JPH0746774A - Charger - Google Patents

Abstract

PURPOSE:To avoid a trickle charge of a secondary battery such as a lithium ion battery which is not resistant against an overcharge and an overdischarge. CONSTITUTION:A charger 1 charges a secondary battery 3 with a power supply current supplied by a power supply part 10 and has a first detecting means which detects the existence of the power supply from the power supply part 10, a second detecting means which detects a charge voltage for the secondary battery supplied by the power supply part and a switching part which switches the connection of the secondary battery to an external load. Further, a control means 13 which performs the switching control of the switching part in accordance with the detected results from the first detecting means and the second detecting means and, further, supplies a predetermined control signal to the power supply part 10 so as to operate the power supply part as a constant voltage source or a constant current source is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device, and more particularly to a charging device for a secondary battery such as a lithium ion storage battery.

[0002]

2. Description of the Related Art A secondary battery is one in which the chemical reaction inside the battery is reversible and can be repeatedly used by charging and discharging.
A battery whose function can be reproduced by charging after discharging. And, as a typical secondary battery, for example, a sealed lead-acid battery, nickel-cadmium (Ni-C)
d) Storage batteries (hereinafter simply referred to as NiCd batteries), lithium-ion storage batteries, and the like.

Conventionally, as a charging device for such a secondary battery, there is a charger 101 as shown in FIG.

FIG. 4 is a circuit diagram of a charger 101 incorporated in a portable electronic device containing a secondary battery. In addition,
For convenience of operation, in the circuit shown in FIG. 4, the switch 114 can connect and disconnect the load 117 to and from the secondary battery 103.

In FIG. 4, a charger 101 includes a power source 102, a secondary battery 103, diodes 104 and 105, and a resistor 106.
-111, transistors 112 and 113, switch 11
4. Switching regulator
) 115, a control unit 116, and a load 117.

The power source 102 supplies DC power to the charger 101, and charges the secondary battery 103.
A DC power supply with high internal impedance is used.

The secondary battery 103 is a storage battery such as a nicad battery which can be repeatedly used by charging and discharging.

The diode 104 is a diode for line protection when the voltage and current applied from the power source 102 are in the opposite direction, and the diode 105 is the secondary battery 103.
This is a diode for preventing the reverse flow of current from the power supply to the power supply 102 side.

The resistor 106 limits the current between the emitter and collector of the transistor 112, the resistor 7 is for biasing the base potential of the transistor 112, and the resistor 108 is
The resistor 109 limits the value of the current flowing through the base of the transistor 112, and the resistor 109 limits the value of the current flowing through the base of the transistor 113.

Further, the resistors 110 and 111 divide the charger output voltage Vout to divide the charger output voltage Vout into an input signal VS of the control unit 116.
It is for generating ENSE.

The transistor 112 is a PNP type bipolar transistor, the transistor 113 is an NPN type bipolar transistor, and the switch 114 switches between connecting and disconnecting the load 117 to the secondary battery 103 as described above. It is a thing. By the way, in the following description, in order to connect the secondary battery 103 and the load 117, it is assumed that the switch 114 is in the “ON” state, while on the other hand, in order to disconnect the secondary battery 103 and the load 117, It is assumed that the switch 114 is in the “off” state.

The switching regulator 115 is composed of a regulator IC (Integrated Circuit).

The control unit 116 controls the input signal V-SENSE.
The output signal Q-CHARGE outputs "L" or "H" based on the potential level of the output signal Q-CHARGE, and the potential of the input signal V-SENSE at which the output signal Q-CHARGE switches from "L" to "H". Level and output signal Q-C
The input signal V at which HARGE switches from "H" to "L"
-Set to be different from the SENSE potential level,
It has a so-called hysteresis characteristic.

The load 117 is connected to the switch 114 via the switching regulator 115, for example,
Each circuit etc. in a portable electronic device are shown.

In the above structure, first, when DC power is supplied as input power to the charger 101 from the power supply 102, the applied input power is applied to the emitter of the transistor 112 via the diode 104.

Here, the charge amount of the secondary battery 103 is 100.
If the state is close to%, the control unit 116 detects that the voltage of the charger output voltage Vout is high according to the potential level of the input signal V-SENSE, and the output signal Q-
"L" (about 0.3V) is output as CHARGE.

Then, the transistor 113 becomes non-conductive because the output signal Q-CHARGE is "L", and the base potential of the transistor 113 becomes substantially equal to the emitter potential. This causes the transistor 112
Also becomes non-conductive, and the input power applied to the transistor 112 is transmitted to the switch 114 and the secondary battery 103 via the resistor 106.

In this state, when the switch 114 is in the "OFF" state, the input power is supplied to the secondary battery 103 for charging, but at this time, the charging current is (1/20) .C by the resistor 106. Since it is suppressed to (1/30) · C, it becomes a charging state by a minute current, that is, a trickle charging state.

Here, when the switch 114 is turned on, the secondary battery 103 and the load 117 are connected via the switching regulator 115, and the power of the secondary battery 103 is supplied to the load 117. As a result, the secondary battery 103 is in a discharged state, and the charger output voltage Vout gradually decreases.

When the load 117 is connected for a long time and the charger output voltage Vout approaches the discharge end voltage, the control unit 116 is controlled by the potential level of the input signal V-SENSE.
The output signal Q-CHARGE output from is "H".

Then, the transistor 113 becomes conductive and the collector potential becomes "L". As a result, the base potential of the transistor 112 becomes “L” and the transistor 112 becomes conductive, and the power of the power source 102 is transmitted to the load 117 and the secondary battery 103 via the transistor 112.

The conduction resistance of the transistor 112 is the resistance 10
Since it is sufficiently lower than the resistance value of 6, a large charging current (load current) is applied and the charger output voltage Vout rises. At this time, as described above, since the control unit 116 has the hysteresis characteristic, the transistor 11
2 and 13 alternately repeat the conducting state and the non-conducting state,
So-called oscillation does not occur.

Here, when the switch 114 is in the "OFF" state, all of the supplied current becomes the charging current, and the charging current becomes (1/5) .multidot.C to (1/3) .multidot.C to charge for a short time. It becomes a state. As a result, the charge amount of the secondary battery 103 is rapidly recovered, and the charger output voltage Vout voltage rises.

When the charger output voltage Vout rises and reaches a predetermined voltage value, the output signal Q-C output from the control unit 116 according to the potential level of the input signal V-SENSE.
HARGE becomes "L" again, and the trickle charge state is set by the above-described operation.

Such a charger 101 has two charging modes of trickle charging and short-time charging (standard charging), and is often used for nickel-cadmium batteries and sealed lead-acid batteries.

[0026]

Since the secondary battery has a larger output capacity and a smaller internal resistance than the primary battery, it is used as a power source for a load that draws a large amount of current and is continuously used for a long time. Further, the self-discharge of the secondary battery during storage at room temperature shows a larger value than that of the primary battery, but since the battery can be charged, the life of the battery is defined by the allowable number of charge / discharge cycles.

In the case of a lead-acid battery, the battery life is shortened by over-discharging, so it is desirable to charge the battery when 50% of the battery capacity has been discharged. Due to its excellent recovery characteristics,
There is no need to choose the charging period as with lead acid batteries. But,
The NiCd battery has a memory effect that the charging capacity gradually decreases if the NiCd battery is charged in a state where it is not sufficiently discharged.

The lithium-ion storage battery has a cycle life of 1200 times or more even at a discharge depth of 100%, and the integrated energy amount (capacity × discharge depth × cycle life) is four times as large as that of the NiCad battery. The volume energy density is 2.9 times that of the NiCad battery and the weight energy density is 3.8 times that of the nickel-cadmium battery. The operating voltage is about 4V (about 3.6V), which is higher than 1.2V for NiCd storage batteries and 2V for sealed lead storage batteries. Self-discharge is about half that of NiCd batteries, and quick charging is It is possible as with batteries,
The operating temperature range is also the same as that of the NiCad battery. further,
It has a number of excellent features such as the lack of memory effect, which is a drawback of NiCad batteries.

However, the above-mentioned conventional charging device has a circuit configuration suitable for charging a secondary battery which is resistant to overcharging and overdischarging, such as a nickel-cadmium battery. There were some problems to mention.

That is, although the lithium-ion storage battery has a number of excellent features as described above, it has a drawback of being extremely weak against overcharge and overdischarge, and therefore has a disadvantage of being overcharged like a charger for a nickel-cadmium battery. When a lithium-ion storage battery is applied to a charger that does not have much countermeasures against charging and over-discharging, for example, it is necessary to change the power supply part to a constant voltage / constant current source, or a trickle. There is a problem that the life of the storage battery deteriorates due to charging.

[Object] The present invention has an object to prevent trickle charge in a secondary battery which is vulnerable to overcharge and overdischarge, such as a lithium ion storage battery.

[0032]

The invention according to claim 1 is
In a charging device for charging a secondary battery with a power supply current supplied from a power supply unit, first detection means for detecting the presence or absence of power supply from the power supply unit, and charging the secondary battery supplied from the power supply unit. Second detection means for detecting a voltage, a switch portion for switching whether to connect the secondary battery to an external load, and the switch portion based on the detection results from the first detection means and the second detection means And a control means for outputting a predetermined control signal to the power supply unit and outputting a control signal for operating as a constant voltage source or a constant current source.

In this case, as in the invention described in claim 2,
The opening / closing control of the switch unit by the control unit preferably has a hysteresis characteristic.

In addition to the first and second aspects of the invention, as in the third aspect of the invention, temperature detection means for detecting the temperature of the secondary battery is provided, and the detection result of the temperature detection means is provided. Based on the above, it is preferable that the control means controls the opening / closing of the switch portion, or
In addition to the above described invention, as in the invention according to claim 4, a current detecting means for detecting a value of a current flowing through the secondary battery is provided, and the control means is configured to perform the above-mentioned operation based on a detection result of the current detecting means. It is effective to control the opening / closing of the switch portion, and, in addition to the inventions of claims 1 and 2, as in the invention of claim 5, timer means for measuring the time for charging the secondary battery. It is effective that the control means controls the opening and closing of the switch portion based on the time information of the timer means.

[0035]

According to the first aspect of the invention, the opening and closing of the switch section is controlled based on the presence or absence of power supply from the first detecting section and the charging voltage value from the second detecting section, and the power source section is fixed. By controlling to operate as a voltage source or a constant current source, trickle charging is prevented for a secondary battery that is weak against overcharging and overdischarging, such as a lithium ion storage battery.

According to the second aspect of the present invention, the invention according to the first aspect is characterized in that the switch portion has a hysteresis characteristic at a point where the switch portion changes from an open state to a closed state and a point where the switch portion changes from a closed state to an open state. In addition to this, trickle charging is more reliably prevented.

In this case, as in the invention described in claim 3,
The open / close control of the switch unit is based on the detection result of the temperature detecting means, the detection result of the current detecting means as in the invention of claim 4, and the time information from the timer means as in the invention of claim 5. In addition to the first and second aspects of the present invention, optimal charging of the secondary battery is performed by taking into consideration.

[0038]

EXAMPLES Examples will be described below with reference to FIGS.

1 to 3 are views showing an embodiment of the charging device according to the present invention.

First, the structure will be described. FIG. 1 is a circuit diagram showing a main part configuration of a charger 1 according to the present embodiment incorporated in a portable electronic device containing a secondary battery. Note that, for convenience of operation, in the circuit shown in FIG. 1, the load 1 is applied to the lithium ion storage battery 3 which is a secondary battery by the switch 14.
6 can be connected and disconnected.

In FIG. 1, a charger 1 includes a power source 2, a lithium ion storage battery (secondary battery) 3, diodes 4, 5, and a resistor 6.
To 9, constant voltage / constant current power supply 10, temperature detection unit 11, current detection unit 12, control unit 13, switch 14, switching regulator 15, load 16, switch circuits SWa, S
It is composed of Wb.

The power source 2 supplies DC power to the charger 1, and the lithium ion storage battery 3 is a secondary battery having various features as described above.

The diode 4 is a diode for line protection when the voltage / current applied from the power source 2 is in the reverse direction, and the diode 5 is for preventing the reverse flow of current from the lithium ion storage battery 3 to the power source 2 side. Is a diode.

The resistors 6 and 7 divide the charger applied voltage Vin from the power source 2 to divide the voltage signal Vin-SE of the control unit 13.
The resistors 8 and 9 are for generating NSE, and for dividing the charger charging voltage Vout from the constant voltage / constant current power supply 10 to generate the voltage signal V-SENSE of the control unit 13. is there.

The constant-voltage / constant-current power supply 10 uses the DC power supplied from the power supply 2 as a constant-voltage power supply or a constant-current power supply based on a charge control signal CHARGE-CONT from the control unit 13 described later. The electric power is supplied to 3.

The temperature detector 11 detects the temperature of the lithium ion storage battery 3 and outputs the temperature detection signal T-SE of the controller 13.
NSE is generated, and the current detection unit 12 detects the value of the current flowing through the lithium-ion storage battery 3, and the control unit 1
The current detection signal I-SENSE of No. 3 is generated.

The controller 13 controls the voltage signal Vin-SENS.
The presence or absence of power supply from the power supply 2 is detected based on the potential level of E, the switch control signal SWb-CONT is output by the voltage signal Vin-SENSE to turn off the switch SWb, and the output of the lithium-ion storage battery 3 is loaded. 1
It is separated from the 6 side. The voltage applied to the charger V
Since in passes through the path of the backflow preventing diode 5 and is connected to the load 16 side via the switch 14, when the switch 14 is turned on, the power of the power supply 2 supplies power to the load 16 side. .

The control unit 13 also controls the voltage signal V-SEN.
The charge voltage to the lithium-ion storage battery 3 supplied from the power supply 2 is detected based on the potential level of SE, and when the load 16 is disconnected, it is in a spontaneous discharge state. The charging voltage Vout drops extremely slowly. Here, in the spontaneous discharge state, when the charge amount reaches about 90% (battery voltage is about 3.9 V), the control unit 13 outputs the SWa-CONT signal, turns on the switch SWa, and sets the constant voltage. The constant current source 10 is connected to the lithium ion storage battery 3 to start charging.

As described above, the switch 14 switches whether the load 16 is connected to or disconnected from the secondary battery 3. The switching regulator 15 is composed of a regulator IC (Integrated Circuit), and the load 16 is , Circuits connected to the switch 14 via the switching regulator 15, for example, in a portable electronic device.

The switch circuits SWa and SWb are switch control signals SWa-CONT and SWb from the control circuit 13.
The switch circuit SWa switches ON / OFF operation of the connection between the constant voltage / constant current source 10 and the lithium ion storage battery 3, and the switch circuit SWb switches the lithium ion storage battery 3 And load 1
The on / off operation of the connection with 6 is switched.

Next, the operation of this embodiment will be described.

First, the charging of the lithium ion storage battery 3 will be described.

FIG. 2 is a diagram showing the charging characteristics of the lithium ion storage battery 3 at a temperature of 20 ° C.

The constant voltage / constant current power supply 10 is first set to the "constant current power supply mode" by the charge control signal CHARGE-CONT from the control section 13, and in this embodiment, the current value is 3 C.mA (that is, , Battery capacity 1000
In the case of mAh, it is charged at 3A).

Next, in the control section 13, the voltage signal V-SE
When the charger charging voltage Vout is detected by the NSE and the charger charging voltage Vout rises to 4.1V, the constant voltage / constant current power supply 10 is changed to the “constant voltage source mode” by the charge control signal CHARGE-CONT. Charging is performed while the charger charging voltage Vout is controlled to be a constant value of 4.1 V. In this case, the charging current gradually decreases as the charging progresses.

Then, the control unit 13 determines that the charging is completed when it is detected that the current flowing through the lithium ion storage battery 3 is almost 0 based on the current detection signal I-SENSE from the current detection unit 12. , The switch 14 is turned off to disconnect the charging path, and the charging operation ends.

That is, in the charging / discharging cycle with the power source 2 being connected, since the lithium-ion storage battery 3 is less naturally discharged, the charging is started with a slight decrease in the charged amount (for example, about -10%). Despite being set, the lithium-ion battery 3
It does not deteriorate the life of the.

Therefore, the lithium ion storage battery 3 is
A sufficient charge capacity can be secured without deteriorating the life.

Next, the discharge of the lithium ion storage battery 3 will be described.

FIG. 3 is a diagram showing the discharge characteristics of a lithium ion storage battery at a temperature of −20 ° C. to 60 ° C.

First, when the power supply 2 is disconnected and the power supply is cut off, the control unit 13 causes the voltage signal Vin-SENSE.
It is detected that the power supply is stopped according to the potential level of the switch SWb, and the switch control signal SWb-CONT turns on the switch SWb. Thereby, the electric power of the lithium ion storage battery 3 is applied to the load 16, and when the switch 14 is off at this time, the lithium ion storage battery 3 is in a self-discharge state.

In this state, when the switch 14 is turned on, the power of the lithium ion storage battery 3 is supplied to the switching regulator 15 and the load 16 side, the power is supplied to the load 16, and the lithium ion storage battery 3 is in a discharged state. .

The control unit 13 determines the discharge amount by detecting the charger charging voltage Vout based on the potential level of the voltage signal V-SENSE. In this process, unlike the case of the self-discharge state described above, the lithium is discharged. The ion storage battery 3 is discharged to the final voltage of 2.75V. This allows the switch 14 to reach the final voltage.
Is turned off or the power supply of the power source 2 is not performed, the lithium ion storage battery 3 reaches the final voltage.

When the controller 13 detects that the final voltage has been reached, the switch control signal SWb-CONT is output, the switch SWb is turned off, and the load 16 is released.
Is separated. This serves to prevent the drawback of the lithium-ion storage battery 3 that the life is remarkably deteriorated due to overdischarge.

When the power supply 2 is connected after this,
As described above, since the load 16 is connected to the power source 2 side and operates with the power supplied from the power source 2, the lithium-ion storage battery 3 is charged when it is in the discharged state,
Restores charging ability.

As shown in FIG. 3, since the lithium-ion storage battery 3 has a discharge characteristic having a temperature characteristic, the temperature detecting section 11 functions to compensate the temperature characteristic.

As shown in FIG. 3, if the temperature range is limited to 0 ° C. to 60 ° C., the temperature dependency is small during this period, so that the temperature compensating operation can be omitted. This also applies to the charging characteristics.

As described above, the present embodiment can provide a charging method for keeping the charge amount of a storage battery in good condition without performing trickle charging. Particularly, when it is used for a charger such as a lithium ion storage battery, its effect is obtained. Is extremely large.

In addition, in the present embodiment, in addition to the above-mentioned configuration, means for preventing over-discharge is added, which makes it more suitable for charging a storage battery such as the lithium-ion storage battery 3 which is vulnerable to over-discharge. Becomes

In the present embodiment, the completion of charging is detected by detecting the current value of the charging current. However, as is clear from the charging characteristics shown in FIG. Since it may be judged that the charging is completed after 1 hour has passed, the charging completion may be detected by adding a timer unit for measuring the charging time.

The switch circuit 14 may be formed by combining the transistor 112 and the transistor 113 shown in FIG. 4, or an IC switch or a relay may be used.

Further, the resistors 6, 7 and
Although the voltage dividing circuit by 8 and 9 is used, a level shifter by a diode or the like may be used regardless of the method of voltage dividing.

[0073]

According to the first aspect of the present invention, the opening / closing of the switch section is controlled based on the presence / absence of power supply from the first detecting section and the charging voltage value from the second detecting section, and the power source section is controlled. By being controlled to operate as a constant voltage source or a constant current source, for example, to a secondary battery that is weak against overcharge and overdischarge, such as a lithium ion storage battery,
Trickle charging can be prevented.

According to the second aspect of the present invention, the switch portion has a hysteresis characteristic at the point where the switch changes from the open state to the closed state and at the point where the switch changes from the closed state to the open state. In addition, trickle charging can be prevented more reliably.

In this case, as in the invention described in claim 3,
The open / close control of the switch unit is based on the detection result of the temperature detecting means, the detection result of the current detecting means as in the invention of claim 4, and the time information from the timer means as in the invention of claim 5. In addition to the inventions according to the first and second aspects, optimal charging of the secondary battery can be performed.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a main configuration of a charging device according to a present embodiment.

FIG. 2 is a diagram showing charging characteristics of a lithium ion storage battery.

FIG. 3 is a diagram showing discharge characteristics of a lithium ion storage battery.

FIG. 4 is a circuit diagram showing a main configuration of a charging device in a conventional example.

[Explanation of symbols]

 1 Charger 2 Power supply 3 Lithium ion storage battery (secondary battery) 4,5 Diode 6-9 Resistance 10 Constant voltage / constant current power supply 11 Temperature detection part 12 Current detection part 13 Control part 14 Switch 15 Switching regulator 16 Load SWa, SWb Switch circuit 101 Charger 102 Power supply 103 Secondary battery 104, 105 Diode 106-111 Resistor 112, 113 Transistor 114 Switch 115 Switching regulator 116 Control part 117 Load

Claims (5)

[Claims] 1. A charging device for charging a secondary battery with a power supply current supplied from a power supply unit, the first detection means detecting whether or not power is supplied from the power supply unit, and the secondary battery supplied from the power supply unit. Second detection means for detecting the charging voltage to the secondary battery, a switch unit for switching whether to connect the secondary battery to an external load, the detection result from the first detection means and the second detection means Based on the opening and closing control of the switch unit based on,
A charging device comprising: a control unit that outputs a predetermined control signal to the power supply unit and outputs a control signal that operates as a constant voltage source or a constant current source. 2. The charging device according to claim 1, wherein the control of opening / closing of the switch portion by the control means has a hysteresis characteristic. 3. A temperature detecting means for detecting the temperature of the secondary battery is provided, and the control means controls the opening / closing of the switch portion based on the detection result of the temperature detecting means. The charging device according to 1 or 2. 4. A current detecting means for detecting a value of a current flowing through the secondary battery is provided, and the control means controls opening / closing of the switch portion based on a detection result of the current detecting means. The charging device according to claim 1, 2 or 3. 5. A timer means for measuring the time for charging the secondary battery is provided, and based on the time information of the timer means,
The charging device according to claim 1, 2, 3 or 4, wherein the control unit controls opening / closing of the switch unit.