JPH10150772A - Rush current prevention circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the inflow of an overcurrent without specially providing a protection circuit such as a fuse by inserting a capacitor to each of a pair of input lines for inputting AC to a rectifier. SOLUTION: An AC/DC power supply equipment 1 has a capacitor 11, 12 respectively for each of a pair of input lines 17a, 17b. Capacity of the capacitors 11, 12 is preferable to be set to about 1/40 to 1/70 of a smoothening capacitor 14. When an AC voltage Vin is applied to the input side of the AC/DC power supply equipment 1, a DC component of this AC voltage Vin is removed at capacitors 11, 12. After the DC component is removed at the capacitors 11, 12, the AC voltage Vin is full wave-rectified by a full wave rectifier 13 and is smoothed by a smoothing capacitor 14. Also, by inserting the respective capacitors 11, 12 in a pair of input lines 17a, 17b, the input side can be insulated from the output side without using a transformer thereby preventing the inflow of an overcurrent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC / DC power supply.

[0002]

2. Description of the Related Art Conventionally, there is an AC / DC power supply as a device for converting an AC voltage into a predetermined DC voltage and outputting the converted DC voltage. Hereinafter, a conventional AC / DC power supply device will be described.

FIG. 7 is a schematic block diagram of a conventional AC / DC power supply device.

Here, 5 is an AC / DC power supply, 51 is an insulating transformer, 52 is a protection circuit such as a fuse, 53 is a full-wave rectifier, 54 is a smoothing capacitor, and 55 is a DC stabilizing circuit. Reference numeral 56 denotes a load connected to the output side of the AC / DC power supply 5.

When an AC voltage is applied to the input side of the AC / DC power supply 5, the DC component of the AC voltage is removed by the transformer 51.

Next, the AC voltage from which the DC component has been removed by the transformer 51 is full-wave rectified by the full-wave rectifier 53, and then smoothed by the smoothing capacitor 54.

Next, the voltage smoothed by the smoothing capacitor 54 is adjusted to a predetermined voltage by the DC stabilizing circuit 55. Then, it is supplied to the load 56.

[0008]

In the conventional AC / DC power supply device 5 shown in FIG. 7, a transformer 5 is provided to insulate an input-side AC voltage from an output-side DC voltage.
1 is used. For this reason, there is a problem that it is difficult to reduce the size and weight of the AC / DC power supply device.
Further, it is difficult for the transformer to obtain characteristics as designed due to the influence of leakage inductance, stray capacitance, characteristics of the core, and the like. For this reason, in order to obtain desired characteristics, it is often the case that a re-creation is made many times and trial and error are repeated.

In the conventional AC / DC power supply 5 shown in FIG. 7, the load 56 connected to the output side is prevented from flowing into the transformer 51 and the smoothing capacitor 54 due to a short circuit or the like. And a protection circuit 52 such as a fuse.
There is also a problem that it must be provided.

The present invention has been made in view of the above circumstances, and an object of the present invention is to reduce the size and weight by insulating the input side and the output side without using a transformer. An AC / DC power supply is provided.

It is another object of the present invention to provide an AC / DC power supply device which can prevent an inflow of overcurrent without providing a protection circuit such as a fuse.

[0012]

In order to solve the above-mentioned problems, the present invention provides an AC / D having a rectifier for rectifying an alternating current and a smoothing capacitor for smoothing an output of the rectifier.
A C power supply device, wherein a capacitor is inserted in each of a pair of input lines for inputting alternating current to the rectifier.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an AC / D according to an embodiment of the present invention.
It is a schematic block diagram of a C power supply device. Here, 1 is the AC / DC power supply of the present embodiment, 13 is a full-wave rectifier, 14
Is a smoothing capacitor, and 15 is a DC stabilizing circuit. Reference numeral 16 denotes a load connected to the output side of the AC / DC power supply device 1 of the present embodiment.

The AC / DC power supply 1 of this embodiment differs from the conventional AC / DC power supply 5 shown in FIG. 7 in that a transformer for insulating the input side from the output side and a transformer for preventing overcurrent. No protection circuit such as a fuse is provided. Instead, capacitors 11 and 12 are inserted into each of the pair of input lines 17a and 17b.

The capacitance of the capacitors 11 and 12 is preferably set to about 1/40 to 1/70 of the capacitance of the smoothing capacitor 14. When the capacity of the capacitors 11 and 12 is larger than about 1/40 of the capacity of the smoothing capacitor 14, the energy stored in the capacitors 11 and 12 increases, and the ripple of the voltage between both ends of the smoothing capacitor 14 increases. On the other hand, when the capacity of the capacitors 11 and 12 is smaller than about 1/70 of the capacity of the smoothing capacitor 14, the energy stored in the capacitors 11 and 12 is reduced, so that the charge on the smoothing capacitor 14 after power is turned on. The charging speed becomes slow.

Next, the operation of the present embodiment will be described.

FIG. 2 is a diagram for explaining a voltage waveform at a predetermined position of the AC / DC power supply device 1 shown in FIG.

The input side of the AC / DC power supply 1 is shown in FIG.
When an AC voltage V _IN as shown in (a) is applied, the DC component of the AC voltage V _IN is removed by the capacitors 11 and 12.

Next, the AC voltage V _IN from which the DC component has been removed by the capacitors 11 and 12 is full-wave rectified by the full-wave rectifier 13 and then smoothed by the smoothing capacitor 14. The voltage V _DC across the smoothing capacitor 14 has a waveform including a ripple as shown in FIG.

Next, the voltage smoothed by the smoothing capacitor 14 is applied to the DC stabilizing circuit 1 as shown in FIG.
5, the voltage is adjusted to a predetermined voltage V _OUT . Then, it is supplied to the load 16.

As described above, in the present embodiment, by inserting the capacitors 11 and 12 into the pair of input lines 17a and 17b, respectively, the input side and the output side can be insulated without using a transformer. For this reason, compared to the case where a transformer is used for insulation between the input side and the output side,
The size and weight of the device can be reduced.

Further, since the capacitor can obtain the characteristics according to the design value to some extent, an AC / DC power supply device can be developed in a relatively short time as compared with the case where a transformer is used.

In the present embodiment, the capacitor 1
The capacities of 1 and 12 are reduced to １ ／ of the capacity of the smoothing capacitor 14.
When set to about 0 to 1/70, the input current I _IN of the AC / DC power supply 1 is determined by the capacitance of each of the capacitors 11 and 12. The input current I _IN can be expressed by the following equation.

I _IN = EC _I πfsin2πft (Equation 1) E: amplitude of input AC voltage V _IN , C _I : capacitor 11,
12 Each capacity f: frequency of input AC voltage, t: time Therefore, the peak value of input current I _IN is ± EC _I πf
Therefore, the inflow of overcurrent can be prevented without providing a protection circuit such as a fuse.

Here, the reason why the input current I _{IN of the} device of the present embodiment can be expressed by Equation 1 will be described.

FIG. 3 is a diagram for explaining an input voltage waveform and an input current waveform of the AC / DC power supply device 1 shown in FIG.

The input side of the AC / DC power supply 1 is
It is assumed that an AC voltage V _IN as shown in FIG. This AC voltage V _IN can be expressed by the following equation.

V _IN = Ecos (2πft) First, in FIG. 3A, the input current I _IN in the period from the point a to the point c will be considered.

When V _IN is about to reach point a,
That is, when it is about to reach a positive peak value (= E), the elements CR ₁ and CR ₄ of the full-wave rectifier 13 shown in FIG. 1 are in a conductive state. Therefore, the terminal 13a of the full-wave rectifier 13
And the voltages V ₁ between 13b, terminal 13 of the full-wave rectifier 13
The voltage V ₂ between b and 13c, is as follows.

V ₁ = V _DC + V _D V ₂ = −V _D V _DC : voltage across the smoothing capacitor 14 V _D : forward voltage of one element of the full-wave rectifier 13 Therefore, V _IN reaches point a Until that time, the total V _C of the voltages across the capacitors 11 and 12 is given by the following equation.

[0032] _{V C = V IN - (V} 1 -V 2) = V IN - Further (V _DC + 2V _D), when V _IN reaches the point a, since the V _IN = E, capacitors 11 and 12 the total V _C of the voltage across,
It becomes like the following formula.

V _C = E− (V _DC + 2V _D ) Next, V _IN gradually decreases after reaching point a. Accordingly, the elements CR ₁ and CR ₄ of the full-wave rectifier 13 are turned off, and the input current I _IN is cut off. Input current I _IN
Is cut off, the sum V _C of the voltages across the capacitors 11 and 12 is constant, so that V ₁ −V ₂ is given by the following equation.

[0034] _{V 1 -V 2 = V IN -V} C Next, V _IN is, when reduced to _{E-2 (V DC + 2V} D), V 1 -V 2 by the above formula, - (V _DC + 2V _D ).
As a result, the elements CR ₂ and CR ₃ of the full-wave rectifier circuit 13 become conductive, and the input current I _IN starts to flow in a direction opposite to the current flow direction.

Therefore, as shown in FIG.
_{After IN} reaches point a (= E), point b (= E-2 (V _DC
The input current I _IN does not flow until it reaches + 2V _D )). After reaching the point b, the input current I _IN starts to flow in a direction opposite to the direction of the flow until reaching the point a.

Since the capacitance C _{I of} each of the capacitors 11 and 12 ≪the capacitance of the smoothing capacitor 14, the input current I _IN flowing during the period from the point b to the point c is expressed by the following equation.

[0037]

(Equation 1)

Therefore, the maximum value of the input current I _IN during the period from the point a to the point c is −EC _I πf, and no more flows.

Next, in FIG. 3A, the input current I _IN in the period from the point c to the point e will be considered.

When V _IN is about to reach point c,
That is when trying to reach a negative peak value (= -E), element CR _2, CR ₃ of the full-wave rectifier is in a conductive state. Therefore, the terminals 13a and 13b of the full-wave rectifier 13
The voltages V ₁ between the terminals 13b and 13 of the full-wave rectifier 13
The voltage V ₂ between c, expressed by the following equation.

V ₁ = −V _D V ₂ = V _DC + V _D Therefore, until V _IN reaches the point c, the total V _C of the voltages across the capacitors 11 and 12 is expressed by the following equation. .

[0042] _{V C = V IN - (V} 1 -V 2) = V IN + (V DC + 2V D) Further, when V _IN reaches the point c, since the V _IN = -E, capacitor 11, The total V _C of the voltages across the terminals 12 is
It becomes like the following formula.

V _C = −E + (V _DC + 2V _D ) Next, V _IN gradually increases after reaching the point c. Accordingly, the elements CR ₂ and CR ₃ of the full-wave rectifier 13 are turned off, and the input current I _IN is cut off. Input current I _IN
Is cut off, the sum V _C of the voltages across the capacitors 11 and 12 is constant, so that V ₁ −V ₂ is given by the following equation.

V ₁ -V ₂ = V _IN -V _C Next, when V _IN increases to -E + 2 (V _DC + 2V _D ), V ₁ -V ₂ becomes V _DC + 2V _{D according} to the above equation. As a result, the elements CR ₁ and CR ₄ of the full-wave rectifier circuit 13 become conductive, and the input current I _IN starts to flow in the opposite direction to the current flow.

Therefore, as shown in FIG.
_{After IN} reaches point c (= -E), point e (= -E + 2)
Until (V _DC + 2V _D )), the input current I _IN does not flow. After reaching the point d, the input current I _IN starts to flow in a direction opposite to the direction of the flow until reaching the point c.

Since the capacitance C _{I of} each of the capacitors 11 and 12 ≪the capacitance of the smoothing capacitor 14, the input current I _IN flowing during the period from the point c to the point e is represented by the following equation.

[0047]

(Equation 2)

Therefore, the maximum value of the input current I _IN in the period from the point c to the point e is EC _I πf, and no more flows.

[0049] Here, when the average value of the input current I _IN and I _A, I _A is represented by the following formula.

[0050]

(Equation 3)

[0051] Therefore, _{I A = C I fE (cosθ} + 1).

Here, cos θ = (E−2 (V _DC + 2V _D )) /
Because it is _{E, I A = 2C I fE} (1+ (V DC + 2V D) / E) if V _DC »2V _{D, substantially, I A = 2C I fE (} 1 + V DC /
E).

[0053] The average value I _A of the input current I _IN is to be taken into account losses, etc., substantially equal to the average input current I _R of the direct current stabilization circuit 15 shown in FIG.

The present inventors observed the input voltage waveform, the input current waveform, and the like using the simulation circuit shown in FIG. 4 in order to confirm the operation of the device of this embodiment.

As shown in FIG. 4, this simulation circuit includes a diode stack (model name:
W02M_001) and an NPN transistor (model: 2SC2720) and a shunt regulator (model
TL431) was manufactured using a capacitor of 56 μF for the smoothing capacitor 14 and a capacitor of 1 μF for each of the capacitors 11 and 12. Further, a resistance of 140Ω was used as the load 16.

An AC power supply 2 having an effective value of 115 V and 400 Hz is connected to the input side of the simulation circuit.
It was set.

FIG. 5 shows voltage waveforms and current waveforms at predetermined positions observed at this time. 5A shows the input voltage V _IN , FIG. 5B shows the input current I _IN , and FIG. 5C shows the voltage V _DC across the smoothing capacitor 14 and the output voltage V _OUT.
Are respectively shown.

As shown in FIG. 5, the peak value of the input voltage V _IN is ± 162 V, and the peak value of the input current I _IN is ± 0.2 A.
Met.

In equation 1 described above, E = 162 and f = 4
Substituting 00, C _I = 10 ⁻⁶ , the input current I _IN is approximately expressed by the following equation.

I _IN = 0.2 sin (800πt) Therefore, the peak value of the input current I _IN is approximately ± 0.2 A, which proves that the equation 1 is correct.

Further, the present inventors, as shown in FIG.
Zener diode (Model name: 1N446)
Using 9), the other conditions were made the same as the simulation circuit shown in FIG.
The input voltage waveform, input current waveform, etc. were observed. Even in this case, it was confirmed that Expression 1 was correct.

In the above embodiment, the capacitors 11, 1 inserted into the pair of input lines 17a, 17b, respectively,
Although a capacitor having the same capacity is used as 2, the present invention is not limited to this. Two capacitors having different capacities may be inserted into the input lines 17a and 17b, respectively. Further, the capacity of these capacitors is not limited to about 1/40 to 1/70 of the smoothing capacitor.

[0063]

As described above, according to the present invention,
Since the input side and the output side can be insulated without using a transformer, downsizing and weight reduction can be achieved.

Further, the inflow of overcurrent can be prevented without providing a protection circuit such as a fuse.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of an AC / DC power supply device according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining a voltage waveform at a predetermined position of the AC / DC power supply device shown in FIG.

FIG. 3 is a diagram for explaining an input voltage waveform and an input current waveform of the AC / DC power supply device shown in FIG.

FIG. 4 is a diagram showing a simulation circuit of the AC / DC power supply device shown in FIG.

FIG. 5 is a diagram for explaining a voltage waveform and a current waveform at a predetermined position observed by the simulation circuit shown in FIG. 4;

6 is a diagram showing a simulation circuit of the AC / DC power supply device shown in FIG.

FIG. 7 is a schematic block diagram of a conventional AC / DC power supply device.

[Explanation of symbols]

 Reference Signs List 1 AC / DC power supply device 2 AC power supply 11, 12 Capacitor 13 Full-wave rectifier 14 Smoothing capacitor 15 DC stabilization circuit 16 Load 17a, 17b Input line

Claims (1)

[Claims] 1. An AC / DC device comprising: a rectifier for rectifying an alternating current; and a smoothing capacitor for smoothing an output of the rectifier.
An AC / D power supply device, wherein a capacitor is inserted into each of a pair of input lines for inputting an alternating current to the rectifier.
C power supply.