JPS62155737A - Battery source change-over circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention is used, for example, in electronic watches, four-child tabletop pruritus machines, game machines, etc. This invention relates to a battery power supply switching circuit in a device equipped with an auxiliary battery for backup.

[Technical background of the invention]

Generally, circuits in which data is stored in RAM, registers, etc. in α-child clocks, electronic desktop calculators, game machines, etc. have the disadvantage that data is destroyed when batteries are replaced due to battery consumption.

Therefore, this LSI has two power supply terminals: 1.5V and 3V, and during normal use, power is supplied from a 3V lithium battery, and when the lithium battery is replaced, 1.5V is supplied. I'm trying to do a pack amp using a silver oxide battery. Silver oxide batteries are used for backup because they are smaller than lithium batteries, easier to incorporate into sets, and are cheaper.

FIG. 2 shows a schematic configuration example of an L8I for a watch, which has a built-in battery power supply switching circuit for backing up with an oxide battery when replacing a lithium battery. In the figure, II
is the main body of the LSI, and this LSI is provided with a 3V system power supply terminal I2 and a 1.5V system power supply terminal 13, and these terminals 12.13 are connected to the negative electrode of a 3V system lithium battery 14, The negative electrodes of the 5-type silver oxide batteries 15 are connected to each other. One end of the N-channel type MO8FEi'16 is connected to the above source supply terminal 12, and this MOS
One end of a 3V power supply line 17 is connected to the other end of the FET 16 and the back gate. The above power supply line 17 includes an example ki RAM 18. Including @ (J'3 V series t
7) A circuit 91& is connected, and one end of a pull-down N-channel MOSFET J9 is connected to the other end. A ground point is connected to the dirt of the MOSFET 9, the other end of the source line 17 is connected to the back dirt, and the & pond changeover switch input terminal 20 is connected to the other end.

This input terminal 2θ has an N-channel type MO8PET 2
7, the first control input terminal of the switch circuit 22, and the input terminal of the inverter 23 are connected to each other.

The above MOSFET is connected to the output end of the upper inverter 23.
I 6 dart is connected. Above L+O8FET21
The power supply terminal 13 is connected to one end of the
is connected, and the other end is a 1.5 V power line 2-7.
is connected. A 1.5V system circuit group 25, an oscillator 26, a counter circuit group 27, and the switch circuit 22 are connected to this power supply line 24.

The output of the oscillator 26 is supplied to the counter circuit group 27, and the output of the counter circuit group 27 is fed to the timer circuit 28.
and is supplied to the step-up/step-down circuit 29. The output of the timer circuit 28 is supplied to the second control input of the switch circuit 22. The switch circuit 2 and the voltage step-up/down circuit 29 are connected to the power supply line 17, respectively, and the output of the voltage step-up/down circuit 29 is supplied to the switch circuit 22. In addition, 30
is the parasitic diode of MOS FET76, 31 is the MOS
Parasitic diode of FET 21 Next, the operation in the above configuration will be explained. When the reverse voltage of the lithium battery 14 is applied to the power supply terminal 12, a reverse voltage lowered by 72 times the forward drop reverse voltage of the parasitic diode 30 of the MOSFET 16 is applied to the power supply line 17. For this reason, MOS FETI for pull-down
9 is turned on, and the battery changeover switch input terminal 20 becomes "L" level. However, this @L level is a reverse voltage that is lowered by the forward drop voltage V of the parasitic diode 30 from the voltage of the lithium battery 14.The potential of this "L" level is inverted by the inverter 23 and becomes MOd. F
This MOS FETz is supplied to the ET16 dart.
t; becomes on state. Therefore, a source voltage of -13V is applied to the source line 17 from the lithium battery 14.

As a result, the step-up/step-down circuit 29 and the switch circuit 22
And 3. A power supply voltage of -3V is supplied to the circuit group 18 of the operation system. In addition, the power supply selector switch input terminal 20
The switch circuit 22 is controlled by the "L" level of the voltage, and the '1 source line 17 and the power supply line 24 are connected.

At this time, MOSFET 21 is the 1L of the input terminal 20.
"The level is off, and the power supply from the silver oxide battery 15 is cut off. Therefore, immediately after the lithium battery power is turned on, the 1.5V system circuit group 25 and the oscillator 26
And the counter circuit group 27 operates at -3V. By supplying power to the power supply line 24, the oscillation circuit 26 starts operating, and the oscillation output is supplied to the counter circuit group 27 and counted. The output of the counter circuit group 27 is supplied to a timer circuit 28 to start a time counting operation, and is also supplied to a boost/step down circuit 29. Boosting the above pressure/
The step-down circuit 29 operates bidirectionally using the signal supplied from the counter circuit group 27 as a clock, and here operates as a step-down circuit to step down the four source voltages from the lithium battery 14 by one step. -1,5■ voltage to the switch circuit 22
to be applied. Then, from the start of the operation of the timer circuit 28, a predetermined fI? ! After time F has elapsed, the switching state of the system child circuit 22 is changed by the output of the timer circuit 28, and the output (-1.5V) of the step-up/step-down circuit 29 is supplied to the power supply line 24. Normal operation takes place.

On the other hand, when the life of the 4-lithium battery I4 is nearing and you want to replace the battery, please connect the A-cell selector switch input terminal 20 to "
This sets the inverter 23 to H” level.
The output becomes #L11 level, and MOS PETl
6 is turned off, the supply of power from the lithium battery 14 is stopped. At this time, MOS FET? J is turned off by the "H" level of the input terminal 20, and the voltage (-1.5V) of the silver oxide battery 15 is applied to the power supply line 24. Further, the switch circuit 22 is switched by the "H" level of the input terminal 20, and the voltage of -1.5V printed on the power supply line 24 is supplied to the step-up/step-down circuit 29.

Here, the step-up/step-down circuit 29 operates as a step-up circuit,
-1.5V applied to the four source lines 24 is twice -
The voltage is boosted to 3.0 cm and applied to the t-source inlet 77. Therefore, the 1.5V system circuit group 25, the oscillator 26, and the counter circuit group 27 are operated at a voltage of -1.5V, and the 3V system circuit group 18 is operated at a voltage of -3V. If the lithium battery 14 is replaced in this state, the operation of the LSIII will not stop, for example, the RAM 1B.

No data will be lost or destroyed.

After replacing the lithium battery 14, by setting the input terminal 20 to the oven state, the pull-down N-channel MOSFET 19 is turned on. As a result, the input terminal 20 becomes @L'' level and MO8FHT2
1 becomes off state, and 1 from silver oxide 4 pond 15! source supply is cut off.

[Problems with background technology]

By the way, after replacing the lithium battery 14, the silver oxide battery 15 will be incorporated into the set as is until the next replacement of the lithium battery. Therefore, the voltage of the stain pond 15 decreases due to self-discharge of the silver oxide battery 15 itself. In this way, when the voltage of the battery 15 decreases, the potential of the power supply terminal 13 decreases to 1.5 when the lithium battery 14 normally supplies power.
The height is higher than that of the V-system power line 24.

At this time, is the same forward bias applied to the parasitic diode 3I of MO8PF and Tl1? ), -4'tAY flows from the silver oxide battery 15 to the power supply line 24 via the power supply terminal 13 and the parasitic diode 31, even though the MOS FET 2Z is in the off state. In other words, oxidation@den/ll! 15, the current will flow backwards. When current flows in the reverse direction through the battery in this manner, an abnormal reaction occurs within the battery, which not only damages the battery 15 but also causes the 11L battery 15 to burst due to the generation of gas.

[Purpose of the invention]

This invention was made in view of the above circumstances,
The purpose of this is to provide four battery sources that can prevent the backflow of the undercurrent when the auxiliary battery is exhausted, in a circuit that is equipped with an auxiliary battery for backing up when replacing this battery in addition to the main 11IL battery. An object of the present invention is to provide a switching circuit.

[Summary of the invention]

That is, in this invention, in order to achieve the above object, the power supply terminal 13 and the 15V in FIG.
Two MOS PETs are connected in series between the power supply lines 24 of the system, and the gates of these MOSFETs are connected to the battery changeover switch input terminal 20, and the pack Y-T is connected so that the parasitic diodes are in opposite directions. This connection prevents a current path from being generated between the power supply terminal 13 and the 'li source line 24 when the two MOSFETs are in the off state.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, the same components as those in FIG. 2 are given the same reference numerals, and detailed explanation thereof will be omitted. That is, an N-channel type MOS FETJ 2.33 is connected in series between the 4-source supply terminal 13 and the 1.5V power line 24, and a battery changeover switch input terminal 2θ is connected to the gate of each of these MOS FETs 32.33. Connected.

A power supply terminal 13 is connected to the pack gate of the MOSFET 32, and a 'tIl source line 24 is connected to the back f-) of the MOSFET 33. In addition, 34 MOS FET, y x parasitic diode,
Reference numeral 35 denotes a parasitic diode of the MOS FET 33, and the connection directions described above are opposite to each other.Next, the operation in the above configuration will be explained. The basic operation is the same as that of the circuit shown in Section 1 and FIG. 2, so it will be omitted and only the differences will be explained in detail. In Figure 1, during normal operation, the LSIII has a lithium battery 14
A voltage of 1-3V is applied. At this time, MOS P
E.T.? ,? .

33 is in an off state, and the supply of #M-Ryo from the silver oxide battery 15 is cut off. After 1 to 2 years of normal operation,
When the lithium battery 14 reaches the end of its service life and needs to be replaced, it is temporarily backed up with a silver oxide battery 15 in the same manner as the circuit shown in FIG. 2, so as not to stop the circuit operation of the LSIII.

The backup silver oxide battery 15 is only used auxiliary when replacing the lithium battery 14, and after replacing the lithium battery 14, the battery changeover switch input terminal 2θ can be set to the oven state. , MOS FgTJ
9 is turned on and this input terminal 20 becomes II L n
level. By this, MOS FgTJ2.3
3 is in the off state, the supply of the 11 source from the silver oxide battery 15 is stopped, and the oxidation M'! The battery 15 is incorporated into the set until the next time the lithium battery 14 is replaced.

Therefore, the silver oxide battery 15 should not be left alone for a long time, and the voltage level of the battery 15 will decrease due to self-discharge or the like.

The potential of the power supply terminal 13 becomes higher than the potential of the '1 source line 24.

At this time, the parasitic diode 34 formed by the MOS FET 32 will be biased in the forward direction,
MOi9 FET? The parasitic diode 35 of 3 will be biased in the reverse direction. Therefore, from the power supply terminal 13 i! No current flows through the m line 24. Also,
Even if the potential of the power supply line 24 becomes higher than the potential of the power supply terminal 13, the parasitic diode 341C of the MOS FET 32 will be reverse biased.
The current path from the power supply line 24 to the power supply terminal 13 can also be eliminated, and damage or explosion of the silver oxide battery 15 due to reverse ftK of current can be prevented.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to prevent backflow of current when the auxiliary battery is exhausted in a circuit equipped with an auxiliary battery for backup when replacing the battery in addition to the main power supply battery. A battery power supply switching circuit is obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining a battery power source switching circuit according to an embodiment of the present invention, and FIG. 2 is a diagram for explaining a conventional battery It source switching circuit. 14... Lithium battery (first battery), 15... Silver oxide battery (second battery), 17, 24... Power line, 18... 3V system circuit group, 25... 1.5v circuit group 1. ? 2, 3 J... 1st. Second M.O.
8FET...? 4...? 5... Parasitic diode.

Claims (1)

[Claims] A first battery as a main power source, a power line from which power is supplied from the battery, and when replacing the first battery, the first battery is operated as a power source by supplying power to the power line. a second battery that supplies backup power to the functional circuit that is used, and a second battery that is connected in series between the second battery and the power supply line and is set to an off state during normal operation and an on state during backup. 1. Second MO
SFET, wherein the back gates of the first and second MOSFETs are connected such that the directions of their respective parasitic diodes are opposite to each other.