JPH07163062A - Constant-current charging circuit - Google Patents

Abstract

PURPOSE:To provide a low-cost constant-current type charging circuit which has a relatively simple circuit arrangement. CONSTITUTION:The emitter-collector of a first transistor Q1 is inserted into a charging path of the positive electrode of a smoothing capacitor C1 to a secondary battery B, and a current detecting resistor R1 is inserted between the negative electrode of the smoothing capacitor C1 and the secondary battery B. The base of the first transistor Q1 is connected with the collector of a second transistor Q2 compares a reference voltage generated by diodes D3, D4 with a voltage between both terminals of the current detecting resistor R1 to control the base current of the first transistor Q1 so that a difference between both voltages becomes small. Therefore, a charging current to the secondary battery B is kept substantially constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant current type charging circuit mainly used for charging nickel-cadmium batteries.

[0002]

2. Description of the Related Art Conventionally, nickel-cadmium batteries have been used for various purposes as secondary batteries. 2 of this kind
In order to prevent overcharge when charging the secondary battery, it is necessary to accurately detect the terminal voltage and temperature change of the secondary battery. Therefore, it is considered that the terminal voltage and temperature of the secondary battery are accurately detected without variation by making the charging current constant. That is, if the charging current is made constant, the terminal voltage of the secondary battery can be easily detected by the voltage change of the charging voltage, and the temperature detecting element for detecting the temperature of the secondary battery generally applies a constant current to both ends of the temperature detecting element. Since the voltage corresponds to the temperature, the temperature can be accurately detected if the charging current is made constant.

As described above, in order to configure the charging circuit in which the charging current is made constant, a control circuit for detecting the charging current and the charging voltage and controlling the charging current is required. The control circuit was configured by using a microcomputer with a built-in analog converter and analog converter.

[0004]

As described above, the conventional constant current type charging circuit has a problem that a microcomputer is required as a control circuit, and the parts constituting the control circuit are expensive. It was The present invention is intended to solve the above problems, and an object of the present invention is to provide a constant current type charging circuit which has a relatively simple circuit configuration and is inexpensive.

[0005]

According to a first aspect of the present invention, a series circuit including an emitter-collector of a first transistor and a current detection resistor is inserted in a charging path from a DC power supply to a secondary battery, and a constant current is inserted. Providing a reference pressure generator that generates a reference voltage,
A collector is connected to the base of the first transistor, and a second transistor for controlling the base current of the first transistor is provided in a direction to reduce the difference between the voltage across the current detection resistor and the reference voltage. To do.

According to a second aspect of the present invention, in the first aspect of the invention, a plurality of current detection resistors each having one end commonly connected and the other end having a terminal are provided, and one current detection resistor is connected to the terminal. The potential of the point is compared with the reference voltage by the second transistor, the secondary battery is connected to at least one terminal, and the remaining current detection resistor is the one current when the corresponding terminal is connected to the secondary battery. It is characterized in that it is connected in parallel to the detection resistor.

A third aspect of the present invention is the third aspect of the present invention according to the first or second aspect, wherein the collector and the emitter of the second transistor are connected in series between the collector and the emitter.
And a series circuit of a pair of resistors connected between the output terminals to the secondary battery, the connection point of both resistors being the third
It is characterized in that it is connected to the base of the transistor.

A fourth aspect of the present invention is the third aspect of the present invention according to the first or second aspect, wherein the collector and the emitter of the second transistor are connected in series between the collector and the emitter.
And a constant voltage element which is connected between one output end of the secondary battery and the base of the third transistor and which conducts when the output voltage becomes equal to or higher than a predetermined voltage.

[0009]

According to the structure of the invention of claim 1, the emitter and collector of the first transistor and the current detecting resistor are inserted in the charging path to the secondary battery, and the voltage across the current detecting resistor and the reference voltage are applied. Since the base current of the first transistor is controlled so as to reduce the difference between the two, the voltage across the current detection resistor is kept substantially constant. That is, the first
The charging current to the secondary battery passing between the emitter and the collector of the transistor is almost constant, and the reference voltage generating section, the first and second transistors, and the current detection resistor are simple configurations. The constant current circuit can be configured with.

According to the configuration of the invention of claim 2, a plurality of current detecting resistors are provided, and each current detecting resistor is provided with a terminal. Depending on which terminal the secondary battery is connected to. You can change the magnitude of the charging current. That is, it suffices to select the terminal to which the secondary battery is connected according to the specifications of the secondary battery, and it is possible to meet various specifications of the secondary battery only by selecting the terminal.

According to the third aspect of the present invention, the base current of the first transistor is controlled according to the output voltage to the secondary battery, and if the output voltage decreases, the base of the third transistor will decrease. The potential is lowered and the base current of the first transistor is reduced, and as a result, the current passing between the emitter and collector of the first transistor is reduced. That is, overheating due to an increase in loss in the first transistor can be prevented when a short circuit occurs between the output terminals.

According to the structure of the invention of claim 4, when the output voltage to the secondary battery decreases to such an extent that the constant voltage element cannot be maintained in the conducting state, the base current stops flowing through the third transistor, and as a result, Like the invention of Item 3, the first transistor can be protected.

[0013]

(Embodiment 1) In this embodiment, as shown in FIG. 1, a charger 1 for charging a secondary battery B with an AC power source such as a commercial power source as an input and a secondary battery B are connected to a terminal T _11. , T ₁₂ , T
An example is shown in which the connection is made detachable via ₂₁ and T ₂₂ . The secondary battery B may be connected to the charger 1 as a single unit, but here, it is housed in a case and connected to the charger 1 as a battery pack 2.

The charger 1 insulates or steps down the input AC power by the transformer T, and then the rectifier diode D
Half-wave rectified by ₁ to obtain the DC power supply by smoothed further by the smoothing capacitor C _1. Between the both ends of the smoothing capacitor C ₁ , the emitter-collector of the pnp-type transistor Q ₁ , the diode D ₂ for blocking the reverse current, the secondary battery B and the current detection resistor R ₁ are arranged in this order from the positive electrode to the negative electrode. Are connected in series. Also, the terminals T ₁₁ , T ₁₂ , T
₂₁ and T ₂₂ are provided between the cathode of the diode D ₂ and one end of the current detection resistor R ₁ and each end of the secondary battery B. A resistor R _{3 for current} limiting is provided between both ends of the smoothing capacitor C _1.
And a series circuit of two diodes D ₃ and D ₄ is also connected. The base of the transistor Q ₁ is connected to the collector of a pnp-type transistor Q ₂ via a resistor R _2, and the emitter of the transistor Q ₂ is connected to the connection point between the terminal T ₁₂ and one end of the current detection resistor R _1. To be done. Diode D
The cathode of ₄ is connected to the other end of the current detection resistor R ₁ , and the anode of the diode D ₃ is connected to the base of the transistor Q ₂ . Here, the diode D ₃ is provided for temperature compensation of the base-emitter voltage of the transistor Q ₂ , and the diode D ₄ is provided for generating a reference voltage. Therefore, a constant voltage element such as a Zener diode can be used as the diode D ₄ .

Next, the operation will be described. When the secondary battery B is charged using the charger 1 and a charging current flows, the voltage across the current detection resistor R ₁ increases or decreases in proportion to the charging current. Since a constant reference voltage is applied to the base of the transistor Q ₂ by the diodes D ₃ and D ₄ serving as a reference voltage generator, the collector current of the transistor Q ₂ is equal to the voltage across the current detection resistor R ₁ and the reference voltage. Changes depending on the difference between. That is, if the charging current increases, the transistor Q ₂
When the charge current decreases, the emitter voltage of the transistor Q ₂ decreases and the collector current decreases, and the emitter voltage of the transistor Q ₂ decreases and the collector current increases. The transistor Q ₁ inserted between the smoothing capacitor C ₁ and the secondary battery B increases the collector current when the base current increases, and decreases the collector current when the base current decreases. As a result, The collector current is controlled so as to be kept constant. That is, the charging current to the secondary battery B is made constant.

As described above, in the circuit configuration of this embodiment, the charging current can be made constant without using a control circuit having a complicated configuration such as a microcomputer, which is a simple configuration. Therefore, the charger 1 can be provided at low cost. (Embodiment 2) In this embodiment, as shown in FIG.
Of the current detection resistor R ₁ and the smoothing capacitor C
_It has a configuration in which a current detection resistor R ₄ having one end connected to the connection point with ₁ and the terminal T ₁₃ connected to the other end is added. The added current detection resistor R ₄ is only 2 for terminals T ₁₁ and T _12.
In the state where the secondary battery B is connected, one end on the terminal T ₁₃ side is opened and a circuit is not formed, so that no function occurs. In this state, the same operation as in Example 1 is performed. On the other hand, as shown in FIG. 2, when the battery pack 2 is provided with a terminal T ₂₃ commonly connected to the terminal T ₂₂ , the current detection resistor R ₄ is connected to the terminal T ₁₃ −terminal T ₂₃ −terminal. T ₂₂ - would be connected in parallel to the current detection resistor R ₁ through terminal T _21. Therefore, the charging current passes through the two current detecting resistors R ₁ and R ₄ , and the charging current can be made large. That is, the charging current can be adjusted according to the specifications of the secondary battery B or the battery pack 2. As a result, it is possible to share the charger 1 with the battery packs 2 having different specifications (charging currents) by performing the internal connection according to the specifications of the battery packs 2.

In this embodiment, two current detection resistors R ₁ and R
By using ₄ , the two types of specifications of the battery pack 2 are supported, but if three or more current detection resistors are used and a terminal is provided for each current detection resistor, it is possible to support more various specifications. Is. (Embodiment 3) In the embodiment described above, when the positive and negative terminals T ₁₁ and T _{12 of} the charger 1 are short-circuited due to the presence of foreign matter having conductivity or the abnormality of the battery pack 2, an increase in output current is suppressed. In order to keep it constant, the emitter of transistor Q ₁
The resistance between the collectors increases. Where transistor Q
_{Since a} constant current flows between the emitter and collector of ₁ , the loss in the transistor Q ₁ increases, the temperature rises, and the transistor Q ₁ is destroyed in some cases.

Therefore, in this embodiment, both terminals T ₁₁ and T _{12 are}
During is not more to protect decreased to stop the current passing through the transistor Q ₁ when it is shorted, the terminals T _11,
The decrease in the voltage between T ₁₂ (the terminal voltage of the secondary battery B) is detected, and the base current of the transistor Q ₁ is decreased or stopped. That is, as shown in FIG. 3, in the configuration of the second embodiment, the anode of the diode D ₁ and the terminal T
Insert a series circuit of two resistors R ₅ and R ₆ between ₁₂ and
An npn-type transistor Q is connected to the connection point of both resistors R ₅ and R _6.
A structure is adopted in which the base of ₃ is connected and the emitter-collector of the transistor Q ₃ is inserted between the emitter of the transistor Q ₂ and the current detection resistor R ₁ . Transistor Q ₃ are the voltage between the terminals T _11, T ₁₂ is turned on if the voltage higher than needed for charging the secondary battery B, the terminal T _11,
The decrease in voltage during T ₁₂ reduces the collector current due to the decrease in base potential. Thus, during normal transistor Q ₃ operates in the same manner as in Example 2 because it is on, the collector current of the transistor Q ₃ is reduced or stopped the base current of the transistor Q ₁ is reduced or stopped in the event of a short circuit of the transistor Q ₁ The passing current is limited. Other configurations and operations are similar to those of the second embodiment.

[0019] (Embodiment 4) This embodiment is a configuration in which a protection against short circuit of the third embodiment similarly to the terminal T _11, T _12, as shown in FIG. 4, the resistance R ₅ of Example 3 , R ₆ in place of a resistor R ₇ for limiting current and a Zener diode D _{5 connected} in series to the base of the transistor Q ₃ and the diode D _2.
Is connected between the anode and the.

[0020] In this configuration, the base terminal T _11, voltage zener diode between the T ₁₂ D ₅ and the transistor Q ₃ - becomes below the voltage determined by the emitter voltage, the collector current of the transistor Q ₃ is reduced As a result, the base current of the transistor Q ₁ drops. That is, as in the third embodiment, when the voltage between the terminals T ₁₁ and T ₁₂ decreases, the loss in the transistor Q ₁ decreases.
Other configurations and operations are similar to those of the third embodiment. Although the Zener diode D ₅ is used as the constant voltage element in this embodiment, another constant voltage element such as a normal diode may be used.

[0021]

According to the invention of claim 1, the emitter-collector of the first transistor and the current detection resistor are inserted in the charging path to the secondary battery, and the difference between the voltage across the current detection resistor and the reference voltage. Since the base current of the first transistor is controlled so as to decrease, the voltage across the current detection resistor is kept substantially constant. That is, the charging current to the secondary battery passing between the emitter and the collector of the first transistor is substantially constant, and is constant with a simple configuration such that the reference voltage generating unit, the transistor and the current detection resistor are used. There is an advantage that a current circuit can be configured.

According to the second aspect of the present invention, a plurality of current detecting resistors are provided, and each current detecting resistor is provided with a terminal. The charging current of the charging current is changed according to which terminal the secondary battery is connected to. Since the size can be changed, it suffices to select the terminal to which the secondary battery is connected according to the specifications of the secondary battery, and it is possible to meet the specifications of the secondary battery only by selecting the terminal. There is.

According to the third aspect of the present invention, the base current of the first transistor is controlled according to the output voltage to the secondary battery. Therefore, when the output terminals are short-circuited, the loss in the first transistor increases. This has the advantage that overheating due to According to the invention of claim 4, when the output voltage to the secondary battery decreases to such an extent that the constant voltage element cannot be maintained in the conducting state, the base current stops flowing through the third transistor,
Similar to the invention of claim 3, there is an advantage that the first transistor can be protected.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment.

FIG. 2 is a circuit diagram showing a second embodiment.

FIG. 3 is a circuit diagram showing a third embodiment.

FIG. 4 is a circuit diagram showing a fourth embodiment.

[Explanation of symbols]

1 Charger 2 Battery pack B Secondary battery D ₄ Diode D ₅ Zener diode Q ₁ 1st transistor Q ₂ 2nd transistor Q ₃ 3rd transistor R ₁ Current detection resistance R ₄ Current detection resistance R ₅ Resistance R ₆ Resistor T ₁₁ terminal T ₁₂ terminal T ₁₃ terminal T ₂₁ terminal T ₂₂ terminal T ₂₃ terminal

Claims (4)

[Claims] 1. A reference pressure generation unit for generating a constant reference voltage by inserting a series circuit between the emitter and collector of the first transistor and a current detection resistor in a charging path from the DC power supply to the secondary battery. A collector is connected to the base of the first transistor, and a second transistor for controlling the base current of the first transistor is provided in a direction to reduce the difference between the voltage across the current detection resistor and the reference voltage. Constant current type charging circuit. 2. A plurality of current detection resistors, each of which has one end commonly connected and the other end having a terminal, respectively. One current detection resistor has a second transistor whose potential at a connection point with the terminal is a reference voltage. Compared, the secondary battery is connected to at least one terminal, and the remaining current detection resistor is connected in parallel to the one current detection resistor when the corresponding terminal is connected to the secondary battery. The constant current type charging circuit according to claim 1. 3. A third transistor having a collector-emitter series connection between the collector and emitter of the second transistor, and a series circuit of a pair of resistors connected between output terminals of the secondary battery. The constant current type charging circuit according to claim 1 or 2, further comprising: a connection point of both resistors connected to a base of the third transistor. 4. A third transistor whose collector-emitter is connected in series between the collector and emitter of the second transistor, and between one output end of the secondary battery and the base of the third transistor. The constant current type charging circuit according to claim 1 or 2, further comprising a constant voltage element that is connected and conducts when an output voltage exceeds a predetermined voltage.