on-voltage control circuit that adjusts a drain-source voltage of the backflow prevention element And
The back gate voltage setting circuit includes a comparator that compares an absolute value of an input voltage and an absolute value of an output voltage of the charging circuit, and a back gate of the backflow prevention element based on an output of the comparator. A switch connected to the larger absolute value of the input voltage and the output voltage of
The on-voltage control circuit adjusts the drain-source voltage of the backflow prevention element to a predetermined value when the absolute value of the input voltage of the charging circuit is greater than or equal to the absolute value of the output voltage of the charging circuit. The charging system according to claim 1.   The charging system according to claim 5, wherein the predetermined value is a voltage value of a predetermined magnification of a drain-source voltage of the charge control element.   The charging system according to claim 5, wherein the predetermined value is a voltage equal to a drain-source voltage of the charge control element.

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