JPS59106830A - Charging circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a charging circuit for charging a secondary battery such as a nickel-cadmium battery.

As a conventional charging circuit, there is one shown in FIG. 1, for example.

In this charging circuit, AC 100V is first stepped down to a required voltage by a transformer T by a charging power supply circuit, and then full-wave rectified by diodes D and D2 to obtain a charging voltage.

Then, this charging voltage is connected to the current limiting resistor R1 and the resistor R.
Power is supplied to a secondary battery (hereinafter also referred to as "battery") B through a parallel circuit with 2 and a light emitting diode LED for indicating completion of charging, and a thyristor SCR.

On the other hand, voltage detection circuit 1 detects the voltage of battery B through resistor R3.
, R4 and variable resistor VR, the detected voltage obtained by dividing the voltage is compared with the internal reference voltage, and if the voltage of battery B is lower than the reference voltage, diode D3 and resistor R
A gate signal is outputted to the thyristor SCR via the terminal 5 to turn it on, and if the voltage of battery B is higher than the reference voltage, the thyristor SCR is turned off.

Therefore, while the voltage of battery B is low, thyristor S
As CR continues to turn on and battery B is charged, the light emitting diode LED lights up, and when the voltage of battery B becomes high, the thyristor SCR is intermittently conductive and the light emitting diode LED blinks. When battery B is fully charged, thyristor SCR turns off,
The power supply (charging current) to battery B is cut off and the light emitting diode L ED is turned off.

In this way, conventional charging circuits have a complicated structure because they separately include a thyristor and its control circuit that cut off power supply to the battery when charging is completed, and a light emitting diode to indicate that charging is in progress. And the cost is high,
For example, when it is installed in a narrow space such as a camera, there is an inconvenience that the space occupancy rate becomes large.

This invention has been made in view of the above points, and aims to simplify the structure of a charging circuit, reduce its size, and reduce its cost.

Therefore, in the charging circuit according to the present invention, a backflow prevention diode is inserted in the charging current supply circuit from the charging power source to the secondary battery, and one end of the light emitting element is connected to the charging power source side, and a charging completion detection function is provided. A circuit detects the completion of charging of the secondary battery, and by bypassing the charging current to this light emitting element and lighting it up, the charging current to the secondary battery is cut off (reduced) and the charging completion is displayed. It is something.

Embodiments of the present invention will be described below with reference to FIG. 2 and subsequent figures of the accompanying drawings.

FIG. 2 is a circuit diagram showing a first embodiment of the invention.

In the figure, this charging circuit connects a battery B, which is a secondary battery such as a nickel-cadmium battery, to a charging power source that outputs a DC power supply voltage VI through a current limiting resistor R1o and a backflow prevention diode DIO. Connected.

Then, the terminal voltage VB of this battery B and the power supply voltage ■
A reference voltage VR obtained by dividing the voltage by a series circuit of a resistor J and a constant voltage diode ZD1 is input to an inverting input terminal and a non-inverting input terminal of a comparator 10, which is a charging completion detection circuit, respectively.

This comparator 10 outputs a high level "H" when the terminal voltage VB of battery B is lower than the reference voltage VR (VB≦VR), and the terminal voltage VB of battery B is lower than the reference voltage VR.
(VB>VR), the completion of charging is detected and the output is set to low level (L).

Then, the anode side of the light emitting diode LED2 for indicating charging completion is connected to the connection point a between the resistors R and IO which are the charging power supply side of the diode DIO, and the cathode side is connected to the comparator 1.
Connected to the 0 output terminal.

Further, a capacitor C1 for preventing oscillation is connected between the output terminal of the comparator 10 and the ground.

Note that the output voltage vo of this charging circuit is supplied to the load 11 via the switch S1.

Next, the operation of the embodiment configured as described above will be explained.

First, when the terminal voltage VB of battery B is lower than the reference voltage VR, the output of the comparator 10 is at a high level "H" (same level as the power supply voltage V), so the light emitting diode L E D 2 lights up. Instead, a charging current flows into battery B from the charging power source via resistor R1 and diode D1, and battery B is charged.

At this time, since the charging current is limited by the current limiting resistor R1o, no overcurrent flows to battery B, and no strain is applied to battery B.

When the battery B is charged and its terminal voltage VB exceeds the reference voltage VR, the output of the comparator 10 becomes low level "L" (earth level), so a forward voltage is applied to the light emitting diode ED2. Therefore, most of the current from the charging power supply goes to this light emitting diode L E
The charge current flows through D2, and the completion of charging is indicated by lighting of the light emitting diode LED2, and since the voltage at point a drops, the backflow prevention diode DIO is cut off, and charging current no longer flows into battery B. Also,
The diode DIO also prevents current from flowing from the battery B to the light emitting diode LED2.

In this way, this charging circuit charges with a substantially constant current from the start of charging, and when charging is completed, the charging current is transferred to the light emitting diode L.
ED2 is bypassed and turned on to cut off the charging current to battery B to prevent overcharging.

Therefore, the bypass of the charging current to the secondary battery when charging is completed and the display of charging completion are performed using one light emitting diode L E
Since this can be done using D2, the configuration becomes simple.

FIG. 3 is a circuit diagram similar to FIG. 1 showing a second embodiment of the invention.

To explain only the differences between this embodiment and the embodiment shown in FIG. 2, the power supply port l! 812, when the power switch S2 is turned on, AC 100V is stepped down, half-wave rectified and smoothed by a step-down, rectification and smoothing circuit consisting of a resistor R10, a capacitor D11 and a capacitor C2, and then the voltage is smoothed by a resistor R13 and a constant voltage diode zD2. It is stabilized by a constant voltage circuit consisting of the following, and outputs a DC power supply voltage V.

In addition, a circuit that generates a reference voltage VR to be input to the comparator 10 as a charging completion detection circuit connects the power supply voltage VI to a resistor R.
11, 4 light emitting diodes LED3 to LED6, and 4 diodes DI2 to DI5 in series circuit, 1 light emitting diode LE03 to LHD B and diode DI2.
By setting the composite voltage of the respective forward voltages of ~DI5 as the reference voltage VR, the reference voltage VR is given a temperature characteristic corresponding to the temperature characteristic of the battery B.

Furthermore, a light emitting diode L E similar to the previous embodiment
The cathode side of D2 is connected to the ground via the emitter-collector of the NPN switching i-transistor Q1, which is controlled on/off by the output of the comparator 10, and the anode side is connected to the ground between the resistor R2° and the diode DIO. Connected to connection point a.

Note that since the comparator 10 inputs the reference voltage VR to the inverting input terminal and the terminal voltage VB of the battery B to the non-inverting input terminal, the outputs are different from those in the previous embodiment.
is reversed.

The output voltages BO and BW of this charging circuit are supplied to, for example, a winder of a camera.

In this embodiment, since the reference voltage VR has a temperature characteristic corresponding to that of battery B, battery B can be charged with higher accuracy.

FIG. 4 is a circuit diagram similar to FIG. 2 showing a third embodiment of the invention.

In this embodiment, a solar cell group BS is used as a charging power source, and a DC power supply voltage V outputted from the solar cell group BS is connected to a backflow prevention diode I)+.

Power is supplied to battery B via.

Then, the terminal voltage VB of battery B is set by resistors R, 5 and R,
While inputting the divided voltage VB' divided by 6 to the non-inverting input terminal of the differential amplifier 13 as a charging completion detection circuit,
The terminal voltage VB of battery B is set by resistor R71 and diode D.
.

The light emitting diode LED2 for indicating charging completion is
It is connected in parallel with the solar cell group BS through a switching circuit consisting of Darlington-connected transistors Q21Q3, and the output of the differential amplifier 13 is connected to the current limiting resistor R1? is applied to the base of transistor Q2 to control lighting.

In addition, when a comparator is used in the charging completion detection circuit,
Although the capacitor C1 shown in FIG. 3 is required, if a differential amplifier is used as in this embodiment, the capacitor C1 shown in FIG. 3 is not necessary.

In this embodiment, when battery B is nearing completion of charging and the voltage VB' corresponding to the terminal voltage VB exceeds the reference voltage VR', the differential amplifier 13 outputs a positive voltage corresponding to the difference. Ru.

Therefore, the collector currents of the transistors Q2 and Q3 increase according to the output voltage of the differential amplifier 13, and the light emitting diode LED2 lights up with the amount of light emitted according to the collector current, thereby bypassing the charging current to the battery B. ,
Displays charging completion.

In this case, the degree of completion of charging can also be known from the brightness of the light emitting diode LED2.

In addition, although the case where a light emitting diode was used as a light emitting element was described in each Example 2, the present invention is not limited to this, and for example, a nonpolar light emitting element such as a miniature lamp may also be used.

As described above, according to the present invention, the structure of the charging circuit becomes simple and compact, and the cost becomes low.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a conventional charging circuit, FIG. 2 is a circuit diagram showing a first embodiment of the present invention, and FIG. 6 is a circuit diagram showing a second embodiment of the present invention. FIG. 4 is a circuit diagram showing a third embodiment of the invention. 10... Comparator (charging completion detection circuit) 13... Differential amplifier (charging completion detection circuit) B... Battery (secondary battery) L E D 2... Light emitting diode for charging completion indication (
Light emitting element) BS...Solar cell Dlo...Backflow prevention diode DIl~D, 6...Diode ZD,...Zena diode L E D3~LED? ...Light emitting diode 'R1o
... Current limiting resistor

Claims (1)

[Claims] 1. In a charging circuit that charges a secondary battery using a charging power source, a backflow prevention diode is inserted in the charging current supply circuit from the charging power source to the secondary battery, and one end of the diode is connected to the charging power source side. What is claimed is: 1. A charging circuit comprising: a light emitting element, and a charging completion detection circuit that detects the completion of charging of the secondary battery and bypasses a charging current from the charging power source to the light emitting element.