JP2015204705A - Charge control circuit and method, and charging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten an entire charging time by performing constant voltage charge at high speed while keeping a battery voltage of a secondary battery equal to or lower than a rating voltage.SOLUTION: A charge control circuit is configured to perform charge control from a DC power source to the secondary battery with constant current charge by a constant current charging circuit or constant voltage charge by a constant voltage charging circuit. The charge control circuit includes: a threshold voltage generation circuit which outputs a threshold voltage for switching between the constant current charge and the constant voltage charge; a charging method switching circuit which compares the threshold voltage with an anode voltage of the secondary battery and switches between the constant current charge and the constant voltage charge on the basis of a comparison result; and a threshold voltage regulation circuit for regulating the threshold voltage on the basis of a charging current in charging the secondary battery. The threshold voltage regulation circuit regulates the threshold voltage in such a manner that the threshold voltage and an output voltage of the constant voltage charging circuit are made rise by a voltage obtained by converting the charging current into a voltage drop caused by internal resistance or wiring resistance of the secondary battery, while keeping the battery voltage of the secondary battery equal to or lower than the predetermined rating voltage.

Description

  The present invention relates to a charge control circuit and method, and more particularly, to a charge control circuit and method for charging a secondary battery with constant current and constant voltage, and a charging device.

  In recent years, with the widespread use of mobile electronic devices, shortening the charging time of secondary batteries has become a major issue. Charging of a secondary battery composed of a lithium ion battery or the like is generally performed using a combination of a constant current and a constant voltage in order to keep the battery voltage below the rating. According to this charging method, constant current charging with constant current control current is performed from the start of charging until the voltage of the secondary battery reaches a predetermined threshold voltage, and after reaching the threshold voltage, the constant voltage It is already known that a constant voltage charge is performed with a control voltage to reach a full charge. This “threshold voltage” is equal to the fully charged voltage of the secondary battery and is generally determined by the rated voltage of the secondary battery. If a voltage exceeding the rating is applied to the battery, it will cause deterioration.

In such a general constant current and constant voltage method, the constant current charging is completed in a relatively short time (for example, 1 hour) (charging rate 90%). However, it takes many times (for example, 5 hours) the time required for constant current charging until the battery voltage exceeds the threshold voltage _Vth to change to constant voltage charging and the battery reaches a fully charged state. This is because when the battery voltage approaches the full charge voltage, the charging current flowing to the secondary battery is limited by the difference between the voltage of the constant voltage control and the battery voltage and the internal resistance of the secondary battery, and the charging rate is slightly increased. This is because it takes a long time. Therefore, the general charging method using a constant current and a constant voltage has a problem that it takes a long time for the voltage of the secondary battery to reach a fully charged voltage.

  In Patent Document 1, for the purpose of shortening the charging time, even after the battery voltage exceeds a threshold value due to constant current charging, constant current charging is performed for a fixed time period to reduce the time for constant voltage charging. A configuration is disclosed. However, the problem that the constant voltage charging method takes time as long as the conventional method has not been solved. In addition, this method cannot solve the problem that the charging time cannot be sufficiently shortened when the variation of the capacitor of the secondary battery is large or when the charging time is set in consideration of the deterioration of the battery.

  The object of the present invention is to solve the above-mentioned problems and to perform constant voltage charging at high speed while keeping the battery voltage of the secondary battery below the rated voltage, thereby reducing the overall charging time. An object of the present invention is to provide a charge control circuit that can be used.

A charge control circuit according to the present invention is a charge control circuit that performs charge control from a DC power source to a secondary battery by either constant current charging by a constant current charging circuit or constant voltage charging by a constant voltage charging circuit,
A threshold voltage generation circuit that outputs a threshold voltage for switching between constant current charging and constant voltage charging;
A charging method switching circuit that compares the threshold voltage and the anode voltage of the secondary battery, and switches between constant current charging and constant voltage charging from the comparison result;
A threshold voltage adjustment circuit for adjusting the threshold voltage based on a charging current when charging the secondary battery,
The threshold voltage adjustment circuit maintains the battery voltage of the secondary battery at a predetermined rated voltage or less, and converts the threshold voltage and the output voltage of the constant voltage charging circuit from the charging current to the secondary battery, respectively. The threshold voltage is adjusted so as to increase by a voltage converted into a voltage drop due to the internal resistance and wiring resistance.

  Therefore, according to the charge control circuit of the present invention, the entire charging time can be shortened by performing constant voltage charging at high speed while keeping the battery voltage of the secondary battery below the rated voltage. In addition, the charging time can be shortened regardless of variations in capacity values of secondary batteries and a decrease due to deterioration.

It is a block diagram which shows the structure of the charging circuit containing the charge control circuit which concerns on one Embodiment of this invention. FIG. 2 is a circuit diagram showing a detailed configuration of a part of the charge control circuit of FIG. 1. FIG. 2 is a circuit diagram showing an equivalent circuit of the secondary battery 20 and the protection circuit 90 of FIG. 1. It is a timing chart of each voltage at the time of charge by a comparative example, patent documents 2, and the charge control circuit concerning an embodiment. 4 is a timing chart of a current Icharge and a voltage Vbat_plus supplied to the secondary battery 20 during charging in the embodiment.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In addition, in each following embodiment, the same code | symbol is attached | subjected about the same component.

  FIG. 3 is a circuit diagram showing an equivalent circuit of the general secondary battery 20 and the protection circuit 90.

In general, a protection circuit 90 is mounted in series with the secondary battery 20 in an electronic device in which the secondary battery is mounted. As shown in FIG. 3, the equivalent circuit of the secondary battery 20 includes a capacitor C _bat and a resistor R _bat , and the equivalent circuit of the protection circuit 90 includes a resistor R _dev . That is, the internal resistance of the circuit mainly includes the internal resistance R _bat (about 150 mΩ to about 200 mΩ) of the secondary battery 20 and the resistance R _dev (about 50 mΩ to about 100 mΩ) of the protection circuit 90. As for the rated voltage, it is necessary to keep the voltage V _bat across the secondary battery 20 in FIG. 3 (hereinafter referred to as the battery voltage) V _bat below the rated voltage. The full charge indicates a state where the voltage V _{bat —} full in FIG. 3 is _increased to the full charge voltage. Further, the normal threshold voltage _Vth is compared with the voltage _{Vbat_plus} in FIG.

Against above-mentioned problems, Patent Document 1, the voltage _{V dev} by the threshold voltage _{V th} switched to constant voltage charging, the voltage drop due to the resistance _{R dev} protection circuit 90, i.e., the charging current _{I charge} × _{R dev} min Is focused on being able to correct. That is, the idea is that constant current charging is possible until the external voltage V _bat — _plus = V _th + I _charge × R _dev . For this purpose, the external voltage V _{bat_plus} is monitored, and after the external voltage V _{bat_plus} exceeds the threshold voltage V _th by constant current charging, constant current charging is performed for a predetermined constant charging time t _i . A method of shortening the constant voltage charging time has been devised. In addition, although there are other resistances that can be corrected, such as wiring resistance, for the sake of simplicity, the description is omitted here as being included in the resistance R _dev .

  This method shortens the constant voltage charge as the constant current charge time becomes longer, so the overall charge time is shortened, but the problem that the speed of the constant voltage charge is not different from the conventional method can be solved. Not.

In order to implement this method, the product specifications of the resistance R _dev of the protection circuit 90 and the capacitance C _bat of the secondary battery 20 are used to correct the voltage V _dev of the protection circuit 90. The charging time t _i needs to be calculated in advance. The charging time t _i, if priority is given to keep the battery voltage below the rated voltage during constant current charging, taking into account the volume reduction caused by deterioration due to variation and the use of the variation and the secondary battery 20 of the protection circuit 90, Must be set to the minimum value. Therefore, the problem that the charging time cannot be sufficiently shortened in many cases has not been solved. The following is a calculation example of the voltage can be corrected with the charging time t _i.

As described above, the voltage V _dev across the protection circuit 90 is expressed by the following equation.

V _dev = R _dev · I _charge (1)

Here, the state where the battery voltage V _bat reaches the threshold voltage V _th, further and ΔQ charging to charge, when the constant current charging time is t _i, charge ΔQ can be expressed by the following equation.

Here, since the charging current _Icharge is a constant value, the following equation is obtained.

C _bat ΔV = I _charge · t _i (3)

  Therefore, the following equation is obtained.

  Therefore, the following equation is obtained from the equations (1) and (4).

t _i = C _bat R _dev (5)

That is, it can be seen that the constant current charging time t _i depends on the capacitor C _bat of the secondary battery 20 as in the above equation (4).

  On the other hand, in one embodiment of the present invention, it is possible to perform constant voltage charging at a higher speed than in the past while keeping the voltage applied to the battery below the rated voltage by simply adding a circuit with a simple configuration. Thus, a charge control circuit capable of shortening the entire charging time is provided.

The charge control circuit according to an embodiment of the present invention is a charge control circuit for charging the secondary battery 20 using a DC voltage or a DC voltage from the DC power supply 10. The charge control circuit includes a constant current charging circuit 30, a constant voltage charging circuit 40, a charging method switching circuit 60, a threshold voltage generating circuit 50, a threshold voltage adjusting circuit 80, and a charging current detecting circuit 70. It is configured with. Here, in the charge control circuit using both constant current charging and constant voltage charging according to the prior art, in particular, the constant voltage charging circuit 40 is configured to output the same voltage as the threshold voltage _Vth . Further, the resistance R _dev in FIG. 3 is assumed to be known. Then, a charging current detection circuit 70 that converts the charging current I _charge into a voltage V _dev (= R _dev × I _charge ), and a threshold voltage V _th that switches from preset constant current charging to constant voltage charging. Then, a threshold voltage generation circuit 50 for adding the voltage V _dev is added. As a result, the constant current control and the constant voltage control are switched at the threshold voltage V _th , that is, V _{bat_plus} = V _th + V _dev . With this configuration, it can be seen that the constant current charging time can be extended and the constant voltage charging time can be shortened. In addition, even after shifting to constant voltage charging, the constant voltage charging circuit outputs the same potential as the threshold voltage, that is, V _th + V _dev , so that a higher voltage than in the conventional method is applied, and at high speed. Can be charged. At these times, since the battery voltage is always controlled by V _bat ≦ V _{bat — plus} −R _dev × I _charge , the battery voltage is kept below the rated voltage.

FIG. 4 is a timing chart of each voltage during charging by the charge control circuit according to the comparative example, Patent Document 2, and the embodiment. FIG. 4 shows in particular the charging current curve and the anode voltage curve of the secondary battery 20 of the present embodiment in these cases. In the charge control circuit according to the present embodiment, compared to the comparative example, the constant current charging is extended only for the interval (Tc2-Tc1), and the constant voltage charging time is started from time Tc2. Furthermore, by setting the output voltage of the constant voltage charging circuit 40 to (V _th + V _dev ) from time Tc2 to time Tv1 (full charge), the general method and Patent Document 1 (Tv2-Tv1) High-speed constant voltage charging is possible only in the section. In addition to the above, with this configuration, it is not necessary to use the battery capacity for calculating the correction voltage. Therefore, the charging time can be shortened regardless of the battery capacity variation and the decrease due to deterioration.

  One embodiment of the present invention will be described below. In this embodiment, in the charge control circuit that performs charge control using both constant current charge and constant voltage charge, the threshold voltage and the constant voltage charge output that are switched during the charge when the control is switched from the constant current control to the constant voltage control. The voltage drop is added to the voltage due to the charging current × the internal resistance of the battery or the like.

  FIG. 1 is a block diagram showing a configuration of a charging circuit including a charging control circuit according to an embodiment of the present invention. FIG. 2 is a circuit diagram showing a detailed configuration of a part of the charge control circuit of FIG.

In FIG. 1, a secondary battery 20, a protection circuit 90, and a charging current detection circuit 70 are connected in series. The charging current detection circuit 70 detects the charging current I _charge and _displays the detection result as a threshold voltage adjustment circuit. Output to 80. Based on the detected charging current _Icharge , the threshold voltage adjusting circuit 80 adjusts the output voltage _Vcompare generated by the threshold voltage generating circuit 50 in proportion to the charging current _Icharge . On the other hand, the constant current charging circuit 30 DC / DC converts the DC power from the DC power supply 10 and charges the secondary battery 20 by constant current charging. The constant voltage charging circuit 40 DC / DC converts DC power from the DC power source 10 and charges the secondary battery 20 by constant voltage charging. The charging method switching circuit 60 uses the operation switching signals SC and SV based on the output voltage V _compare of the threshold voltage generation circuit 50 so as to become one of the following, the constant current charging circuit 30 and the constant voltage charging circuit 40. To control.
(1) The operations of the constant current charging circuit 30 and the constant voltage charging circuit 40 are both turned off.
(2) The operation of the constant current charging circuit 30 is turned on, and the operation of the constant voltage charging circuit 40 is turned off.
(3) The operation of the constant current charging circuit 30 is turned off, and the operation of the constant voltage charging circuit 40 is turned on.
Here, in principle, the charging method switching circuit 60 starts from the constant current charging by the constant current charging circuit 30 when the anode voltage V _{bat — plus} of the secondary battery 20 becomes the output voltage V _compare of the threshold voltage generating circuit 50. Control is performed to switch to constant voltage charging by the voltage charging circuit 40.

  Next, the operation of the charge control circuit of FIG. 1 will be described below.

Charging method switching circuit 60 compares the output voltage _{V The compare} the anode voltage _{V Bat_plus} and the threshold voltage generation circuit 50 of the rechargeable battery _20, when the _V bat_plus _{<V compare} to halt the constant voltage charging circuit 40 The constant current charging circuit 30 charges the battery. Here, when V _{bat — plus} ≧ V _compare , the constant voltage charging circuit 40 charges and the constant current charging circuit 30 is stopped.
(2) The output voltage V _compare of the threshold voltage generation circuit 50 is set in advance to a predetermined threshold voltage _Vth .
(3) The anode voltage V _{bat_plus} of the secondary battery 20 is equal to the voltage V _bat of the secondary battery 20 itself and the internal resistance R _bat × charge current I _{charge that} does not need to be considered in the rated voltage as shown in FIG. It includes the drop V _dev . During charging detects the charging current _{I charge} by the charging current detecting circuit 70, in terms of voltage _{V dev} proportional to the charging current _{I charge} by the threshold voltage adjusting circuit 80, the output voltage _{V compare V compare} = _{V th Raise} to + V _dev . As a result, until the voltage V _bat of the secondary battery 20 itself becomes V _bat = V _th , since V _{bat_plus} <V _compare during that period, the charging method switching circuit 60 selects constant current charging and continues charging. To do.
(4) When the anode voltage V _{bat_plus} of the secondary battery 20 exceeds the output voltage V _compare of the threshold voltage generation circuit 50, the constant voltage charging circuit 40 is operated by the operation switching signals SV and SC of the charging method switching circuit 60. Operates and the constant current charging circuit 30 stops. At this time, the output voltage of the constant voltage charging circuit 40 becomes the same potential as the output voltage V _compare of the threshold voltage generation circuit 50, that is, V _th + V _dev , and a higher voltage is applied compared to the conventional method, so that the high speed is achieved. Can be charged. In short, the threshold voltage V _th for switching from constant current control to constant voltage control during charging and the output voltage of constant voltage charging are respectively the charging current I _charge × the voltage drop due to the internal resistance of the secondary battery 20 or the like. It is characterized by adding. As a result, the secondary battery 20 can be charged up to its rated voltage.

  Furthermore, the Example which concerns on embodiment of this invention is demonstrated below.

  In FIG. 1, a DC power supply 10 supplies a DC power supply to each circuit of FIG. 1, where the voltage is set to 5.0 [V].

Further, the secondary battery 20 has the equivalent circuit of FIG. 3, and the voltage V _bat needs to be kept below the rated voltage. The fully charged state refers to a state in which the voltage V _{bat_full} has increased to the fully charged voltage. Here, during charging of the secondary battery 20, a charging current I _charge flows through the secondary battery 20. The secondary battery 20 is, for example, a lithium ion battery, and the full charge voltage and the rated voltage are both 4.2 [V]. It is assumed that the secondary battery 20 has a resistance R _bat and a resistance R _dev shown in FIG. 3 as internal resistance. The respective resistance values are R _bat = 100 [mΩ] and R _dev = 100 [mΩ].

  The output terminal of the constant current charging circuit 30 is connected to the anode of the secondary battery 20, and generates and outputs a constant current from the DC power supply 10 during operation. During charging, the charging method switching circuit 60 operates when the constant voltage charging circuit 40 is stopped, and stops when the constant voltage charging circuit 40 operates. Here, the current value of constant current charging is 2 [A].

The output terminal of the constant voltage charging circuit 40 is connected to the anode of the secondary battery 20 and generates and outputs a constant voltage from the DC power supply 20 during operation. During charging, the battery is operated or stopped by the operation switching signal SV of the charging method switching circuit 60. The constant voltage charging voltage is connected to the threshold voltage generation circuit 50 and is determined by the output voltage V _compare of the threshold voltage generation circuit 50.

The threshold voltage generation circuit 50 is connected to the threshold voltage adjustment circuit 80 and outputs a comparison voltage V _compare to the charging method switching circuit 60 and the constant voltage charging circuit 40. Although the output voltage V _compare of the threshold voltage generation circuit 50 is set to the threshold voltage V _th in advance, it receives the control signal of the threshold voltage adjustment circuit 80 and generates the output voltage V _compare . Here, the threshold voltage V _{th is set to} 4.2 [V].

As shown in FIG. 2 of the equivalent circuit, the threshold voltage generation circuit 50 is configured by a DA converter and has an output resistance R _dacout . The connection point 52 of the threshold voltage generation circuit 50 is connected to the drain of the MOS transistor Q3 of the threshold voltage adjustment circuit 80. The DA converter via a connection point 52 from the threshold voltage adjustment circuit 80, poured the threshold voltage adjustment current _{I adjust,} constant-voltage charging the output voltage _{V The compare} as _{V compare = V th + R dacout} × I adjust Output to the circuit 40 and the charging method switching circuit 60. Here, R _dacout = 100 [kΩ].

The charging method switching circuit 60 includes a comparator. The pair of input terminals of the comparator is connected to the anode of the secondary battery 20 and the output terminal of the threshold voltage generation circuit 50, and compares the voltage V _{bat_plus} of the anode of the secondary battery with the output voltage V _compare. Thus, the operation switching signal SV is output to the constant voltage charging circuit 40 as described above. The constant voltage charging circuit 40 operates when the operation switching signal SV is at a high level, and stops when the operation switching signal SV is at a low level.

The charging current detection circuit 70 is connected to the secondary battery 20, detects the charging current I _charge, and outputs an output voltage V _sense proportional to the current value to the threshold voltage adjustment circuit 80. The charging current detection circuit 70 includes a resistor R11 as shown in FIG. Here, one end of the resistor R <b> 11 is connected to the connection point 71 of the charging current detection circuit 70, and then connected to the negative electrode of the secondary battery 20 through the protection circuit 90. The other end of the resistor R11 is grounded. The same amount of I _{charge as the} charging current flows through the resistor R11. Further, the connection point 71 is connected to one end of the resistor R2 of the threshold voltage adjustment circuit 80, and the detection voltage _Vsense (= I _charge × R11) is output. Here, the resistance value of the resistor R11 is set to 100 [mΩ].

As shown in FIG. 2, the threshold voltage adjustment circuit 80 includes a reference voltage source 81, four resistors R1 to R4, an operational amplifier OP1, and P channel MOS transistors Q1 to Q3. Here, the input voltage to the threshold voltage adjustment circuit 80 is the detection voltage V _sense from the charging current detection circuit 70, the output current from the threshold voltage adjustment circuit 80 is I _adjust , and the threshold voltage It is output to the generation circuit 50. The threshold voltage adjustment circuit 80 converts the detection voltage V _sens into a current value of the charging current I _charge and outputs a signal indicating an amount for correcting the output voltage V _compare by a voltage drop (R _dev × I _charge) as a threshold. The voltage is output to the voltage generation circuit 50.

The detection voltage V _sense from the charging current detection circuit 70 is applied to the non-inverting input terminal of the operational amplifier OP1 through the resistor R2. Further, the reference voltage source 81 of the threshold voltage adjusting circuit 80 applies the reference voltage _Vadjust to the non-inverting input terminal of the operational amplifier OP1 through the resistor R1 and to the inverting input terminal of the operational amplifier OP1 through the resistor R3. To do. Therefore, the _divided voltage V _inp obtained by dividing the reference voltage V _adjust by the resistors R 1 and R 2 with respect to the detection voltage V _sense is applied to the non-inverting input terminal of the operational amplifier OP 1. On the other hand, a _divided voltage V _inm obtained by dividing the reference voltage V _adjust by the resistors R3 and R4 with respect to the ground voltage is applied to the inverting input terminal of the operational amplifier OP1. The output terminal of the operational amplifier OP1 is connected to the gate of the MOS transistor Q2, and the drain of the MOS transistor Q2 is grounded via the resistor R4. As a result, the MOS transistor Q2 is controlled so that the voltage V _inp and the voltage V _inm have the same potential by feedback control, and the operating current I _op is supplied to the resistor R4. The operating current I _op of the MOS transistor Q2 is supplied from the MOS transistor Q1 connected to its source.

The MOS transistors Q1 and Q3 constitute a current mirror circuit, and the MOS transistor Q3 uses a current of I _op × (size ratio M _Q of Q1 and Q3) as a threshold voltage adjustment current _Iadjust , and a threshold voltage generation circuit Output to 50.

A formula for _obtaining I _adjust by summarizing the above operations is shown below. However, since R1 = R3 and R2 = R4 are set in this configuration, R1 = R3 = R _top and R2 = R4 = R _bottom are set.

  The following equation is obtained from FIG.

Here, since the operational amplifier OP1 operates so that V _inm = V _inp , the following equation is obtained.

here,
Since I _adjust = M _Q × I _{op, the} following equation is obtained.

Next, in FIG. 2, since it is necessary to determine the size ratio M _Q and the resistances R1, R2, R3, and R4 from the value of the resistance R _dev of the secondary battery 20, an expression for determination is shown below. Here, the voltage V _dev that does not need to be taken into consideration for the rated voltage indicates a voltage drop caused by the resistor R _dev and the resistor R 11, and thus the following equation is obtained.

V _dev = (R _dev + R11) × I _charge (9)

Also,
V _dev = R _dacout × I _adjust (10)
Therefore, the following equation is obtained.

Here, the following equation is obtained from the equation (8).

V _sense = R11 × I _charge
Therefore, the following equation is obtained.

  The above equation is modified to obtain the following equation.

Here, when the values of the resistor R11 and the resistor _Rdacout are substituted for each variable, the following equation is obtained.

Substituting the value of the resistor R _dev into the equation (12) and setting the size ratio M _Q = 8, the following equation is obtained.

From the equation (13), the resistance R _bottom = 300 [kΩ] is substituted into the equation (13), so that R _top = 900 [kΩ]. From the above, the size ratio M _Q = 8, the resistance R1 = R3 = 900 [kΩ], and the resistance R2 = R4 = 300 [kΩ] are determined.

From equation (12), if this method, the resistance values of the resistors R1~R4 and, by varying the size ratio _{M Q,} it can be seen that can change the setting of the resistance _{R dev.} Moreover, it turns out that it is not necessary to calculate the capacity | capacitance of the secondary battery 20 from said series of calculation formulas. Therefore, the secondary battery 20 does not need to be specified.

Next, an operation when the charge control circuit of FIG. 1 is in charge of the secondary battery 20 will be described with reference to FIG. 5 using the circuit of FIG. For each set value, the value described above is used. The voltage V _bat and the voltage V _{bat_full} are shown in FIG.

(S1) Operation when V _{bat — plus} <4.2 [V] (S1-1) The constant current charging circuit 30 charges the secondary battery 20 with a constant current 2 [A].
(S1-2) The charging current detection circuit 70 outputs the detection voltage V _sense = R11 × I _charge = 0.1 × 2 = 0.2 [V] from FIG.
(S1-3) The threshold voltage adjustment circuit 80 outputs an adjustment current _Iadjust of the following equation from the equation (9).

(S1-4) The threshold voltage generation circuit 50 outputs an output voltage V _compare of the following equation.

V _compare
= V _th + I _adjust × R _dacout
= 4.2 + 4 × 10 ⁻⁶ × 100 × 10 ³
= 4.6 [V]

(S1-5) charging method switching circuit 60 because _{V bat_plus <V compare,} and outputs the operation switching signal SV at a low level, the constant voltage charging circuit 40 is stopped. At this time, V _{bat_plus} <4.2 [V], and V _bat is equal to or lower than the rated voltage.

(S2) Operation when V _{bat — plus} ≧ 4.2 [V] and V _bat <4.2 [V] (S2-1) V _{bat — plus} ≧ V _th , but as in (S1-4) In addition, since the output voltage V _compare of the threshold voltage generation circuit 50 is 4.6 [V], constant current charging can be continued.
(S2-2) Operates in the same manner as (S1-1) to (S1-4) above.
(S2-3) At this time, the anode voltage V _{bat — plus} ≧ 4.2 [V] of the secondary battery 20 is obtained, which exceeds the rated voltage. However, the battery voltage V _bat of the secondary battery 20 itself is expressed by the following equation.

V _bat
= V _{bat_plus-} (R _dev + R11) × I _charge

Further, since the battery voltage V _bat = V _bat — _plus −0.4 [V], the battery voltage V _bat is lower than the rated voltage. Therefore, the secondary battery 20 does not deteriorate.

(S3) Operation when V _bat — _plus = 4.6 [V] and V _bat = 4.2 [V] (S3-1) The anode voltage V _bat — _plus of the secondary battery 20 with constant current charging is 4.6 When [V] is reached, the battery voltage V _bat is given by the following equation.
V _{bat
= V bat_plus - (R dev ×} R11) × I charge
= 4.6-0.4
= 4.2 [V]

(S3-2) When the anode voltage V _bat — _plus of the secondary battery 20 exceeds 4.6 [V], the charging method switching circuit 60 outputs the high-level operation switching signal SV because V _{bat — plus} > V _compare. Then, the constant voltage charging circuit 40 is operated. Further, the low-level operation switching signal SC is output to stop the constant current charging circuit 30. Since the output voltage V _compare = 4.6 [V], the constant voltage charging circuit 40 outputs 4.6 [V]. By this operation, the secondary battery 20 can continue to be charged while maintaining the voltage below the rated voltage.

(S3-3) At this time, the anode voltage V _{bat — full} of the secondary battery 20 is expressed by the following equation.

V _{bat_full}
= V _bat -R _bat × I _charge
= 4.2-0.1 × 2
= 4.0 [V]

  Therefore, the secondary battery 20 has not reached the full charge voltage. Therefore, constant voltage charging is further performed.

(S3-4) The charging current _Icharge during constant voltage charging is expressed by the following equation.

I _charge
= (V _{bat_plus} -V _{bat_full} ) / (R _bat + R _dev + R11)

Therefore, when the anode voltage V _{bat_plus} = 4.6 [V] of the secondary battery 20 and the battery voltage V _{bat_full} = 4.0 [V], the constant voltage charging circuit 40 charges at 2 [A].

(S4) Operation when 4.0 [V] <V _{bat_full} <4.2 [V] (S4-1) Further charging continues, for example, when battery voltage V _{bat_full} = 4.01 [V] The charging current I _charge is reduced to 1.97 [A].
(S4-2) At this time, the charging current detection circuit 70 outputs a detection voltage V _sense of the following equation.
V _sense
= R11 × I _charge
= 0.197 [V]

(S4-3) The threshold voltage adjustment circuit 80 outputs an adjustment current _{Iadjust according} to the following equation from equation (9).

(S4-4) The threshold voltage generation circuit 50 outputs an output voltage V _compare of the following equation from the equation of (S1-4).
V _compare
= V _th + I _adjust × R _dacout
= 4.2 + 3.94 × 10 ⁻⁶ × 100 × 10 ³
= 4.594 [V]

(S4-5) Accordingly, the charging current _{I charge is} reduced to I charge = 1.947 [A], the battery voltage _V bat = 4.2 keep [V].
(S4-6) That is, during the constant voltage charging, when the anode voltage V _{bat_full} of the secondary battery 20 increases, the charging current I _charge decreases. As a result, the output voltage V _compare of the threshold voltage generation circuit 50 is reduced, and the output voltage V _{bat_plus} from the constant voltage charging circuit 40 is reduced. This operation is repeated to continue charging while maintaining the battery voltage V _bat = 4.2 [V]. By this operation, the voltage (V _th + V _dev ) can be applied to the anode of the battery while maintaining the rating, and charging can be continued. Therefore, the operation is faster than the constant voltage charging circuit of Patent Document 1 which is a general constant voltage charging circuit. Charging is possible.

(S5) Operation when V _bat — _full = 4.2 [V] (S5-1) When constant voltage charging is further continued, the output voltage V _{bat — plus} of the constant voltage charging circuit 40 is expressed by the following equation.

V _{bat_plus}
= V _{bat_full}
= 4.2 [V]

Accordingly, the charging current _Icharge does not flow and the battery is fully charged.

FIG. 5 is a timing chart of the current I _charge and the voltage V _{bat_plus} supplied to the secondary battery 20 during charging in the embodiment. FIG. 5 shows the _{behavior of} the voltages V _{bat_plus} , V _bat , and V _{bat_full} until charging starts when the anode voltage V _{bat_full} of the secondary battery 20 is 3V and reaches full charge.

In the above embodiment, the correction can resist said the resistance R _de protection circuit. However, in the embodiment, as shown in the determination of the size ratio M _Q and the resistances R1, R2, R3, and R4, the resistance value that can be corrected has a range by making the circuit resistance and the transistor ratio variable. Can do.

  In the above embodiment, although the charge control circuit was demonstrated, this invention is not restricted to this, You may apply to the charging device provided with DC power supply, for example in the charge control circuit.

  As described above, according to the present embodiment, the charging time can be shortened in many secondary batteries by having the configuration of the charging control circuit of FIG. Further, not only the resistance value of the protection circuit 90 but also the resistance value such as the wiring resistance of the resistance substrate can be corrected.

In the present embodiment, the configuration of the charging control circuit of FIG. 1 is used. However, the present invention is not limited to this, and at least the charging current _Icharge may be detected and configured as follows.
(1) The threshold voltage for switching between constant current charging and constant voltage charging is increased by V _dev .
(2) Increase the output voltage of the constant voltage charging circuit 40 by V _dev .
(3) While achieving the above (1) and (2), the voltage V _{bat — full} of the secondary battery 20 is kept below the rated voltage.

  Note that, as described in the embodiment, the capacity of the secondary battery 20 is not necessary for the calculation and thus has a specific effect that it is not necessary to consider.

Summary of embodiments.
The charge control circuit according to the first aspect of the present embodiment is a charge control that controls charging from a DC power source to a secondary battery by either constant current charging by a constant current charging circuit or constant voltage charging by a constant voltage charging circuit. A circuit,
A threshold voltage generation circuit that outputs a threshold voltage for switching between constant current charging and constant voltage charging;
A charging method switching circuit that compares the threshold voltage and the anode voltage of the secondary battery, and switches between constant current charging and constant voltage charging from the comparison result;
A threshold voltage adjustment circuit for adjusting the threshold voltage based on a charging current when charging the secondary battery,
The threshold voltage adjustment circuit maintains the battery voltage of the secondary battery at a predetermined rated voltage or less, and converts the threshold voltage and the output voltage of the constant voltage charging circuit from the charging current to the secondary battery, respectively. The threshold voltage is adjusted so as to increase by a voltage converted into a voltage drop due to the internal resistance and wiring resistance.

The charge control circuit according to the second aspect of the present embodiment is the charge control circuit according to the first aspect, wherein the threshold voltage adjustment circuit is:
By flowing a charging current through a resistor connected in series with the secondary battery, a detection voltage proportional to the charging current is detected,
The detection voltage is compared with a predetermined reference voltage, and when the detection voltage is larger than the reference voltage, a current corresponding to the difference is caused to flow as an adjustment current in the threshold voltage generation circuit. The threshold voltage is adjusted.

The charge control circuit according to a third aspect of the present embodiment is the charge control circuit according to the second aspect, wherein the threshold voltage adjustment circuit is
A reference voltage source for generating the reference voltage;
An operational amplifier for comparing the detection voltage with a predetermined reference voltage;
A first transistor constituting a current source for supplying a predetermined current;
A second transistor for controlling a current from the current source based on an output voltage of the operational amplifier;
A current mirror circuit configured by the first transistor and the third transistor, the current mirror circuit including a current mirror circuit that supplies a current corresponding to a current flowing through the second transistor as the adjustment current. To do.

10 ... DC power supply,
20 ... secondary battery,
30 ... constant current charging circuit,
40 ... constant voltage charging circuit,
50: Threshold voltage generation circuit,
51 ... Reference voltage source,
52 ... Connection point,
60: Charging method switching circuit,
70: Charging current detection circuit,
71 ... Connection point,
80... Threshold voltage adjustment circuit,
81: Reference voltage source,
90 ... protection circuit,
C _bat ... capacitor
OP1 ... operational amplifier,
Q1-Q3 ... MOS transistors,
_{R1~R4, R11, R bat, R} dacout, R dev ... resistance.

JP-A-6-0325794 JP 2004-274874 A

Claims (5)

A charge control circuit that controls charging from a DC power source to a secondary battery by either constant current charging by a constant current charging circuit or constant voltage charging by a constant voltage charging circuit,
A threshold voltage generation circuit that outputs a threshold voltage for switching between constant current charging and constant voltage charging;
A charging method switching circuit that compares the threshold voltage and the anode voltage of the secondary battery, and switches between constant current charging and constant voltage charging from the comparison result;
A threshold voltage adjustment circuit for adjusting the threshold voltage based on a charging current when charging the secondary battery,
The threshold voltage adjustment circuit maintains the battery voltage of the secondary battery at a predetermined rated voltage or less, and converts the threshold voltage and the output voltage of the constant voltage charging circuit from the charging current to the secondary battery, respectively. A charge control circuit, wherein the threshold voltage is adjusted so as to increase by a voltage converted into a voltage drop due to the internal resistance and wiring resistance of the circuit. The threshold voltage adjustment circuit is
By flowing a charging current through a resistor connected in series with the secondary battery, a detection voltage proportional to the charging current is detected,
The detection voltage is compared with a predetermined reference voltage, and when the detection voltage is larger than the reference voltage, a current corresponding to the difference is caused to flow as an adjustment current in the threshold voltage generation circuit. 2. The charge control circuit according to claim 1, wherein the threshold voltage is adjusted. The threshold voltage adjustment circuit is
A reference voltage source for generating the reference voltage;
An operational amplifier for comparing the detection voltage with a predetermined reference voltage;
A first transistor constituting a current source for supplying a predetermined current;
A second transistor for controlling a current from the current source based on an output voltage of the operational amplifier;
A current mirror circuit configured by the first transistor and the third transistor, the current mirror circuit including a current mirror circuit that supplies a current corresponding to a current flowing through the second transistor as the adjustment current. The charge control circuit according to claim 2.   A charging device comprising the charge control circuit according to claim 1. A charge control method for controlling charging from a DC power source to a secondary battery by either constant current charging by a constant current charging circuit or constant voltage charging by a constant voltage charging circuit,
A threshold voltage generation circuit that outputs a threshold voltage for switching between constant current charging and constant voltage charging;
A charging method switching circuit that compares the threshold voltage and the anode voltage of the secondary battery, and switches between constant current charging and constant voltage charging from the comparison result;
In a charge control method for a charge control circuit comprising a threshold voltage adjustment circuit for adjusting the threshold voltage based on a charging current when charging the secondary battery,
While the threshold voltage adjustment circuit maintains the battery voltage of the secondary battery below a predetermined rated voltage, the threshold voltage and the output voltage of the constant voltage charging circuit are respectively changed from the charging current to the secondary battery. A charge control method comprising the step of adjusting the threshold voltage so as to increase by a voltage converted into a voltage drop due to the internal resistance and wiring resistance.

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