JPH0421356A - Switching power circuit - Google Patents

Abstract

PURPOSE:To produce an output voltage without employing a transformer or the like, i.e., a source of electromagnetic noise, by producing a voltage through switching operation, cutting off DC component through a capacitor and then subjecting to rectification and smoothing operation. CONSTITUTION:A switching power circuit comprises an oscillation circuit 2 oscillating with a preset frequency to produce first and second square waves, a capacitor 5 for coupling transistors 3, 4, a full-wave rectifying circuit 6, and a smoothing capacitor 7 for feeding power to a load 9. The oscillation circuit 2 produced first and second square waves for alternately turning the transistors 3, 4 ON/OFF thus converting the source voltage into a pulse voltage. The capacitor 5 cuts off DC component in the pulse voltage to produce an AC voltage having amplitude half that of the source voltage which is then full-wave rectified and smoothed to produce an output voltage. Consequently, an output voltage can be produced from the source voltage with high conversion rate without requiring an inductance or a transformer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a switching power supply circuit used in various electronic devices.

(Prior Art) A circuit shown in FIG. 5 has been known as a switching power supply circuit used in various electronic devices.

The switching power supply circuit shown in this figure includes a switching transistor 102 that switches the power supply voltage (voltage value is "Ei") output from a power supply 101, a smoothing inductance 103, and a smoothing capacitor 10.
4, the pulse voltage obtained by the switching operation of the transistor 102 is smoothed to produce an output voltage (voltage value is "E").

) and supplying the smoothing circuit 105 to the load 106;
and a flywheel diode 107 that supplies current when a back electromotive force is generated in the inductance 103, and supplies a pulse signal to the base of the transistor 102 to switch it and connect the power supply 101.
A pulse voltage is generated from the power supply voltage outputted from the power supply voltage, and the pulse voltage is smoothed by a smoothing circuit 105 to generate an output voltage, which is supplied to a load 106.

(Problem to be Solved by the Invention) However, in the conventional switching power supply circuit described above, a pulse voltage of a high voltage value obtained by operating the transistor 102 and switching the power supply voltage is transferred to the inductance 103 of the smoothing circuit 105. Therefore, there is a problem in that the electromagnetic wave noise radiated from the inductance 103 is very large and has an adverse effect on surrounding electronic equipment.

For this reason, some devices have been developed that eliminate this inconvenience by installing noise suppression filters, etc. However, even with such filters, the inductance 1
There was a problem that it was not possible to completely prevent electromagnetic noise from 03.

In view of the above circumstances, the present invention aims to provide a switching power supply circuit that can generate an output voltage from a power supply voltage at a high conversion rate without using inductances, transformers, etc., which are sources of electromagnetic noise. There is.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, a switching power supply circuit according to the present invention includes a switching circuit that generates a pulse voltage by switching manually applied DC voltage, and A capacitor that cuts the DC component of pulse voltage to generate AC voltage, a rectifier circuit that rectifies the AC voltage obtained by this capacitor to generate DC voltage, and a rectifier circuit that smoothes the DC voltage obtained by this rectifier circuit. The present invention is characterized in that it includes a smoothing circuit that generates an output voltage.

(Function) In the above configuration, the input DC voltage is switched by the switching circuit to generate a pulse voltage, and the DC component of the pulse voltage is cut by the capacitor and converted to an AC voltage, which is then converted to an AC voltage by the rectifier circuit. After being rectified by a smoothing circuit, it is smoothed and output as an output voltage.

(Embodiment) FIG. 1 is a block diagram showing a first embodiment of a switching power supply circuit according to the present invention.

The switching power supply circuit shown in this figure oscillates at a preset frequency to
The oscillation circuit 2 generates a second square wave, and the power supply voltage (voltage value is "Ei") from the power supply 1 input to the collector is switched based on the first square wave output from the oscillation circuit 2. a transistor 3 that generates a pulse voltage and outputs it from its emitter; a transistor 4 that intermittently grounds the emitter of the transistor 3 based on a second square wave output from the oscillation circuit 2; and each of the transistors 3. .Cut the DC component of the pulse voltage (see Figure 2 (c)) obtained by the on/off operation of step 4 to generate an AC voltage based on "0■" as shown in Figure 2 (d). a coupling capacitor 5, a full-wave rectifier circuit 6 for full-wave rectifying the AC voltage output from the capacitor 5, and a full-wave rectifier circuit 6 for smoothing the full-wave rectified voltage. The output voltage shown in (e) (the voltage value is “
A smoothing capacitor 7 generates a signal Eo'') and supplies the generated signal to a load 9.

In this switching power supply circuit, as shown in Fig. 2(a)
, as shown in FIG. 2(b), the oscillation circuit 2 outputs the first and second square waves to turn on the transistors 3.4 alternately, thereby switching the power supply voltage output from the power supply 1, as shown in FIG. The pulse voltage shown in c) was generated, and the DC component of the pulse voltage was cut off by a capacitor 5 to produce an AC voltage as shown in FIG. 2(d), which was then full-wave rectified by a full-wave rectifier circuit 6. Thereafter, it is smoothed by a capacitor 7 to generate an output voltage shown in FIG. 2(e), which is supplied to a load 9.

In this case, the AC voltage output from the capacitor 5 is “O
Since the amplitude value is 1/2 of the pulse voltage value "Ei" input to this capacitor 5 using "V" as a reference point, it is full-wave rectified by the full-wave rectifier circuit 6 and smoothed by the capacitor 7. The output voltage value "Eo" obtained by this is 1/2 of the power supply voltage value Ei.

In this way, in this embodiment, the two transistors 3.4 are turned on and off alternately to convert the power supply voltage into a pulse voltage, and the DC component of the pulse voltage is cut by the capacitor 5 to obtain the power supply voltage value. After generating an AC voltage with an amplitude value of 1/2 of and full-wave rectifying it,
Since the output voltage is generated by smoothing this, the output voltage can be generated from the power supply voltage at a high conversion rate without using inductances, transformers, etc., which are sources of electromagnetic noise.

FIG. 3 is a block diagram showing a second embodiment of the switching power supply circuit according to the present invention. Note that in this figure, the first
The same reference numerals are given to parts corresponding to those in the figure.

The switching power supply circuit shown in this figure differs from the circuit shown in FIG. 1 in that a coupling capacitor 10 is inserted between the emitter of the transistor 4 and the ground input terminal of the gold wave rectifier circuit 6.

Even if configured as in 2, the voltage value of the output voltage can be reduced to 1/2 of the power supply voltage at a high conversion rate without using inductances, transformers, etc., which are sources of electromagnetic noise, as is the case with the above-mentioned embodiment. In addition, the power source 1 side and the load 9 side can be completely separated, increasing the versatility of the circuit.

FIG. 4 is a block diagram showing a third embodiment of the switching power supply circuit according to the present invention. Note that in this figure, the first
Components corresponding to those in the figure are given the same reference numerals.

The switching power supply circuit shown in this figure is different from the circuit shown in FIG.
4 was established.

In this switching power supply circuit, the positive voltage side of the AC voltage output from the capacitor 5 is taken out by the positive voltage rectifying diode 12 constituting the positive and negative voltage extraction circuit 11, and the positive voltage side is smoothed by the capacitor 7, and then the positive voltage is In addition to generating an output voltage and supplying it to the load 9, the negative voltage side of the AC voltage output from the capacitor 5 is taken out by the diode 13 for negative voltage rectification that constitutes the positive and negative voltage take-out circuit 11, and is connected to the capacitor. 14 to generate a negative output voltage, which is supplied to a load 15.

With this configuration, it is possible to prevent the generation of electromagnetic noise as in each of the embodiments described above, and also to reduce the voltage value "El" which is 1/2 of the voltage value "El" of the power supply voltage.
It is possible to obtain a positive output voltage "10EO" with "E i /2" and a negative output voltage "-Eo".

Furthermore, in each of the embodiments described above, since the input voltage can be halved and output, the switching power supply circuits described above can be connected in multiple stages to reduce the power supply voltage to 1/4.
．． It may be set to 1/8, . . . .

[Effects of the Invention] As described above, according to the present invention, it is possible to generate an output voltage from a power supply voltage at a high conversion rate without using an inductance, a transformer, or the like, which is a source of electromagnetic noise.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of a switching power supply circuit according to the present invention, FIG. 2 is a waveform diagram showing an example of the operation of the embodiment shown in FIG. 1, and FIG. 3 is a block diagram showing a first embodiment of a switching power supply circuit according to the present invention. FIG. 4 is a block diagram showing a third embodiment of the switching power supply circuit according to the present invention; FIG. 5 is a block diagram showing an example of a conventionally known switching power supply circuit. . 1... Power supply 3.4... Switching circuit (transistor) 5...
・Capacitor 6... Rectifier circuit (full wave rectifier circuit) 7... Smoothing circuit 9... Load M patent attorney Hidekazu Miyoshi 1 Figure 3 Figure

Claims (1)

[Claims] (1) A switching circuit that switches input DC voltage to generate a pulse voltage, a capacitor that cuts the DC component of the pulse voltage obtained by this switching circuit to generate AC voltage, and a capacitor that generates AC voltage by switching the input DC voltage. A switching power supply circuit comprising: a rectifier circuit that rectifies an AC voltage obtained by the rectifier to generate a DC voltage; and a smoothing circuit that smoothes the DC voltage obtained by the rectifier circuit to generate an output voltage.