JP3349340B2 - amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier for preventing an amplifier from being damaged when an output terminal of the amplifier is abnormally connected.

[0002]

2. Description of the Related Art When a vehicle-mounted audio device is mounted on a vehicle, it is sometimes mistakenly wired to a ground or a power supply voltage. For example, if the output terminal of the audio amplifier is erroneously connected to the ground or the power supply voltage, an excessive current flows through the output transistor constituting the amplifier, and the output transistor is destroyed. Conventionally, a protection circuit for protecting an output transistor of an amplifier when an output terminal of the amplifier is abnormally connected to a ground fault or a power short has been configured as shown in FIG.

In FIG. 2, a standby switch (1)
Is turned on, the output voltage of the constant voltage source (3) is applied to the base of the transistor (2), and the transistor (2) is turned on. The transistors (5) and (6) are turned on by the voltage drop of the resistor (4) according to the collector current of the transistor (2), and the bias current is supplied to the protection circuit (6). Is in operation. Further, the transistors (8) and (9) are turned on, and the capacitor (10) for the ripple filter is charged. Since the transistor (11) and the first and second diodes (12) and (13) are turned on by the terminal voltage of the capacitor (10), the anode voltage of the first diode (12) becomes a constant voltage. The transistor (14) is turned on in accordance with the anode voltage, and the collector current of the transistor (14) is changed to a current mirror circuit (1).
It is supplied as a bias current to the amplifier (16) via 5). Therefore, the amplifier (16) is in operation, amplifies the input signal, and the speaker (17) is driven by the output signal of the amplifier (16).

Here, for example, when the output terminal of the amplifier (16) is grounded, a detection signal of a circuit for detecting a ground fault in the amplifier (16) is applied from the amplifier (16) to the protection circuit (7). Is done. The protection circuit (7) generates a protection signal, the transistor (18) turns on, and the base of the transistor (14) is grounded. Therefore, the transistor (14) is turned off, and the bias current is not supplied to the amplifier (16), so that the output transistor of the amplifier (16) is turned off.
Therefore, no excessive current flows through the output transistor, and the protection of the output transistor is achieved. Also, at the time of short-to-power, a protection signal is generated from the protection circuit (7), the transistors (18) and (14) are sequentially turned off, and the output transistor of the amplifier (16) is protected.

[0005]

When the standby switch (1) is turned off, the transistor (2) is turned off, so that the transistors (5) and (6) are turned off.
The protection circuit (7) turns off. The turned off protection circuit (7) does not generate a protection signal even if an abnormal connection is detected, so that the transistor (18) remains off. Therefore, at the same time when the standby switch (1) is turned off, the first and second diodes (12) and (13) and the transistor (14) are not controlled.

Further, when the transistor (2) is turned off,
When the transistors (8) and (9) are turned off, the capacitor (10) is discharged with a time constant determined by the capacitance of the capacitor (10) and the resistance of the resistor (19). Decreases slowly and the transistor (11) for a predetermined period determined by the time constant
Is kept on. The predetermined period, the first and second
The diodes (12) and (13) and the transistor (1
4) turns on, and a bias current is supplied to the amplifier (16). Therefore, the output transistor in the amplifier (16) is in the operating state for the predetermined time.

As described above, when the standby switch (1) is turned off during abnormal connection of the output terminal of the amplifier (16), the output transistor operates and the protection circuit (7) is turned off. Excessive current flows through
There has been a problem that the output transistor is destroyed.

[0008]

SUMMARY OF THE INVENTION The present invention relates to an amplifier provided with a protection circuit for protecting the amplifier when the output terminal of the amplifier is abnormally connected, wherein a capacitor for removing a ripple component of a power supply and a standby switch are turned on. A first power supply circuit that applies a power supply voltage to the amplifier based on a terminal voltage of the capacitor; and a second power supply circuit that applies a power supply voltage to the protection circuit in response to turning on the standby switch. Two power supply circuits,
A discharge circuit for discharging the electric charge of the capacitor; and a maintenance circuit for maintaining an operation state of the second power supply circuit in accordance with a discharge operation of the discharge circuit. The operation state of the circuit is maintained, and the protection circuit is maintained in the operation state.

Further, when the standby switch is turned off, the operation state maintaining period of the protection circuit is set longer than the operation state maintaining period of the amplifier.

[0010]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. (19) and (20) are switching transistors which are turned on / off in response to the operation of a standby switch (1). (21) and (22) are resistors that generate a terminal voltage by a voltage drop according to the collector current of the transistors (19) and (20), and (23) is a transistor whose base is connected to the collector of the transistor (8). (24), a transistor (25) whose base and collector are respectively connected to the collector and the emitter of the transistor (24), a resistor (26) connected to the collector of the transistor (24), and a transistor (2).
5) A resistor (27) for limiting the collector current and a discharge circuit, (28) a resistor for generating a base voltage of the transistor (25), and (29) a resistor in response to an output signal of the discharge circuit (23). The transistor serves as an operation control circuit for controlling the transistors (5) and (6). In FIG. 1, the same reference numerals as in the conventional example of FIG. 2 denote the same reference numerals, and a description thereof will be omitted. Also, the transistor (8)
And (9) constitute a charging circuit and include a transistor (1).
1) and (14), a current mirror circuit (15), a transistor (20), and a resistor (22) constitute a first power supply circuit, and include transistors (5), (6) and (1).
9) and the resistor (21) constitute a second power supply circuit.

In FIG. 1, a standby switch (1)
, The transistors (19) and (20) are turned on, and the collector currents of the transistors (19) and (20) flow through the resistors (21) and (22). Resistance (2
Transistor (5) due to the voltage drop of (1) and (22)
And (8) are on. The operation of the circuit in FIG. 1 by turning on the transistors (5) and (8) is the same as that of the conventional example in FIG. However, in the discharge circuit (23), the transistor (24)
The terminal voltage Vc of the capacitor (10) is applied to the emitter of the transistor (24), and the resistor (28) is
Is applied. Resistance value R28 of resistance (28)
Is given assuming that the base-emitter voltage of the transistor (24) is Vbe and the collector current of the transistor (8) is Ic8.

[0012]

(Equation 1)

It is set so that Therefore, when the standby switch (1) is turned on, the transistor (2)
4) is off, and the discharge circuit (23) is off. Next, the operation when the standby switch (1) is turned off will be described with reference to FIG. Transistor (1
9) and (20) are turned off, and the collector currents of the transistors (19) and (20) are stopped. Therefore, the transistors (5), (6), (8) and (9) are turned off. When the transistor (9) is turned off, the terminal voltage Vc of the capacitor (10) is kept substantially equal to the voltage when the switch (1) is turned on as shown in FIG. The terminal voltage of the resistor (28) becomes 0 at the same time when the transistor (8) is turned off as shown in FIG. Accordingly, the voltage difference between the emitter and the base of the transistor (24) becomes equal to or higher than the base-emitter voltage Vbe of the transistor, so that the transistor (24) is turned on, and further, the transistor (25) is turned on. The discharge circuit (23) is turned on, and the discharge current of the capacitor (10) flows through the transistors (24) and (25). The capacitor (10) is discharged, and the voltage Vc decreases as shown in FIG. The resistor (27) is a limiting resistor for limiting the discharge current.

The collector current of the transistor (24) flows through the resistor (26), and the terminal voltage of the resistor (26) becomes as shown in FIG. When the collector current of the transistor (24) is Ic24 and the base-emitter voltage of the transistor (29) is Vbe, the resistance value R26 of the resistor (26) is as follows.

[0015]

(Equation 2)

The transistor (29) is sufficiently turned on. When the transistor (29) is turned on, the collector current of the transistor (29) flows through the resistor (21). The transistors (5) and (6) are turned on by the voltage drop of the resistor (21), and the protection circuit (7)
Is in operation. Terminal voltage V of capacitor (10)
3B, the voltage between the emitter and the base of the transistor (11) is Vbe, the emitter resistance is RE, the emitter current is Ie11, and the first and second diodes (12) are VD (=). Vbe), the voltage Vc
1 is

[0017]

(Equation 3)

Then, the transistor (11) and the first
And the second diodes (12) and (13) are turned off. Therefore, the anode voltage of the first diode (12) drops from 2 × Vbe to 0. Therefore, the transistor (14) turns off, no bias current is supplied to the amplifier (16), and the output transistor of the amplifier (16) turns off.

Further, when the capacitor (10) is discharged, the terminal voltage Vc decreases, and the resistance value of the resistor (27) and the current flowing therethrough are R27 and I27.
The voltage Vc2 is

[0020]

(Equation 4)

Then, the transistors (24) and (2)
5) is turned off, and the discharge circuit (23) is turned off. For that reason,
The discharge of the condenser (10) stops. When the transistor (24) is turned off, the terminal voltage of the resistor (26) becomes 0 as shown in FIG. 3C, and the transistor (29) is turned off. Since no current is supplied to the resistor (21), the transistors (5) and (6) are turned off, and the protection circuit (7) is also turned off.

Even if the standby switch (1) is turned off in a state where the output terminal of the amplifier (16) is abnormally connected, the protection circuit (7) operates and the amplifier (16) due to the abnormal connection. The protection of destruction of the output transistor can be achieved. Further, since the amplifier (16) is turned off before the protection circuit (7) is turned off, the protection of the output transistor from being broken can be more reliably achieved.

[0023]

FIG. 4 shows a specific example of an abnormal connection detection circuit built into the amplifier (16), that is, a short-to-power / ground-fault detection circuit. In FIG. 4, the output transistors (30) and (3)
1) In the amplifier connected to the SEPP, when the output terminal (32) is short-to-power, that is, the output terminal (32)
When the midpoint voltage becomes the power supply voltage Vcc, an excessive current flows through the output transistor (31). Since the base-emitter voltage of the output transistor (3) increases due to the excessive current, the midpoint voltage of the connection between the resistors (33) and (34) increases, and the transistor (35) turns on. When the transistor (35) is turned on, the Zener diode (3
Since the potential difference between the cathode of 6) and the cathode of the diode (37a) is substantially equal to the power supply voltage Vcc, the transistor (8), the zener diode (36), and the diodes (37a) and (37b) are turned on. Then, since the base-emitter voltage of the transistor (38) becomes equal to the voltage between both terminals of the diodes (37a) and (37b), the transistor (38) is turned on and a collector current is generated. The collector current of the transistor (11) is supplied to the protection circuit (7), and the occurrence of a power short is detected.

When the output terminal (32) is grounded,
The midpoint voltage is grounded and the output transistor (30)
Excessive current flows through. Since the base-emitter voltage of the output transistor (30) increases due to the excessive current, the transistor (39) is turned on, and further, the Zener diode (40) and the diodes (41a) and (4).
1b) is turned on. Accordingly, transistors (4
2) is turned on, and its collector current is applied to the protection circuit (7).

[0025]

As described above, according to the present invention, after the standby switch of the standby switch is turned off, the operation of the second power supply circuit is maintained and the operation of the protection circuit is maintained.
It is possible to protect the output transistor from being destroyed when the standby switch is turned off while the output terminal of the amplifier is abnormally connected.

When the standby switch is turned off,
Since the protection circuit is turned off after the amplifier is turned off, more reliable protection of the output transistor can be performed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional example.

FIG. 3 is a waveform chart for explaining the operation of the present invention.

FIG. 4 is a specific example of an abnormal connection detection circuit of the amplifier 16;

[Explanation of symbols]

 Reference Signs List 1 standby switch 7 protection circuit 10 capacitor 16 amplifier 23 discharge circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) H03F 1/52 H02M 1/00 G05F 1/10 304 H02J 1/00 309

Claims (1)

(57) [Claims] An amplifier having a protection circuit for protecting the amplifier when an output terminal of the amplifier is abnormally connected, a capacitor for removing a ripple component of a power supply, and charging for charging the capacitor in response to a standby switch being turned on. A first power supply circuit that applies a power supply voltage to the amplifier based on a terminal voltage of the capacitor; a second power supply circuit that applies a power supply voltage to the protection circuit in response to turning on of the standby switch; A discharge circuit that discharges electric charge, a maintenance circuit that keeps the operation state of the second power supply circuit after the discharge circuit starts to be discharged, and that puts the second power supply circuit into an inoperative state when the discharge of the capacitor is completed; And maintaining the operation state of the second power supply circuit when the standby switch is turned off, and maintaining the protection circuit in the operation state. Amplifier for the butterflies.