JPS633551B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply circuit, and more particularly to a power supply circuit that combines a sine wave rectifier capacitor input type rectifier circuit and a DD converter.

An audio circuit requires a stable DC power supply, and the part that generates this DC power is the power supply circuit in the audio device. In this case, in the DC power supply commonly used in the past, a power supply circuit having a capacitor input type rectifier circuit is used to stabilize the DC power supply. This power supply circuit with a capacitor input type rectifier circuit performs full-wave rectification of the output of a transformer that transforms commercial power, and connects a relatively large-capacity capacitor between the output terminals to obtain full-wave rectified output. It smoothes the current and sends out DC output.

However, in the above configuration, since the full-wave rectified output is charged in a capacitor and smoothed, the charging current to the capacitor begins to flow with some delay with respect to the rise in the rectified output, and as the rectified output rises, the current flows out. The charging current increases and decreases as charging progresses, and charging is completed and becomes zero before the rectified output reaches its maximum value. Therefore, since the charging current has a peak shape, there is a problem in that the 100 Hz charging current and the musical tone signal generate a beat and deteriorate the sound quality. Furthermore, since the charging current is only twice as high as the commercial power supply frequency, its period becomes longer, and its peak value becomes higher accordingly. As a result, vibrations occur in the charging capacitor, and the accompanying change in capacitance affects musical tone signals, degrading sound quality. Furthermore, since the charging cycle is long and the charging time is short, there are various problems such as a decrease in the output after charging and a fluctuation in the power supply voltage when the load is heavy.

In addition, a power supply circuit using a DD converter is a solution to this problem, but a power supply circuit using a DD converter has a short charging cycle and cannot drive a large capacity load. However, switching noise becomes a problem under light loads.

Therefore, an object of the present invention is to provide a power supply circuit that can provide a stable output without noise generation or level fluctuation over a wide range from light loads to heavy loads.

In order to achieve such an object, the present invention provides a sine wave rectifier capacitor input type power supply circuit that transforms and rectifies a commercial power source and supplies the smoothing capacitor with a DD converter installed in parallel to its output. is supplied to the smoothing capacitor, and the output voltage of the sine wave rectifier capacitor input type power supply circuit is set to be higher than the output voltage of the D-D converter under light loads and lower under heavy loads. Set the voltage fluctuation rate characteristics to
During light loads where noise from the D-D converter becomes a problem, it operates as a sine wave rectifier capacitor input power supply circuit, and during heavy loads it operates as a D-D converter input type power supply circuit.
-It charges the output of the D converter into a smoothing capacitor to improve voltage fluctuation characteristics. Hereinafter, a power supply circuit according to the present invention will be explained in detail using the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a power supply circuit according to the present invention. In the figure, 1 is a power transformer whose primary winding 1a is connected between power terminals IN ₁ and IN ₂ to which commercial power of 100 V and 50 Hz is supplied. Further, both ends of the secondary winding 1b of the power transformer 1 are connected between the input terminals of a full-wave rectifier 2, and the output terminals of the full-wave rectifier 2 are connected to the positive output terminal 3a and the negative output terminal 3c of the power supply circuit, respectively. It is connected. Further, the midpoint output end of the secondary winding 1b is connected to the midpoint output end 3b. 4a, 4b
are smoothing capacitors connected between the positive output terminal 3a and the midpoint output terminal 3b and between the midpoint output terminal 3b and the negative output terminal 3c, respectively. and,
These constitute a sine wave rectifier capacitor input type power supply circuit as shown by dotted line A. 1c
is an auxiliary winding wound around a part of the power transformer 1,
Reference numeral 5 denotes a synchronization section that receives the output of the auxiliary winding 1c as an input and generates a synchronization pulse synchronized with the zero cross of the commercial power supply, and is composed of a comparator 6, a capacitor 7, and a resistor 8 that constitute a differentiating circuit. . Reference numeral 9 denotes a switching pulse generating section which generates a sawtooth wave having a phase shift of 90 degrees and a frequency twice that of the commercial power supply in synchronization with the output of the synchronizing section 5.
The switching pulse generating section 9 includes an operational amplifier 11 having a feedback resistor 10, the output of the operational amplifier 11 being input through a resistor 12, and a feedback capacitor 13 forming an integral circuit. amplifier 14 and this operational amplifier 14
A feedback resistor 15 supplies the output of the amplifier 11 to the positive input side of the operational amplifier 11. Reference numeral 16 denotes a switching section, which includes a transformer 17 that transforms the output of the switching pulse generator 9, and a diode 20a that full-wave rectifies the output of the transformer 17 and supplies it to a transistor 18 as a switching element via a resistor 19. , 20b, and an emitter resistor 21. 22 is a full-wave rectifier that rectifies the commercial power supplied between the power terminals IN ₁ and IN ₂ , 23 is a capacitor that smoothes the output of the full-wave rectifier 22, and 24 is an auxiliary charging transformer for auxiliary charging. The primary winding 24a is connected between the output terminals of the full-wave rectifier 22 via the transistor 18 and the emitter resistor 21. Further, both ends of the secondary winding 24b of the auxiliary power transformer 24 are connected to the positive output terminal 3a and the negative output terminal 3c via diodes 25 and 26, respectively, and the midpoint of the secondary winding 24b is connected to the midpoint output terminal. 3b. These constitute a DD converter B which is arranged in parallel to the sine wave rectifier capacitor input type power supply circuit A, and its output is supplied to smoothing capacitors 4a and 4b. In addition, the voltage fluctuation rate characteristic of the sine wave rectifier capacitor input power supply circuit A is such that as the load current I ₀ increases, the output voltage V decreases, as shown by characteristic X in Fig. 2. On the other hand, the voltage fluctuation characteristic of DD converter B has a relatively flat characteristic as shown by characteristic Y in Fig. 2, and is lower than characteristic X under light loads and is lower under heavy loads. The output voltage V is set to be higher than the characteristic X.

In the power supply circuit configured in this manner, when commercial power is supplied between the power supply terminals IN ₁ and IN ₂ , a step-down output is generated in the secondary winding 1 b of the power transformer 1 . The secondary output of this power transformer 1 is
After being rectified by the full-wave rectifier 2, it is smoothed by the capacitors 4a and 4b, and the positive output terminal 3a is smoothed by the capacitors 4a and 4b.
and the midpoint output end 3b, and between the negative output end 3c and the midpoint output end 3b as two power outputs.

On the other hand, the full-wave rectifier 22 outputs the full-wave rectified commercial power supply, and the DC output obtained by smoothing it with the capacitor 23 is connected to the resistor between both ends of the primary winding 24a of the auxiliary power transformer 24. 21
Supplied via. In this state, when the auxiliary winding 1c of the power transformer 1 generates an AC signal a synchronized with the commercial power source shown in FIG. As shown in FIG. b, a rectangular wave signal b is generated which is inverted at the zero cross point of the AC signal a. Then, this rectangular wave signal b is transmitted to the capacitor 7
The signal is differentiated in a differentiating circuit constituted by a resistor 8 and a resistor 8, and is outputted from the synchronizer 5 as a differential signal c shown in FIG. 3c. This differential signal c
is extracted through the operational amplifier 11, whereby a rectangular wave signal d having an opposite phase to the rectangular wave signal b is extracted as shown in FIG. 3d. This rectangular wave signal d is taken out via the operational amplifier 14, whereby a sawtooth wave signal e whose phase is delayed by 90 degrees with respect to the cycle of the commercial power supply as shown in FIG. 3e is switched. It is generated from the pulse generator 9. This sawtooth wave signal e is output as a bipolar signal with the midpoint as a reference via a transformer 17 provided in the switching section 16.
This sawtooth wave signal e is output as a bipolar signal with the midpoint as a reference via a transformer 17 provided in the switching section 16.
The output signal of 7 is full-wave rectified via diodes 20a and 20b, and as shown in Figure 3f, the frequency is twice that of the commercial power supply and the phase is delayed by 90 degrees, so that each zero cross point of the AC signal a is A sawtooth wave signal f, which has a maximum at , is generated and supplied to the transistor 18. In this case, since the transistor 18 is used in the saturation region and cut-off region, it is connected from the diodes 20a and 20b through the resistor 19 as shown in FIG.
When the sawtooth wave signal f shown in is supplied, the output of the full-wave rectifier 22 smoothed by the smoothing capacitor 23 changes into a trapezoidal shape and flows through the primary coil 24a of the auxiliary power transformer 24. . Therefore, by adjusting the level of the sawtooth wave signal f supplied to the base of the transistor 18, the output of the secondary winding 1b of the power transformer 1 decreases below the set level, and the charging of the capacitors 4a and 4b is reduced. A trapezoidal current flows through the primary side of the auxiliary power transformer 24 only during the period when the auxiliary power transformer 24 is not operated. As a result, a trapezoidal output is also generated in the secondary winding 24b of the auxiliary power transformer 24, and this output is rectified by the diodes 25 and 26 and then supplied to the capacitors 4a and 4b for charging. It can be done. Therefore, the capacitors 4a, 4 due to the output of the secondary winding 24b of this auxiliary power transformer 24
The charging period for battery b is a charging suspension period using the output of the full-wave rectifier 2 that performs full-wave rectification of the output of the secondary winding 1b of the power transformer 1, thereby making up for the non-charging period that occurs during the charging period. become. For this reason, the charging cycles for the smoothing capacitors 4a and 4b are doubled and averaged, and the peak value of the charging current as a whole is lowered. In this way, when the peak value of the charging current is lowered and its cycle is doubled, the charging currents for the capacitors 4a and 4b are averaged, and vibrations of the capacitors 4a and 4b are prevented. Even in this case, the current replenishment period is doubled to prevent fluctuations in the power supply. Since a trapezoidal current flows through the auxiliary power transformer 24 as the transistor 18 turns on, more energy can be sent than in the case of a sine wave.

In this case, the voltage fluctuation rate characteristics of the sine wave rectifier capacitor input type power supply circuit A and the DD converter B are determined as shown by characteristics X and Y in FIG. In other words, the sine wave rectifier capacitor input type power supply circuit A generally has the characteristic X shown in Figure 2.
As shown in , the output voltage V has a characteristic that as the load current I ₀ increases, the output voltage V decreases relatively rapidly. On the other hand, the voltage fluctuation rate characteristic B of the DD converter B, as shown by characteristic Y in Fig. 2, shows that the output voltage V decreases as the load current I ₀ increases. Compared to power supply circuit A, the number is sufficiently small. The voltage fluctuation rate characteristics X and Y in both circuits are set to intersect approximately in the medium load region, as shown in FIG. In other words, when the load is light, the output voltage of the sine wave rectifier capacitor input power supply circuit A is D.
- The output voltage of the sine wave rectifier capacitor input power supply circuit A is set to be higher than the output voltage of the D-D converter B, and lower than the output voltage of the DD converter B during heavy loads. Therefore, if the characteristics of both circuits are set as described above, the output voltage of sine wave rectifier capacitor input type power supply circuit A becomes equal to the output voltage of D-D converter B at light load as shown in Fig. 2. , and along with this, the smoothing capacitors 4a, 4
b is charged by the output of the sine wave rectifier capacitor input type power supply circuit. When the load is heavy, the output voltage of the DD converter B increases, contrary to the case described above, as shown in FIG. It will be charged by the output of the DD converter B having the following characteristics. Therefore, the smoothing capacitors 4a and 4b are charged with the higher output level side of the voltage fluctuation rate characteristics X and Y shown in FIG. 2 selected. As a result, the voltage fluctuation rate characteristic as a whole becomes as shown by characteristic Z in FIG. 4, and the regulation as a whole is improved accordingly.

In a circuit configured in this way, switching noise becomes a problem when the load is light.
By eliminating the D converter and making it a sine wave rectifier capacitor input type power supply circuit, the D
It will operate as a power source using a D converter. Therefore, it is possible to obtain a power supply circuit with good voltage fluctuation rate characteristics while preventing the generation of noise.

Incidentally, in the above embodiment, a case has been described in which a DD converter having a special structure is used, but it goes without saying that a DD converter having any structure may be used.

As explained above, the power supply circuit according to the present invention has a sine wave rectifier capacitor input type power supply circuit in which a DD converter that generates an output during the charging suspension period of the smoothing capacitor is installed in parallel. In addition to charging the smoothing capacitor provided in the wave rectifier capacitor input type power supply circuit, the output of the D-D converter during light load is set to be higher than the output voltage of the sine wave rectifier capacitor input type power supply circuit. It is set low, and is set high when the load is heavy. Therefore, in order to operate as a sine wave rectifier capacitor input type power supply circuit under light loads and as a power supply circuit using a DD converter under heavy loads, a D-D converter was used. In addition, the voltage fluctuation rate characteristics can be greatly improved while preventing switching noise at light loads, and since the peak value of the charging current to the smoothing capacitor is reduced, cross-modulation distortion due to the charging current can be reduced. It has various excellent effects such as reducing

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the power supply circuit according to the present invention, FIGS. 2 and 4 are characteristic diagrams of the circuit shown in FIG. 1, and FIGS. 3 a to 3 are shown in FIG. 1. FIG. 4 is a waveform chart showing the operation of each part of the circuit. 1...Power transformer, 3, 22...Full wave rectifier, 4
a, 4b...Smoothing capacitor, 5...Synchronizing part, 9...
Switching pulse generation circuit, 16... Switching section, 24... Auxiliary power transformer, 25, 26... Diode, A... Sine wave rectifier capacitor input type power supply circuit, B... DD converter.

Claims (1)

[Claims] 1. In a sine wave rectifier capacitor input type power supply circuit that transforms and rectifies a commercial power source and supplies it to a smoothing capacitor, a D-D converter is installed in parallel to generate an output during the period when the smoothing capacitor is not charged. The peak value of the charging current is lowered by supplying the output to the smoothing capacitor, and the output voltage of the DD converter is changed to the sine wave rectifier capacitor input type power supply circuit output when the load is light. By setting the voltage to be lower than the voltage and higher at heavy loads, it is possible to prevent switching noise at light loads, improve voltage fluctuation characteristics, and reduce the charging current to the smoothing capacitor. A power supply circuit characterized in that intermodulation distortion due to charging current is reduced by lowering the peak value of .