JPH0574147U - Power circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] After the ignition switch is turned off, charging of the secondary battery for backup of the semiconductor memory of vehicle-mounted electrical equipment is automatically stopped to protect the battery. [Composition] After the ignition switch 2 is turned off, the comparator 5 is supplied with power from the supercapacitor 4 and when the inter-terminal voltage Vb of the secondary battery 9 is lower than the reference voltage Va, the output is set to LOW and the transistor 6 is turned on. Then, the secondary battery 9 is continuously charged, and when the voltage Vb becomes higher than the voltage Va, the output is set to HI, the transistor 6 is turned off, and 2
The charging of the next battery 9 is completed.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a power supply circuit mounted on, for example, a vehicle, and more particularly to a power supply circuit for backing up a memory element.

[0002]

[Prior Art]

 2. Description of the Related Art Conventionally, as shown in FIG. 2, a power supply circuit that is mounted on a vehicle such as an automobile and supplies power to electric components is a first power supply system VCC that supplies the current of a battery 1 via an ignition switch 2. , And has two systems of the second power supply system VDD that is directly supplied.

This is because after the engine is stopped, in addition to the electrical components (eg car stereo, vehicle interior light, etc.), it is sufficient for the automobile to operate only while the ignition switch 2 is on, that is, while the engine is moving. This is because the electric power continues to be supplied to electrical components that need to be operated for a predetermined period of time (eg, clocks, semiconductor memories of various electronic control devices, etc.).

However, in the power supply circuit having such a configuration, if the battery 1 is removed while the engine is stopped and the battery 1 is removed, power cannot be supplied to the semiconductor memory, and the contents of the memory are lost. As shown in FIG. 3, the capacitor 3 is attached to the second power supply system V DD, and the discharge current of the capacitor 3 backs up the memory for a predetermined time. When the backup time is very long or the power consumption of the backup circuit is large, a rechargeable secondary battery (NiCd battery, etc.) is used instead of the capacitor 3.

[0005]

[Problems to be solved by the device]

 However, when a secondary battery such as a nickel-cadmium battery is used, charging takes time. Therefore, if the engine operating time (vehicle running time) is short, charging is not completed within the engine operating time and the engine stops. Even after that, since the battery 1 supplies electric power to the nickel-cadmium battery, there is a problem that the battery 1 goes up.

[0006]

[Means for Solving the Problems]

 In order to solve such a problem, the present invention provides a battery as a power supply, a first power supply system supplied from this battery through a switch means, and a second power supply system directly supplied from the battery. In a power supply circuit including: a supercapacitor that is charged by the first power supply system, a secondary battery that is charged from the second power supply system through a transistor, and a terminal voltage of the secondary battery. And a detection means for stopping the charging of the secondary battery by turning off the transistor when the completion of charging is detected, and the power supply of this detection means is supplied from the first power supply system and the supercapacitor. .

[0007]

[Action]

 According to the present invention, when the charging of the secondary battery is not completed even after the switch means is turned off, the detection circuit receives power supply from the supercapacitor and drives the transistor to continue charging the secondary battery. .

[0008]

【Example】

 An embodiment according to the present invention will be described with reference to FIGS. The same components as those in the conventional technique are designated by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 1, in the charging circuit of this embodiment, a supercapacitor 4 is connected to a first power supply system VCC supplied from a battery 1 via an ignition switch 2 via a backflow prevention diode 13. It is connected. This supercapacitor 4 is made of an electric dipole and has a very large capacitance. To the second power supply system VDD directly connected to the battery 1, the emitter of the PNP type transistor 6 is connected via the backflow preventing diode 11. The collector of this transistor 6 is connected to the positive side of a rechargeable NiCd battery 9. The positive side of the Ni-Cd battery 9 is connected to VDD via a discharging diode 10. The comparator 5 divides the positive side voltage of the battery 1 by the resistors 7 and 8 into the positive input and inputs it as the reference voltage Va, and inputs the positive side voltage Vb of the nickel-cadmium battery 9 into the negative input and inputs the comparator 5 The output is connected to the base of the transistor 6. The power supply 12 of the comparator 5 is connected to the plus side of the supercapacitor 4.

In such a configuration, the supercapacitor 4 is charged when the ignition switch 2 is turned on. If the nickel-cadmium battery 9 is not charged and the positive voltage Vb of the nickel-cadmium battery 9 is lower than the reference voltage Va, the output of the comparator 5 becomes LOW. Therefore, the transistor 6 is turned on, and the NiCd battery 9 is charged through the diode 11 and the transistor 6. In this state, even if the ignition switch 2 is turned off, the supercapacitor 4 is still charged, so the comparator 5 continues to operate. When the charging of the nickel-cadmium battery 9 is completed and the voltage Vb becomes higher than the reference voltage Va, the output of the comparator 5 is inverted to HI and the transistor 6 is turned off. When the supercapacitor 4 finishes discharging, the comparator 5 stops operating.

As described above, according to the present embodiment, the comparator 5 is operated by the supercapacitor 4 for a predetermined time even after the ignition switch 2 is turned off, and the nickel-cadmium battery 9 is charged during that time. It is possible to prepare for the backup of the memory without imposing an excessive load on the battery 1.

[0012]

[Effect of the device]

 As described above, according to the present invention, the detection means for detecting the charging completion of the nickel-cadmium battery for the backup of the semiconductor memory is provided, and the supercapacitor is attached to the power source of the detection means. Even if a secondary battery such as a nickel-cadmium battery is used, the battery will not be burdened more than necessary after the ignition switch is turned off.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment according to the present invention.

FIG. 2 is a circuit diagram of a conventional technique.

FIG. 3 is a prior art circuit diagram.

[Explanation of symbols]

 1 Battery 2 Switch Means 4 Super Capacitor 5 Detection Means (Comparator) 6 Transistor 9 Secondary Battery (NiCd Battery) 10 Discharge Diode 12 Power Supply for Detection Means

Claims (1)

[Scope of utility model registration request] 1. A power supply circuit comprising a battery as a power supply, a first power supply system supplied from the battery via a switch means, and a second power supply system directly supplied from the battery, The supercapacitor charged by the first power supply system, the secondary battery charged from the second power supply system through the transistor, and the voltage between the terminals of the secondary battery are measured to detect the completion of the charging. A power supply circuit comprising: a detection means for turning off a transistor to stop the charging of the secondary battery, the power supply of the detection means being supplied from the first power supply system and the supercapacitor.