JPH03207215A - Surge current preventing circuit for dc power supply - Google Patents

Abstract

PURPOSE:To suppress surger current to a smoothing capacitor upon recovery of an AC power supply from power interruption by operating a short circuit thyristor according to the charging voltage of the smoothing capacitor. CONSTITUTION:A drive circuit 30 monitors charging voltage of a smoothing capacitor 7 on the output side of a rectifier, and when the charging voltage drops below a predetermined level a short circuit thyristor 5 is turned OFF to feed charging current through a current limiting(first) resistor 4. When the charging voltage exceeds the predetermined level, the short circuit thyristor 5 is turned ON to short circuit the resistor 4. Consequently, surge current to the smoothing capacitor 7 can be blocked upon recovery of an AC power supply 2 from a short time power interruption. When the first resistor 4 is short- circuited by connecting a second resistor 40 having resistance considerably lower than that of the first resistor 4, surge current can appropriately be suppressed at the time of short circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inrush current prevention circuit for a DC power supply device comprising a rectifying means, a smoothing capacitor, and a current limiting means between the two. [Prior Art] FIG. 4 is an example of a general circuit diagram of a conventional DC power supply device equipped with an inrush current prevention circuit.

In FIG. 4, the rectifier 3 converts the AC power from the AC power source 2 into DC power, and is equipped with a smoothing capacitor 7 to absorb and remove the lithoplast contained in this DC power. There is. A DC/DC converter configured with a switching transistor 11, a transformer 12, a rectifier diode 13, a freewheel diode 14, and a smoothing circuit 15 and supplies power to a load 16 is a rectifier 3.
By inputting the DC power output by the and smoothing capacitor 7 and controlling the conduction rate of the switching transistor 11, even if there is a voltage fluctuation in the AC power supply 2, this DC/D
The DC voltage output by the C converter can be maintained at a predetermined value.

Incidentally, the smoothing capacitor 7 generally requires a large capacitance. Therefore, in order to prevent an excessive rush current from flowing into the smoothing capacitor 7 at the moment when the AC power supply 2 is connected to the rectifier 3, a current limiting resistor 4 and a short-circuit thyristor 5 as a switch element are connected in parallel. Insert the current limiting circuit between the rectifier 3 and the smoothing capacitor 7,
By connecting the AC power source 2 while the short-circuit thyristor 5 is off, rush current to the smoothing capacitor 7 is suppressed.

The drive circuit 20 using the smoothing capacitor 7 as a power source starts the operation of the switching transistor 11 after a predetermined time has passed after the voltage of the smoothing capacitor 7 rises, so that the third winding of the transformer 12 The short-circuit thyristor 5 is turned on by a gate drive signal from the short-circuit thyristor drive circuit 6 whose power source is 6A, and the current-limiting resistor 4 is short-circuited.

Figure 5 shows a drive circuit 20 used in the circuit shown in Figure 4.
1 is a circuit diagram showing a conventional example of the present invention, and particularly shows a portion related to determination of operation start conditions of a switching transistor 11 whose conduction rate is controlled.

The conventional circuit shown in FIG. 5 is composed of a control power supply section 21 using a smoothing capacitor 7 as a power source, a delay circuit 22, a drive transistor 28, and a pulse transformer 29. , 24, delay resistor 2
5, a delay capacitor 26 and a comparator 27.

With this circuit configuration, comparator 2
7 compares the reference voltage from the control power supply section 2l with the voltage that rises with a delay due to the action of the delay resistor 25 and the delay capacitor 26, and when the delayed voltage exceeds the reference voltage after a predetermined period of time has elapsed. , the output of the comparator 27 is given to the switching transistor 11 via the drive transistor 28 and the pulse transformer 29, so that the DC/
The DC converter starts its operation and turns on the short-circuit thyristor 5 via the short-circuit thyristor drive circuit 6. As a result, the current limiting resistor 4 is short-circuited, and the full voltage output from the rectifier 3 is applied to the smoothing capacitor 7, but at this time, the smoothing capacitor 7 is not charged! Since the voltage was increased to an appropriate voltage close to the output voltage value of the rectifier 3, an excessive current was prevented from flowing into the smoothing capacitor 7.

[Problem to be solved by the invention]

However, in the case of the conventional circuit shown in FIGS. 4 and 5, there are the following two problems regarding the rush current to the smoothing capacitor.

That is, the first problem occurs when a power outage occurs in the AC power fI2 within a sufficiently short time compared to the delay time in the drive circuit 20, and in this case, the smoothing capacitor 7 discharges its accumulated charge. However, when the power outage of the AC t source 2 is restored and power transmission starts again before the discharge is completed, the short-circuit thyristor 5 is in the on state, that is, the current is Limiting resistor 4 is in a short-circuited state. Therefore, AC power supply 2
When power is retransmitted, the full voltage is applied to the smoothing capacitor 7, causing an inconvenience that an excessive inrush current flows. Ta.

Figure 6 shows the fourth example when using the conventional example circuit shown in Figure 5.
FIG. 6(A) is an operation waveform diagram showing the operation of the DC power supply shown in FIG.
B) shows the change in the charging voltage of the smoothing capacitor 7, FIG. 6C shows the change in the output of the comparator 27, and FIG. is the reference voltage).

In this FIG. 6, To is the point in time when the AC power supply 2 is on,
T, is the time when the short-circuit thyristor 5 is on, and then the AC power supply 2 is turned off at the time T2, and after a short period of time T.
It is shown that when this AC power supply 2 is turned on again at time (3), an excessive input current flows as indicated by the peak current Ir+i.

Next, the second problem is related to the voltage difference between the output voltage of the rectifier 3 and the charging voltage of the smoothing capacitor 7 at the moment when the current limiting resistor 4 is shortened, and whether the voltage of the AC power supply 2 increases or changes. Current limiting resistor? If the differential voltage is too large due to a combination of factors, such as whether the voltage is too large or the delay time of the drive circuit 20 is too short, an excessive current will rush into the smoothing capacitor 7 at the moment the resistor is shorted. It turns out. This pattern is also shown in FIG. 6 above.

As shown in FIG. 6, at time T0, the AC power supply 2 is connected to the rectifier 3.
When connected, a first peak current IPI1 flows, but this is limited by the current limiting resistor 4 and does not reach a very large value. On the other hand, the voltage of the smoothing capacitor 7 rises according to a time constant determined by the resistance value of the current limiting resistor 4 and the capacitance of the smoothing capacitor 7, and at the time T1 when this voltage reaches a predetermined value, the short-circuiting thyristor 5 is activated. When the current limiting resistor 4 is short-circuited, the second peak current ■2■1 flows at that moment due to the voltage difference ΔVl+, but at this time there is no resistor to suppress the rush current, so this second peak current
The peak current r pz+ is larger than the first peak current Lz, which may cause problems such as element damage and overcurrent tripping.

SUMMARY OF THE INVENTION An object of the present invention is to provide an inrush current prevention circuit that prevents excessive current from flowing into the smoothing capacitor when power is restored after a short power outage in an AC power supply and when a current limiting resistor is short-circuited.

[Means to solve the problem]

In order to achieve the above object, the inrush current prevention circuit of the DC power supply device of the present invention includes a rectifying means for converting alternating current into direct current, and a smoothing capacitor connected between the positive and negative poles of the direct current output side of the rectifying means. A DC power supply device consisting of a current limiting resistor inserted between the rectifying means and the smoothing capacitor, a switch element that short-circuits this resistor, and a terminal voltage of the smoothing capacitor that detects the detected voltage. A drive circuit that issues a closing command for the switch element when a predetermined value is exceeded, and furthermore, the current limiting resistor is composed of a first resistor and a second resistor whose resistance value is smaller than that of the first resistor. The resistors are connected in series, and the first resistor is to be short-circuited by the Swiss element.

[Effect]

This invention solves the problem of charging the smoothing capacitor provided on the DC output side of the rectifier. The voltage is monitored, and when the voltage is below a predetermined value, the switch element is opened to allow charging current to flow through the current limiting resistor, and when the voltage exceeds the predetermined value, the switch element is closed to limit the current. By shorting the resistor, an excessive rush current is prevented from flowing to the smoothing capacitor when the AC power source is applied, including when a short power outage occurs in the AC power source, and furthermore, the current limiting resistor is connected in series with a first resistor and a second resistor, and only the first resistor that limits the rush current is short-circuited by a switch element, and from then on, the second resistor causes the voltage difference caused by the short-circuit of the first resistor. Since this voltage difference is not a large value, the resistance value of the second resistor can be set to a sufficiently small value compared to the resistance value of the first resistor. It is possible.

〔Example〕

1 and 3 are circuit diagrams showing the first and second embodiments of the present invention, respectively, and FIG. 2 is an operation waveform diagram corresponding to FIGS. 1 and 3. In FIG. 1 and FIG. 3, the same functional elements are denoted by the same reference numerals in FIG. 5 and FIG. is omitted. First, in FIG. 1 showing the first embodiment, the drive circuit 30
is composed of a control power supply section 21, a charging voltage detecting circuit 32, a driving transistor 28, and a pulse transformer 29, and the charging voltage detecting circuit 32 includes a charging voltage detecting resistor 33,
This is controlled by the detection voltage setting resistor 34 and the comparator 27.

Since the series circuit of the charging voltage detection resistor 33 and the detection voltage setting resistor 34 is connected to both ends of the smoothing capacitor 7, a voltage proportional to the charging voltage of the smoothing capacitor 7 is supplied to the positive input terminal of the converter 27. is input. On the other hand, is there a control on the negative polarity terminal of the converter 27? Since the reference voltage is input from the Ht source section 21, when the reference voltage is higher, the output of the comparator 27 is a logic L signal, so the drive transistor 28 is inactive and the short-circuit thyristor 5 is in the off state. . Therefore, the charging current from the rectifier 3 to the smoothing capacitor 7 passes through the current limiting resistor 4.

When the charging voltage of the smoothing capacitor 7 rises and the magnitude relationship with the reference voltage is reversed, the output of the comparator 27 switches to a logic H signal, and as a result, the short-circuit thyristor 5 is turned on. Since the voltage of the smoothing capacitor 7 has increased to a certain extent, the voltage difference between the output voltage of the rectifier 3 and the terminal voltage of the smoothing capacitor 7 is small, and therefore there is no possibility that the charging current of the smoothing capacitor 7 will become excessive.

In the above operation, even when the AC power supply 2 is repeatedly turned on and off, the short-circuit thyristor 5 is turned on or off (that is, the current-limiting resistor 4 is short-circuited or inserted into the circuit) in accordance with the voltage of the smoothing capacitor 7. The charging current does not become excessive.

Figure 2 shows the third circuit when the example circuit shown in Figure 1 is used.
FIG. 2(a) is an operation waveform diagram showing the operation of the DC power supply shown in the figure, and FIG.
) is the change in the charging pressure of the smoothing capacitor 7, the second
Figure (c) shows the change in the output of the comparator 27, and Figure 2 (2) shows the change in the human power of the comparator 27.

As shown in FIG. 2, the detection voltage applied to the comparator 27 changes in accordance with the voltage of the smoothing capacitor 7, and when this detection voltage falls below the reference voltage, the short-circuit thyristor 5 is turned off. Therefore, even when the AC power supply 2 turns on and off, no excessive charging current flows.

Next, in FIG. 3 showing a second embodiment, the current limiting resistor 4 shown in FIG. , the resistor short-circuiting by the short-circuiting thyristor 5 is performed only to the first resistor. Note that the resistance value of the second resistor is selected to be sufficiently smaller than that of the first resistor.

The operating functions of both the first and second resistors are as shown in the operating waveform diagram of FIG. 2. In other words, at time T0, rectifier 3
When the AC power supply 2 is connected to the
resistor 40, and the second resistor 40
Since the resistance value of is small, the current peak value is almost the same as the first peak current IPI1 shown in FIG. Further, the voltage rise curve of the smoothing capacitor 7 also rises along a curve similar to that shown in FIG. 6 (b) because the time constants of the circuits are approximately equal.

When the voltage of the smoothing capacitor 7 reaches a predetermined value at time T, and the short-circuit thyristor 5 becomes conductive, the first resistor 4 is short-circuited, but the second resistor 40 remains inserted in the circuit. 4. Difference voltage ΔV between the voltage of smoothing capacitor 7 and the output voltage of rectifier 3 at the time of short circuit. The second peak value r pzz of the current flowing into the smoothing capacitor 7 based on t is:
It is suppressed by the second resistor 40 and does not have a large value. Further, the voltage of the smoothing capacitor 7 also gradually increases according to a time constant determined by the resistance value of the second resistor 40 and the capacitance of the smoothing capacitor 7.

〔Effect of the invention〕

The DC power supply device, which consists of a rectifier and a smoothing capacitor connected to the AC power supply, uses current control to suppress the rush current to the smoothing capacitor. It is equipped with a resistor and a switch element short-circuited to the resistor, but according to the present invention, by making the switch element operate in accordance with the charging voltage of the smoothing capacitor, short-term power outages, etc. in the AC power supply can be avoided. Even if the inrush current occurs, it is possible to suppress the inrush current by appropriately shorting or releasing the current limiting resistor, and further, a second resistor whose resistance value is sufficiently small is connected in series with the current limiting resistor. By short-circuiting the current-limiting resistor when the charging voltage of the smoothing capacitor reaches a predetermined value or higher, the rush current at the time of the short-circuit can be appropriately suppressed by the second resistor. Become.

Furthermore, any of the above cases can be realized using almost the same circuit as the conventional inrush current prevention circuit.

[Brief explanation of drawings]

1 and 3 are circuit diagrams showing the first and second embodiments of the present invention, respectively, FIG. 2 is an operation waveform diagram corresponding to FIGS. 1 and 3, and FIGS. 5 is a circuit diagram showing an example of the prior art, and FIG. 6 is an operation waveform diagram corresponding to FIGS. 4 and 5. 2... AC power supply, 3... Rectifier, 4... Current limiting resistor (first resistor), 5... Short circuit thyristor, 6... Short circuit thyristor drive circuit, 6A...
・Third winding, 7... Smoothing capacitor, 11... Switching transistor, 12... Transformer, 13...
Rectifier diode, 14... Freewheel diode, 15... Smoothing circuit, 16... Load, 20.30.
...Drive circuit, 21...Control power supply unit, 22...Delay circuit, 23.24...Voltage dividing resistor, 25...Delay resistor, 26...Delay capacitor, 27...Comparator , 28... Drive transistor, 29... Pulse transformer, 32... Charging voltage detection circuit, 33... Charging voltage detection resistor, 34... Detection voltage setting resistor, 40 Fig. 1? ■ h Input karma, Fuiwasufu'Jshihachi Shōshu T2 T3 T4 People's greatness Input karma ηirista↑fu ]Otsujin Tomo 1 work 2 Figure 3

Claims (1)

[Scope of Claims] 1) A DC power supply device comprising a rectifying means for converting alternating current into direct current, and a smoothing capacitor connected between the positive and negative electrodes on the DC output side of the rectifying means, wherein the rectifying means and A current limiting resistor inserted between the smoothing capacitor, a switch element that short-circuits this resistor, and a terminal voltage of the smoothing capacitor that detects the terminal voltage and issues a closing command for the switch element when the detected voltage exceeds a predetermined value. An inrush current prevention circuit for a DC power supply device, comprising a drive circuit. 2) In the inrush current prevention circuit for a DC power supply according to claim 1, the current limiting resistor is connected in series with a first resistor and a second resistor having a resistance value smaller than that of the first resistor, and the switch An inrush current prevention circuit for a DC power supply device, characterized in that the first resistor is the object of short-circuiting by the element.