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DESCRIPTION JP2012223029

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DESCRIPTION JP2012223029
A power supply voltage fluctuation due to a regenerative current flowing backward from an
inductive load can be effectively suppressed without increasing the capacity of an output
capacitor. A transformer for isolating a primary side and a secondary side, a rectifying diode
connected to the secondary side of the transformer, and an output capacitor charged with a
current rectified by the diode In the power supply circuit, another diode is connected in parallel
with the output capacitor such that the positive electrode side of the charge of the output
capacitor is a cathode and the negative electrode side is an anode. [Selected figure] Figure 1
Power supply circuit
[0001]
The present invention relates to a power supply circuit suitable for a class D power amplifier.
[0002]
As a power supply circuit for a class D power amplifier, there is a circuit as shown in FIG. 2 (see,
for example, Non-Patent Document 1).
In FIG. 2, reference numeral 10A denotes a power supply circuit, which isolates the primary side
and the secondary side, and transforms the transformer 11 for transforming the AC voltage AC
input to the primary side, and the voltage output to the secondary side of the transformer 11 It is
comprised of diodes D1 to D4 in a bridge connection for full-wave rectification and output
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capacitors C1 and C2 for smoothing the rectified voltage. A class D power amplifier 20 includes a
PWM modulation circuit 21 that PWM-modulates an input audio signal Vin, and an output PMOS
transistor MP1 that is alternately switched on / off by the output PWM signal of the PWM
modulation circuit 21; And an NMOS transistor MN1. A low pass filter (LPF) circuit 30 is
composed of a coil L1 and a capacitor C3. A speaker 40 is connected between the output side of
the filter circuit 30 and the ground GND.
[0003]
In this circuit, the positive voltage + V and the negative voltage -V generated by the power supply
circuit 10A are supplied to the sources of the output transistors MP1 and MN1 of the class D
power amplifier 20. The output transistors MP1 and MN1 are turned on / off by the PWM signal
generated by the PWM modulation circuit 21 to output a PWM voltage to the common drain, and
the PWM voltage is converted to an analog voltage by the filter circuit 30. After being
demodulated, the signal is supplied to the speaker 40 to drive the voice coil L2 of the speaker.
[0004]
Authored by Jun Honda, "Design and Production of Class D / Digital Amplifier", pp. 155-165,
published by CQ, November 1, 2004, 1st edition.
[0005]
However, in the power supply circuit 10A of the class D power amplifier 20, power is returned
from the side of the class D power amplifier 20 to the power supply side 10, and the values of
the power supply voltages + V and -V are fluctuated.
This is because a regenerative current due to the inductive component, in particular, the
electromagnetic energy accumulated in the coil L1 of the filter circuit 30, flows into the power
supply circuit 10A.
[0006]
In the class D power amplifier 20, when the power supply voltages + V and -V fluctuate, the
amplitude of the PWM voltage input to the filter circuit 30 fluctuates when the transistors MP1
and MN1 are switched. The output voltage applied to the signal becomes a distorted voltage with
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respect to the input signal Vin input to the PWM modulation circuit 21, causing a problem that
the distortion factor is deteriorated.
[0007]
The solution is to increase the capacitance of the output capacitors C1 and C2 of the power
supply circuit 10A. However, as the capacitance of the output capacitors C1 and C2 increases,
the external shape also increases. Is difficult.
[0008]
An object of the present invention is to provide a power supply circuit capable of effectively
suppressing power supply voltage fluctuation due to regenerative current flowing back from an
inductive load without increasing the capacity of an output capacitor.
[0009]
In order to achieve the above object, the power supply circuit of the invention according to claim
1 comprises: a transformer for isolating the primary side and the secondary side; a rectifying
diode connected to the secondary side of the transformer; In a power supply circuit including an
output capacitor charged with a current rectified by the diode, another diode is connected in
parallel with the output capacitor such that the positive electrode side of the charge of the output
capacitor is a cathode and the negative electrode side is an anode. It is characterized by
The invention according to claim 2 is characterized in that, in the power supply circuit according
to claim 1, an inductive load is connected as a load.
The invention according to claim 3 is characterized in that, in the power supply circuit according
to claim 1 or 2, the diode is a SiC diode.
[0010]
According to the present invention, even when an inductive load is connected as a load, the diode
is connected in parallel with the output capacitor so that the positive electrode side of the charge
of the output capacitor is the cathode and the negative electrode side is the anode. The
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regenerative current flowing from the load side can be absorbed by the diode, and the fluctuation
of the output power supply voltage can be suppressed.
At this time, it is not necessary to use a large capacity output capacitor, and the power supply
circuit can be prevented from being enlarged.
[0011]
FIG. 1 is a circuit diagram of a power supply circuit according to an embodiment of the present
invention and a circuit related thereto. It is a circuit diagram of the conventional power supply
circuit and a circuit related to it.
[0012]
FIG. 1 shows a power supply circuit 10 according to a first embodiment of the present invention.
In the power supply circuit 10, diodes D5 and D6 are connected in parallel to the smoothing
output capacitors C1 and C2 in the power supply circuit 10A described with reference to FIG.
That is, the cathode of the diode D5 is connected to the positive side of the charge of the
capacitor C1, and the anode is connected to the negative side (ground GND). Further, the cathode
of the diode 6 is connected to the positive side (ground GND) of the charge of the capacitor C2,
and the anode is connected to the negative side. The class D power amplifier 20, the filter circuit
30, and the speaker 40 are the same as those described in FIG.
[0013]
Now, for example, when the current flowing through the speaker 40 is a positive current after
being demodulated by the filter circuit 30, the transistors MP1 and MN1 alternately repeat on /
off repeatedly during this period, but the diodes D5 and D6 When not connected, the following
operation is performed.
[0014]
When the output transistor MP1 is turned on by the PWM signal output from the PWM
modulation circuit 21 of the class D power amplifier 20, a certain voltage is applied to both ends
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of the coil L1, and the current flowing in the coil L1 continues to increase.
At this time, energy is supplied to the coil L1 from the positive power source + V, and magnetic
energy Ea is stored.
[0015]
Next, when the output transistor MN1 is turned on, a voltage of the opposite polarity to the
previous time is applied to both ends of the coil L1, and the current flowing to the coil L1
continues to decrease by the reverse voltage while the transistor MN1 is on . At this time, part of
the magnetic energy Ea stored in the coil L1 returns to the negative power supply -V, the
capacitor C2 is charged with the regenerative current Ia, and the voltage -V increases.
[0016]
That is, there is a problem that a part of the magnetic energy Ea stored in the coil L1 when the
transistor MP1 is turned on is stored in the capacitor C2 when the transistor MN1 is turned on
next, causing the negative voltage -V to increase and fluctuate. .
[0017]
Incidentally, with regard to the magnetic energy Eb stored in the coil L1 when the transistor
MN1 is turned on, a part of the energy Eb is stored in the capacitor C1 by the regenerative
current Ib flowing next when the transistor MP1 is turned on. There is a problem of increasing
and fluctuating.
[0018]
Therefore, in the present embodiment, the diodes D5 and D6 are connected in parallel to the
capacitors C1 and C2 so as to be opposite in polarity to the polarity of the charge.
As a result, when the transistor MP1 is turned on, the regenerative current Ia due to the energy
Ea stored in the coil L1 disappears via the diode D6, and the voltage -V of the capacitor C2 is
prevented from increasing.
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Further, when the transistor MN1 is turned on, the regenerative current Ib due to the energy Eb
stored in the coil L1 disappears via the diode D5, and the voltage + V of the capacitor C1 is
prevented from increasing. In addition, also for the coil L2 of the speaker 40, by connecting the
diodes D5 and D6, it is possible to alleviate the influence of the value of the positive voltage + V
or the negative voltage -V by the energy stored therein.
[0019]
As the diodes D5 and D6, for example, a diode made of SiC (silicon carbide) or GaN (gallium
nitride) having a small on resistance of 1 Ω or less can be used, but in particular, SiC capable of
flowing a large current is used Preferred is a diode. As for diodes D1 to D4 constituting a bridge,
if a diode using SiC is similarly used, the loss there is reduced, which contributes to downsizing of
output capacitors C1 and C2.
[0020]
As described above, according to this embodiment, the variations of the voltages + V and -V due
to the inductive load can be suppressed by the diodes D5 and D6, and the capacitances of the
capacitors C1 and C2 do not have to be particularly large. .
[0021]
Although the power supply circuit of the two power supply system of + V, -V, and GND has been
described above, also for the power supply circuit of the single power supply system by + V and
GND, a diode is similarly connected to the output capacitor. Power supply voltage fluctuation due
to the regenerative current of
[0022]
10, 10A: Power supply circuit 20: Class D power amplifier 30: Filter circuit 40: Speaker
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