JPH0154942B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an overcharge prevention circuit used in a charger to prevent overcharging of a secondary battery.

The charger is equipped with an inverter that operates using a DC output obtained by rectifying an AC power source as a driving power source, and rectifies the voltage induced in the output winding of the oscillation transformer of this inverter to charge a secondary battery such as a Ni-Cd battery. There are some that charge quickly. Note that this type of quick charger is equipped with an oscillation frequency control means for operating the inverter at a constant frequency, and a collector current control means for making constant the peak value of the collector current of the switching transistor of the inverter, and is equipped with an AC power source. There are some types that can be used even when the voltages are different.

By the way, with this type of charger that rapidly charges secondary batteries, the charging current that flows through the secondary battery is large, so just before the secondary battery becomes overcharged, some kind of control is applied to reduce the charging current. or 2
2. Stopping the supply of charging current to the next battery.
It is necessary to prevent overcharging of the battery. Furthermore, since the above-mentioned charger is used even when the voltage of the AC power supply varies, it is necessary to reliably prevent overcharging of the secondary battery without being affected by changes in the voltage of the AC power supply. There is.

The present invention has been made in view of the above-mentioned points, and its purpose is to prevent overcharging of a secondary battery, and to prevent the overcharging of a secondary battery from being affected even when the voltage of an AC power source changes. The purpose is to provide an overcharge prevention circuit.

An embodiment of the present invention is shown in FIGS. 1 to 3.
Incidentally, FIG. 1 shows a block diagram showing a schematic configuration of this embodiment, and FIG. 2 shows its specific circuit. The charger of this embodiment includes a transistor inverter 2 that operates using a DC output obtained by rectifying an AC power source _AC as a driving power source. This is for charging the battery 3. Here, the driving power for the inverter 2 is obtained by rectifying (or rectifying and smoothing) an alternating current power supply AC in a rectifier circuit 1. The inverter 2 includes a switch section 5 consisting of a transistor _Q3 .
, a power exchange section 4 consisting of the primary winding _L1 of the oscillation transformer T, a feedback circuit section 6 that positively feeds back the voltage induced in the feedback winding _L2 to the base of the transistor _Q3 , and an output winding L. The secondary output rectifier circuit section 8 rectifies the voltage induced in the secondary battery ₃ and charges the secondary battery 3.

Incidentally, this charger is provided with a switching control means 20 so that the secondary battery 3 can be charged with a fixed rechargeable battery even when the voltage of the AC power source AC varies. This switching control means 20 includes an oscillation circuit 22 that generates a sawtooth wave as a reference frequency according to the constant of a CR circuit 15 consisting of a capacitor C ₈ and a resistor R ₆ , and a T circuit that shapes the output of the oscillation circuit 22 into a pulse wave. flipflop 25
, a hold circuit 27 that holds the output of this T flip-flop 25, and a transistor 29 that is turned on and off by the output of this hold circuit 27. With the above configuration, the oscillation frequency of the inverter 2 can be controlled regardless of the voltage of the AC power supply AC. An oscillation frequency constant means is configured to keep the oscillation frequency constant. The switching control means 20 also includes a sensor circuit 16 which is composed of resistors R ₁₁ to R ₁₃ and which detects the collector current I _IP (peak value) of the transistor Q ₃ ;
Comparison circuit 26 that compares the output of
and a transistor 28 which is turned on and off by the output of the comparator circuit 26, and these structures constitute a collector current constant means for controlling the peak value of the collector current of the transistor _Q3 to be constant. That is, when the voltage of the AC power source AC changes and the voltage of the drive power source changes, the oscillation frequency of the inverter 1 changes. Therefore, the oscillation frequency constant means is provided to keep the oscillation frequency constant using the inverter 2. Further, even if the oscillation frequency is kept constant in this way, the collector current I _IP of the transistor Q ₃ changes due to a change in the voltage of the drive power source. Therefore, the collector current constantization means makes the peak value of the collector current constant, thereby making the voltage induced in the output winding _L3 of the inverter 2 constant regardless of changes in the voltage of the AC power supply AC, and The charging current of No. 3 is kept constant. Note that the configuration surrounded by double broken lines in FIG. 1 indicates an integrated part, and the numbers surrounded by circles in the figure indicate the numbers of the terminal pins of the IC 14. This IC14 is the 4th part of the oscillation transformer T.
It operates with the output of the power supply circuit 9, which rectifies and smoothes the voltage induced in the next winding _L4 to create a DC voltage.The internal stabilizing power supply circuit 21 stabilizes the output voltage from the power supply circuit 9, and further stabilizes the output voltage from the power supply circuit 9. A reference voltage is created in a voltage circuit 23 and power is supplied to each part. Also,
The reference voltage Vref of the comparison circuit 26 is the reference voltage circuit 2.
It is obtained by dividing the output of 3. Further, this switching control means 20 is provided with a charging completion display circuit 18 that is made up of a resistor R ₇ and a light emitting diode D ₇ and displays the completion of charging of the secondary battery 3. _D7 is designed to light up depending on the supply state of the reference voltage. Furthermore, the IC 14 is a low voltage protection circuit 24.
It is equipped with

This charger is provided with an overcharge prevention circuit 19 according to the present invention that prevents overcharging of the secondary battery 3.
This overcharge prevention circuit 19 is connected to the secondary battery 3 with a resistor.
a first constant current supply means that supplies a first constant current via R ₁₄ ; and a second constant current larger than the first constant current that bypasses the starting current supplied to the transistor of the inverter 2. The secondary battery 3 indicates that charging is completed from the voltages on both sides of the series circuit to which the first constant current is supplied from the second constant current supply means that supplies the voltage to the series circuit, and the first constant current supply means from the first constant current supply means. When it is detected that the voltage has been charged to a voltage higher than the first predetermined voltage, the first constant current supply means stops supplying constant current to the series circuit, and the second constant current means supplies a constant current to the series circuit. is supplied, and the voltage across the series circuit to which the second constant current is supplied from the second constant current supply means drops to a second predetermined voltage of the secondary battery that is lower than the first predetermined value. Detecting this, the second constant current means stops supplying constant current to the series circuit, and the first constant current means stops supplying constant current to the series circuit.
and charging completion detection means for causing the constant current supply means to supply a constant current to the series circuit.
Here, this overcharge prevention circuit 19 specifically includes a constant voltage circuit 12 that stabilizes the output of the rectifier circuit 1 and obtains a constant voltage, which is composed of a resistor R ₃ , a capacitor C ₇ , and a Zener diode Z ₁ ; Constant voltage circuit 12
It has transistors Q 1 and Q 2 that perform switching operations using the output of the transistor Q ₁ and Q ₂ as a power source. Note that the transistor _Q2 is controlled by switching by turning on and off the transistor _Q1 , and operates in the opposite direction to that of the transistor _Q1 . In this overcharge prevention circuit 19, the voltage across the series circuit of the resistor R ₁₄ and the secondary battery 3 is low, and the emitter potential of the transistor Q ₁ is less than or equal to the value obtained by subtracting the base-emitter voltage from the base potential. When transistor Q ₁ turns on, the voltage across the series circuit is high, and transistor Q1 turns on.
When the emitter potential of Q ₁ is greater than or equal to the base potential minus the base-emitter voltage, transistor Q ₁ is turned off. In other words, transistor
_Q1 functions as a charging completion voltage detection means for detecting the charging completion state of the secondary battery 3. In addition, the transistor Q ₁ and the constant voltage circuit 12 connect the first transistor to the series circuit.
The transistor _Q2 and the constant voltage circuit 12 constitute a second constant current supply means that supplies a second constant current to the series circuit. . Note that the constant voltage circuit 12
A starting current is supplied from the inverter 2 to the transistor Q ₃ of the inverter 2 via the diode D ₁ and the resistor R ₄ . By the way, the Zener diode Z _D connected between the connection point between the transistor Q ₂ and the resistor R ₁₄ and the ground line of the constant voltage circuit 12 is
This is a protection circuit that clamps the overvoltage and protects the overcharge prevention circuit 19 when an overvoltage is applied across the series circuit of the resistor R ₁₄ and the secondary battery ₃ . No current flows except when it is applied, and therefore has no relation to the operation of the overcharge prevention circuit 18. In addition, as described above, the resistance
The reason why the constant current supplied to the series circuit of R ₁₄ and the secondary battery 3 is changed is that the voltage generated across the resistor R ₁₄ due to this current changes the voltage across the series circuit, and the overcharge prevention circuit 19 This is to cause the overcharge prevention circuit 19 to operate in hysteresis so that the overcharge prevention circuit 19 does not cause a so-called chattering operation. That is, when the transistor Q ₁ is on, the first constant current is passed through the series circuit of the resistor R ₁₄ and the secondary battery 3, and the voltage across the series circuit (strictly speaking, the emitter potential) at this time is applied to the transistor Q _1. detects the completion of charging of the secondary battery 3 by comparing it with the base potential, and once the completion of charging is detected, a second constant current larger than the first constant current flows from the transistor Q ₂ to the series circuit. At this time, immediately after the operation of the inverter 2 is stopped due to the increase in the voltage across the resistor _R14 , the transistor _Q1 is turned on due to a slight drop in the voltage across the series circuit, and the overcharge prevention circuit 19 stops the operation of the inverter 2. This is to prevent the operation stop state from being canceled. Note that the resistor R ₁₄ is used not only to cause the overcharge prevention circuit 19 to operate in hysteresis as described above, but also to serve as an adjustment resistor to prevent the operation of the overcharge prevention circuit 19 from varying due to different battery voltages for each secondary battery 3. It also has a function as a current limiting resistor that prevents the currents from the first and second constant current supply means from changing significantly depending on the state of charge of the secondary battery 3. Further, the current supplied to the series circuit by the first and second constant current supply means described above changes depending on the battery voltage of the secondary battery 3, and is not a constant current in the strict sense. However, as mentioned above, the current change due to the state of charge of the secondary battery 3 is reduced by the action of the resistor _R14 , and the series circuit has a constant output voltage even when the voltage of the AC power supply AC changes. Since current is supplied by the constant voltage circuit 12, the AC power supply
The current supplied to the series circuit does not change when the AC voltage changes. Therefore, it can be safely said that the current supplied to the series circuit by the first and second constant current supply means is constant. The output of the overcharge prevention circuit 19 is ORed with the output of the switching control means 20 by an OR circuit (wired OR) 10 and input to the inverter 2.

The operation of this embodiment will be explained below. Now, when the AC power supply AC is supplied, a starting current is supplied from the constant voltage circuit 12 to the base of the transistor Q ₃ of the inverter 2, the transistor Q ₃ is turned on, and at this time, the primary winding L of the oscillation transformer T By positively feeding back the voltage induced in the feedback winding _L2 by the current flowing through the transistor _Q3 to the base of the transistor _Q3 , the ON state of the transistor _Q3 is deepened. Here, in this embodiment, since the switching control means 20 is provided with an oscillation frequency constant means for controlling the oscillation frequency of the inverter 2 to be constant, and a collector current constant means for keeping the peak value of the collector current constant,
When we reach the point where we turn off transistor _Q3 ,
Alternatively, when the collector current of the transistor _Q3 reaches a predetermined value, the transistor _Q3 is turned off by the output of either the oscillation frequency constant means or the collector current constant means. Transistor like this
When _Q3 is turned off, the polarity of the voltage across the primary winding _L1 is instantaneously reversed, and the transistor is connected to the feedback winding _L2.
A reverse bias voltage is induced across _Q3 , and this reverse bias voltage holds transistor _Q3 in an off state. Further, when the transistor Q ₃ is turned off in this manner, a voltage is also induced in the output winding L ₃ , so that the secondary battery 3 is charged via the diode D ₂ by this voltage. And the return winding
After the energy for reverse biasing the transistor Q ₃ induced by L ₃ is consumed, when the output of the oscillation frequency constant means for constant the oscillation frequency of the inverter 2 of the switching control means 20 becomes a low level, A starting current is supplied from the constant voltage circuit 12 to turn on the transistor _Q3 as described above, and thereafter the same operation as described above is repeated. In this way, the oscillation frequency of inverter 2 and the transistor
Switching control means 20 for collector current of _Q3
If the voltage is made constant, the charging battery of the secondary battery 3 can be kept constant even when the voltage of the AC power supply AC is different, and this charger can be used in other countries as well.

Here, the above operation is an operation before charging of the secondary battery 3 is completed, and at this time, the voltage across the series circuit of the resistor R ₁₄ and the secondary battery 3 becomes lower than the voltage that turns off the transistor Q ₁ . Therefore, transistor Q ₂ is off and overcharge prevention circuit 19 does not operate. In this case, depending on the state of charge,
As shown in the figure, the voltage V ₀ of the secondary battery 3 gradually increases, and the voltage across the series circuit also gradually increases.
When the secondary battery 3 is fully charged, the 3rd battery
When the voltage of the secondary battery 3 reaches _the determination voltage indicating completion of charging, which is indicated by _the upper broken line in FIG. Therefore, the starting current supplied from the constant voltage circuit 12 to the transistor _Q3 is bypassed by the transistor _Q2 , and the operation of the inverter 2 is stopped. At this time, the constant current supplied to the series circuit of resistor R ₁₄ and secondary battery 3 increases because it is supplied via transistor Q ₂ , and the voltage across resistor R ₁₄ increases, resulting in The voltage across the circuit increases. In other words, this means that the collector potential compared to the base potential of transistor Q ₁ is raised, which apparently indicates the completion of charging of the secondary battery 3, as shown by the lower broken line in Figure 3a. It is the same as if the voltage to be judged was lowered. Therefore, secondary battery 3
Even if the voltage of the overcharge prevention circuit 19 slightly decreases, the operation of the overcharge prevention circuit 19 is not canceled, and the overcharge prevention circuit 19 operates stably. Note that the voltage V ₀ of the secondary battery 3 decreases as shown in FIG. 3a due to natural discharge or the like. In this way the battery voltage V ₀
When the voltage becomes lower than the voltage indicated by the lower broken line in the figure, transistor Q ₁ is turned on and transistor Q ₂ is turned off, and the inverter 2 of the overcharge prevention circuit 19 is released from the stopped state, and the above-mentioned process is completed. The inverter 2 starts the oscillation operation in the same manner as before charging is completed, and charging of the battery 3 is restarted. Thereafter, the oscillation and stopping operations of the inverter 2 are repeated. For example, by adjusting the resistance value of resistor _R14 , the transistor
If the on period of Q ₃ is set to 1/2 to 1/5 of the steady state,
The secondary battery 3 will not be overcharged after the charging of the secondary battery 3 described above is completed.

4 to 6 show another embodiment, in which the starting current of the transistor _Q3 of the inverter 2 is supplied using a constant voltage diode CRD. In this case, the constant current diode CRD functions as the starting circuit 11, and together with the transistor _Q2 constitutes the second constant current supply means. In addition, constant current diode CRD
As shown in FIG. 6, the output current I has a characteristic that the output current I remains substantially constant even if the input voltage V changes. This embodiment operates in the same manner as the first embodiment.

As described above, the present invention includes a first constant current supply means that supplies a first constant current to the secondary battery via a resistor, and a first constant current supply means that bypasses the starting current supplied to the transistor of the inverter. and a second constant current supply means for supplying a second constant current larger than the constant current to the series circuit, so that the constant current is passed through the series circuit of the resistor and the secondary battery to supply the secondary battery with a second constant current larger than the constant current. The state of charge can be detected, so even if the voltage of the AC power supply changes, there will be no variation in the state of charge detection of the secondary battery. The charging status of the battery can be detected. Moreover, it is equipped with a charging completion detection means,
The charging completion detection means detects that the secondary battery has been charged to a voltage equal to or higher than the first predetermined voltage indicating the completion of charging from the voltage across the series circuit to which the first constant current is supplied from the first constant current supply means. Then, the first constant current supply means stops supplying constant current to the series circuit, and the second constant current supply means supplies constant current to the series circuit, and the second constant current supply means stops supplying constant current to the series circuit. The charging completion detection means detects that the voltage across the series circuit to which the second constant current is supplied has decreased to a second predetermined voltage lower than the first predetermined value, and the second The supply of constant current to the series circuit by the constant current means of the first circuit is stopped, and the first
Since a constant current is supplied to the series circuit by the constant current supply means, the secondary battery is lower than the charging completion voltage due to the first predetermined value for detecting the completion of charging of the overcharge prevention circuit and the natural discharge of the secondary battery. The voltage width with respect to the second predetermined value for detecting a decrease in voltage, that is, the amount of hysteresis, can be kept constant regardless of fluctuations in the power supply voltage, and therefore overcharging of the secondary battery can be stably prevented.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG.
The figure is a concrete circuit diagram of the same as the above, Figures 3a and b are operation explanatory diagrams of the same as the above, Figure 4 is a block diagram of another embodiment of the same as the above, Figure 5 is a concrete circuit diagram of the same as the above, and Figure 6 is the same as the above. FIG. 2 is a characteristic diagram of a constant current diode. 2 is an inverter, 3 is a secondary battery, 12 is a power supply circuit, 19 is an overcharge prevention circuit, 20 is a switching control means, _Q1 to _Q3 are transistors, CRD is a constant current diode, T is an oscillation transformer, and _L2 is Output winding, R ₁₄ indicates resistance.

Claims (1)

[Claims] 1 Equipped with an inverter that operates using a DC output obtained by rectifying an AC power source as a driving power source, the voltage induced in the output winding of the oscillation transformer of this inverter is rectified to charge a secondary battery, and the voltage of the AC power source is different. In this case, the oscillation frequency of the inverter and the peak value of the collector current flowing through the switching transistor of this inverter are controlled to be constant,
An overcharge prevention circuit used in a charger equipped with a switching control means for charging a secondary battery with a constant charging current, the circuit comprising: a first constant current that supplies a first constant current to the secondary battery via a resistor; a constant current supply means, a second constant current supplying means for bypassing the starting current supplied to the transistor of the inverter and supplying a second constant current larger than the first constant current to the series circuit consisting of the secondary battery and the resistor; A series circuit comprising a constant current supply means and a charge completion detection means for detecting the completion of charge of the secondary battery from the voltage across the series circuit, and a first constant current is supplied from the first constant current supply means. The charging completion detection means detects from the voltage across the circuit that the secondary battery has been charged to a first predetermined voltage indicating completion of charging, and at this time, the first constant current supply means supplies a constant current to the series circuit. At the same time, the second constant current means supplies a constant current to the series circuit, and the voltage across the series circuit to which the second constant current is supplied from the second constant current supply means is 2. The charging completion detection means detects that the voltage of the next battery has decreased to a second predetermined voltage lower than the first predetermined value, and stops the supply of constant current to the series circuit by the second constant current means. In addition, an overcharge prevention circuit characterized in that a first constant current supply means supplies a constant current to the series circuit.