JPH0528057B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a power supply circuit.

[Prior Art] Conventionally, the power source of a management device that uses a microcomputer to perform disaster prevention and crime prevention management of, for example, a building is as shown in FIG. The AC power source S, rectifier circuit K, and constant voltage circuit E are used as power sources during normal times, and the configuration is such that the backup power source B is switched to in the event of a power outage. That is, under normal conditions, the output of the rectifier circuit K causes the diode D ₁
The transistor Tr is kept off through the diode _D2 , and the standby power supply B is charged through the diode D2, and the output voltage of the constant voltage circuit E is transferred from the terminal P through the diode _D5 to the microcomputer, alarm, etc. of the load.

In the event of a power outage, transistor Tr is forward biased and turned on, supplying backup power B to the load. The loads include a microcomputer with low current consumption that is constantly operating and an alarm device with high current consumption that operates intermittently by control signals from this microcomputer, and these are commonly connected to terminal P. ing.

[Problems to be Solved by the Invention] In the above configuration, the base current of the transistor Tr is set assuming a load that is not constantly operating and consumes a large amount of current. In other words, an excessive base current was constantly flowing in order to be able to cope with a large load such as an alarm being turned on at any time. As a result, the backup power source is quickly consumed and the power failure compensation time is shortened.

The present invention is designed to suppress wasteful current consumption without any special operations.

[Means for Solving the Problems] The present invention provides a first transistor that forward biases the bases of a first transistor connected to a light load and a second transistor connected to a large load consuming a large current. A series circuit consisting of a second resistor with a smaller resistance value and a third transistor is connected in parallel to the first resistor, and the third transistor is activated when the large load is operated. It is equipped with a control circuit for operation.

[Example] In FIG. 1, AC is a commercial power source, K is a rectifier circuit, and _C1 is a smoothing capacitor, which constitute a main power source. B is a backup power supply for power outage compensation.
Under normal conditions, the current from the main power supply will cause the diode to
D ₂ and is charged via resistor R ₂ . E is a constant voltage circuit that serves as a power source for the large load _L1 and light load _L2 except during power outages. Tr ₁ has large load L ₂
The second driving transistor Tr ₂ is the first transistor for driving the light load L ₁ . As the light load _L1 , for example, a microcomputer for crime prevention and disaster prevention management is used. It operates at low current all the time. The large load L ₂ uses a device that consumes a large amount of current, such as an alarm device consisting of a transistor that is on/off controlled by the control output from the light load L ₁ and a buzzer connected in series with the transistor. R ₃ is a small resistance for passing the base current for driving a large load, and R ₄ is a large resistance for passing the base current for driving a light load. Tr ₄ is the third transistor, Tr ₃ is the transistor that constitutes the control circuit, D ₁
~ _D8 is a diode, and _R1 ~ _R6 are resistors.

Next, the operation will be explained. Normally light load
_L1 is driven using the constant voltage circuit E as a power source.
That is, the transistors Tr ₁ and Tr ₂ are reversely biased and held off by the output voltage of the rectifier circuit K, and the output of the constant voltage circuit E is applied to each light load.
Supplied to L ₁ and large load L ₂ . Under normal conditions, only the light load _L1 is driven by the voltage of the constant voltage circuit E. Since the large load _L2 is not normally driven, only the light load _L1 is driven by the constant voltage circuit E in the above state.

In this state, for example, when a control output is generated from the light load _L1 and a transistor (not shown) connected in series with the alarm at the large load _L2 is forward biased, the voltage from the constant voltage circuit E is This turns on this transistor and drives this large load _L1 .

When a power outage occurs, the voltages of the main power supply and the constant voltage circuit E stop, so that both transistors Tr ₁ and Tr ₂ are biased in the forward direction by the resistor R ₄ .
Therefore, in this case, the voltage of the backup power source B turns on the transistor Tr ₂ , and the voltage of the backup power source B is applied to the light load L ₁ via this transistor Tr ₂ .
is supplied to and driven.

On the other hand, since the large load L ₂ connected to the transistor Tr ₁ is not always operating, only a small base current determined by the resistor R ₄ flows through the transistor Tr ₁ , suppressing unnecessary current consumption. be done.

Then, when the large load L ₂ is operated by the control output from the light load L ₁ , that is, the transistor connected in series with the alarm in the large load L ₁ is activated by the control output from the light load L ₁ . When forward biased, transistors Tr ₁ ,
Current begins to flow through the diode D ₇ into the large load L ₂ , and a voltage drop occurs across the diode D ₇ .
Therefore, transistor Tr ₃ is forward biased and turned on, and transistor Tr ₄ is forward biased. Therefore, transistor Tr ₄ is turned on and transistor Tr ₁ is biased by the small resistor R ₃ and turns on with a large base current. As a result, the large load _L2 is supplied with current from the backup power source B via the transistor _Tr1 and the diode _D7 , and is driven. When the operation of large load L ₂ stops, the previous state is restored.

[Effects of the Invention] According to the present invention, when a large load that consumes a large current is operated, a large base current is automatically caused to flow through the driving transistor.
There is no need for special operations such as mode switching,
Under normal conditions, only a small amount of base current is consumed, and wasteful current consumption when a large load is not driven can be suppressed.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram showing an embodiment of the present invention, and FIG. 2 is an electric circuit diagram showing an example of a conventional circuit configuration. _L1 ...Light load, _L2 ...Large load, B...Backup power supply, _Tr1 ...First transistor, _Tr2 ...Second
transistor, Tr ₃ ... control circuit, Tr ₄ ... third transistor, R ₃ , R ₄ ... resistance.

Claims (1)

[Claims] 1. A power source consisting of a main power source, a backup power source for power outage compensation that is connected to the main power source and charged, and a constant voltage circuit that generates a constant voltage based on the voltage of the main power source. A light load that is constantly driven using the constant voltage circuit or the backup power source as a power source, and a light load that operates intermittently using the constant voltage circuit or the backup power source as a power source and consumes a larger current than the light load during operation. a large load; a first transistor connected in series between the backup power source and the light load; a second transistor connected in series between the backup power source and the large load; A series circuit consisting of a first resistor that is commonly connected to the bases of the two transistors and biases them in the forward direction, a second resistor whose resistance value is smaller than the first resistor, and a third transistor is connected to the first resistor. A power supply circuit comprising: a control circuit connected in parallel to the resistor to operate the third transistor in accordance with the operation of the large load.