JPS61280109A - Thermal feedback control type power amplifier - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

BACKGROUND OF THE INVENTION This invention relates to power amplifiers, such as audio frequency amplifiers, which operate over a wide range of voltage frequencies and amplitudes and drive varying effective load impedances (e.g., speakers). be.

A power amplifier for playing music through speakers must amplify and reproduce the input voltage by a suitable amount, typically in the range of 20 to 40 aB, and supply this to a load, which is a resistive load. or active or any combination of the two, having a nominal or average value of approximately 2 ohms to 10 ohms, but varying from 1 ohm to 100 ohms in the audio frequency range. It increases with temperature and changes instantaneously with level. This voltage varies between O and Clippinder levels and typically has a peak-to-average ratio of 5 to 20 aB.

One important problem with this is that a transformerless output stage with a fixed supply voltage designed for one particular load impedance will operate very inefficiently and On the other hand, for much higher impedances, a fraction of that normal power -
It is important to only supply

Varying the supply voltage proportional to the square root of the load impedance solves this problem, but this method is not an optimal solution.

An important object of this invention is to provide a voltage varying device configured such that at very low average powers and at very high average powers the maximum safe power available is much greater than for an amplifier with a fixed supply voltage. An object of the present invention is to provide an improvement in a power amplifier power supply with.

Another object of the invention, in accordance with one or more of the preceding objects, is that when the signal processed by the amplifier is music or a similar irregular waveform and the load is a loudspeaker or the like. The amplifier operates at a higher voltage during most of its operating time and therefore exhibits a much higher available peak output level than the levels used for regular waveforms and simple resistive loads. It is to do so.

It is another object of the invention, consistent with one or more of the preceding objects, that the amplifier provides substantially the same power into any impedance from 2 to 8 ohms and that the power supply is constant for worst case dissipation. regulated (preset its maximum voltage).

Still another object of the invention, consistent with one or more of the preceding objects, is that thermal feedback seeks to stabilize power consumption, and thus temperature, so that the output stage temperature remains within a relatively small range. The result is improved long-term reliability.

Still another object of the invention, consistent with one or more of the preceding objects, is to make the variable power supply an efficient, simple and inexpensive low frequency thyristor switching power supply, so that losses are lost in the transformer line (power end) of the power supply. is substantially limited to the IR drop at .

Yet another object of the invention, consistent with one or more of the preceding objects, is to provide an amplifier with a given power supply and output power stage as if the power rating of a conventional amplifier with the same power supply and output stage is It is to operate as if it were at least twice as large.

SUMMARY OF THE INVENTION The foregoing aspects provide, in accordance with the present invention, a heat-generating power output stage in a power amplifier, a power source for powering said power amplifier, and a method for detecting and generating heat generated by said power output stage. The voltage output level of the power supply is controlled by applying a signal inversely proportional to the voltage, thereby continuously adjusting the supply voltage to a level appropriate for changing load impedance and stabilizing the current in the output stage. This is accomplished by a power amplifier comprising a device such as this.

The feedback is configured to have a non-linear response such that the degree of negative feedback increases when the detected heat (power consumption) reaches a predetermined limit value.

The power amplifier safe operating range is defined by the allowed instantaneous VI product of the power amplifier output stage. a power output stage, or more specifically a heat sink mounting the semiconductor of the output stage;
The heat associated with is approximately proportional to the average power consumption of the output stage. Therefore, by negative feedback of temperature information in the heat sink,
The voltage level of the power supply driving the power amplifier and its output stage can be controlled. In this way, the temperature of the heat dissipation level of the output stage can be kept at or below safe limits at all times, while at the same time ensuring that the operating voltage level of the power supply is at its highest possible rail. The feedback signal is inversely proportional to the detected temperature. Therefore, as the temperature increases, the voltage output of the power supply decreases.

If the amplifier is operating at very low or very high average power, resulting in a high impedance compared to the musical spectrum in question, then the temperature is very low (and the supply voltage is at its maximum), so The dynamic free height is very high.

This dynamic free height is a free height that lasts for several minutes. This is because the thermal time constant of the heat sink is about 10 minutes. Therefore, high level timbres with uniform tone, such as voices or solo instruments, are not clipped. The response is essentially desensitized to such short-term peaks. Automatic implementation of this method is provided by the improved amplifier power supply of the present invention.

If the power consumption is very high, for example when playing music with a small long-term peak-to-average ratio such as 4aB, the supply voltage is lowered to reduce the power consumption;
Eventually the temperature will stabilize to a safe value. Fortunately, the types of music that require the highest dynamic range are typically those that place the least demands on the amplifier in terms of power consumption. In most classical music the average power for most of the time is very low, eg less than 5 watts, with occasional very high level peaks.

Relevant short-term peaks are up to 400 watts, with average levels as high as 150 watts during passages lasting several minutes.

The amplifier power supply of the present invention allows the following amplifier conditions.

1. The amplifier has a very large dynamic headroom (4aB) no matter what the impedance, λ The substantial performance required for solo voices and instruments over short periods of time (several minutes). Continuous clipping power, 3. Maximum free height when most needed,9 i.e. when the peak-to-average ratio is very large, 4. Under all practical conditions of use, the amplifier will exceed the equivalent prior art. provide more undistorted power than the amplifier to both 8 ohm and 8 ohm rated speakers; 5. combined with design for long term reliability; 6. with a minimum rating of 100 watts; and With enough power to meet state-of-the-art stereo listening requirements,
2 IKW, which means that even low-efficiency speakers can be driven to sound pressure levels of almost 120 dB; Short-term output well beyond.

Other objects, features and advantages will be found from the following description of selected embodiments, made with reference to the accompanying drawings.

Referring now to FIG. 1A, there is shown a power supply 10 according to an exemplary embodiment of the invention.

This power supply includes (based on typical component selections):

Transformer TR-1: 117V, single phase rectifier diode D
1~D4: IN5401, DIO-)"D5:
lN4002, and D6: IN 914°5CR-1: 0116B Transistor Tl: BD 139 Resistor R-1:
27k ohm, y4W# T2: z
z R-2:22 #x'r3:
j # R-3:27 g#R-4:if #R-5:1# %W Constant current source: 10YG2.0 Capacitor C-1C-1 (10 and C-2 (4700I
f.

80 volts).

This circuit configuration is based on a thyristor (for example, the 5GR-
1 or equivalent) to provide a slow-acting layer source that connects the entire rectified voltage supply (from bridge rectifiers D1-D4) once for each cycle of the full-wave rectified signal. The phase shifting network PSN changes the conduction angle to connect terminals 12.
Just enough current is drawn to maintain the average output voltage at 14 at the desired level.

Power supply 10 connects the output voltage at terminals 12.14 to amplifier A.
(with input 1 and output 0). A feedback loop from the amplifier output stage provides a current flow that adapts the circuit of FIG. 1 to vary directly with the product of the instantaneous voltage and current in the output stage.

For single-phase 60-cycle operation, the period of the power supply frequency (
wavelength) is approximately 18 milliseconds. The conduction period of 5CR-x is generally in the range of 3 to 15 milliseconds each cycle.

The selection of components for the device 10 described above ensures that the reaction time of the device is approximately one-half the period of the mains frequency. That is, it satisfies the general condition of the present invention of 18 to 36 milliseconds. For this purpose, transiently occurring high level peaks are passed undistorted before the supply voltage at terminal 12.14 is reduced by device 10.

To this end, the short-term ability of the amplifier to operate above rated steady-state conditions can be exploited to increase the dynamic power available for the amplification 3A. For example, an amplifier's output transistor may be rated for operation at 3.5 amps and 150 volts DC, but can withstand up to 7 amps at the same voltage for a duration of 1099 seconds.

In order to make more dynamic power available, this control constraint should be combined with a device for limiting the maximum consumption in absolute value. This occurs when the output transistor of the amplifier rises above a certain temperature υ (as indicated by the corresponding VI product or by direct temperature sensing at the transistor heatsink). This can be done by introducing a gain.

The output supply voltage Vs of the device 10 is determined by the reference voltage vrof, and this reference voltage is connected to the resistive network R1 to R
4 and the east-emitter voltage Vbe of transistor T3, which decreases linearly by 2-2.5 mV/° C. with increasing temperature and is in thermal contact with the output stage heatsink. Voltage VEI follows the following equation as a function of Vbe.

v8 is also an electric current MEi which is proportional to the integrated VI product at the output stage (1×v2 shown in the block diagram of FIG. 2), thus 1=2×Pd2. determined in part by

Taking this current into account, the 7th day will be as follows.

=Ka Vbe -Ks i Figure 2 shows the same circuit or equivalent in block diagram form. Power amplifier A drives an impedance load (e.g., the voice coil of a speaker) with a current and a voltage vO, and (
At least for its final output stage) the supply voltage v8 is utilized.

As shown in FIG. 1B, the voltage-current multiplier AVM consists of transistors T4 and T5 and a resistor R7. AvM is the current value obtained by detecting the voltage across resistor R6 and the voltage (Vs-Vo) at the output of transistor T6 generated across resistor R7.
An output current factor 2 proportional to VI is generated by multiplying by

Va is generated from the reference voltage Vrsf using a summing amplifier Az. This summing amplifier A2 has two inputs.

One input is a current 1 proportional to the short-term integrated voltage-current product in the output transistor obtained from the multiplier AVM. v4 is developed across a resistor in series with the output transistor power line and is therefore proportional to the output transistor current. v2 is the voltage at the output transistor 6 (=Vs-Vo). 1=to 2Pa2=l),
KokotePd2=viX■2. The other input to the summing amplifier is a thermal (rather than electrical) connection in which transistor T3 is in contact with the output stage, which tracks the temperature of the output stage and determines the base temperature of its temperature dependence. The emitter voltage decreases 7 days with increasing temperature according to equation (1).

Since this input is proportional to the long-term Pa (power consumption) in the output stage, this input will be referred to as 1 Pa. An increase in temperature causes a decrease in Vs (long-term integral consumption) (Vref = Vs) according to equation (1), and the short-term integral VI product 1 becomes Vref (=Va) by passing through the inverted integral fraction. causing an additional decrease in and increasing Pa. These two feedback paths generate an input to the summing amplifier A2 of Pd1 at 2Pd2+. Therefore, Vref decreases as a function of short-term and long-term power consumption in the output stage.

The correspondence between the general diagram of FIG. 2 and the more specific embodiment of the circuit of FIG. 1 is as follows.

Figure 2 Figure 1A Vref source E TR-1, DI ~ D4, 5CR
-1. PSNRR5 AvMR1-R4 T/V Ta Several variations can be made within the scope of this invention from the apparatus specifically and generally described above. For example, in the circuit of FIG. 1, feedback loop 1 may be replaced by a thermal loop or a thermal loop may be added to the feedback loop so that R3 (configured as a thermistor) and/or transistor T3 are thermally connected to the output transistor of amplifier A. They may be in an exchange relationship.

Feedback control can be applied to transformer TR-1, for example by providing an auxiliary high resistance winding and a balancing reference resistor to the transformer.
can arise from.

Figures 3A and 3B show two free height situations, in the first of which (Figure 3A) rock music is being played with a dynamic range of 4 dB and 150
The average sound of Watts is 400 Watts. The supply voltage is gradually reduced until the clippinder level reaches 200 watts. Therefore, the peak is clipped by 3aB.

However, ripping as provided in this invention (FIG. 3B) does not appreciably change the acoustics.

Once given the benefit of the foregoing disclosure, one skilled in the art will not depart from the inventive concept (as there are numerous uses and variations of the specific embodiments described herein, as well as implementation thereof). Obviously, departures from the examples may be made.Thus, this invention resides in novel features and features existing in or possessed by the apparatus and technology disclosed herein. and combinations thereof, and should be limited only by the scope and spirit of the claims.

[Brief explanation of drawings]

FIG. 1A is a circuit diagram of an amplifier with an improved power supply according to an exemplary embodiment of the invention. FIG. 1B is a circuit diagram of the analog multiplier (AVM) of FIG. 1A. FIG. 2 is a block diagram of a more generalized form of the apparatus of FIG. 1A. FIGS. 3A and 3B are semi-log power vs. time plots showing the effect of operating at rms power levels far and near the level of ripping power available. FIG. 4 is a series of power consumption versus power diagrams on a linear scale at various supply voltages. In these drawings, 10 is a power supply, A is an amplifier, AV
M is a voltage/current calculator, TR-1 is a transformer, D1 to D4
is a bridge rectifier, 5GR-1 is a thyristor, PSN
is a phase shift network, R1-R4 are resistors, TI, T2, T3 are transistors, Vs is an output supply voltage, and Vref is a reference voltage. No. 212] Aoi/Figure B Target 1 Fukiei 89 01

Claims (7)

[Claims] (1) (a) a power amplifier arrangement having a heat generating power output stage; (b) an arrangement for defining a power source for supplying power to said power amplifier; (c) a heat generating power output stage; (d) detecting heat generated by the power source and providing a control signal that varies as a function of power consumption in the power output stage; and (d) adjusting a voltage output level of the power supply in response to the control signal. A power amplifier comprising a device for controlling in a time-delay manner, thereby making it possible to continuously adjust the supply voltage to an optimum level for changing load impedances and to stabilize the current in the output stage. 2. The power amplifier of claim 1, wherein the feedback has a non-linear response to increase the degree of negative feedback when the detected heat reaches a predetermined limit value. (3) The power amplifier according to claim 2, further comprising a device for suppressing the sensitivity of the response to short-term peaks of the VI product in the output stage. (4) The power amplifier according to claim 3, comprising a device for limiting the maximum consumption to a predetermined value. (5) (a) A power amplifier with a heat-generating power output stage, (
b) a power source for powering said power amplifier; (c) a control that detects heat generated by said power output stage and varies as a function of power consumption in said power output stage; apparatus for generating a signal; and (d) apparatus for controlling the voltage level of said power supply in a time-delayed manner and limiting the supply voltage as a function of said detected heat in said time-delayed manner. Equipped with power amplifier assembly. (6) (a) a power amplifier having a predetermined maximum time average operating power; (b) a power supply supplying power to said power amplifier; (c) responsive to the power dissipated in said amplifier; a control device for controlling the power supplied by said power supply device to said power amplifier such that under steady-state conditions the instantaneous power supplied to said power amplifier is at most equal to said maximum time average operating power; and (d) delaying operation of said controller for a predetermined period of time such that the power supplied by said power supply to said power amplifier is equal to said maximum time average operating power for said predetermined period of time. A power amplifier assembly comprising a device for making it possible to exceed. (7) a device for reducing the power supplied to the power amplifier by the power supply after the predetermined time in response to time-average power supplied to the amplifier; 7. A power amplifier assembly according to claim 6.