JPH0374148A - Power source using battery - Google Patents

Abstract

PURPOSE:To reduce the size of a structure by energizing a load with a second battery when the output voltage of a DC/DC converter to be energized by a first battery becomes less than a predetermined value. CONSTITUTION:When the voltage Vcc of a DC/DC converter 7 reaches 5V and a reset generator 24 outputs a signal of high level to a line 28, a common contact 14 of switching means 9 is conducted to individual contacts 11, and an output VDD is produced at the output of the converter Vcc as it is. Thus, a memory 2 is energized by the output of the converter 7. If the remaining capacity of a battery 4 becomes small, the BD signal of a battery voltage detector 21 becomes a high level. Thus, the means 9 outputs a voltage VLi to be output to a line 19 through a voltage drop circuit 18 from a battery 5 as an output VDD. Thus, the memory 2 is backed up by the battery 5, and continuously energized.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a power supply circuit using batteries that switches and derives the outputs of a plurality of batteries to energize a load.

BACKGROUND OF THE INVENTION Traditionally, C-MOS (Complementary Metal Oxide Semiconductor) Static Random Access Memories (abbreviated as SRAMs) have been used as so-called backup memories in, for example, word processors. This SR
AM has a small current consumption of only a few microamperes, and the voltage needed to power it only needs to be 2 or more.Therefore, four dry batteries connected in series are used as the main power source to power processing circuits such as word processors. By using a connected configuration, backup of the SRAM is possible even if there is almost no remaining battery capacity of the main power source.

In contrast, in recent years, pseudo-static RAM (abbreviated as P
S RAM) tends to be used. This PSR
AM is a relatively large current, e.g. 100-200μ
Although A requires power activation, it has the advantage that the cost per bit is about half that of the SRAM. The voltage for powering this PSRAM is 4
．． The problem is that it requires 5-5.5V, which is higher than the voltage required for powering the SRAM. Therefore, in order to back up such a PSRAM, it is necessary to set the voltage of the T4 battery, which is the main power supply, relatively high so that even if the battery capacity is low, the backup voltage of the PSRAM can be obtained, or Also,
It is necessary to prepare a battery as a dedicated sub power source for backing up and energizing this PSRAM.

Problems to be Solved by the Invention When such a PSRAM is used as a backup memory, if the number of batteries used as the main power source is increased and the voltage is increased as described above, it will cause problems in electronic devices such as word processors. Difficult to downsize. Also, if only a main power source is provided and no battery is provided as a sub power source, it will be impossible to back up the PSRAM when replacing the main power source battery, and the data stored in the PSRAM will be lost. cannot be protected.

If a battery is provided as a dedicated sub-power supply for backing up the PSRAM, separate from the main power supply, the battery for the sub-power supply must have a large capacity, otherwise it will consume PSRA with large current
Long-term backup power activation of M is not possible. Therefore, it is extremely unreasonable to prepare a large-capacity battery as a sub-power source in addition to a battery as a main power source, and it is difficult to miniaturize electronic devices.

An object of the present invention is to use a plurality of batteries to back up and energize a load such as a memory that consumes relatively large amount of power, and to miniaturize the configuration of a power supply circuit using batteries. The goal is to provide the following.

Means for Solving the Problems The present invention comprises a first battery, a DC/DC converter powered by the output of the first battery, a second battery, and an output voltage of the DC/DC converter that is predetermined. above the value, the output of that DC/DC converter is derived and this D
A power supply circuit using a battery, characterized in that it includes a switching means that switches and derives the output of the second battery when the output voltage of the C/DC converter becomes less than the predetermined value.

Effect According to the present invention, the power of the first battery causes DC/
A DC converter is powered, and a load is powered by the output of the DC/DC converter.

This DC/DC converter has the function of extracting a large current from the first battery and energizing the load so that the output voltage remains constant even if the output voltage of the first battery decreases. have

When the output voltage of the DC/DC converter drops below a predetermined value, the output of the second battery is supplied to the load instead of powering the load with the output of the DC/DC converter. This allows the first battery that can be used as a main power source to have a large capacity, and the second battery that can be used as a sub power source to have a small capacity, thereby making it possible to downsize the entire configuration.

Also, when replacing the first battery, the load
battery output, so the load is constantly energized and backed up.

Embodiment FIG. 1 is a block diagram of an embodiment of the present invention. The load 1 is, for example, the main body of a word processor,
Pseudo static random access memory (abbreviated as PSR)
It is electrically connected to a memory 2 such as AM) and exchanges electrical signals with each other, and the stored contents of this memory 2 are constantly energized and backed up by the power of voltage VDD via line 3. be done. A battery 4 is provided as a main power source to power the load 1 and memory 2 . Further, a battery 5 as a sub power source is provided to power the memory 2. The battery 5 as this sub-power source may have a configuration in which, for example, 2M lithium batteries are connected in series.The output of the battery 4 is given to a DC/DC converter 7 via a line 6, and this DC/DC The DC converter 7 is energized with power f. DC/
The output of the DC converter is applied via line 8 to load l for power energization and switching means 9
is applied to the individual contacts 11 of the changeover switch 10. This DC/DC converter 7 stably outputs a voltage of +5.sup. during normal operation to the line 8 as the output voltage Vcc, regardless of some fluctuations in the output voltage vp of the battery 4.

The power on line 6 is also applied to constant voltage circuit 5.

This constant voltage circuit 15 has a configuration in which an impedance element such as a transistor is interposed between its input and output, and the impedance is changed to stably derive the voltage VBU to be outputted to the line 16, using a so-called series regulation method. The voltage VBU is, for example, a voltage of +5 cm, and this voltage is stably output.

The output voltage of the other battery 5 is provided to a voltage drop circuit 18 via line 17. When the battery 5 is configured by connecting two lithium batteries in series as described above, the voltage on the line 17 is approximately 6V, which is relatively high, and therefore the voltage drop circuit 18 has an upper limit on one line. A voltage V Li whose value is less than 5.5V is derived. In the switching means 9 the line 19 is connected to the individual contact 12, the line 16 is connected to the individual contact 13 and the common contact 14
roughly switches these individual contacts 11 to 13, and the output of the common contact 14 is connected to the memory 2 via line 3.

When the output voltage VP of the battery 4 is equal to or higher than a predetermined voltage 5■, the battery voltage detection circuit 21 derives a high-level signal on the line 22 indicating that the battery 4 is normal, and detects this voltage V.
When P becomes less than 5V, a low level signal is generated on the line 22 indicating that the capacity of the battery 4 has decreased. The signal on line 22 will be referred to as a battery down (abbreviated as BD) signal.

The control circuit 23 functions to control the DC/DC converter 7 and the reset generation circuit 24, and is connected to a manually operated power switch 25.

When the power switch 25 is operated, a start signal is applied to the DC/DC converter 7 via a line 26, and a reset signal is applied to the reset generation circuit 24 via a line 27.

The reset generation circuit 24 has a DC/DC
The voltage VCC of the converter 7 is applied, and the start signal is applied via the line 27 from the control circuit 23 as described above. This reset generation circuit 24 is connected to the line 2
In response to the activation signal via line 28, the voltage Vcc on line 8 is monitored, and when the voltage Vcc is less than the predetermined voltage 5, a low level reset signal RESET is derived on line 28, and this voltage Vcc is A predetermined time Wl after the voltage rises to 5V or more, for example, 100m.
When 5ec has elapsed, the reset signal RE on line 28 is activated.
Set SET to high level.

The switching means 9 responds to each input of the BD double signal reset signal RESET from the line 22 and changes the switching state of the switch 10 to change the line voltage VDD to the first level.
Switch and derive as shown in the table.

Table 1 The battery 4 has a configuration in which, for example, five dry batteries are connected in series.

FIG. 2 is a waveform diagram for explaining the operation of the embodiment shown in FIG. 1. Figure 2 (1) shows the power switch 25.
The operation is shown below. At time tl, before the power switch 25 is turned on by operating the power switch 25, the lines 26 and 27 are at a low level and no start signal is derived, so the DC/DC converter 7 has stopped oscillating. The voltage Vcc on line 8 remains at a low level as shown in FIG. 2(2). At this time, the reset signal RESET on the line 28 is at a low level as shown in FIG. 2(3). Voltage V derived from battery 4 to line 6
p is shown in FIG. 2 (4).

When the voltage VP derived to the line 6 of the battery 4 is 5V or more, the BD double signal derived from the battery voltage detection circuit 2 to the line 22 remains at a low level as shown in FIG. 2 (5). It is. Therefore, in the switching means 9, the common contact 14 of the changeover switch IO is connected to the individual contact 13, as shown in Table 1 above, and the voltage V of the line 3 is
DD is the output voltage VBU of the constant voltage circuit 15. In this way, the memory 2 is constantly energized and backed up. The state of the voltage VDD derived from this line 3 is shown in FIG. 2 (6>).

When the power switch 25 is turned on at time tl, the control circuit 23 outputs a high-level activation signal to the lines 26 and 27. As a result, the DC/DC converter 7 starts an oscillation operation, and its output voltage Vcc increases over time after time t1 as shown in FIG. 2(2). The reset generation circuit 24 monitors the voltage Vcc on the line 8, clocks a predetermined time Wl from time t2 when the voltage Vcc reaches 5V, and sets the line 28 to a high level at time t3 when the time W1 has elapsed. shall be. During the period from time t1 to time t3, when the output voltage vP of the battery 4 is always high and is 5V or more, the BD double signal on the line 22 remains at the low level. Therefore, even during this period from time 11 to t3, the switching means 9 changes the voltage VOD of the line 3 to the voltage VBU of the line 16.
Leave it as .

After time t3, when the reset generation circuit 24 derives a high-level signal on the line 28, the V on the line 22
Regardless of whether the D signal is at a low level or a high level, the common contact 14 of the switching means 9 is connected to the individual contact 1
1, and the output voltage VDD is directly derived from the voltage of the DC/DC converter Vcc.9 In this way, when the capacity of the battery 4 is relatively large, the memory 2 is powered by the output of the DC/DC converter 7. energized.

The remaining capacity of the battery 4 is decreasing, so the conduction operation of the power switch 25 at time tl is also reduced to DC/
The current flowing through the line 6 to the DC converter 7 increases, and due to the internal resistance of the battery 4, its voltage VD drops below 5V at time tll to t12, as shown by the dashed line in 211(4). Assume a value that has decreased in .

At this time, the switching state of the switching means 9 is in the second state.
The state shown in Figure (7) is reached. That is, this time t1
In the range from 1 to t12, the BD multiplied signal derived to the line 22 of the battery voltage detection circuit 21 becomes high level as shown in FIG. 2 (5). Therefore, the switching means 9
As shown in the table, the voltage VLi derived from the battery 5 via the voltage drop circuit 18 to the line 19 is connected to the individual contact 1
2 through the common contact 14 to the output voltage VDD on line 13.
Derive it as This voltage VLi is 5■ unless the battery 5 is exhausted. In this way, even when the capacity of the battery 4 is running low, the memory 2 is backed up by the battery 5 and continues to be powered. Therefore, the contents stored in the memory 2 will not be erased.

When the output voltage vP of the battery 4 drops below 5V before the power switch 25 is turned on at time tl, the BD double signal outputted to the line 22 of the battery voltage detection circuit 21 becomes high level. The reset signal RESET on line 28 is at a low level. The switching means 9 therefore conduct the common contact 14 to the individual contacts 12 and derive the voltage VLi on the line 19 as the output voltage VDD. In this way, the memory 2 is backed up by the battery 5. Generally, before time tl when the DC/DC converter 7 is at rest, the current flowing through the line 6 is:
For example, when the voltage VBU from the constant voltage circuit 15 is very small, on the order of μA, and therefore the battery 4 is not consumed, the output voltage VBU from the constant voltage circuit 15 is the output voltage V from the switching means 9.
Since the memory 2 is backed up by the power of the battery 4, the battery 5 does not run out.In this way, the memory 2 has a relatively low current consumption like the PSRAM mentioned above. If the memory is large, the power from the large-capacity battery 4 may cause the power to be turned on even before the power switch 5 is turned on.
Since the memory 2 is energized, there is no need for the battery 5 to have a large capacity, and therefore miniaturization is possible. Furthermore, when replacing the battery 4 with a new battery, the memory 2 is backed up by another battery 5, and its stored contents are protected. Furthermore, even when replacing the battery 5, the memory 2 is energized by the power of the battery 4 as described above, so that its stored contents are protected.

Effects of the Invention As described above, according to the present invention, for example, the first battery is used as the main power source, and thereby the electric power D
When the output voltage of the C/DC converter falls below a predetermined value, the second battery as a sub power source is used to energize the load, so all you have to do is increase the capacity of the first battery. In addition, the second battery also does not need to have a large capacity, and therefore the configuration can be made smaller. Further, when replacing either the first battery or the second battery with a new battery, the load can be constantly energized and backed up.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG. 2 is a block diagram of an embodiment of the present invention.
FIG. 3 is a waveform chart for explaining the operation of the embodiment shown in the figure. 1...Load, 2...Memory, 4, 5...Battery, 7
...DC/DC converter, 9... switching means, 1
5... Constant voltage circuit, 18... Voltage drop circuit, 21.
...Battery voltage detection circuit, 23...Control circuit, 24...
・Reset generation circuit, 25...power switch

Claims (1)

[Claims] A first battery, a DC/DC converter energized by the output of the first battery, a second battery, and a DC/DC converter whose output voltage exceeds a predetermined value. Deriving the output of the DC/DC converter, this D
A power supply circuit using a battery, characterized in that it includes a switching means for switching and deriving the output of the second battery when the output voltage of the C/DC converter becomes less than the predetermined value.