JPH0937486A - Power backup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power backup device which can dissolve malfunction such as drop of output voltage of to a load, occurrence of a sub power source, etc., even if the voltages of the main power source and the sub power source are reversed, and besides can save expenses with simple circuit constitution. SOLUTION: A power backup device has a DC-DC converter 1 to boost the battery BAT1, load DRAM 2, resistors R1 and R2 to divide the power voltage 12V, switching diodes D1, D2, D3, and an ideal diode D4 by the base grounding of a PNP transistor. When the voltage accuracy of the main power +5V is +5±0.25V, the Vcc of the load 2 is supplied with 4.75-5.25V by the ideal diode D4. If the output voltage of the diode D4 is 4.75V and the output voltage of the diode D3 is 5.3V, the supply voltage to the load 2 is reversed, but the reference voltage Vref is supplied with 5.3V or over through the switching diode D1, and the DC-DC converter 1 does not perform boost operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply backup device for backing up a power supply such as for holding data stored in a memory.

[0002]

2. Description of the Related Art Heretofore, the following power supply backup devices of this type have been known. That is, there is a system which has a main power supply and a sub power supply, and switches to the sub power supply to back up the power supply when the supply voltage of the main power supply drops.
In the power supply backup device, a lithium secondary battery or the like is used as a sub power supply when the supply voltage range at the time of backup and the supply voltage range at the time of operation overlap, for example, when the DRAM is backed up. Since the lithium secondary battery is 3V, if the power supply voltage of the DRAM is 5V, a voltage conversion circuit is required.
A DC converter is used. Switching between the main power supply and the sub power supply is performed by the high output priority switching circuit by connecting the cathode of the diode. FIG. 6 is a circuit block diagram showing the configuration of a power supply backup device using a conventional DC-DC converter.

[0003]

However, the above-mentioned conventional example has the following problems. That is, the main power supply 5V
Is 4.75 to 5.25V and the voltage conversion circuit has a voltage range of 4.75 to 5.25V, for example, the main power supply is 4.75V and the voltage conversion circuit is 5.25V. Since the magnitude of the voltage is reversed, the current is always supplied to the load from the voltage conversion circuit side instead of the main power supply.

However, since the output of the voltage conversion circuit, which is the sub-power supply, has a low current specification at the time of backup, if power is always supplied during operation, an overcurrent will result. As a result, there are problems that the output voltage drops and the voltage conversion circuit generates heat due to overcurrent.

FIG. 7 is a timing chart showing the waveform of the collector voltage VL of the transistor driven by the chopper driver when current is supplied by the DC-DC converter. When the supply current becomes larger than the expected output current, the chopper driver performs continuous oscillation. When the load current further increases, the output voltage decreases and is supplied from the + 5V side of the main power supply, but when the potential difference is large, the output voltage is balanced at the intermediate point. At this time, if the heat capacity of the DC-DC converter is small, it may overheat and be destroyed.

As a countermeasure against the above-mentioned problem, a current protection circuit has been inserted into the output of the voltage conversion circuit.
Not only did this lead to higher costs, but the heat generation could not be reduced sufficiently. Also, as a measure against the above problem, an overheat protection circuit is also inserted in the voltage conversion circuit, but despite the fact that the voltage of the main power supply is within the normal voltage range,
There was a new problem that the overheat protection circuit worked and the voltage conversion circuit did not work due to the overheat protection circuit working when the voltage of the main power supply dropped.

Further, as a countermeasure against the above-mentioned problems, it is also practiced to make the supply voltage range during backup and the supply voltage range during operation not overlap. For example, when the voltage range of the main power supply 5V is 5.00 to 5.25V, the voltage range of the voltage conversion circuit is 4.75 to 5.00.
If they are V, they do not overlap. However, increasing the accuracy of the supply voltage of the main power source leads to cost increase and is not the best countermeasure.

Therefore, the present invention can solve the problems that the output voltage of the load is lowered and the over-current is generated in the sub power supply even if the voltages of the main power supply and the sub power supply are reversed, and the cost is increased by a simple circuit configuration. An object of the present invention is to provide a power supply backup device that can suppress the power consumption.

[0009]

In order to achieve the above object, a power source backup device according to claim 1 of the present invention comprises:
A main power supply and a sub-power supply that has a supply voltage range that at least partially overlaps the supply voltage range of the main power supply, and that supplies a load current smaller than that of the main power supply, and the supply voltage of the main power supply is In a power supply backup device that switches to the sub power supply to back up the power supply when the voltage drops, current supply stopping means for supplying or stopping the load current of the sub power supply, and voltage detection means for detecting the supply voltage of the main power supply. When the detected supply voltage of the main power supply is in a predetermined voltage range, the load current of the sub power supply is stopped by the current supply stopping means, and when the supply voltage of the main power supply is lower than the predetermined range, the current is stopped. Control means for supplying the load current of the sub power supply by the supply stopping means. According to this power supply backup device, it is possible to solve the problem that the output voltage is lowered or heat is generated due to overcurrent. Further, it is possible to suppress cost increase with a simple configuration.

According to a second aspect of the present invention, there is provided the power source backup device according to the first aspect, wherein the auxiliary power source comprises a battery and a voltage converting means for converting the battery voltage into a predetermined voltage, and the current supply stopping means is the It is characterized in that the operation of the voltage converting means is stopped or started. According to this power supply backup device, it is possible to suppress an increase in cost with a simple configuration that only controls the operation of the voltage conversion means.

According to a third aspect of the present invention, there is provided the power source backup device according to the first aspect, wherein the auxiliary power source includes a battery and a voltage converting means for converting the battery voltage into a predetermined voltage, and the current supply stopping means is the It is characterized in that the battery connected to the voltage converting means is turned on and off. According to this power backup device, cost increase can be suppressed by a simple configuration in which the battery is turned on and off.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a power supply backup device of the present invention will be described.

[First Embodiment] FIG. 1 is a circuit block diagram showing a configuration of a power supply backup device according to the first embodiment. In the figure, 1 is a DC-DC converter for boosting the battery BAT1, 2 is a load DRAM,
R1 and R2 are resistors that divide the power supply voltage 12V. D
1, D2, D3 are switching diodes, D4 is PN
It is an ideal diode with the base of the P-transistor grounded.

First, the operation of the DC-DC converter 1 will be described. FIG. 2 is a circuit diagram showing the configuration of the DC-DC converter 1. In the figure, reference numeral 25 is a reference voltage generating circuit, which outputs a reference voltage of 0.85V. Two
6 is an oscillator, 27 is a chopper driver, and 28 is a comparator.

The comparator 28 compares the reference voltage of 0.85 V with the divided voltage obtained by dividing the output voltage Vout by the resistors R6 and R7, and when the divided voltage is lower than the reference voltage, the chopper driver 27. Generate a comparison output signal to activate the. When the chopper driver 27 operates, the transistor TR21 turns on, and the boosted current flows through the inductor L1 and the diode D5. In the present embodiment, the operation is performed so that the output voltage Vout becomes 5V.
FIG. 3 is a graph showing the characteristics of the output voltage with respect to the input voltage. It shows that the output voltage Vout becomes 5V in the region where the input voltage Vin is 1V or more. Although not shown, the DC-DC converter 1 has a reference voltage Vref.
Is provided, and the DC-DC converter 1 is configured to stop the boosting operation when the reference voltage Vref becomes 5.3 V or less.

Switching diodes D1 and D2 are connected to the input terminal of the reference voltage Vref, and when the main power supply supplies a normal output voltage, the step-up operation of the DC-DC converter 1 is stopped, but the operation of the operation is stopped. Stop and start will be described.

If the divided voltage obtained by dividing the power source voltage 12V by the resistors R1 and R2 is 6.0 to 6.6V and the forward voltage drop of the switching diode is 0.7V,
An attempt is made to supply 5.3V to 5.9V to the reference voltage Vref.

On the other hand, the set voltage of the output voltage Vout is 5.
If the voltage is set to 2V to 6.0V, the power supply voltage Vcc of the load will be 4.5 to 5.3V. Further, it also tries to supply 4.5V to 5.3V to the reference voltage Vref.

Voltage accuracy of main power source + 5V is + 5 ± 0.25
Assuming that D4 forms an ideal diode by grounding the base of the PNP transistor at V, Vcc of the load 2
Tries to supply 4.75 to 5.25V to. If the output voltage of the diode D4 is 4.75V and the output voltage of the diode D3 is 5.3V, the supply voltage is reversed,
Since 5.3 V or more is supplied to the reference voltage Vref through the switching diode D1, the DC-DC converter 1 does not perform the boosting operation. Therefore, Vout of the DC-DC converter 1 drops to 4.75 V or less (see the state a in FIG. 4). FIG. 4 is a timing chart showing the voltage of each part of the power backup device.

On the other hand, when the voltage of the main power supply drops, when the output voltage of the switching diode D1 becomes 5.3 V or less, the change of the output voltage of the switching diode D2 directly appears in the reference voltage Vref. D
The C-DC converter 1 outputs an output voltage Vout of 5.2V-
It operates to output 6.0V.

In a normal power source, both + 5V and + 12V drop at the same time. Since the + 5V load capacitance is often larger than + 12V, the + 5V voltage drop is 4.75.
It becomes possible to supply current from the DC-DC converter 1 through the switching diode D3 before the voltage drops from V to 4.5V or less. Therefore, the guaranteed lower limit voltage of 4.5 V when the load is backed up can be satisfied (see state b in FIG. 4).

[Second Embodiment] A power supply backup device according to the second embodiment will be described. FIG. 5 is a circuit block diagram showing the configuration of the power supply backup device according to the second embodiment. The same numbers are attached to the same components as those of the first embodiment.

That is, in the figure, 1 is a DC-DC converter for stepping up the battery BAT1 and 2 is a load DR.
AM, R1 and R2 are resistors for dividing the power supply voltage 12V, D
3 is a switching diode, and D4 is an ideal diode with the base of the PNP transistor grounded. TR51
Is a switching transistor for connecting and disconnecting the DC-DC converter 1 and the battery BAT1.

First, the basic operation of the DC-DC converter 1 is the same as that of the first embodiment. In the present embodiment, when the main power supply outputs a normal voltage by connecting the transistor TR51 to the input Vin of the DC-DC converter 1, the operation of the DC-DC converter 1 is stopped. The stop operation will be described. .

In FIG. 5, the power supply voltage +5 V is applied to the resistors R1 and R
The voltage is divided by 2 and the voltage dividing point is connected to the base of the transistor TR51. The divided voltage at the normal voltage is a voltage at which the transistor TR51 is turned off. When the voltage accuracy of the power supply voltage + 5V is + 5 ± 0.25V, the ideal diode D
4 forms an ideal diode due to the grounded base of the PNP transistor, Vcc of the load 2 is 4.75.
Try to supply ~ 5.25V.

If the output voltage of the diode D4 is 4.75V and the output voltage of the diode D3 is 5.3V, the supply voltage is reversed, but the input voltage Vin is the same as the transistor T.
Since the supply voltage of the battery BAT1 is not input due to the interruption of R51, the DC-DC converter 1 does not perform the boosting operation. Therefore, the output voltage Vout of the DC-DC converter 1 decreases to 4.75V or less. Therefore, the output voltage of the diode D4 is 4.75V in the load 2.
Is supplied.

On the other hand, when the voltage of the main power supply drops, the base voltage of the transistor TR51 also drops and is grounded through the resistor R2, so that the transistor TR51 is turned on.
A current is supplied to the input of the DC-DC converter 1 from the battery BAT1, and the output voltage Vout is 5.2V to 6.0V.
It operates to output.

If the switching timing of the transistor TR51 is late, a separate voltage drop detection circuit may be provided and its output may be used for switching the transistor TR51. Alternatively, a comparator may be used to speed up the switching operation.

[Modified Embodiment] In the power supply backup device according to the modified embodiment, a terminal for prohibiting current supply is added to the output Vout of the DC-DC converter.
A voltage detecting means for detecting a voltage drop of the main power source such as a reset IC may be connected to the terminal for prohibiting the current supply.

With this configuration, the current supply of the DC-DC converter is prohibited when the voltage of the main power supply is within the predetermined voltage range, and when the voltage of the main power supply is below the predetermined voltage range, the DC-DC converter is stopped. Alternatively, the current supply may be started.

[0031]

According to the power supply backup device of the first aspect of the present invention, the auxiliary power supply has a supply voltage range that overlaps at least a part of the supply voltage range of the main power supply, and is smaller than the main power supply. When supplying a load current, when switching the main power supply to the sub power supply to back up the power supply when the supply voltage of the main power supply drops, the supply voltage of the main power supply is detected by the voltage detection means, The control means is
When the detected supply voltage of the main power supply is in a predetermined voltage range, the load current of the sub power supply is stopped by the current supply stopping means, and when the supply voltage of the main power supply is lower than the predetermined range, the current supply is stopped. Since the load current of the sub-power supply is supplied by the stop means, it is possible to solve the problem that the output voltage is lowered or the overcurrent causes heat generation. Further, it is possible to suppress cost increase with a simple configuration.

According to another aspect of the power source backup device, the sub power source includes a battery and a voltage converting means for converting the battery voltage into a predetermined voltage, and the current supply stopping means stops the operation of the voltage converting means. Or start, so
The cost increase can be suppressed by a simple configuration that only controls the operation of the voltage conversion means.

According to another aspect of the power source backup device, the sub power source includes a battery and a voltage converting means for converting the battery voltage into a predetermined voltage, and the current supply stopping means is connected to the voltage converting means. Since the battery is turned on and off, the cost can be suppressed with a simple configuration in which the battery is turned on and off.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing a configuration of a power supply backup device according to a first embodiment.

FIG. 2 is a circuit diagram showing a configuration of a DC-DC converter 1.

FIG. 3 is a graph showing characteristics of output voltage with respect to input voltage.

FIG. 4 is a timing chart showing voltages of respective parts of the power backup device.

FIG. 5 is a circuit block diagram showing a configuration of a power supply backup device according to a second embodiment.

FIG. 6 is a circuit block diagram showing a configuration of a power supply backup device using a conventional DC-DC converter.

FIG. 7 is a timing chart showing a waveform of a collector voltage VL of a transistor driven by a chopper driver when current is supplied by a DC-DC converter.

[Explanation of symbols]

 1 DC-DC converter 2 load D1, D2, D3 switching diode BAT1 battery

Claims (3)

[Claims] 1. A main power supply, and a sub-power supply that has a supply voltage range that at least partially overlaps the supply voltage range of the main power supply and that supplies a load current that is smaller than that of the main power supply. In a power supply backup device that switches to the sub power supply to back up the power supply when the supply voltage of the power supply drops, a current supply stopping unit that supplies or stops the load current of the sub power supply, and detects the supply voltage of the main power supply. And a detected voltage supplied to the main power supply is within a predetermined voltage range, the current supply stopping means stops the load current of the sub power supply, and the supply voltage of the main power supply is lower than the predetermined range. A power supply backup device comprising: a control means for supplying the load current of the auxiliary power supply by the current supply stopping means if the load is low. 2. The sub-power supply includes a battery and a voltage conversion means for converting the battery voltage into a predetermined voltage, and the current supply stopping means stops or starts the operation of the voltage converting means. The power supply backup device described in 1. 3. The sub power supply includes a battery and a voltage conversion unit that converts the battery voltage into a predetermined voltage, and the current supply stopping unit turns on and off the battery connected to the voltage conversion unit. The power supply backup device according to claim 1.