JPS64916B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a power supply circuit that converts a DC input voltage to a desired DC output voltage.

[Background of the invention]

A power supply circuit that converts a DC input voltage into a desired DC output voltage is called a DC/DC converter. It uses a transistor to convert the DC input voltage into a rectangular wave or a sine wave, and a transformer and a rectifier and smoothing circuit. DC output voltage is obtained. The type that converts the input voltage into a square wave is highly efficient because the transistor is switched between conduction and non-conduction, but the sharp rise and fall of the square wave generates noise and adversely affects the load. On the other hand, the type that converts the input voltage into a sine wave is less affected by noise, but is less efficient because the transistor is always in the operating region.

[Purpose of the invention]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a DC/DC conversion power supply circuit with high efficiency and low noise.

[Summary of the invention]

The power supply circuit of the present invention includes a parallel circuit of a first coil and a capacitor connected to one end of a first output terminal of a DC voltage source, a switching transistor whose emitter is connected to a second output terminal of the DC voltage source, and a parallel circuit of a first coil and a capacitor connected to one end of a first output terminal of a DC voltage source. a second coil connected between the other end of the circuit and the collector of the switching transistor; a series circuit of a third coil and a diode coupled to the second coil; and a series circuit of a third coil and a diode connected to the base of the switching transistor. a control circuit that controls conduction and non-conduction of the DC voltage source; and an output circuit that is coupled to the first coil of the parallel circuit to obtain an output voltage;
Connected between the output terminals. Since it is a parallel resonant circuit of the first coil and the capacitor, the waveform transmitted to the output circuit is a sine wave, and noise can be reduced. Furthermore, the transistor performs a switching operation, resulting in high efficiency. Note that the second coil absorbs the difference between the switching output of the transistor and the sine wave output of the parallel circuit as electromagnetic energy, and the series circuit returns this excess energy to the DC voltage source. Therefore, the efficiency of the power supply circuit is further increased.

[Embodiments of the invention]

Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings. The DC voltage source 10 includes, for example, a 100 volt AC voltage source 12 and a rectifying and smoothing circuit 14 to which the output voltage is supplied. The first output 16 of the DC voltage source 10 is connected to the DC voltage source 10 via a parallel circuit 24 of a first coil 20 and a capacitor 22, a second coil 26 with a large inductance, and a collector-emitter path of an NPN switching transistor 28. It is connected to the second output terminal 18 . Note that the coil 20 is the primary winding of the transformer 30, and forms a parallel resonant circuit together with the capacitor 22. Further, the coil 26 is the primary winding of the transformer 32 and acts as a chiyoke coil.
The secondary winding 34 of the transformer 32 (second coil) forms a series circuit with the diode 36, and this series circuit is connected between the outputs 16 and 18 of the DC voltage source 10. To control the switching operation of transistor 28, the base and emitter of transistor 28 are connected across a secondary winding 40 of transformer 32 via a resistor 38. Further, in order to synchronize the switching operation of the transistor 28 with the sine wave generated in the parallel circuit 24, the base and emitter of the transistor are connected to one end and the middle point of the secondary winding 44 of the transformer 30 via a resistor 42.
The secondary winding 40 of the transformer 32 and the secondary winding 44 of the transformer 30 constitute a control circuit that controls the switching operation of the transistor 28. The secondary windings 46 and 48 of the transformer 30 are rectified and
Smoothing circuits 50 and 52 are connected to form an output circuit. The polarities of the windings of transformers 30 and 32 are indicated by black circles.

A series circuit of a resistor 54 and a capacitor 56 is connected between the output terminals 16 and 18 of the DC voltage source 10, and a resistor 58 and a unijunction transistor (UJT) are connected between the output terminal 16 and the base of the transistor 28. 60 and a resistor 62 are connected in series. Resistor 54 and capacitor 56
The common connection of the UJT 60 is connected to the emitter of the UJT 60, and also connected to the common connection point of the coil 26 and the transistor 28 via the diode 64. These elements 54 to 64 serve as a starter (operation starting circuit) of the power supply circuit. One end of the secondary winding 44 of the transformer 30 is connected to the output end 18 of the DC power supply 10 via a diode 66 and a capacitor 68 to constitute a positive voltage auxiliary power supply circuit. The collector of the transistor 70, which acts as a comparator, is connected to the auxiliary power supply circuit through a resistor 72, and the base is connected to the secondary winding 44.
The emitter is connected to the output end 18 of the DC voltage source 10. A capacitor 74 is connected between the emitter and collector of transistor 70, and the base and emitter of transistor 76, which acts as a comparator, is connected to the collector and emitter of transistor 70, respectively. The collector of the transistor 76 is connected to the base of the transistor 28, and the base of the transistor 76 is connected to the output end 18 of the DC voltage source 10 via a phototransistor 80 of the optical coupler 78. The comparator 84 compares the output voltage of the rectifier/smoothing circuit 50 and the reference voltage V _ref and supplies the output signal to the light emitting section (photo diode) 82 of the optical coupler 78 . These elements 70 to 84 also constitute a voltage stabilization circuit for stabilizing the output voltage of the power supply circuit. Note that the input side of the power supply circuit is completely floating from the output side due to the transformer 30 and the optical coupler 78. The output 18 of the DC voltage source 10 thus becomes a floating reference.

Next, the operation of this embodiment will be explained. First, the DC voltage source 10 outputs a voltage (the output end 16 side is the output end 1
8), the emitter voltage of the UJT 60 increases according to a time constant determined by the resistor 54 and capacitor 56 because the diode 64 is non-conductive. When the emitter voltage reaches a predetermined value, UJT 60 becomes conductive, allowing the charge stored in capacitor 56 to pass through the emitter and first base of the UJT, switching transistor 28 from non-conductive to conductive. When the discharge of the capacitor 56 is completed, the UJT 60 becomes non-conductive. on the other hand,
The circuit centered around transistor 28 begins to oscillate, and this oscillation frequency is much higher than the oscillation frequency of UJT 60, which is determined by resistor 54 and capacitor 56. Furthermore, since diode 64 also becomes conductive each time transistor 28 conducts, capacitor 56 always discharges through diode 64 before reaching the conduction voltage of UJT 60. Therefore
UJT60 is not conductive except at the start of operation.

On the other hand, when the transistor 28 becomes conductive, a pulse voltage is generated at its collector, but since the coil 20 and capacitor 22 are parallel resonant circuits, the coil 28
A sinusoidal voltage is generated across 0. coil 26
Due to the effect of the inductance of transistor 2
The difference between the pulse voltage of the collector of 0 and the sine wave voltage of the parallel circuit 24 is generated as electromagnetic energy in the coil 26.
absorbs. Since the coil 26 is the primary winding of the transformer 32, the energy absorbed by the coil 26 is 2
It is transmitted to the next winding 34, and the backflow prevention diode 3
6 to the DC voltage source 10. On the other hand, due to the action of the secondary winding 40 of the transformer 32, the base voltage of the transistor 28 changes to the opposite polarity to its collector voltage, so that the transistor 28 thereafter repeats the switching operation of conducting and non-conducting. Here, since the sine wave generated in the parallel circuit 24 and the switching operation of the transistor 28 must be synchronized, the output signal of the secondary winding 44 of the transformer 30 is superimposed on the output signal of the secondary winding 40 of the transformer 32. and is supplied to the base of transistor 28.

Since the gain of the transistor 70 is large, the transistor 70 alternately becomes conductive and non-conductive due to the sine wave applied to the base. Yotsute capacitor 74
repeats charging and discharging and generates repeated ramp waves. On the other hand, the rectifier/smoothing circuits 50 and 52 generate DC output voltages, and one of the output voltages is compared with a reference voltage by a comparator 84 to obtain a differential voltage. The DC component of the ramp voltage at the base of transistor 76 is controlled by this differential voltage via optical coupler 78 . Since the transistor 76 becomes conductive when its base voltage exceeds a predetermined value, the output signals of the secondary windings 40 and 77 flow to the transistor 76 side, forcing the transistor 28 to become non-conductive. That is, since the point at which the transistor 28 is turned off can be controlled based on the difference between the output voltage of the rectifier/smoothing circuit 50 and the reference voltage, the output voltage can be stabilized at a predetermined value. Note that the reference voltage can be obtained by connecting a constant voltage diode to the rectifier/smoothing circuit 52.

〔Effect of the invention〕

As described above, according to the present invention, the efficiency is high because the transistor performs a switching operation, and the noise is low because the sine wave is obtained by the parallel resonant circuit. Furthermore, excess energy is returned to the DC voltage source, further increasing efficiency.

[Modification of the embodiment]

Although the above description describes one preferred embodiment of the present invention, those skilled in the art will appreciate that various modifications can be made without departing from the spirit of the invention. For example, the DC voltage source may be a battery, or a transformer 3
The secondary windings 34 and 40 of 2 are of 1 with an intermediate tap.
It is also possible to use a secondary winding of Furthermore, the switching transistor 28 may be of the PNP type, taking into account the polarity of the DC voltage source 10 and the polarities of other elements.

[Brief explanation of the drawing]

The attached figure is a circuit diagram of a preferred embodiment of the present invention. 10: DC voltage source, 20: first coil, 2
2: Capacitor, 26: Second coil, 28: Switching transistor, 34: Third coil, 3
6: Diode.

Claims (1)

[Claims] 1. A parallel circuit of a first coil and a capacitor, one end of which is connected to the first output terminal of the DC voltage source, a switching transistor whose emitter is connected to the second output terminal of the DC voltage source, and the other parallel circuits. a second coil connected between the end and the collector of the switching transistor; a series circuit of a third coil and a diode coupled to the second coil; and a series circuit of a third coil and a diode connected to the base of the switching transistor to conduct the switching transistor. and a control circuit for controlling non-conduction, and an output circuit coupled to the first coil of the parallel circuit to obtain an output voltage, the series circuit being connected between the first and second output terminals of the DC voltage source. A power supply circuit characterized in that it is connected.