JPH0785529B2 - Amplifier circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] This invention is a complementary type SEPP (single ended p).
The present invention relates to an amplifier circuit that prevents abnormal operation when the power supply voltage of a push-pull circuit or the like is drastically reduced.

[Conventional technology]

FIG. 2 shows an amplifier circuit using a general complementary SEPP circuit.

This amplifying circuit adds an input signal from the signal source 2 to the differential amplifier 4 on the preceding stage side and amplifies it, and then applies its output to the SEPP circuit 8 through the drive circuit 6 to amplify it. Taken out.

[Problems to be solved by the invention]

In such an amplifier circuit, the power supply voltage V _CC drastically decreases during normal amplification operation due to a sudden increase in load or interruption of the power switch, and the voltage value is a bias circuit composed of resistors 12, 14 and capacitor 16. When the bias voltage becomes less than the bias voltage V _B set by 18, the transistors 20, 22, 24, 26 of the differential amplifier 4 shift to non-conducting, and the transistor 28 and the diodes 30, 32 of the drive circuit 6 also become non-conducting. Then, the transistor 34 on the high potential side of the SEPP circuit 8 becomes non-conductive. Originally, in a normal amplification operation, the transistor 34 becomes conductive in the positive half cycle and the transistor 44 becomes conductive in the negative half _{cycle.However} , due to the decrease in the power supply voltage V _CC , the transistor 34 is turned off and the transistor 44 is turned on. It becomes abnormal operation.

At this time, transistors 36, 38, 40 and resistors forming a constant current source for flowing a current through the differential amplifier 4 and the drive circuit 6
Since the operation of 42 is maintained irrespective of the bias voltage V _B set by the bias circuit 18, SEPP is responded to in response to this operation.
The transistor 44 on the low potential side of the circuit 8 becomes conductive.
That is, since the transistor 34 is turned off,
Since the transistor 44 draws a current from the side of the capacitor 46, an abnormal sound (pop sound) is generated in the reproduced sound of the speaker 10 due to the drawing of the current.

Therefore, the present invention prevents generation of a pop sound due to an abnormal operation due to a sudden change in the power supply voltage in such an amplifier circuit.

[Means for solving problems]

In the amplifier circuit of the present invention, as illustrated in FIG. 1, the first transistor (34) is placed on the high potential side and the second transistor (44) is placed on the low potential side between the power supply voltage point and the ground point. Connected in series with each other, and a load (eg, at the connection point of these first and second transistors) (eg,
An amplifier circuit configured with a SEPP circuit (8) for connecting a speaker (10), comprising a resistor voltage dividing circuit (resistors 12, 14) for dividing a power supply voltage, and a second capacitor (16) for providing a bias voltage. A bias circuit (18) for generating a constant DC voltage, and a first current mirror circuit (transistors 36, 38, 40) for flowing a current to the base side of the first and second transistors of the SEPP circuit, Installed in the previous stage of the SEPP circuit, transistor differential pair (transistors 20, 22)
And an operating current is supplied to the transistor differential pair by the first
The current mirror circuit, the input signal from the signal source (2) is applied to the base of one transistor of the transistor pair, and the bias voltage is applied from the bias circuit to amplify the input signal from the signal source, A differential amplifier (4) that applies its output to the SEPP circuit and the DC voltage set by the bias circuit are added as a drive voltage, and a DC voltage obtained by dividing the power supply voltage is applied to the base side. And a third transistor (50) that conducts when the power supply voltage is reduced to a value obtained by adding the base-emitter voltage to the bias voltage generated by the bias circuit, and the third transistor (50) By receiving the current when conducting and drawing this current from the first current mirror circuit, the operation of the differential amplifier and the SEPP circuit is performed. And a second current mirror circuit (60) for stopping.

[Action]

With this configuration, the power supply voltage V _CC is reduced so that the high potential side transistor 34 of the transistors 34 and 44 forming the SEPP circuit 8 is cut off and the low potential side transistor 44 is turned on. When the voltage value shifts to a voltage value that is the bias voltage plus the base-emitter voltage of the transistor (50), the operation of the transistor 44 on the low potential side can be stopped to prevent the generation of abnormal sound. .

〔Example〕

 FIG. 1 shows an embodiment of the amplifier circuit of the present invention.

In this amplifier circuit, the first transistor 34 is connected in series between the power supply voltage point and the ground point with the high potential side and the second transistor 44 on the low potential side, and these first and second transistors 34 are connected in series. , 44 connected to the speaker 10 as a load via the first capacitor 46. A differential amplifier 4 is installed in the preceding stage of the SEPP circuit 8, and this differential amplifier includes a transistor differential pair composed of transistors 20 and 22. A first current mirror circuit is constituted by transistors 36, 38 and 40 and a resistor 42 as a means for supplying a current to the emitter side of the transistor differential pair and the base sides of the transistors 34 and 44.

In this amplifier circuit, the bias circuit 18 includes a resistance ratio of the resistors 12 and 14 and a second capacitor which form a resistance division circuit.
16 by setting the bias voltage V _B, but the bias voltage V _B is set to, for example, the value of V _CC / 2.

Meanwhile, the power supply voltage V _CC varies, the base potential of the transistor 34 transitions from the on state to the off state, since its output DC potential is the bias voltage V _B, the high potential side to the bias voltage V _B transistor 34 plus emitter-base voltage V _F Given in. With this DC potential, the transistor 44 on the low potential side satisfies the operating condition and maintains the conductive state.

Therefore, the operation stop circuit 48 detects that the power supply voltage V _CC is reduced and the value thereof is reduced to the voltage V _B + V _F or less, and the operation of the transistor 44 on the low potential side is forced based on the detection. It is installed to stop the amplification operation.

This operation stop circuit 48 includes bias voltage V _B and power supply voltage.
A third transistor 50 is provided as a comparison means for comparing with the reduced value of V _CC , and the transistor 50 has a bias voltage V _B from the capacitor 16 via the resistor 52 to the emitter, and diodes 54 and 56 and a resistor 58 to the base. Through the power supply voltage V
Voltage V _CC -2 V _F of the value obtained by subtracting the forward voltage 2V _F from _CC diodes 54 and 56 are added.

That is, the power supply voltage V _CC changes abruptly due to a sudden increase in load or interruption of the power switch, and its value is V _CC '(V _CC ′
_When it shifts to _CC ), its base potential becomes V _CC ′ −2V _F. At this time, the capacitor 16 maintains the normal bias voltage V _B against the sudden change in the power supply voltage V _CC , so that the transistor 50 must be in the forward direction between its emitter potential and base potential in order to be conductive. Voltage V _{F It} is sufficient if there is an abnormal voltage difference. Therefore, as the conduction condition, Is established. From this equation (2), the power supply voltage after fluctuation
V _CC ′ is Then, when the power supply voltage V _CC shifts below this value, the transistor 50 becomes conductive.

When the transistor 50 is turned on, the transistor 50
A current I flowing therethrough flows into the transistor 62 of the second current mirror circuit 60, and a similar current I is drawn into the transistor 64 from the collector side of the transistor 36 by the current mirror effect.

Therefore, the operation stop circuit 48 operates and the transistor 64
Is conducted, the operation of the transistor 36 is stopped and the operation of the transistor 40 is stopped, so that the base current of the transistor 44 on the low potential side of the SEPP circuit 8 is cut off and the operation of the transistor 44 is stopped. That is, when the power supply voltage V _CC becomes V _B + V _F or less, the operation of the transistor 34 is stopped, and the operation of the operation stop circuit 48 stops the operation of the transistor 44 and also stops all the amplification operations of the amplifier circuit. The generation of an abnormal sound (pop sound) due to an abnormal operation in which only the transistor 44 selectively operates is prevented.

〔The invention's effect〕

As described above, according to the present invention, in the amplifier circuit configured by the SEPP circuit, the operation of the SEPP circuit and the differential amplifier can be stopped when the power supply voltage sharply decreases, and the power supply voltage decreases. It is possible to prevent an abnormal sound from being generated due to an abnormal operation at the time, and to prevent the abnormal sound from being generated with a simple configuration.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an amplifier circuit of the present invention, and FIG. 2 is a circuit diagram showing a conventional amplifier circuit. 2 ... Signal source 4 ... Differential amplifier 8 ... SEPP circuit 10 ... Speaker (load) 12,14 ... Resistance (resistor voltage divider circuit) 16 ... Second capacitor 20,22 ... Transistor (transistor) Differential pair) 34 ... first transistor 36, 38, 40 ... transistor (first current mirror circuit) 44 ... second transistor 46 ... first capacitor 50 ... third transistor 60 ... ... Second current mirror circuit

Claims (1)

[Claims] 1. A first transistor is connected in series between a power supply voltage point and a ground point with the high potential side and the second transistor being a low potential side, and the connection point of these first and second transistors is connected. SEPP connecting the load to the first capacitor via the first capacitor
A bias circuit for generating a constant direct current voltage as a bias voltage, comprising: a resistance divider circuit for dividing a power supply voltage and a second capacitor; and a first bias circuit for the SEPP circuit. And a first current mirror circuit that allows a current to flow to the base side of the second transistor, and a transistor differential pair that is installed in the preceding stage of the SEPP circuit, and the operating current is supplied to the transistor differential pair as the first current. A mirror circuit is used to apply an input signal from a signal source to the base of one of the transistors of the transistor pair, and the bias voltage is applied from the bias circuit to amplify the input signal from the signal source, the output of which is the SEPP. A differential amplifier to be added to the circuit, the DC voltage set by the bias circuit is added as a drive voltage, and A DC voltage obtained by dividing the power supply voltage is applied, and when the power supply voltage is reduced to a value obtained by adding the base-emitter voltage to the bias voltage generated by the bias circuit, the third conductive circuit is provided. A second current mirror circuit for stopping the operation of the differential amplifier and the SEPP circuit by receiving a current when the transistor and the third transistor are conductive and drawing this current from the first current mirror circuit. And an amplifier circuit characterized by including.