JPH08205400A - Power supply circuit for electronic apparatus - Google Patents

Abstract

PURPOSE: To stop the operation of a CPU under a state of auto-power-off and to prevent the consumption of a battery by providing a thyristor which receives a power off signal of level H outputted from the CPU and turns on, and supplying this on-current from the collector of a provided transistor through a resistor. CONSTITUTION: A system-power-voltage forming function is inactivated, by providing a control circuit containing a thyristor Q3 which is turned off by a power off signal outputted by a CPU 4 and a transistor Q1 which supplies on-current to this through a collector resistor R3, and applying the anode side voltage of the thyristor Q3 dropped to level L from level H by a voltage drop generated in the collector resistor R3. Consequently, it becomes possible to obtain a power off state easily and to maintain the state surely, without the need of a power device for a CPU's exclusive use.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit for electronic devices, and more particularly, to a device using a battery as a power source, in which power is automatically supplied when a predetermined time elapses after power supply is started. The present invention relates to a power supply circuit having an automatic power-off function for turning off the power.

[0002]

2. Description of the Related Art FIG. 2 shows a general example of a conventional device. In the figure, when the power switch S is turned on, the voltage V _{B of the} battery 1 is applied to the source side of the FET 2 and the bias voltage is applied to the gate side via the resistor R 1, so that the FET 2 is turned on.
Becomes Therefore, the battery voltage V _B is applied to the terminal Vin of the DC-DC converter 3 and the constant voltage circuit 5.

[0003] DC-DC converter 3 has a power supply terminal Vin is supplied, and terminal OFF is active state (Active) next if the H level, to form a certain level of the system power supply voltage Vcc from the battery voltage _{V B} Terminal V
Output from o. This voltage Vcc is applied to other units in the device. Further, the power supply voltage + Vcc, which is set to a constant level by the constant voltage circuit 5, is applied to the CPU 4,
4 starts operation.

In this case, the output port OUT of the CPU 4 is internally connected to the ground side, for example, and is set to the L level, so that the transistor Q2 is turned off. On the other hand, the transistor Q1 is on and the terminal is off.
The voltage applied to is compared with a reference voltage (not shown) inside the DC-DC converter 3, for example.

If this voltage exceeds the reference voltage, D
Since the C-DC converter 3 is adapted to form the system power supply voltage, the transistor Q1 is controlled so that the voltage applied to the terminal OFF becomes the H level exceeding the reference voltage.
The operating point of is set.

Here, for example, when the auto power off is set by an operation key (not shown), the information is CP
Input to U4. When a predetermined time, for example, 5 minutes has elapsed after the power supply voltage Vcc was supplied from the constant voltage circuit 5, the CPU 4 switches the output port from the ground side to a predetermined voltage path and connects it, and sends out an H level power-off signal.

As a result, the transistor Q2 is turned on, and a relatively large current flows from the battery power source to the ground side through the transistors Q1 and Q2. Resistor R3 at this current
Due to the voltage drop that occurs at the terminal, the voltage at the terminal OFF rapidly decreases. In this case, when the voltage at the terminal OFF becomes L level, which is lower than the reference voltage, the DC-DC converter 3 stops the function of forming the system power supply voltage. Therefore, the output voltage Vcc of the terminal Vo becomes zero, and battery consumption due to forgetting to turn off the switch S or the like is reduced.

[0008]

The above-mentioned conventional device has the advantage that the structure is relatively simple. By the way, when the operation of the auto power off is started, the DC-DC converter 3 stops its function, so that there is almost no power consumption, but the CPU 4 receives the power supply from the constant voltage circuit 5 and the power off signal of H level. Power is consumed to keep the power on.

Alternatively, for example, it is possible to shift to a low power consumption operation mode by software to save power, but in any case, a power source dedicated to the CPU is required, and even in the low power mode. The CPU consumes a considerable amount of power, which is not preferable.

The present invention has been made in consideration of the above circumstances, and an object thereof is to completely stop the operation of the CPU in the state of the auto power off so that the consumption of the battery can be almost eliminated. It is to provide a power supply circuit.

[0011]

In order to solve the above-mentioned problems, in the present invention, H issued from, for example, a CPU
A thyristor which is turned on upon receiving a level power-off signal is provided, and the ON current of the thyristor is supplied from the collector of the transistor Q1 arranged similarly to the conventional device through the resistor R3.

[0012]

The thyristor is turned on when the gate receives the H-level power-off signal from the CPU, and the anode side thereof becomes the L-level due to the voltage drop generated in the resistor R3 by the ON current. Therefore, the anode side of the thyristor is DC-DC
If it is connected to the OFF terminal of the converter, the system power supply voltage forming circuit in the converter stops functioning and its output voltage Vcc becomes zero.

In this case, the power supply voltage Vcc of the CPU also stops being supplied and the power-off signal disappears, but the thyristor is turned on because the current is supplied through the transistor Q1 even when the gate signal is lost. continue,
The power off state is reliably maintained.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, which illustrates an embodiment of the present invention, the transistor Q2 of the prior art is replaced by a thyristor Q3 in the present invention. Further, the power supply voltage Vcc is directly supplied to the CPU 4 from the DC-DC converter 3, and accordingly, the conventional constant voltage circuit is omitted in the present invention because it is unnecessary, but other configurations are It is similar to the conventional device.

Now, it is assumed that the power switch S is turned on and then auto power off is set. FET2 is ON
And the battery power source V _B is connected to the transistor Q1 and DC-DC.
Both are added to the converter 3 and turned on. D
C-DC converter 3 outputs to form a system power supply voltage Vcc from the battery power source _{V B,} CPU 4 is the power supply voltage Vc
Upon receiving the supply of c, it is turned on and the predetermined operation is performed.

At this time, the output port OUT of the CPU 4
Is internally connected to the ground side, and the thyristor Q3 is turned off because no gate current flows. Although the transistor Q1 is on, the current flowing is small, so the voltage drop across the resistor R3 is small, and the DC
A voltage of H level, which is almost equal to the collector voltage, is applied to the terminal OFF of the DC converter 3.

When a predetermined time has passed, the CPU 4
Connects the output port OUT to the voltage terminal of H level inside thereof. This voltage is applied as a power-off signal to the gate of the thyristor Q3 from the output port OUT, a gate current flows, and the thyristor Q3 is turned on.

As a result, a current flows from the battery voltage path through the transistor Q1 and the resistor R3 to the cathode of the thyristor Q3, and the voltage drop across the resistor R3 causes the voltage applied to the terminal OFF to drop to the L level. DC
In the -DC converter 3, when the terminal voltage becomes lower than the reference voltage (not shown), the function of forming the system power supply voltage is stopped, and the output voltage Vcc at the terminal Vo drops to zero and the power is turned off.

When the output of the terminal Vo becomes zero, the CPU 4
The power supply voltage is cut off to stop the operation, and the H-level power-off signal sent from the output port OUT becomes zero. In this case, once the thyristor Q3 is turned on, the power is turned off even if the power off signal from the CPU 4 disappears.
Since the N operation is continued, the power-off state is reliably maintained even if the power switch S is on the ON side.

[0020]

As described above, according to the present invention, the CP
The power-off state can be easily obtained and the state can be reliably maintained without requiring a power supply device dedicated to U or the like.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electrical configuration of a power supply circuit to which the present invention is applied.

FIG. 2 is a block diagram showing an electrical configuration of a conventional device.

[Explanation of symbols]

1 battery 3 DC-DC converter 4 CPU Q1 transistor Q3 thyristor R2 base resistor R3 collector resistor R4 of voltage dividing resistors R5 divider resistor S power switch V _B cell power supply Vcc system power supply voltage

Claims (4)

[Claims] 1. In a power supply circuit of an electronic device, which supplies power from a battery power source to a load and automatically stops power supply to the load after a lapse of a predetermined time, the battery is turned on by operating a power switch. It operates by receiving power,
A DC-DC converter that forms a certain level of system power supply voltage from the battery power supply and supplies it to the load, and a DC-DC converter that operates by receiving the battery power and outputs H to the DC-DC converter.
A control circuit including a semiconductor element for applying a level voltage signal to activate the system power supply voltage forming function of the DC-DC converter, or for supplying an L level voltage signal to deactivate the system power supply voltage forming function. , Operates by receiving the system power supply voltage, and outputs an L level voltage signal to the control circuit before the predetermined time is reached, and sends an H level voltage signal from the control circuit to the DC-DC converter (terminal OFF). And a CPU for issuing an H level voltage signal to the control circuit when a predetermined time is reached and sending an L level voltage signal from the control circuit to the DC-DC converter (terminal OFF). A power supply circuit for electronic devices characterized by the above. 2. The control circuit includes a transistor and a thyristor, the emitter of the transistor is connected to the battery power path, the base is grounded through a base resistance by turning on the power switch, and the collector is the collector. The anode of the thyristor is commonly connected to the DC-DC converter (terminal OFF) via a resistor, the cathode of the thyristor is grounded, and the gate of the thyristor is connected to the voltage signal output port (OUT) of the CPU through a voltage dividing resistor. ) Is connected to the power supply circuit for electronic devices according to claim 1. 3. In the control circuit, when an L-level voltage signal is applied to the gate of the thyristor from the output port (OUT) of the CPU, the thyristor becomes inactive (OFF), its anode and the DC The power supply circuit for electronic devices according to claim 1, wherein a common connection point with the DC converter (terminal OFF) has an H level voltage substantially equal to the collector voltage of the transistor. 4. In the control circuit, when an H-level voltage signal is applied to the gate of the thyristor from the output port (OUT) of the CPU, the thyristor is in an operating state (ON), its anode and the DC- The power supply circuit for electronic devices according to claim 1, wherein a common connection point with the DC converter (terminal OFF) becomes an L level voltage due to a voltage drop generated in the collector resistance due to an ON current flowing in the thyristor.