JP3084979B2 - Capacitor voltage divider circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitor voltage dividing circuit for equalizing the voltage of each capacitor when a plurality of capacitors are connected in series and connected to a power supply.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing a conventional example of a capacitor voltage dividing circuit for equally sharing the voltage of each capacitor when a plurality of capacitors are connected in series and connected to a power supply. In FIG. 4, the rectifier 3 connected to the AC power supply 2 converts the input AC power into DC power and outputs it. The rectifier 3 is generally configured by a diode bridge connection. However, the DC voltage output from the rectifier 3 contains a ripple component as it is.
When an electronic device such as a computer is connected as the load 8, a malfunction may occur due to the ripple. Therefore, a capacitor is connected to the DC output side of the rectifier 3 to absorb and remove the ripple.

[0003] A capacitor that absorbs and removes the ripple component is called a smoothing capacitor. However, a smoothing capacitor having a small capacity cannot provide a smooth DC voltage containing almost no ripple component. It is necessary to connect a smoothing capacitor with a capacity. By the way, since an electrolytic capacitor can have a large capacitance even if it is small, it is widely used as a smoothing capacitor. However, the disadvantage is that electrolytic capacitors cannot be used at high voltages. Therefore, when the DC output voltage V _D of the rectifier 3 is a high value, a plurality of electrolytic capacitors are connected in series and used.

In the conventional circuit shown in FIG. 4, two electrolytic capacitors, that is, a first smoothing capacitor 4 and a second smoothing capacitor 5 are provided.
The While series connection to connected to the DC output side of the rectifier 3, the DC output voltage is V _D. When a plurality of capacitors are used in series as described above, the capacitance of each capacitor is usually set to the same value so that the voltage sharing of each capacitor is equalized. Therefore, the first smoothing capacitor 4
And the second smoothing capacitor 5 share a voltage of V _D / 2, respectively. In order to maximize the performance of these smoothing capacitors, the smoothing capacitor rated voltage VC is changed to the shared voltage V _C. Choose a value slightly higher than _D / 2. Therefore, when the voltage shared by the smoothing capacitors is unbalanced for some reason, for example, when the voltage shared by the first smoothing capacitor 4 decreases, the voltage shared by the second smoothing capacitor 5 increases by the reduced amount, and Voltage V
_{If the} situation exceeds _C , the second smoothing capacitor 5 will be damaged by overvoltage.

In order to use a plurality of capacitors connected in series, a resistor is connected in parallel to each capacitor.
An imbalance does not occur in the shared voltage of each capacitor. In the conventional circuit shown in FIG. 4, a first voltage dividing resistor 6 is connected in parallel to the first smoothing capacitor 4, and a second voltage dividing resistor 7 is connected in parallel to the second smoothing capacitor 5. Here, since the capacitance of the first smoothing capacitor 4 and the capacitance of the second smoothing capacitor 5 have the same value, the resistance of the first voltage dividing resistor 6 and the resistance of the second voltage dividing resistor 7 Have the same value.

[0006]

Assuming that the resistance value of the voltage-dividing resistor connected in parallel to the smoothing capacitor is infinite, this is the same as not connecting the voltage-dividing resistor. The effect of maintaining the voltage of the capacitor even cannot be expected. That is, the resistance values of the first voltage dividing resistor 6 and the second voltage dividing resistor 7 cannot be made too large. Therefore, assuming that the resistance value of the first voltage dividing resistor 6 and the second voltage dividing resistor 7 is R, the DC voltage is V _D , and the power loss W generated by the two voltage dividing resistors 6 and 7 is as follows. The value shown in FIG.

[0007]

(Equation 1)

That is, the higher the DC voltage V _D or the smaller the dividing resistance value R, the greater the loss W, so that not only the efficiency of the device is reduced but also the temperature of the dividing resistor rises and Inconveniences such as becoming Therefore, an object of the present invention is to reduce power loss generated in a capacitor voltage dividing circuit and to reduce the size of a device.

[0009]

In order to achieve the above object, a capacitor voltage dividing circuit according to the present invention comprises a plurality of capacitors connected in series to a power supply, and a separate resistor is provided for each of these capacitors. In a capacitor voltage dividing circuit configured to be connected in parallel, a series connection circuit of a surge absorbing element and a resistor is separately connected in parallel to each of the capacitors, but a voltage applied to the surge absorbing element is a voltage of the power supply. When the voltage is divided by the number of capacitors connected in series, the current flowing through this surge absorbing element is a small value, but if the applied voltage is slightly higher, a suddenly large current flows, An element shall be selected.

[0010]

According to the present invention, when a plurality of capacitors are connected in series and connected to a power source, a circuit constituted by a series connection of a surge absorbing element and a resistor is separately connected in parallel to each of the capacitors to divide the voltage. A circuit is configured.
With such a circuit configuration, only a small leakage current of the surge absorbing element always flows through the resistor connected in series with the surge absorbing element. Even if an imbalance occurs in the shared voltage, the voltage shared by the series resistance of the surge absorbing element is suppressed, so the current flowing through this series resistance is small, and the unbalanced voltage is corrected while suppressing the loss generated. Is what you do.

[0011]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention. In FIG. 1, an AC power supply 2, a rectifier 3, and a first
Smoothing capacitor 4, second smoothing capacitor 5, and load 8
Are the same as in the case of the conventional circuit described above with reference to FIG.

In the present invention, as shown in the circuit of the first embodiment, a first surge absorbing element 11 and a first resistor 12 are provided.
Are connected in parallel to the first smoothing capacitor 4, and a series connection circuit of the second surge absorbing element 13 and the second resistor 14 is connected in parallel to the second smoothing capacitor 5. Here, the surge absorbing elements 11 and 13 are made of ceramics mainly composed of zinc oxide and sintered by adding other metal oxides such as praseodymium oxide and cobalt oxide. Therefore, when the voltage constantly applied to the first smoothing capacitor 4 is V _D / 2, the leakage current of the first surge absorbing element 11 is extremely small, and the first resistor 12 through which this leakage current flows Is very small.

Here, an unbalance occurs in the voltage sharing between the first smoothing capacitor 4 and the second smoothing capacitor 5 for some reason, and the shared voltage of the first smoothing capacitor 4 becomes V _D / 2.
Assuming that the voltage rises to the smoothing capacitor rated voltage V _{C of a} higher value, the first surge absorbing element 11 shares the voltage of V _D / 2, and the first resistor 12 outputs the voltage difference between V _C and V _D / 2. Will be shared. Here, the first surge absorbing element 11
Is selected so that the smoothing capacitor leakage current I _C flows at the aforementioned voltage V _C.

That is, the shared voltage of the first smoothing capacitor 4 is
When it rises, it is connected in parallel with the first smoothing capacitor 4
Current flowing through the surge absorbing circuit increases to I _C
Correct the imbalance of the shared voltage of the smoothing capacitor. Each smooth
Normally, when the voltage sharing of the capacitor is balanced,
The voltage applied to the absorption circuit is V _D / 2 or less,
Loss due to the first resistor 12
Is also slight.

FIG. 2 is a graph showing the second embodiment of the present invention, and shows the characteristics of the surge absorbing element in the case of the circuit of the first embodiment shown in FIG. The current and the vertical axis indicate voltage. As shown in FIG. 2, shared voltage per smoothing capacitor when the DC voltage V _D is V _D / 2, the surge absorbing element characteristics such as leakage current at this time is about 1mA Is selected. The left side of the leakage current 1 mA is a leakage current region, and the right side thereof is a limited voltage region.
Current at _C is I ₁₁ described above.

FIG. 3 is an equivalent circuit diagram showing an equivalent circuit of the surge absorbing element. A series connection of a capacitance component 22 and a non-linear resistance component 23 has a series inductance component 21 and a series resistance component 24 connected in series. Circuit configuration.

[0017]

According to the present invention, when a plurality of capacitors are connected in series and connected to a power supply, a series connection circuit of a surge absorbing element and a resistor is separately connected in parallel to each of these capacitors. With such a circuit configuration, when each capacitor equally shares the voltage, only a small leakage current from the surge absorbing element flows through the resistance of the parallel circuit. The losses are negligible. When the voltage distribution becomes unbalanced, the current flowing through the parallel resistor belonging to the capacitor sharing the high voltage has a small value as shown in Expression 2. Therefore, the loss generated by the resistors constituting the voltage dividing circuit for equalizing the voltage shared by the capacitors can be significantly suppressed compared to the conventional art. It is possible to reduce the size, and also to obtain the effect of improving the efficiency of the entire apparatus by suppressing the generation loss.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a graph showing a second embodiment of the present invention.

FIG. 3 is an equivalent circuit diagram showing an equivalent circuit of the surge absorbing element.

FIG. 4 is a circuit diagram showing a conventional example of a capacitor voltage dividing circuit for equally sharing the voltage of each capacitor when a plurality of capacitors are connected in series and connected to a power supply.

[Explanation of symbols]

 Reference Signs List 2 AC power supply 3 Rectifier 4 First smoothing capacitor 5 Second smoothing capacitor 6 First voltage dividing resistor 7 Second voltage dividing resistor 11 First surge absorbing element 12 First resistor 13 Second surge absorbing element 14 Second resistor 21 Series inductance Min 22 Capacitance 23 Non-linear resistance 24 Series resistance

Claims (1)

(57) [Claims] A capacitor voltage divider having a configuration in which a plurality of capacitors are connected in series to a power supply obtained by rectifying an AC voltage, and a series connection circuit of a surge absorbing element and a resistor is separately connected in parallel to each of the capacitors. In the circuit, the server
The voltage applied to the absorption element converts the voltage of the power supply.
When the value is divided by the number of series connected
The current flowing through the element is small, but the applied voltage is
If it is slightly higher than this, a suddenly large current will flow.
Voltage divider circuit, characterized by selecting a surge absorbing element with a characteristic.