JP2000049543A - Power voltage boosting type amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an amplifire capable of being operated with low DC voltage and constituting a small and lightweight portable device by providing a boosting circuit for boosting DC voltage supplied from a DC power source to the DC voltage of the level required for the operation of a pulse width modulation type amplifier circuit, and supplying boosted DC voltage to the pulse width modulation type amplifier circuit. SOLUTION: A microphone 1 supplies a sound signal to a pulse width modulation-type amplifier circuit 5. The amplified sound signal is radiated from a speaker 3. Power voltage required for the operation of the pulse width modulation-type amplifier circuit 5 is supplied from a boosting circuit 6. A power source part 7 which is formed of the appropriate number of batteries and supplies voltage lower than voltage required for the operation of the pulse width modulation-type amplifier circuit 5 is connected to the boosting circuit 6. A control circuit 8 is connected to the power source part 7 for holding the fluctuation of the output voltage of the power source part 7 to be constant. The deterioration of efficiency by the installation of the boosting circuit 6 is compensated by the efficient pulse width modulation-type amplifier circuit 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a power supply voltage step-up amplifier suitable for a portable device such as a portable loudspeaker.

[0002]

2. Description of the Related Art FIG. 4 schematically shows the structure of a known portable loudspeaker. This loudspeaker includes a microphone 1, an amplifier circuit 2 connected to the microphone for amplifying audio from the microphone 1, and a speaker 3 for outputting the audio amplified by the amplifier circuit. For example, in the case of a megaphone circuit having an output of 6 watts, when an AB class amplifier circuit is used as the amplifier circuit 2, 1.5 volts is supplied to supply 12 volts, which is a power supply voltage required to operate the amplifier circuit 2. It is necessary to use one of the eight single dry batteries 4 connected in series.

However, as many as eight single-cell batteries connected in series are not only bulky but also have a considerable weight, so that in portable devices such as portable loudspeakers which emphasize ease of use, It has long been strongly desired to reduce the size of the power supply unit and the weight of the device. It is easiest to reduce the number of dry batteries for size and weight reduction.However, simply reducing the number of dry batteries only reduces the supply voltage value that can be supplied, and the required operation of the amplifier circuit is reduced. Can not be done. However, if a DC-DC converter is used to boost the lowered power supply voltage, DC
-The loss of the DC converter itself is added, resulting in a decrease in the efficiency of the entire device, and a problem that the life of the dry battery is rather shortened occurs.

[0004]

SUMMARY OF THE INVENTION The present invention has been proposed in order to solve the above-mentioned problems, and constitutes a small and lightweight portable device which can operate at a low DC voltage. It is an object of the present invention to provide an amplifier that can perform such an operation.

[0005]

In order to achieve the above object, the present invention provides a pulse width modulation type amplifier circuit for amplifying an audio signal and a DC voltage supplied from a DC power supply. A booster circuit for boosting the DC voltage to a level necessary for the operation of the circuit and supplying the boosted DC voltage to the pulse width modulation type amplifier circuit. I do.

[0006] In one embodiment of the present invention,
The pulse width modulation type amplifier circuit compares the amplitude of the audio signal supplied from the input terminal with the amplitude of the triangular wave signal supplied from the triangular wave generation circuit, and the amplitude of the triangular wave signal is larger than the amplitude of the audio signal. A comparator is provided that outputs a series of pulses having a duration corresponding to the period. Also,
The booster circuit receives a pulse width modulation type DC-DC converter that boosts a DC voltage from the DC power supply, an output voltage of the pulse width modulation type DC-DC converter, and a triangular wave signal from the triangular wave generation circuit. And a control circuit for keeping the output voltage constant.

[0007]

The booster circuit boosts the voltage from the DC power supply to a voltage required for the operation of the pulse width modulation type amplifier circuit and supplies the boosted voltage. The drop in efficiency due to the provision of a booster circuit
It is compensated by an efficient pulse width modulation type amplifier circuit.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a power supply voltage boosting type amplifier according to the present invention will be described below with reference to FIG. In FIG. 1, a microphone 1 supplies an audio signal to a pulse width modulation type amplifier circuit 5, and the audio signal amplified by the pulse width modulation type amplifier circuit 5 is output from a speaker 3. The power supply voltage required for the operation of the pulse width modulation type amplifier circuit 5 is supplied from the booster circuit 6, and the booster circuit 6 is composed of an appropriate number of dry cells 4 and has the pulse width modulation type amplifier circuit 5.
Power supply unit 7 that supplies a voltage lower than the voltage required for the operation of
Is connected. A control circuit 8 is connected to the power supply 7 in order to keep the fluctuation of the output voltage of the power supply 7 constant.

FIG. 2A shows an example of the circuit configuration of the pulse width modulation type amplifier circuit 5, and the operation thereof will be described with reference to FIG. As shown in FIG. 2A, the pulse width modulation type amplifier circuit 5 is a circuit in which a modulation circuit 51, a driver 52, and a low-pass filter 53 are connected in this order. The modulation circuit 51 outputs the audio signal Vin supplied from the microphone 1
And a triangular wave signal T supplied from a triangular wave generating circuit (not shown), and a series of pulses having a duration corresponding to a period in which the amplitude of the triangular wave signal T is larger than the amplitude of the audio signal Vin. 2 (B in FIG. 2). That is, the modulation circuit 51 outputs the pulse train P that has been subjected to pulse width modulation in accordance with the input audio signal Vin.
Is output. This pulse train P is amplified by the push-pull type amplifier circuit of the driver 52, and then the low-pass filter 53
Removes high frequency components. As a result, a low-frequency signal Vout having an amplitude corresponding to the duration of each pulse in the pulse train P is output from the low-pass filter 53 and supplied to the speaker 3, as shown in FIG.

In a conventional amplifier circuit, a driving transistor is connected in series with a speaker, and an audio signal is output from the speaker by changing a resistance component of the driving transistor. Power is consumed. For example, in a class B amplifier circuit, the efficiency at the maximum output is only about 78%. On the other hand, in the pulse width modulation type amplifier circuit 5 shown in FIGS. 1 and 2, the input audio signal is converted into a pulse width modulated pulse train, and this pulse train is amplified. The transistors in the transistor 52 need only be turned on and off substantially, and it is sufficient to switch only between resistance zero and resistance infinity. Therefore, in principle, power is not consumed by the driver 52 and the efficiency is improved. 100%.

FIG. 3 is a circuit diagram showing an example of the configuration of the booster circuit 6, the power supply unit 7, and the control circuit 8, and constitutes a pulse width modulation type DC-DC converter as a whole. Power supply unit 7
Is a DC power supply 71, the positive potential side of which is connected to the drain of the switching transistor 62 and the anode of the diode 63 via the coil 61 of the booster circuit 6, and the cathode of the diode 63 is connected to the high potential side of the capacitor 64 and the output. Connected to terminal 65. The voltage vout at the output terminal 65 is supplied to the pulse width modulation type amplifier circuit 5 and is also divided by a resistance voltage divider and applied to one input terminal of a comparator 81 of the control circuit 8 as a voltage vin. A reference triangular wave signal is applied to the other input of the comparator 81, and the output of the comparator 81 is applied to the gate of the switching transistor 62.

Note that a reference triangular wave signal may be supplied to the comparator 81 from a triangular wave generating circuit that supplies a triangular wave signal to the comparator 54 in FIG.

The comparator 81 compares the amplitude of the voltage vin with the amplitude of the reference triangular wave signal, and outputs a series of pulses having a duration corresponding to a period in which the amplitude of the reference triangular wave signal is larger than the voltage vin, to output the switching transistor 62. Is turned on and off. When the switching transistor 62 is on, current flows from the DC power supply 71 to the ground through the coil 61, and energy is stored in the coil 61. Then
When the switching transistor 62 is turned off, the diode 63 is turned on, and the capacitor 64 is connected to the DC power supply 71.
And a voltage equal to the sum of the voltage appearing at the coil 61.

Therefore, voltage vou at output terminal 65
When t increases, the duration of the pulse output from the comparator 81 decreases, so that the switching transistor 62
Is turned on, the voltage vout and therefore the voltage vin decrease. Conversely, when the voltage vout decreases, the duration of the pulse output from the comparator 81 increases, and the ON period of the switching transistor 62 also increases, so that the voltage vout increases. Thus, the voltage vout output from the booster circuit 6 is kept constant.

For example, in a conventional portable loudspeaker, eight dry cells are connected in series to supply a power supply voltage. In an amplifier manufactured according to the present invention, four dry cells are used. The same output can be obtained by connecting in series. Thus, to get the same output,
According to the present invention, it can be seen that the number of dry batteries can be reduced.

[0016]

As described above, the present invention has been described in detail based on the embodiments thereof. As is apparent from the above description, the present invention realizes a portable amplifier having the same output as a conventional portable amplifier. The DC power supply voltage may be lower than that of the amplifier, and therefore, when the DC power supply voltage is obtained from dry cells, the number of dry cells used can be reduced. Play. In addition, since an efficient circuit such as a pulse width modulation type amplifier circuit is used, it is possible to compensate for a decrease in efficiency in the booster circuit.

A pulse width modulation type DC-DC as a booster circuit
When the converter is used, the booster circuit and the pulse width modulation type amplifier circuit can share the triangular wave generator, so not only can the circuit be simplified, but also because the reference oscillation frequency is single, The effect that noise countermeasures such as unnecessary radiation can be easily achieved can be achieved.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically showing a configuration of a power supply voltage step-up amplifier according to the present invention.

2A is a circuit diagram showing an example of the configuration of the pulse width modulation type amplifier circuit in FIG. 1, and FIG. 2B is a waveform diagram for explaining its operation.

FIG. 3 is a circuit diagram illustrating an example of a configuration of a booster circuit, a power supply unit, and a control circuit in FIG. 1;

FIG. 4 is a block diagram showing a configuration of a conventional portable loudspeaker.

[Explanation of symbols]

1: microphone, 3: speaker, 5: pulse width modulation type amplifier circuit, 6: booster circuit, 7: power supply section, 8: control circuit, 51: modulation circuit, 52: driver, 53:
Low-pass filter, 54, 81: comparator

Continued on the front page F term (reference) 5J091 AA02 AA26 CA37 CA92 FA03 FA20 HA09 HA19 HA25 HA29 HA33 HA39 KA00 KA17 KA19 KA24 KA42 KA53 KA62 KA64 TA01 TA06 UW01 5J092 AA02 AA26 CA37 CA92 FA03 FA20 GR01 HA09 HA19 HA19 HA19 HA19 HA19 KA24 KA42 KA53 KA62 KA64 TA01 TA06

Claims (3)

[Claims] 1. A pulse width modulation type amplifier circuit for amplifying an audio signal, and a DC voltage supplied from a DC power supply is boosted to a DC voltage required to operate the pulse width modulation type amplifier circuit. And a booster circuit for supplying the obtained DC voltage to the pulse width modulation type amplifier circuit. 2. The pulse width modulation type amplifier circuit compares the amplitude of an audio signal supplied from an input terminal with the amplitude of a triangular wave signal supplied from a triangular wave generation circuit, and the amplitude of the triangular wave signal is larger than the amplitude of the audio signal. 2. The amplifier of claim 1 further comprising a comparator that outputs a series of pulses having a duration corresponding to a period greater than the amplitude of the pulse. 3. A pulse width modulation type DC-DC converter, wherein the boosting circuit boosts a DC voltage from the DC power supply, an output voltage of the pulse width modulation type DC-DC converter, and a triangular wave signal from the triangular wave generating circuit. 3. The amplifier according to claim 2, further comprising: a control circuit for receiving the output voltage and keeping the output voltage constant.