JPH0357077Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a power supply device, and more particularly to a power supply device including a so-called backup power supply for a memory circuit.

BACKGROUND ART In a circuit system having a memory circuit, when AC power to the device is temporarily cut off due to a power outage or the like, the contents of the memory circuit may be lost. Therefore, a so-called backup power supply dedicated to the memory circuit is required. FIG. 1 is a diagram showing an extremely simple circuit configuration having such a backup power supply function.

In the figure, an AC input power source is rectified by a rectifier 1 and smoothed by a smoothing capacitor 2. This smoothed output is made into a voltage having a constant DC level in the stabilizing circuit 3, and becomes an operating power source for the memory circuit 5 through the unidirectional diode 4. A capacitor (storage element) 6 is provided which is charged by this operating power supply voltage, and operates as a backup power supply when the power supply is temporarily interrupted. Furthermore, a display circuit 7 for displaying the contents of the memory circuit 5
is provided, and the DC voltage from the stabilizing circuit 3 serves as the operating power source for the display circuit 7. Reference numeral 8 indicates a signal line. The diode 4 prevents power from being supplied to the display circuit 7 from the backup power supply 6 of the storage circuit.

In order to increase the capacity of the backup power supply, methods such as increasing the capacity of the capacitor 7 or smoothing capacitor 2 in the power supply circuit can be considered, but the larger the capacitor capacity, the larger the device becomes. This will lead to priceization.

In addition, although the backup power supply 6 and the display circuit 7 are separated using the diode 4, when the power supply is temporarily cut off, the circuit time constant of the power supply circuits 2 and 3 prevents the display 7 from being turned off. During this time, the backup power supply 6 consumes power. Therefore, it is desirable to increase the capacity of the backup power supply 6 as much as possible, but this increase in capacity is accompanied by the above-mentioned drawbacks.

Summary of the invention An object of the invention is to provide a power supply device that allows the capacity of a backup power supply for a storage circuit to be increased without requiring an increase in the capacity of a capacitor.

In the power supply device according to the present invention, the rectified and smoothed voltage in the voltage source for the circuit system other than the memory circuit is applied to the backup power supply capacitor and is applied to the backup power supply capacitor to substantially increase the backup power supply capacity.

Example The present invention will be explained below using the drawings.

FIG. 2 is a circuit diagram of an embodiment of the present invention, and parts equivalent to those in FIG. 1 are designated by the same symbols.
The explanation will be omitted. Since there is generally another circuit system (not shown) in addition to the memory circuit 5 and display circuit 7, a power supply for this other circuit system is usually provided. This power source is connected to a rectifier 9 that rectifies the AC input power source as shown in the figure.
, smoothing capacitor 10, and voltage stabilizing circuit 11
It has Since this power supply voltage is generally set higher than the power supply voltage for the memory circuit 5, the terminal of the smoothing capacitor 10 is connected to the terminal of the backup power supply capacitor 6 via the switching PNP transistor 16, and the power supply voltage is set higher than that for the memory circuit 5. When the power is off, the switching transistor 16 is turned on and controlled, and the capacitors 10 and 6 are connected in parallel to add and superimpose the charges of both capacitors.
At this time, it is equivalent to connecting the capacitor 6 in parallel with the smoothing capacitor 10 having a higher charging voltage, and since the charging charges of these parallel-connected capacitors increase compared to the case of FIG. 1, the increased charges Voltage will be supplied to the memory circuit 5. The on/off control of the transistor 16 is performed by the control circuit 14. When the control circuit 14 detects a power outage due to a power outage or the like, the control circuit 14 instantly sets the base of the transistor 16 to the ground potential, and during normal operation, applies a high level voltage to the base of the transistor 16. to control this off.

In each of the above embodiments, the case where the display circuit 7 is added has been described, but the present invention can also be applied to a case where the display circuit is not provided, and the present invention can also be applied to a circuit system other than the memory circuit as the operating power source of the display circuit. The present invention can also be applied to a system in which the power is supplied from a power supply circuit. The key point is that the smoothed output of another power source is added to the capacitor of the backup power source or the smoothing capacitor of the power supply for the storage circuit.

Effects of the Invention As described above, according to the present invention, the capacity of the backup power supply of the memory circuit can be increased without any increase in the capacitance of the capacitor, so that a small and low-cost power supply device can be realized.

In particular, the current consumption of the memory circuit is large until it enters the backup state (for example, the standby state of a microcomputer), and the voltage drop temporarily becomes large immediately after the current is cut off. By using a sufficiently high voltage input to the circuit 11 to prevent a voltage drop immediately after the power is turned off, it is possible to suppress the voltage drop before entering the complete backup state, thereby increasing the backup time. .

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of a conventional power supply circuit, and FIG. 2 is a circuit block diagram of an embodiment of the present invention. Explanation of symbols of main parts, 2, 10...Smoothing capacitor, 5...Memory circuit, 6...Backup power supply capacitor.

Claims (1)

[Scope of utility model registration request] a memory circuit, a circuit system other than the memory circuit, first and second rectifiers that rectify the AC input voltage, and first and second smoothing capacitors that smooth the respective output powers of the first and second rectifiers. a first voltage source that receives the output voltage of the first smoothing capacitor and supplies an operating voltage to the circuit system; and a first voltage source that receives the output voltage of the second smoothing capacitor and supplies the output of the first smoothing capacitor to the memory circuit. a second voltage source that supplies an operating voltage lower than the operating voltage; a backup capacitor that is charged by the second voltage source and serves as a backup power source for the memory circuit; and an output of the first smoothing capacitor when the AC input voltage is interrupted. A power supply device comprising: a unidirectional switching circuit that applies and superimposes a voltage to the backup capacitor.