JPH0210664Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a power supply circuit, and by supplying a low value power supply voltage to the amplifier when the load impedance of the amplifier is low, it reduces the temperature rise due to excessive heat generation, and also reduces the temperature rise due to excessive heat generation. It is possible to miniaturize transformers, etc., and it is also possible to output a large output from the amplifier for a short period of time for low load impedances, and to control load impedances with high sensitivity.
It is an object of the present invention to provide a power supply circuit that can reliably detect load impedance including a reactance component.

In a typical amplifier, the lower the load impedance, the greater the output that can be obtained; for example, about twice as much output can be obtained with a 4Ω load as with an 8Ω load.
However, as the output increases, the amount of heat generated by the amplifier also increases, so the heat dissipation conditions for this increase become stricter and the cost also increases. Therefore, recently when a 4Ω load is connected, the power supply voltage of the amplifier is lowered by some method, and the maximum output when a 4Ω load is connected is reduced to 8Ω.
Efforts are being made to reduce heat generation to the same level as when a load is connected.

One of the above-mentioned ideas is to allow the user to externally switch the power supply voltage of the amplifier according to the impedance of the speaker being used, but this is inconvenient. Another idea was to provide two types of voltage taps on the secondary side of the power transformer, and use a relay to select this tap to switch the power supply voltage depending on the load impedance. You can hear the sound of the operation when it is activated, so this operation must be completed immediately after the power is turned on.
It had drawbacks such as requiring a large-capacity relay and being expensive.

On the other hand, if the amplifier is configured with a complementary SEPP circuit, let's consider how to detect the load impedance in this circuit.

Conventionally, as a circuit for detecting changes in load impedance in a complementary SEPP circuit,
There is a circuit that configures a bridge with each side being the emitter resistance of an NPN transistor or a PNP transistor, a load impedance, etc., and detects when the equilibrium condition of the bridge is no longer satisfied due to a change in the load impedance. This device had the disadvantage that it could not detect a change in impedance unless the load impedance changed by a relatively larger amount than a predetermined value that satisfies the equilibrium condition, and the detection accuracy was low.

Therefore, the applicant proposed the following circuit in order to eliminate this drawback.

Figure 1 is a circuit diagram of an example of an impedance detection circuit previously proposed by the present applicant on March 29, 1982 (Utility Application No. 57-44329 (Utility Model Application No. 1982-146968)).
shows. In the figure, transistor Q ₂ is turned off only when positive direction input is applied to transistors Q ₁ and Q ₂ , and as a result, resistors R ₁ , R ₃ , R ₄ , load impedance (input signal source Vs In the case of , the speaker) R _L constitutes a bridge and performs impedance detection operation. The equilibrium condition of the bridge is R ₁ ·R ₄ =R ₃ · _RL , and each resistance value is selected so that this equilibrium condition is satisfied when the load impedance _RL is a predetermined value. When this equilibrium condition is established, the potential difference between the points is zero, so the differential amplifier _A1 is in an off state, and no output is taken out to the output terminal 10, so that It can be detected that the load impedance R _L is at a predetermined value.

On the other hand, when the load impedance R _L becomes smaller than the above predetermined value, (potential at the point) < (potential at the point)
Therefore, differential amplifier A ₁ is activated,
An output is taken out to the output terminal 10, and thereby,
It can be detected that the load impedance R _L has become smaller than a predetermined value.

In this case, there is a differential amplifier A ₁ between the points.
is provided to detect the potential difference therebetween, so that a minute potential difference between points (that is, a minute change in the load impedance R _L ) can be detected with high precision.

Here, consider the load line of transistors Q ₁ and Q ₂ in the case where the load impedance R _L is a resistance including pure resistance and reactance components.
FIG. 2 shows the load lines of transistors Q ₁ and Q ₂ with the horizontal axis representing the potential V ₀ and the vertical axis representing the emitter current I _E of the transistor Q ₁ . In the figure, curves a and b represent the load lines of transistors Q ₁ and Q ₂ at a frequency where the load impedance R _L is 8Ω in absolute value and the phase shift of voltage and current is 45°, respectively.
Straight lines c and d are the load lines when the load impedance R _L is pure resistance 8Ω and 4Ω, respectively.
Those in the middle, third and third quadrants are transistors.
Q ₁ , those in the fourth quadrant and those in the fourth quadrant are the respective load lines of the transistor Q ₂ .

In the circuit shown in Figure 1, the load impedance R _L changes due to a change in the emitter current I _E of the transistor Q ₁ .
Since the configuration detects
You only need to think about the load line in _Q1 .

By the way, if the bridge is configured so that the load impedance R _L is an element whose absolute value is 8Ω and includes a reactance component and satisfies the above formula,
When the load line a of the transistor Q ₁ is in the shaded area in FIG. 2, the differential amplifier A ₁ detects the load impedance R _L as being lower than the actual 8Ω. In particular, when the output voltage V ₀ is a low value (that is, the shaded area in the first quadrant near the vertical axis in Figure 2),
Although the load impedance R _L is actually 8Ω, it is detected as being around 0Ω.

As described above, the circuit shown in FIG. 1 has a problem in that when the load impedance R _L is an element containing a reactance component, the differential amplifier A ₁ malfunctions and the actual impedance change cannot be detected accurately.

The present invention eliminates the above-mentioned drawbacks and solves the above-mentioned problems, and one embodiment thereof will be described with reference to FIG. 3 and subsequent figures.

FIG. 3 shows a circuit system diagram of an embodiment of the power supply circuit according to the present invention. In the figure, _T1 is a power transformer,
Its primary side is connected to AC plug 1, and its secondary side is provided with two taps.The tap on the high voltage side is connected to the anode of the thyristor SCR, and the tap on the low voltage side. is connected to the anode of diode D ₁₀ . The cathode of the thyristor SCR and the cathode of the diode D ₁₀ are respectively commonly connected to the non-grounded terminal of the smoothing capacitor C ₁₀ , while the power input terminal of the amplifier 3 configured with a complementary SEPP circuit, and the voltage fluctuation detection circuit 4 are connected to each other. The voltage fluctuation detection circuit 4 is a circuit that detects fluctuations in the power supply voltage across the capacitor C ₁₀ , and its detection signal is supplied to the conduction angle control circuit 5 . The conduction angle control circuit 5 is configured to operate or stop operating according to the impedance detection signal from the load impedance detection circuit 6, and furthermore, when it is in operation, the thyristor is activated or stopped according to the output detection signal from the voltage fluctuation detection circuit 4.
The signal that controls the conduction angle of the SCR is transferred to the thyristor SCR.
output to the gate.

The amplifier 3 amplifies the audio signal from the input terminal 2 and outputs it to the speaker 7, and the connection point between the output terminal and the speaker 7 is connected to the load impedance detection circuit 6. As will be described in detail later, the load impedance detection circuit 6 is composed of a bridge circuit whose one side is the load impedance of the amplifier 3, that is, the input impedance of the speaker 7, and detects the load impedance depending on whether the balanced condition is established. This detection circuit operates only when an output audio signal of a predetermined level or higher is extracted from the amplifier 3, and outputs the impedance detection signal to the conduction angle control circuit 5 to control its operation. Here, the conduction angle control circuit 5 operates when the load impedance is 8Ω, and the conduction angle control circuit 5 operates when the load impedance is 8Ω.
When , the operation is stopped. A specific circuit of the load impedance detection circuit 6 is shown in FIG.

Next, to explain the operation of the circuit shown in the third diagram above, when no audio signal is input to the input terminal 2 after the power switch (not shown) is turned on, or when an audio signal with an extremely low level is input, When the current is flowing, the load impedance detection circuit 6 is inactive, and the conduction angle control circuit 5 is operated. As a result, the gate of the thyristor SCR is driven, and the AC voltage taken out from the secondary side of the power transformer _T1 is rectified and taken out from the thyristor SCR, and is applied to the capacitor _C10 . Therefore, the voltage across the capacitor C ₁₀ is of a high value, which is applied to the amplifier 3 as the supply voltage.

Next, assuming that the input impedance of the speaker 7 is 8Ω and an audio signal of a predetermined level or higher is supplied to it, the load impedance detection circuit 6 operates and supplies an 8Ω detection signal to the conduction angle control circuit 5. , 8Ω detection signal is at the same level as the signal during non-operation, so the conduction angle control circuit 5 continues to operate. Therefore, the thyristor
The DC voltage taken out from the SCR and smoothed by the capacitor _C10 continues to be supplied to the amplifier 3 as the power supply voltage.
Meanwhile, the voltage fluctuation is detected by the voltage fluctuation detection circuit 4, and fed back to the conduction angle control circuit 5, whereby the voltage is regulated to a predetermined voltage.

On the other hand, the input impedance of speaker 7 is 4Ω.
If an audio signal of a predetermined level or higher is supplied to this, a 4Ω detection signal is extracted from the load impedance detection circuit 6 and supplied to the conduction angle control circuit 5, thereby stopping its operation. As a result, the thyristor SCR is turned off, so that the AC voltage on the secondary side of the power transformer _T1 is taken out from the Tatsupro, rectified by the diode _D10 , and then smoothed by the capacitor _C10 .
The voltage across the capacitor _C10 at this time is smaller than that when the thyristor SCR is on,
It is applied to the amplifier 3 as a power supply voltage. Therefore,
The power supply voltage of the amplifier 3 is reduced by, for example, about 30% compared to when an 8Ω load is connected. The value of the power supply voltage at this time is set, for example, so that the output of the amplifier 3 is approximately the same as the output when an 8Ω load is connected.

As a result, even when connected to a 4Ω load, the amount of heat generated by the set can be significantly reduced.

Now, regarding the configuration and operation of the load impedance detection circuit 6, in FIG. 4, a resistor _R3 is connected between the emitter of the transistor _Q1 and the ground.
(first resistor) and resistor R ₄ (second resistor) are connected in series. In addition, the base of the NPN transistor _Q3 is connected to the point and the non-grounded terminal of the load impedance R _L , respectively, and its emitter is
It is connected to the emitter of the NPN transistor _Q4 , while being grounded via a diode _D2 and a resistor _R5 , and its collector is connected to the power supply voltage +Vcc terminal via a resistor _R6 . Transistor Q ₄ has its base connected to a point that is the common connection point of resistors R ₃ and R ₄ , while
It is connected to the emitter of transistor Q ₂ via R ₁₁ (a value equal to or smaller than the resistance value of resistor R ₃ ), and its collector is connected to the power supply voltage +Vcc terminal via resistor R ₇ . has been done. A differential amplifier A ₂ is configured by transistors Q ₃ and Q ₄ .

On the other hand, the base of PNP transistor _Q5 is connected to the collector of transistor _Q4 , and
It is grounded via a resistor _R10 , its collector is grounded, and its emitter is further connected to the power supply voltage +V _CC terminal via a resistor _R8 . The base of the PNP transistor Q ₆ is connected to the collector of the transistor Q ₃ , the collector of which is connected to the output terminal 10 and the resistor
It is grounded via R ₉ and its emitter is connected to the emitter of transistor Q ₅ .
A differential amplifier _A3 is configured by transistors _Q5 and _Q6 .

Generally, the emitter resistors R ₁ and R ₂ are selected to have the same value, respectively, while the transistors Q ₁ and Q ₂ biased to class AB, which is close to class B, by the voltage sources E ₁ and E ₂ have Since an idle current of several tens of mA flows when there is no signal, a potential difference of several tens of mV is generated between both ends of the resistors R ₁ and R ₂ when there is no signal. Therefore, if the ladder R ₁₁ is not connected, the potential at the point will be several tens of mV higher than the point, and transistor Q ₄ of transistors Q ₃ and Q ₄ that make up the differential amplifier will turn on, and the transistor Q ₃ is close to being off. For this reason, when looking at the collector current of transistor _Q4 , it becomes impossible to obtain a sufficient amount of change in the increasing direction. Therefore, in this example, the resistor
By connecting R ₁₁ , its resistance value can be changed to resistor R ₃
If you select a value equal to
The collector currents of Q ₃ and Q ₄ are made approximately equal when there is no signal. In this case, it goes without saying that the resistance value of the resistor _R11 may be selected to be smaller than that of the resistor _R3 to reduce the collector current of the transistor _Q3 .

In addition, the resistance values of the resistors R ₅ , R ₆ , and R ₇ are set so that the absolute value of the output voltage V ₀ in the positive direction _or only in the negative direction is greater than or equal to the voltage V ₁ shown in the second diagram. It is selected to operate only when In this case, when the forward voltage drop of diode D2 is V _F and the voltage between the base and emitter of transistor Q ₃ is V _BE , the voltage becomes {(V ₁ − V _F − V _BE )/R ₅ }×R ₆ . must be selected such that it can turn on transistor _Q6 .

Next, the operation of this impedance detection circuit 6 will be explained. When the output voltage V ₀ of the complementary SEPP circuit consisting of transistors Q ₁ and Q ₂ is negative, the current flowing through the resistor R ₅ becomes zero due to the diode D ₂ , so the differential amplifiers A ₂ and A ₃ are turned off.
(That is, the load line a is in the first quadrant in FIG. 2), and the differential amplifier _A2 does not perform an impedance detection operation.

Next, when the output voltage V ₀ is positive, the diode D ₂ turns on as it swings in the positive direction, and the current flowing through the resistor R ₅ gradually increases. In this case, the resistance
Since the resistance values of R ₅ , R ₆ , and R ₇ are selected as described above, when the output voltage V ₀ reaches the voltage V ₁ , the differential amplifier A ₂ enters the operating state and performs an impedance detection operation. Amplifier A ₂ is now operational,
The voltage across each of resistors R ₆ and R ₇ is the voltage across transistors Q ₅ and Q ₆
When the voltage is sufficient to turn on, amplifier _A3 becomes operational.

When the output voltage V ₀ is positive, the resistor R ₁₁ is equivalent to being connected in parallel between the points, so the resistors R ₁ , R ₃ , R ₄ and the load impedance R _L are connected on each side, respectively. A bridge is constructed, and its equilibrium condition is the same as the above equation. In this case, if the load impedance R _L is a predetermined value and the bridge is balanced, a predetermined voltage is taken out at the terminal 10.

On the other hand, when the load impedance R _L becomes smaller than the predetermined value, the potential at the point becomes higher than that at the point, and as a result, a voltage higher than the voltage taken out at the above equilibrium is taken out at terminal 1, and the impedance increases. Changes can be detected.

In this case, as mentioned above, amplifier A ₂ has an output voltage of
It does not operate when V ₀ is near zero V, and does not perform impedance detection operation unless voltage V ₁ or higher. That is,
Amplifier A ₂ does not operate in the same operating state as shown in FIG. 2 when load line a is in the cross-hatched area surrounded by load line C and line e of voltage V ₁ . Therefore, as is clear from the figure, the load impedance
If R _L includes a reactance component and its absolute value is, for example, 8Ω, it will only be detected as a resistance within the range of about 8Ω to 5Ω, and it will be near 0Ω as in the circuit shown in Figure 1. (In the circuit shown in _Figure 1, amplifier A ₁ is detected as a resistance value that is extremely different from the actual resistance value.) (shaded area), load impedance R _L is erroneously detected as being around 0 Ω even though it is actually 8 Ω).

Note that the resistor _R10 is a bias resistor that allows a slight bias current to flow through the transistor _Q5 to keep the collector current of the transistor _Q6 at zero when the bridge is balanced.

Note that the present invention is not limited to the above-mentioned embodiment, and for example, as shown in FIG. 5, a backflow prevention diode _D20 may be connected between the tap and the anode of the thyristor SCR. can simplify the circuit configuration. Further, the number of taps on the secondary side of the power transformer _T1 may be three or more, in which case only one tap from which the lowest voltage can be obtained is connected to a diode, and the other taps are connected to a thyristor. Furthermore, in the above embodiment, the conduction angle of the thyristor SCR is controlled in order to stabilize the DC voltage, but the thyristor SCR may also be controlled to simply turn on (however, in this case, the DC voltage cannot be stabilized. Can not).

As mentioned above, the power supply circuit according to the present invention includes a diode with one end connected to the tap that obtains the lowest voltage among the plurality of taps provided on the secondary side of the power transformer, and one end connected to the other taps. between a thyristor, a rectifier circuit in which one end of a capacitor to which the other ends of the diode and the thyristor are commonly connected to the power input terminal of the complementary SEPP circuit, and the emitter of the NPN transistor and ground. One input terminal is connected to a common connection point between the first and second resistors connected in series, and the other input terminal is connected to a common connection point between the emitter resistors. The differential amplifier is connected to the ground so that the differential amplifier operates only when the absolute value of the positive or negative output voltage taken out to the common connection point between the differential amplifier and the emitter resistor exceeds a predetermined voltage. and a detection signal output terminal connected to the power supply terminal side of the differential amplifier, and a common connection point of the emitter resistor and a common connection point of the first and second resistors. A load impedance detection circuit extracts a load impedance detection signal obtained by detecting the potential difference between A control signal is supplied to the thyristor, and the control signal turns off the thyristor only when the load impedance detection circuit detects a low load impedance, and when the low load impedance is not detected or a high load impedance is detected, the control signal turns the conduction angle of the thyristor to the capacitor. Since the voltage at both ends is controlled to be a constant voltage or the control circuit turns on the thyristor, the power supply voltage can be reduced by about 30% when detecting low load impedance compared to when detecting high load impedance, and therefore the set The amount of heat generated can be significantly reduced,
Therefore, the heatsink and power transformer can be downsized, making the set consisting of the power supply circuit, amplifier, etc. smaller, lighter, and lower in cost. Voltage switching can be done automatically and silently, making operation easier. By providing a time constant to the circuit that detects the load impedance, it is possible to eliminate the complexity of
Within a short period of time until the thyristor is turned off based on low load impedance detection, a larger output can be obtained than when connected to a high load impedance, which is advantageous for playing music with a wide dynamic range such as PCM. Moreover, the load impedance detection circuit can detect load impedance with higher sensitivity than conventional impedance detection circuits, and the differential amplifier does not perform impedance detection operation unless the output voltage exceeds a certain value. When a load containing a reactance component is connected, unlike the circuit proposed earlier by the applicant, the load will not be detected as a value that is extremely different from the actual value, and the load impedance containing a reactance component such as a speaker will be detected. can be detected with high sensitivity and reliably, which allows for example 8Ω load and 4Ω load
Since the power supply voltage can be reliably switched between large and small depending on the load, there is no risk of using the same power supply voltage no matter the load, unlike conventional circuits that are not equipped with a circuit that can reliably switch the power supply voltage. However, it has the advantage of being able to reduce power consumption compared to the conventional type, and therefore, with the same power consumption, the power can be increased by about 50% compared to the conventional type.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of an example of the load impedance detection circuit previously proposed by the applicant, Figure 2 is the load line of the SEPP circuit transistor when each load impedance is connected, and Figure 3 is the circuit diagram of the circuit of the present invention. FIG. 4 is a circuit diagram showing a main part of the circuit of the present invention, and FIG. 5 is a circuit diagram showing the main part of another embodiment of the circuit of the present invention. 2...Input terminal, 3...SEPP circuit (amplifier),
4... Voltage fluctuation detection circuit, 5... Continuity angle control circuit, 6... Load impedance detection circuit, 7
(R _L )...Speaker (load impedance), 1
0... Impedance detection signal output terminal, T ₁ ...
...power transformer, SCR...thyristor, D ₁₀ ,
D ₂₀ ... Diode, C ₁₀ ... Smoothing capacitor,
Q ₁ , Q ₂ ... SEPP circuit transistor, Q ₃ ~ _{Q 6} ...
... Differential amplifier transistor, A ₂ , A ₃ ... Differential amplifier, R ₁ , R ₂ ... Emitter resistance, R ₃ , R ₄ ... Impedance detection resistor, R ₅ to _{R 7} ... Differential amplifier operation Resistor for voltage setting.

Claims (1)

[Claims for Utility Model Registration] A complementary transistor in which the emitters of an NPN transistor and a PNP transistor are commonly connected via respective emitter resistors, and a load impedance is connected between the common connection point of the emitter resistors and ground. In the power supply circuit that supplies the power supply voltage to the SEPP circuit, one end of the diode is connected to the tap that obtains the lowest voltage among the multiple taps provided on the secondary side of the power transformer, and one end of the diode is connected to the other tap. a thyristor; a capacitor connected to one end of the diode and the other end of the thyristor; the one end of the capacitor is connected to the complementary
a rectifier circuit connected to the power input terminal of the SEPP circuit; first and second resistors connected in series between the emitter of the NPN transistor or the PNP transistor and the ground, respectively; one input terminal is connected to the common connection point of the resistors, and
A differential amplifier whose other input terminal is connected to the common connection point of the emitter resistors, and when the absolute value of only the positive or negative direction of the output voltage taken out to the common connection point of the emitter resistors is equal to or higher than a predetermined voltage. The emitter resistor consists of a resistor connected between the differential amplifier and ground so that the differential amplifier operates, and a detection signal output terminal connected to the power supply terminal side of the differential amplifier. A detection signal of the load impedance obtained by detecting a potential difference between a common connection point of and a common connection point of the first and second resistors is extracted from the differential amplifier and output from the detection signal output terminal. a load impedance detection circuit; supplying a control signal to the thyristor in response to the detection signal of the load impedance supplied from the load impedance detection circuit;
The load impedance detection circuit turns off the thyristor only when detecting a low load impedance,
It is characterized by comprising a control circuit that controls the conduction angle of the thyristor so that the voltage across the capacitor becomes a constant voltage or turns on the thyristor when low load impedance is not detected or when high load impedance is detected. power supply circuit.