JPH0613354U - Backup power supply circuit - Google Patents

Abstract

(57) [Summary] [Objective] A backup power supply using a secondary battery 27 outputs a stable backup voltage. [Structure] A first constant voltage circuit 31 for reducing the voltage of a main power source to a charging voltage of a secondary battery, and the first constant voltage circuit 3
The secondary battery 27 charged by the output of No. 1 and the second constant voltage circuit 3 that lowers the output of the first constant voltage circuit 31 and the output of the secondary battery 27 to the operation stop voltage of the secondary battery or less.
2. A backup power supply circuit 30 comprising: a second constant voltage circuit 32; and a third constant voltage circuit 33 for boosting the output of the second constant voltage circuit 32 to a predetermined voltage.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a backup power source used for memory backup of a microcomputer or the like.

[0002]

[Prior art]

 Today, a variety of electronic devices containing microcomputers are used, and these devices also incorporate a random access memory together with a microprocessor. In these devices, a backup power supply is used to hold the data written in the random access memory even when the power switch is turned off. A voltage lower than the normal operating voltage may be applied, and some work processing may be continued even when the power switch of the electronic device is turned off due to a clock signal with a lowered frequency.

In this state, power is supplied to the random access memory and the microprocessor by the backup power source to hold the data recorded in the random access memory and to perform the minimum necessary work by the microprocessor. A rechargeable lithium battery is often used as a backup secondary battery for the backup power source.

An example of a backup power supply circuit using this lithium battery as a secondary battery is, as shown in FIG. 2, when the voltage of the main power supply 11 is higher than 3 volts, such as 5 volts. The input terminal 21 connected to the main power supply 11 via the power switch 15 is connected to the output terminal 23 connected to the load 17 such as a microprocessor or a random access memory via the eleventh diode 61, and the input terminal 21 is connected. Is connected to the ground terminal 25 through the eleventh resistor 66 and the twelfth resistor 67 so that the midpoint between the eleventh resistor 66 and the twelfth resistor 67 has a potential of about 3 volts. The main power supply voltage is divided by the resistor 66 and the twelfth resistor 67, and the intermediate point is connected to the anode of the secondary battery 27 via the thirteenth resistor 68 and the thirteenth diode 63. Further, the anode of the secondary battery 27 is connected to the output terminal 23 via the twelfth diode 62, and the cathode of the secondary battery 27 is connected to the ground terminal 25.

The thirteenth resistor 68 as a protection resistor for limiting the charging current may be omitted depending on the resistance values of the eleventh resistor 66 and the twelfth resistor 67, and the main power source may be omitted. When the voltage of 11 is 3 volts which is approximately equal to the charging voltage or rated output voltage of the secondary battery 27, the secondary battery 27 and the anode of the 12th diode 62 are connected to the input terminal 21 via the 13th resistor 68. The backup power supply circuit 20 is formed by omitting the eleventh resistor 66, the twelfth resistor 67, and the thirteenth diode 63 by connecting them.

Therefore, using this backup power supply circuit 20, when the power switch 15 is in the ON state, the voltage of the main power supply 11 is supplied from the output terminal 23 to the load 17 via the eleventh diode 61, and the power switch 15 Even when is turned off, the power of the secondary battery 27 is supplied to the load 17 via the twelfth diode 62.

[0007]

[Problems to be solved by the device]

 As mentioned above, as a secondary battery, a lithium battery having a long life and a relatively stable output voltage is widely used today, but the output voltage of this lithium battery is about 3 volts. Considering the voltage effect of the diode (twelfth diode) used for switching with the main power supply voltage, the voltage output from the power supply circuit at the time of backup may be 3 V or less.

Although this reduction in backup voltage does not significantly affect the operation of the random access memory, it may cause a malfunction in the operation of the microprocessor, and requires a stable backup voltage of 3 V or the like. There is an increasing demand for a suitable small backup power supply that can maintain the voltage for a long time.

[0009]

[Means for Solving the Problems]

 The present invention has a first constant voltage circuit that outputs a charging voltage of a secondary battery based on a main power supply voltage, and a secondary battery that is charged by the output of the first constant voltage circuit. The output of the voltage circuit and the output of the secondary battery are input, and the second constant voltage circuit that temporarily lowers the input voltage, and the third constant voltage that boosts the output of the second constant voltage circuit to a predetermined voltage such as 3 volts. Circuit, and the output of the third constant voltage circuit is output to the output terminal via the diode.

[0010]

[Work]

 Since the present invention has the second constant voltage circuit that temporarily lowers the output of the secondary battery, it is possible to obtain a stable and constant potential without specifying the discharge of the secondary battery. Since the output of the voltage circuit is boosted to a predetermined voltage by the third constant voltage circuit, a stable and necessary potential can be output using the secondary battery.

[0011]

【Example】

 As shown in FIG. 1, the embodiment of the present invention is a power supply circuit 20 including a backup power supply circuit 30 which outputs a predetermined backup voltage and which also outputs a voltage for normal operation higher than the backup voltage. This power supply circuit 20 has an input terminal 21 to which the voltage from the main power supply 11 is input, and a fourth constant voltage circuit 55 which normally supplies 5 V higher than the backup voltage when the power switch 51 is turned on. It has an output terminal 23 which outputs an operating voltage and also outputs a backup 3 volt voltage from the backup power supply circuit 30, and the fourth constant voltage is supplied from the input terminal 21 via the power switch 51. The voltage circuit 55 and the fourth constant voltage circuit 55 are further connected to the output terminal 23 via the fourth diode 57, and the backup power supply circuit 30 is also connected to the output terminal 23 via the third diode 38. .

As the voltage of the main power supply 11, an appropriate main power supply battery or the like that outputs 7 to 9 volts is used, and the fourth constant voltage circuit 55 uses a regulator such as a regulator whose output voltage is 5 volts. It uses a voltage circuit. The backup power supply circuit 30 connects the input side of the first constant voltage circuit 31 to the input terminal 21, and as the first constant voltage circuit 31, the output voltage of the lithium battery used as the secondary battery 27 is used. An appropriate step-down switching regulator having a voltage of 3.2 V suitable for the charging voltage is used, and the output side of the first constant voltage circuit 31 is connected to the second constant voltage circuit 32 via the first diode 36. Further, the output side of the second constant voltage circuit 32 is connected to the third constant voltage circuit 33, and the output side of the third constant voltage circuit 33 is connected to the third diode 38. As the circuit 32, an appropriate step-down switching regulator whose output voltage is 1.8 V, which is slightly lower than the safe discharge potential of the secondary battery 27, and as the third constant voltage circuit 33, the output voltage is the required voltage. And using an appropriate step-up switching-regulation data to some 3.0 volts.

The output side of the first constant voltage circuit 31 is connected to the anode of a lithium battery, which is a secondary battery 27, via a second diode 37 and a limiting resistor 39, and the secondary battery 27 has a secondary battery 27. The anode is connected to the input side of the second constant voltage circuit 32 together with the cathode of the first diode 36 via the protection cutoff circuit 41. The protection cutoff circuit 41 has its input terminal connected to the voltage detector 43 and the emitter of the switching transistor 45, the collector of the switching transistor 45 being connected to the second constant voltage circuit 32, and the switching transistor 45 being connected to the second constant voltage circuit 32. The base is grounded via a control transistor 46, and the base of the control transistor 46 is connected to the output terminal of the voltage detector 43. This voltage detector 43 has a detection voltage of, for example, a safety output of a lithium battery. When the voltage becomes 2.0 V or less, the detection signal output from the output terminal is stopped, the control transistor 46 is made non-conductive, and the switching transistor 45 is turned off.

Therefore, the power supply circuit 20 including the backup power supply circuit 30 has the normal operating voltage of 5 V output from the fourth constant voltage circuit 55 when the power switch 51 is turned on. It is output to the output terminal 23 via the fourth diode 57. At this time, in the backup power supply circuit 30, the output of the first constant voltage circuit 31 is output to the second constant voltage circuit 32 via the first diode 36. Further, although a backup voltage of 3.0 V is output from the third constant voltage circuit 33 by being applied to the third constant voltage circuit 33, this backup voltage is cut off by the third diode 38.

Then, the output voltage of the first constant voltage circuit 31 via the first diode 36 is applied to the second constant voltage circuit 32, and the input side of the protection / interruption circuit 41 is connected to the second diode. Since the voltage is input via the battery 37 and the limiting resistor 39, the output terminal side voltage of the protection cutoff circuit 41 is higher than the input terminal side voltage during charging of the secondary battery 27, and the protection cutoff circuit 41 is In the off state, the secondary battery 27 is stably charged via the second diode 37 and the limiting resistor 39.

When the power switch 51 is turned off, the voltage of 3.2 V obtained by stepping down the voltage of the main power supply 11 by the first constant voltage circuit 31 is supplied to the second constant voltage circuit 32 or the secondary voltage. The electric charge stored in the battery 27 is supplied to the second constant voltage circuit 32 via the protection cutoff circuit 41. At this time, in this embodiment, a lithium battery is used as the secondary battery 27, and the output voltage of the lithium battery in a fully charged state is about 3.2 V, which means that the main power source 11 is exhausted or the main power source 11 is consumed. When the battery pack 11 is removed, the voltage from the secondary battery 27 is supplied to the second constant voltage circuit 32 via the protection circuit 41, and the output potential of the secondary battery 27 drops with the passage of time. The output voltage of the secondary battery 27 is set to a stable 1.8 V by the second constant voltage circuit 32, and this stable voltage is further boosted to 3.0 V by the third constant voltage circuit 33. A stable voltage of about 3.0 V is output from the output terminal 23 of the power supply circuit 20 via 38.

If the output voltage of the secondary battery 27 drops to 2.0 volts after a few days or months have passed since the main power supply 11 has been exhausted, the protection cutoff circuit 41 causes the control transistor 46 to Also, the switching transistor 45 is turned off to cut off the output from the secondary battery 27 to the second constant voltage circuit 32 and prevent the secondary battery 27 from being completely discharged so that the secondary battery 27 is not damaged.

[0018]

[Effect of device]

 The present invention provides a first constant voltage circuit for charging a secondary battery with the voltage of the main power source as a constant voltage, a second constant voltage circuit for temporarily reducing the output of the charged secondary battery, and a second constant voltage. Since it has a third constant voltage circuit that boosts the output of the circuit to the required voltage, it is a backup power supply circuit that can always output a stable required voltage with the output of the secondary battery.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a power supply circuit including an embodiment of a backup power supply circuit according to the present invention.

FIG. 2 is a diagram showing an example of a conventional power supply circuit including a backup power supply.

[Explanation of symbols]

11 main power supply 15 power switch 17 load 20 power supply circuit 21 input terminal 23 output terminal 25 ground terminal 27 secondary battery 30 backup power supply circuit 31 first constant voltage circuit 32 second constant voltage circuit 33 third constant voltage circuit 36 first diode 37 Second Diode 38 Third Diode 39 Limiting Resistor 41 Protection Breaking Circuit 51 Power Switch 55 Fourth Constant Voltage Circuit

Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location H02J 7/34 E 9060-5G

Claims (1)

[Scope of utility model registration request] 1. A first constant voltage circuit for reducing the voltage of a main power source to a charging voltage of a secondary battery, a secondary battery charged by an output of the first constant voltage circuit, and a first constant voltage circuit. A second constant voltage circuit for stepping down the output and the output of the secondary battery below the operation stop voltage of the secondary battery; and a third step for boosting the output of the second constant voltage circuit to a predetermined voltage.
A backup power supply circuit, comprising: a constant voltage circuit.