JPH0744399B2 - BTL connection push-pull amplifier - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a BTL-connected push-pull amplifier used for audio amplifiers and the like.

2. Description of the Related Art FIG. 2 shows a conventional BTL-connected push-pull amplifier. 1, 2 are input terminals, 3 and 4 are amplification circuit blocks before the output stage including the first stage, and 5 and 6 are output terminals. , 7, 8, 9, and 10 are output transistors, 11, 12, 13, and 14 are transistors for driving the output transistors, 15 is a power supply terminal, and 16 is a load resistor.

Problems to be Solved by the Invention In the push-pull amplifier connected in BTL with the above configuration, if the output terminals 5 and 6 are erroneously short-circuited (hereinafter, this state is referred to as a load short-circuit), the input signal is dealt with. hand,
Since a large current flows through each of the output transistors 7, 8, 9 and 10, there is a disadvantage that the output transistors 7, 8, 9 and 10 are easily destroyed when the load is short-circuited.

The present invention has been made to eliminate the above inconvenience, and an object of the present invention is to provide a BTL-connected push-pull amplifier having a novel configuration in which the output transistor is less likely to be destroyed even when the load is short-circuited. .

Means for Solving the Problems The present invention for solving the problems includes an amplifier circuit block before an output stage and a first-conductivity-type transistor having a base connected to an output terminal of the amplifier circuit block. A first-conductivity-type second transistor having a base connected to the emitter of the first transistor via a first resistor and an emitter connected to an output terminal; and an emitter of the first transistor and the output terminal Second, third, and fourth resistors connected in series between them, a collector connected to the base of the first transistor, and an emitter connected to the output terminal, and the second and third resistors A third transistor of one conductivity type whose base is connected to the connection point of, and a fourth transistor whose emitter is connected to the connection point of the third and fourth resistors and whose collector is connected to the output terminal. I had one push A push-pull amplifier and another push-pull amplifier having the same circuit configuration as the push-pull amplifier and outputting an output signal having a phase opposite to that of the push-pull amplifier. A first resistor including a fifth resistor connected between the base of the transistor and the output terminal of the other push-pull amplifier;
And a second series circuit of a sixth resistor and a plurality of diodes connected between the base of the fourth transistor of the other push-pull amplifier and the output terminal of the one push-pull amplifier. It is a BTL connection push-pull amplifier equipped with.

Operation With this configuration, it is possible to reduce the maximum value of the emitter current flowing through the output transistor when the load is short-circuited, and it is possible to realize a BTL-connected push-pull amplifier in which the output transistor is not easily destroyed.

Example 1 FIG. 1 shows an example of an STL-connected push-pull amplifier according to the present invention. In the figure, 1 and 2 are input terminals, and 3 and 4 are amplification circuit blocks before an output stage including an input stage. , 5,6 are output terminals, 7,8,9,10 are output transistors, 11,12,13,14 are transistors for driving output transistors 7,8,9,10 respectively, 15 is a power supply terminal, 16 is a load Resistors 17,18 are resistors for detecting the base current of output transistors 7,9, 19,20,21,2
2,23 and 24 are resistors connected in series between the emitters of the transistors 11 and 13 and the output terminals 5 and 6, respectively, 25 is a base at a connection point between the resistors 19 and 20, and an emitter is at the output terminal 5. A transistor whose collector is connected to the base of the transistor 11 respectively, 26 is a transistor whose base is connected to the connection point of the resistors 22 and 23, whose emitter is connected to the output terminal 6 and whose collector is connected to the base of the transistor 13 A transistor whose emitter is connected to the connection point of the resistors 20 and 21 and whose collector is connected to the output terminal 5,
The base of 27 is connected to the output terminal 6 via a resistor 28 and diodes 29, 30, 31. 32 is a resistor 23
Is a transistor whose collector is connected to the output terminal 6 and whose base is connected to the output terminal 5 via the resistor 33, the diodes 34, 35 and 36.
It is connected to the.

In the BTL-connected push-pull amplifier of FIG. 1 configured as described above, the base current of the transistor 11 that drives the output transistor 7 is drawn, and the connection between the resistors 19 and 20 when the transistor 25 having a protection function is turned on. The potential difference between the point and the output terminal 5 is
If the potential difference between the emitters is V _D , it is V _D (V). The potential difference between the emitter potential of the transistor 11 and the output terminal 5 at this time is the resistance value of the resistors 19, 20, and 21 is R, respectively.
₁₉ , R ₂₀ , R ₂₁ Becomes

At this time, the emitter current I _Q7 flowing in the output transistor 7 has a DC amplification factor h _{FE of} the output transistor 7 and a resistance value of the resistor 17 of R ₁₇ ,
When the potential difference between the base and emitter when V is ON is V _D , Becomes

Here, a potential difference is generated between the output terminals 5 and 6, and the base current of the transistor 27 changes to the resistor 28, the diodes 29, 30, 3
When it goes to the output terminal 6 after passing through 1, the resistor 28
By setting the resistance value of the transistor 27, the transistor 27 can be saturated. At this time, assuming that the saturation voltage of the transistor 27 is 0 (V), the maximum emitter current value I _Q7 that the output transistor 7 can flow at this time is the value obtained by substituting 0 for R ₂₁ of the equation (2). Is equivalent to Becomes

Here, in the equations (2) and (3), V _D = 0.7 (V), R ₁₇ =
Substituting 10 (Ω), R ₁₉ = R ₂₀ = R ₂₁ = 1000 (Ω), and h _FE = 99, I _Q7 = 3.5 (A) …… (4) I _Q7 = 7.0 (A)… … (5) This means that output terminal 5,
When 6 is short-circuited with low impedance,
A large potential difference does not occur between the output terminals 5 and 6, and as shown in the equation (4), the maximum value of the emitter current of the output transistor 7, that is, the current corresponding to the emitter current of the output transistor 10 is 3.5 (A). This value is obtained when driving a normal load resistor as a BTL-connected push-pull amplifier, that is, when the output transistor carries a large current and the potential difference between the output terminals is large, The current value that the output transistor 7 can pass is smaller than 7.0 (A) shown in the equation (5), and the circuit element 17,
The circuit part consisting of 19,20,21,25,27,28,29,30,31 is
It can be seen that the output transistors 7 and 10 are protected when the load is short-circuited.

In addition, the circuit element 18,22,23,24,2
It can be seen that the circuit portion composed of 6,32,33,34,35,36 protects the output transistors 9 and 8 when the load is short-circuited.

As described above, according to the present invention, when the load resistance is normal, a sufficiently large current can be supplied according to the input signal, but an abnormal resistance component such as a load short circuit occurs. When a small load has to be driven, the maximum current value that can be supplied by the output transistor is small, and it is possible to realize a BTL-connected push-pull amplifier that is not easily destroyed even when the load is short-circuited. Great value.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a BTL connection push-pull amplifier according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional BTL connection push-pull amplifier. 1,2 …… Input terminals, 3,4 …… Amplifier circuit block before the output stage including the input stage, 5,6 …… Output terminals, 7,8,9,10 …… Output transistors, 11,12,13 , 14 …… Drive transistor, 15
...... Power supply terminal, 16 ...... Load resistance, 17,18,19,20,21,22,2
3,24,28,33 …… Resistors, 25,26,27,32 …… Transistors, 29,30,31,34,35,36 …… Diodes.

Claims (1)

[Claims] 1. An amplifier circuit block before an output stage, a first-conductivity-type transistor having a base connected to an output terminal of the amplifier circuit block, and a first resistor at the emitter of the first transistor. A second transistor of one conductivity type whose base is connected through the emitter and whose emitter is connected to the output terminal, and second, third and fourth transistors connected in series between the emitter of the first transistor and the output terminal. A resistor and the first
A third conductive type transistor having a collector connected to the base of the transistor, an emitter connected to the output terminal, and a base connected to the connection point of the second and third resistors; A push-pull amplifier having a fourth transistor having an emitter connected to a connection point of a fourth resistor and a collector connected to the output terminal; and a circuit configuration identical to that of the push-pull amplifier, The push-pull amplifier includes another push-pull amplifier that outputs an output signal having an opposite phase, and is provided between the base of the fourth transistor of the one push-pull amplifier and the output terminal of the other push-pull amplifier. First of a connected fifth resistor and a plurality of diodes
And a sixth resistor connected between the base of the fourth transistor of the other push-pull amplifier and the output terminal of the one push-pull amplifier, and a second diode of a plurality of diodes.
BTL-connected push-pull amplifier equipped with a series circuit.