JPH04101666A - Surge current limiting circuit for switching power supply - Google Patents

Abstract

PURPOSE:To block surge current with a low loss surge current limiting circuit by employing the output voltage from an auxiliary power supply section as a power supply for operating a switching control section and as a control signal at the switching element control terminal in a surge limiting section thereby turning the switching element in the surge limiting section ON simultaneously with or prior to the actuation of the switching control section. CONSTITUTION:In the primary surge interval, a capacitor C1 is charged through a current limiting resistor R1 simultaneously with turn ON of power. In the secondary surge interval, a switching control section 20 is actuated and a switching element Q2 in a surge limiting section 40 is turned ON. Consequently, the surge limiting section 40 has the ON resistance of the switching element Q2 which is lower than the resistance of the current limiting resistor R1. Furthermore, since the duty ratio of a switching element Q1 is enlarged untill the output voltage from a booster converter section 10 reaches a rated level, an input current larger than the steady current flows into the capacitor C1.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an inrush current limiting circuit for a switching power supply, and particularly relates to an improvement when the circuit includes a power factor correction circuit using an active smoothing filter.

<Prior Art> A power factor correction circuit will be described below. Figure 6 shows AC-
FIG. 2 is an explanatory diagram of a DC converter, in which (A) is a circuit diagram and (B) is a waveform diagram of input voltage vE and input current IE. The applied alternating current AC is rectified by a diode bridge DB and smoothed by a capacitor C. Since the output current of the diode bridge DB is directly applied to the capacitor C, it is called capacitor input type rectification. The waveform of the input current I[ is narrower than that of the input voltage ■ε, and its effective value is low.

Figure 7 is an explanatory diagram of choke input type rectification, (A)
is a circuit diagram, and (B) is a waveform diagram of input voltage V= and input current IE. Compared to capacitor input type, ripple current is reduced. In this case, although the waveform of the input current IE is wider than that of the capacitor input type, the phase difference with the input voltage V= increases and the improvement in power factor is not so great.

Figure 8 is an explanatory diagram of the active smoothing filter type, (A)
is a circuit diagram, and (B) is a waveform diagram of input voltage Vε and input current IE. The active smoothing filter type has a switching element Q inserted at the connection point between the choke coil L and the diode D, and is also called the step-up converter addition type.

FIG. 9 shows waveforms explaining the operation of the active smoothing filter type, where (A) is the input current iEn, [B] is the switching current Ic, (C) is the rectified voltage Vrn, and (D) is the output voltage Vllllt. . Due to the action of the switching element, the switching operation is performed over the entire cycle of the input current IE, so that the power factor is improved.

<Problems to be Solved by the Invention> However, in the active smoothing filter type power supply, since the switching element Q is not operating when the power is turned on, the active smoothing filter function is not operating. Furthermore, in the commercial power supply frequency range, the choke coil L does not have the function of limiting the rush current when the power is turned on.

Therefore, if the inductance is set to satisfy the inrush limiting function, the coil becomes extremely large, and the power factor decreases due to the influence of the coil, making it meaningless to employ an active smoothing filter.

It is also conceivable to add a triac, which is generally used as an inrush limiting method for switching power supplies. However, the loss in the triac is large when the input voltage is 1 oov, and in addition to this, the active smoothing filter itself has increased loss compared to the conventional smoothing circuit. Therefore, there is a problem that the heat dissipation fins have to be made large, which increases the cost.

SUMMARY OF THE INVENTION An object of the present invention is to provide a device that includes an inrush limiting circuit with low loss and prevents an excessive inrush current of a switching power supply having an active smoothing filter.

Means for Solving the Problems> Figure 1 is a block diagram illustrating the present invention. In Figure 0, this switching power supply inputs rectified alternating current through an inductance (L1), (Q1) turns on and off, and diode (D2)
A boost converter g (10) that stores electricity in a capacitor (C1) via G and outputs a voltage higher than the input voltage.
A switching control section (2) that controls the on/off of this switching element to stabilize the output voltage of the boost converter section.
0), an auxiliary power supply section (30) that generates a direct current of a predetermined voltage from the alternating current, a current limiting resistor (R1) inserted on the capacitor input side of this boost converter section, and a current limiting resistor (R1) in parallel with this current limiting resistor. The inrush limiter (40) is provided with a switch element (C2) having an input terminal and an output terminal connected to each other.

The output voltage of the auxiliary power supply section is used as a power supply for operating the switching control section, and is also used as a sub-leg signal of the switch element control terminal of the inrush limiting section, and is used simultaneously with or in advance of the start of operation of the switching control section. It is characterized by turning on the switch element of the rush control @ section.

Functions Each component of the present invention has the following functions. The inrush limiting section has a current limiting resistor, so that the primary inrush situation when the power is turned on is determined by the current limiting resistor and the value of the capacitor in the boost converter section.

The inrush limiting section has a switching element connected in parallel with the current limiting resistor, and is turned on by the auxiliary power supply section when the boost converter section starts operating, so that a secondary inrush occurs.

The loss in the inrush limiter is determined by the on-resistance of the switch element,
Since it is present on the boost side of the boost converter section, the duty of the flowing current is small, which reduces loss.

Since the auxiliary power supply section supplies power to the switching control section and the inrush limiting section, the operation timings of both are coordinated.

<Example> The present invention will be explained below using the drawings.

FIG. 2 is a configuration block diagram showing an embodiment of the present invention. In FIG. 6, the boost converter unit 10 converts the alternating current rectified by the diode bridge DB into
and is stored in the capacitor C1 via the diode D2. The switching element Q1 is an FET or a transistor, and the drain terminal (input terminal) is connected to the inductance L1.
and the diode D2, the source terminal (output terminal) is connected to the common line, and the gate terminal (control terminal) is turned on and off according to the control signal applied to the gate terminal (control terminal).

The switching control section 20 controls the on/off of the switching element Q1 to adjust the output voltage V(
For example, an active smoothing filter control IC such as ML4812 manufactured by Microlinear Co., Ltd.
is used. The output signal of the die INE ord bridge DB is applied to the synchronous terminal I of this control IC via the resistor R2, and the voltage of the capacitor C1 is applied to the output voltage detection terminal VO via the voltage dividing resistors R3 and R4. , drain current detection terminal 1 in
The secondary current of the current transformer T1 inserted into the input terminal of the switching element Q1 is applied through the circuit of the diode D3 and resistors R5 and R6, and the output terminal 0 is connected to the control terminal of the switching element Q1. There is.

The auxiliary power supply section 30 generates a direct current of a predetermined voltage from the alternating current, and an RCC (ringing choke converter) power supply having a transformer T2 is used here. The RCC power supply has a primary winding n1 whose one end is connected to the capacitor C1, a control winding n3 having a switching element Q3 connected to the other end of the primary winding n1, and a secondary winding n2°R4. There is. The control terminal of the switching element Q3 includes a starting resistor R7 whose other end is connected to the capacitor C1, and a feedback resistor R whose other end is connected to the control winding n3.
It has 8. The secondary winding n2 is connected to a rectifying and smoothing circuit consisting of a diode D4 and a capacitor C2,
This output is connected to the control terminal of the switching element Q2 and the t source terminal of the control IC of the switching control section 20. The secondary winding n4 is connected to a rectifying and smoothing circuit consisting of a diode D5 and a capacitor C3, and its output is used for other purposes.

The inrush control section 40 includes a current limiting resistor R1 inserted into the input side of the capacitor C1, and a switching element Q2 having an input terminal and an output terminal connected in parallel with the current limiting resistor. Here, since the current limiting resistor R1 is inserted on the common line side, the output voltage of the auxiliary power supply section 30 is used as it is as a control signal sent to the control terminal of the switch element Q2.

FIG. 3 is a waveform diagram illustrating the operation of the circuit of FIG. 2.

When alternating current is applied to this switching power supply, a negative inrush occurs first, followed by a secondary inrush period, and finally a steady current period.

- During the next inrush period, there is no power supply from the auxiliary power supply section 30, so the switching control section 20 continues to operate, and the switching element Q2 of the inrush control section Ii1 section 40 is also in an off state.

Therefore, the capacitor C1 is charged through the current limiting resistor R1 at the same time as the power is turned on. The peak value of the input current increases exponentially with Vrn/R1 being the maximum value.

During the secondary inrush period, power is supplied from the auxiliary power supply section 3o, so that the switching control section 20 starts operating, and the switch cable Q2 of the inrush limiting section 4o is also turned on. Therefore, the resistance value of the inrush limiter 40 becomes the on-resistance value of the switching element Q2, which is smaller than the value of the current limiting resistor R1. Since the switching control section 20 acts to expand the duty ratio of the switching element Q1 until the output voltage of the boost converter section 10 reaches the rated value, an input current larger than the steady current flows into the capacitor c1. Normally, the charging voltage of capacitor C1 has reached the peak value of the input voltage.

During the steady current period, the boost converter section 10 works as an active smoothing filter, so the power factor approaches 1 and the input current becomes a sinusoidal wave. The input '& current value changes somewhat due to load fluctuations and input voltage fluctuations.

Next, the output of the power factor correcting switching power supply is 5oow,
The output voltage is 380v. , the first embodiment and the conventional triac type will be compared with the input voltage of 90 VAo. Assuming that the forward voltage drop of the triac is 1v and the on-resistance of the MOSFET is 0.5Ω, the loss P is as shown in the following table. 38
is obtained. Compared to the conventional example, FIG. 4 shows the second example of the present invention.
It is an explanatory diagram of an example.

When compared with the circuit shown in FIG.
is not on the common line side of capacitor C1 but on the diode D2 side. Therefore, an auxiliary power supply section 32 is provided to drive the switch element Q2. Auxiliary power supply section 32
is the inductance L that magnetically couples with the inductance L1
2, and the signal induced therein is converted into DC by a rectifying and smoothing circuit including a diode D6 and a capacitor C4, and is applied as a control signal to the control terminal of the switching element Q2.

Although the switching control section 20 is originally the circuit shown in FIG. 2, it is shown here in a simplified manner.

This embodiment is effective when the circuit shown in FIG. 2 cannot be used due to the arrangement of parts or the pattern of the printed circuit board.

FIG. 5 is an explanatory diagram of a third embodiment of the present invention.

Compared to the circuit shown in FIG. 4, the switching element Q2 of the inrush limiting section 40 is a thyristor. The control terminal of the thyristor is connected via a resistor R9 to an auxiliary power supply provided by a choke coil of a boost converter of an active smoothing filter.

<Effects of the Invention> As explained above, according to the present invention, the switching element Q2 of the inrush limiter is connected to the input side of the capacitor C3, which has the effect of significantly reducing the loss compared to the triac type. .

Further, as in the first embodiment, when the auxiliary power supply section 30 supplies the driving power and control signals to the switching control section 20 and the rush limiting section 40, there is an effect that the operations of the two can be easily coordinated.

[Brief explanation of the drawing]

FIG. 1 is a block diagram illustrating the present invention, FIG. 2 is a block diagram illustrating an embodiment of the present invention, FIG. 3 is a waveform diagram explaining the operation of the circuit in FIG. 2, and FIG. Second aspect of the present invention
Embodiment FIG. 5 is an explanatory diagram of a third embodiment of the present invention. FIG. 6 is an explanatory diagram of an AC-DC converter, FIG. 7 is an explanatory diagram of choke input type rectification, and FIGS. 8 and 9 are explanatory diagrams of an active smoothing filter. DESCRIPTION OF SYMBOLS 10... Boost converter part, 20... Switching control part, 30... Auxiliary power supply part, 40... Inrush restriction part. No. 1 (AI (B) Fig. 7/A+/1 CB)

Claims (1)

[Claims] A rectified alternating current is input through an inductance (L1), turned on and off by a switching element (Q1), and stored in a capacitor (C1) through a diode (D2), so that the voltage is lower than the input voltage. a step-up converter section (10) that outputs a high voltage; a switching control section (20) that controls on/off of this switching element to stabilize the output voltage of the step-up converter section; a DC current of a predetermined voltage from the alternating current; Auxiliary power supply section (30), a current limiting resistor (R1) inserted on the capacitor input side of this boost converter section, and a switching element (Q2) whose input terminal and output terminal are connected in parallel with this current limiting resistor. an inrush limiting section (40), which uses the output voltage of the auxiliary power source as an operating power source for the switching control section and as a control signal for a switch element control terminal of the inrush limiting section, and An inrush current limiting circuit for a switching power supply, characterized in that a switch element of an inrush limiting section is turned on at the same time or in advance of the start of operation of the inrush limiting section.