JP3197698B2 - Battery charge / discharge 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 charge / discharge circuit for a secondary battery. In particular, the present invention connects a load and a secondary battery to a power supply, supplies power to the load from the power supply when the power is on, and charges the secondary battery.When the power is off, the secondary battery supplies the load. The present invention relates to a so-called floating charge / discharge circuit for supplying power to a load.

[0002]

2. Description of the Related Art FIG. 1 shows a conventional floating charge / discharge circuit.
Shown in In the charge / discharge circuit shown in this figure, a load 1 is connected to a DC power supply via a diode D1 in order to supply power from the power supply to the load 1. Further, in order for the DC power supply to charge the secondary battery 2, the secondary battery 2 is connected to the power supply via the constant voltage charging circuit 3. The constant voltage charging circuit 3 lowers the power supply voltage to make the voltage constant, and charges the secondary battery 2 while limiting it to a constant voltage. The one-way rectifier 4 is connected between the load 1 and the secondary battery 2 so that no current flows from the load 1 to the secondary battery 2 when the power is on.

[0003] In this specification, a "one-way rectifier" refers to a semiconductor element that can flow a current to one side but cannot flow a current in the opposite direction, such as a diode, a thyristor, a transistor, or the like. Shall mean. A thyristor can trigger a gate to conduct current, much like a diode. The transistor can be controlled so that a base current flows and a current flows.

[0004]

The charge / discharge circuit shown in FIG. 1 supplies power to the load 1 from the DC power supply when the DC power supply is turned on. At this time, the voltage of the power supply is controlled to a constant voltage by the constant voltage charging circuit 3 to charge the secondary battery 2. When the power is turned off, power is supplied from the secondary battery 2 to the load 1 via the one-way rectifier 4.

[0005] This charge / discharge circuit does not overcharge the secondary battery 2 as long as the one-way rectifier 4 operates ideally. However, the adverse effect of overcharging the secondary battery 2 occurs due to the leakage current of the one-way rectifier 4. In particular, the unidirectional rectifier 4 needs to reduce the forward voltage drop. Therefore, a Schottky barrier diode with small voltage loss is suitable. However, the Schottky barrier diode has a property that the reverse leakage current increases at high temperatures. The reverse leakage current of the one-way rectifier element 4 charges the secondary battery 2 to a voltage higher than the set voltage and overcharges the secondary battery 2. Since the current passing through the one-way rectifier 4 is blocked by the diode D3, the current cannot be made constant by the Zener diode D4. For this reason, if the power-on time is prolonged, the secondary battery 2 is overcharged and deteriorated.

The adverse effect that the secondary battery 2 is overcharged by the reverse leakage current of the one-way rectifying element 4 is caused by changing the Zener diode D4 of the constant voltage charging circuit 3 from the position of the solid line to the position of the broken line in FIG. Can be eliminated. However, the zener diode D4 connected at the position indicated by the broken line has a drawback that the secondary battery 2 is discharged and the battery 2 is wasted when the power is turned off. To prevent the Zener diode D4 from discharging the secondary battery 2, the secondary battery 2 and the Zener diode D
It is necessary to connect a diode between them. Since a diode is connected between the secondary battery 2 and the Zener diode D 4, the Zener diode D 4 cannot prevent the voltage of the secondary battery 2 from rising due to the reverse leakage current of the one-way rectifier 4. Thus, the circuit for charging the secondary battery at a constant voltage cannot prevent the voltage of the secondary battery from abnormally rising due to the reverse leakage current of the one-way rectifying element, and if the time for turning on the power becomes longer, There is a disadvantage that the secondary battery is deteriorated by the reverse leakage current. In particular, when a lithium ion secondary battery is used as a secondary battery, there is a problem that battery performance is significantly reduced due to overcharging. Therefore, in a floating charging circuit using a lithium ion secondary battery, it is particularly important to prevent the secondary battery from being overcharged.

The present invention has been developed to solve this drawback. An important object of the present invention is to provide a charge / discharge circuit of a power supply that prevents overcharge of a secondary battery due to leakage current of a one-way rectifier.

[0008]

The battery charging / discharging circuit according to the present invention has the following configuration to achieve the above object. The battery charge / discharge circuit connects the secondary battery 2 to a power supply via a constant voltage charging circuit 3. The secondary battery 2 is connected to the load 1 via the one-way rectifier 4. The one-way rectifier 4 is capable of flowing current from the secondary battery 2 to the load 1, but is connected so as to prevent current from flowing from the load 1 to the secondary battery 2. A diode is usually used for the one-way rectifier 4. When the power is on, the constant voltage charging circuit 3 charges the secondary battery 2 while preventing the secondary battery 2 from rising to a certain set voltage or higher. Further, power is supplied from the power supply to the load 1. When the power is off, power is supplied from the secondary battery 2 to the load 1 via the one-way rectifier 4.

Further, the charge / discharge circuit of the present invention has the following unique configuration. A constant voltage charging circuit 3 for charging the secondary battery 2 at a constant voltage includes a constant voltage switching circuit 3 connected in parallel with the secondary battery 2 via the switching element 5.
A is built in. When the power is on, the switching element 5 is turned on, and the constant voltage switching circuit 3A
Are connected in parallel with the secondary battery 2, and the constant voltage switching circuit 3A prevents the voltage of the secondary battery 2 from rising above a set value. That is, the voltage of the secondary battery 2 is prevented from abnormally rising due to the reverse leakage current of the one-way rectifier 4.
When the power is off, the switching element 5 is turned off, and the connection between the constant voltage switching circuit 3A and the secondary battery 2 is cut off. That is, it prevents the constant voltage switching circuit 3A from discharging the secondary battery 2.

[0010]

The operation of the charge / discharge circuit of the present invention will be described with reference to FIG. 2 showing a preferred embodiment. [When the power supply is on] Power is supplied from the power supply to the load 1 via the diode D1. At this time, the secondary battery 2 is charged at a constant voltage via the constant voltage charging circuit 3. Reverse leakage current ID2 flows through diode D2, which is one-way rectifier element 4. The reverse leakage current ID2 is bypassed by the constant voltage switching circuit 3A to prevent the secondary battery 2 from being overcharged. When the power is turned on, the constant voltage switching circuit 3A turns on the switching element 5, and connects the constant voltage switching circuit 3A to the secondary battery 2 in parallel. The constant voltage switching circuit 3A connected in parallel to the secondary battery 2 prevents the voltage of the secondary battery 2 from abnormally rising and being overcharged. When the voltage of the secondary battery 2 is lower than the set value, the secondary battery 2 is charged with the reverse leakage current ID2 of the constant voltage charging circuit 3 and the one-way rectifier 4. However,
When the voltage of the secondary battery 2 rises to the set value, the constant voltage switching circuit 3A switches the reverse leakage current ID2 of the one-way rectifier 4
To prevent the voltage of the secondary battery 2 from rising. Therefore, the secondary battery 2 is not overcharged by the reverse leakage current ID2 of the one-way rectifier 4.

[When the power is off] When the power is turned off, the power is supplied from the secondary battery 2 to the load 1 through the diode D2 which is the one-way rectifying element 4. Switching element 5 of constant voltage switching circuit 3A
Turns off. Therefore, the constant voltage switching circuit 3
A is no longer connected to the secondary battery 2 in parallel, and the secondary battery 2
Is prevented from discharging.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. However, the following embodiments illustrate charge / discharge circuits for embodying the technical idea of the present invention, and the present invention does not specify the following charge / discharge circuits.

Further, in this specification, in order to make it easy to understand the claims, the numbers corresponding to the members shown in the embodiments will be referred to as "claims", "actions", and "actions". In the column of "Means for solving the problem". However, the members shown in the claims are
It is by no means specific to the members of the embodiment.

The charge / discharge circuit of the battery 2 shown in FIG. 2 has a diode D 1 connected between the power supply and the load 1. Between the diode D1 and the load 1, that is, the output side of the diode D1 is connected to the secondary battery 2 via the diode D2 which is the one-way rectifying element 4. The negative side of the secondary battery 2 is
It is connected to the load 1 and the negative side of the power supply. Diode D2
Are connected so that power can be supplied from the secondary battery 2 to the load 1. As the secondary battery, a lithium ion secondary battery or a nickel cadmium secondary battery is used.

Further, the output side of the diode D1 is provided so that the secondary battery 2 can be charged at a constant voltage when the power is on.
It is connected to the secondary battery 2 via the constant voltage charging circuit 3.
The constant voltage charging circuit 3 sets a current limiting resistor 6 for limiting the charging current of the secondary battery 2 and a charging voltage of the secondary battery 2 and, when the power is off, wastefully discharges the secondary battery 2 And a constant voltage switching circuit 3A for blocking the voltage.

The constant voltage switching circuit 3A includes a Zener diode D4 and a switching element 5, and is connected in parallel with the secondary battery 2. The Zener diode D4 and the switching element 5 that constitute the constant voltage switching circuit 3A are connected in series with each other. The Zener diode D4 is connected to a connection point between the current limiting resistor 6 and the secondary battery 2, and the switching element 5 is connected to the Zener diode D4.
It is connected between 4 and the minus side of the power supply. The switching element 5 in FIG. 2 is a MOSFET. The gate of the FET is connected to the + side of the power supply. Accordingly, the switching element 5 is turned on when a power supply is on, and a gate current is cut off when the power supply is off.

This constant voltage switching circuit performs the following operations to charge the secondary battery and to supply power to the load from the secondary battery. [When the power is on] The FET that is the switching element 5 is turned on, and the secondary battery 2 is charged while being held at the Zener voltage of the Zener diode D4. At this time, power is supplied from the power supply to the load 1 via the diode D1. In a state where the switching element 5 is turned on, the reverse leakage current ID2 of the diode D2 does not increase the voltage at the time of charging the secondary battery 2 beyond the set value. This is because the secondary battery 2 is directly connected to the Zener diode D4. That is, the secondary battery 2 is connected to the Zener diode D4 without passing through the diode D3 essential for the conventional charge / discharge circuit shown in FIG. Zener diode D4 bypasses reverse leakage current ID2 of diode D2. This prevents the secondary battery 2 from being overcharged by the reverse leakage current ID2 of the diode D2.

[When the power is off] In this state, no current flows through the gate of the switching element 5, and the switching element 5 is turned off. At this time, electric power is supplied from the secondary battery 2 to the load 1. When the switching element 5 is turned off, the connection between the Zener diode D4 and the secondary battery 2 is cut off. Therefore, the secondary battery 2 and the Zener diode D4
Current does not flow through the loop of the switching element 5.
That is, the secondary battery 2 is not discharged via the Zener diode D4.

FIG. 3 shows a second embodiment of the present invention. The charge / discharge circuit shown in this figure uses voltage dividing resistors R1 and R2 instead of the Zener diode D4 in the embodiment of FIG. The switching element 5 of the constant voltage switching circuit 3A
A transistor is used instead of the MOSFET. The voltage of the power supply is set to, for example, 5V. Therefore, the power supply voltage can be divided by the voltage dividing resistors R1 and R2 to charge the secondary battery 2 at a constant voltage. This charge / discharge circuit sets the charging voltage of the secondary battery 2 by the ratio of the resistance values of the voltage dividing resistors R1 and R2. The voltage dividing resistor R1 is connected in parallel with the diode D2, and the voltage dividing resistor R2 is connected in parallel with the secondary battery 2 via a transistor. The base of the transistor is connected to the + side of the power supply via a resistor.

The transistor is turned on when a base current flows from the power supply when the power supply is on, and when the power supply is off,
The base current stops flowing and turns off. Therefore,
This charge / discharge circuit performs the following operation to charge the secondary battery 2 at a constant voltage.

[When the power is on] The transistor which is the switching element 5 is turned on, and the secondary battery 2 is charged while maintaining the voltage of the voltage dividing ratio of the voltage dividing resistors R1 and R2. In this state, the diode D1
Power is supplied from the power supply to the load 1 via the. In a state where the switching element 5 is turned on, the reverse leakage current ID2 of the diode D2 does not increase the voltage at the time of charging the secondary battery 2 beyond the set value. Reverse leakage current ID2
Is bypassed by the voltage dividing resistor R2. This prevents the secondary battery 2 from being overcharged by the reverse leakage current ID2 of the diode D2.

[When the power is off] In this state, the switching element 5 is turned off since no current flows to the base. When the switching element 5 is turned off, the voltage dividing resistor R2
And the connection of the secondary battery 2 is cut off. Therefore, the secondary battery 2 is not discharged via the voltage dividing resistor R2.

FIG. 4 shows a charge / discharge circuit according to a third embodiment of the present invention. The charge / discharge circuit of this figure uses a shunt regulator IC instead of the Zener diode D4 of the embodiment of FIG. Also, a transistor Q2 is used instead of the diode D1 and a constant voltage switching circuit 3A.
A transistor Q1 is used for the switching element 5 in place of the MOSFET.

The shunt regulator IC 7 turns on when the voltage of the voltage detection terminal is 2.5 V or more, and turns off when the voltage is less than this voltage. The shunt regulator IC divides the battery voltage with a resistor and inputs the voltage to the voltage detection terminal 8. The charging voltage of the secondary battery 2 can be adjusted by a resistance value that divides the voltage of the secondary battery 2. The shunt regulator IC 7 turns on when the voltage of the secondary battery 2 becomes higher than the set voltage, turns off when the voltage becomes lower than the set voltage, and charges the secondary battery 2 until it reaches the set voltage.

The base of the transistor Q1 is connected to the power supply via a resistor so as to be turned on when the power supply is turned on. The base of the transistor Q2 is connected to the collector of the transistor Q1 so that the transistor Q2 is turned on when the power is turned on.

The charge / discharge circuit performs the following operation to charge the secondary battery 2 at a constant voltage. [When power is on] Transistor Q2 and constant voltage switching circuit 3
The transistor Q1 which is the switching element 5 of A is turned on. Power is supplied from the power supply to the load 1 via the transistor Q2. The secondary battery 2 is charged at a constant voltage by the shunt regulator IC until it reaches the set voltage. The transistor Q1, which is the switching element 5,
Bypass the reverse leakage current of the diode D2. Therefore, the secondary battery 2 is prevented from being overcharged by the reverse leakage current.

[When the power is off] The transistor Q1 and the transistor Q2 are turned off. Power is no longer supplied from the power supply to the load 1, and power is supplied from the secondary battery 2 to the load 1. The transistor Q1 is turned off, and the connection between the shunt regulator IC and the secondary battery 2 is cut off. Therefore, the secondary battery 2 is not discharged by the shunt regulator IC.

FIG. 5 shows a charge / discharge circuit according to a fourth embodiment of the present invention. The charge / discharge circuit of this figure replaces the Zener diode D4 of the embodiment of FIG.
Use a constant voltage circuit. Further, a transistor Q1 is used for the switching element 5 of the constant voltage switching circuit 3A in the same manner as in the circuit of FIG.

The constant voltage circuit including the transistor Q3 is
The base is connected to the DC power source through a Zener diode D5.
Side to make the output voltage of the emitter constant. This constant voltage circuit has a difference between the base voltage and the emitter voltage of about 0.6.
The output voltage of the emitter is controlled to be V. Therefore, the set voltage of the secondary battery 2 can be adjusted by the Zener voltage of the Zener diode D5 connected to the base.

This charge / discharge circuit performs the following operation to charge the secondary battery at a constant voltage. [When the power is on] The secondary battery 2 is charged at a constant voltage by controlling the output voltage to a set value via the transistor Q3 of the constant voltage circuit. Power is supplied from the power supply to the load 1 via the diode D1. Switching element 5 of constant voltage switching circuit 3A
Is turned on, and the transistor Q1 bypasses the reverse leakage current ID2 of the diode D2. This prevents the rechargeable battery 2 from being overcharged by the reverse leakage current ID2.

[When the Power is Off] Power is no longer supplied from the power supply to the load 1, and power is supplied from the secondary battery 2 to the load 1. The transistor Q1 is turned off, and the secondary battery 2
Discharging stops at the resistor R3.

[0032]

The battery charge / discharge circuit of the present invention can prevent the secondary battery from being overcharged by the reverse leakage current of the one-way rectifier. For this reason, even if the time for turning on the power becomes considerably long, it is possible to prevent the secondary battery from being overcharged and deteriorated by the reverse leakage current, thereby extending the life of the secondary battery. Further, even if a Schottky barrier diode having a large reverse leakage current but a small voltage loss is used as the one-way rectifier, the secondary battery is not overcharged. For this reason, it is possible to use a Schottky barrier diode with a small voltage loss for the one-way rectifying element, and it is possible to effectively use the power of the secondary battery and prevent the life of the secondary battery from being shortened. is there.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a conventional battery charge / discharge circuit.

FIG. 2 is a circuit diagram of a battery charge / discharge circuit according to one embodiment of the present invention.

FIG. 3 is a circuit diagram of a battery charge / discharge circuit according to another embodiment of the present invention.

FIG. 4 is a circuit diagram of a battery charge / discharge circuit according to another embodiment of the present invention.

FIG. 5 is a circuit diagram of a battery charge / discharge circuit according to another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Load 2 ... Battery 3 ... Constant voltage charging circuit 3A ... Constant voltage switching circuit 4 ... One-way rectifier element 5 ... Switching element 6 ... Current limiting resistor 7 ... Shunt regulator IC 8 ... Voltage detection terminal

Claims (1)

(57) [Claims] 1. A secondary battery (2) via a constant voltage charging circuit (3).
Is connected to a power source, and the secondary battery (2) is a battery (2).
Although current can flow from the load (1) to the load (1), the load (1) can be supplied through a one-way rectifier (4) that prevents the current from flowing from the load (1) toward the secondary battery (2). ), And when the power is on, the constant voltage charging circuit (3)
Is charging the secondary battery (2), power is supplied from the power supply to the load (1), and when the power is off, the one-way rectifier is
In the battery charge / discharge circuit configured to supply power from the secondary battery (2) to the load (1) via (4), constant voltage charging of the secondary battery (2) is performed at a constant voltage. The circuit (3) has a built-in constant voltage switching circuit (3A) connected in parallel with the secondary battery (2) via the switching element (5),
When the power is on, the switching element (5) is turned on, and the constant voltage switching circuit (3A) is connected to the secondary battery (2).
To prevent the voltage of the secondary battery (2) from rising above a set value.When the power is off, the switching element (5) is turned off, and the constant voltage switching circuit (3A ) And the secondary battery (2) are disconnected to prevent the secondary battery (2) from being discharged by the constant voltage charging circuit (3). circuit.