JP3331777B2 - Charging circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging circuit.
The present invention relates to a charging circuit for charging a battery with a specified current.

[0002]

2. Description of the Related Art FIG. 6 shows a configuration diagram of a conventional charging circuit 70 as an example. The charging circuit 70 is a circuit for charging the battery BT to a specified voltage, and includes a PNP output transistor Q
_71, NPN-type control transistor Q _72, external resistor R _D charging current detection amplifier 74 and resistors R _21, consisting of R ₂₂ amplifier circuit 73, the switch S _W11, the current control circuit 75,7
6. _Consisting of a constant current source 79 for a constant current _IS79 , a comparator 77 for switching the switch _SW11, and a comparator 78 for stopping charging. The portion of the charging circuit 70 other than the external resistor _RD is configured as, for example, an integrated circuit.

[0003] A current control circuit 75 is a circuit for low current charging, and a current control circuit 76 is a circuit for rapid charging.

The input voltage V _IN is supplied via an input terminal 81 to
It is supplied to the emitter of the output transistor Q _71. An output terminal connected to the collector of the output transistor Q ₇₁ 82
Is connected to the positive electrode of the battery BT,
The negative electrode of T is grounded via an external resistor _RD .

A charging current I _BAT flows from the collector of the output transistor Q ₇₁ to the battery BT. A voltage drop (detection voltage) is proportional to the charging current I _BAT across the resistor _RD.
Occurs. This detection voltage is amplified by the amplifier circuit 73.

[0006] In the charging circuit 70 performs low-current charging when the battery voltage V _BAT is less than the reference voltage V _r13, perform quick charge when the following reference voltage V _r14 to stop the reference voltage V _r13 or more and charging. Therefore, as will be described later, the current control circuits 75 and 76 are switched by the battery voltage V _BAT to switch the charging current I _BAT .

A battery monitoring circuit provided separately from the charging circuit 70 monitors the battery voltage V _BAT at the time of low current charging and at the time of rapid charging to determine whether the state of the battery BT is normal or abnormal. it can. Thus, in order to determine the quality of the battery BT, a two-stage charging current is provided.

When the voltage V _{BAT of the} battery BT is equal to the reference voltage V
_If it is less than _{r13, the} switch S
_W11 is controlled, and the contact of the switch _SW11 is connected to the terminal a. At this time, the detection voltage detected by the resistor _RD is amplified by the amplifier circuit 73 and supplied to the non-inverting input terminal of the current control circuit 75.

The current control circuit 75 generates an output current proportional to the difference between the voltage at the non-inverting input terminal and the reference voltage _{Vr11 at} the inverting input terminal. The polarity of the output current is such that it flows into the output terminal when the non-inverting input terminal side is positive with respect to the inverting input terminal. When the voltage at the non-inverting input terminal is lower than the reference voltage _{Vr11 at the} inverting input terminal, no output current flows.

[0010] In the output current of the constant current I _S79 and the current control circuit 75 of the constant current source 79, and controls the base current of the transistor Q _72, which determines the collector current of the transistor Q _71.

[0011] The current control circuit 75 compares the voltage with a reference voltage V _r11 is amplified by the amplifier circuit 73, and controls the charging current I _BAT by controlling the base current of the transistor Q _72.

FIG. 7 shows the battery voltage V _BAT and the charging current I.
It is a characteristic view which shows the relationship of _BAT . As shown in the figure, the value of the reference voltage V _r11 is set so that when the voltage V _BAT of the battery BT is lower than the reference voltage V _r13 , low-current charging is performed at I _BAT = I _BAT11. .

When the voltage V _{BAT of the} battery BT is equal to the reference voltage V
_{When r13} or more, the switch S
_W11 is controlled, and the contact of switch _SW11 is connected to terminal b. At this time, the detection voltage detected by the resistor _RD is amplified by the amplifier circuit 73 and supplied to the non-inverting input terminal of the current control circuit 76.

The current control circuit 76 controls the output current by comparing the voltage at the non-inverting input terminal with the reference voltage _Vr12 at the inverting input terminal. The polarity of the output current is such that it flows into the output terminal when the non-inverting input terminal side is positive with respect to the inverting input terminal. When the voltage at the non-inverting input terminal is lower than the reference voltage _{Vr12 at the} inverting input terminal, no output current flows.

[0015] the difference between the output current of the constant current I _S79 and the current control circuit 76 of the constant current source 79 current becomes a base current of the transistor Q _72, the collector current of the transistor Q ₇₂ is,
It serves as a base current of the output transistor Q _71.

The current control circuit 76 compares the voltage with a reference voltage V _r12 is amplified by the amplifier circuit 73, and controls the charging current I _BAT by controlling the base current of the transistor Q _72.

As shown in FIG. 7, the voltage V of the battery BT
_{When BAT} is equal to or higher than the reference voltage _Vr13 , I _BAT = I
In _BAT12, so quick charging is performed, the reference voltage V _r12
Is set.

[0018] The comparator 78 compares the reference voltage V _r14 and the battery voltage V _BAT, a current output type comparator. When the battery voltage V _BAT does not reach the reference voltage V _r14 , the output terminal of the comparator 78 is open, and no output current flows into the output terminal. In this case, as described above, rapid charging by a low current charging or I _BAT12 by I _BAT11 performed.

When the battery voltage V _BAT reaches the reference voltage V _r14 , all the current I _S79 from the constant current source 79 flows into the output terminal of the comparator 78, and the transistor Q ₇₂
Becomes zero. As a result, I _BAT = 0, and charging is stopped.

[0020]

As described above, the conventional charging circuit 70 of FIG. 6 requires an external current detection resistor _RD to detect the charging current I _BAT . For this reason, there is a problem that the number of parts increases and the occupied space increases. In addition, a high-precision resistor is required for the external resistor _RD , which increases the cost.

In addition, it is necessary to provide a high-precision amplifier circuit 73, which complicates the circuit configuration and raises the cost.

The present invention has been made in view of the above points, and has as its object to provide a charging circuit which does not require a current detecting resistor and can simplify a circuit configuration.

[0023]

[0024]

[0025]

According to a first aspect of the present invention, there is provided a charging circuit, comprising: an output transistor for supplying a charging current to a secondary battery; the output transistor having a base and an emitter commonly connected; An area ratio is set, a charging current output from the output transistor and a current detection transistor that outputs a detection current of a predetermined ratio, and a current corresponding to a set value of the charging current according to a voltage value of the secondary battery. A current compression ratio switching circuit for switching a compression ratio and outputting a compression current obtained by compressing a detection current supplied from the current detection transistor at the current compression ratio, a compression current supplied from the current compression ratio switching circuit, An error current detection circuit that generates an error current corresponding to a difference from the current value; and an error current supplied from the error current detection circuit. And generate output transistor drive current has a structure in which an output transistor driving circuit for supplying to said output transistor.

The invention of claim 2 is the charging circuit according to claim 1, further compares the voltage with a reference voltage of the secondary battery, when the voltage of the secondary battery reaches the reference voltage ,
A charge stop circuit for controlling the output transistor drive current to stop charging is provided.

[0027]

[0028]

[0029]

[0030]

According to the first aspect of the present invention, since the charging current is detected by the current detecting transistor, there is no need to provide a current detecting resistor in series with the secondary battery.

Further, unlike the conventional circuit, a high-precision amplifier circuit for amplifying the detection voltage detected by the current detection resistor is not required. Also, by changing the current compression ratio of the current compression ratio switching circuit having a simple circuit configuration in accordance with the voltage value of the secondary battery, the set value of the charging current can be switched, and the error current detection circuit is an extremely simple circuit. It can be realized by the configuration. Therefore, the circuit configuration can be simplified as compared with the conventional configuration in which a plurality of current control circuits are switched.

According to the second aspect of the present invention, when the voltage of the secondary battery reaches the reference voltage, the charging stop circuit can control the output transistor drive current to stop charging.

[0033]

FIG. 1 shows a charging circuit 10 according to a first embodiment of the present invention.
FIG. The charging circuit 10 is a circuit for charging a battery BT (secondary battery) such as a lithium ion battery to a specified voltage. The charging circuit 10 includes an output transistor Q ₁ ,
It comprises a current detection transistor Q ₂ , an output transistor drive circuit 21, a current compression circuit 22, an error current detection circuit 12, a comparator 31, and a charge stop comparator 26 (charge stop circuit). The error current detection circuit 12 includes constant current circuits 23 and 24, a switch circuit S _Wa , a current mirror circuit 25, and a constant current source 27. Charging circuit 1
0 is configured as an integrated circuit, for example. The input voltage V _IN is supplied to the output transistor Q ₁ via the input terminal 35.
Are supplied to the emitters. Output terminal 36 connected to the collector of the output transistor Q ₁ is connected to the positive electrode of the battery BT, the negative electrode of the battery BT is grounded.

The charging current I _BAT of the battery BT is approximately
Matching the collector current I _C1 of the output transistor Q _1.

The current detection transistor Q ₂ is connected to the output transistor Q ₁ by a current mirror connection, and has a base and an emitter commonly connected. The transistor Q ₁ and the transistor Q ₂ have an emitter area ratio of n ₁ : n ₂ , and therefore have a collector current ratio of n ₁ : n ₂ . As a result, the collector current I _C2 of the transistor Q ₂ becomes as shown in the following equation (1).

I _C2 = (n ₂ / n ₁ ) · I _C1 = (1 / k ₁ ) · I _C1 (1) As shown in the equation (1), the collector current I _C2 of the transistor Q ₂ is equal to the output transistor This is (1 / k ₁ ) of the collector current I _C1 of Q ₁ . Since I _C1 ≒ I _BAT ,
Equation (2) holds.

I _C2 = (1 / k ₁ ) · I _BAT (2) As shown in the equation (2), the charge I _{BAT of the} battery BT is
The detection current compressed to (1 / k ₁ ) is equal to the transistor Q ₂
Is detected as the collector current I _C2 .

The current compression circuit 22 outputs a compression current _IO22 obtained by compressing the input current I _C2 supplied from the transistor Q ₂ at a compression ratio (1 / k ₂ ). From the equation (2), the current I _{O2 2} is expressed by the following equation (3).

I _O22 = (1 / k ₂ ) · I _C2 = (1 / (k ₁ · k ₂ )) · I _BAT (3) The output terminal of the current compression circuit 22 is the error current detection circuit 12.
Is connected to one end of a constant current circuit 23, an input terminal of a current mirror circuit 25, and to a constant current circuit 24 via a switch circuit S _Wa . Constant current circuit 23, 2
4 generates constant currents I _S23 and I _S24 , respectively.

The charging circuit 10 performs low-current charging when the battery voltage V _BAT is lower than the reference voltage V _r1 ,
Rapid charging is performed when the voltage is equal to or higher than _r1 and equal to or lower than the reference voltage _Vr2 for stopping charging. Therefore, as described later, the battery voltage V
By monitoring _BAT , the reference current value of the error current detection circuit 12 is switched, and the charging current I _BAT is switched.

A battery monitoring circuit provided separately from the charging circuit 10 monitors the battery voltage V _BAT at the time of low-current charging and at the time of rapid charging, thereby determining whether the state of the battery BT is normal or abnormal. it can.

The comparator 31 compares the voltage V _{BAT of the} battery BT with the reference voltage V _r1, and when the voltage V _{BAT of the} battery BT is lower than the reference voltage V _r1 , the switch circuit S _Wa
Is turned off, and the voltage V _{BAT of the} battery BT becomes the reference voltage V _r1.
In the above case, the switch circuit S _Wa is turned on.

When the switching circuit S _Wa is off, the input current I _I25 of the current mirror circuit 25 can be expressed by the following equation (4).

I _I25 = I _O22 −I _S23 (4) When the switch circuit S _Wa is on, the input current I _I25 of the current mirror circuit 25 can be expressed by the following equation (5).

[0045] _{I I25 = I O22 -I S23 -I} S24 (5) current mirror circuit 25 produces an output current I _O25 equal to the input current I _I25.

Therefore, when the switch circuit S _Wa is off, the output current I _O25 of the current mirror circuit 25 _becomes
(6)

I _O25 = I _O22 −I _S23 (6) When the switch circuit S _Wa is ON, the output current I _O25 of the current mirror circuit 25 can be expressed by the following equation (7).

I _O25 = I _O22 −I _S23 −I _S24 (7) The output terminal of the current mirror circuit 25 is connected to the constant current source 27 of the constant current I _S27 and is connected to the input terminal of the output transistor drive circuit 21. It is connected. When the switch circuit S _Wa is off, the value of I _S27 + I _S23 is the reference current value of the error current detection circuit 12. When the switch circuit S _Wa is on, the value of I _S27 + I _S23 + I _S24 becomes
This is a reference current value of the error current detection circuit 12.

Switch circuit S_WaIs off, the output trigger
The transistor drive circuit 21 includes I_{S2 7}-I_O25= I_S27
+ I_S23-I_O22Error current is supplied as input current
Is done. Switch circuit S_WaIs on, the output transformer
The driver circuit 21 includes I _S27-I_O25= I_S27+ I
_S23+ I_S24-I_O22Error current as the input current
Supplied. The output transistor driving circuit 21
An amplified output current is generated. This output current
Force transistor Q₁Base drive current I_B1(Output
Transistor drive current) as output transistor Q₁of
Supplied to the base.

The current amplification factor of the output transistor Q ₁ is represented by h
When _FE1, the output transistor Q ₁ is, the base current I
To generate a h _FE1 times the collector current I _C1 of _B1. Note that n
To be set to ₁ >> n _2, the base current I _B2 << I _B1, and the base current I _B2 of the transistor Q ₂ of the transistor Q ₂ is negligible.

The output transistor drive circuit 21
Is set to an extremely large value. Therefore, the output transistor Q is set so that I _O25 ≒ I _S27.
1 of the base current I _B1, the output transistor to Q ₁ collector current I _C1, the collector current I _C2 of the transistor Q ₂ is controlled. As a result, the charging current I _BAT is controlled to a constant value.

When the voltage of the battery BT is _lower than the reference voltage V _r1 and the switch circuit S _Wa is off, I _O25 ≒ I _S27
Then, the following equation (8) holds from the above equation (6).

I _O25 = I _S27 = I _O22 −I _S23 (8) By using the equations (8) and (3), the following equation (9) is established.

I _S27 = (1 / k ₂ ) · I _C2 −I _S23 = (1 / (k ₁ · k ₂ )) · I _BAT −I _S23 (9) From the equation (9), the charging current I _BAT is Can be expressed by the following equation (10).

I _BAT = I _BAT1 = (k ₁ · k ₂ ) · (I _S27 + I _S23 ) (10) FIG. 3 is a characteristic diagram showing the relationship between the battery voltage V _BAT and the charging current I _BAT in the charging circuit 10. It is. As shown in FIG. 3, when the voltage V _BAT of the battery BT is lower than the reference voltage V _r1 , the battery BT is charged at a low current with the constant charging current I _BAT1 determined by the equation (10).

When the voltage of the battery BT is equal to or higher than the reference voltage V _r1 and the switch circuit S _Wa is on, I _O25 ≒ I _S27
Then, the following expression (11) is established from the expression (7).

I _O25 = I _S27 = I _O22 −I _S23 −I _S24 (11) By using the equations (11) and (3), the following equation (12) is established.

I _S27 = (1 / k ₂ ) · I _C2 −I _S23 −I _S24 = (1 / (k ₁ · k ₂ )) · I _BAT −I _S23 −I _S24 (12) From the equation (12) , The charging current I _BAT can be expressed by the following equation (13).

I _BAT = I _BAT2 = (k ₁ · k ₂ ) · (I _S27 + I _S23 + I _S24 ) (13) As shown in FIG. 3, the voltage of the battery BT is equal to the reference voltage V _r1.
In the above case, with the constant charging current I _BAT2 determined by the equation (13),
The battery BT is rapidly charged.

The comparator 26 for stopping charging is provided with a reference voltage
Pressure V_r2And battery voltage V_BATCompare the current output type
It is a comparator. Battery voltage V_BATIs the reference voltage V
_r2, The output terminal of the comparator 26 is turned off.
It becomes open and the output current does not flow into the output terminal. this
Then, as described above,_BAT1Low current charging or I
_BAT2Quick charging is performed.

When the battery voltage V _BAT reaches the reference voltage V _r2 , all the current I _S27 from the constant current source 27 flows into the output terminal of the comparator 26, and the input current of the output transistor drive circuit 21 becomes 0. , I _B1 = 0. As a result, I _BAT = 0, and charging is stopped.

FIG. 2 is a detailed circuit diagram of the charging circuit 10 of the first embodiment. 2, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description will be appropriately omitted.

The output transistor drive circuit 21 is an NPN
Type transistor Q₃₃~ Q₃₆, Resistance R _Five~ R₇, R₁, R
_TwoConsists of

The current compression circuit 22 comprises NPN transistors Q ₃ and Q ₄ , resistors R ₃ and R ₄ , diodes Q ₅ and Q ₆
Consists of Transistor Q ₃ and the transistor Q ₄
Is a current mirror connection, the base is commonly connected, and the emitters are connected via resistors R ₃ and R ₄ .

[0065] and the emitter area ratio of the transistor Q ₃ and the transistor Q _4, by setting the resistance R _3, R _4, the collector current ratio of the transistor Q ₃ and the transistor Q ₄ is, n
_3: is set to n _4.

The collector current I _C4 of the transistor Q ₄ becomes
It becomes the output current _IO22 of the current compression circuit 22. Output current I
_O22 = current compression ratio 1 / k ₂ of input current I _C2 of I _C4
Is given by the following equation (14).

1 / k ₂ = n ₄ / (n ₃ + n ₄ ) (14) The current mirror circuit 25 is composed of NPN transistors Q ₃₁ and Q ₃₂ , and the collector of the transistor Q ₃₁ as an input terminal is , is connected to the collector of the transistor Q ₄ is an output terminal of the current compression circuit 22.

PNP transistor Q_Ten, Q₁₁, Q₂₆,
Q₂₀Is the current mirror connection, the base and the emitter
Are connected in common. Transistor Q_Ten, Q₁₁,
Q₂₆, Q ₂₀Reference voltage V_r2Is supplied
I have. Also, a PNP transistor Q₁₂, Q_FifteenThe
The transistor is connected to the base of the transistor. rear
As described above, the transistor Q₁₂, Q_FifteenIs the battery B
Voltage V of T_BATIs the reference voltage V_r2When it is lower,
It is in the state of off.

The constant current circuit 32 is an NPN type transistor
Q₁₇, Q₁₈, Current I_S33Of the constant current source 33,
Current I_S33Constant current I equal to_S32With transistor Q₁₇of
Collector current I_C17Output as Of the constant current circuit 32
Transistor Q as output terminal₁₇Collector of the tran
Jista Q_Ten, Q₁₁, Q₂₆, Q₂₀Connected to the base of
You. Diode-connected transistor Q_TenThrough the constant current
Constant current I _S32Flows.

The constant current circuit 23 includes PNP transistors Q ₂₀ and Q ₂₁ , and NPN transistors Q ₂₂ and Q ₂₃ connected to a current mirror. The base of transistor Q ₂₁ is grounded through the diode Q _24, Q _25.

[0071] The transistor Q ₂₀ is a transistor Q ₁₀ and the current mirror connection, the collector current I _C20 of the transistor Q _20, the collector current I of the transistor Q _10
It is equal to _C10 . The collector current of the transistor Q ₂₀ flows to the collector of the transistor Q ₂₂ via the emitter of the transistor Q _21, the collector. Transistor Q ₂₃
A transistor Q ₂₂ is the emitter area ratio of 1: Since is set to 1, the transistor Q _23, the transistor Q
A collector current having a value equal to the collector current of ₂₂ flows.
The collector current of the transistor Q ₂₃ is an output current I _S23 of the constant current circuit 23.

The value of the constant current I _S23 is almost equal to the collector current of the transistor Q ₂₀ ,
_It is almost equal to _S32 . The collector of the transistor Q ₂₃ is connected to the collector of the transistor Q ₄ is an output terminal of the current compression circuit 22.

The constant current circuit 24 is composed of PNP transistors Q ₂₆ and Q ₂₇ and NPN transistors Q ₂₈ and Q ₂₉ connected to a current mirror. A portion corresponding to the switch circuit S _Wa of Figure 1, switch S _W1 voltage V _S1 is supplied to one end, and a transistor Q ₃₀ having a base connected to the other end of the switch S _W1.

The transistor Q ₂₆ is connected to the transistor Q ₁₀ by a current mirror connection, and the collector current I _C26 of the transistor Q ₂₆ is _{equal to} the collector current I _C of the transistor Q _10.
It is equal to _C10 . To the collector of the transistor Q ₂₇ is,
The collector current of the value substantially equal to the collector current of the transistor Q ₂₆ flows.

The comparator 31 compares the voltage V _{BAT of the} battery BT with the reference voltage V _r1, and turns on the switch SW ₁ when the voltage V _{BAT of the} battery BT is lower than the reference voltage V _r1 . At this time, the transistor Q ₃₀ is turned on,
The collector current of the transistor Q _26, the transistor Q ₂₇
It flows to the collector of the transistor Q ₃₀ through the. As a result, the transistor Q ₂₉ is turned off, transistor Q
_The output current _IS24 is not output from the collector of ₂₉ .
At this time, the switch circuit _Sw in FIG. 1 corresponds to an off state.

The voltage V _{BAT of the} battery BT is equal to the reference voltage V _r1.
When the above, the comparator 31 turns off the switch S _W1, the transistor Q ₃₀ is turned off. At this time, the collector current of the transistor Q ₂₆ flows to the collector of the transistor Q ₂₈ via the transistor Q _27. Emitter area ratio of the transistor Q ₂₈ and the transistor Q ₂₉ is 1:
m ₁ . Therefore, the collector current of the transistor Q _29, i.e., the output current I _S24 of the constant current circuit 24
Is a m ₁ times the collector current of the transistor Q _28.

[0077] The collector current of the transistor Q ₂₈ is approximately equal to the collector current of the transistor Q _26, approximately equal to the current I _S32 of the constant current circuit 32. Therefore, the constant current I
The value of _S24, becomes a nearly m ₁ times the current I _S32 of the constant current circuit 32, also is approximately m ₁ times the current I _S23.

Transistor of current mirror circuit 25
Q₃₁And transistor Q₃₂The emitter area ratio is set to 1: 1.
Transistor Q₃₂Collector current
Transistor Q₃₁Of the collector current. current
Input current I of mirror circuit 25 _I25Is the transistor Q₃₁of
Collector current and output current I_O25Is the transistor Q
₃₁Of the collector current. Output of current mirror circuit 25
Transistor Q which is a force terminal₃₂The collector of the output
The transistor Q which is an input terminal of the transistor drive circuit 21
₃₃Connected to the base.

The constant current source 27 has a collector
Q₃₃Transistor Q connected to the base of₁₁Consists of
ing. Transistor Q₁₁Is the transistor Q_TenAnd Carre
Mirror connection, and the transistor Q₁₁This
The transistor Q _TenCollector current I_C10When
Equal collector current I_C11Is constant current I_S27Flowing out as
You.

The comparator 26 includes a PNP transistor Q ₁₂ and a current mirror-connected NPN transistor Q ₁₂ .
It is composed of _13, Q _14. The collector of the transistor Q ₁₄ is an output terminal of the comparator 26 is connected to the base of the transistor Q _33.

The voltage V of the battery BT_BATIs the reference voltage V_r2
If lower, transistor Q ₁₂Is off and
Transistor Q₁₃, Q₁₄Also turns off. For this reason,
Jista Q₁₄The output current does not flow through the collector.

Voltage V of battery BT_BATIs the reference voltage V_r2
, The transistor Q ₁₂Turns on and
Transistor Q₁₃, Q₁₄Is also turned on. At this time,
Jista Q₁₂The collector current of transistor Q_TenThis
Current I_C10Becomes equal to Transistor Q₁₃And tiger
Transistor Q₁₄The emitter area ratio is set to 1: 1.
Transistor Q₁₄Collector current I_C14Also transi
Star Q₁₂Of the collector current. At this time,
Transistor Q₁₁Collector current I_C11= I_S27Are all tigers
Transistor Q₁₄Flows into the collector.

Next, the operation of the charging circuit 10 of FIG. 2 will be described.

(1) When V _BAT <V _r1 When the voltage V _{BAT of the} battery BT is _lower than the reference voltage V _r1 ,
Since the reference voltage V _r1 <reference voltage V _r2, the base-emitter voltage V _BE12 of the transistor Q _12, the transistor Q
The base-emitter voltage V _BE15 of _15, transistor Q
_The transistor Q ₁₂ and Q ₁₅ are turned off because it is considerably smaller than the base-emitter voltage V _BE10 of ₁₀ . On the other hand, the transistors Q ₁₀ , Q ₁₁ , Q ₂₆ , and Q _{20 of} the current mirror connection
Is on. At this time, I _S32 = I _C17 = I
_C10 .

When the voltage V _{BAT of the} battery BT is equal to the reference voltage V _r1
When less than, as described above, the switch S _W1 is on,
The transistor Q ₂₉ of the constant current circuit 24, the collector current I _{S2 4} does not flow. On the other hand, the output current I of the constant current circuit 23
_S23 is, flows to the collector of the transistor Q _23.

As described above, the input current I _I25 and the output current I _O25 of the current mirror circuit 25 are both equal, and I _O25
= I _I25 = I _O22 −I _S23 = I _C4 −I _S23 . In addition, from the collector of the transistor Q _11, a constant current I _S27
Flows out. Both I _S23 and I _S27 are substantially equal to the current I _S32 of the constant current circuit 32, and I _S27 = I _S23 .

As described above, the amplification of the output transistor drive circuit 21 is set to an extremely large value. Therefore, the output current I _O25 of the current mirror circuit 25 = I
The base current I _B1 and the collector current I _C1 of the output transistor Q ₁ and the collector current I _C2 of the transistor Q ₂ are controlled so as to be _S27 . As a result, the charging current I _BAT is controlled to a constant value.

From the equations (10) and (14), I _S27 = I _S23 ,
The charging current I _BAT can be expressed by the following equation (15).

I _BAT = I _BAT1 = (k ₁ · k ₂ ) · (I _S27 + I _S23 ) = (n ₁ / n ₂ ) · ((n ₃ + n ₄ ) / n ₄ ) · 2 · I _S27 (15 As shown in FIG. 3, the voltage of the battery BT is changed to the reference voltage V _r1.
If it is less than the constant charging current I _BAT1 determined by the equation (15),
Low current charging of battery BT is performed.

(2) When V _r1 ≦ V _BAT <V _r2 −Vα The voltage V _{BAT of the} battery BT is close to the reference voltage V _r2.
r2 of less than -Buiarufa, the base-emitter voltage V _BE12 of the transistor Q _12, the base-emitter voltage V _BE15 of the transistor Q ₁₅ is smaller than the base-emitter voltage V _BE10 of the transistor Q _10, the transistor Q ₁₂ , Q
₁₅ is off. On the other hand, the transistors Q ₁₀ , Q ₁₁ , Q ₂₆ , and Q ₂₀ connected to the current mirror are in an ON state.

When the voltage V _{BAT of the} battery BT is equal to the reference voltage V _r1
When the above, as described above, the switch S _W1 is off,
The transistor Q ₂₉ of the constant current circuit 24, the collector current I _{S2 4} flows. On the other hand, the output current I of the constant current circuit 23
_S23 is, flows to the collector of the transistor Q _23. In addition,
As mentioned above, I _S24 = m ₁ · I _S23 .

As described above, the current mirror circuit 25
Input current I_I25And output current I_O25Are equal and I_O25
= I_I25= I_O22-I_S23-I_S24= I_C4-I_S23-I
_S24Becomes Also, the transistor Q₁₁From the collector
Is the constant current I_S27Flows out. I_S23, I_S27Together
Current I of constant current circuit 32_S23Approximately equal to_S27= I
_S23It is.

Output current _IO25 of current mirror circuit 25
, _So that I _O25 = I _S27.
1 of the base current I _B1, the collector current I _C1, the collector current I _C2 of the transistor Q ₂ is controlled. As a result, the charging current I _BAT is controlled to a constant value.

In the above formulas (13) and (14), I_S24= M₁・
I_S23, I_S27= I_S23From the charging current I _BATIs
It can be expressed by equation (16).

I _BAT = I _BAT2 = (k ₁ · k ₂ ) · (I _S27 + I _S23 + I _S24 ) = (n ₁ / n ₂ ) · ((n ₃ + n ₄ ) / n ₄ ) · (2 + m ₁ ) I _S27 (16) As shown in FIG. 3, when the voltage V _{BAT of the} battery BT is equal to or higher than the reference voltage V _r1 and lower than V _r2 −Vα, the battery BT is charged with the constant charging current I _BAT2 determined by the equation (16). Is rapidly charged.

(3) When V _r2 −Vα ≦ V _BAT When the voltage V _{BAT of the} battery BT is close to the reference voltage V _r2 ,
becomes equal to or larger than _r2 -Buiarufa, the base-emitter voltage V _BE15 of the transistor Q ₁₅ is increased, the collector current I _C15 begins to flow in the transistor Q _15. For this reason, I _S32
= The _{I C17 = I C1 0 + I} C15.

[0097] The emitter area ratio of the transistor Q ₁₀ and the transistor Q ₁₅ is large specific, for example, 1: is set to 5. Therefore, at the point of V _BAT = V _r2 , I _C15
= 5 · I _C10 .

Therefore, at this time, the transistors Q ₁₁ and Q ₁₁
The collector currents of the transistors ₂₀ and ₂₆ and the values of I _C11 , I _C20 and I _C26 are I _C10 = I _C11 = I _C20 = I _C26 = I _S32 / 6.

V_r2−Vα ≦ V_BATIn the range of_BATBut
V increases_r2As you approach, I _C11, I_C20, I
_C26Is I_S32/ 6
And I_{S2 7}, I_S23, I_S24Is I_S32Gradually to / 6
To decrease. As a result, the charging current I_BATAlso gradually
Decreasing.

Voltage V of battery BT_BATIs the reference voltage V
_r2, The transistor Q of the comparator 26₁₂of
Base-emitter voltage V_BE12Is the transistor Q_Tenof
Base-emitter voltage V_BE10Equal to
Star Q₁₂, Q₁₃, Q₁₄Turns on. As mentioned above,
Transistor Q₁₂Is the transistor Q_Ten, Q₁₁And emitter
The area ratio is set to 1: 1.
Q₁₄Collector current I _C14Is the transistor Q₁₂This
Is equal to the Therefore, the transistor Q ₁₄This
Current I_C14Is the transistor Q₁₁Collector current I
_C11And I_C14= I_C11= I_S27Becomes

[0102] Therefore, the collector current I _C11 = I _S27 of the transistor Q ₁₁ are all flows into transistor Q _14, the transistor Q ₃₃ of the output transistor drive circuit 21,
No base current is supplied. Thus, the transistor _{Q 33, Q 34, Q 35} , Q 36 are turned off, the output transistor Q ₁ to the base current I _B1 is not supplied, the output transistor Q ₁ is turned off. As a result, the charging current I _BAT = 0, and charging is stopped. Thus, when the voltage V _BAT of the battery BT reaches the reference voltage V _r2 , as shown in FIG. 3, the charging current I _BAT = 0, and charging is stopped.

As a specific example of the charging circuit 10, for example, n
Assuming that ₁ = 220 and n ₂ = 2, 1 / k ₁ = 2/220 =
Set to 1/110, and assuming that n ₃ = 6 and n ₄ = 1, 1/110
Consider the case where k ₂ = 1/7 is set.

Here, I _BAT1 at the time of low current charging is
_{When BAT1} = 5 mA, from the equation (15), I _S23 = I
_S27 = 3.25 μA is obtained as the set value.

When I _BAT1 = 5 mA, I _C2 = (n ₂
/ N ₁ ) · I _BAT1 = 45.5 μA, and I _O22 = I _C4
= (1 / k ₂ ) · I _C2 = 45.5 / 7 = 6.5 μA.

Therefore, I _S23 = I _S27 = 6.5 / 2 =
When set to 3.25 μA, when I _O22 = 6.5 μA, I _O25 = I _O22 −I _S23 = I _S27 , and the charging current I _BAT during low-current charging is controlled to a constant value of I _BAT1 = 5 mA. Is done.

For quick charging, for example, m ₁ = 16
, From equations (15) and (16), I _BAT2 = 9 · I
_BAT1 = _9.5 = 45 mA is set.

Here, when I _BAT2 = 45 _mA , I _BAT2 = 45 mA
_{C2 = (n 2 / n 1} ) · I BAT2 = 409μA next, I
_O22 = I _C4 = (1 / k ₂ ) · I _C2 = 409/7 ≒ 58.
It becomes 5 μA.

If m ₁ = 16, then I _S24 = m ₁ ·
I _S23 = 16 × 3.25 μA = 52 μA.

Then, when I _O22 = 58.5 μA,
I _O25 = I _O22 -I _S23 -I _S24 = I _S27 , and the charging current I _BAT during quick charging is controlled to a constant value of I _BAT2 = 45 mA.

As described above, the charging circuit 10 of the first embodiment
Since the charging current I _BAT is detected with sufficient accuracy by the current detection transistor Q ₁ , there is no need to provide an external current detection resistor in series with the battery BT. Reductions and costs.

Unlike the conventional circuit, a high-precision amplification circuit for amplifying the detection voltage by the current detection resistor is not required, and the current compression circuit 22 can be realized with a very simple circuit configuration of a current mirror configuration. set value of the charging current I _{BA T} in the error current detection circuit 12 of simple circuit configuration I _BAT1, I _BAT2
Can be switched. Therefore, the circuit configuration can be simplified as compared with the conventional configuration in which a plurality of current control circuits are switched. If necessary, a constant current circuit 2
By providing a plurality of constant current circuits that can be turned on and off in the same manner as in No. 4, it is possible to easily realize a configuration in which more set values of the charging current I _BAT are switched.

FIG. 4 shows a charging circuit 4 according to a second embodiment of the present invention.
FIG. The charging circuit 40 is a circuit that charges the battery BT to a specified voltage. 4, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description will be appropriately omitted. The charging circuit 40 includes an output transistor Q ₁ , a current detection transistor Q ₂ , an output transistor drive circuit 21, a current compression ratio switching circuit 44, a comparator 51, an error current detection circuit 42, and a charge stop comparator 26. The error current detection circuit 42 includes a constant current circuit 23,
It comprises a current mirror circuit 25 and a constant current source 27. The charging circuit 40 is configured as, for example, an integrated circuit.

The charging current I _BAT of the battery BT is approximately
Matching the collector current I _C1 of the output transistor Q _1.
Current detection transistor Q ₂ is the output transistor Q _1, a current mirror connection, the base, the emitter is commonly connected. Transistor Q ₁ and transistor Q ₂
Has the emitter area ratio set to n ₁ : n ₂ , and therefore the collector current ratio is set to n ₁ : n ₂ . As in the circuit of FIG. 1, the above equations (1) and (2) hold.

The current compression ratio switching circuit 44 comprises a current compression section 45 and a switch circuit _SWc . The current compressing section 45 receives the input current I _C2 supplied from the transistor Q _2.
Is compressed at a compression ratio (1 / k _12B ), and a compression current _IO44B is output from one output terminal. Also, I _C2 is _reduced by the compression ratio (1 /
The compressed current I _O44C compressed at k _12C ) is output from the other output terminal.

The comparator 51 compares the voltage V _{BAT of the} battery BT with the reference voltage V _r1, and when the voltage V _{BAT of the} battery BT is lower than the reference voltage V _r1 , the switch circuit _SWc
Is turned on, and the voltage V _{BAT of the} battery BT becomes equal to the reference voltage V _r1.
In the above case, the switch circuit _SWc is turned off.

When the switching circuit _SWc is on, the compression current I output from the current compression ratio switching circuit 44 is
_O44 can be expressed by the following equation (17).

I _O44 = I _O44A = I _O44B + I _O44C (17) In this case, the current compression ratio 1 / k ₁₂ of the compression current I _O44 to the input current I _C2 is represented by the following equation (18).

1 / k ₁₂ = 1 / k _12A = 1 / k _12B + 1 / k _12C (18) From the equations (2) and (18), the compression current I _O44 can be expressed by the following equation (19).

I _O44 = (1 / k _12A ) · I _C2 = (1 / (k ₁ · k _12A )) · I _BAT (19) When the switch circuit _SWc is off, the current compression ratio switching circuit 44 The output compression current _IO44 can be expressed by the following equation (20).

I _O44 = I _O44B (20) In this case, the current compression ratio 1 / k ₁₂ of the output current I _O44 to the input current I _C2 is represented by the following equation (21).

1 / k ₁₂ = 1 / k _12B (21) From the above equations (2) and (21), the compression current _IO44 can be expressed by the following equation (22).

I _O44 = (1 / k _12B ) · I _C2 = (1 / (k ₁ · k _12B )) · I _BAT (22) From the equations (18) and (21), 1 / k _12B <1 / k _12A . Thus, when the switch circuit S _Wc is off, the switch circuit S _Wc than if on, the compression ratio 1 / k ₁₂ becomes smaller.

The output terminal of the current compression ratio switching circuit 44 is connected to the input terminals of the constant current circuit 23 and the current mirror circuit 25 in the error current detection circuit 42. The constant current circuit 23 generates a constant current _IS23 .

The input current I _I25 and the output current I _O25 of the current mirror circuit 25 can be expressed by the following equation (23).

I _O25 = I _I25 = I _O44 −I _S23 (23) The output terminal of the current mirror circuit 25 is connected to the constant current source 27 of the constant current I _S27 and to the input terminal of the output transistor drive circuit 21. It is connected. I _S27 + I
The value of _S23 is the reference current value of the error current detection circuit 42.

The output transistor drive circuit 21 has I
_An error current of _S27− I _O25 = I _S27 + I _S23 −I _{O4 4} is supplied as an input current. The output transistor drive circuit 21 generates an output current obtained by amplifying the error current.
The output current, as the base drive current I _B1 of the output transistor Q _1, is supplied to the base of the output transistor Q _1.

[0127] The current amplification factor of the output transistor Q ₁ h
When _FE1, the output transistor Q ₁ is, the base current I
To generate a h _FE1 times the collector current I _C1 of _B1. Note that n
To be set to ₁ >> n _2, the base current I _B2 << I _B1, and the base current I _B2 of the transistor Q ₂ of the transistor Q ₂ is negligible.

The output transistor drive circuit 21
Is set to an extremely large value. Therefore, the output transistor Q is set so that I _O25 ≒ I _S27.
1 of the base current I _B1, the output transistor to Q ₁ collector current I _C1, the collector current I _C2 of the transistor Q ₂ is controlled. As a result, the charging current I _BAT is controlled to a constant value.

If I _O25 = I _S27 , the following equation (24) is established from the above equation (23).

I _O25 = I _S27 = I _O44 −I _S23 (24) When the voltage V _{BAT of the} battery BT is less than the reference voltage V _r1 and the switch circuit _SWc is on, the equation (24) and the equation (19) are used. Using the equation, the following equation (25) is established.

I _S27 = (1 / k _12A ) · I _C2 −I _S23 = (1 / (k ₁ · k _12A )) · I _BAT −I _S23 (25) From the equation (25), the charging current I _BAT is Can be expressed by the following equation (26).

I _BAT = I _BAT1 = (k ₁ · k _12A ) · (I _S27 + I _S23 ) (26) As in FIG. 3 in the first embodiment, the voltage V of the battery BT is
When _BAT is less than the reference voltage V _r1, with a constant charging current I _BAT1 determined by equation (26), low current charging of the battery BT is performed.

When the voltage of the battery BT is equal to or higher than the reference voltage V _r1 and the switch circuit S _Wc is off, I _O25 = I _S27
Then, the following equation (27) is established using the equations (24) and (22).

I _S27 = (1 / k _12B ) · I _C2 −I _S23 = (1 / (k ₁ · k _12B )) · I _BAT −I _S23 (27) From the equation (27), the charging current I _BAT is Can be expressed by the following equation (28).

I_BAT= I_BAT2= (K₁・ K_12B) ・ (I_S27+ I_S23(28) As described above, 1 / k_12B<1 / k_12A, So I
_BAT2> I_BAT1Becomes As in FIG. 3 of the first embodiment,
The voltage of the battery BT of the battery BT is the reference voltage V _r1More than
When the constant charging current I determined by the equation (28)_BAT2So, Batte
The re-BT is rapidly charged.

When the battery voltage V _BAT does not reach the reference voltage V _r2 , the output terminal of the charge stop comparator 26 is open, and no output current flows into the output terminal. In this case, as described above, low current charging by I _BAT1 or I
Rapid charging by _BAT2 is performed.

When the battery voltage V _BAT reaches the reference voltage V _r2 , all the current I _S27 from the constant current source 27 flows into the output terminal of the comparator 26, and the input current of the output transistor drive circuit 21 becomes zero. , I _B1 = 0. As a result, I _BAT = 0, and charging is stopped.

FIG. 5 is a detailed circuit diagram of the charging circuit 40 of the second embodiment. 5, the same components as those in FIGS. 2 and 4 are denoted by the same reference numerals, and the description will be appropriately omitted.

The current compression section 45 of the current compression ratio switching circuit 44 includes NPN transistors Q ₄₃ , Q ₄₄ , Q ₄₅ , resistors R ₁₃ , R ₁₄ , R ₁₅ , and diodes Q ₄₈ , Q ₄₉ . A portion corresponding to the switch circuit S _Wc, the switch S _W2 is supplied a voltage V _S2 on one end, the transistors Q _47, Q ₄₆
Consists of

The transistors Q ₄₃ , Q ₄₄ and Q ₄₅ are in a current mirror connection, the bases are connected in common, and the emitters are connected via resistors R ₁₃ , R ₁₄ and R ₁₅ .

[0141] and the emitter area ratio of transistors _{Q 43, Q 44, Q 45} , by setting the resistance _{R 13, R 14, R 15} , the collector current ratio of the transistor Q _43, Q _44, Q ₄₅ is, n _13: n
_14: is set to n _15.

[0142] collector current I of the transistor Q _44
C44 is one output current _{IO44B of the} current compression unit 45. Current compression ratio 1 / k for input current I _C2 of I _O44B
12B is given by the following equation (29).

1 / k _12B = n ₁₄ / (n ₁₃ + n ₁₄ + n ₁₅ ) (29) The collector current I _C43 of the transistor Q ₄₃ becomes the other output current I _{O44C of the} current compression section 45. Current compression ratio 1 / k _12C with respect to the input current I _C2 of the I _O44C becomes below (30).

1 / k _12C = n ₁₃ / (n ₁₃ + n ₁₄ + n ₁₅ ) (30) From the above equation (18), the following equation (31) holds.

1 / k _12A = 1 / k _12B + 1 / k _12C = (n ₁₃ + n ₁₄ ) / (n ₁₃ + n ₁₄ + n ₁₅ ) (31) The comparator 51 compares the voltage V _{BAT of the} battery BT with the reference voltage V _r1. compared to, when the voltage V _BAT of the battery BT is lower than the reference voltage V _r1, turn off the switch S _W2, the transistor Q ₄₇ is turned off. At this time, the transistor Q
₄₃ of the collector current flows into the emitter of the transistor Q _46, the collector of the transistor Q _46, the output current I
_O44C is output. At this time, the switch circuit S _Wc corresponds to the ON state, the compressed current _{I O44 = I O44B + I O44C} .

The voltage V _{BAT of the} battery BT is equal to the reference voltage V _r1.
In the above case, the comparator 51 turns on the switch _SW2 . At this time, the transistor Q ₄₇ is turned on,
The collector current of the transistor Q _43, the transistor Q ₄₇
Flows to the collector. Thus, the transistor Q ₄₆ is turned off, from the collector of the transistor Q _46, the output current I _O44C is not output. At this time, the switch circuit S
_Wc corresponds to the OFF state, and the compression current I _O44 = I _O44B .

The collector of the transistor Q ₃₁ , which is the input terminal of the current mirror circuit 25, is connected to the collector of the transistor Q ₄₄ which is the output terminal of the current compression ratio switching circuit 44.

The transistors Q ₁₀ , Q ₁₁ and Q ₂₀ are in a current mirror connection, and have a base and an emitter commonly connected. The emitter of the transistor Q _10, Q _11, Q _20, the reference voltage V _r2 is supplied. The bases of the transistors Q ₁₂ and Q ₁₅ are commonly connected to the bases of the transistors.

The constant current circuit 32 for the constant current I _S32 is connected to the bases of the transistors Q ₁₀ , Q ₁₁ and Q ₂₀ . Through the transistor Q ₁₀ of the diode-connected, a constant current I _S32 is flowing through the constant current circuit 32.

[0150] The collector current of the transistor Q ₂₃ of the constant current circuit 23 is the output current I _S23 of the constant current circuit 23.
The value of the constant current I _S23 is substantially equal to the collector current of the transistor Q _20, approximately equal to the current I _S32 of the constant current circuit 32. The collector of the transistor Q ₂₃ is connected to the collector of the transistor Q ₄₄ is an output terminal of the current compression ratio switching circuit 44.

Transistor Q of current mirror circuit 25
_31, the collector current of Q ₃₂ are equal. Input current I _I25 and the output current I _O25 of the current mirror circuit 25, respectively, the collector current of the transistor Q _31, Q _32.

[0152] From the collector of the transistor Q ₁₁ of the constant current source 27, the collector current I _C11 is equal to the collector current I _C10 of the transistor Q ₁₀ flows out as a constant current I _S27.

[0153] The comparator 26, when the voltage V _BAT of the battery BT is lower than the reference voltage V _r2, the transistor Q ₁₂ is turned off, the transistor Q _13, Q ₁₄ is also turned off. Therefore, the collector of the transistor Q _14, the output current does not flow.

Voltage V of battery BT_BATIs the reference voltage V_r2
, The transistor Q ₁₂Turns on and
Transistor Q₁₃, Q₁₄Is also turned on. At this time,
Jista Q₁₄Collector current I_C14Is a transistor
Q₁₂, Q₁₁Equal to the collector current of the transistor
Q₁₁Collector current I_C11= I_S27Are all transistors
Q ₁₄Flows into the collector.

Next, the operation of the charging circuit 40 of FIG. 5 will be described.

(1) When V _BAT <V _r1 When the voltage V _{BAT of the} battery BT is _lower than the reference voltage V _r1 ,
Since the reference voltage V _r1 <reference voltage V _r2, the base-emitter voltage V _BE12 of the transistor Q _12, the transistor Q
The base-emitter voltage V _BE15 of _15, transistor Q
_The transistor Q ₁₂ and Q ₁₅ are turned off because it is considerably smaller than the base-emitter voltage V _BE10 of ₁₀ . On the other hand, the transistors Q ₁₀ , Q ₁₁ , Q _{20 of} the current mirror connection are on. At this time, I _S32 = I _C10 .

When the voltage V _{BAT of the} battery BT is equal to the reference voltage V _r1
If less than, the switch _SW2 is off as described above,
I _O44 = I _O44B + I _O44C .

[0158] As described above, the input current I _I25 and the output current I _O25 of the current mirror circuit 25 are both equal, I _O25
= I _I25 = I _O44 −I _S23 = I _O44B + I _O44C −I _S23 Both I _S23 and I _S27 are the current I _S of the constant current circuit 32.
_It is almost equal to _S32 , and I _S27 = I _S23 .

As described above, the amplification of the output transistor drive circuit 21 is set to an extremely large value. Therefore, the output current I _O25 of the current mirror circuit 25 = I
The base current I _B1 and the collector current I _C1 of the output transistor Q ₁ and the collector current I _C2 of the transistor Q ₂ are controlled so as to be _S27 . As a result, the charging current I _BAT is controlled to a constant value.

From the expressions (26) and (31), I _S27 = I _S23 ,
The charging current I _BAT can be expressed by the following equation (32).

I _BAT = I _BAT1 = (k ₁ · k _12A ) · (I _S27 + I _S23 ) = (n ₁ / n ₂ ) · ((n ₁₃ + n ₁₄ + n ₁₅ ) / (n ₁₃ + n ₁₄ )) · _{2.I S27} (32) As in FIG. 3 of the first embodiment, when the voltage of the battery BT is _lower than the reference voltage V _r1 , the constant charging current I determined by the equation (32) is obtained.
_{At BAT1} , low-current charging of the battery BT is performed.

(2) When V _r1 ≦ V _BAT <V _r2 −Vα Similarly to the case where V _BAT <V _r1 , the transistors Q ₁₂ and Q ₁₅
Is off. On the other hand, the transistors Q ₁₀ , Q ₁₁ , Q _{20 of} the current mirror connection are on.

The voltage V _{BAT of the} battery BT is equal to the reference voltage V _r1
In the above case, as described above, the switch _SW2 is turned on,
I _O44 = I _O44B .

Output current I _O25 of current mirror circuit 25
_{Is, I O25 = I I25 = I} O44 -I S2 3 = I O44B -I S23
Becomes

Output current I _O25 of current mirror circuit 25
= I _S27 so that the base current I _B1 and the collector current I _C1 of the output transistor Q ₁ and the collector current I _C2 of the transistor Q ₂ are controlled. As a result, the charging current I
_BAT is controlled to a constant value.

From the equations (28) and (29), I _S27 = I _S23 ,
The charging current I _BAT can be expressed by the following equation (33).

I _BAT = I _BAT2 = (k ₁ · k _12B ) · (I _S27 + I _S23 ) = (n ₁ / n ₂ ) · ((n ₁₃ + n ₁₄ + n ₁₅ ) / n ₁₄ ) · 2 · I _S27 (33) As in FIG. 3 of the first embodiment, when the voltage of the battery BT is equal to or higher than the reference voltage V _r1 and lower than V _r2 −Vα, (33)
The battery BT is rapidly charged at a constant charging current I _BAT2 determined by the equation.

(3) V_r2−Vα ≦ V_BATAt the time, as in the first embodiment, the voltage V_BATIs the standard
Voltage V_r2V close to _r2-Vα or more,
Star Q_FifteenBase-emitter voltage V_BE15Is bigger
Transistor Q_FifteenAnd the collector current I_C15Begins to flow
You. Therefore, I _S32== I_C10+ I_C15Becomes

[0169] The emitter area ratio of the transistor Q ₁₀ and the transistor Q ₁₅ for example, 1: When is set to 5, V
_At the point of _BAT = V _r2 , I _C15 = 5 · I _C10 .

Therefore, at this time, the transistors Q ₁₁ , Q
_20, the collector current, the value of I _C11, I _{C2 0} is, I _C10 =
I _C11 = I _C20 = I _S32 / 6.

V_r2−Vα ≦ V_BATIn the range of_BATBut
V increases_r2As you approach, I _C11, I_C20Is the value of
I_S32/ 6, and thus I_S27,
I_{S2 Three}Is I_S32It gradually decreases to / 6. this
The charging current I_BATAlso gradually decreases.

When the voltage V _{BAT of the} battery BT is equal to the reference voltage V
Upon reaching _r2, the base-emitter voltage V _BE12 of the transistor Q ₁₂ of the comparator 26 becomes equal to the base-emitter voltage V _BE10 of the transistor Q _10, the transistors Q _12, Q _13, Q ₁₄ is turned on. Transistor Q ₁₄
The collector current I _C14 of the is equal to the collector current I _C11 of the transistor Q _11, the _{I C14 = I C11 = I S27} .

Therefore, all the collector current I _C11 of the transistor Q ₁₁ flows into the transistor Q ₁₄ , and no base current is supplied to the transistor Q ₃₃ of the output transistor drive circuit 21. Thereby, the transistors Q ₃₃ , Q
_34, Q _35, Q ₃₆ is turned off, the base current I _B1 is not supplied to the output transistor Q _1, the output transistor Q ₁ is turned off. As a result, the charging current I _BAT = 0, and charging is stopped. Thus, the voltage V of the battery BT
_{When BAT} reaches the reference voltage V _r2 , the charging current I _BAT = 0, and charging is stopped.

As a specific example of the charging circuit 40, for example, n
₁ = 220, n ₂ = 2, 1 / k ₁ = 2/220, and n ₁₃ = 8, n ₁₄ = 1, n ₁₅ = 54, 1 / k
k _{12 B} = n ₁₄ / (n ₁₃ + n ₁₄ + n ₁₅ ) = 1/63, 1 /
k _12C = n ₁₃ / (n ₁₃ + n ₁₄ + n ₁₅ ) = 8/63, 1 /
Consider a case where k _12A = 1 / k _12B + 1 / k _12C = _1/7 (see the above equations (29) to (31)).

Here, I _BAT1 at the time of low current charging is
_{When BAT1} = 5 mA, from the equation (32), I _S23 = I
_S27 = 3.25 μA is obtained as the set value.

When I _BAT1 = 5 mA, I _C2 = (n ₂
/ N ₁ ) · I _BAT1 = 45.5 μA, and I _O44 = I
_O44B + I _O44C = (1 / k _12A ) · I _C2 = 45.5 / 7 =
It becomes 6.5 μA.

Therefore, I _S23 = I _S27 = 6.5 / 2 =
When 3.25 μA is set, when I _O44 = 6.5 μA, I _O25 = I _O44 −I _S23 = I _S27 , and the charging current I _BAT during low-current charging is controlled to a constant value of I _BAT1 = 5 mA. Is done.

With respect to quick charging, from the equations (32) and (33), I _BAT2 = 9 × I _BAT1 = 9 × 5 = 45 mA is set.

Here, when I _BAT2 = 45 _mA , I _BAT2 = 45 mA
_{C2 = (n 2 / n 1} ) · I BAT2 = 409μA next, I
_O44 = I _O44B = (1 / k _12B ) · I _C2 = _409/63 ≒
It becomes 6.5 μA.

When I _O44 = 6.5 μA, I _O25 = I
_O44− I _S23 = I _S27 , and the charging current I during rapid charging
_BAT is controlled to a constant value of I _BAT2 = 45 mA.

As described above, similarly to the first embodiment, in the charging circuit 40 of the second embodiment, the charging current I _BAT is detected with sufficient accuracy by the current detection transistor Q ₁ , so that the charging circuit 40 is connected in series with the battery BT. It is not necessary to provide an additional current detection resistor, so that the number of components and the occupied space can be reduced as compared with the conventional circuit, and the cost can be reduced.

Unlike the conventional circuit, a high-precision amplification circuit for amplifying the detection voltage by the current detection resistor is not required, and the charging current I _{BAT is changed} by the current compression ratio switching circuit 44 having a simple circuit configuration using a current mirror configuration. setting I _BAT1, can switch I _BAT2, the error current detection circuit 42 can be realized by a very simple circuit configuration. Therefore, the circuit configuration can be simplified as compared with the conventional configuration in which a plurality of current control circuits are switched.

If necessary, the ON / OFF timing of the transistors Q ₄₃ , Q ₄₆ and Q _{47 of} the current compression ratio switching circuit 44 is the same.
By providing a plurality of compression current output circuits that can be turned off, a configuration in which more set values of the charging current I _BAT are switched can be easily realized.

[0184]

[0185]

[0186]

[0187]

As described above, according to the first aspect of the present invention,
In order to detect the charging current by the current detection transistor,
There is no need to provide a current detection resistor in series with the secondary battery,
Accordingly, the number of parts and the occupied space can be reduced, and the cost can be reduced.

Unlike the conventional circuit, a high-precision amplification circuit for amplifying the detection voltage by the current detection resistor is not required, and the set value of the charging current can be switched by the current compression ratio switching circuit having a simple circuit configuration. Further, since the error current detection circuit can be realized with an extremely simple circuit configuration, the circuit configuration can be simplified as compared with the conventional configuration in which a plurality of current control circuits are switched. Further, it is possible to easily switch the set values of a plurality of charging currents as needed.

According to the second aspect of the present invention, when the voltage of the secondary battery reaches the reference voltage, the output transistor drive current can be controlled to stop charging by the charging stop circuit.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a charging circuit according to a first embodiment of the present invention.

FIG. 2 is a detailed circuit diagram of a charging circuit according to the first embodiment.

FIG. 3 is a characteristic diagram illustrating a relationship between a battery voltage and a charging current in the charging circuit according to the first embodiment.

FIG. 4 is a configuration diagram of a charging circuit according to a second embodiment of the present invention.

FIG. 5 is a detailed circuit diagram of a charging circuit according to a second embodiment.

FIG. 6 is a configuration diagram of an example of a conventional charging circuit.

FIG. 7 is a characteristic diagram showing a relationship between a battery voltage and a charging current in the charging circuit of FIG.

[Explanation of symbols]

Reference Signs List 10 charging circuit 12 error current detection circuit 21 output transistor drive circuit 22 current compression circuit 23, 24 constant current circuit 25 current mirror circuit 26 charging stop comparator 27 constant current source 31 comparator 42 error current detection circuit 44 current compression ratio switching circuit 45 Current compression unit 51 Comparator Q ₁ output transistor Q ₂ current detection transistor BT battery S _Wa switch circuit S _Wc switch circuit V _BAT battery voltage I _BAT charging current

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02J 7/10 G05F 1/56 310 H01M 10/44

Claims (2)

(57) [Claims] An output transformer for supplying a charging current to a secondary battery.
Transistor, the output transistor and the base and the emitter are connected in common
A predetermined emitter area ratio with the output transistor.
And the charge output from the output transistor.
Current detection transistor that outputs a detection current with a predetermined ratio to the current
AndCorresponds to the set value of charging current according to the voltage value of the secondary battery
The current compression ratio for the current detection
The detected current supplied from the star is compressed at the current compression ratio.
A current compression ratio switching circuit for outputting a compressed current,  A compression current supplied from the current compression ratio switching circuit;
An error current that generates an error current according to the difference from the reference current value
A detection circuit, and amplifies the error current supplied from the error current detection circuit.
Output transistor drive current generated by the
Output transistor driving circuit for supplying to the transistor
A charging circuit characterized in that: 2. A charge stop that compares the voltage of the secondary battery with a reference voltage, and controls the output transistor drive current to stop charging when the voltage of the secondary battery reaches the reference voltage. The charging circuit according to claim 1, further comprising a circuit.