JPH07325633A - Power source switching circuit for battery-driven equipment - Google Patents

Abstract

PURPOSE:To provide a power source system switching circuit for the battery- driven equipment which supplies a backup current from a battery terminal by maximizing the performance of a battery and extending the use time of the device if the battery terminal voltage drops and the output voltage of a step-down type regulator falls. CONSTITUTION:This circuit is equipped with a regulator circuit which lowers the battery voltage to a source voltage, a detecting circuit 5 which detects the source voltage value, a control circuit 6 which outputs a control signal on the basis of the detection result of the detecting circuit 5, and a switching circuit 4 which switches the supply power sources with the control signal from the control circuit 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
Simply referred to as "apparatus"] power supply system switching circuit.

[0002]

2. Description of the Related Art In recent years, battery-powered portable electronic devices have been rapidly increasing. A schematic diagram of a conventional battery-driven electronic device is shown in FIG. Reference numeral 1 is a battery, 2 is a regulator, and 3 is a device main circuit. The regulator 2 is put into operation by setting the battery 1, and the regulator main body circuit 3 is constantly supplied with a prescribed power supply voltage.

[0003]

In the conventional configuration, when the battery voltage drops and the potential difference from the power supply voltage supplied by the regulator becomes small, the output voltage of the regulator becomes lower than the specified voltage, and the battery itself Replace the battery though it is possible to drive the circuit directly,
Or had to recharge.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a power supply system switching circuit for a battery-driven device that draws out the performance of the battery and extends the usage time of the electronic device in the battery. .

[0005]

In order to achieve the above-mentioned object, the present invention provides a detection circuit for detecting a power supply voltage, a control circuit for outputting a control signal according to the detection result, and a device circuit for a device main body by the control signal. It is composed of a switching circuit that switches the power supply from the regulator output to the battery end output. When the regulator output voltage falls below the specified range, the conversion loss in the regulator is eliminated by directly supplying the power source of the device main body from the battery end, and the battery performance can be obtained. In other words, it has a step-down regulator circuit that converts the battery voltage and supplies power to the equipment, and can select either the path that directly supplies the power to the equipment from the battery or the path that supplies from the regulator. A power supply system switching circuit for a battery-powered device, which includes a circuit, a control circuit that controls the switching circuit, and a circuit that detects the value of the power supply voltage.

Further, the power supply system switching circuit of the battery-driven device described in the preceding paragraph, which has a regulator stop circuit capable of stopping the operation of the regulator when the power supply to the device is supplied from the battery.

Further, although the voltage difference between the battery voltage and the regulator output voltage is equal to or higher than the specified voltage, for some reason, the control signal of the switching circuit is added to the side where the battery voltage is directly supplied to the device power supply. In some cases, a protection circuit is provided to control the switching circuit to supply the regulator output voltage to the power supply of the device.

Further, when the power of the device is off, a backup current to the storage element of the device is supplied from a battery for driving the device.

[0009]

With the above construction, when the battery voltage drops and the regulator voltage becomes equal to or lower than the specified voltage, it is possible to automatically supply the battery end voltage directly to the power source of the apparatus main body.

[0010]

1 shows the circuit configuration of a first embodiment of a battery-driven electronic device according to the present invention. 1 is a battery, 2 is a regulator, 3 is a device main circuit, 4 is a switching circuit, 5 is a voltage detection circuit, and 6 is a control circuit.

In FIG. 1, the apparatus main body circuit 3 uses the output voltage of the regulator 2 as a power source. The battery is consumed,
When the voltage value detected by the detection circuit 5 becomes lower than the specified voltage value when the voltage drops, the control circuit 6
Outputs a control signal to the switching circuit 4 and the regulator 2. The detection circuit 5 can be composed of a comparator or an AD converter. The control circuit 6 is composed of a CPU of the apparatus body or a dedicated circuit.

First, an example of the control flow is shown in FIG. Here, the control signal "L" represents the GND level and "H" represents the high level. This control routine is called in a certain fixed cycle, and thereby monitors whether the battery voltage has dropped. In the control routine, first, determination step 5
At 1, it is determined whether the control signal is set to "L". Here, if the control signal is set to "L",
The process moves to decision step 52.

Here, it is determined whether the power supply voltage is within the specified value. If the power supply voltage is within the specified value, the control signal is set to "L" again, and the processing ends. If the power supply voltage is not within the specified value, the process proceeds to decision step 53. Here, it is determined whether the battery end voltage is within the specified value. If the battery end voltage is equal to or lower than the specified value, the control signal is set to "H" in processing step 57, and the battery end voltage is directly supplied to the power source.

If the decision step 53 is negative, it indicates that the operation of the regulator is abnormal. When the control signal is "H" in the judgment step 51, the process proceeds to the judgment step 58, and it is judged whether or not the battery end voltage is equal to or lower than the specified value. Here, if the battery end voltage is equal to or lower than the specified value, the control signal is set to "H" in processing step 57, and the processing ends. When the battery end voltage is larger than the specified value in the judgment step 58, the control signal is set to "L" in the processing step 54 and the processing is ended.

When the control signal from the control circuit 6 is set to "H" by the above processing, the switching circuit 4 becomes
The power source of the apparatus main body is switched from the regulator output to the battery end output, and the regulator 2 stops its operation.
At this time, the output impedance of the regulator circuit is high impedance.

Next, an embodiment will be described in which the output impedance of the regulator circuit does not become high impedance when the operation of the regulator 2 is stopped.

The circuit configuration of the second embodiment of the present invention is shown in FIG. The elements 1 to 6 have the same configuration as that of FIG. 7 is a switch circuit.

In the case of a regulator circuit whose output impedance does not become high impedance, a switch circuit 7 for disconnecting the output terminal of the regulator 2 from the power supply circuit is provided before the switching circuit 4. The switch circuit 7 has a function of disconnecting the regulator circuit from the apparatus main body circuit 3 by a control signal from the control circuit 6. This makes it possible to eliminate the current leaking from the power supply of the apparatus main body circuit 3 to the regulator 2.

With the above structure, the power supply voltage can be directly supplied to the apparatus main body circuit 3 from the battery end.

FIG. 3 shows a basic circuit of a regulator circuit whose operation can be stopped by a control signal from the control circuit. 1 is a battery, COMP1 is a comparator, Vref is a reference voltage, SW1 is a switch that is switched by a control signal, 3Q1 is a switching transistor, L1 is a reactor, and 3D1
Is a freewheeling diode, 3R1 is a bias resistor, 3R2 is a base resistor, 3R3 and 3R4 are voltage dividing resistors, and C1 is a smoothing capacitor.

Here, FIG. 3 has almost the same circuit configuration as a general step-down (step-down) regulator 2, but is characterized by including a switch SW1 for setting a reference voltage to a ground level by a control signal.

In FIG. 3, when the switch SW1 is on the reference voltage Vref side, the regulator outputs the specified power supply voltage, but when it is on the ground side, the output of the comparator COMP1 is always high. The switching transistor 3Q1 remains closed and the regulator stops operating. In this way, the operation of the regulator 2 can be controlled by the control signal.

FIG. 4 shows an example of a basic circuit of the switching circuit. In FIG. 4, switching is performed by a main gate transistor of 4Q1, 4Q3 is a gate control digital transistor having a built-in resistor for controlling ON / OFF of 4Q1, 4D1 is a diode for bias current, and 4R1.
Is the base resistance of the main gate transistor 4Q1, 4R3
Is a bias resistor of 4Q1, and these elements realize the basic function of the switching circuit 4. Reference numeral 4Q2 is a transistor forming a protection circuit of the switching circuit, and the operating condition of the protection circuit is determined by the base resistor 4R2 and the bias resistor 4R3. 4D2 is a diode that defines the direction of the backup current.

The operation of the circuit shown in FIG. 4 will be described below. The overvoltage protection circuit transistor 4Q2 is turned on when the potential difference between the emitter side potential (battery voltage) of the main gate transistor 4Q1 and the device body side potential (regulator output voltage) is larger than a specified value, and the main gate transistor 4Q2 is turned on. 4Q
The base potential of 1 is made almost equal to the emitter potential. In this way, when the voltage drop of the battery is small, for example, when the battery is fully charged, even if the control signal is added for some reason to turn on the gate controlling digital transistor 4Q3, the main gate is turned on. The main gate transistor 4Q1 serving as a circuit is not turned on to prevent a high battery voltage from being applied to the main body of the apparatus. Therefore, this circuit operates as a protection circuit that prevents the voltage of the power supply of the device from exceeding a specified value by directly applying the battery voltage to the device body circuit 3.

The relationship between the battery terminal voltage and the power source voltage of the main body of the apparatus, which is the operating condition of the protection circuit, is determined by the ON resistance of the backup current diode 4D2 and the resistance values of the base resistance 4R2 and the bias resistance 4R4. When the power is off (when the regulator operation is stopped), a minute current flows through the device body through the bias resistor 4R4, the diode 4D2, and the base resistor 4R2 in this order from the battery end. Can be used as.

As a result, the current consumption of the backup battery can be reduced. The feature of this circuit is that the circuit scale is minimized by including this backup circuit in the protection circuit.

[0027]

As described above, the present invention is provided with the switching circuit capable of directly supplying the power source of the device from the battery terminal, so that the battery terminal voltage drops and the power source voltage supplied through the regulator is supplied. When the battery voltage drops below the voltage that drives the main body of the device, the battery voltage can be automatically supplied to the main device without conversion loss in the regulator, and the device can be driven by the battery for a longer time. Can be realized.

Further, by providing the protection circuit, the device cannot be destroyed even when the control circuit malfunctions.

Further, since the protection circuit includes a circuit capable of supplying a backup current, it is possible to prolong the service life of the backup battery of the electronic element in the apparatus main body circuit.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a circuit configuration according to a second embodiment of the present invention.

FIG. 3 is a basic circuit diagram showing an example of a regulator capable of stopping operation in an embodiment of the present invention.

FIG. 4 is a basic circuit diagram showing an example of a switching circuit according to an embodiment of the present invention.

FIG. 5 is a control flowchart in the embodiment of the present invention.

FIG. 6 is a block diagram showing a conventional circuit configuration.

[Explanation of symbols]

 1 Battery 2 Regulator 3 Device Main Circuit 4 Switching Circuit 5 Detection Circuit (Voltage) 6 Control Circuit 7 Switch Circuit

Claims (4)

[Claims] 1. In a device driven by a battery, a step-down regulator path for converting a battery voltage to supply power to the device, a control circuit for controlling a switching circuit, and a circuit for detecting a value of the power supply voltage. A power supply system switching circuit for a battery-operated device, comprising: 2. A power supply system for a battery-powered device according to claim 1, further comprising a regulator stop circuit capable of stopping the operation of the regulator when power is supplied to the device from a battery. Switching circuit. 3. The control signal of the switching circuit is added to the side where the battery voltage is directly supplied to the device power supply for some reason, although the voltage difference between the battery voltage and the regulator output voltage is equal to or greater than the specified voltage. The power supply system switching circuit for a battery-powered device according to claim 1 or 2, further comprising a protection circuit that controls the switching circuit so as to supply the regulator output voltage to the power supply of the device. 4. A battery for driving a device can supply a backup current to a storage element of the device when the device is powered off. A power supply system switching circuit for a battery-driven device according to any one of items.