JPH0670539A - Rush current preventive circuit - Google Patents

Abstract

PURPOSE:To prevent the supply of a control voltage to be impressed on a gate terminal of an on-off element which short-circuits a resistor for limiting a rush current from the primary winding of a transformer. CONSTITUTION:A terminal voltage of a capacitor C2 for clamp which is connected in parallel with a switching element Q1 is impressed on a gate terminal of a thyristor SCR through a diode D1. By supplying not a pulse voltage, but a DC voltage, a sufficient gate power can be given to the gate terminal, and therefore the thyristor SCR can be made to operate reliably as an on-off element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inrush current prevention circuit for suppressing a peak of an inrush current generated when a DC power supply is switched and converted into a high frequency.

[0002]

2. Description of the Related Art As a kind of switching regulator, one having a structure shown in FIG. 11 is known. Vin is a DC power supply including a rectifying circuit, C1 is a smoothing electrolytic capacitor, T is an insulating transformer (high frequency transformer), N1, N
2, N3 are primary windings, N4 is a secondary winding, S1 is a switch, Q1 and Q2 are switching elements, D1 to D3 are diodes, R1 to R3 are resistors, C2 and C3 are capacitors, L1 is an inductor, SCR. Is a thyristor, CON is a PWM control circuit, and TO is an output terminal.

In the switching regulator having such a configuration, when the switch S1 is turned on, the DC voltage input from the DC power source Vin is supplied to the pair of switching elements Q1 and Q2.
After being switched by and converted into a high frequency, the high frequency is boosted by the insulating transformer T and the secondary coil N4
The boosted high frequency is converted into direct current by the rectifying and smoothing circuit composed of D3, L1 and C3 and output from the terminal TO. Here, the PWM control circuit CON is
Each element Q is controlled by controlling a pair of switching elements Q1 and Q2.
The control operation is performed so that the DC voltage output from the terminal TO becomes constant by adjusting the pulse width of the high frequency output by the switching operation of 1 and Q2. Further, the capacitor C2 connected in parallel with the switching element Q1 is a clamping capacitor that works so as to suppress (clamp) the voltage when the Q1 is turned on and off to some extent.

When performing such an operation, the switch S1
Based on the charging current that flows from the DC power source Vin to the large-capacity smoothing electrolytic capacitor C1 in a short time at the moment when is turned on,
A large rush current (inrush current) is generated, which affects peripheral circuits and the like. Therefore, normally, a resistor R1 is provided in the charging current path and the resistor R1 is operated as a resistor for limiting the inrush current to suppress the peak value of the inrush current.

After the completion of charging, the voltage output from the primary winding N3 is applied to the gate terminal of the thyristor SCR via the diode D1 to turn on the thyristor SCR and short-circuit the resistor R1. That is, the resistor R1 is used only when the capacitor C1 is charged. M constitutes an inrush current prevention circuit. Figure 1
Reference numeral 0 shows a waveform diagram of the applied voltage a and the input current b to the capacitor C1. The inrush current Ip is (square root of 2 · E
in / R1).

FIG. 12 shows another configuration of the switching regulator, which is different from FIG. 11 in that only one switching element Q1 is used. Based on this, the primary winding N2 in which the switching element Q2 is connected in series in FIG. 11 is also unnecessary. The operation is performed according to the case of FIG.

[0007]

The conventional inrush current prevention circuit has the following problems.

1. In order to obtain the control voltage applied to the gate terminal of the thyristor SCR that short-circuits the resistor R1 that operates as the inrush current limiting resistor, the primary winding N3 must be purposely prepared.

2. Since the control voltage obtained from the primary winding N3 is proportional to the magnitude of the DC power source Vin, the control voltage also increases as the DC power source Vin increases. Therefore, the resistor R3 that functions as the gate current limiting resistance of the thyristor SCR. Power loss increases.

3. Since the control voltage obtained from the primary winding N3 is a pulse voltage, the gate power applied to the gate terminal of the thyristor SCR becomes insufficient when the pulse width becomes narrow, so that the thyristor SCR operates reliably. It is impossible to let them do it.

The present invention has been made in consideration of the above problems, and provides a rush current prevention circuit which solves the conventional problems by using a clamping capacitor connected in parallel with a switching element. That is the purpose.

[0012]

In order to achieve the above object, the present invention is directed to a direct current power source, a primary winding of a transformer and a switching element connected in series, and a rush into an intermediate path of a circuit connected in series. In an inrush current prevention circuit in which a current limiting resistor and a resistance short-circuiting switching element that short-circuits this resistor are connected in parallel, and a clamping capacitor is connected in parallel to the switching element, the clamping capacitor is connected via a diode. It is characterized in that it is connected to the gate terminal of the resistance short-circuiting switching element and the terminal voltage of the clamping capacitor is applied to the gate terminal to control the opening / closing operation of the resistance shorting switching element.

[0013]

According to the structure of the present invention, the clamping capacitor connected in parallel to the switching element is connected to the gate terminal of the switching element for resistance short circuit through the diode. A terminal voltage obtained not from the primary winding but from the clamping capacitor is applied as a control voltage. Therefore, it is not necessary to prepare the primary winding N3 for that purpose, the control voltage is not proportional to the magnitude of the DC power supply, and the control voltage is not the pulse voltage but the DC voltage.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a connection diagram showing a first embodiment of an inrush current prevention circuit according to the present invention. Vin is a DC power source including a rectifying circuit, C1 is a smoothing electrolytic capacitor, and T is an insulating transformer (high frequency transformer). , N1 and N2 are primary windings, N4
Is a secondary winding, S1 is a switch, Q1 and Q2 are switching elements, D1 to D3 are diodes, R1 to R3 are resistors, C2 and C3 are capacitors, L1 is an inductor, and SC.
R is a thyristor, CON is a PWM control circuit, TO is an output terminal, and M is an inrush current prevention circuit.

The DC power source Vin, the primary winding N1 of the insulating transformer T, and the switching element Q1 are connected in series, and a resistor R1 acting as a rush current limiting resistor in the intermediate path of the series-connected circuit and this resistor R1. Is connected in parallel with a thyristor SCR which functions as a switching element for resistance short-circuiting. Further, a clamping capacitor C2 is connected in parallel with the switching element Q1, and another switching element Q1 is connected.
2 is connected in series to the primary winding N2.

Next, the operation of this embodiment will be described.

When the switch S1 is turned on, the DC power source Vi
The DC voltage input from n is applied to a pair of switching elements Q
After being converted to a high frequency by 1, Q2, this high frequency is boosted by the insulating transformer T and output to the secondary coil N4, and the boosted high frequency is rectified by D3, L1, C3,
It is converted to direct current by the smoothing circuit and output from the terminal TO.

Here, the PWM control circuit CON controls a pair of switching elements Q1 and Q2 to control each element Q1 and Q2.
By adjusting the pulse width of the high frequency output by the switching operation of, the control operation is performed so that the DC voltage output from the terminal TO becomes constant. Here, the output voltage Vout output from the terminal TO is shown as follows.

Vout = Vin · (N2 / N1) · {TON / (TON + TOFF)} (1)

FIG. 8 shows the control operation by the PWM control circuit CON when the input voltage of the DC power source Vin is low,
Based on (1), TON is controlled to be larger than TOFF. The ON part indicates VG and the OFF part indicates Vin.
Is shown. VN1 indicates the output voltage of the secondary winding N1.

FIG. 9 shows the control operation by the PWM control circuit CON when the input voltage of the DC power source Vin is high,
Based on (1), TON is controlled to be smaller than TOFF. The following expressions are established in FIGS. 8 and 9.

TON · Vin = TOFF · VG (2)

Therefore, the area of the ON portion is set equal to the area of the OFF portion in FIGS. 8 and 9 based on the equation (2).

In such an operation, in the present embodiment, the clamping capacitor C2 is connected to the gate terminal of the thyristor SCR via the diode D1. The terminal voltage obtained from the clamp capacitor C2 is applied as the control voltage VG.

As shown in FIGS. 8 and 9, the control voltage VG varies depending on the level of the input voltage of the DC power source Vin, and is represented by the following equation.

VG = Vin × (TON / TOFF) (3)

FIG. 3 shows the input power supply voltage Vin based on the equation (3).
It shows the relationship of the gate applied voltage VG (vertical axis) with respect to (horizontal axis), where A is the characteristic of this embodiment and B is the characteristic of the conventional one. As is clear from a comparison between the two, according to the present embodiment, the change in the gate applied voltage VG which is the control voltage of the thyristor SCR is small. on the other hand,
Conventionally, the change in the gate applied voltage VG is extremely large. Therefore, according to the present embodiment, it is shown that the change of the gate voltage with respect to the change of the input voltage of the inrush current prevention circuit M can be suppressed to be small.

As described above, according to this embodiment, the following effects can be obtained.

1. In order to obtain the control voltage applied to the gate terminal of the thyristor SCR that short-circuits the resistor R1 that operates as a rush current limiting resistor, it is not necessary to purposely prepare the primary winding N3.

2. Since the control voltage applied to the gate terminal is not proportional to the magnitude of the DC power supply Vin, the thyristor SCR
The loss power of the resistor R3, which works as the gate current limiting resistor of, does not increase.

3. The control voltage applied to the gate terminal is not a pulse voltage but a DC voltage due to the terminal voltage of the clamping capacitor C2, and since the change is small, the gate power applied to the gate terminal is sufficient, so that the thyristor should be operated reliably. You can

FIG. 2 shows another embodiment of the present invention.
Compared to FIG. 1, it shows an example in which only one switching element Q1 is used. Based on this, the secondary winding N2, which was necessary in FIG. 1, is also unnecessary. Since the operation according to the above-described embodiment is performed also in this embodiment, the same effect can be obtained.

In each embodiment, the thyristor SCR is used as an example of the switching element for resistance short circuit connected in parallel with the resistor R1, but the invention is not limited to this and other elements can be used. 4 to 7 show these examples. FIG. 4 shows an example using a triac, and FIG. 5 shows M.
FIG. 6 shows an example using an OSFET, FIG. 6 shows an example using a transistor, and FIG. 7 shows an example using an IGBT. In short, any element may be used as long as it has a gate terminal to which the control voltage VG is applied, and the switching operation is performed by this gate terminal voltage.

[0035]

As described above, according to the present invention, the clamping capacitor connected in parallel with the switching element is connected to the gate terminal of the resistance short-circuit switching element through the diode. A control voltage can be applied without using a winding, a control voltage that is not proportional to the magnitude of a DC power supply can be applied, and a DC voltage that is not a pulse voltage and that does not change can be applied.

[Brief description of drawings]

FIG. 1 is a connection diagram showing an embodiment of an inrush current prevention circuit of the present invention.

FIG. 2 is a connection diagram showing another embodiment of the present invention.

FIG. 3 is a characteristic diagram showing a relationship between an input power supply voltage and a gate applied voltage in the present invention and the related art.

FIG. 4 is a connection diagram showing a specific example of a switching element for resistance short circuit used in an embodiment of the present invention.

FIG. 5 is a connection diagram showing another specific example of the switching element for resistance short circuit used in the embodiment of the present invention.

FIG. 6 is a connection diagram showing another specific example of the switching element for resistance short circuit used in the embodiment of the present invention.

FIG. 7 is a connection diagram showing another specific example of the switching element for resistance short circuit used in the embodiment of the present invention.

FIG. 8 is a waveform diagram illustrating the operation of the embodiment of the present invention.

FIG. 9 is a waveform diagram illustrating the operation of the embodiment of the present invention.

FIG. 10 is a waveform diagram of an applied voltage and an input current in a conventional example.

FIG. 11 is a connection diagram showing a conventional inrush current prevention circuit.

FIG. 12 is a connection diagram showing a conventional inrush current prevention circuit.

[Explanation of symbols]

 Vin DC power supply S1 Switch C1 Smoothing capacitor C2 Clamping capacitor Q1, Q2 Switching element R1 Inrush current limiting resistor SCR Thyristor (switching element for resistance short circuit) M Inrush current prevention circuit CON PWM control circuit

Claims (2)

[Claims] 1. A DC power supply, a primary winding of a transformer, and a switching element are connected in series, and an inrush current limiting resistor and a resistance short-circuit switching element for short-circuiting this resistor are provided in the intermediate path of the series-connected circuit. In a rush current prevention circuit in which a switching capacitor and a clamping capacitor are connected in parallel, the clamping capacitor is connected to the gate terminal of the resistance shorting switching element via a diode, An inrush current prevention circuit, characterized in that a terminal voltage of a capacitor for application is applied to the gate terminal to control the opening / closing operation of the resistance short-circuiting switching element. 2. The inrush according to claim 1, wherein a second primary winding is connected in parallel to the primary winding of the transformer, and a second switching element is connected in series to the second primary winding. Current prevention circuit.