JPS6260437A - Power source backup 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 relates to an improvement in a 118 backup circuit that supplies power to a memory, a clock circuit, etc. when the main power is cut off.

[Technical background of the invention]

In microcomputers, the contents of counters, memory, clock circuits, etc. must be retained even if the power supply from the main power supply is cut off, so a backup power supply is provided to back up the power supply. . The circuit used is a combination of a C-MO8 circuit and a battery, since the consumption 'R current during operation is small and the operating voltage range is wide. FIG. 3 is a block diagram of a conventional 18 backup circuit that employs such a combination. 1 is a circuit to be backed up having functions such as a counter, memory, and clock circuit.

2 is a logic/analog circuit that does not require backup;
Data is normally exchanged with the analog circuit 2 via the bus 3. Therefore, power is supplied to the circuit 1 to be backed up from both the power supply III (not shown) connected to the power supply terminals a1 and +a2 via the diode D1, and from the backup power supply 4 via the diode D2. It is being done. Further, power is supplied to the logic/analog circuit 2 from the main power supply via a diode D3. Therefore, if the main power supply is normal, the diode D1 becomes conductive and the backed-up circuit 1
However, when the main power supply is cut off, diode D1 becomes non-conductive, and diode D2 becomes conductive, and the backup power supply 4
Power is supplied to the circuit 1 to be backed up from.

[Problems with background technology]

However, since the diode D2 is connected between the circuit to be backed up 1 and the backup power source 4, a voltage drop of about 0.5 to 0.7 V occurs due to the diode D2. Therefore, the voltage level of the backup power supply 4 must be set sufficiently higher than the holding voltage of the circuit 1 to be backed up. Therefore, there is a problem that current consumption increases and the usable period of the backup power source 4 becomes shorter. In other words, the voltage actually applied to the backed-up circuit 1 approaches the voltage level necessary for the holding operation applied to the backed-up circuit 1 by the voltage drop of the diode D2, so the period becomes shorter. In addition, when the backed-up circuit 1 operates periodically, a large amount of current is required during this operation, so the amount of current supplied to the backed-up circuit 1 fluctuates, causing the voltage drop across the diode D2 to fluctuate. There is a problem in that the voltage level supplied to the circuit to be backed up 1 fluctuates.

[Purpose of the invention]

The present invention has been made based on the above-mentioned circumstances, and its objectives are: 1. To provide a power supply backup circuit capable of extending the period of use of the backup power supply without increasing the voltage level of the backup power supply and stably supplying power.

[Summary of the invention]

According to the present invention, when the voltage level of the main power supply drops to a predetermined level, the backup element detects this and becomes conductive, thereby causing the backup 'R8! This power supply backup circuit supplies power to the circuit to be backed up from the back-up circuit, and when the circuit to be backed up operates in the backup state, the amount of current supplied to the circuit to be backed up is increased by a current control circuit.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a power backup circuit. In the figure, reference numeral 10 denotes a circuit to be backed up, which has the functions of a counter, a memory, a clock mechanism, etc., and also has the function of sending an operation signal S indicating the operation to the operation component.

Further, 11 is a signal processing circuit that does not require backup when the main power is cut off, and has a configuration including a logic/analog circuit 12 and resistors R1 and R2 connected in series. And these backed up circuits 10
and the signal processing circuit 11 are connected via a bus B, and data is exchanged when the voltage level of the main power supply is normal. By the way, these backed up circuit 10 and signal processing circuit 11 have terminals a1 and a.
The main power supply is supplied from 2. Note that a diode D10 is connected between the main power supply and the terminal a1 with the direction of the backup circuit 10 being the forward direction, and power from the main power supply is supplied to the backup target circuit 10 through this diode D10.

Now, a backup power supply 13 consisting of a battery is connected to the backup circuit 10 via the collector emitter of a PNP transistor Q1. This transistor Q1 has a function of becoming conductive when the voltage level of the main power supply drops to a predetermined level and supplying power from the backup power supply 13 to the circuit 10 to be backed up.

Therefore, the collector of transistor Q1 is connected to terminal a1 via diode D10, and the base is directly connected to terminal a1. Roughly speaking, this base is connected to ground GN[) through resistors R1 and R2, that is, terminal a2.
The base current can be changed by changing the values of these resistors R1 and R2. Reference numeral 14 denotes a current control circuit, which has a function of increasing and controlling the collector current of the transistor Q1 in response to an operation signal S sent from the backed-up circuit 10 when the backed-up circuit 10 operates in the backup state. It has Specifically, a series circuit consisting of a resistor R3 and the collector-emitter of an NPN transistor Q2 is connected to the base of the transistor Q1, and a series circuit is connected to the base of the transistor Q1.
A series circuit of a resistor R4 and an inverter 15 is connected to the base of the inverter 2.

Next, the backup operation of the circuit configured as described above will be explained. If the mains supply is supplying power at a normal voltage level, this voltage level is
1 and the transistor Q1 is in a non-conducting state. Therefore, the circuit to be backed up 1o
Both the signal processing circuit 11 and the signal processing circuit 11 operate by receiving power from the main power source.

Here, when the main power supply is cut off due to a power outage, etc., the base of the transistor Q1 is connected to the ground via the resistors R1 and R2, so the voltage level drop in the power supply line causes the transistor Q1 to become conductive. becomes. "Thus, - power is supplied from the backup power source 1B to the circuit to be backed up 10, and the contents of the circuit to be backed up 10 are held. At this time, the resistor R
If the combined resistance value of 1 and R2 is large, the base current of the transistor Q1 is small, and therefore the battery consumption is reduced. By the way, when the backed-up circuit 10 operates in this backup state, for example, when the contents of the memory are read periodically or at an arbitrary time, low-level operation signals s and Q are sent from the backed-up circuit 10. This operating signal @S passes through the inverter 15, becomes high level, and is applied to the base of the transistor Q2.

This causes transistor Q2 to become conductive, increasing the base current of transistor Q1. With that, collector 1 of transistor Q1! The current increases and is supplied to the backed-up circuit 1o.

Thus, the circuit 10 to be backed up operates with this collector current. Then, when the operation of the backed-up circuit 10 is completed, the operation signal S becomes high level and the transistor Q2 becomes non-conductive, so that the collector current of the transistor Q1 is changed to the backed-up circuit 10.
It decreases to a value that can maintain the holding state at 0.

In this way, in the above embodiment, when the voltage level of the main power supply drops to a predetermined level, the transistor Q1 becomes conductive, and the backup power supply 13 supplies power to the circuit to be backed up 10, and furthermore, in this backup state, the circuit to be backed up is When the backup circuit 10 operates, the current control circuit 14 increases the amount of current supplied to the circuit 10 to be backed up, so that the usage period of the battery can be extended and stable power can be supplied to the circuit 10 to be backed up. In other words, since the saturation voltage between the collector and emitter of transistor Q1 is smaller than the voltage drop in the forward direction of the diode, if the voltage level of the battery itself is VB as shown in FIG. is VD when a diode is used, and VT when a transistor is used. Therefore, it is clear that for the same supply voltage level, a transistor can be used for a longer period of time, for example a zero period. Therefore, it is not necessary to set the voltage level of the battery to a high level, and furthermore, the battery can be used until the voltage level of the battery is exhausted and lowered to near the limit of the voltage level required to be maintained in the circuit 10 to be backed up. Further, since the amount of supplied current is increased only when the backed-up circuit 10 operates, battery consumption is reduced and stable supply operation is possible.

Note that the present invention is not limited to the above-mentioned embodiment, and can be modified without departing from the spirit thereof.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to provide a power supply backup circuit that can extend the usage period of the backup power supply without increasing the voltage level of the backup power supply and can provide stable power supply.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the power backup circuit according to the present invention, Fig. 2 is a block diagram showing the voltage level supplied to the circuit to be backed up by the circuit of the present invention, and Fig. 3 is a block diagram of a conventional circuit. be. 10... Circuit to be backed up, 11... Signal processing circuit, 12... Logic/analog circuit, 13... Backup power supply, 14... Current control circuit, Ql...
・PNP type transistor, Q2...NPN type transistor. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2

Claims (1)

[Claims] A backup power supply, a circuit to be backed up that receives power from a main power supply that normally supplies power to circuits that do not require power supply backup, and which includes a memory etc., and a circuit to be backed up that receives power from the main power supply, which is comprised of a memory, etc., and detects the voltage level of the main power supply and determines the voltage level. A backup element with a small resistance value that becomes conductive when the level drops to a predetermined level and supplies power from the backup power source to the backed up circuit; 1. A power backup circuit comprising: a current control circuit that increases the amount of current supplied from the backup element to the circuit to be backed up when the backup circuit operates.