JPH0717240Y2 - Battery backup circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a battery backup circuit that supplies backup power from a battery when the power supply of a control system is in a power failure state, and in particular, a switching element is provided on the output side of the battery. The present invention relates to a backup circuit for a battery that is connected in series and turns on the switching element due to a power failure of a control system power source to supply backup power from the battery.

[Conventional technology]

As a conventional battery backup circuit, a battery is directly connected to the control system power supply, but in this case, the initial voltage of the battery is generally higher than the control system power supply voltage, so the battery is The control system power supply is discharged and a leak current flows. Due to this leakage current, the initial voltage of the battery drops to the same potential as the power supply voltage of the control system even though the battery does not supply backup power. Then, due to the decrease in the initial voltage of the battery, there is a drawback that the backup time of the battery is shortened. If a secondary battery that is charged from a power source is used, a charging circuit is required, which causes a new problem of increased manufacturing cost.

In order to eliminate this drawback, a switching element is connected in series to the output side of the battery, and when the control system power supply is energized, the voltage is detected and the switching element is turned off, while the control system power supply goes into a power failure state. A battery backup circuit configured to turn on the switching element and supply backup power from the battery has already been developed.

However, in the conventional backup circuit of this type, when an inexpensive current control element such as a general bipolar transistor is used as a switching element, the leakage current from the battery is controlled when the initial voltage of the battery is higher than the control system power supply voltage. However, as in the case where the battery is directly connected to the control system power supply, the initial voltage of the battery is lowered and the backup time is shortened.

In order to eliminate this drawback, conventionally, a voltage control element such as a field effect transistor (FET) is used in order to increase the cutoff resistance and completely cut off the leakage current from the battery.

[Problems to be solved by the device]

When this voltage control element is used, the leakage current from the battery can be completely cut off, but the voltage control element has a drawback that it is expensive as compared with the current control element such as a bipolar transistor.

An object of the present invention is to solve this drawback and to provide a battery backup circuit which can completely cut off the leakage current from the battery by using an inexpensive switching element.

[Means for Solving the Problems]

In order to achieve the above object, the present invention uses a PNP type transistor as a switching element, connects the base of the PNP type transistor to a negative electrode side of a battery through a resistor, and has a second voltage higher than the battery voltage. The control system power supply is connected to the base of the PNP type transistor via a diode.

[Action]

When the control system power supply is energized, a second control system power supply voltage higher than the battery voltage is supplied to the base of the PNP type transistor through the diode, and the emitter of the PNP type transistor has a negative potential difference with respect to the base. As a result, the PNP transistor is turned off, and the leakage current flowing from the battery to the collector of the PNP transistor is completely cut off. On the other hand, at the time of power failure of the control system power supply, the negative potential difference with respect to the base of the emitter is eliminated, so that the PNP transistor is turned on, and the power supply voltage is supplied from the battery to the control system.

〔Example〕

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

The power supply V _DD of the first control system is supplied from the regulator 2 connected to the commercial power supply via the terminal 1 when the commercial power supply is energized.
It is configured to supply a voltage of 5V. Also, the second
The control system power supply V _SS is configured to be supplied with a voltage of 8 V from the regulator 3 which is also connected to the commercial power supply via the terminal 1 when the commercial power supply is energized.

The output side of the regulator 3 is connected to the anode side of the diode D1, and the cathode side of the diode D1 is connected to the base of the PNP type transistor Q1. The base is
It is connected to the negative electrode side of the battery 4 having an initial voltage of 6 V through a resistor R of 10 KΩ, and the positive electrode side of the battery 4 is connected to the emitter of the transistor Q1. The collector of the transistor Q1 is a backup power supply V for supplying the power supply voltage of the first control system when the commercial power supply fails.
_It is connected to _BP and the anode side is regulator 2
Is connected to the cathode side of the diode D2 connected to the output side of. Furthermore, the base of the transistor Q1 is a resistor R
Grounded through.

Since the present embodiment is configured as described above, when the commercial power source is in the energized state, the power source V _DD of the first control system is 5 V and the power source V of the second control system is V via the regulators 2 and 3. with the voltage of 8V is supplied to the _SS, while consuming base voltage equal to the second control system power supply V _SS via the diode D1 of the transistor Q1, the power supply V _BP through the diode D2 second A voltage equal to the control system power supply V _{DD of} 1 is applied. Therefore, the base potential V _BO of the transistor Q1 is (8−V _F ) V, where V _F is the voltage drop of the diode D1. On the other hand, the emitter potential V of the transistor Q1
_EO is 6V which is equal to the initial voltage of the battery 4. Therefore, the emitter potential V _EO is sufficiently smaller than the base potential V _BO , the emitter potential V _EB with reference to the base has a negative value, and the transistor Q1 is turned off. As a result, there is no leakage current flowing from the battery 4 to the collector of the transistor Q1 when the commercial power source is energized, and complete cutoff is possible.

When the commercial power supply goes into a power failure state, there is no voltage equal to the power supply V _SS applied to the base of the transistor Q1 via the diode D1 and the voltage equal to the power supply V _DD applied to the power supply V _BP via the diode D2. Therefore, the emitter potential V _EO becomes sufficiently larger than the base potential V _BO ,
The emitter potential V _EB based on the base becomes a positive value, the base current flows from the battery 4 through the resistor R, and the transistor Q1 is turned on. by this,
Transistor Q1 for the backup power supply V _{BP of the} control system
6V voltage is supplied from the battery 4 through the collector of the.

It should be noted that the present invention is not limited to the above-described embodiment, and for example, an 8V power supply via the regulator 3 is used as the second control system power supply voltage higher than the battery voltage applied to the base of the transistor Q1. In addition, when there is no 8V power supply, the power supply before inputting to the regulator 2 may be connected to the base so that the emitter potential V _EB based on the base becomes a somewhat large negative potential.

〔effect〕

As is apparent from the above description, according to the present invention, when using a non-chargeable battery having a voltage value higher than that of the first control system power source, one inexpensive PNP transistor is used. The leakage current from the battery can be completely cut off, and the backup time of the battery can be extended.

[Brief description of drawings]

 FIG. 1 is a circuit diagram showing a preferred embodiment of the present invention. 2,3 …… Regulator 4 …… Battery Q1 …… Transistor D1, D2 …… Diode

Claims (1)

[Scope of utility model registration request] 1. A switching element is connected in series to the output side of a non-chargeable battery, and the switching element is turned on by a power failure of a first control system power supply having a voltage value lower than the voltage value of the battery. In a battery backup circuit that supplies backup power from the battery, a PNP transistor is connected as the switching element, the base of the PNP transistor is connected to the negative electrode side of the battery through a resistor, and the voltage of the battery is A backup circuit for a battery, characterized in that a second control system power supply having a voltage value higher than that is connected to the base of the PNP type transistor via a diode.