JPH02307109A - Constant voltage power supply circuit - Google Patents

Abstract

PURPOSE:To eliminate the potential difference between a main power supply and a back-up power supply with no addition of a back-up IC by setting a power voltage monitoring point at the cathode side of a diode connected to the main power supply and controlling the voltage of the main power supply so as to keep the voltage of the back-up power supply at a fixed level. CONSTITUTION:The diodes 3 and 4 have the forward voltage-forward current characteristic so that the same drop level is secured for the anode-cathode forward voltage in terms of the current consumption between a main power supply and a back-up power supply. The diode 4 having a larger forward current to the constant forward voltage drop is connected to the main power supply. While the diode 3 having a small forward current is connected to the back-up power supply. A power supply control IC 1 controls the voltage of both the main and back-up power supplies by setting a power monitoring point 8 at the cathode side of the diode 4. As a result, the same potential is secured between the main and back-up power supplies without using a back-up IC.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a constant voltage power supply circuit for digital circuits that divides the power supply into a backup power supply and a main power supply.

[Conventional technology]

Generally, in digital circuits that require a constant voltage power supply circuit,
For power supply voltage control, a power supply control IC (Toshiba TA7
9003, etc.) to form a circuit configuration as shown in FIG. In Fig. 4, 1 is for power control I
C and 2 are transistors, 5 is a control power supply input line, 7 is a main power supply line, and 8 is a power supply voltage monitoring point. In such a configuration, the external power supply control ICI monitors the collector output voltage of the transistor 2 and controls the base current of the transistor 2 to obtain a constant voltage. In this circuit, if a backup power source that continuously supplies power is required, the constant voltage power source must be separated into a main power source and a backup power source. A backup power supply is a circuit that charges a battery etc. when current is being supplied from a constant voltage power supply, and temporarily supplies power from the battery when the power supply goes down for some reason. Supplying power to the entire system from the battery when the power is down will consume a lot of current, necessitating a battery with a large capacity. However, it is only necessary to back up only a portion of the memory, the contents of which should not change when the power is turned off. For this purpose, a circuit configuration as shown in FIG. 5 has been considered. In FIG. 5, the same reference numerals as in FIG. Diode 10. A battery 11 is provided. In this way, in the circuit shown in FIG. 5, a diode 10 is connected to the backup power line 6 side to isolate the parts that require backup from the entire system when the power goes down, and a backup power battery is connected to the main power line 7 side. 11
This prevents current from flowing from the FIG. 6 shows another circuit configuration in which only a portion of the memory, etc., can be backed up when the power is turned off. The difference between the circuit in Figure 6 and the circuit in Figure 5 is that instead of the diode 10, a backup IC (Fujitsu MB
3780 etc.) to control the power supply voltage as well.

[Problem to be solved by the invention]

When a diode is connected only to the backup power supply as shown in FIG. 5, there is a problem in that the potential of the backup power supply becomes lower than that of the main power supply by the forward voltage drop of the diode. In addition, in order to control the power supply voltage in a circuit that requires a backup power supply, the method shown in Figure 6 requires the addition of a separate backup IC, which not only increases cost but also increases the mounting area. There was a problem with this. In view of the above, the present invention makes it possible to control the power supply voltage without adding a separate backup IC when the main power supply and the backup power supply are separated, and also to keep the main power supply and the backup power supply at the same potential. It is an object of the present invention to provide a constant voltage power supply circuit that enables

[Means to solve the problem]

When a diode is connected only to the backup power supply,
In order to solve the problem of the voltage of the backup power supply being lower than the voltage of the main power supply, as shown in Figure 1, diodes are connected to both the main power supply and the backup power supply.
A voltage monitoring point by a power supply control IC is provided on the cathode side of a diode connected to the main power supply side. Furthermore, the current consumption is different between the main power supply and the backup power supply, and the main power supply usually consumes a large amount of current. Therefore, diodes with different current capacities are used so that the forward voltage drop between the anode and cathode is equalized depending on the current consumption of both.

[For use]

By connecting diodes with different current capacities depending on the current consumption of both the main power supply and the backup power supply, the voltage drop across the diodes of the main power supply and the backup power supply will be the same. From this, the power supply control IC
By providing a power supply voltage monitoring point on either the main power supply or the backup power supply, it becomes possible to control both power supply voltages. That is, by providing a power supply voltage monitoring point on the cathode side of the diode connected to the main power supply and controlling the voltage of the main current, it is possible to maintain the backup power supply at the same voltage.

【Example】

FIG. 1 is a circuit diagram showing an embodiment of a constant voltage power supply circuit according to the present invention. In the circuit of FIG. 1, 3 and 4 are diodes, and the components indicated by other symbols are the same as those in FIG. 5. The diodes 3 and 4 are selected to have forward voltage-forward current characteristics such that the voltage drop is the same in the current consumption of the main power source and the backup power source. Fig. 3 is a forward voltage-forward current characteristic diagram of two diodes 3 and 4. For the same forward voltage drop, diode 4 with a large forward current is connected to the main power supply side, and diode 3 with a small forward current is connected to the main power supply side. Connect to the backup power supply side. The power supply control ICI controls the voltages of both the main power supply and the backup power supply by providing a power supply monitoring point 8 on the cathode side of the diode 4. It goes without saying that the power supply monitoring point 8 may be provided on the cathode side of the diode 3. FIG. 2 is a circuit configuration diagram showing another embodiment of the constant voltage power supply circuit according to the present invention. In the circuit of FIG. 2, diodes 12 and 13 are used which have forward voltage-forward current characteristics such that the voltage drop is the same as in the embodiment of FIG. .6 V), the output voltage from the constant voltage power supply 10 is increased in advance by the voltage drop.

【Effect of the invention】

According to the present invention, in a circuit that requires a backup power source, the main power source and the backup power source can be separated and the potential difference between the two power sources can be eliminated. Here, even if the current consumption of the main power supply changes during operation, as shown in the graph of Figure 3, by using a diode with a large current capacity, the ratio of forward voltage drop change to forward current change will be small, so that the power supply voltage fluctuations can be kept small. Furthermore, since only two diodes are required as new components, the mounting area is small, the cost is low, and reliability is not compromised.

[Brief explanation of drawings]

Figure 1 is a circuit configuration diagram showing one embodiment of the constant voltage power supply circuit according to the present invention, Figure 2 is a circuit diagram showing another embodiment of the constant voltage power supply circuit according to the present invention, and Figure 3 is the order of the diodes. Voltage-forward current characteristic diagram, Fig. 4,
FIGS. 5 and 6 show circuit configuration diagrams of conventional constant voltage power supply circuits. 1: Power control IC12: Transistor, 3.4°10
．． 12, 13: Diode, 5: Control power input line,
6: Backup power line, 7: Main power line, 8: Power supply voltage monitoring point, 9: Backup IC1ll: Backup power battery. Akira 1 Figure 2 Figure 3 Ryo 4 Punishment Figure 5 Figure 6

Claims (1)

[Claims] 1) Connect the anode sides of two diodes in parallel to the output side of a constant voltage power supply, each having a characteristic that the forward voltage drop between the anode and the cathode is equal according to the current consumption of the power supply. A constant voltage power supply circuit characterized by connecting the cathode side of the diode to the main power supply line and backup power supply line. 2) In the constant voltage power supply circuit according to claim 1, the constant voltage power supply has the control transistor and the cathode side of one of the two diodes as a voltage monitoring point, and the voltage at the erroneous voltage monitoring point. A constant voltage power supply circuit comprising a power supply control IC that controls the control transistor accordingly. 3) The constant voltage power supply circuit according to claim 1, wherein the output voltage value of the constant voltage power supply is set to a value higher by the voltage drop of the diode.