JPH03196319A - Backup power unit - Google Patents

Abstract

PURPOSE:To curtail the power consumption by providing a second transistor which is turned ON/OFF by an operating signal from a microcomputer, forms a bypass circuit and increases/decreases a base current supplied to a first transistor. CONSTITUTION:When a power source switch 14 is turned off, and set to a second state that an operation of a microcomputer 12 stops, the microcomputer 12 judges this state and turns off a CNT signal. In such a state, a transistor 13 is nonconductive and a second transistor 21 also becomes nonconductive, therefore, as for a voltage applied to the emitter of the transistor 21, a voltage drop caused by a resistor 22 is generated, and a potential difference is held between the emitter and the collector. A voltage supplied to a constant-voltage diode 24 through a resistor 23 from the collector is a value being lower than the Zener level of the constant-voltage diode 24, and this voltage is supplied to a base of a first transistor 25. Subsequently, the transistor 25 outputs the second current of a smaller value than that of a first current to the emitter side, and supplies it to the terminal 12a of the microcomputer 12. In such a manner, the power of the backup power source can be curtailed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device for supplying backup power that is constantly supplied to a microcomputer (hereinafter referred to as microcomputer) that controls the functions of various parts of an audio reproduction device.

[Prior Art] A sound reproduction device having various functions such as a radio tuner, a cassette player, and an amplifier is usually equipped with a microcomputer, and the reproduction operation of each of the above functions is systematically controlled by the microcomputer.

A microcomputer consisting of an integrated circuit is equipped with a control section and a memory section, and a backup power supply is continuously supplied to this part of the memory in order to always retain the information stored in this part of the memory.

FIG. 2 shows a conventional example of a power supply device for an on-vehicle playback device. In the figure, 1 is a backup power supply terminal to which backup power is constantly supplied, and 2 is a power supply terminal to which Acc power of the vehicle is supplied.

- The microcomputer power supply circuit 3 receives the power supplied from the power supply terminal 1゜2 through the reverse current blocking diode D, and generates a voltage level necessary as the power supply to the control section of the microcomputer 5, and also Generates backup power and supplies it to part of the memory.

On the other hand, the main power supply circuit 4 for the tuner generates and outputs a stabilized power supply to be supplied to the tuner 7.

This output is provided through a transistor switch 6. The microcomputer 5 is connected to a power switch 8 that opens and closes the power for the cassette player, and a power switch 9 for the tuner, and the microcomputer 5 determines the open/close states of these switches 8 and 9 and controls the transistor switch 6. It is designed to supply power.

Note that the power supply circuit supplied to the cassette player is the same as the power supply circuit of the tuner, so it is omitted.

[Problems to be Solved by the Invention] There is a large difference in consumption of the backup power supply power supplied from the microcomputer power supply circuit 3 to a part of the memory of the microcomputer 5 when the control function of the microcomputer 5 is operating and when the control function of the microcomputer 5 is inactive. be.

This is because when the microcomputer is operating, power consumption increases due to access operations for a portion of the memory. Generally, the power consumption of a part of the memory when the microcomputer is inactive is extremely low, and the current consumption is on the order of several tens of microamperes.

By the way, when actually designing a backup power supply device, the power supply is naturally determined by taking into consideration the power consumption when the microcomputer is operating.

As a result, most of the power supply power for backing up part of the long-term memory is consumed in the power supply circuit itself. This shows how little power is effectively used.

Particularly, in a playback device equipped with a battery as a backup power source, this power consumption is negligible and there is an inconvenient problem in that the battery must be frequently replaced or recharged.

The present invention has been made in view of the above circumstances, and an object of the present invention is to suppress power loss in a power supply circuit during memory backup and to save power in a backup power supply.

[Means for Solving the Problems] In order to achieve the above object, the backup power supply device of the present invention includes a microcomputer that detects ON/OFF of the main power supply and outputs an operation signal (CNT) associated with this, and a backup power supply. The first step increases or decreases the current supplied to the microcontroller from
and a second transistor that is turned ON/OFF by an operation signal from the microcomputer to form a bypass circuit and increase/decrease the base current supplied to the first transistor, and when the main power supply is ON. state, the operation signal causes the second transistor to switch to the first transistor.
operates to increase the base current of the transistor,
When the main power source is OFF, the second transistor operates in response to an operation signal to reduce the base current of the first transistor.

[Function] 4- A first state in which the main power is supplied to the microcomputer and the control function of the microcomputer is in operation, and a first state in which the main power is cut off and the control function of the microcomputer is inactive, and a part of the memory has a backup power supply. The microcomputer itself determines the second state where the second state is being supplied, and the current output of the backup power supply circuit is selectively switched depending on the two states.

In the first state, the backup power supply circuit supplies the microcomputer with a first current necessary for operating the control function of the microcomputer, and in the second state, supplies a second current that is smaller than the first current. Supplies to microcontroller.

Therefore, during memory backup, only the current necessary for memory retention is supplied, reducing power consumption of the backup power supply.

[Example] The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment. In the figure, 10 is a backup power supply, 11 is a main power supply, 12 is a microcomputer, and a circuit 20 within a dotted line frame is a pack-in power supply circuit.

The backup power supply 10 consists of a primary or secondary battery, and is constantly supplied to the backup power supply terminal 12a of the microcomputer 12 through a power supply circuit 2o. Further, the power from the main power supply device 11 is supplied to the Vcc input terminal 12b of the microcomputer 12 via the power switch 14, and is also supplied to each function 15 of the playback device (not shown).

The backup power supply circuit 20 selectively outputs a first current and a second current to the emitter of the first transistor 25 by controlling the power supplied from the main power source 1°, and controls the microcomputer 12. This is a constant current circuit that holds part of the memory. This circuit includes two transistors, and the second PNP transistor 21 whose emitter is connected to the collector of the first transistor 25 functions as a switch.

An input resistor 29 is connected to the base of the second transistor 21, and is grounded by a capacitor 27 connected in series with the input resistor 29. The connection point between the resistor 29 and the capacitor 27 is an input section that receives the CNT signal from the microcomputer 12, and is connected to an open collector transistor 13 built into the microcomputer 12.

A resistor 22 is connected between the emitter and collector of the transistor 21, and the collector is further connected to the base of the first transistor 25 via a resistor 23. The base thereof is grounded via a constant voltage diode 24 and a capacitor 28.

Next, the operation of the embodiment will be explained. When the power switch 14 connected to the main power supply device 11 is turned on, each part function 15 of the playback device is supplied with power and enters the operating state, and
Main power is also supplied to the microcomputer 12. The control function of the microcomputer 12 operates to turn on the transistor 13.

That is, the microcomputer 12 transitions to the first state and outputs the CNT signal from the transistor 13. transistor 13
Due to the conduction of , the transistor 21 also becomes conductive, and the voltage applied to the emitter bypasses the resistor 22 and is output to the collector, so that the voltage between the emitter and the collector 7 is kept at approximately the same potential. Further, the collector voltage is supplied to a constant voltage diode 24 and a capacitor 28 through a resistor 23, and is set to a Zener level. This voltage is applied to the base of transistor 25.

As a result, a first current flows between the collector and emitter of the transistor 25, and a first current flows into a part of the memory of the microcomputer 12.
current is supplied.

Next, when the power switch 14 is turned off and the operation of the microcomputer 12 is set to a second state where the operation of the microcomputer 12 is suspended, the microcomputer 12
determines this state and turns off the CNT signal. In the second state, transistor 13 is non-conductive and transistor 21 is also non-conductive.

Therefore, the voltage applied to the emitter of the transistor 21 is dropped by the resistor 22, and a potential difference is maintained between the emitter and the collector. The voltage supplied from the collector to the constant voltage diode 24 through the resistor 23 has a value lower than the zener level of the constant voltage diode 24, and this voltage is supplied to the base of the transistor 25. transistor 2
5 is this 8- As a result, a second current having a smaller value than the first current is outputted to the emitter side and supplied to the terminal 12a of the microcomputer 12.

In this way, the power supply circuit 20 supplies the first current, which is a constant current, to a part of the memory of the microcomputer 12 in the first state, so that the part of the memory receives a sufficient power supply and the memory Can perform commanded actions, such as accessing information.

Further, in the second state, the part of the memory is supplied with a second current having a smaller current value than the first current, so that the information stored in the part of the memory can be retained for a long period of time.

In the power supply circuit 20 of the present invention, during the first current supply, the reverse current flowing through the constant voltage diode 24 and the power consumed by the circuit elements are consumed, but the values thereof are small. However, in the second state, transistor 2
5 is below the zener level, no reverse current flows through the constant voltage diode 24, and the power consumed by the entire power supply circuit 20 is negligible. Therefore, the limited power of the backup power supply section can be used efficiently.

[Effects of the Invention] As explained above, according to the backup power supply device of the present invention, there is a microcomputer that detects 0N10 F F of the main power supply and outputs an accompanying operation signal, and a microcomputer that is supplied from the backup power supply to the microcomputer. A first transistor that increases or decreases the current, and an operation signal from the microcomputer mentioned above to turn on/off.
Since a second transistor is provided to form an OFFL bypass circuit and increase/decrease the base current supplied to the first transistor, a backup power supply with limited supply power can be used efficiently and its power consumption can be reduced. It became possible to save money. As a result, maintenance of the power supply device becomes easy, and the effect is great.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a conventional example showing a power supply device for an on-vehicle playback device. 10... Backup power supply, 11...
...Main power supply, 12...Microcomputer, 2o...Power supply circuit, 21...
. . . second transistor, 22 . . . bypass resistor, 24 . . . constant voltage diode, 25 . . . first transistor.

Claims (1)

[Claims] Detects the ON/OFF of the main power supply and the accompanying operation signal (
A microcomputer (12) that outputs CNT) and a first microcomputer that increases or decreases the current supplied to the microcomputer from the backup power supply.
and a second transistor (25) that is turned on/off by an operation signal from the microcomputer to form a bypass circuit to increase or decrease the base current supplied to the first transistor, When the main power supply is ON, the operation signal causes the second transistor to operate to increase the base current of the first transistor, and when the main power supply is OFF, the operation signal causes the second transistor to operate to increase the base current of the first transistor. A backup power supply device that operates to reduce the base current of the first transistor.