JPH0717241Y2 - 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 PNP transistor is connected in series on the output side of the battery. Connected to the above PN due to a power failure of the control system power supply.
The present invention relates to a battery backup circuit that turns on a P-type transistor and supplies backup power from a battery.

[Prior Art] A battery backup circuit that uses an inexpensive bipolar transistor as a conventional switching element has a PNP transistor connected in series on the output side of the battery, and the PNP transistor is turned off when the control system power is turned on. On the other hand, when the power supply of the control system goes into a power failure state,
The PNP type transistor is turned on to supply backup power from the battery. However, when the control system power supply is at or below the battery voltage, there is a drawback in that leakage current from the battery cannot be prevented during energization. To solve this,
According to Japanese Patent Application No. 63-89809, the present applicant connects a control system power supply higher than the battery voltage to the base of the PNP transistor via a diode, and controls the base bias with the control system power supply having a voltage higher than the battery voltage. I suggest what to do.

[Problems to be Solved by the Invention] However, in the above proposed one, the voltage of the control system power supply voltage decreases according to the discharge curve of the ripple capacitor at the time of power failure, so that there is a time delay in turning on the PNP transistor, Meanwhile, there is a drawback that the power supply from the battery is not supplied and the control system power supply voltage is not guaranteed.

[Means for Solving the Problem] In order to solve such a problem, the battery backup circuit according to the present application detects a power failure of the first control system power source and sends a power failure detection signal to the PNP type. A first diode connected to an output terminal of a power failure detection circuit for turning on the transistor and having an anode connected to the base of the PNP transistor; and an anode connected to a control system power output terminal higher than the battery voltage and a cathode And a second diode connected to the base of the PNP transistor.

[Operation] The power failure detection signal from the power failure detection circuit cancels the reverse bias to the base of the PNP type transistor, turns on the PNP type transistor, and then the control system power supply falls and the reverse bias to the base disappears.
The type transistor remains on.

[Embodiment] The present invention will be described in detail below with reference to an embodiment shown in the drawings.

The control system power supply V _DD is configured to be supplied with a voltage of 5 V from the regulator 4 connected to the commercial power supply via the terminal 1 when the commercial power supply is energized. Further, 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 D2, and the cathode side of the diode D2 is connected to the base of the transistor Q1. Similarly transistor Q1
The base of is also connected to the anode side of a diode D1 whose cathode side is connected to the output side of the point-point detection circuit 2 whose input side is the terminal 1. The power failure detection circuit 2 is configured so that the output side becomes high impedance when the input side voltage disappears. 10KΩ for the base of transistor Q1
Is connected to the negative electrode side of the battery 5 having an initial voltage of 6 V and the ground GND via the resistor R, and the positive electrode side of the battery 5 is connected to the emitter of the transistor Q1. The collector of the transistor Q1 supplies the backup power supply V _BP to the control system when the commercial power supply fails, and the anode side is connected to the cathode side of the diode D3 connected to the output side of the regulator 4.

Since the present embodiment is configured as described above, when the commercial power supply is energized, the control system power supply V _DD is supplied with 5 V and the power supply V _SS is supplied with 8 V through the regulators 3 and 4, respectively. Supplied. A voltage equal to the power supply V _SS is applied to the base of the transistor Q1 via the diode D2, while a voltage equal to the power supply V _DD is applied to the power supply V _BP via the diode D3. Therefore, the base potential of transistor Q1 is
If the voltage drop of D2 is V _F , it becomes (8−V _F ) V.
on the other hand,
The emitter potential of the transistor Q1 is 6V, which is equal to the initial voltage of the battery 5. Therefore, the emitter potential becomes sufficiently smaller than the base potential and the base is reverse biased, and the transistor Q1 is turned off. Therefore, there is no leakage current flowing from the battery 5 to the collector of the transistor Q1 when the commercial power source is energized, and complete cutoff is possible.

On the other hand, at the same time that the commercial power supply goes into a power failure state, the output side of the power failure detection circuit 2 outputs a potential sufficiently lower than the emitter potential of the transistor Q1 and the transistor D1 outputs the potential through the transistor D1.
The base potential of Q1 is the same. Therefore, the emitter potential becomes sufficiently higher than the base potential, the reverse bias with respect to the base is eliminated, and the base current flows from the battery 5 into the power failure detection circuit 2 via the diode D1 and the transistor Q1 is turned on. As a result, a 6V voltage is supplied from the battery 5 to the backup power supply V _BP of the control system via the collector of the transistor Q1. Next, when no voltage is applied to the input side of the power failure detection circuit 2, the output side becomes high impedance
Q1 base control becomes impossible. However, when the output of the power failure detection circuit 2 became high impedance, the power supply V _SS and the power supply V that gradually dropped in voltage at the same time as the power failure.
_DD output voltage is gone. Therefore, the base current flows from the battery 5 through the resistor R, the ON state of the transistor Q1 is maintained, and the power supply of the control system continues from the battery 5 via the transistor Q1 to the backup power supply V _BP.
Supplied as.

The present invention is not limited to the above-described embodiment, and for example, as the control system power supply voltage higher than the battery voltage applied to the base of the transistor Q1, the 8V power supply via the regulator 3 is used. If there is no 8V power supply, the power supply before inputting to the regulator 4 may be connected to the base so that the emitter potential based on the base voltage reference becomes a large negative potential.

Also, replace the power failure detection circuit 2 with a relay that operates when energized and makes during a power failure, such that one terminal of that contact is connected to the cathode of diode D1 and the other terminal is connected to ground GND. It may be configured.

[Effect] As is apparent from the above description, according to the present invention, a power failure is detected immediately after a power failure, the PNP transistor is turned on without any time delay, and the power supply from the battery to the control power supply is delayed. Has the effect of preventing.

[Brief description of drawings]

FIG. 1 shows an embodiment of a battery backup circuit according to the present invention. 2 ... Blackout detection circuit, 3, 4 ... Regulator, 5 ... Battery, Q1 ... Transistor, D1, D2, D3 ... Diode

Claims (1)

[Scope of utility model registration request] 1. A PNP transistor whose base is connected to a negative electrode side of a non-chargeable battery via a resistor R is connected in series to a positive electrode side of the battery, and a voltage value lower than the voltage value of the battery is set. A backup circuit of a battery that supplies backup power from the battery by turning on the PNP type transistor due to a power failure of the first control system power supply that has detected a power failure of the first control system power supply and sends a power failure detection signal A power failure detection circuit that turns on the PNP transistor, a first diode whose cathode is connected to the output terminal of the power failure detection circuit, and whose anode is connected to the base of the PNP transistor; Is connected to the second control system power supply output terminal having a high voltage value and the cathode of which is the base of the PNP transistor. Second diode and battery backup circuit, characterized in that it is constituted by connected to.