JPS59146204A - Single ended push-pull amplifier circuit - Google Patents

Abstract

PURPOSE:To protect an output trnsistor (TR) from being destoryed even if an abnormal voltage is impressed by providing a switching element conducting the TR when a voltage having a specified value or over is impressed. CONSTITUTION:When a voltage higher than a voltage Vcc 1 is impressed, a diode 31 is conductive in response to voltage impression. Thus, the TR4 is conductive by a current flowing from an emitter of the TR4 to a base. When the TR4 is conductive, a TR11 is forward-biased via a TR30 and the TR11 is also conducted. Then, an abnormal voltage impressed to an output terminal 40 is absorbed by the output stage TR11 at the lower side and a voltage component impressed to an output stage TR10 of the upper side as a reverse bias is decreased. As a result, the TR10 is prevented from destruction.

Description

DETAILED DESCRIPTION OF THE INVENTION The pilot refers to an amplifier circuit in which first and second transistors whose collector-emitter paths are connected in series between power supply terminals to form an output stage, and which are The present invention relates to a single-ended push-pull amplifier circuit having a third transistor for phase inversion connected to the input side of the second transistor for pull-pull.

In such an amplifier circuit, an abnormal voltage may be applied to the output terminal from the outside. For example, when attempting to connect a power supply to an amplifier circuit in order to operate it, the power supply may accidentally come into contact with the output terminal, or the voltage from another voltage source may be incorrectly applied.

As described above, when an abnormal voltage is applied to the output terminal, there is a drawback that the transistors constituting the output stage, particularly the first transistor, are reversely biased and destroyed by the abnormal voltage.

SUMMARY OF THE INVENTION An object of the present invention is to provide a single Φ-ended Φ-type Sossible amplifier circuit that can protect the output transistor from destruction even when such an abnormal voltage is applied.

In the present invention, when an abnormal voltage, that is, a voltage higher than a specified value is applied to the output Jj between the output '::i+ and the third transistor for phase inversion, the third) l-transistor is applied. 1) The provision of a switching element that allows

Among the transistors forming the output stage, the second transistor is driven by the third transistor. Therefore, by providing a switching element, when the third transistor is rendered conductive when an abnormal voltage is applied, the second transistor is also rendered conductive. That is, the voltage of the output Z and the negative terminal is pumped to the voltage of the second transistor, which is less than the specified value. As a result, the abnormal 1st stroke pressure is the 1st male)
This voltage is no longer applied to the transistor, and the first transistor can be protected from destruction. It is preferable to use a diode as a switching element.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention. Tiger,
A/registers 0 and 11 have their collector emitter paths connected in series between the power supply Vcc1 terminal and the ground terminal to form an output stage. Transistor 3 is connected to transistor 10, and transistor 30 is connected to transistor 11 by Darlington connection. In particular, the collector of transistor 30 is connected to the power supply Vccl terminal to drive transistor 11 to its saturation region. A PNP transistor 4 for phase inversion is connected to the base of the transistor 30, that is, to the input side of the transistor 11. Each base of transistors 3 and 4 is connected to input signal source 1. Therefore, the transistor 3.10 becomes conductive in the upper main cycle of the input signal, and the transistors 4.30 and 11 become conductive in the lower cycle, performing a push-pull operation, and an output signal is obtained at the output terminal 40. The bias circuit 2 is connected between the output terminal 40 and the transistor 4, and adjusts the idling power supply when there is no signal. Power is supplied to the bias circuit 2 from a resistor 32. A 14-wire coil 6 is connected to the output terminal 40 through the capacitor 5. Output description: A capacitor 9 is further connected to the output terminal 40. capacitor 9
The bootstrap circuit with resistors 7 and 8 is 4.7
9 has been completed.

Diode 4. ') The base is further connected to the power supply Vcc2 terminal of 182 via a diode 20.

The diode 31 is a switching element provided according to the invention, and has its anode connected to the output terminal 40 and its cathode connected to the emitter of the transistor 4.

The operation of the power amplification circuit shown in FIG. 1 when an abnormal voltage is applied will be described first for the case where the diode 31 is not provided. For example, if the power supply Vccl voltage is mistakenly applied to the connection point between the capacitor 5 and the coil 6 that is the load, the capacitor 5
When the accumulated voltage of is zero, the voltage C01 is output through the capacitor 5 and supplied to the terminal 40.The voltage of the output terminal 400 during normal operation is approximately equal to the voltage Vccl. Since the voltage changes up to the ground voltage, Vccl is applied to the output terminal 4o.
The transistor 10 will not be destroyed by the applied voltage. However, if there is an accumulated charge in the capacitor 5, a voltage that is the sum of Vccl, the i pressure, and the voltage at the capacitor 5 is applied to the output terminal 40. That is, transistor 10 is reverse biased at a voltage greater than the Vcc 1 voltage. As a result, since the emitter of transistor 10 is connected to output terminal 40, transistor 1
0 is easily destroyed.

Next, a circuit according to the invention including a diode 31 will be described. The diode 31 has its anode connected to the output terminal 40 and its cathode connected to the emitter of the transistor 4, that is, the Vccl terminal via the resistor 32, so that it is in a cut-off state during normal operation. Now, as described above, when a voltage higher than the VCCIK voltage is applied to the output terminal 540, the diode 31
is conductive. As a result, a current flows from the emitter to the base of the transistor 4, and the transistor 4 becomes in a conductive state. When transistor 4 becomes conductive, transistor 11 is forward biased via transistor 30, and transistor 1↓ also becomes conductive. Therefore, the abnormal voltage applied to the output terminal 40 is absorbed by the lower output stage transistor 11, and the voltage applied as a reverse bias to the upper output stage transistor 10 is reduced. As a result, the transistor 10 can be prevented from being destroyed.

The purpose of the diode 20 is to allow current to quickly flow through the diode 31 and the emitter base of the transistor 4, and this diode 20 is also reverse biased during normal operation.

Also, a part of the charge accumulated in the capacitor 5 is quickly discharged through the diode D1, so that the power supply Vcc
The voltage of the capacitor 5 added to the 1K voltage also decreases, and the adverse effect on destruction is alleviated accordingly.

Note that the abnormal voltage applied to the output terminal 40 is not limited to only via the capacitor 5, but is applied to the output terminal 40Kj+! Contact V
When a voltage exceeding the voltage is applied to +Lc, I・ko0
In case 7, the output transistor can be prevented from being destroyed by the action of the damper 31:.

The circuit shown in FIG.
Denotes a current supply, for example, a current supply to a deflection coil in a television receiver. in this case,
The coil 6 also generates a high voltage during the addition period. Diodes 31 and 20 turn on transistor 11 in response to this high electromotive voltage, thereby allowing the accumulated charge in coil 6 to be discharged. That is, it is not necessary to operate the transistor 10 as an inverse transistor and to connect a diode for discharging charges between the output terminal 40 and the Vcc1 terminal, making it extremely suitable for integrated circuit implementation.

As described above, the amplifier circuit according to the present invention can prevent the output transistor from being destroyed by abnormal voltage applied to the output terminal, and its integrated circuit can be easily integrated.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention. 1. Signal source, 2. Bias circuit, 3.4
．． 10, engineering 1.30...o transistor, 5.91
・・Capacitor, 6・φ meeting-Coil Ca load>, 7.8.
32...Resistance, 31.20...## diode, 4
0...- Output terminal 1st old

Claims (1)

[Claims] In a single-ended push-pull amplifier circuit having first and second transistors constituting an output stage and a third transistor for phase inversion connected to the input side of the second transistor, the output terminal and said third
When a voltage equal to or higher than a specified value is applied to the output terminal between the third transistor and the third transistor, the third transistor becomes conductive.