JP4650101B2 - Switching power supply device and audio amplifier system - Google Patents

Description

  The present invention relates to a switching power supply that achieves both peak power securing and power factor improvement (measures against power harmonics), and an audio amplifier system including the switching power supply.

Conventionally, as a high power factor type switching power supply, there is one using a capacitorless one-converter type switching power supply (hereinafter referred to as a C-less converter type switching power supply) (for example, Patent Documents). 1).
JP 2002-300780 A

  FIG. 1 is a schematic circuit diagram of a conventional C-less converter type switching power supply and a two-converter type switching power supply. As shown in FIG. 1A, the C-less converter type switching power supply device does not have a large-capacity electrolytic capacitor on the primary side, operates the flyback converter in the current discontinuous mode, and The response is made sufficiently slow relative to the AC frequency to make the input current proportional to the input voltage. Since the C-less converter type switching power supply device is configured and operated as described above, it is simpler than the two-converter type switching power supply device to which a converter dedicated to countermeasures against power harmonics shown in FIG. It has the advantages of being inexpensive, having good conversion efficiency, and suppressing the generation of harmonics.

  However, in the C-less converter type switching power supply, in principle, the primary input current is proportional to the primary input voltage (sine wave). Therefore, the peak value of the input current is 1.5 to 2 times that of a two-converter type switching power supply device having the same output power and having an electrolytic capacitor on the primary side. Therefore, it is necessary to use a MOSFET having a larger current capacity than a MOS FET or transformer used in a two-converter type switching power supply. In addition, the C-less converter type switching power supply device needs to use a MOS FET or transformer having a larger current capacity as its output increases, and accordingly, the size of the MOS FET or transformer increases. There was a problem that the overall size was increased.

  In addition, since the C-less converter type switching power supply device can suppress the generation of harmonics as described above, the power factor can be improved by adopting it in an audio amplifier as a countermeasure against harmonics. However, since the C-less converter type switching power supply device uses a MOS FET or a transformer having a large current capacity, there is a problem that the size of the audio amplifier itself is also increased.

  Therefore, the present invention eliminates the disadvantages of the C-less converter type switching power supply, and achieves a compact switching power supply that achieves both power factor improvement (measures for power supply harmonics) and high power output, and the switching power supply. An object of the present invention is to provide an audio amplifier system including

  The present invention has the following configuration as means for solving the above problems.

(1) a rectifier circuit for rectifying an AC input;
A flyback transformer having a primary winding, a secondary winding, and an auxiliary winding;
The input voltage applied to the primary winding of the flyback transformer after rectification by the rectifier circuit is switched by a switching element, and the switching voltage induced in the secondary winding of the flyback transformer is rectified by the rectification element and the capacitor. Capacitor-less flyback converter circuit that smoothes and outputs,
A voltage control circuit that steps down the voltage output from the capacitorless flyback converter circuit and controls the output voltage applied to the load to a constant voltage;
A negative feedback circuit that feeds back the fluctuation of the output current supplied to the load to the converter circuit at a speed slower than the AC input frequency, and makes the AC input current proportional to the AC input voltage;
An output power detection circuit for detecting output power;
A primary capacitor for smoothing the input voltage rectified by the rectifier circuit;
When the output power detected by the output power detection circuit is greater than or equal to a threshold value, the primary side capacitor is connected to the output terminal of the rectifier circuit, and the output power detected by the output power detection circuit is less than the threshold value, A primary capacitor contact / separation circuit for disconnecting the primary side capacitor from the output terminal of the rectifier circuit;
It is provided with.

  In this configuration, the primary side capacitor that smoothes the input voltage is connected to and separated from the output terminal of the rectifier circuit according to the magnitude of the output power with respect to the threshold power of the switching power supply device. Therefore, when the output power is less than the threshold power, the switching power supply device is an input capacitor-less flyback method, so that the generation of harmonics can be suppressed, and an inrush current prevention element is not required. In addition, when the output power is greater than or equal to the threshold power, the input voltage is smoothed by the primary side capacitor, and the peak value of the input current is suppressed, so that a large current capacity can be used without using a switching element or transformer. Output can be achieved.

  Also, the negative feedback circuit improves the power factor by feeding back the fluctuation of the output current supplied to the load to the converter circuit at a speed slower than the AC input frequency and making the AC input current proportional to the AC input voltage. be able to.

(2) The output power detection circuit is configured to include an auxiliary winding of the flyback transformer, a rectifying element and a capacitor for rectifying and smoothing the output of the auxiliary winding,
The primary capacitor contact / separation circuit compares a contact / separation part that contacts and separates the primary capacitor with respect to the output terminal of the rectifier circuit, a voltage corresponding to the output power of the output power detection circuit, and a threshold value. And a comparator for controlling the contact / separation portion according to the result.

  Since the auxiliary winding of the flyback transformer has direct current resistance ≠ 0 and leakage inductance ≠ 0, the output power of the auxiliary winding always increases when the output power of the secondary winding increases. In this configuration, the output voltage of the auxiliary winding that is proportional to the output power is detected using the above-described characteristics of the auxiliary winding. Then, the comparator compares the output voltage of the auxiliary winding and the threshold voltage set according to the threshold power by the comparator, and controls the contact / separation unit according to the result, to the output terminal of the rectifier circuit Connect or separate the primary capacitor. Therefore, since the voltage according to the output power can be detected by using the auxiliary winding of the existing flyback transformer, the circuit configuration can be simplified. In addition, since the comparator is used to compare the output voltage of the output power detection circuit and the threshold voltage, the contact / separation operation of the contact / separation part can be easily controlled according to the comparison result.

  (3) The contact / separation part is a MOS FET or a relay.

  In this configuration, since the MOS FET or the relay is used as the contact / separation portion, the primary side capacitor can be easily connected to and separated from the primary winding of the flyback transformer.

  (4) A switching power supply device according to any one of (1) to (3) and a feedback type digital audio amplifier are provided.

  In this configuration, the feedback digital audio amplifier is connected to a switching power supply device that connects and separates a primary side capacitor that smoothes the input voltage according to the magnitude of the output voltage with respect to the output terminal of the rectifier circuit. Yes. Therefore, since the capacity of the primary side capacitor can be switched in accordance with the output voltage, for example, the switching power supply device is switched to a C-less converter type switching power supply up to an output of about 1/8 of the maximum output or slightly higher than that. By operating as a device and operating as a converter-type switching power supply device having a smoothing capacitor at higher outputs, the power factor can be improved in most of the time when the output of the audio amplifier is an average value. Also, during the remaining time when the output of the audio amplifier is at or near the peak value, the input current is smoothed by the primary side capacitor, so that a MOS FET or transformer having a large current capacity can be used like a conventional C-less converter. Even if it is not used, a large output can be achieved.

  According to the present invention, the capacitorless flyback converter circuit connects and disconnects the primary side capacitor for smoothing the input voltage with respect to the output terminal of the rectifier circuit according to the magnitude of the output power with respect to the threshold power of the switching power supply device. Therefore, when the output power is less than the threshold power, the switching power supply is of the input capacitor-less flyback system, so that the generation of harmonics can be suppressed and the inrush current prevention element is not required. In addition, when the output power is greater than or equal to the threshold power, the input voltage is smoothed by the primary side capacitor, and the peak value of the input current is suppressed, so that a large current capacity can be used without using a switching element or transformer. Output can be achieved. Also, the negative feedback circuit can improve the power factor by feeding back the fluctuation of the output current supplied to the load to the converter circuit at a speed slower than the AC input frequency and making the AC input current proportional to the AC input voltage. .

  In addition, according to the present invention, since the voltage corresponding to the output power can be detected by using the auxiliary winding of the existing flyback transformer, the circuit configuration can be simplified. In addition, since the comparator is used to compare the output voltage of the output power detection circuit and the threshold voltage, the contact / separation part can be easily controlled (contact / separation) according to the comparison result.

  Furthermore, according to the present invention, since the MOS FET or the relay is used as the contact / separation portion, the primary side capacitor can be easily connected to and separated from the primary winding of the flyback transformer.

  In addition, according to the present invention, the capacity of the primary side capacitor can be switched in accordance with the output voltage in the audio amplifier system. For example, the switching power supply device is about 1/8 of the maximum output or slightly higher than that. By operating as a C-less converter up to a certain level of output, and operating as a converter with C at higher output, the power factor can be improved in most time when the output of the audio amplifier is an average value. Also, during the remaining time when the output of the audio amplifier is at or near the peak value, the input current is smoothed by the primary side capacitor, so that a MOS FET or transformer having a large current capacity can be used like a conventional C-less converter. Even if it is not used, a large output can be achieved.

  Hereinafter, embodiments of the switching power supply device of the present invention will be described in detail. FIG. 2 is a circuit diagram showing a configuration of the switching power supply device according to the embodiment of the present invention. In the following description, a case will be described in which the switching power supply device 1 of the present embodiment is applied to a power supply circuit of an audio amplifier system including a feedback digital audio amplifier.

  The switching power supply device 1 is connected to a commercial AC power supply 2, and includes a noise filter 3, a rectifier circuit 4, an input capacitor-less flyback converter circuit (hereinafter referred to as a C-less converter circuit) 5, a noise filter 6, and voltage control. A circuit 7, a negative feedback circuit 8, an output power detection circuit 9, and a primary capacitor contact / separation circuit 10 are provided. In addition, a feedback digital audio amplifier is connected to the switching power supply device 1 as a load 100.

  The noise filter 3 includes a plurality of capacitors and coils, and removes common mode noise and normal mode noise.

  The rectifier circuit 4 is composed of a bridge diode in which four diodes are bridge-connected, and outputs an input AC voltage by full-wave rectification.

  The C-less converter circuit 5 includes a capacitor C1, a flyback transformer T1, a switching element Q1, a PWM control IC 11, a smoothing rectifier circuit 12, and the like. The capacitor C1 is provided for noise removal, and its capacity is about several μF. The flyback transformer T1 includes a primary winding Np1, a secondary winding Ns1 having a polarity opposite to that of the primary winding, and an auxiliary winding Np2 having a polarity opposite to that of the primary winding. The switching element Q1 is a MOS FET and switches an input voltage applied to the primary winding Np1 of the flyback transformer T1. Although not shown, the PWM control IC 11 operates with power induced in the auxiliary winding Np2, and controls the switching operation of the switching element Q1 to perform PWM control. The smoothing rectifier circuit 12 includes a rectifying element D201 and a large-capacitance capacitor C201, and rectifies and smoothes the switching voltage induced in the secondary winding Ns1 of the flyback transformer T1 and outputs it.

  The C-less converter circuit 5 stores power in the flyback transformer T1 while the switching element Q1 is ON, and supplies the load 100 with power stored in the flyback transformer T1 when the switching element Q1 is OFF. It is a converter of the method to do. The C-less converter circuit 5 applies the input AC voltage that has been full-wave rectified by the rectifier circuit 4 to the flyback transformer T1. The PWM control IC 11 controls the switching element Q1 to switch (intermittently) the current input to the primary winding Np1 of the flyback transformer T1, thereby performing PWM control in the current discontinuous mode, and the flyback transformer T1. The switching voltage induced in the secondary winding Ns1 is rectified and smoothed by the smoothing rectifier circuit 12 and output. Note that AC ripple is superimposed on the output of the C-less converter circuit 5, but when the load 100 is an audio amplifier, there is no problem if the AC ripple is within a predetermined range.

  The noise filter 6 includes a coil L201 and a capacitor C202, and removes spike noise and the like.

  The voltage control circuit 7 includes a shunt regulator IC2 having a reference voltage Vref1 and two resistors R1 and R2 that divide and apply the output voltage Vo to the reference of the shunt regulator IC2. The voltage control circuit 7 steps down the voltage output from the C-less converter circuit 5 and controls the output voltage Vo applied to the load 100 to a constant voltage.

  The negative feedback circuit 8 includes a photocoupler PC1 and a capacitor C4. In the photocoupler PC1, the light emitting diode D202 is connected between the shunt regulator IC2 of the voltage control circuit 7 and the resistor R207, and the collector of the phototransistor Tr101 is connected to the PWM control IC11. The capacitor C4 is connected between the cathode of the shunt regulator IC2 and the reference. The capacity of the capacitor C4 is set to several μF to several tens of μF. The negative feedback circuit 8 feeds back the fluctuation of the output current supplied to the load 100 to the C-less converter circuit 5 at a speed slower than the input AC frequency.

  The output power detection circuit 9 includes an auxiliary winding Np2 of the flyback transformer T1 whose output voltage changes according to a change in output power of the secondary winding Ns1, a diode D1 that rectifies and smoothes the output of the auxiliary winding Np2, and And a smoothing capacitor C3.

  Since the auxiliary winding Np2 of the flyback transformer T1 has DC resistance ≠ 0 and leakage inductance ≠ 0, when the output power of the secondary winding Ns1 increases, the output power of the auxiliary winding increases in proportion to this. . In this way, the output power detection circuit 9 outputs a voltage corresponding to the change in the output power of the secondary winding Ns1 to the primary capacitor contact / separation circuit 10.

  The degree of increase in the output voltage in the auxiliary winding Np2 of the flyback transformer T1 varies depending on the degree of coupling between the auxiliary winding Np2 and the secondary winding Ns1, and the coupling between the secondary winding Ns1 and the primary winding Np1. That is, by changing the structure of the flyback transformer, the degree of increase of the output voltage in the auxiliary winding Np2 can be easily changed.

  The primary capacitor contact / separation circuit 10 compares a power supply Vt that outputs a preset threshold voltage Vth with the output voltage of the output power detection circuit 9 and the threshold voltage, and outputs a signal corresponding to the result. And an inverter In1 that inverts the output signal of the comparator Cp1, a primary capacitor C2 that smoothes the output of the rectifier circuit 4, and a switching element Q2 that contacts and separates the primary capacitor C2 from the circuit. Yes. FIG. 2 shows a case where the switching element Q2 is formed of a MOS FET as an example. In addition, a relay can also be used as the switching element Q2. Further, as the primary side capacitor C2, it is preferable to use an electrolytic capacitor of several hundred μF used on the primary side of a general switching power supply device.

  FIG. 3 is a waveform diagram of an input voltage, an input current, and an output current in the flyback transformer of the switching power supply device. When the output voltage of the output power detection circuit 9 is equal to or higher than the threshold voltage Vth, the primary capacitor contact / separation circuit 10 turns on the switching element Q2 and connects the primary capacitor C2 to the output terminals 4o1 and 4o2 of the rectifier circuit 4. Further, when the output voltage of the output power detection circuit 9 is less than the threshold voltage Vth, the primary capacitor contact / separation circuit 10 turns off the switching element Q2 and disconnects the primary side capacitor C2 from the output terminals 4o1 and 4o2 of the rectifier circuit 4. .

  Thus, when the output voltage is equal to or lower than the threshold voltage Vth, the primary-side capacitor C2 is disconnected from the output terminal of the rectifier circuit 4, so that the switching power supply device 1 is a C-less converter circuit. Therefore, the generation of harmonics can be suppressed, and an inrush current preventing element is not necessary. Further, since a high-frequency power transformer (flyback transformer T1) that is smaller than the low-frequency power transformer is used as the transformer, the apparatus can be reduced in size and weight.

  On the other hand, when the output voltage exceeds the threshold voltage Vth and approaches the peak value, the primary side capacitor C2 is connected to the output terminal of the rectifier circuit 4, so that the peak value is the same as that of the conventional converter type switching power supply device. It becomes. Therefore, a large output can be achieved at peak output without using a large switching element Q1 (MOS FET) or flyback transformer T1.

  Furthermore, in the switching power supply device 1 of the present invention, the negative feedback circuit 8 feeds back the fluctuation of the output current supplied to the load to the C-less converter circuit 5 at a speed slower than the input AC frequency. Therefore, by adjusting the feedback speed of the negative feedback circuit, as shown in FIG. 3, the input AC current can be in phase with the input AC voltage, and the input AC current Iac can be proportional to the input AC voltage Vac. Power factor can be improved.

  Here, when chattering occurs in a linear region near the threshold voltage Vth, one end of the resistor Rth is connected to the inverting input terminal of the comparator Cp1, and the other end is connected to the output terminal, as shown by a dotted line in FIG. It is better to connect and configure a hysteresis comparator. Thereby, the occurrence of chattering as described above can be prevented, and the loss in the linear region near the threshold voltage Vth can be eliminated.

  Next, in the switching power supply device 1 of the present invention, as described above, the light emitting diode D202 of the photocoupler PC1 of the negative feedback circuit 8 is connected to the shunt regulator IC2 of the voltage control circuit 7, and the output of the voltage control circuit 7 is output. Even if the voltage fluctuates, it is fed back to the PWM control IC 11 by the photocoupler PC1, so that the PWM control IC 11 can perform PWM control to stabilize the output voltage Vo to a constant voltage. Here, the output voltage of the voltage control circuit 7 is determined by the reference voltage Vref1 of the shunt regulator IC2 and the two resistors R1 and R2 that divide and apply the output voltage Vo to the reference of the shunt regulator IC2, and Vo = Vref1 X (1 + R1 / R2).

  The switching power supply device 1 is used by being connected to a commercial AC power supply 2, and the input AC is full-wave rectified by a rectifier circuit 4 after noise is removed by a noise filter 3, and PWM controlled by a C-less converter circuit 5. Then, the signal is smoothed and rectified by the smoothing rectifier circuit 12, and noise is removed by the noise filter 6. Then, the voltage is adjusted by the voltage control circuit 7 and a DC output is supplied to the load 100. Further, when the output voltage is lower than the threshold voltage Vth, the primary side capacitor C2 is not connected to the output terminal of the rectifier circuit 4, so that it becomes a C-less converter circuit and the generation of harmonics can be suppressed. When the output voltage is equal to or higher than the threshold voltage Vth, the primary side capacitor C2 is connected to the output terminals 4o1 and 4o2 of the rectifier circuit 4, so that the output of the rectifier circuit 4 is smoothed and the peak value of the input current is obtained. Is suppressed.

  As described above, the switching power supply device of the present invention does not require countermeasures against power supply harmonics, can have the same output characteristics as a power supply device using a low-frequency power transformer, and uses a low-frequency power transformer. The size can be reduced as compared with the apparatus. When the output power (voltage) approaches the peak value, the primary side capacitor C2 is connected to the output terminal of the rectifier circuit 4, so that a large switching element Q1 (MOS FET) or flyback transformer T1 is used. Without use, a high output can be achieved at the peak output. Therefore, the switching power supply device of the present invention is suitable as a power supply device for an audio amplifier.

  Here, when the switching power supply device of the present invention is incorporated in an audio amplifier to form an audio amplifier system, for example, the following settings may be made. That is, in the audio amplifier, the upper limit of the average output is set to about 1/8 of the maximum output. Therefore, when applied to the power supply device for the audio amplifier, about 1/8 of the maximum output or slightly higher than that. It is preferable to set the threshold power so that it operates as a C-less converter type switching power supply device up to the output, and operates as a converter type switching power supply device having a smoothing capacitor at higher outputs. For example, in the case of an audio amplifier with a maximum output of 600 W, the threshold power may be set to 75 W.

  FIG. 2 shows a configuration in which the output voltage is detected by the auxiliary winding Np2 of the flyback transformer T1, and the primary capacitor contact / separation circuit 10 contacts and separates the primary capacitor C2. The invention is not limited to this and may have other configurations. For example, an output power measuring circuit is provided after the smoothing rectifier circuit 12 connected to the secondary winding Ns1 of the flyback transformer T1 to detect the output power. Then, it is possible to compare the output power with a predetermined threshold power, and the primary capacitor contact / separation circuit 10 can connect and disconnect the primary capacitor C2 with respect to the circuit according to the comparison result.

It is a schematic circuit diagram of a conventional C-less converter type switching power supply device and a two-converter type switching power supply device. It is a circuit diagram which shows the structure of the switching power supply device which concerns on embodiment of this invention. It is a waveform diagram of the input voltage, the input current, and the output current in the flyback transformer of the switching power supply device.

Explanation of symbols

1-switching power supply device 2-commercial AC power source 3-noise filter 4-rectifier circuit 5-capacitor-less flyback converter circuit 6-noise filter 7-voltage control circuit 8-negative feedback circuit 9-output power detection circuit 10-primary capacitor Contact / separation circuit 11-PWM control IC 12-smoothing rectifier circuit

Claims (4)

A rectifier circuit for rectifying an AC input;
A flyback transformer having a primary winding, a secondary winding, and an auxiliary winding;
The input voltage applied to the primary winding of the flyback transformer after rectification by the rectifier circuit is switched by a switching element, and the switching voltage induced in the secondary winding of the flyback transformer is rectified by the rectification element and the capacitor. Capacitor-less flyback converter circuit that smoothes and outputs,
A voltage control circuit that steps down the voltage output from the capacitorless flyback converter circuit and controls the output voltage applied to the load to a constant voltage;
A negative feedback circuit that feeds back the fluctuation of the output current supplied to the load to the converter circuit at a speed slower than the AC input frequency, and makes the AC input current proportional to the AC input voltage;
An output power detection circuit for detecting output power;
A primary capacitor for smoothing the input voltage rectified by the rectifier circuit;
When the output power detected by the output power detection circuit is greater than or equal to a threshold value, the primary side capacitor is connected to the output terminal of the rectifier circuit, and the output power detected by the output power detection circuit is less than the threshold value, A primary capacitor contact / separation circuit for disconnecting the primary side capacitor from the output terminal of the rectifier circuit;
A switching power supply device comprising: The output power detection circuit is configured to include an auxiliary winding of the flyback transformer, a rectifying element and a capacitor for rectifying and smoothing the output of the auxiliary winding,
The primary capacitor contact / separation circuit compares a contact / separation part that contacts and separates the primary capacitor with respect to the output terminal of the rectifier circuit, a voltage corresponding to the output power of the output power detection circuit, and a threshold value. The switching power supply device according to claim 1, further comprising: a comparator that controls the contact / separation portion according to a result.   The switching power supply device according to claim 2, wherein the contact / separation part is a MOS FET or a relay.   An audio amplifier system comprising the switching power supply device according to any one of claims 1 to 3 and a feedback type digital audio amplifier.

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