JPH06103449B2 - Capacitor charging circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitor charging circuit for a backup capacitor at the time of power failure of an electronic circuit or the like.

Configuration of Conventional Example and Problems Thereof FIG. 3 is a circuit diagram showing a conventional capacitor charging circuit, in which a DC power source 2 connected to a commercial power source 1 includes a transformer 3, a rectifier 4, a capacitor 5, a resistor 6, a transistor 7, It is composed of a constant voltage diode 8. This DC power source 2 has a large-capacity capacitor 9 (electric double layer capacitor, etc.) and a resistor.
A series circuit of 10 and an electronic circuit 11 are connected.

The operation of the conventional capacitor charging circuit configured as described above will be described below.

The commercial power supply 1 is transformed by a transformer 3, rectified by a rectifier 4, smoothed by a capacitor 5, and made a constant voltage by a resistor 6, a transistor 7 and a constant voltage diode 8 to become a DC voltage. The large-capacity capacitor 9 is for backup to supply direct current to the electronic circuit 11 at the time of power failure, and the resistor 10 limits the charging current from the direct current power source 2 to the capacitor 9 so that the voltage across the electronic circuit 11 is short at the beginning of charging. The current is supplied from the capacitor 9 to the electronic circuit 11 in the event of a power failure. Generally, a backup capacitor 9 should be used within the operating time of the equipment so that it can be put to practical use.
In order to complete the charging of the resistor 10, the value of the resistor 10 that limits the charging current must be decreased, and conversely, the value of the resistor 10 must be increased in order to increase the voltage across the electronic circuit 11 quickly in the initial charging stage. However, in actual design, it is unavoidable to set a relatively small value within a range in which the above two conditions are moderately satisfied.

However, in the conventional configuration as described above, when the resistance value is selected so that the delay of the voltage rise is optimally prevented when the capacitance of the capacitor 9 is increased in order to lengthen the backup time, FIG. As shown in (3), the voltage of the capacitor 9 does not rise easily, and it takes a very long time to charge it, and there is a possibility that the charging is not completed within the usage time of the device. On the other hand, the voltage across the electronic circuit 11 does not rise immediately at the initial stage of charging when the resistance value is selected so that the charging time is optimal, and the electric charge of the capacitor 5 is used for the charging current of the capacitor 9 during a power failure. Capacitor 9
Will drop to a voltage almost equal to.

In that case, if the capacitor 9 is completely charged, a predetermined backup time can be obtained, as shown in FIG.
As shown in (b), at the time of power failure immediately after the charging of the capacitor 9 is started, the charge is not yet accumulated in the capacitor 9, so the charge accumulated in the capacitor 5 is the same as the current of the electronic circuit 11 and the capacitor. The voltage of the capacitor 9 still does not reach the voltage required for the operation of the electronic circuit 11 even if it becomes the charging current for 9 and is instantly discharged. That is, the amount of charge transferred from the capacitor 5 to the capacitor 9 is Q, the capacity of the capacitor 9 is C, and the voltage increase of the capacitor 9 is V.
Then, the relationship of Q = CV is established. Therefore, the larger the capacity of the backup capacitor 9 is, the larger the capacity of the capacitor 9 becomes.
The amount of voltage rise of is small. Therefore, the backup time at the time of power failure is extremely short.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a capacitor charging circuit having a long backup time when no charge is stored in a backup capacitor.

To achieve this object, a capacitor charging circuit of the present invention is a DC power supply that rectifies a commercial power supply and smoothes it with a capacitor, a backup capacitor for an electronic circuit that becomes a load of this DC power supply, and a commercial power supply voltage. A zero volt pulse generating circuit for generating a zero volt pulse near the zero voltage of, a charging current supply circuit for supplying a charging current from a DC power supply to the backup capacitor, and a backup current from the backup capacitor to the electronic circuit. And a resistor for supplying a charging current from the DC power supply to the backup capacitor only while the zero volt pulse is not generated.

With the above configuration, charging of the capacitor is stopped when the commercial power source is at zero voltage.Therefore, even in the power failure immediately after the charging of the capacitor is started, the load of the DC power source is practically only the electronic circuit, and it takes only a short time. For example, it is possible to back up the electronic circuit by the electric charge accumulated in the DC power supply.

Description of Embodiments An embodiment of the present invention will be described below with reference to the drawings.
In FIG. 1, the DC power supply 2 connected to the commercial power supply 1 is
It is composed of a transformer 3, a rectifier 4, a capacitor 5, a resistor 6, a transistor 7, and a constant voltage diode 8. The above is the same as the configuration of FIG. 3 (conventional example). This DC power supply 2 has a series circuit of a large capacity capacitor 9 and a resistor 22,
And an electronic circuit 11 is connected. The capacitor 9 is a backup capacitor for the electronic circuit 11, and an electric double layer capacitor is used in this embodiment. The resistor 22 supplies a backup current from the capacitor 9 to the electronic circuit 11 in case of power failure. The zero volt pulse generation circuit 12 includes resistors 13 and 1
4, composed of transistors 15 and 16. The charging current supply circuit 17 is a constant current circuit composed of resistors 18 and 21, a constant voltage diode 19 and a transistor 20.
Supply the charging current to.

Regarding the capacitor charging circuit configured as described above,
The operation will be described below. The commercial power supply 1 becomes a DC voltage by the DC power supply 2 and serves as a power supply for the electronic circuit 11.
On the other hand, the transistors 15 and 16 of the zero-volt pulse generation circuit 12
Is OF near the zero voltage of the commercial power source 1 by the resistors 13 and 14.
One of the transistors is O except at F and zero voltage.
It becomes N and a zero volt pulse is generated. This zero volt pulse is input to the charging current supply circuit 17, current flows through the resistor 18 only while the zero volt pulse is generated (when the voltage of the commercial power supply 1 is not near the zero voltage), and the constant voltage diode 19 A constant voltage is generated at both ends. The voltage Vz, the base of the transistor 20, the emitter voltage V _BE, the resistance value of the resistor 21 if R _E, the resistor 21, constant current flows in the _{(VZ-V BE) / R} E. This current is I _E. If the direct current amplification factor of the transistor 20 and the resistance value of the resistor 22 are sufficiently large,
I _E becomes the charging current of the capacitor 9, and the capacitor 9 is charged with the constant current I _E. The resistance value of this resistor 22 is
The value is sufficiently larger than the resistance value of the resistor 10 of the conventional example within the range that can supply the backup current to 11. On the other hand, since the current does not flow in the resistor 18 near the zero voltage of the commercial power supply 1 and during a power failure, the transistor 20 is turned off and the charging current supply circuit 1
Charging of the capacitor 9 by 7 is stopped. For this reason,
Even in the case of a power failure in which electric charge is not sufficiently stored in the capacitor 9, most of the discharge current from the capacitor 5 flows only to the electronic circuit 11 and the constant voltage diode 8, and as shown in FIG. If so, it becomes possible to back up the electronic circuit 11 by the charge of the capacitor 5.

As described above, according to the present embodiment, the charging of the backup capacitor 9 is stopped in the vicinity of the zero voltage of the commercial power source 1, so that the backup capacitor 9 is stored in the capacitor 5 when the charging is not completed. The electric charges present can be effectively used as a backup of the electronic circuit 11.

Further, as described above, in this embodiment, the charging current to the backup capacitor 9 is a constant current, so that the charging time can be shortened.

EFFECTS OF THE INVENTION As described above, the present invention rectifies and smoothes a commercial power source, a backup capacitor for an electronic circuit that is a load of the DC power source, and a zero volt pulse near the zero voltage of the commercial power source. By the zero volt pulse generating circuit and the charging current supply circuit that supplies the charging current from the DC power supply to the capacitor only while the zero volt pulse is not generated,
By changing the charging current to the capacitor when the commercial power source is at zero voltage and at a time other than zero voltage, the electronic circuit can be backed up for a short time even in the case of a power failure immediately after the capacitor starts to be charged. Becomes Further, if the charging current supply circuit is configured by a constant current circuit, the charging current is a constant current, so that the charging time can be shortened as compared with the conventional method, and its practical effect is great.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a capacitor charging circuit according to an embodiment of the present invention, FIG. 2 is a characteristic diagram for explaining the operation of the capacitor charging circuit, and FIG. 3 is a circuit diagram of a conventional capacitor charging circuit. FIG. 4 is a characteristic diagram for explaining the operation of the capacitor charging circuit. 2 ... DC power supply, 9 ... Capacitor, 11 ... Electronic circuit,
12 …… Zero volt pulse generation circuit, 17 …… Charging current supply circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsunori Zaizen 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Yoshitada Nakao, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A DC power supply that rectifies a commercial power supply and smoothes it with a capacitor, a backup capacitor for an electronic circuit that becomes a load of this DC power supply, and a zero volt that generates a zero volt pulse near the zero voltage of the commercial power supply voltage. A pulse generator circuit, a charging current supply circuit that supplies a charging current from a DC power supply to the backup capacitor, and a resistor that supplies a backup current from the backup capacitor to the electronic circuit, and a zero volt pulse is generated. A capacitor charging circuit that supplies a charging current from the DC power supply to the backup capacitor only when it is not generated. 2. The capacitor charging circuit according to claim 1, wherein the charging current supply circuit is a constant current circuit.