JP2542934Y2 - Protection circuit - Google Patents

Description

[Detailed description of the invention] Industrial application Field of the invention is a protection circuit, especially a push-pull type power amplifier for power amplification, when an overcurrent flows between the output and the power supply during standby due to short-to-power or the like. It relates to a circuit for protecting an amplifier.

Conventional technology In push-pull power amplifiers for power amplification,
Some trouble output V ₀ to the power supply V _CC, for example, when contacted by miswiring or the like during the assembly (power supply fault), because the amplifier reaches the breakdown a large current flows, the protection circuit is needed.

Next, a specific example of the above protection circuit will be described with reference to FIG. 3. In the drawing, V _CC is a power supply terminal, V ₀ is an output terminal, S
T-By the second control terminal of the standby circuits S _1, V _CC2 is the voltage by the operation of standby circuits S ₁ is applied
Power supply line, Q ₀₁ and Q ₀₂ are NPN type power transistors, Q
_D1 is for the NPN-type driver transistor, the overcurrent detection circuit S ₂ is for detecting a current flowing in the power transistors Q _01, S
₃ off driver turns off the driver transistor Q _D1 by a signal from the overcurrent detection circuit S _2, GND is a ground terminal, V _in the signal input terminal, SG external signal source, C ₁ is an external signal source SG and the signal coupling capacitor between the input terminal V _in, AMP1, AMP2 first amplifier stage constituting the preamplifier circuit to provide the base of the external signal source SG to amplify from the signal of the driver transistor Q _D1, a second amplifier stage, Q ₁ is the second stage AM
P2 PNP type transistor, R _1, R ₂ is the feedback resistor of the first amplifier stage AMP1, R ₃ the resistance, R _4, R ₅ is a feedback resistor of the second amplifier stage AMP2.

The output terminal V ₀ is connected to a speaker or the like,
Collectors and emitters of a pair of power transistors Q ₀₁ and Q ₀₂ are connected between the ground terminal GND and the power supply terminal V _CC .

Overcurrent detection circuit S ₂ is connected to the base of the power transistor Q _01, it is further connected to the off driver S _3. Off driver S ₃ includes a second power supply line V _CC2, it is connected to the base of driver transistor Q _D1.

Based of the driver transistor Q _D1 is connected to the collector of the transistor to Q ₁ second amplification stage AMP2 to the resistor R _3, the base of the transistor Q ₁ is connected to the resistor R _2, the resistance
R _2, is connected to the signal input terminal V _in through a resistor R _1.

Standby circuits S _1, the power supply V _CC and the second power supply line V _CC2
Inserted between

In the above configuration, during normal operation, i.e. to operate standby circuit S ₁ is, in a state where the voltage to the second power supply line V _CC2 is applied, when an overcurrent flows through the power transistor Q ₀₁ by the top絡等overcurrent detection circuit S ₂ is operated, operating off the driver S ₃ by the signal, the driver transistor Q _D1 cut off, off driver power supply operating the power transistor Q _01, the power transistor Q ₀₁
Turn off the overcurrent flowing to

Problems to be solved by the invention By the way, with the power supply connected to the power supply terminal V _CC ,
By turning off the standby circuit S _1, the second power supply line
When the voltage of V _CC2 is turned off, the output terminal V ₀
When the power supply voltage is applied, to the emitter of the transistor Q ₁ is passed through the resistor R _4, the voltage is applied from the output terminal V _0, the base current I _B1 is through resistor R _2, R _1, input terminal V is connected to _in continues to flow until the charge capacitor C _1.

By the base current I _B1 of the transistor Q ₁ is flowing, the base current I _BD1 driver transistor Q _D1 flows, operating the power transistor Q _01.

At this time, although the overcurrent detection circuit S ₂ is operated, power-off driver S ₃ is supplied from the second power supply line V _CC2,
Off driver S ₃ does not operate, and destroy continues overcurrent flows to the power transistor Q _01.

Means for Solving the Problems The present invention has the following configuration.

A push-pull connection is made between the power supply terminal to which the power supply voltage is applied and the ground terminal, and an output terminal is provided at the intermediate connection point. A Stein-by circuit for applying or not applying a voltage to the second power supply line based on the
A driver transistor connected between the power supply terminal and the ground terminal for driving and controlling the power transistor on the ground terminal side; and an external signal source when a voltage is applied to the second power supply line by operating the ste-by circuit. Amplify the signal from the driver and send it to the driver transistor. By cutting off the standby circuit, when the voltage is applied to the output terminal when the voltage is not applied to the second power supply line, the voltage for operating the driver transistor is changed. An overcurrent detection circuit for protecting a power amplifier having a preamplifier circuit to be transmitted, the overcurrent detection circuit detecting an overcurrent of a power transistor on a ground side when a voltage is applied to a second power supply line. A short-to-power detection circuit for detecting that a voltage is applied to the output terminal when no voltage is applied to the second power supply line; Protection circuit and a clear driver for cutting off the driver transistor draws current to the base of the transistor driver based on the output of the circuit or power supply fault detection circuit.

Operation According to the above configuration, even when the standby circuit is cut off and the voltage is not applied to the second power supply line, when a voltage is applied to the output terminal due to a dotted line or the like, this voltage is detected by the short-to-power detection circuit. Then, the off-driver is operated, the drive current is cut off, and the power amplifier is protected.

Embodiment Hereinafter, the present invention will be described with reference to FIG.

In FIG. 1, V _CC is a power supply terminal, V ₀ is an output terminal, GND
Is a ground terminal, Q ₀₁ and Q ₀₂ are power transistors, Q _D1 is a driver transistor, S ₁ is a standby circuit, S ₂ is an overcurrent detection circuit, S ₃ is an off driver, and S ₄ is a short-to-power detection circuit.

The off-driver S ₃ is composed of NPN transistors Q ₂ , Q ₄ , Q ₅ and P
And NP transistor Q _3, a resistor _{R 3, R 4, R 5} , R 6, R 7. The emitter of the transistor Q ₂ is grounded, the base is one overcurrent detection circuit S ₂ and the output of the top fault detection circuit S ₄ of the resistor R ₃
Is the connection to the output, the other of the resistor R ₃ is grounded. Base and the resistance of the collector of the transistor Q ₂ is transistor Q ₃ R ₄
It is connected to one and the other of the resistor R ₄ is connected to the emitter to the output terminal V ₀ which transistor Q _3. One and the collector of the transistor Q ₃ of the resistor R _5, R _6, R ₇ and connect the other of the resistor R ₅ is grounded, the other of the resistor R ₆ is connected to the base of the transistor Q _4, the other of the resistor R ₇ It is connected to the base of the transistor Q _5. The emitters of the transistors Q ₄ and Q ₅ are grounded, and the collector of the transistor Q ₄ is connected to the driver transistor Q _D1.
Of being connected to the base, the collector of the transistor Q ₅ is used to stop the operation of other circuits.

Power supply fault detection circuit S _4, the resistance and the PNP transistor Q ₆ R _8, R ₉
Made, one of the resistor R ₈ is connected to the output terminal V _0, the other is connected to one of the emitter and the resistor R ₉ of the transistor Q _6, and the other resistor R ₉ is grounded. Furthermore the base of the transistor Q ₆ is connected to the second power supply line V _CC2, the collector of the transistor Q ₆ is the output of the power supply fault detection circuit S _4.

The operation of the present invention based on the above configuration will be described below. First normal operation, i.e. to operate standby circuit S ₁ is, when the voltage to the second power supply line V _CC2 is applied, the base potential of the transistor Q ₆ rises, transistor Q ₆ does not operate. Here, when the output terminal V ₀ is short-to-supply, the overcurrent detection circuit S ₂ operates and a bias voltage is applied between the emitter and the base of the transistor Q ₂ by the output thereof, and the transistor
Q ₂ is operated. When the output terminal V ₀ is the supply voltage, to the emitter potential of the transistor Q ₃ are high, the transistor Q ₂ is operated, a bias voltage is applied between the emitter base of the transistor Q _3, transistor Q ₃ are becomes operational As a result, the transistors Q ₄ and Q ₅ are operated to lower the base potential of the driver transistor QD _{1 and the} like, thereby protecting the circuit.

Then, it cuts the standby circuit S _1, second power supply line V _CC2
If no voltage is applied, the base potential of the transistor Q ₆ is low. In this case the output terminal V ₀ is the supply voltage, to the transistor Q ₆ is operated, giving a bias voltage between the emitter base of the transistor Q _2, to protect the description same circuit.

In this configuration, during normal operation, since there is a case where the voltage of the output terminal V ₀ exceeds a voltage of the second power supply line V _CC2, at this time,
As power supply fault detection circuit S ₄ is not malfunction, determines the sensitivity of the top fault detection circuit S ₄ by the resistance ratio of the resistors R _8, R _9. Resistance R ₃ , R ₄ , R ₅
Knocked operation sensitivity off driver S _3, R _3, R ₅ is about 10 k.OMEGA, R ₄ is about 8k. The resistors R ₆ and R ₇ are connected to the transistor Q ₄
To the case where any of the Q ₅ is saturated, because the resulting draw the base potential of the other transistor, as a countermeasure
It needs to be about 1KΩ.

Embodiment 2 FIG. 2 is a circuit diagram of a second embodiment of the present invention. In a circuit having two or more output terminals, the output terminals V ₀₁ , V
_02, V ₀₃ ... Each of the diodes _{D 1, D 2, D 3} ... it is connected to the anode of the diode _{D 1, D 2, D 3} ... cathodes of the common resistor R _8, R _4, transistor Q Connected to ₃ emitters.

In this embodiment, a plurality of output terminals V ₀₁ , V ₀₂ , V ₀₃ .
Except diode D _1, through D _2, D ₃ ... points connected to point short detection circuit S _4, because the first is similar to the embodiment, a the same parts thereof will be denoted by the same reference numerals Omitted. In this embodiment, the same circuit configuration can be used even when there are two or more output terminals, and there is an advantage that even if the number of output terminals increases, the number of circuit elements does not increase much.

Effect of the present invention As described above, in the present invention, in a power amplifier for a push-pull type power amplifying device, a standby circuit is cut off, and a voltage is not applied to the second power supply line. When a voltage is applied, the off-driver operates even if no voltage is applied to the second power supply line because the operating power of the off-driver is obtained from the output terminal.
In addition, the addition of the short-to-power detection circuit in the standby state has an effect of protecting the circuit diagram even in the short-to-power in the standby state.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a main part showing an embodiment of the protection circuit according to the present invention, FIG. 2 is a circuit diagram of another embodiment of the protection circuit of the present invention, and FIG. It is a circuit diagram including a block diagram showing a specific example. V _CC …… Power supply terminal, V ₀ , V ₀₁ , V ₀₂ , V ₀₃ …… Output terminal, V
_CC2 ...... second power line, Q _01, Q ₀₂ ...... power transistor, Q _D1 ...... driver transistors, S ₁ ...... standby circuit, S ₂ ...... overcurrent detection circuit, S ₃ ...... off driver,
S ₄ …… A short circuit detection circuit.

Claims (1)

(57) [Scope of request for utility model registration] 1. A power transistor on a power terminal side and a power terminal on a ground terminal side, which are push-pull connected between a power supply terminal to which a power supply voltage is applied and a ground terminal, and provided with an output terminal at an intermediate connection point. A standby circuit for applying or not applying a voltage to the second power supply line based on the applied power supply voltage, and a driver connected between the power supply terminal and the ground terminal for driving and controlling the power transistor on the ground terminal side Operating the standby transistor and the standby circuit to amplify a signal from an external signal source while applying a voltage to the second power supply line, send the amplified signal to the driver transistor, and disconnect the standby circuit. When the voltage is applied to the output terminal when no voltage is applied to the second power supply line, the driver transistor operates. A protection circuit for protecting a power amplifier having a preamplifier circuit for transmitting a voltage to be applied, wherein an overcurrent of the power transistor on the ground side is detected when a voltage is applied to the second power supply line. An overcurrent detection circuit, a short-to-power detection circuit for detecting that a voltage is applied to the output terminal when no voltage is applied to the second power supply line, and the overcurrent detection circuit or the short-to-power detection A protection circuit comprising: an off driver that draws a current to a base of the driver transistor based on an output of the circuit and cuts off the driver transistor.