JP2638192B2 - Charging device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a charging device for a secondary battery.

2. Description of the Related Art In recent years, battery chargers have been widely used in response to an increase in demand for portable consumer appliances powered by secondary batteries.

Hereinafter, a conventional charging device will be described with reference to the drawings.

FIG. 4 shows a conventional charging device. In FIG. 4, 1 is a battery voltage detection circuit, 2 is a charge control circuit for switching between quick charge and trickle charge, and 3 is a constant voltage / constant current control circuit which receives a signal from the charge control circuit and controls the voltage and current of a switching power supply. Reference numeral 4 denotes a switching power supply unit including the constant voltage / current control circuit, and reference numeral 5 denotes a battery to be charged.

The operation of the charging device configured as described above will be described.

First, the battery 5 to be charged is rapidly charged by the switching power supply unit 4 with a constant current. Next, the rise or fall of the battery voltage accompanying the progress of charging is detected by the battery voltage detecting circuit 1 and the charging control circuit 2, and the charging is switched from the rapid charging to the trickle charging to complete the charging.

Problems to be Solved by the Invention However, in the above configuration, when a battery whose terminal voltage is significantly reduced due to overdischarge due to long-term storage or the like is charged, the output voltage of the switching power supply unit 4 becomes equal to the battery voltage. The power supply voltage of the voltage constant current control circuit 3 also drops, the operation becomes incomplete, an excessive charging current flows, the over-output protection circuit of the switching power supply unit 4 operates, and the switching power supply unit 4 is in an intermittent operation state or an operation stop state. become,
There is a problem that the overdischarge battery cannot be charged quickly and reliably.

The present invention has been made in view of the above problems, and provides a charging device that can quickly and reliably charge a secondary battery that has been overdischarged and whose terminal voltage has been significantly reduced.

Means for Solving the Problems In order to achieve this object, a charging device according to the present invention comprises a PNP-type first transistor connected in series to a positive electrode side of a charging path, and a first transistor connected between an emitter and a base of the first transistor. A second resistor of NPN type driving the base of the first transistor; a second resistor connected between the emitter of the second transistor and ground; A constant voltage circuit for driving the base of the transistor; a battery voltage detection circuit for detecting the voltage of the battery to be charged based on the voltage between the collector and the ground of the first transistor; And a switching power supply unit.

When charging a battery whose terminal voltage has been significantly reduced due to overdischarge by this configuration, the collector voltage of the first transistor is equal to the terminal voltage of the battery to be charged, but the emitter voltage of the first transistor is equal to the terminal voltage of the battery. From the emitter-base voltage of the first transistor, the saturation voltage between the emitter and collector of the second transistor, and the emitter voltage of the second transistor, ie, the output voltage of the constant voltage circuit, the emitter of the second transistor -The voltage is maintained at or above the voltage obtained by adding the voltage obtained by subtracting the voltage between bases. By setting this voltage to be equal to or higher than the operation guarantee voltage of the constant voltage / constant current control circuit of the switching power supply unit, the operation of the constant voltage / constant current control circuit does not become incomplete. By the way, since the emitter-collector of the first transistor is in an unsaturated state as described above, a power loss occurs by multiplying the emitter-collector voltage of the first transistor by a charging current. Therefore, the terminal voltage of the battery to be charged is detected by the battery voltage detection circuit, and a trickle charge signal is sent to the constant voltage / constant current control circuit by the charge control circuit until the terminal voltage of the battery to be charged exceeds a certain set value. The power loss in the first transistor can be reduced, and when the terminal voltage rises to a certain set value or more by initially performing trickle charging on a battery that has been overdischarged and the terminal voltage has been significantly reduced. Can be quickly and reliably charged by rapid charging.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a circuit of a charging device according to an embodiment of the present invention. 1 is a battery voltage detection circuit, 2 is a charge control circuit, 3 is a constant voltage and constant current control circuit, 4 is a switching power supply unit, 5 is a battery to be charged, and the above is the same as the configuration in FIG. 6 is a PN that is connected in series to the positive side of the charging path and holds the output voltage of the switching power supply unit at a certain voltage or higher.
A first transistor of P type, 7 is a first resistor connected between the emitter and the base of the first transistor, 8 is a second transistor of NPN type driving the base of the first transistor, 9 Is a second resistor connected between the emitter of the second transistor and ground, and 10 is a step-down constant voltage circuit that takes an input from the output of the switching power supply and drives the base of the second transistor. 11 is a constant voltage element connected between the base of the first transistor and the collector of the second transistor.

The operation of the charging device configured as described above will be described below. First, the output voltage of the switching power supply unit 4, that is, the emitter voltage of the first transistor 6 is represented by V _E ,
The emitter-base voltage is V _BE1 , the emitter-collector voltage is V _CE1 , the voltage between the constant voltage elements is V _ZD , the emitter-collector voltage of the second transistor 8 is V _CE2 , and the emitter-base voltage is V _BE2 , the output voltage of the constant voltage circuit 10
V _R, the terminal voltage V _BAT of the rechargeable battery 5, when the terminal voltage of the rechargeable battery 5 to shift from the trickle charge to rapid charge and V _T is established following two formulas.

The reason why the constant voltage element 11 is connected here is to ensure the minimum input-output voltage difference of the step-down type constant voltage circuit.

The operation of each part will be described by taking as an example a case where a battery (V _BAT ≪V _T ) which is overdischarged and whose terminal voltage is significantly reduced as shown in FIG.

First, during the V _BAT <V _T is the signal of the trickle charge is constant current charged at Dispatched charging current I ₁ from the charging control circuit. In this case between the emitter and the collector of the second transistor 8 most emitter current at saturation _{((V R -V BE2) /} R 2) is the base current supplied from the constant voltage circuit 10, the remaining collector current Is the DC current gain of the first transistor 6
_Assuming that h _FE1 and the resistance value of the first resistor 7 are R ₁ , I ₁ / h _FE1 + V
_BE1 / R _1, and the constant voltage element is driven by the collector current. Wherein said and the emitter-collector saturation voltage of the second transistor 8, V _CES2 (2) equation of _{V EMIN = V BE1 + V ZD} + V CES2 + V R -V BE2 expressed as ...... (3) V _E This is an expression indicating the minimum value. Therefore, when the terminal voltage is extremely low (V _BAT ≪V _T ), V _E is kept at the minimum value given by the equation (3), and the emitter-collector of the first transistor 6 becomes unsaturated.

Next, as the charging progresses, the terminal voltage V _{BAT of the} battery to be charged at 5
Rises, V _CE1 of the first transistor 6 falls, and eventually saturates. Here, _assuming that the saturation voltage between the emitter and the collector of the first transistor 6 is V _CES1 (1)
The equation is expressed as V _E = V _CES1 + V _BAT (4), and after the emitter-collector of the first transistor 6 is saturated, the terminal voltage V _BAT of the battery 5 to be charged is in proportion to the increase, the emitter voltage V _E of the first transistor 6 is increased. At this time, the second transistor 8
The emitter-collector is unsaturated, and most of the emitter current is the collector current supplied via the constant voltage element 11. When V _BAT further rises and reaches _VT or more, the charging current is switched from the trickle charging current I ₁ to the rapid charging current I ₀ to continue charging. However by setting the V _T above V _EMIN, when between the emitter and the collector of the first transistor 6 is unsaturated state, not significant power loss in the first transistor 6 because it is the trickle charge The first transistor 6 having a small power loss rating can be used.

According to this embodiment, as described above, when charging a battery terminal voltage authored the overdischarge has fallen, V _E is V
Because it is held in the _EMIN the V _EMIN constant-voltage constant-current control circuit 3
Minimum operating operation of the constant-voltage constant-current control circuit 3 by setting the voltage above the would be guaranteed at the trickle charge current I ₁ when V _BAT is less than V _T, also rapidly when higher than V _T of quickly in the charging current I _0, reliable charging is possible.

As described above, according to the present invention, the output voltage of the switching power supply unit, that is, the emitter voltage of the first transistor connected in series to the positive electrode side of the charging path is equal to the first voltage of the output voltage of the constant voltage circuit. Adding the emitter-base voltage of the transistor and the saturation voltage between the emitter and collector of the second transistor driving the base of the first transistor;
If the holding voltage is set higher than the minimum operating voltage of the constant voltage constant current control circuit of the switching power supply, the operation of the switching power supply is guaranteed and overdischarged. Even when a battery whose terminal voltage is significantly reduced is charged, quick and reliable charging is possible, and its practical effect is large.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a charging device according to an embodiment of the present invention, FIG. 2 is an output voltage-current characteristic diagram of the charging device according to the embodiment,
FIG. 3 is a time-series transition diagram of a terminal voltage and a charging current in charging the overdischarged battery in the charging device according to the embodiment, FIG. 4 is a circuit diagram of the conventional charging device, and FIG. 5 is an output of the conventional charging device. FIG. 6 is a time-series transition diagram of terminal voltage and charging current at the time of charging the overdischarged battery in the conventional charging device. 1 ... Battery voltage detection circuit, 2 ... Charge control circuit, 3 ...
Constant voltage / constant current control circuit, 4 switching power supply section, 5
... Battery to be charged, 6 first transistor, 7 first resistor, 8 second transistor, 9 second resistor, 10 constant voltage circuit, 11 constant voltage element.

Claims (2)

(57) [Claims] 1. A PNP connected in series to the positive side of a charging path
A first transistor, a first resistor connected between the emitter and the base of the first transistor, and a second NPN type driving the base of the first transistor.
, A second resistor connected between the emitter of the second transistor and ground, a constant voltage circuit for driving the base of the second transistor, and a battery voltage detection for detecting the voltage of the battery to be charged A charging device comprising: a circuit; a charge control circuit that switches between rapid charging and trickle charging based on a signal from the battery voltage detection circuit; and a switching power supply unit. 2. A step-down type constant voltage circuit having an input connected to the emitter of the first transistor as a constant voltage circuit, and connected between a base of the first transistor and a collector of the second transistor. The charging device according to claim 1, further comprising a constant voltage element.