JPH04325838A - Charging circuit - Google Patents

Abstract

PURPOSE:To suppress temperature rise of a charging current control transistor by interrupting charging current even upon application of abnormal voltage due to incorrect use. CONSTITUTION:The charging circuit controls the voltage across a charging current setting resistor to be equal to a reference voltage 11 by feeding a current proportional to that of a charging current control transistor Q1 to the charging current setting resistor. When the input voltage Vi increases abnormally, the charging current control transistor Q1 is heated intensely but a thermally coupled thermal shut circuit 12 lowers the reference voltage 11 and lowers the charging current Ia thus suppressing temperature rise of the charging current control transistor Q1.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging circuit for a rechargeable battery in which a thermal shut circuit is incorporated into a charging control circuit.

0002

[Prior Art] In recent years, a large number of portable devices using rechargeable batteries have been commercialized, and most of them have built-in rechargeable batteries and charging circuits inside the devices, and when power is supplied from an external source, the built-in rechargeable batteries are used. The battery is configured to charge the battery.

The above-mentioned conventional charging circuit will be explained below with reference to the drawings. FIG. 6 shows a circuit diagram of a conventional charging circuit, and FIG. 7 is a perspective view showing the external appearance of a portable device receiving power supply from the outside. In FIG. 6, 1 is a rechargeable battery, 4 is a power supply + terminal connected to the rechargeable battery 1, 5 is a power supply - terminal, and 9 is a charging terminal connected between the rechargeable battery 1 and the power supply - terminal 5. It is a current control resistor. Vi is the input voltage applied to the circuit, Vb is the battery voltage across the rechargeable battery 1, and Ia is the charging current flowing through the rechargeable battery 1. In FIG. 7, 21 is a rechargeable battery-based device, 21a is an external power supply socket provided on the rechargeable battery-based device 21, and 22 is a commercial power adapter that converts commercial power into a power source that can be used by the rechargeable battery-based device 21. 22a is an output terminal of the commercial power adapter 22, which is a power supply plug connected to an external power supply socket, and 23 is a commercial power outlet.

The operation of the conventional charging circuit configured as described above will be explained below. First, the rechargeable battery-using device 21 shown in FIG. 7 and the power supply plug 22a are connected, and the commercial power adapter 22 and the commercial power outlet 23 are connected. At this time, an input voltage Vi is applied between the power supply + terminal 4 and the power supply - terminal 5 shown in FIG. and flows to the power supply terminal 5. Here, if the resistance value of the charging current control resistor 9 is R, the flowing charging current Ia is

[0005]

[Math 1]

It is expressed as 0006.

[0007]

However, in the conventional charging circuit as described above, since the charging current Ia of the rechargeable battery 1 is determined by the charging current control resistor 9, it is difficult for the user to charge the commercial power adapter 22. If the input voltage Vi is abnormally high, such as when a device other than the specified battery type device 21 is used by mistake, the battery voltage Vb of the rechargeable battery 1 is constant almost regardless of the charging current Ia, so charging current control is not performed. The power lost in the resistor 9 increases extremely, and the charging current control resistor 9 generates abnormal heat. This heat generation may cause thermal deformation of the exterior resin of the rechargeable battery-using device 21 in some cases, and in extreme cases, this may lead to a fire.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, it is an object of the present invention to provide a charging circuit that cuts off the charging current when the temperature of the charging current control circuit becomes abnormally high, thereby greatly improving safety. That is.

[0009]

[Means for Solving the Problems] In order to solve the above problems, the charging circuit of the present invention has a charging current control terminal that connects a rechargeable battery, and a charging current that controls the charging current connected to the charging current control terminal. It includes a control transistor, a charging current control circuit that detects the current of the charging current control transistor and controls the current to a preset current value, and a thermal shut circuit that is thermally coupled to the charging current control transistor.

0010

[Operation] With the above-described configuration, the present invention cuts off the control current of the charging current control transistor when the temperature of the thermal shut circuit reaches a preset temperature even in an abnormal situation, so that the charging current is cut off. temperature does not become abnormally high.

[0011]

[Example] The following is a charging circuit according to an example of the present invention.
This will be explained in detail with reference to FIGS. 1 and 2.

FIG. 1 shows a circuit diagram of a charging circuit according to a first embodiment of the present invention, and FIG. 2 is an internal circuit diagram of the charging control circuit shown in FIG.

In FIG. 1, 1 is a rechargeable battery, 2 is a charging control circuit connected to the rechargeable battery 1, 2a is a charging control output terminal of the charging control circuit 2, and 2b is a charging current setting terminal of the charging control circuit 2. , 2c is a charging control reference terminal of the charging control circuit 2, which is connected to a power supply - terminal to be described later, and 2d is a charging control circuit power terminal of the charging control circuit 2, which is connected to a power supply + terminal to be described later.
connected to the terminal. 3 is a charging current setting resistor connected to the charging current setting terminal 2b, and 4 is a power supply + of the charging circuit.
Terminal 5 is a power supply terminal of the charging circuit. Also, V
i is the input voltage applied to the circuit, Vb is the battery voltage across the rechargeable battery 1, and Ia is the charging current flowing through the rechargeable battery 1. In FIG. 2, 2a, 2b, 2c, and 2d correspond to the explanation of FIG. 11 is a reference voltage generation circuit, 12 is a thermal shut circuit thermally coupled to a charging current control transistor to be described later, and 13 is a constant current generation circuit. Q1~Q1
0 is a transistor, and Q1 in particular is used as a charging current control transistor (charging current control means). R1 to R7 are resistors.

The operation of the charging circuit according to an embodiment of the present invention constructed as described above will be explained below.

First, power supply + terminal 4 and power supply - terminal 5
When an input voltage Vi is applied between the charging control circuit power supply terminal 2d and the charging control circuit power supply terminal 2d, the internal circuit of the charging control circuit 2 operates.

Next, the operation of the internal circuit of the charging control circuit 2 will be explained. One of the outputs of reference voltage 11 is sent to transistor Q7 through resistor R5. transistor Q7
and transistor Q6 constitute a differential amplifier. The constant current generated by the constant current generation circuit 13 is transmitted through the transistor Q9.
The signal is sent to a differential amplifier through a mirror circuit consisting of a transistor Q8 and a transistor Q8. The output of transistor Q7 of the operational amplifier is sent to transistor Q5 with resistor R4 as a load, and the output of transistor Q5 is sent to transistor Q2 and transistor Q1 with resistor R3 as a load. Here, the charging current Ia flows from the charging control output terminal 2a through the transistor Q1 to the charging control reference terminal 2c, but the transistor Q1 and the transistor Q2 are connected to each other, although the protective resistor R2 is attached to the base of the transistor Q1. Because the bases are connected, the transistor Q
The current IceQ1 flowing between the collector and emitter of transistor Q1 and the current I flowing between the collector and emitter of transistor Q2
It is proportional to ceQ2 at a specific ratio. For this circuit,
Assuming R2=0, let reQ1 be the emitter equivalent resistance of transistor Q1, and reQ2 be the emitter equivalent resistance of transistor Q2.

[0017]

[Math 2]

[0018] Therefore, the charging current Ia can be detected by the transistor Q2 as IceQ2 flowing between the collector and emitter of the transistor Q2. This Ic
eQ2 is sent to the base of transistor Q6, which is the other input of the operational amplifier, through a mirror circuit consisting of transistor Q3 and transistor Q4, and the base of transistor Q6 is connected to charging current setting terminal 2b, so that the charging current is Since setting resistor 3 is connected, the above I
Most of ceQ2 flows through charging current setting resistor 3. Further, the charging current Ia is controlled so that the voltage across the charging current setting resistor 3 becomes equal to the output voltage of the reference voltage generating circuit 11 by the action of the operational amplifier composed of the transistor Q6 and the transistor Q7. Therefore, the current flowing through the charging current setting resistor 3 is equivalent to IceQ2, and the current flowing through the charging current setting resistor 3 is equal to IceQ2.
When the resistance value of is R0 and the output voltage of the reference voltage generation circuit 11 is Vref, IceQ2 is

[0019]

[Math 3]

It can be expressed as: Also, the relationship between the charging current setting resistor 3 and the charging current Ia is

[0021]

[Math 4]

[0022] In other words, the charging current Ia can be set by the charging current setting resistor 3. If the power loss of the charging control circuit 2 at this time is W, then

[0023]

[Math 5]

[0024] In addition, the thermal shut circuit 12
connects the voltage dividing resistors R6 and R to the base of the transistor Q10 using a reference voltage whose voltage does not change even when the temperature changes.
7, and its output, the collector of transistor Q10, is connected to the reference voltage supply side of the operational amplifier. Resistors R6 and R7 are connected to transistor Q in normal use.
10 is set to a resistance that does not operate. Here, assuming that an abnormality occurs and the input voltage Vi becomes high, the charging current Ia is constant due to the charging control circuit 2, but the battery voltage V
Since b is also constant, the power loss of the charging control circuit 2 will be large. Since this power loss occurs in the transistor Q1 that directly controls the charging current, the heat generated by the transistor Q1 becomes extremely large. This heat is transmitted to the transistor Q10 of the thermal shut circuit 12 which is thermally coupled, and the base-emitter voltage Vbe of the transistor decreases as the temperature increases, so the operating point of the transistor Q10 also decreases. The base-emitter voltage Vb of transistor Q10 is higher than the voltage
eQ10 becomes lower and transistor Q10 is turned on.
do. In other words, the reference voltage supplied to the operational amplifier composed of transistors Q7 and Q6 is lowered. This reduces the charging current due to the above-described operation, thereby reducing the amount of power loss in the transistor Q1 and lowering the temperature. In other words, the temperature will not exceed the temperature set in advance by the thermal shut circuit 12.

As described above, according to this embodiment, the charging current control terminal to which the rechargeable battery is connected, the charging current control transistor connected to the charging current control terminal and controlling the charging current, and the charging current control transistor It is equipped with a charging current control circuit that detects the current and controls the current to a preset current value, and a thermal shut circuit that is thermally coupled to the charging current control transistor, and when the temperature of the thermal shut circuit reaches the preset temperature. By adopting a configuration that sometimes cuts off the control current of the charging current control transistor, the charging current can be cut off even in abnormal situations because the control current of the charging current control transistor is cut off when the temperature of the thermal shut circuit reaches a preset temperature. This will prevent the temperature of the charging current control circuit from becoming abnormally high.

Next, regarding the second embodiment, FIGS. 2 and 3
This will be explained in detail with reference to. FIG. 2 is an internal circuit diagram of the charging control circuit used in the explanation of the first embodiment. FIG. 3 shows a circuit diagram of a charging circuit in a second embodiment of the present invention.

In FIG. 3, reference numeral 2d denotes a charging control circuit power supply terminal of the charging control circuit 2, which is connected to a charging control output terminal 2a to which the rechargeable battery 1 is connected. The rest of the configuration is the same as the configuration in FIG. 1, so detailed explanation will be omitted.

The operation of the charging circuit configured as described above will be explained below. First, when an input voltage Vi is applied between the power supply + terminal 4 and the power supply - terminal 5, the voltage is applied to the charge control circuit power supply terminal 2d through the rechargeable battery 1, and the internal circuit of the charge control circuit 2 operates. . The details of the operation are the same as in the first embodiment, but since the charging control circuit power terminal 2d of the charging control circuit 2 is connected to the charging control output terminal 2a to which the rechargeable battery 1 is connected, the charging control circuit Current flows into the power supply terminal 2d via the rechargeable battery 1. This means that the charging circuit including the charging current setting resistor 3 has a two-terminal network configuration and can be used as a replacement for the circuit described as an example of a conventional charging circuit.

As described above, according to the second embodiment of the present invention, the power source for the entire charging current control circuit that controls the charging current is taken out from the charging current control terminal, and the rechargeable battery and the entire charging current control circuit are connected in series. By adopting a configuration that connects and controls, not only the effect of the first embodiment but also the charging circuit becomes a two-terminal network configuration, which can be used in place of a conventional charging circuit configured with a resistor. .

Next, a third embodiment of the present invention will be described in detail with reference to FIGS. 2 and 4.

FIG. 2 is an internal circuit diagram of the charging control circuit used in the explanation of the first embodiment. FIG. 4 shows a circuit diagram of a charging circuit in a third embodiment of the present invention.

[0032] In FIG. 4, detailed explanation of the same configuration as in FIG. 1 will be omitted. 3a to 3c are charging current setting resistors connected to the charging current setting terminal 2b; 6a and 6b are charging current setting switching circuits for changing the constant of the charging current setting resistor connected to the charging current setting terminal 2b; and 7 is a charging current setting switching circuit for changing the constant of the charging current setting resistor connected to the charging current setting terminal 2b. The charging state of the rechargeable battery 1 is detected from the voltage across the rechargeable battery 1, and the charging current setting switching circuits 6a and 6b are controlled so that the charging current becomes an appropriate value for the charging state of the rechargeable battery 1. These are a charging state detection circuit and a current setting control circuit. Vi is the input voltage applied to the circuit, and Ia is the charging current flowing through the rechargeable battery 1.

The operation of the charging circuit configured as described above will be explained below. First, when an input voltage Vi is applied between the power supply + terminal 4 and the power supply - terminal 5, a voltage is applied to the charge control circuit power supply terminal 2d, and the internal circuit of the charge control circuit 2 operates. At the same time, the charging state detection circuit and current setting control circuit 7 detect the charging state of the rechargeable battery 1 from the voltage across the rechargeable battery 1, and the charging current becomes an appropriate value for the charging state of the rechargeable battery 1. The charging current setting switching circuits 6a and 6b are controlled to set the constant of the charging current setting resistor. For example, if the charging state of the rechargeable battery 1 is an uncharged state, the voltage across the rechargeable battery 1 is lower than the normal state, so it can be determined that the rechargeable battery 1 is in an uncharged state, and the constant of the charging current setting resistor is controlled as much as possible to the set minimum resistance value, and the charging current Ia is maximized (quick charging). For example, if the state is fully charged, the voltage across the rechargeable battery 1 is higher than the normal state, so it can be determined that it is fully charged, and the constant is controlled to be the maximum resistance value set. Then, the charging current Ia is minimized (trickle charging). As an example of setting the charging current Ia, quick charging is set to the maximum charging current value that rechargeable battery 1 can withstand, and trickle charging is set to a charging current value that does not cause performance deterioration even if rechargeable battery 1 continues to be charged for a long period of time. It is recommended to set it to . By varying the charging current Ia in accordance with the charging state of the rechargeable battery 1 in this manner, charging can be completed in a shorter time. Moreover, an overcharge state, which is a state of overcharging, does not occur, and charging can be performed more safely.

As described above, according to the third embodiment, the charging state detection circuit detects the charging state of the rechargeable battery and the control current of the charging current control transistor is selected from among a plurality of preset current values. By providing a charging current control circuit that selects a current value suitable for the state of charge of the rechargeable battery and sets the current value to that current value, not only the effects of the first embodiment but also the rechargeable battery can be charged in a shorter time. This means that the process can be completed. Moreover, an overcharge state, which is a state of overcharging, does not occur, and charging can be performed more safely.

Furthermore, regarding the fourth embodiment, FIG.
, will be explained in detail with reference to FIG.

FIG. 2 is an internal circuit diagram of the charging control circuit used in the explanation of the first embodiment. FIG. 5 shows a circuit diagram of a charging circuit in a third embodiment of the present invention. Detailed description of the same configuration as in FIG. 1 will be omitted.

In FIG. 5, 3a and 3b are charging current setting resistors 6 to be connected to the charging current setting terminal 2b, and charging current setting switching resistors 6 to change the constant of the charging current setting resistor connected to the charging current setting terminal 2b. Circuit 8 is a charging current setting switching circuit 6 after a certain period of time has passed after voltage is applied.
This is a timer circuit that controls the The charging current setting switching circuit 6 has a structure in which both ends of the charging current setting resistor 3b are connected when there is no output from the timer circuit 8, and conversely, when there is an output from the timer circuit 8, the charging current setting switching circuit 6 connects both ends of the charging current setting resistor 3b. It shall have a structure in which both ends are open. Further, Vi is an input voltage applied to the charging circuit.

The operation of the charging circuit configured as described above will be explained below. First, when an input voltage Vi is applied between the power supply + terminal 4 and the power supply - terminal 5, a voltage is applied to the charge control circuit power supply terminal 2d, and the internal circuit of the charge control circuit 2 operates. At the same time, the timer circuit 8 starts to count the time, but when the preset time is not reached, it does not output to the charging current setting switching circuit 6, so both ends of the charging current setting resistor 3b are connected. Therefore, the charging current Ia becomes the current value set by the charging current setting resistor 3a. Next, when the preset time has elapsed and the time limit timer circuit 8 outputs an output to the charging current setting switching circuit 6, the charging current setting switching circuit 6 opens both ends of the charging current setting resistor 3b, so that charging The current Ia has a current value set by the series connection value of the charging current setting resistors 3a and 3b. Charging current setting resistor 3
Set the charging current Ia (1) set only by a to the maximum charging current value (quick charging) that the rechargeable battery 1 can withstand,
The charging current Ia (2), which is set by the series connection value of the charging current setting resistors 3a and 3b, is set to a charging current value (trickle charging) at which performance deterioration is unlikely to occur even if the rechargeable battery 1 is continuously charged for a long period of time. Then, charging can be completed in a shorter time. However, the value of the charging current Ia(1) for quick charging in this case differs from the charging current value shown in the third embodiment described above because the charging state of the rechargeable battery 1 is not detected. Even if the battery 1 is in a fully charged state, rapid charging will occur for a period of time preset in the timer circuit 8, so the current value must be set in consideration of this state.

As described above, according to the fourth embodiment, there is a timer that operates for a preset time after the power is turned on, and a charging current that controls the charging current value using a signal from the timer. By providing a control circuit, not only the effects of the second embodiment but also the charging of the rechargeable battery can be completed in a shorter time. Moreover, an overcharge state, which is a state of overcharging, does not occur, and charging can be performed more safely.

[0040]

As described above, according to the present invention, there is provided a charging current control terminal for connecting a rechargeable battery, a charging current control transistor for controlling a charging current connected to the charging current control terminal, and a charging current control transistor for controlling a charging current. A charging current control circuit detects the current of the transistor and controls the current to a preset current value, and a thermal shut circuit is thermally coupled to the charging current control transistor. By cutting off the control current of the charging current control transistor when the thermal shutoff circuit reaches a preset temperature, the charging current is cut off because the control current of the charging current control transistor is cut off even in abnormal situations. , the temperature of the charging current control circuit does not become abnormally high and charging can be performed safely.

[Brief explanation of drawings]

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

[Figure 2] Internal circuit diagram of charging control circuit

FIG. 3 is a circuit diagram of a charging circuit according to a second embodiment of the present invention.

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

[Figure 5]
Circuit diagram of a charging circuit according to a fourth embodiment of the present invention

[Figure 6] Circuit diagram of conventional charging circuit

[Figure 7] External perspective view of portable equipment receiving external power supply

[Explanation of symbols]

1 Rechargeable battery 2 Charging control circuit 2a Charge control output terminal 2b Charging current setting terminal 2c Charging control reference terminal 2d Charging control circuit power supply terminal 12 Thermal shut circuit Q1~Q10 Transistor R1~R7 Resistance Vi input voltage Vb Battery voltage Ia Charging current

Claims (4)

[Claims] 1. A charging current control terminal to which a rechargeable battery is connected, a charging current control means connected to the charging current control terminal for controlling the charging current, and a current flowing through the charging current control means, the current being detected. a charging current control circuit that controls the current to a preset current value; and a thermal shut circuit thermally coupled to the charging current control means, and when the temperature of the thermal shut circuit reaches the preset temperature, the A charging circuit characterized in that a control current of a charging current control means is cut off. 2. The charging current control circuit according to claim 1, wherein a power source for the entire charging current control circuit that controls the charging current is taken out from a charging current control terminal, and the rechargeable battery and the entire charging current control circuit are connected in series and controlled. charging circuit. 3. A state of charge detection circuit that detects the state of charge of the rechargeable battery, and a control current of the charging current control means that selects a current suitable for the state of charge of the rechargeable battery from among a plurality of preset current values. 2. The charging circuit according to claim 1, further comprising a charging current control circuit that selects a value and sets the current value to that value. 4. When the rechargeable battery is connected, power is applied to the control circuit, and a timer is operated for a preset time after the power is turned on, and a charging current is controlled by a signal from the timer. 3. The charging circuit according to claim 2, further comprising a charging current control circuit for controlling the value.