JPS5942741Y2 - Speaker protection and muting circuit - Google Patents

Description

[Detailed explanation of the invention] The invention is a two-power OCL (Output Cap
DC current flows to the output terminal due to abnormal operation in the circuit, which prevents damage to the voice coil of the speaker and performs muting operation when the power is turned on and off.Shi:-Power protection and muting The purpose is to provide a circuit.

More specifically, the present invention aims to provide a technology that is a further improvement on the technology described in Utility Model Application No. 112,602/1987, which was previously proposed by the applicant of the present application.

That is, the circuit of the prior application has a circuit configuration as shown in FIG.
When the power switch SO is opened, the charge in the capacitor C2 is discharged through the diode D5 and the resistor R14.
There is a slight time lag before I turns OFF, and it is not possible to sufficiently prevent pop noises and distorted sounds that occur during this time.

The present invention aims to provide a speaker protection/muting circuit that can completely eliminate pop noise and distorted sounds that tend to occur when the power is turned off.

Next, the present invention will be explained with reference to FIG.

Transistors Ql-Q2 and q□, Q2 are the positive and negative two of the left channel and right channel, respectively, for stereo.
This is a power supply 2〇〇L amplifier circuit.

Its output end is connected to the speaker S I * S r via the relay switch S 1 s S 2 and to one end of the non-polar AC signal bypass capacitor C1 via the resistor R0°R2.

R8 is a filter resistor, Q3 is a signal inversion transistor, Q4 is a control transistor, Q5 is a relay switch drive transistor, R4 and R5 are base bleeder resistors,
R6 is a collector load resistance, R7 is a resistance for supplying current to the positive temperature characteristic resistor Rp, R8 and R9 are base/leader resistances, Q6 is a switching transistor, 1 is a commercial power outlet, 2 is a power transformer, D7. DB is a rectifier for two positive and negative power supplies, and D6 is a separately provided rectifier.

Next, the operation will be explained.

1 Normal operation When the power switch So is turned on, the resistors R3 to Q3 are turned on and transistor Q4 is turned off at room temperature.
R9 is set in advance.

That is, when the power switch So is turned on, the capacitor C3
As the charging voltage increases, current flows to the base of the switching transistor Q6 through the base resistor R15,
Q6 is in the ON state, one end of the positive temperature coefficient resistance element Rp is grounded via Q6, and the control transistor Q4 is in the OF state.
Maintain F state.

On the other hand, the operation of transistor Q5 is as follows.

That is, when the power supply voltage is applied, the capacitor C2 is gradually charged via the resistor RIO, and the base current begins to flow slightly through the resistor R11, but as the charging voltage of C2 further increases, the base current of Q5 also increases. When the collector current of Q5 exceeds the sensitivity current value of relay RI, the relay operates and relay switch S□S2 switches OCL output terminal 1 (
A) 11B) and speakers SI and Sr are connected.

In this way, the muting operation is performed when the power is turned on.

Next, when the power switch So is turned OFF, the charge in the capacitor C3 that has been charged through the separate power rectifier D6 is discharged through the resistor R14, so the voltage across C3 decreases, the base current of the transistor Q6 decreases, and the instantly shifts from the ON state to the OFF state.

Therefore, the base current flows to Q4 through resistor R7 and diode D4, Q4 changes from OFF to ON state, and the charge in capacitor C2 is discharged through Q4, so Q5
Since the base current of Q5 rapidly decreases and the collector current of Q5 stops flowing, the relay switches S□ and S2 are turned OFF, and the connection between the OCL output and the speakers SI and Sr is opened.

In this way, the muting operation is performed when the power is turned off.

In addition, in accordance with the above, the thickness of capacitors C2 and C3 is C3.
<In the case of C2, the time from when the power switch So is turned off until the relay RI is opened is much shorter than in the case of Fig. 1, and the pop noise etc. that occurs when the power is turned off is completely suppressed. can do.

2. Protection against damage caused by direct current.Due to some abnormal operation of the OCL circuit, the OCL output terminal (
A positive or negative DC voltage appears at AXB), and this voltage causes a DC current to flow through the speaker S I S S r, which may damage the voice coil of the speaker. An operation to prevent this will be described.

For example, if a negative DC voltage is generated at the output terminal (4), this voltage is applied to the capacitor C1 via the resistor R0, and a negative voltage is generated across C0.

Therefore, resistor R5 is connected from the 1B power supply through diode D2.
A current flows in the direction of →D2 →R3, the base potential of Q3 decreases, Q3 changes from ON to OFF state, and the collector voltage of Q3 increases.

As a result, current flows from the 10B power supply through R6 → D3 → R6 to the base of control transistor Q4, and Q4 is turned off.
state changes to ON state.

Therefore, the collector potential of Q4 decreases, the base current of the drive transistor Q5 stops flowing, and the collector current of Q5 stops flowing, so the relay RI turns OFF and the O
The CL output terminal (4) and speaker SI are opened, and no direct current flows through the voice coil of speaker S1.

Next, when a positive DC voltage is generated at the output terminal (1), a positive voltage is applied to C1 via the resistor R1, so the diode Dl is turned on and the Q
A current flows to the base of Q4, turning Q4 from the OFF state to ON, thereby protecting the speaker SI in the same manner as described above.

In addition, in the normal state, the output that appears at the output terminal (4) or No voltage is applied and therefore the relay switch S 1 s
S2 is never released.

! In addition, in the above case, when DC voltage appears only at either the output terminal (4) or the output terminal (4), the relay switch S
Although both 1sS2 are designed to operate, if one more circuit corresponding to the transistors Q3tQ4-Q5 is provided, the left and right channels can be controlled separately.

3. Protection from excessive current due to high temperature The resistance value of the positive temperature coefficient resistance element Rp is very low at normal temperature, but reaches several kilohms at high temperature.

Therefore, at room temperature, the voltage applied to the anode of diode D4 is very low, so the base current of Q4 does not flow.
Q4 is one trench in the OFF state.

Also, this resistance element Rp is the main amplifier's output transistor Q 1 * Q 2 ? Since it is installed very close to the heat sink of Q'1 t Q'2, when the output of the output transistor is small, the temperature rise of the heat sink is low and the resistance value of the resistance element Rp is also small, so Q4 is in the OFF state. 11.

However, if the output increases or the heat dissipation effect of the transistor is poor, the temperature of the heat sink will also rise, and when that temperature reaches the set temperature of the resistor element, this resistance value will increase and R
7 and D4, current flows to Q4, Q4 turns ON, relay RI operates, the connection between the output terminal (AXB) and speaker SIwSr is opened, and the output transistor Q
1t Qzt Q'1t Since the load of Q'2 is released, the temperature rise of the output transistor is suppressed.0 As described above, according to the circuit of the present invention, the dual power OCL
Damage to the voice coil of the speaker due to positive or negative DC voltage appearing at the output terminal due to abnormal operation in the circuit can be easily and reliably prevented, and pop noises etc. generated when the power is turned on and off can be suppressed.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional speaker protection/muting circuit, and FIG. 2 is a diagram showing a speaker protection/muting circuit according to the present invention. Q□, Q 2 t Q'l s Q'2...O
CL circuit, SI. Sr・・・Speaker, R■・・・Relay,
51ts2...Relay switch, C□...
... Capacitor, R0R2 ... Impedance, Q4 ... Control transistor, Q5 ...
...Relay switch drive transistor, Q6...
・Switching transistor, C3, R14...
・Time constant circuit, Rp...Positive temperature coefficient resistance element.

Claims (1)

[Scope of utility model registration request] Two power supply system: A relay switch is connected between the output end of the CL circuit and the speaker, and the output end is connected to one end of a capacitor whose other end is connected to a reference potential point via an impedance element, and both ends of the capacitor are connected. The reference potential that appears at both ends of the capacitor is applied to the control electrode of the control transistor via a signal inversion transistor that inverts the polarity of the voltage that appears at The output side of the control transistor, which performs the same operation in response to different positive or negative DC voltages, is connected to the control electrode of the relay switch drive transistor, and a resistor, a temperature-dependent resistance element, and the collector of the switching transistor are connected between the power supply terminals. e emitter wire in series, a connection point between the resistor and the temperature-dependent resistance element is connected to the base of the control transistor, and a time constant circuit including a capacitor connected to the power supply terminal is connected to the switching transistor. When a positive or negative voltage appears across the capacitor, the relay switch is opened to prevent direct current from flowing to the speaker, and the temperature-dependent resistance element prevents overload of the output transistor. Overheating caused by the load is detected, the control transistor is controlled to open the relay switch, and when the power switch is opened, the switching transistor is made conductive by the capacitor of the time constant circuit, and the relay switch is opened and the mute switch is turned on. A speaker protection and □neating circuit that is characterized by performing