JPH0341281Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a power amplifier circuit for a tape recorder that is suitable for being integrated into an integrated circuit.

BACKGROUND ART AND PROBLEMS Conventionally, a power amplification circuit for a tape recorder as shown in FIG. 1 has been proposed. That is, in this FIG. 1, 1 indicates an audio signal input terminal to which an audio signal from a microphone or the like is supplied, and the audio signal obtained from this audio signal input terminal 1 is supplied to amplifier circuits 2 and 3 for driving speakers, respectively. be done.
These speaker driving amplifier circuits 2 and 3 each have two power transistors connected in parallel to the output terminal and in series to the power supply, so that they operate in a push-pull manner. This amplifier circuit 2
Terminals 4 and 5 for speaker connection are led out from the output terminals of and 3, respectively, and a speaker 6 is connected between these terminals 4 and 5. In this case, these amplifier circuits 2 and 3 are connected in a so-called balanced transformerless (BTL) manner and driven in opposite phases to each other, and directly drive the speaker 6. Further, the audio signal obtained at the audio signal input terminal 1 is transmitted to an amplifier circuit 7 for driving the earphone.
A terminal 8 for connecting an earphone jack is led out from the output terminal of this amplifier circuit 7, and this terminal 8 is connected to a movable terminal 9a of an earphone jack 9. It is grounded through a series circuit of a resistor 10 and a capacitor 11. Reference numerals 12 and 13 indicate switching NPN type transistors connected between the ground terminals of the amplifier circuits 2 and 3 and the ground, respectively. In this case, the ground terminals of amplifier circuits 2 and 3 are connected to transistor 1.
The emitters of transistors 12 and 13 are grounded. 1
Reference numeral 4 denotes a read signal supply terminal, to which a read signal indicating whether or not the tape recorder is in a recording state is supplied with a low level signal "0" and a high level signal "1". This read signal input terminal 14 is connected to the transistors 12 and 1.
3 to each base. 15 is a detection circuit for detecting the state of the earphone jack 9; an input terminal of this detection circuit 15 is connected to a normally closed contact 9c for a movable terminal 9a of the earphone jack 9 via a terminal 16; The output terminals of are connected to the bases of transistors 12 and 13, respectively. In this case, the detection circuit 15 detects whether a DC potential is obtained at the terminal 16 depending on whether the earphone plug is inserted into the earphone jack 9,
When the plug is inserted, a low level signal "0" is generated at the output terminal, and when the plug is not inserted, the output terminal becomes high impedance.

In the power amplifier circuit of the tape recorder constructed in this way, the amplifier circuits 2, 3, and 7 are driven during reproduction, and reproduced sound is obtained from the speaker 6. When the earphone plug is inserted into the earphone jack 9 in this state, the detection circuit 15 turns off the transistors 12 and 13, respectively, and the amplifier circuits 2 and 3 become inactive, and the audio signal input terminal 1 The obtained audio signal is power-amplified in the amplifier circuit 7, and this power-amplified audio signal is reproduced by the earphone via the earphone jack 9 to obtain reproduced sound.

Also, during recording, transistor 1 is activated by the rec signal.
2 and 13 are respectively cut off, and the amplifier circuit 2
and 3 are rendered inactive, and the audio signal to be recorded is amplified by the amplifier circuit 7 and provided to the earphone jack 9. By inserting an earphone plug into this jack 9, the recorded audio signal can be monitored.

By the way, in the conventional power amplifier circuit of a tape recorder as shown in FIG. 1, two amplifier circuits 2 and 3 connected to the BTL for driving a speaker are
and an amplifier circuit 7 for driving the earphones were separately required. Furthermore, when attempting to integrate the power amplification circuit shown in FIG. and were needed separately.

Purpose of the invention In view of the above, an object of the present invention is to provide an earphone drive device that does not require a separate amplifier circuit for driving the earphones and has a relatively small number of terminal pins when integrated into an integrated circuit.

Summary of the invention This invention provides a first and a second drive unit driven in opposite phases to each other.
an amplifier circuit, the output terminal of the first amplifier circuit is connected to a movable contact, the fixed contact is grounded in an alternating current manner, and the normally closed contact is connected to the output terminal of the second amplifier circuit via a speaker. an external output jack of the terminal, a detection circuit that detects insertion of an external output plug into the external output jack by a change in the output impedance of the second amplifier circuit, and a first and second amplifier circuit that disables the amplifier circuit during recording. The first and second amplifier circuits constitute a BTL circuit to drive the speakers during playback, and an external output plug is inserted into the external output jack during recording. This is a power amplification circuit for a tape recorder, in which the first switching element is rendered inactive by the output signal of the detection circuit, and the output signal of the first amplification circuit is supplied to an external output jack, and the tape recorder according to the present invention According to the power amplification circuit of the recorder, there is no need for a separate amplification circuit for driving the earphones, and it is possible to obtain an integrated circuit with a relatively small number of terminal pins.

Embodiment Hereinafter, an embodiment of the power amplifier circuit of the tape recorder of the present invention will be described with reference to FIG. In FIG. 2, parts corresponding to those in FIG. 1 are given the same reference numerals, and detailed explanation thereof will be omitted.

In FIG. 2, 2' indicates a preamplifier circuit whose input terminal is connected to the audio signal input terminal 1, and the output signal from this preamplifier circuit 2' is supplied to the power amplification circuit 2, and the power amplification circuit 2' is connected to the audio signal input terminal 1. The output signal from circuit 2 is supplied to terminal 4. 3' indicates a preamplifier circuit whose input terminal is connected to the audio signal input terminal 1 and operates in opposite phase to the preamplifier circuit 2', and the output signal from this preamplifier circuit 3' is sent to the power amplifier circuit. 3, and the output signal from this power amplifier circuit 3 is connected to terminal 5.
supply to.

Here, the power amplifier circuit 3 will be further explained with reference to FIG. This power amplifier circuit 3 includes a differential amplifier circuit in which a pair of transistors 3a and 3b are differentially connected, and two complementary and symmetrical transistors 3c,
It consists of a so-called complementary push-pull circuit consisting of transistors 3c and 3d.
The output terminal 3e is derived from the connection point _of
It is connected to the base of transistor 3b via a 30KΩ resistor 3f. 3g is this power amplifier circuit 3
This is the power supply terminal to which voltage 1/2・Vcc equal to the center potential of is supplied, and this power supply terminal 3g has the resistance value
R _B is connected to the respective bases of transistors 3a and 3b via resistors 3h and 3i of, for example, 1KΩ. 3j is a differentially connected transistor 3a,
This is a constant current source circuit provided between the common connection point of the emitters 3b and ground. This constant current source circuit 3
j is controlled by a transistor 13 connected to this power amplifier circuit 3. When the power amplifier circuit 3 constructed in this manner is in an operating state by activating the constant current source circuit 3j, its output impedance R _P is relatively small, approximately zero.
Further, when the constant current source circuit 3j is in an inoperative state by being cut off, its output impedance R _P is equal to the feedback resistor 3f.
The sum (R _NF +R _B ) of the resistance value R _NF of the resistor 3h and the resistance value R _B of the resistor 3h is relatively large. or,
Power amplifier circuit 2 is configured similarly to power amplifier circuit 3. In this power amplifier circuit 2, the constant current source circuit is always in an active state.

Incidentally, the power amplifier circuits 2 and 3 are connected to terminals 4 and 5 in a BTL manner. In this example, the terminal 4 is connected to the movable terminal 9a of the earphone jack 9, and the normally closed contact 9c for the movable terminal 9a is connected to the terminal 5 via the speaker 6.

On the other hand, the read signal input terminal 14 is connected to the resistor 17a.
is connected to the base of an NPN type transistor 18a for receiver output, and the emitter of this transistor 18a is grounded.
The collector of 8a is connected to a current terminal 19a to which a constant current _I1 is supplied, and this current terminal 19a is connected to the base of an NPN type transistor 12 for switching connected to the preamplifier circuit 2', and a diode 20a. ground through the anode and cathode of the Reference numeral 21 indicates a constant current source of the power amplifier circuit 2. In addition, the read signal input terminal 14 is connected to the resistor 17b.
The emitter of this transistor 18b is grounded, and the transistor 1
8b is connected to a power supply terminal 19b to which a constant current _I2 is supplied, and this power supply terminal 19b is connected to NPN type transistors 13' and 13 for switching which are connected to the preamplifier circuit 3' and the power amplification circuit 3.
are connected to the bases of the diodes 20b and 20b.
ground through the anode and cathode of the

On the other hand, the resistance value of terminal 5 as a bleeder resistor
Resistor 22 with R ₁ e.g. 100Ω and R ₂ e.g. 1KΩ
and 23 are connected to the ground through a series circuit, the connection point of these resistors 22 and 23 is connected to the base of an NPN type transistor 24, the emitter of this transistor 24 is grounded, and the collector of this transistor 24 is connected to a resistor 25. The connection point between the collector of this transistor 24 and the resistor 25 is connected to the power supply terminal 26 to which DC power is supplied through the resistor 27.
The emitter of this transistor 28 is grounded, and the collector of this transistor 28 is connected to the connection point between the resistor 17a and the base of the transistor 18a. In this example, when the tape recorder is in the recording state, the rec signal is a high level signal "1", and when the tape recorder is in the playback state, the rec signal is a low level signal "0", and the other configuration is the same as the conventional one. do.

The operation of the power amplifier circuit of the tape recorder constructed in this way will be explained.

During recording, the REC signal supplied to the REC signal input terminal 14 causes the transistor 18b to
is turned on, which causes transistor 13'
and 13 are turned off, and the preamplifier circuit 3'
and the power amplifier circuit 3 are rendered inactive. At this time, the center potential 1/2·Vcc of the power amplifier circuit 2 is obtained at the terminal 5 via the terminal 4 and the jack 9. This voltage is divided by the relatively small output impedance R _P (≒0) of the power amplifier circuit 2 and the resistors 22 and 23, and the transistor 24
is turned on and transistor 28 is turned off. For this reason, transistor 1 is
8a is turned on, and transistor 18a is turned on, thereby turning off transistor 12 and rendering preamplifier circuit 2' inoperative. Therefore, the power amplifier circuit 2 is in an operating state, the preamplifier circuits 2', 3', and the power amplifier circuit 3 are in an inoperative state, and the speaker 6 is not driven and the earphone jack 9 receives a power-amplified audio signal. is not obtained.

In this recording state, the earphone jack 9
When the plug is inserted into the earphone and the earphone is connected, the normally closed contact 9c of the earphone jack 9 is placed in an electrically floating state. Then, the center potential 1/2·Vcc is obtained from the power amplifier circuit 3 at the terminal 5. This voltage is divided by the resistors 22 and 23, but the output impedance of the power amplifier circuit 3
Since R _P (=R _NF +R _B ) is relatively large, transistor 24 is turned off, which turns transistor 28 on. For this reason, the read signal is absorbed by the transistor 28 and the transistor 18a
is turned off, transistor 12 is turned on, and preamplifier circuit 2' is put into operation. Therefore, when the earphone plug is inserted into the earphone jack 9 during recording, the preamplifier circuit 2' and the power amplifier circuit 2 are in the operating state, and the preamplifier circuit 3' and the power amplifier circuit 3 are in the disabled state. It is in the operating state, the speaker 6 is not driven, and a power amplified audio signal is provided to the earphone jack 9.

Further, during reproduction, transistors 18a and 18b are turned off by a read signal indicating the reproduction state, and transistors 12, 13' and 1 are turned off.
3 are respectively turned on, the preamplifier circuits 2' and 3' and the power amplifier circuits 2 and 3 are respectively put into operation, and the speaker 6 is directly driven by the power amplifier circuits 2 and 3 connected by BTL. Then, by inserting the earphone plug into the earphone jack 9 in this state, the speaker 6 is made inactive, and the audio signal can be monitored from the earphone.
Note that in this case, transistors 24 and 28 are turned on and off, respectively.

As described above, according to the power amplifier circuit of the tape recorder of this example, since the two power amplifier circuits 2 and 3 connected by BTL can drive the speaker 6 or the earphone, the dedicated power for driving the earphone is used. There is an advantage that an amplifier circuit is not required and the configuration can be simplified accordingly. Moreover, the power amplifier circuit 2,
Since the speaker 6 and the earphone can be driven by simply deriving the two terminals 4 and 5 from 3, the number of terminals can be reduced when integrated circuitry is achieved, resulting in better productivity and lower cost. be able to.

It goes without saying that the present invention is not limited to the above-described embodiments, and can take various other configurations without departing from the gist of the present invention.

Effects of the invention The power amplifier circuit of the tape recorder of the invention does not require a dedicated power amplifier circuit for driving earphones, which simplifies the configuration and reduces the number of terminals when integrated. There is an advantage in that the product can be manufactured at a higher productivity and at a lower price.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a power amplifier circuit of a conventional tape recorder, FIG. 2 is a block diagram showing an example of a power amplifier circuit of a tape recorder according to the present invention, and FIG.
The figure is a circuit diagram for explaining the power amplifier circuit. 2 and 3 are power amplifier circuits, 2' and 3' are preamplifier circuits, 4 and 5 are terminals, 6 is a speaker, 9 is an earphone jack, 12, 13, 1
3', 18a and 18b are transistors, respectively.

Claims (1)

[Scope of utility model registration request] First and second amplifier circuits are driven in opposite phases to each other, and the output terminal of the first amplifier circuit is connected to a movable contact, the fixed contact is grounded in an alternating current manner, and the normally closed contact is connected to the above through a speaker. A three-terminal external output jack connected to the output terminal of the second amplifier circuit, and a detection circuit that detects insertion of an external output plug into the external output jack by a change in the output impedance of the second amplifier circuit. and first and second switching elements that disable the first and second amplification circuits during recording, and the first and second amplification circuits constitute a BTL circuit during reproduction. In addition to driving the speaker, when the external output plug is inserted into the external output jack during recording, the first switching element is made inoperable by the output signal of the detection circuit, and the first switching element is inactivated. A power amplifier circuit for a tape recorder, characterized in that the output signal of the circuit is supplied to the external output jack.