JPS63107457A - Capacitor-input type rectification and smoothing circuit - Google Patents

Abstract

PURPOSE:To reduce the ripple of charging current, by connecting a smoothing capacitor on the output stage of a rectifier through a resistance or an impedance element such as an inductance, etc. CONSTITUTION:Between a pair of DC power lines 3 through a current limiting impedance element 7 composed of resistances a capacitor-input type rectification and smoothing circuit connects a smoothing capacitor 5, to which a diode 8 is connected in parallel. In this connection, the diode 8 is connected in the turning-ON direction when the charging voltage of the capacitor 5 is higher than the output voltage of a rectifier. The capacitor 5 is charged from a rectifier 2 through an impedance element 7, while a capacitor terminal voltage is impressed to a load circuit 6. At this moment, no discharge current of the capacitor 5 flows through the impedance element 7, so that unnecessary power loss and the voltage drop is restricted to occur.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a capacitor input type rectifying and smoothing circuit suitable as a DC power source for a switching regulator or the like.

[Prior art and its problems] As shown in FIG. 3, a typical conventional capacitor input type rectifying and smoothing circuit connects a high frequency rectifier 2 to an AC power source 1, and connects a pair of output lines 3 of this rectifier 2. .4 by connecting a smoothing capacitor 5 between them.

Note that the load circuit l! connected to the pair of output lines 3 and 4! 36 is a circuit including, for example, a switching regulator.

When a sinusoidal AC voltage is supplied from the AC power supply 1 in the circuit shown in FIG. 3, a full-wave rectified voltage shown in FIG. 4(A) is obtained from the rectifier 2. The charging current of the capacitor 5 shown in FIG. 4(B) starts from t1 when the output voltage of the rectifier 2 of FIG. 4(A) is higher than the charging voltage of the capacitor 5 shown in FIG. 4(C).
It flows during the t2 period and the 73rd to t4 period. t2 when the charging voltage of the capacitor 5 becomes higher than the output voltage of the rectifier 2
73 period, the capacitor 5 is discharged.

By the way, since the capacitor 5 is directly connected to the output stage of the rectifier 2, the capacitor 5 is charged at times t1 to t2 and t3 to t4, at which the rectifier output voltage is higher than this charging voltage.
A charging current with a large peak value flows during this period. When current flows through the capacitor 5, it generates heat due to internal loss, which shortens its life.The internal loss occurs in response to the effective value of the current, and the fourth
If the peak value of the charging current is large as shown in Figure (B),
The effective value and internal loss also increase. Therefore, as the smoothing capacitor 5, it is necessary to use a large capacitor with a large allowable ripple current withstand capacity and a large external dimension, which is a major factor that hinders miniaturization of the device.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a capacitor input type rectifying and smoothing circuit that can reduce ripples in the charging current of a smoothing capacitor and easily downsize the capacitor.

[Means for Solving the Problems] The present invention for solving the above problems and achieving the above objects will be described with reference to the reference numerals in FIG. 1 showing the embodiments.
A rectifier 2 connected to the AC power source 1; a smoothing capacitor 5 connected in parallel to the output stage of the rectifier 2 via a current limiting impedance element; and a charging voltage of the capacitor 5 that is higher than the output voltage of the rectifier 2. This circuit relates to a capacitor input type rectifying and smoothing circuit comprising a diode 8 connected in parallel to the impedance wire 7 and turned on when the impedance is high.

[Function] In the above invention, since the smoothing capacitor 5 is connected via the impedance element 7 such as a resistor or inductance, a charging current with a large peak value does not flow even though it is a capacitor input type. The charging voltage will also be relatively low relative to the rectifier output voltage. As a result, it takes a relatively long time to charge the capacitor 5, and the discharging period becomes short. Since the rectifier output voltage is directly applied to the load circuit 6 during the charging period of the capacitor 5, the ripple of the voltage supplied to the load circuit 6 inevitably becomes large, but it is sufficient for, for example, a DC/DC converter. Applicable.

Embodiment Next, a capacitor input type rectifying and smoothing circuit according to an embodiment of the present invention shown in FIG. 1 will be explained.

However, since those indicated by reference numerals 1 to 6 are substantially the same as those in FIG. 3, their explanation will be omitted.

In FIG. 1, a smoothing capacitor 5 is connected between a pair of DC power lines 3.4 via a current limiting impedance element 7 made of a resistor, and a diode 8 is connected in parallel to this impedance element 7. . Note that the diode 8 is connected in such a direction that it turns on when the charging voltage of the capacitor 5 becomes higher than the rectifier output voltage.

Now, if the rectifier 2 is generating a full-wave rectified sine wave voltage as shown in Figure 2 (A), the capacitor 5 is charged via the impedance element 7, so the peak value of the rectifier output voltage is lower than the peak value of the rectifier output voltage. Also, most of them are charged low. The solid line in FIG. 2C shows the charging voltage of the capacitor 5, and the dotted line shows the rectifier output voltage.

As is clear from the relationship between t1 and t2, t3
During the period from t4 to t4, the rectifier output voltage becomes higher than the charging voltage of the capacitor 5, and a yellow current flows as shown in FIG. 2(B). On the other hand, the charging voltage E of the capacitor 5 also becomes lower toward the rectifier output voltage. During the period t2 to t3, the diode 8 is turned on, a discharge circuit not passing through the impedance element 7 is formed, and the capacitor terminal voltage is applied to the load circuit 6.

At this time, since the discharge current of the capacitor 8 does not flow through the impedance element 7, the occurrence of unnecessary power loss and voltage drop is restricted.

In this circuit, since the ripple in the charging current of the capacitor 5 is reduced as shown in FIG. 2(B), the capacitor 5 can be made to have a small capacity and a small external dimension. If the color of the impedance element is increased and the capacitance of the capacitor 5 is decreased, the charging period becomes longer and the discharging period becomes shorter, so that the ripple of the voltage supplied to the load circuit 6 becomes larger. Therefore, the value of the impedance element 7 and the capacitance of the capacitor 5 are determined so as to produce a smoothing effect that meets the requirements of the load circuit 6. The load circuit 6 is
For example, in the case of a circuit that includes a switching regulator in which a switching element is connected in series to the primary winding t of a transformer, and a rectifying and smoothing circuit is connected to the secondary winding of the transformer, the ripple in the power supply voltage is large. However, there is no problem as long as the output voltage ripple is small. The rectifying and smoothing circuit shown in FIG. 1 is suitable as a power supply section of a DC/DC converter.

If it is necessary to absorb high transient voltages caused by the on/off operation of a switching regulator, use a small dry film capacitor or ceramic capacitor that does not have a useful life like an electrolytic capacitor (Line 3.4).
[Modification] The present invention is not limited to the above-described embodiment, but can be modified. For example, the impedance element 7 may be a series circuit of a resistor and a diode to completely prevent a discharge circuit from being formed through it.

[Effects of the Invention] As is clear from the above, according to the present invention, the period during which the smoothing capacitor discharges to the load can be shortened, the ripple of the charging current of the capacitor can be reduced, and the capacitor can be made smaller and smaller. become possible. Furthermore, since a diode is connected in parallel to the impedance element and the discharge current flows through the diode without passing through the impedance element, an increase in power loss can be suppressed.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a rectifying and smoothing circuit according to an embodiment of the present invention, FIG. 2 is a waveform diagram showing the states of each part in FIG. 1, and FIG. 3 is a circuit diagram showing a conventional rectifying and smoothing circuit. FIG. 4 is a circuit diagram showing the state of each part in FIG. 3. 1... AC power supply, 2... Rectifier, 5... Smoothing capacitor, 6... Load, 7... Impedance element, 8
···diode.

Claims (2)

[Claims] (1) Rectifier connected to AC power supply (1) (2), and a smoothing capacitor () connected in parallel to the output stage of the rectifier (2) via a current limiting impedance element (7).
5); and a diode (8) connected in parallel to the impedance element (7) with a direction of turning on when the charging voltage of the capacitor (5) is higher than the output voltage of the rectifier (2). A capacitor input type rectifying and smoothing circuit consisting of.