GB2159351A

GB2159351A - Charge/discharge circuit

Info

Publication number: GB2159351A
Application number: GB08512714A
Authority: GB
Inventors: Chiaki Nakamura
Original assignee: Seiko Instruments Inc
Current assignee: Seiko Instruments Inc
Priority date: 1984-05-23
Filing date: 1985-05-20
Publication date: 1985-11-27
Also published as: JPS60249821A; GB8512714D0

Abstract

A power source 1, particularly a solar battery, is connected via reverse current prevention diodes 5, 6 to a capacitor circuit C1, C2 for holding electric charge from the source 1, and a voltage clamping 3 limits the voltage across the capacitor circuit. The capacitor circuit includes a capacitor C1 having a relatively large capacitance, a switching circuit 2 in series with capacitor C1 and a capacitor C2 having a relatively small capacitance. The switching circuit 2 is controlled by a circuit 4 which has voltage threshold detection circuits (8 to 11), (Fig. 4), responsive to the voltages at points a and c in Fig. 1. Provision of the small capacitor C2 reduces the initial delay time before the output voltage on the capacitance circuit, when charging from source 1, rises to a level sufficient to operate integrated circuit load 7. Switch 2 is thereafter turned on and off so as to maintain the output voltage at point c in the range above the minimum operating voltage of the load 7 while the capacitor C1 is charging up. <IMAGE>

Description

SPECIFICATION Charge/discharge circuit This invention relates to charge/discharge circuits for power sources, for example, solar batteries.

A conventional charge/discharge circuit for a power source consists of a charge/discharge condenser or a secondary battery, a voltage clamping circuit and a reverse-current prevention device. Such conventional charge/discharge circuits have defects and disadvantages because they have either a single condenser or a single secondary battery.

In the case where the conventional charge/discharge circuit has one condenser of relatively small capacitance, operation of an integrated circuit, connected with the charge/discharge circuit, once the power source no longer supplies power thereto is relatively short because the electric charge stored in the condenser is relatively small.

On the other hand, in the case where the conventional charge/discharge circuit has one condenser of relatively large capacitance there is a time delay between the power source delivering power and that power being applied to the integrated circuit because time is taken to charge the condenser.

Further, in the case where the conventional charge/discharge circuit, for example as shown in U.S. Patent Specification No.

4,409,538, has a secondary rechargeable battery, the secondary battery can, in practice, reduce the lifetime of the charge/discharge circuit because of leakage of liquid from the secondary battery. Moreover, replacement of the secondary battery when necessary takes a great deal of effort.

Although the present invention is primarily directed to any novel integer or step, or combination of integers or steps, herein disclosed and/or as shown in the accompanying drawings, nevertheless, according to one particular aspect of the present invention to which, however, the invention is in no way restricted, there is provided a charge/discharge circuit for a power source comprising: condenser means for holding electric charge from said power source; reverse-current prevention means arranged to be connected between said power source and to said condenser means; a voltage clamping circuit connected to said condenser means for limiting of the voltage thereacross; and a switch control circuit for controlling the charge on said condenser means, said condenser means including a first condenser having a relatively large capacitance, a switching circuit connected in series with said first condenser and a second condenser having a relatively small capacitance, said switching circuit being controlled by the output of said switch control circuit in response to the voltage across said condenser means.

The charge/discharge circuit may include a solar battery as the power source.

Said reverse-current prevention means may be a diode.

Preferably said condenser means comprises a further reverse-current prevention circuit for preventing reverse-current flow from the second condenser.

The invention is illustrated, merely by way of example, in the accompanying drawings, in which: Figure 1 is a circuit diagram of one embodiment of a charge/discharge circuit according to the present invention; Figure 2 is a diagram showing electric potential change relative to charge and discharge of energy and the state of a switching circuit of the charge/discharge circuit of Fig.

1; Figure 3 is a detailed circuit diagram showing a switch control circuit and the switching circuit of the charge/discharge circuit of Fig.

1; and Figure 4 is a circuit diagram of a voltage detection circuit forming part of the switch control circuit of Fig. 3.

Referring now to the drawings and in particular to Fig. 1, there is illustrated one embodiment of a charge/discharge circuit according to the present invention. The charge/discharge circuit comprises a solar battery 1, a condenser C1 of relatively large capacitance, a condenser C2 of relatively small capacitance, a switching circuit 2, a voltage clamping diode 3, a switch control circuit 4, reversecurrent prevention diodes 5,6 and an integrated circuit 7.

Fig. 2 shows electric potential change at points a-c in Fig. 1 in dependence on the charge and discharge of the condensers C1,C2 and shows the states of the switching circuit 2 at time t The operation of the charge/discharge circuit of Fig. 1 will now be described in relation to Fig. 2.

(1) Electric charge is stored in the condenser C2 when the solar battery 1 provides energy to the charge/discharge circuit. As a result, the condenser C2 makes it possible for the switch control circuit 4 and the integrated circuit 7 to operate immediately because it has a relatively small capacitance. In this state, the voltage potential at the point c, representing that of the condenser C2, falls to a clamping voltage level - VF. This operation takes place during period A during which the switching circuit 2 is OFF so that the voltage potential at the point a, representing that of the condenser C1, is maintained OV.

(2) When the voltage potential at the point c becomes equal to the voltage level - VF, the output of the switch control circuit 4 is inverted and the switching circuit 2 becomes ON so that the electric charge from the solar battery starts charging the condenser C1.

The electric charge stored in the condenser C2 flows to the switch control circuit 4 and integrated circuit 7 through the diodes 5,6 so that the voltage potential at point c increases from voltage level - VF to voltage level - VOP, where -VST0 > -VOP > -VF voltage level - VEST0 being the voltage below which operation of the integrated circuit 7 ceases. This operation takes place during period B.

(3) When the voltage potential at point c becomes equal to the voltage level - VOP, the output of the switch control circuit 4 is inverted, the switching circuit 2 becomes OFF and electric charge from the solar battery charges the condenser C2 again so that the voltage potential drops to the voltage level - VF. The electric charge accumulated in the condenser C1 is not discharged because the switching circuit 2 if OFF. This operation takes place during period C.

The voltage potential at point a continues to fall as the condenser C1 maintains the electric charge without the integrated circuit 7 ceasing to operate during the repetetive operation of (2) and (3) above.

(4) At time d, the switching circuit 2 becomes ON when the voltage potential at the point c ceases to fall below the voltage - VF while the voltage potential at point a drops by an amount corresponding to the voltage drop across the diode 6.

The charge operation is then completed.

(5) The electric charge stored in the condensers C1,C2 makes it possible for the integrated circuit 7 to operate in the case where energy is not provided from the solar battery.

If the condensers C1,C2 are not provided with energy from the solar battery for a relatively long time after they have been charged sufficiently, the voltage potential at the points a and c increases. Herein, voltage level - VSTB is set so that -VSTO > -VSTB > -VOP.

When the voltage potential at the point c becomes equal to the voltage level - VSTB, the output of the switch control circuit 4 is inverted and the switch circuit 2 becomes OFF so that the voltage potential at the point C increases abruptly. On the other hand, the voltage pptential at the point a is determined in dependence on the self-discharge of the condenser C1. This operation takes place during periods E and F. However, to initialise the charge/discharge circuit, the switching circuit 2 changes at time G from ON to OFF. The above description (5) relates to the discharge operation.

Referring now to Fig. 3, the switching circuit 2 and the switch control circuit 4 are shown in greater detail. The switch control circuit 4 consists of a plurality of voltage detection circuits 8 and 11 and a condenser 12. The switching circuit 2 comprises a switching element 1 3.

The voltage detection circuit 8 detects the voltage potential at the point a in Fig. 1 and the voltage detection circuits 9 to 11 detect the voltage potential at the point c. The detection voltages of the voltage detection circuit 8 to 11 are the voltage level - VF, - VSTB, - VF, and - VOP, respectively.

The condenser 12 keeps the switching circuit 2 OFF prior to the start of operation of the switch control circuit 4. The switching circuit 2 and the switch control circuit 4 may be incorporated with the integrated circuit 7.

Fig. 4 is a detailed circuit diagram of one of the voltage detection circuits of Fig. 4 which includes a reference voltage generating section 1 5 and a comparator section 14. The reference voltage generating section 15 is constructed to produce a reference voltage by using the voltage difference between the threshold voltage of a transistor Tr2 and that of a transistor Tr4. The comparator section 14 compares the reference voltage inputted to a transistor Tr5 with the voltage inputted to a transistor Tr7.

Claims

1. A charge/discharge circuit for a power source comprising: condenser means for holding electric charge from said power source; reverse-current prevention means arranged to be connected between said power source and to said condenser means; a voltage clamping circuit connected to said condenser means for limiting of the voltage thereacross; and a switch control circuit for controlling the charge on said condenser means, said condenser means including a first condenser having a relatively large capacitance, a switching circuit connected in series with said first condenser and a second condenser having a relatively small capacitance, said switching circuit being controlled by the output of said switch control circuit in response to the voltage across said condenser means.

2. A circuit as claimed in claim 1 including a solar battery as the power source.

3. A circuit as claimed in claim 1 or 2 in which said reverse-current prevention means is a diode.

4. A circuit as claimed in any preceding claim in which said condenser means comprises a further reverse-current prevention circuit for preventing reverse-current flow from the second condenser.

5. A charge/discharge circuit substantially as herein described with reference to and as shown in the accompanying drawings.

6. In a charge-and-discharge circuit having a power source, a condenser means for hold ing an electric charge from said power source, first reverse-current prevention means connected between said power source and said condenser means and a voltage clamping circuit for limiting a voltage across said condenser means and connected to said condenser means, the improvement comprising a switch control circuit for controlling the charge of said condenser means, said condenser means including a large capacitive condenser, a switching circuit connected in series with said large capacitive condenser and a small capacitive condenser, said switching circuit being controlled ON and OFF under the output of said switch control circuit responsive to said voltage across said condenser means.

7. Any novel integer or step, or combination of integers or steps, hereinbefore described and/or as shown in the accompanying drawings, irrespective of whether the present claim is within the scope of, or relates to the same or a different invention from that of, the preceding claims.