JPH0467778A - Rectifying and smoothing circuit - Google Patents

Abstract

PURPOSE:To prevent an overvoltage caused by a transient vibration at the time of closing a power supply and to contrive to miniaturize an apparatus by intermittently controlling the charging current of a smoothing capacitor by the use of a switching element to limit an electromagnetic energy accumulated in an inductor. CONSTITUTION:A transistor 3 and a primary winding 71 constitute the charging circuit of a smoothing capacitor 8. At the time of charging said circuit, the transistor 3 shows intermittent conducting characteristics and the primary winding 71(transformer 7) functions mainly as an inductor. The inductor(7) is used as a transformer and a secondary winding 72 is especially added thereto for the purpose of controlling the transistor 3. For a period during which the current of the primary winding 71 increases, the voltage of the secondary winding 72 is applied as a forward voltage between the base and emitter of the transistor 3 via a capacitor 9. On the other hand, when the increasing period has elapsed, the voltage of the capacitor 9 or that of the secondary winding 72 is applied as a reverse voltage between the base and emitter. The magnitude of this reverse voltage is limited by a diode 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rectifying and smoothing circuit that includes a full-wave rectifier and a smoothing capacitor.

[Prior Art] A conventional circuit is shown in FIG. In the figure, 1 is an AC power supply, 2 is an aftereffect rectifier, 4 and 6 are diodes, 8 is a smoothing capacitor, 12 is an inductor, and 11 is a load. This is a type that charges the smoothing capacitor 8 through the inductor 12.

[Problems to be Solved by the Invention] In the circuit shown in FIG. 2 above, the inductor 12 is
It operates under low frequencies corresponding to

Therefore, it becomes large. Further, when the AC power supply 1 is turned on, a transient voltage is generated on both sides of the smoothing capacitor 8 due to the LC vibration with the inductor 12, and the voltage exceeds the peak value of the AC power supply voltage. Therefore, a harmful overvoltage is generated on the load 11 side.

SUMMARY OF THE INVENTION An object of the present invention is to prevent overvoltage caused by transient vibration when power is turned on, and to achieve miniaturization.

[Means for Solving the Problems] In order to achieve the above object, a switching element is used to intermittently control the charging current of a smoothing capacitor, thereby limiting the electromagnetic energy stored in the inductor.

[Function] Since the charging current to the smoothing capacitor is controlled by the intermittent conduction characteristics of the switching element, the value is smaller than that in the case of complete conduction. Therefore, the level of electromagnetic energy in the inductor is low, which results in a smaller size. Moreover, no overvoltage occurs.

[Example] An embodiment of the present invention will be described below with reference to FIG.

A commercial AC power supply 1 is connected to an AC input terminal of a full-wave rectifier 2 . The + side terminal of the full-wave rectifier 2 is connected to the collector of a transistor 3 as a switching element, and is also connected to the base of the transistor 3 via a base resistor 5. The emitter of transistor 3 is the primary winding 7 of transformer 7.
1 and a smoothing capacitor 8 to one side terminal of the full-wave rectifier 2 , and a diode 4 to one side terminal of the full-wave rectifier 2 . A diode 6 is connected between the base and emitter of the transistor 3. Further, the base of the transistor 3 is connected to the emitter of the transistor 3 via the capacitor 9 and the secondary winding 72 of the transformer 7. A connection point between the secondary winding 72 of the transformer 7 and the smoothing capacitor 8 is connected to the + side terminal of the full-wave rectifier 2 via a diode 10. A load resistor 11 is connected between the + side and - side terminals of the full-wave rectifier 2 .

Now, when the AC power supply 1 is turned on, the transistor 3 is turned on by the current flowing through the base resistor 5, and the transistor 3,
- Current flows through the secondary winding 71 and the smoothing capacitor 8 and charges the smoothing capacitor 8. When the current flowing through the -order winding 71 reaches a constant value, the transistor 3 is turned off, and the current in the -order winding 71 flows through the smoothing capacitor 8 and the diode 4 to further charge the smoothing capacitor 8.

- When the current in the secondary winding 71 becomes zero, a voltage obtained by subtracting the voltage of the smoothing capacitor 8 from the instantaneous value of the rectified output voltage at that time acts on the base circuit, and the transistor 3 is turned on again. In this way, the operation is repeated until the voltage of the smoothing capacitor 8 almost matches the rectified output voltage (AC power supply voltage). When the voltage of the smoothing capacitor 8 becomes equal to or higher than the rectified output voltage (including the case where the instantaneous value of the output voltage decreases and exceeds the voltage), the electric charge of the smoothing capacitor 8 is released to the load resistor 11 side via the diode 10. . At this time transistor 3
, - Since the voltage at the end of the secondary winding 71 becomes negative, the transistor 3
remains off.

As described above, the transistor 3 and the primary winding 71 constitute a charging circuit for the smoothing capacitor 8. During this charging, the transistor 3 exhibits intermittent conduction characteristics, and the -order winding 71
(Transformer 7) mainly acts as an inductor.

The reason why the inductor (7) is a transformer and especially the secondary winding 72 is added is to help control the transistor 3. - during the period when the current in the secondary winding 71 increases, the secondary winding 7
2 is applied as a forward voltage between the base and emitter of the transistor 3 via the capacitor 9. On the other hand, after the increase period has passed, the voltage of the capacitor 9 or the voltage of the secondary winding 72 is applied as a reverse voltage between the base and emitter. The magnitude of this reverse voltage is limited by diode 6.

Conventionally, charging of the smoothing capacitor 8, which is performed for each half cycle of the AC power source 1, is completed in a series of one operation, but in the case of the present invention, it is subdivided into individual operations and is divided into multiple operations. It will be done. Among its individual operations, the inductor (7
) The electromagnetic energy stored per time is also small. This increases the frequency of operation of the inductor (7) and results in a reduction in the size of the inductor (7). On the other hand inductor (7)
The electromagnetic energy is transferred to the smoothing capacitor 8 along with the LC vibration. Along with this, smoothing capacitor 8
The voltage increases and theoretically can exceed the peak value of the rectified output voltage (AC power supply voltage), but in the present invention, the original electromagnetic energy level is small, so the overvoltage caused by this is within a minor range. Stay in.

Note that the capacitor 13 connected in parallel to the DC output terminal of the full-wave rectifier 2 is connected to the AC power source 1 by the transistor 3 performing a switching operation at a higher frequency than the AC power source 1.
This is to alleviate the high frequency of the input current supplied from the capacitor, and the capacitance may be small.

[Effects of the Invention] According to the present invention, since the smoothing capacitor is charged via the switching element exhibiting intermittent conduction characteristics, the inductor can be downsized and overvoltage can be reduced.

[Brief explanation of drawings]

FIG. 1 is a rectifying and smoothing circuit diagram according to the present invention, and FIG. 2 is a conventional circuit diagram. 1... Alternating current, 2... Full wave rectifier, 3... Switching element, 7... Inductor, 8... Smoothing capacitor

Claims (1)

[Claims] 1. A rectifying and smoothing circuit having a full-wave rectifier and a smoothing capacitor, characterized in that a series circuit of a switching element and an inductor exhibiting intermittent conduction characteristics during charging is inserted into the charging circuit of the smoothing capacitor. circuit.