JPH048134A - Backup power supply circuit for dc drive circuit - Google Patents

Abstract

PURPOSE:To simplify and select charge properties and discharge properties independently by connecting a diode for reverse flow prevention and resistance for setting charge properties between a DC power terminal and a backup capacitor. CONSTITUTION:In a charge property setting circuit 1, the first current path, which includes resistance R1 for limiting a discharge current, and the second current path, which includes a diode D2 for reverse flow prevention and resistance R2 for limiting a charge current, are connected in parallel. At the time of charging a capacitor C is charged from a DC power source circuit A through diodes D1 and D2 and the resistance R2. For the resistance R1, the value is selected larger than that of the resistor R2, and it can be ignored at the time of charging. According to the value of the resistance R2, the excessive current in charging is limited. In charge, it becomes only the capacitor C for backup and the resistance R1 for limiting a discharge. The discharge property in charge can be set by selecting the resistor R1.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a DC power supply circuit, and more particularly to a backup source circuit for a DC drive circuit.

3. Prior Art] FIG. 5 shows an example of a backup power supply circuit for a DC drive circuit according to the prior art.

DC power supply terminal A via one diode D1.

The interconnection point between the diode D1 connected to the power input terminal B of the DC drive circuit and the power input terminal of the DC power supply circuit is connected to the backup capacitor C via the resistor R1.
It is connected to the.

If the auxiliary charging circuit 10 shown on the right side is not present, during charging, the capacitor C is charged from the DC power supply circuit A via the diode D1 and the resistor R1. At this time, the resistor R1 serves to limit the charging current and protect the capacitor C and the diode D1.

On the other hand, if the DC power supply becomes defective due to a power outage, etc., the power input terminal B of the DC drive circuit is connected from the capacitor C through the resistor R1.
A current flows through the resistor R1 to perform backup.
becomes a flow limiting resistance t which limits the bank-up 'rj& flow. If the backup current flows excessively, the charge accumulated in the capacitor C will disappear in a short period of time, shortening the backup time. Therefore, in order to extend the guaranteed backup time, select a large value for the resistor R1. Must.

However, if you select a large value for resistor R1, resistor R1 will also limit the charging current during charging, which will lengthen the charging time. If this is not done, you will not be able to perform a backup even though a backup source is provided.

Therefore, in the conventional technique shown in FIG. 5, an auxiliary charging circuit 10 is provided. From the other DC power supply terminal
Via the transistor Tr, the capacitor C can receive a charge t. A resistor R3 and a Zener diode ZD having constant voltage characteristics are connected between the other DC power supply terminal X and the ground potential. That is, a substantially constant S current flows through the Zener diode ZD via the resistor R3, and the Zener diode ZD generates a constant voltage between its terminals. This constant voltage is applied to the base of the transistor Tr. When the voltage between the capacitor C/') ##i and F is low, the emitter voltage of the transistor Tr decreases, and since the base voltage is at a constant potential, the base-emitter voltage increases. Then, the transistor Tr is turned on, and a charging current flows from the DC power supply terminal X to the capacitor C. Since the characteristics of the charging circuit 10 can be selected separately from the resistor R1 of the discharging circuit, the charging time can be selected to be sufficiently short and the guaranteed backup time can be selected to be sufficiently long.

According to the conventional technology shown in FIG. 5, if the charging and discharging characteristics of the t# backup capacitor C are set separately, the number of components in the charging circuit increases. , the structure becomes complicated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a backup power supply circuit for a DC drive circuit that is simpler and allows the charging and discharging characteristics to be selected independently.

``Means for Solving the Problems'' The backup power supply circuit for a DC drive circuit of the present invention includes a backup capacitor that can store charge and supply backup current, a DC power supply circuit, and a backup capacitor. A series connection including a reverse current prevention diode and a charging characteristic setting resistor connected between one pole and a discharge current limiting resistor connected between the backup capacitor and the S source terminal of the DC drive circuit. including
.

1 action] A series connection including a reverse current prevention diode and a charging characteristic setting resistor is connected between the DC ti terminal and the backup capacitor, and a discharge current is connected between the backup capacitor and the power supply terminal of the DC drive circuit. Since a limiting resistor is connected, the charging and discharging characteristics of the capacitor can be selected almost independently. In other words, the discharge characteristics can be determined only by the current limiting resistor, and the charging characteristics are as follows:
It can be set by the charging characteristics setting resistor and the characteristics of the backup capacitor.

Figure 1 shows a bank-up power supply circuit for a DC drive circuit according to an embodiment of the present invention.The DC power supply terminal A is connected to the power supply input terminal B of the DC drive circuit via a backflow prevention diode D1. It is connected to the. A power input terminal B of the DC drive circuit is connected to a backup capacitor C via a charge/discharge characteristic setting circuit 1.

This charge/discharge characteristic setting circuit 1 includes a group S that limits the discharge current.
A first current path including a current limiting resistor R1, a backflow prevention diode D2, and a second current path including a charging resistor R2.
Includes parallel connection with current path.

An equivalent circuit of the backup power supply circuit shown in FIG. 1 or in charging mode is shown in FIG.

During charging, the diode Di D2 is connected from the DC power supply circuit A.
- Capacitor C is charged via resistor R2. Resistance R
1 is selected to have a larger value than resistor R2, and can be ignored during charging. By selecting the value of the resistor R2 with respect to the capacitor capacitance C, the time constant R2·C during charging can be selected. Further, the excessive flow during charging is limited by the value of the resistor R2.

FIG. 3 shows an equivalent circuit during discharging of the backup power supply circuit of FIG. 1.

When the potential of the DC power supply terminal A decreases due to a power outage or the like, discharge from the backup capacitor begins. During discharging, the DC ta terminal A is typically grounded or floating and is ignored in the circuit because it is isolated by the diode D1. Backflow prevention diode D2
Also, let go! Since it is connected in the opposite direction to the current and prevents the passage of current, it can be ignored in terms of the equivalent circuit. Therefore, the equivalent circuit during discharging consists of only the backup capacitor C and the discharge current limiting resistor R1. The discharge characteristics during discharge are determined by the resistance R
It can be set by selecting 1.

As explained above, by independently selecting the resistors R1 and R2, the charging characteristics and discharging characteristics of the backup power supply circuit can be independently selected.

Moreover, when compared with the conventional technique shown in FIG. 4, the above-described embodiment can achieve the same effect with a smaller number of parts and a simpler structure.

FIG. 4 shows a backup power supply circuit for a DC drive circuit according to another embodiment of the present invention.

The power supply input terminal B of the DC drive circuit is supplied with a DC voltage from the DC power supply terminal A via the backflow prevention diode D3. The DC power supply terminal A is connected to the positive electrode of the backup capacitor C through a series connection of a backflow prevention diode D4 and a charging characteristic setting resistor R2. The positive electrode of the backup capacitor C is connected to the power input terminal B of the DC drive circuit via a discharge current limiting resistor R1.

The equivalent circuit during charging of the circuit in FIG. 4 is the one in which the diodes DI and D2 in FIG. 2 are replaced with the diode D4,
The equivalent circuit during discharge is the same as that shown in FIG. Therefore, functionally the circuit of FIG. 4 is substantially equivalent to the circuit of FIG. 3.

Furthermore, the number of parts is also the same.

In the above embodiment, the resistors R1 and R2 may be any resistor as long as it functions as a resistor in terms of an equivalent circuit. For example, the resistors R1 and R2 may be internal resistances of a reverse current prevention diode, or may have a value sufficient to limit the charging flow. When the external resistance is R
It is not necessary to connect the resistor 2 separately, and it is also possible to construct the resistor with a transistor structure in an integrated circuit.

Although the present invention has been described above with reference to examples, it will be obvious to those skilled in the art that the present invention is not limited to these examples, and that, for example, various changes, improvements, combinations, etc. can be made.

Effects of the Invention As explained above, according to the present invention, the charging characteristics and discharging characteristics of the backup power supply circuit for the DC drive circuit can be independently set with a simple circuit configuration.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a backup source circuit according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing an equivalent circuit during charging of the embodiment of FIG. 1, and FIG. FIG. 4 is a circuit diagram showing a bank amplifier power supply circuit according to another embodiment of the present invention, and FIG. 5 is an example of a backup power supply circuit according to the prior art. FIG. DC power supply terminal DC drive circuit power input terminal Capacitor diode resistance Charge/discharge characteristic setting circuit Charging circuit DC source terminal Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] (1) A backup capacitor capable of accumulating charge and supplying a backup current, connected between a DC power supply terminal and one pole of the backup capacitor, and a backflow prevention diode and a charging characteristic setting device. A backup power supply circuit for a DC drive circuit, comprising: a series connection including a resistor; and a discharge current limiting resistor connected between the backup capacitor and a power supply terminal of the DC drive circuit.