JPH01149507A - Switching power amplifier circuit - Google Patents

Abstract

PURPOSE:To decrease a power loss at the time of no signal and, simultaneously, to execute a direct current amplification by providing a polarity detecting circuit, a gate circuit and a communicating circuit which are equipped with prescribed functions, respectively. CONSTITUTION:A polarity detecting circuit 60 detects the polarity of an input signal Si, and it causes a gate circuit 70 to execute on/off actions according to such a detecting signal. By the on/off of the gate circuit, the actions of first and second output switching transistors 80 and 81 are regulated. A communicating circuit 90 supplies a current by an energy remaining at a coil 101 of a smoothing circuit 100 through a gland to a load Rl based on the detecting signal from the detecting circuit 60, and the circuit 90 works to suppress an unnecessary charge to a power source side. Thus, the power loss at the time of no signal can be decreased, and simultaneously, the direct current amplification can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention provides single-ended output pulse width modulation (hereinafter referred to as
This invention relates to a PWM switching power amplifier circuit.

(Prior Art) Conventionally, there have been switching power amplifier circuits of this type, such as those shown in FIGS. 2 and 3, for example. The configuration will be explained below.

FIG. 2 is a circuit diagram of the main parts of a conventional single-ended switching power amplifier circuit.

This switching power amplifier circuit consists of NPs connected in series.
It has an N transistor 1 and a PNP transistor 2, and diodes 3 and 4 are connected in parallel to both transistors 1 and 2, respectively.

A filter consisting of a coil 5 and a capacitor 6 connected in series is connected to the emitters of the NPN transistor 1 and the PNP transistor 2, and a power supply 7 and a smoothing capacitor 8 are connected between the capacitor 6 and the collector of the NPN transistor 1. and roughly connect the capacitor 6 and PNP
Is there an electric current between the collector of transistor 2? Ii9 and a smoothing capacitor 10 are connected. A load Rρ is connected in parallel with the capacitor 6, and the load R,l! One end of is grounded.

In the above configuration, when an input signal is supplied, the NPN transistor 1 and the PNP transistor
Transistor 2 alternately turns on and off. NP
N transistor 1 is on and PNP transistor 2
is in the off state, the main current 11 flowing from the power supply 7 is N
Through the PN transistor 1, the coil 5 and the capacitor 6
After smoothing, it is supplied to a loader. At this time, the energy generated in the coil 5 becomes a commutation current I2, and the capacitor 6 and the load R, l! It flows through the route → power supply 9 → diode 4. Furthermore, when the PNP transistor 2 is in the on state and the NPN transistor 1 is in the off state, the main current flowing from the power supply 9 is transferred to the capacitor 6 and the loads R, I
! The main current flows through the route → coil 5 → PNP transistor 2, and the main current is smoothed by the coil 5 and capacitor 6 and is supplied to the load. At this time, the energy generated in the coil 5 becomes a commutated current as described above, and flows through the diode 3 → power supply 7 → capacitor 6 and load Rρ.

FIG. 3 is a circuit diagram of the main parts of a conventional balanced transfer i-Mares type (hereinafter referred to as BTL type) switching power amplifier circuit.

This switching power amplifier circuit has four NPN transistors 21, 22, 23, and 24, and each of these transistors 21 to 24 has a diode 25, 26, respectively.
, 27, and 28 are connected in parallel. A filter consisting of a coil 29 and a capacitor 30 is connected between the emitter of the NPN transistor 21 and the collector of the NPN transistor 23, and the emitter of the NPN transistor 24 and the collector of the NPN transistor 22, and a load R is connected in parallel with the capacitor 30. ,l! is connected. Also,
A power supply 31 and a smoothing capacitor 32 are connected between the collectors of the NPN transistors 21 and 24 and the ground.

In this type of switching power amplifier circuit, NPN transistors 21, 22 and 23, 24 located on the diagonal line alternately turn on and off depending on the polarity of the input signal, and the PWM wave generated thereby After being smoothed by the coil 29 and capacitor 30, the load R,l! is supplied to

(Problems to be Solved by the Invention) However, the circuit with the above configuration has the following problems.

In the switching power amplifier circuits of FIGS. 2 and 3, even in a no-signal state where no input signal is supplied, the switching action of the transistors 1, 2.21 to 24 continues, so the transistors 1, 2.21 to 24, diodes 3 and 4, 25 to 28, and coils 5 and 29 have a problem in that power loss increases.

In addition, in the switching power amplifier circuit shown in Fig. 2, when the input signals have the same polarity, that is, when performing DC amplification, the NP
Either the N transistor 1 or the PNP transistor 2 is always off, and the energy generated in the coil 5 becomes a commutated current that intermittently charges the power supply 7 or 9 on one side, so the power supply voltage continues to increase. , it becomes impossible to maintain normal operation as a power amplifier circuit. On the other hand, in the switching power amplifier circuit shown in Fig. 3, DC amplification is possible, but since the output side to which the load R1 is connected is floating from the ground, the grounding system path on the input signal side and power supply side and the grounding on the output side It is necessary to separate the system from the system, which is disadvantageous and inconvenient in use.

The present invention is a single-end-output type PWM type switching power amplifier that solves the problems of the prior art, such as power loss during no signal and the inability to obtain DC output with a single-ended type switching amplifier circuit. It provides a circuit.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides that the input signal is
A PWM circuit that converts into M waves, first and second output switching transistors that are connected in series to a power source and are alternately turned on and off by the PWM waves, and a coil and a capacitor, and the first and second In a single-end output PWM type switching power amplifier circuit equipped with a smoothing circuit that smoothes the output of an output switching transistor and supplies power to a load, the polarity of the input signal is detected and a detection signal corresponding to the polarity is output. a polarity detection circuit, a gate circuit that turns on and off the PWM wave supplied to the first and second output switching transistors based on the detection signal, and a current generated by energy remaining in the coil based on the detection signal. A commutation circuit that supplies the load to the load through the ground is provided.

(Function) According to the present invention, since the switching power amplifier circuit is configured as described above, the polarity detection circuit turns on and off the gate circuit according to the polarity of the input signal, and turns the gate circuit on and off. The operations of the first and second output switching transistors are regulated by. Furthermore, the commutation circuit works to supply current from the energy remaining in the coil to the load through the ground based on the detection signal, thereby suppressing unnecessary charging to the power supply side. This makes it possible to reduce power loss when there is no signal, and to perform DC amplification. Therefore, the above-mentioned problem can be eliminated.

(Example) Figure 1 shows a single-end output type P
FIG. 2 is a circuit diagram of a WM type switching power amplifier circuit.

This switching power amplifier circuit has an input terminal 40 for the input signal 3i.
A PWM circuit 50 that converts the input signal Si into a PWM wave 350 is connected to a polarity detection circuit 60 that detects the polarity of the input signal Si and outputs a detection signal S60 corresponding to the polarity of the input signal Si. The PWM circuit 50 includes, for example, a comparator 51 whose (+) side input terminal is connected to the input terminal 40, and a triangular wave generator 5 for generating a triangular wave 352 connected to the (-) side input terminal of this comparator 51.
2. Further, the polarity detection circuit 60 includes, for example, a comparator 61.

On the output side of the comparator 51, diodes 71, 72 and N
A gate circuit 70 consisting of PN transistors 73 and 74 is connected, and the output side of the gate circuit 70 is connected to a first terminal connected between power supplies +ycc and -vee. NPN transistor 8 which is the second output switching transistor
0 and the bases of the PNP transistor 81 are connected to each other. On the other hand, on the output side of the comparator 61, an NPN transistor 82 and a PNP transistor 8 for driving the gate circuit are connected.
3 bases are connected.

An output terminal 84 for the output signal SO is connected to each emitter of the NPN transistor 80 and the PNP transistor 81, and a commutation circuit 90 is connected to the output terminal 84 and the output side of the comparator 51.61. . Furthermore, a smoothing circuit 100 consisting of a coil 101 and a capacitor 102 is connected to the output terminal 84, and a load Rρ is connected in parallel with the coil 102. The commutation circuit 90 receives the detection signal 36
0, the current due to the energy remaining in the coil 101 is passed through the ground to the load R,l! This circuit supplies diodes 91, 92, 93°94, NPN transistors 95.97, and PNP transistors 96.98. The output side of the comparator 51 is connected to a diode 91.
The transistor 92 is connected to the bases of an NPN transistor 95 and a PNP transistor 96 . The output side of the comparator 61 is connected to the bases of an NPN transistor 97 and a PNP transistor 98, and the collectors of the NPN transistor 97 and PNP transistor 98 are connected to the NPN transistor 97 and the PNP transistor 98, respectively.
It is connected to the bases of an N transistor 95 and a PNP transistor 96, respectively. NPN transistor 9
The collector of the PNP transistor 96 is connected to the output terminal 84 via the diode 93, and the collector of the PNP transistor 96 is connected to the output terminal 84 via the diode 94.

FIG. 4 is a signal waveform diagram of FIG. 1, and the operation of FIG. 1 will be explained with reference to this diagram.

First, when the input signal 3i is supplied to the input heir 40, the input signal 3i is compared with the triangular wave S52 in the comparator 51, the PWM signal S50 is output from the comparator 51, and the gate circuit 70 and the commutation circuit 90 given to. On the other hand, the polarity of the input signal 3i is determined by a comparator 61;
1 outputs a square wave detection signal S60 having the same polarity as the input signal 3i, and the detection signal S60 is applied to the bases of the NPN transistor 82 and the PNP transistor 83, and is also supplied to the commutation circuit 90.

When the detection signal S60 has positive polarity, the NPN transistor 8
2 is on and the PNP transistor 83 is off, so
PNP transistor 73 is on, NPN transistor 7
4 is off. When the PNP transistor 73 is turned on, the NPN transistor 80 is turned on and off by the PWM wave 850, and a pulse train of positive polarity appears on the output terminal 84. Conversely, when the detection signal S60 has negative polarity, NP
N transistor 82 and PNP transistor 73 are off, PNP transistor 83 and NPN transistor 74
turns on. When the NPN transistor 74 turns on,
The PNP transistor 81 is turned on and off by the PWM wave S50, and a negative pulse train appears on the output terminal 84.

When the detection signal S60 is zero, the transistors 82, 83 .
73 and 74 are all off and nothing appears at the output terminal 84.

In this way, unlike a normal PWM waveform, an output signal SO consisting only of a pulse train having the same polarity as the input signal S1 appears at the output terminal 84.
By smoothing with the coil 101 and the capacitor 102, the desired power is applied to the load R, l! can be supplied to

・Although FIG. 4 shows a sine wave input signal @Si, almost the same operating state will occur with a DC input.

Next, the operation of the energy commutation circuit 90 will be explained.

First, when a positive input signal S1 is applied, even if a positive pulse voltage is generated at the output terminal 84, the detection signal 360 turns on the NPN transistor 97, turns off the NPN transistor 95, and the diode 94 turns on. Since it is a bias, the commutation circuit 90 does not operate. When the voltage of the output signal So becomes zero due to PWM modulation, the PNP transistor 98 is turned off and the PNPI-transistor 96 is turned on, allowing commutation current to flow through the route of ground → PNP transistor 96 → diode 94 → coil 101. can. Even for negative input signal 3i voltage, coil 1
A commutating current can flow through the route 01→diode 93→NPN transistor 95→ground.

As described above, in this embodiment, when there is no signal, the output NPN transistor 80 and the PNP transistor 81
Since there is no switching, power loss can be reduced. Furthermore, since the commutation circuit 90 is provided, the power supply side is not charged more than necessary, and as a result, efficient DC amplification is possible despite the single-end output type power amplification circuit.

Note that the present invention is not limited to the illustrated embodiment, and various modifications are possible. Examples of such modifications include the following.

(a) The PWM circuit 50 may be configured with other circuits such as a sawtooth generator and a comparator.

(b) The polarity detection circuit 60 may be configured with other circuits such as an operational amplifier.

(C) Gate circuit 701 output transistor 80.
81, the commutation circuit 90, etc. may be configured with other transistors such as MOS transistors.

(Effects of the Invention) As described above in detail, according to the present invention, since the polarity detection circuit, the gate circuit, and the commutation circuit are provided, the output switching transistor does not operate when there is no signal, and thereby Power loss can be reduced. Furthermore, since the energy remaining in the coil in the commutation circuit is supplied to the load through the ground, unnecessary charging to the power supply side can be suppressed, thereby enabling efficient DC amplification.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a switching power amplifier circuit showing an embodiment of the present invention, FIGS. 2 and 3 are circuit diagrams of main parts of a conventional switching power amplifier circuit, and FIG. 4 is a signal waveform of FIG. 1. It is a diagram. 50...PWM circuit, 60...Polarity detection circuit, 70...Gate circuit, 80...
・NPN transistor, 81... PNP transistor, 90... Commutation circuit, 100...
・Smoothing circuit, Rg...Load. Applicant's agent Yasushi Kakimoto Conventional switching power amplifier circuit (Figure 2) Conventional switching power amplifier circuit Figure 3

Claims (1)

[Claims] A pulse width modulation circuit that converts an input signal into a pulse width modulated wave, and first and second output switching transistors that are connected in series to a power source and are alternately turned on and off by the pulse width modulated wave. and a smoothing circuit having a coil and a capacitor and smoothing the outputs of the first and second output switching transistors to supply power to a load, the switching power amplifier circuit comprising: detecting the polarity of the input signal; a polarity detection circuit that outputs a detection signal corresponding to the detection signal; a gate circuit that turns on and off the pulse width modulated wave supplied to the first and second output switching transistors based on the detection signal; A switching power amplifier circuit comprising: a commutation circuit that supplies current from energy remaining in the coil to the load through ground.